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Intellectual disability v6.18 RNU4-2 Arina Puzriakova Added comment: Comment on list classification: The two papers (PMID: 38821540; 38645094) corroborate mutual findings and report over 100 unrelated individuals with a clinically overlapping neurological disorder and variants the non-coding gene RNU4-2.

Overall there is sufficient evidence to promote this gene to Green status at the next GMS panel update.
Intellectual disability v6.11 RPS6KA3 Sarah Leigh reviewed gene: RPS6KA3: Rating: GREEN; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v6.11 RPL10 Sarah Leigh commented on gene: RPL10: The mode of inheritance of this gene has been updated to X-LINKED: hemizygous mutation in males, biallelic mutations in females following NHS Genomic Medicine Service approval.
Intellectual disability v6.11 PPP1R3F Sarah Leigh reviewed gene: PPP1R3F: Rating: GREEN; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v6.11 FAR1 Sarah Leigh commented on gene: FAR1: The mode of inheritance of this gene has been updated to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal following NHS Genomic Medicine Service approval.
Intellectual disability v6.11 CDK16 Sarah Leigh commented on gene: CDK16: The rating of this gene has been updated to green and the mode of inheritance updated to X-LINKED: hemizygous mutation in males, biallelic mutations in females following NHS Genomic Medicine Service approval.
Intellectual disability v6.10 RPS6KA3 Achchuthan Shanmugasundram Source NHS GMS was added to RPS6KA3.
Mode of inheritance for gene RPS6KA3 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v6.10 RPL10 Achchuthan Shanmugasundram Source NHS GMS was added to RPL10.
Mode of inheritance for gene RPL10 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v6.10 FAR1 Achchuthan Shanmugasundram Source NHS GMS was added to FAR1.
Mode of inheritance for gene FAR1 was changed from BIALLELIC, autosomal or pseudoautosomal to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v6.5 ISCA-46743-Loss Arina Puzriakova changed review comment from: The rating of this region has been updated to Green and the mode of inheritance set to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' following NHS Genomic Medicine Service approval. Evidence: multiple unrelated cases curated in ClinGen plus several others - sufficient evidence for this region. Phenotype: syndromic intellectual disability (congenital anomalies, behavioural problems and facial dysmorphism), seizures in about 30%. Modulated phenotype in females is reported.; to: The rating of this region has been updated to Green and the mode of inheritance set to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' following NHS Genomic Medicine Service approval. Evidence: two cases (PMID: 30158690; 33758131) with intragenic STAG2 deletions but listed as sufficient evidence in ClinGen. Region encompasses STAG2 and some of XIAP. Phenotype: holoprosencephaly and/or developmental delay/ID based on LOF of STAG2 gene. Affected females are reported.
Intellectual disability v6.2 ISCA-46743-Loss Arina Puzriakova Region: ISCA-46743-Loss was added
Region: ISCA-46743-Loss was added to Intellectual disability. Sources: Expert Review Green,ClinGen
Mode of inheritance for Region: ISCA-46743-Loss was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v6.2 ISCA-46743-Gain Arina Puzriakova Region: ISCA-46743-Gain was added
Region: ISCA-46743-Gain was added to Intellectual disability. Sources: Expert Review Green,ClinGen
Mode of inheritance for Region: ISCA-46743-Gain was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.532 CEP295 Zornitza Stark gene: CEP295 was added
gene: CEP295 was added to Intellectual disability - microarray and sequencing. Sources: Expert Review
Mode of inheritance for gene: CEP295 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CEP295 were set to 38154379
Phenotypes for gene: CEP295 were set to Seckel syndrome 11, OMIM # 620767
Added comment: 4 children from 2 unrelated families with Seckel-like syndrome - severe primary microcephaly, short stature, developmental delay, intellectual disability, facial deformities, and abnormalities of fingers and toes. WES identified biallelic pathogenic variants in CEP295 gene (p(Q544∗) and p(R1520∗); p(R55Efs∗49) and p(P562L)).

Patient-derived fibroblasts and CEP295-depleted U2OS and RPE1 cells were used to clarify the underlying mechanisms. Depletion of CEP295 resulted in a decrease in the numbers of centrioles and centrosomes and triggered p53-dependent G1 cell cycle arrest. Loss of CEP295 caused extensive primary ciliary defects in both patient-derived fibroblasts and RPE1 cells. The results from complementary experiments revealed that the wild-type CEP295, but not the mutant protein, can correct the developmental defects of the centrosome/centriole and cilia in the patient-derived skin fibroblasts.
Sources: Expert Review
Intellectual disability v5.506 ZFX Tracy Lester reviewed gene: ZFX: Rating: GREEN; Mode of pathogenicity: None; Publications: 38325380; Phenotypes: Intellectual disability, developmental delay, behavioural abnormalities, hypotonia, dysmorphic facies; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.502 CLEC16A Sarah Leigh edited their review of gene: CLEC16A: Added comment: Heterozygous CLEC16A variants have been identified as a genetic risk factor for several autoimmune disorders and for Parkinson disease (PMID: 37175930). PMID: 36538041 reports the neurological effect of homozygous terminating CLEC16A variants in two families. In family 1, the first child died at 5 months, he had progressive microcephaly, failure to thrive and cranial CT showed brain atrophy, dilatation of both central and peripheral liquor spaces, hypoplasia of the corpus callosum (no genetic testing was done), the third pregnancy was terminated (17 weeks of gestation) after prenatal ultrasound showed ventriculomegaly, agenesis of corpus callosum (no genetic testing was done), the fourth pregnancy was also terminated (22 weeks of gestation) as the prenatal ultrasound showed agenesis of corpus callosum. This fetus was homozygous for NM_001243403.1(CLEC16A):c.2062 + 5G > A, RT-PRC showed that this variant resulted in the deletion of exon 19 and a frame shift. Both parents and an unaffected sibling were heterozygous for this variant. In family 2, a single affected child was homozygous for NM_001243403.1(CLEC16A):c.-4_12del, p.Met1fs*. This child had progressive microcephaly, failure to thrive, severe global developmental delay, global brain atrophy and died at 6 years. There is no genetic data from the parents or unaffected siblings in Family 2. PMID: 37175930, also presents zebrafish experiments, where mutagenesis of
clec16a by CRISPR–Cas9 resulted in accumulated acidic/phagolysosome compartments, in neurons
and microglia, and dysregulated mitophagy. This was rescued by wild type CLEC16A, but not by the C-terminal truncated variant. The authors conclude that dysregulation of CLEC16A-mediated endosomal sorting is associated with neurodegeneration.; Changed rating: GREEN; Changed publications to: 36538041; Changed mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Intellectual disability v5.485 ZFX Sarah Leigh reviewed gene: ZFX: Rating: GREEN; Mode of pathogenicity: None; Publications: 38325380; Phenotypes: X-linked neurodevelopmental disorder with recurrent facial gestalt; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.472 EFNB1 Arina Puzriakova reviewed gene: EFNB1: Rating: AMBER; Mode of pathogenicity: None; Publications: 23335590, 25679214, 27650623, 31088393, 24520368; Phenotypes: Craniofrontonasal dysplasia, OMIM:304110; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.421 HSD17B10 Arina Puzriakova Mode of inheritance for gene: HSD17B10 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.396 RPL10 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: As reviewed by Sarah Leigh and Dmitrijs Rots, all the cases reported previously in literature and recently in PMID:35876338 were males with hemizygous RPL10 variants. The females were carriers and showed fully skewed X inactivation of the mutation-bearing X chromosomes.

In addition, this gene has been associated with relevant phenotypes in both OMIM (MIM #300998) and Gene2Phenotype (with 'definitive' rating on the DD panel). The MOI has been recorded as 'X-linked recessive' in OMIM.

The MOI should therefore be updated from 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' to 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' in the next GMS review.
Intellectual disability v5.396 RPL10 Achchuthan Shanmugasundram Mode of inheritance for gene: RPL10 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.395 RPL10 Achchuthan Shanmugasundram reviewed gene: RPL10: Rating: GREEN; Mode of pathogenicity: None; Publications: ; Phenotypes: Intellectual developmental disorder, X-linked syndromic 35, OMIM:300998; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.357 TRPC5 Sarah Leigh gene: TRPC5 was added
gene: TRPC5 was added to Intellectual disability - microarray and sequencing. Sources: DD-Gene2Phenotype,Expert Review Red
Mode of inheritance for gene: TRPC5 was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Publications for gene: TRPC5 were set to 36323681
Phenotypes for gene: TRPC5 were set to TRPC5-related neurodevelopmental disorder
Intellectual disability v5.332 AGPAT3 Zornitza Stark gene: AGPAT3 was added
gene: AGPAT3 was added to Intellectual disability - microarray and sequencing. Sources: Literature
Mode of inheritance for gene: AGPAT3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: AGPAT3 were set to 37821758
Phenotypes for gene: AGPAT3 were set to Neurodevelopmental disorder (MONDO#0700092), AGPAT3-related
Review for gene: AGPAT3 was set to AMBER
Added comment: - Single consanguineous family with four individuals with severe intellectual disability and retinitis pigmentosa
- All affected individuals were homozygous for a nonsense variant in AGPAT3, healthy unaffected individuals who were tested were heterozygous for the variant
- Overexpression of mutant transcript revealed absence of AGPAT3 protein compared to WT transcript via Western blot analysis
- KO AGPAT3 mouse demonstrated impaired neuronal migration
Sources: Literature
Intellectual disability v5.286 ZMYM3 Arina Puzriakova reviewed gene: ZMYM3: Rating: GREEN; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.286 TCEAL1 Arina Puzriakova reviewed gene: TCEAL1: Rating: GREEN; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.286 KIF4A Arina Puzriakova reviewed gene: KIF4A: Rating: GREEN; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.286 IQSEC2 Arina Puzriakova reviewed gene: IQSEC2: Rating: ; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.286 HUWE1 Arina Puzriakova reviewed gene: HUWE1: Rating: ; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.286 IQSEC2 Arina Puzriakova Source NHS GMS was added to IQSEC2.
Mode of inheritance for gene IQSEC2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.286 HUWE1 Arina Puzriakova Source NHS GMS was added to HUWE1.
Mode of inheritance for gene HUWE1 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.277 PPP1R3F Achchuthan Shanmugasundram reviewed gene: PPP1R3F: Rating: GREEN; Mode of pathogenicity: None; Publications: 37531237; Phenotypes: neurodevelopmental disorder, MONDO:0700092, intellectual disability, MONDO:0001071; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.271 PPP1R3F Zornitza Stark gene: PPP1R3F was added
gene: PPP1R3F was added to Intellectual disability - microarray and sequencing. Sources: Literature
Mode of inheritance for gene: PPP1R3F was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Publications for gene: PPP1R3F were set to 37531237
Phenotypes for gene: PPP1R3F were set to Neurodevelopmental Disorder, MONDO:0700092,PPP1R3F-related
Review for gene: PPP1R3F was set to GREEN
Added comment: 13 unrelated hemizygous individuals reported with functional evidence
Sources: Literature
Intellectual disability v5.232 RPS6KA3 Arina Puzriakova Mode of inheritance for gene: RPS6KA3 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.163 TCEAL1 Achchuthan Shanmugasundram gene: TCEAL1 was added
gene: TCEAL1 was added to Intellectual disability - microarray and sequencing. Sources: Literature
Mode of inheritance for gene: TCEAL1 was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for gene: TCEAL1 were set to 36368327
Phenotypes for gene: TCEAL1 were set to Neurodevelopmental disorder with gait disturbance, dysmorphic facies and behavioral abnormalities, X-linked, OMIM:301094
Review for gene: TCEAL1 was set to GREEN
Added comment: PMID:36368327 reported seven unrelated individuals with de novo variants (2 nonsense, 2 frameshift, 2 CNVs & 1 missense variants) in TCEAL1 gene and presenting with an X-linked dominant neurodevelopmental disorder. All these seven individuals had intellectual disability (mild to severe). The other major clinical presentations include hypotonia, abnormal gait, speech impairment, autistic-like behavior, and mildly dysmorphic facial features.

This gene is associated with relevant phenotypes in OMIM (MIM #301094), but not in Gene2Phenotype.
Sources: Literature
Intellectual disability v5.135 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.135 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.134 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.135 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.135 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.134 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.134 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from BIALLELIC, autosomal or pseudoautosomal to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.133 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to BIALLELIC, autosomal or pseudoautosomal
Intellectual disability v5.132 FAAH2 Achchuthan Shanmugasundram Mode of inheritance for gene: FAAH2 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.131 FAAH2 Achchuthan Shanmugasundram reviewed gene: FAAH2: Rating: AMBER; Mode of pathogenicity: None; Publications: 25885783, 34645488; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.107 ITPR1 Tracy Lester edited their review of gene: ITPR1: Added comment: PMID:29925855 - All 7 EOA patients with ITPR1 de novo variants (3 from cohort #1; 4 from cohort #2) presented with infantile onset cerebellar ataxia starting before the age of 2 years, including delayed motor milestones (Table 2). Cognitive deficits of variable degree were observed in 3 out of 4 patients where this information was available, reaching from only mild dyscalculia (P2) to severe intellectual disability with a speech vocabulary of only a few words (P7 at age 12 years). In contrast, patient P1 showed normal intelligence with an IQ of 97.

PMID:27108797 - Here, we report that both recessive and dominant ITPR1 mutations cause Gillespie syndrome. ITPR1 is a predominant isoform in the brain among the three types of ITPRs and is strongly expressed in cerebellar Purkinje cells.31 Mice with complete homozygosity for Itpr1 ablation suffer from severe epilepsy and ataxia and die either in utero or before weaning.32 Consistently, ITPR1 mutations have been reported to cause cerebellar diseases including late-onset spinocerebellar ataxia type 15 (SCA15 [MIM: 606658]),33 congenital nonprogressive spinocerebellar ataxia and mild cognitive impairment (SCA29 [MIM: 117360]),34 infantile-onset cerebellar ataxia with mild cognitive deficit,35 and childhood-onset ataxic cerebellar palsy with moderate intellectual disability36 (see ITPR1 schematic diagram in Figure 3A).
Affected individuals had similar iris anomalies and neonatal ataxia with progressive cerebellar atrophy (Figure 2). Moderate to severe intellectual disabilities were noted in the three individuals with recessive mutations (F1:II1, F2:II1, and F3:II1; Table 1). In contrast, the affected individual F4:II1 aged 18 years and harboring the de novo c.7687_7689del mutation was reported to have normal intelligence (Table 1).

As de novo variants are associated with ID/DD the inheritance should be updated to be BOTH AD and AR.; Set current diagnostic: yes
Intellectual disability v5.100 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.101 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.101 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.101 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.100 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.100 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.101 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.100 CSTF2 Achchuthan Shanmugasundram Mode of inheritance for gene: CSTF2 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.98 CSTF2 Achchuthan Shanmugasundram reviewed gene: CSTF2: Rating: AMBER; Mode of pathogenicity: None; Publications: 32816001; Phenotypes: Intellectual disability, MONDO:0001071; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.71 KIF4A Achchuthan Shanmugasundram reviewed gene: KIF4A: Rating: GREEN; Mode of pathogenicity: None; Publications: 24812067, 34346154; Phenotypes: ?Intellectual developmental disorder, X-linked 100, OMIM:300923; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.70 INTS11 Achchuthan Shanmugasundram changed review comment from: PMID:37054711 reported ten unrelated families with biallelic variants in INTS11 gene and they present with intellectual disability, global developmental and language delay, impaired motor development, and brain atrophy.

Functional studies in Drosophila showed that dIntS11 (fly ortholog of INTS11) is essential and expressed in the central nervous systems in a subset of neurons and most glia in larval and adult stages. In addition, genes with two variants (p.Arg17Leu and p.His414Tyr) fail to rescue the lethality of null mutants in the Drosophila model, indicating that they are strong loss-of-function variants. The other five variants (p.Gly55Ser, p.Leu138Phe, p.Lys396Glu, p.Val517Met and p.Ile553Glu) rescue lethality but cause a shortened lifespan and bang sensitivity and affect locomotor activity, indicating that they are partial loss-of-function variants.
Sources: Literature; to: PMID:37054711 reported ten unrelated families with biallelic variants in INTS11 gene and they present with intellectual disability, global developmental and language delay, impaired motor development, and brain atrophy.

Functional studies in Drosophila showed that dIntS11 (fly ortholog of INTS11) is essential and expressed in the central nervous systems in a subset of neurons and most glia in larval and adult stages. In addition, genes with two variants (p.Arg17Leu and p.His414Tyr) fail to rescue the lethality of null mutants in the Drosophila model, indicating that they are strong loss-of-function variants. The other five variants (p.Gly55Ser, p.Leu138Phe, p.Lys396Glu, p.Val517Met and p.Ile553Glu) rescue lethality but cause a shortened lifespan and bang sensitivity and affect locomotor activity, indicating that they are partial loss-of-function variants.

This gene has not yet been associated with relevant phenotypes in OMIM or in Gene2Phenotype.
Sources: Literature
Intellectual disability v5.68 INTS11 Achchuthan Shanmugasundram gene: INTS11 was added
gene: INTS11 was added to Intellectual disability - microarray and sequencing. Sources: Literature
Mode of inheritance for gene: INTS11 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: INTS11 were set to 37054711
Phenotypes for gene: INTS11 were set to intellectual disability, MONDO:0001071
Review for gene: INTS11 was set to GREEN
Added comment: PMID:37054711 reported ten unrelated families with biallelic variants in INTS11 gene and they present with intellectual disability, global developmental and language delay, impaired motor development, and brain atrophy.

Functional studies in Drosophila showed that dIntS11 (fly ortholog of INTS11) is essential and expressed in the central nervous systems in a subset of neurons and most glia in larval and adult stages. In addition, genes with two variants (p.Arg17Leu and p.His414Tyr) fail to rescue the lethality of null mutants in the Drosophila model, indicating that they are strong loss-of-function variants. The other five variants (p.Gly55Ser, p.Leu138Phe, p.Lys396Glu, p.Val517Met and p.Ile553Glu) rescue lethality but cause a shortened lifespan and bang sensitivity and affect locomotor activity, indicating that they are partial loss-of-function variants.
Sources: Literature
Intellectual disability v5.67 GRIA1 Achchuthan Shanmugasundram changed review comment from: Four different heterozygous variants in GRIA1 (p.Ala636Thr, p.Gly745Asp, p.Ile627Thr & p.Arg345Gln) have been identified in six unrelated individuals and they were all reported with intellectual disability, moderate to severe cognitive impairment, delayed motor development, speech impairment and behavioural issues such as anxiety, autism spectrum disorder and attention deficit hyperactivity disorder.

Homozygous variant (p.Arg377Ter) has been identified in one individual, who presented with intellectual disability, severe cognitive impairment, delayed motor development, speech impairment (non-verbal) and self-injurious behaviour.

In vitro functional studies with major GluA1-containing AMPAR subtypes carrying the GRIA1 variant mutations showed that three of the four missense variants profoundly perturb receptor function. The homozygous stop-gain variant completely destroyed the expression of GluA1-containing AMPARs. The Xenopus gria1 models also show transient motor deficits, an intermittent seizure phenotype, and a significant impairment to working memory in mutants.; to: Four different heterozygous variants in GRIA1 (p.Ala636Thr, p.Gly745Asp, p.Ile627Thr & p.Arg345Gln) have been identified in six unrelated individuals and they were all reported with intellectual disability, moderate to severe cognitive impairment, delayed motor development, speech impairment and behavioural issues such as anxiety, autism spectrum disorder and attention deficit hyperactivity disorder.

Homozygous variant (p.Arg377Ter) has been identified in one individual, who presented with intellectual disability, severe cognitive impairment, delayed motor development, speech impairment (non-verbal) and self-injurious behaviour.

In vitro functional studies with major GluA1-containing AMPAR subtypes carrying the GRIA1 variant mutations showed that three of the four missense variants profoundly perturb receptor function. The homozygous stop-gain variant completely destroyed the expression of GluA1-containing AMPARs. The Xenopus gria1 models also show transient motor deficits, an intermittent seizure phenotype, and a significant impairment to working memory in mutants.

This gene has also been associated with relevant phenotypes in both OMIM (MIM #619927 & MIM #619931) and Gene2Phenotype (with 'moderate' rating).
Intellectual disability v5.43 NDUFS1 Arina Puzriakova Phenotypes for gene: NDUFS1 were changed from Mitochondrial complex I deficiency, 252010; LEIGH SYNDROME (NUCLEAR DNA MUTATION) to Mitochondrial complex I deficiency, nuclear type 5, OMIM:618226
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence (>3 female cases with monoallelic variants causing ID) to suggest that MOI should be updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' in the next major review.

In addition, intellectual disability (MIM #309530) has been associated in both OMIM and Gene2Phenotype with X-linked dominant inheritance.
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Mode of inheritance for gene: IQSEC2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence (>3 female cases with monoallelic variants causing ID) to suggest that MOI should be updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' in the next major review.

In addition, intellectual disability (MIM #309530) has been associated in both OMIM and Gene2Phenotype with X-linked dominant inheritance.
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Mode of inheritance for gene: IQSEC2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence (>3 female cases with monoallelic variants causing ID) to suggest that MOI should be updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' in the next major review.

In addition, intellectual disability (MIM #309530) has been associated in both OMIM and Gene2Phenotype with X-linked dominant inheritance.
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Mode of inheritance for gene: IQSEC2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence (>3 female cases with monoallelic variants causing ID) to suggest that MOI should be updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' in the next major review.

In addition, intellectual disability (MIM #309530) has been associated in both OMIM and Gene2Phenotype with X-linked dominant inheritance.
Intellectual disability v5.37 IQSEC2 Achchuthan Shanmugasundram Mode of inheritance for gene: IQSEC2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.36 IQSEC2 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence (>3 female cases with monoallelic variants causing ID) to suggest that MOI should be updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' in the next major review.

In addition, intellectual disability (MIM #309530) has been associated in both OMIM and Gene2Phenotype with X-linked dominant inheritance.
Intellectual disability v5.36 IQSEC2 Achchuthan Shanmugasundram Mode of inheritance for gene: IQSEC2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.36 IQSEC2 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence (>3 female cases with monoallelic variants causing ID) to suggest that MOI should be updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' in the next major review.

In addition, intellectual disability (MIM #309530) has been associated in both OMIM and Gene2Phenotype with X-linked dominant inheritance.
Intellectual disability v5.36 IQSEC2 Achchuthan Shanmugasundram Mode of inheritance for gene: IQSEC2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.35 IQSEC2 Achchuthan Shanmugasundram changed review comment from: There are more than 20 unrelated cases identified with variants in IQSEC2 gene, as reported in publications. Moderate to severe intellectual disability was present in all affected males.

De novo, truncating variants correlate with severe disease in both female and male patients harboring an IQSEC2 alteration. Missense variants in male and female patients account for a milder disease overall, with more severe symptoms in males than females. This evidence suggests that the MOI should be 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)'.

Both OMIM and Gene2Phenotype have associated X-linked dominant variants in IQSEC2 with intellectual disability (MIM #309530); to: There are more than 20 unrelated cases identified with variants in IQSEC2 gene, as reported in publications. Moderate to severe intellectual disability was present in all affected males.

De novo, truncating variants correlate with severe disease in both female and male patients harboring an IQSEC2 alteration. Missense variants in male and female patients account for a milder disease overall, with more severe symptoms in males than females.
Intellectual disability v5.34 IQSEC2 Achchuthan Shanmugasundram reviewed gene: IQSEC2: Rating: GREEN; Mode of pathogenicity: None; Publications: 20473311, 23674175, 30842726, 31415821, 33368194; Phenotypes: Intellectual developmental disorder, X-linked 1, OMIM:309530; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.34 HUWE1 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence for updating the MOI of this gene from 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)'.
Intellectual disability v5.34 HUWE1 Achchuthan Shanmugasundram Mode of inheritance for gene: HUWE1 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.34 HUWE1 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence for updating the MOI of this gene from 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)'.
Intellectual disability v5.34 HUWE1 Achchuthan Shanmugasundram Mode of inheritance for gene: HUWE1 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.34 HUWE1 Achchuthan Shanmugasundram changed review comment from: Comment on mode of inheritance: There is sufficient evidence for updating the MOI of this gene from 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)'.; to: Comment on mode of inheritance: There is sufficient evidence for updating the MOI of this gene from 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' in the next major review.
Intellectual disability v5.34 HUWE1 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence for updating the MOI of this gene from 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)'.
Intellectual disability v5.34 HUWE1 Achchuthan Shanmugasundram Mode of inheritance for gene: HUWE1 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.33 HUWE1 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence for updating the MOI of this gene from 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)'.
Intellectual disability v5.33 HUWE1 Achchuthan Shanmugasundram Mode of inheritance for gene: HUWE1 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.33 HUWE1 Achchuthan Shanmugasundram Added comment: Comment on mode of inheritance: There is sufficient evidence for updating the MOI of this gene from 'X-LINKED: hemizygous mutation in males, biallelic mutations in females' to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)'.
Intellectual disability v5.33 HUWE1 Achchuthan Shanmugasundram Mode of inheritance for gene: HUWE1 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v5.30 HUWE1 Achchuthan Shanmugasundram reviewed gene: HUWE1: Rating: GREEN; Mode of pathogenicity: None; Publications: 29180823; Phenotypes: Intellectual developmental disorder, X-linked syndromic, Turner type, OMIM:309590; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v5.18 SPG7 Sarah Leigh Mode of inheritance for gene: SPG7 was changed from BOTH monoallelic and biallelic, autosomal or pseudoautosomal to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v4.54 ISCA-46304-Gain Arina Puzriakova Region: ISCA-46304-Gain was added
Region: ISCA-46304-Gain was added to Intellectual disability. Sources: Expert Review Green,ClinGen
Mode of inheritance for Region: ISCA-46304-Gain was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for Region: ISCA-46304-Gain were set to 22679399; 29141583; 29618507; 32043567
Intellectual disability v4.53 KDM5C Arina Puzriakova commented on gene: KDM5C: The mode of inheritance of this gene has been updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' following NHS Genomic Medicine Service approval.
Intellectual disability v4.53 ARHGEF9 Arina Puzriakova commented on gene: ARHGEF9: The mode of inheritance of this gene has been updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' following NHS Genomic Medicine Service approval.
Intellectual disability v4.53 AP1S2 Arina Puzriakova commented on gene: AP1S2: The mode of inheritance of this gene has been updated to 'X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)' following NHS Genomic Medicine Service approval.
Intellectual disability v4.52 ZC4H2 Arina Puzriakova Source NHS GMS was added to ZC4H2.
Mode of inheritance for gene ZC4H2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v4.52 KDM5C Arina Puzriakova Source NHS GMS was added to KDM5C.
Mode of inheritance for gene KDM5C was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v4.52 ARHGEF9 Arina Puzriakova Source NHS GMS was added to ARHGEF9.
Mode of inheritance for gene ARHGEF9 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v4.52 AP1S2 Arina Puzriakova Source NHS GMS was added to AP1S2.
Mode of inheritance for gene AP1S2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v4.31 STAT5B Arina Puzriakova Mode of inheritance for gene: STAT5B was changed from to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v4.15 RPL10 Dmitrijs Rots reviewed gene: RPL10: Rating: GREEN; Mode of pathogenicity: Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments; Publications: 35876338; Phenotypes: ID, dysmorphic features, progressive postnatal microcephaly, and retinal anomalies; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v4.14 FRMD5 Arina Puzriakova gene: FRMD5 was added
gene: FRMD5 was added to Intellectual disability. Sources: Literature
Q4_22_promote_green tags were added to gene: FRMD5.
Mode of inheritance for gene: FRMD5 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: FRMD5 were set to 36206744
Phenotypes for gene: FRMD5 were set to Neurodevelopmental disorder with eye movement abnormalities and ataxia, OMIM:620094
Review for gene: FRMD5 was set to GREEN
Added comment: Lu et al. 2022 (PMID: 36206744) report 8 unrelated individuals with de novo missense FRMD5 variants who presented with developmental delay (8/8), intellectual disability (7/7), ataxia (7/8), seizures (5/8), and abnormalities of eye movement (8/8). LOF mutant flies exhibited motor impairment, defective responses to light and heat-induced seizures. Fly phenotypes were rescued by expression of the wildtype gene but not by two of the patient missense mutants.

FRMD5 is associated with a relevant phenotype in OMIM (MIM# 620094) but is not yet listed in G2P.
Sources: Literature
Intellectual disability v4.3 SHOX Arina Puzriakova Mode of inheritance for gene: SHOX was changed from Unknown to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.1759 FMR1 Arina Puzriakova reviewed gene: FMR1: Rating: GREEN; Mode of pathogenicity: None; Publications: 21267007, 25171808, 28176767, 29178241; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1733 MTSS1L Arina Puzriakova gene: MTSS1L was added
gene: MTSS1L was added to Intellectual disability. Sources: Literature
new-gene-name, Q4_22_rating tags were added to gene: MTSS1L.
Mode of inheritance for gene: MTSS1L was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: MTSS1L were set to 36067766
Phenotypes for gene: MTSS1L were set to Global developmental delay; Intellectual disability; Ophthalmological anomalies; Microcephaly; Mild facial dysmorphisms
Review for gene: MTSS1L was set to GREEN
Added comment: Huang et al. 2022 (PMID: 36067766) reported five unrelated individuals with the same heterozygous de novo variant (c.2011C>T; p.Arg671Trp) in MTSS2 (formally known as MTSS1L). Linkage analysis was not performed but given the variants arose de novo and the mixed ethnicity of the affected individuals (4 European, 1 Chinese) a founder effect can be ruled out.

Subjects displayed a shared phenotype of GDD and/or ID, ophthalmological anomalies (most commonly nystagmus), microcephaly (primary in 2, relative in 3) and shared mild facial dysmorphisms. The single adult patient also presented with seizures and optic atrophy.

Functional studies showed the variant leads to a decrease in mRNA level but does not impact protein levels of MTSS2. However, a Drosophila model demonstrated that loss of the fly ortholog results in defects in locomotor and visual functions which were rescued by human MTSS2 and only partially rescued by the MTSS2 c.2011C>T variant. Overexpression of the c.2011C>T variant caused similar phenotypes as the LoF mutant indicating a possible dominant-negative effect.
Sources: Literature
Intellectual disability v3.1732 RELN Dmitrijs Rots reviewed gene: RELN: Rating: GREEN; Mode of pathogenicity: None; Publications: 35769015; Phenotypes: Lisencephaly, seizures, autism; Mode of inheritance: BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.1701 UBAP2L Konstantinos Varvagiannis gene: UBAP2L was added
gene: UBAP2L was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: UBAP2L was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: UBAP2L were set to 35977029
Phenotypes for gene: UBAP2L were set to Delayed speech and language development; Motor delay; Intellectual disability; Autistic behavior; Seizures; Microcephaly; Abnormality of head or neck; Short stature; Abnormality of the skeletal system
Penetrance for gene: UBAP2L were set to unknown
Review for gene: UBAP2L was set to GREEN
Added comment: Based on Jia et al (2022 - PMID: 35977029) speech, motor delay as well as ID are observed in individuals harboring de novo pLoF variants in UBAP2L. The gene encodes a regulator of the stress granule (SG) assembly. Extensive evidence is provided on the effect of variants as well as the role of UBAP2L and other genes for components and/or regulation of SG in pathogenesis of NDDs. Among others a Ubap2l htz deletion mouse model (behavioral and cognitive impairment, abnormal cortical development due to impaired SG assembly, etc). Data from 26 previous studies, aggregating 40,853 probands with NDDs (mostly DD/ID, also ASD) suggest enrichment for DNMs in UBAP2L or other genes previously known and further shown to be important for SG formation (incl. G3BP1/G3BP2, CAPRIN1).

Details provided below.

Not associated with any phenotype in OMIM, G2P or SysNDD.

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Jia et al (2022 - PMID: 35977029) describe 12 affected individuals with heterozygous de novo pLoF variants in UBAP2L.

Phenotype: Features included hypotonia, speech (11/11) and motor delay (8/12), ID (8/10 with formal evaluation), variable behavioral concerns (ADHD 5/11, ASD in 4/10, etc). Seizures were reported in 7/12 with 3/10 having a formal diagnosis of epilepsy. Few had microcephaly (3/10). Facial dysmorphisms were common (9/9) and included abnormal palpebral fissures, deep prominent concha, high broad forehead, hypertelorism, thin upper lip and mild synophrys (each in 4 or less individuals). Short stature or skeletal alterations were described in some (4/10 each).

Role of the gene: UBAP2L encodes an essential regulator of stress granule assembly. Stress granules are membraneless cytoplasmic compartments in eukaryotic cells, induced upon a variety of stressors and playing a role in regulation of gene expression.

Variants identified : 9 nonsense/frameshift UBAP2L variants and 3 splicing ones were reported, in all cases as de novo events, upon trio/quad exome sequencing. All were absent from gnomAD. There were no other causative variants.

Variant effect/studies (NM_014847.4 / NP_055662.3) :
- Minigene assays revealed that the 3 splice variants all resulted in out-of-frame exon skipping.
- In patient fibroblasts one of these splice variants was demonstrated to result to reduced protein levels.
- 8 of the 9 nonsense/frameshift variants were predicted to result to NMD.
- 1 nonsense variant (c.88C>T/p.Q30*) was shown to result to decreased protein expression in patient fibroblasts, with detection of the protein using an antibody for the C terminus but not the N terminus. Protein N-terminal sequencing confirmed that the protein lacked the N terminus, with utilization of an alternative start site (11 codons downstream).
- Generation of HeLa UBAP2L KO cell lines resulted in significant reduction of SG numbers which was also the case for 4 variants studied, under stress conditions.
- The protein has a DUF domain (aa 495-526) known to mediate interaction of UBAP2L with G3BP1 (a stress granule marker) with deletions of this domain leading to shuttling of UBAP2L from the cytoplasm to the nucleus. Truncating variants upstream of the DUF domain were shown to result in nuclear localization.

Mouse model :
- The authors generated Ubap2l KO model with hmz deletion of Ubap2l resulting in a lethal phenotype (2.6% survived) and htz deletion leading to behavioral issues (low preference for social novelty, anxious-like behaviors) and cognitive impairment.
- Ubap2l haploinsufficiency resulted in abnormal cortical development and lamination with reduction of neural progenitor proliferation.
- Ubap2l deficiency was shown to impair SG assembly during cortical development both under physiological stress conditions or upon utilization of an oxidative stress inducer.

Additional evidence of UBAP2L and SG overall in pathogenesis of NDDs:
- Based on DNMs from 40,853 individuals with NDDs from 26 studies (9,228 with ASD, 31,625 with DD/ID) the authors demonstrate significant excess of DNM in 31 genes encoding SG components, regulators or both, the latter being the case for UBAP2L and 2 further genes (G3BP1 and G3BP2 - both with crucial roles in SG assembly).
- Excess dn splice-site (N=3) and missense (N=5) variants in G3BP1 were observed in the above cohort [c.95+1G>A, c.353+1G>T, c.539+1G>A / p.S208C, R320C, V366M].
- Excess dn missense (N=7) variants in G3BP2 were observed in the above cohort [p.R13W, D151N, E158K, L209P, E399D, K408E, R438C].
- Generation of G3BP1 or G3BP2 KO HeLa cell lines and immunofluorescence upon use of oxidative stress inducer revealed significant reduction of stress granules.
- Generation of HeLa cell lines for 5 G3BP1 mutants (R78C*, R132I*, S208C*, R320C*, V366M) and 7 G3BP2 mutants (p.R13W*, D151N*, E158K, L209P*, E399D, K408E, R438C) revealed that several (those in asterisk) resulted in significantly fewer SG formation under oxidative stress compared to WT while the subcellular distribution of the proteins under stress was identical to WT.
- Among the identified genes for SG enriched for DNMs, CAPRIN1 was implicated in previous publications as a NDD risk gene with 3 dn missense SNVs reported (p.I373K, p.Q446H, p.L484P). CAPRIN1 binding to G3BP1/2 has been shown to promote SG formation. Significant reduction of SG was observed in CAPRIN1 KO HeLa lines. p.I373K abolished interaction with G3BP1/2 and disrupted SG formation.
Sources: Literature
Intellectual disability v3.1632 TAF8 Jana Jezkova changed review comment from: Eight patients reported in total. Six patients are homozygous for a recurrent NM_138572.2, c.781-1G>A variant. In two sibling patients, two novel compound heterozygous TAF8 splice site mutations, c.45+4A > G and c.489G>A were identified, which cause aberrant splicing as well as reduced expression and mislocalization of TAF8.
Sources: Literature; to: Eight patients reported in total. Six patients are homozygous for a recurrent NM_138572.2, c.781-1G>A variant. In two sibling patients, two novel compound heterozygous TAF8 splice site mutations, c.45+4A > G and c.489G>A were identified, which cause aberrant splicing as well as reduced expression and mislocalization of TAF8.
Sources: Literature
Intellectual disability v3.1632 TAF8 Jana Jezkova gene: TAF8 was added
gene: TAF8 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TAF8 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TAF8 were set to PMID: 35759269
Phenotypes for gene: TAF8 were set to severe developmental delay; feeding problems; microcephaly; growth retardation; spasticity; epilepsy
Penetrance for gene: TAF8 were set to unknown
Review for gene: TAF8 was set to AMBER
Added comment: Eight patients reported in total. Six patients are homozygous for a recurrent NM_138572.2, c.781-1G>A variant. In two sibling patients, two novel compound heterozygous TAF8 splice site mutations, c.45+4A > G and c.489G>A were identified, which cause aberrant splicing as well as reduced expression and mislocalization of TAF8.
Sources: Literature
Intellectual disability v3.1628 PPFIBP1 Konstantinos Varvagiannis gene: PPFIBP1 was added
gene: PPFIBP1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PPFIBP1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PPFIBP1 were set to 35830857; 30214071
Phenotypes for gene: PPFIBP1 were set to Global developmental delay; Intellectual disability; Microcephaly; Seizures; Abnormality of brain morphology; Abnormality of the cerebral white matter; Cerebral calcification; Abnormal cortical gyration; Hypertonia; Spastic tetraplegia; Generalized hypotonia; Small for gestational age; Growth delay; Failure to thrive; Feeding difficulties; abnormal heart morphology; Hearing abnormality; Cryptorchidism; Abnormality of vision
Penetrance for gene: PPFIBP1 were set to Complete
Review for gene: PPFIBP1 was set to GREEN
Added comment: Consider inclusion with green rating in the ID, epilepsy as well as other likely relevant gene panels (microcephaly, white matter disorders, corpus callosum abnormalities, intracerebral calficication disorders, malformations of cortical development, hereditary spastic paraplegia, growth failure in early childhood, etc) based on the summary below.

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Rosenhahn et al (2022 - PMID: 35830857) describe the phenotype of 16 individuals - belonging to 12 unrelated families - with biallelic PPFIBP1 pathogenic variants. Most (14/16) were born to consanguineous parents. One of these families was previously reported by Shaheen et al (2019 - PMID: 30214071) who first identified PPFIBP1 as a candidate gene for congenital microcephaly. In the current study, Rosenhahn also identified a fetus homozygous for a missense variant and similar features.

All individuals presented global DD/ID (16/16 - in 15 cases profound/severe) and epilepsy (16/16 - onset 1d-4y / median 2m - focal seizures in 11/16, epileptic spams in 7/16, generalized onset in 7/16, myoclonic in 6/16 - drug-resistant : 13/16). Almost all (15/16) had microcephaly, commonly congenital (9/16) and progressive (11/16). Other neurological findings included hypertonia (10/16), spastic tetraplegia (6/16), hypotonia (5/16), dystonic movements (3/16) or nystagmus (4/16). Brain abnormalities were identified in all investigated with MRI and included leukoencephalopathy (11/14) mostly periventricular, abnormal cortex morphology (7/14 - polymicrogyria 1, increased cortical thickness 4, pachygyria 3), cortical atrophy, corpus callosum hypoplasia (7/14). Intracranial calcifications were identified in all (9/9) investigated with CT scan. Abnormal growth was reported for several (SGA in 9/16, FTT 8/16, short stature 7/16) often associated with feeding difficulties (7/16). Other features incl. abnormal hearing (4/16), congenital heart defects (7/16), ophthalmologic findings (8/16), undescended testes (3/10). There were no overlapping facial features.

The fetus displayed similar features incl. SGA, microcephaly, intracranial calcifications.

Investigations incl. exome/genome sequencing (singleton or trio) with Sanger for confirmation/segregation of variants where necessary. Variable previous investigations incl. metabolic screening, TORCH screening, chromosomal studies (CMA) are mentioned in the supplement and were non-diagnostic. Additional candidate variants were identified in few cases although cases with plausible dual diagnoses (e.g. ind14) were not included in the overall phenotypic description.

9 pLoF variants (nonsense, frameshift, 1 splicing) predicted to lead to NMD were identified. There were no functional studies performed.
The missense variant c.2177G>T / p.Gly726Val (NM_003622.4) was predicted deleterious by in silico tools while the AA change causing severe steric problems upon modelling.

PPFIBP1 encodes PPFIA-binding protein 1 also known as liprin-β1. As the authors discuss: The liprin family of proteins comprises liprins α1 to 4 and liprin β1 and β2 in mammals. Liprin β1 is known to homodimerize and heterodimerize with α-liprins. In fibroblast cultures liprins β1 and α1 colocalize to cell membrane and periphery of focal adhesions. Members of the liprin-α fam. are scaffold proteins playing a role in synapse formation/signaling and axonal transport.

A ko model of the PPFIBP1 ortholog in C.elegans displayed abnormal locomotion behavior. In Drosophila, null-allele mutants resulted in altered axon outgrowth and synapse formation of R7 photoreceptors and reduced neuromuscular junction size (Refs provided in article).

Using a PPFIBP1/hlb-1 ko C.elegans model the authors demonstrated defects in spontaneous and light-induced behavior. Sensitivity of the worms to an acetylcholinesterase inhibitor (aldicarb) was suggestive of a presynaptic defect.

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There is currently no PPFIBP1 - associated phenotype in OMIM / G2P.
SysNDD lists PPFIBP1 among the ID genes (limited evidence based on the 3 sibs reported by Shaheen et al, 2019 - PMID: 30214071).
In PanelApp Australia the gene is listed with green rating for ID, epilepsy, microcephaly based on the medRxiv pre-print.
Sources: Literature
Intellectual disability v3.1622 WNK3 Arina Puzriakova Mode of inheritance for gene: WNK3 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1618 WNK3 Arina Puzriakova reviewed gene: WNK3: Rating: GREEN; Mode of pathogenicity: None; Publications: 35678782; Phenotypes: Intellectual disability, MONDO:0001071; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1580 DROSHA Konstantinos Varvagiannis gene: DROSHA was added
gene: DROSHA was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DROSHA was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: DROSHA were set to 35405010
Phenotypes for gene: DROSHA were set to Global developmental delay; Intellectual disability; Seizures; Cerebral white matter atrophy; Abnormality of the corpus callosum; Abnormality of movement; Stereotypic behavior; Abnormality of head or neck; Short foot
Penetrance for gene: DROSHA were set to unknown
Mode of pathogenicity for gene: DROSHA was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: DROSHA was set to AMBER
Added comment: Profound DD, ID and seizures have been reported in 2 unrelated subjects with de novo missense variants. The gene has a role in miRNA biogenesis. Both variants described have been shown to have effect on DROSHA's function in Drosophila / C. elegans (partial loss-of-function vs possibility of antimorphic effect discussed || in gnomAD several individuals with LoF alleles / Z=3.98 – pLI : 0.09).

There is currently no DROSHA-related phenotype in OMIM, G2P, SysNDD. In PanelApp Australia the gene has amber rating in genetic epilepsy and microcephaly panels (not currently included in the ID one).

Consider inclusion in the current panel with amber rating. Also consider inclusion in other possibly relevant panels (given postnatal microcephaly, abn. corpus callosum, progressive white matter atrophy, etc) [ NOT added ]

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Barish, Senturk, Schoch et al (2022 - PMID: 35405010) describe the phenotype of 2 unrelated individuals with de novo missense DROSHA variants.

Features included generalized hypotonia, postnatal microcephaly (-2,6 and -6 SD), feeding difficulties, profound DD and ID, seizures, abnormal movements (choreoathetosis / stereotypic movements), variable respiratory symptoms (in one case episodes of hyperventilation/apnea), cardiovascular or skeletal findings. Brain MRI demonstrated white matter atrophy and thin corpus callosum in both. Brachycephaly with broad face as well as short feet were also among the shared features.

Both were investigated by trio ES/GS which were otherwise non diagnostic and without other candidate variants. The 1st individual harbored a de novo htz missense DROSHA variant (c.3656A>G/p.Asp1219Gly) while the 2nd subject had another missense variant (c.4024C>T/p.Arg1342Trp) [NM_013235.4] confirmed by Sanger seq.

DROSHA (on 5p13.3) encodes a ribonuclease, subunit of the microprocessor complex, involved in miRNA biogenesis. Specifically, miRNAs are transcribed as part of pri-miRNAs (primary-miRNAs) which are cleaved to pre-miRNAs (precursor-miRNAs) in the nucleus by DROSHA (and its partner DGCR8 or Pasha) and then exported to the cytoplasm for further processing. Cleavage of pre-miRNAs by DICER1 generates mature miRNAs subsequently loaded to the RISC (RNA-induced silencing) complex which uses miRNA as template for recognition and cleavage of complementary mRNA with RNAse.

As the authors discuss, miRNA defects have a well-established role in development of model organisms e.g. (several Refs. provided):
- in C. elegans miRNA mutants causing lethality, developmental arrest and heterochronicity
- in Drosophila playing a role in the development of ovary, eye, nervous system etc.
- in mice mRNAs play a role in BMP and TGF-beta signaling while neuronal loss of miRNA processing leads to neurodegeneration/anatomical defects.

Feingold syndrome 2 is the single Mendelian disease associated to date with miRNAs, through deletion of a cluster containing 6 MIR genes.

miRNA dysregulation is also observed in Rett syndrome - and DROSHA implicated in the pathogenesis of the syndrome - as MECP2 and FOXG1 are cofactors of the microprocessor complex regulating processing of miRNA. One of the individuals here reported had a clinical diagnosis of Rett spectrum while both had overlapping features with Rett s.

Studies of DROSHA-dependent miRNAs in fibroblasts from one individual revealed significantly altered expression of mature miRNA (e.g. increased miR98, a miRNA with reduced expression in studies of somatic DROSHA variants) although this was not likely due to processing errors (given only a modest decrease of precursor miRNAs).

Previous studies have demonstrated that drosha (the Drosophila ortholog) null mutants die during post-embryonic development with 100% lethality before adulthood (3rd instar larval stage/beginning of pupariation). Mosaic flies with mutant eyes are small-eyed, while viable hypomorphic alleles display synaptic transmission defects (several Refs provided).

Here, homozygous flies for null alleles died at the end of 3rd instar larval stage/beginning of pupariation, while loss of drosha resulted in lack of imaginal disc tissue (which surrounds the larval brain) and severely reduced brain size, the latter similar to the microcephaly phenotype. [To the best of my understanding] introduction of a mutated genomic rescue construct (carrying similar substitutions as those observed in human subjects) in eye-specific drosha null (W1123X) flies was partially able to rescue eye/head size for wt or Asp1219Gly (human:Asp1084Gly) suggesting that the latter is a partial LoF allele. Arg1210Trp (corresponding to human Arg1342Trp) was able to rescue the eye phenotype and was not damaging to the function in the specific assay. Drosha expression levels were similar for genomic rescue flies either for wt or for the Asp-Gly variant suggesting that the effect was not due to expression levels (but rather function). Expression of mature miRNAs known to be regulated by Drosha were not affected when comparing wildtype larvae with genomic construct for wt or Asp1084Gly.

Upon expression of human cDNA using GAL4/UAS system in drosha mutant (null) eye clones, the reference partially rescued the eye size defect, Asp-Gly behaved as partial loss-of-function allele (~50% function compared to ref), while the Arg-Trp variant was shown to behave as a weaker loss-of-function allele.

The authors generated eye-specific drosha mutant clones to study the aging adult eye using ERG recordings. While null mutants display almost no response to light (7- and 20-day old flies), wt genomic rescue was shown to rescue ERG responses, Asp-Gly variant had significant defects (at both 7 and 20 days) and the Arg-Trp had defects approaching statistical significance only at the age of 20 days. Overall these data suggested that Arg-Trp had less severe effect compared to Asp-Gly (as above) while both variants led to progressive neuronal dysfunction.

Using CRISPR/Cas9 the authors generated C.elegans knock-ins for a variant analogous to the Asp1219Gly human one. Homozygous animals were inviable at larval stages, displayed a heterochronic phenotype (heterochronicity : development of cells or tissues at an abnormal time relative to other unaffected events in an organism / miRNAs are known to be involved in the heterochronic gene pathway) while this variant was deleterious to the Drosha's ability to process miRNAs.
Sources: Literature
Intellectual disability v3.1568 ROBO1 Konstantinos Varvagiannis gene: ROBO1 was added
gene: ROBO1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: ROBO1 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: ROBO1 were set to 35348658; 35227688; 34193621; 31448886; 30692597; 29194579; 28592524; 28402530; 28286008
Phenotypes for gene: ROBO1 were set to ROBO1-related NDD
Penetrance for gene: ROBO1 were set to unknown
Review for gene: ROBO1 was set to AMBER
Added comment: DD/ID has been reported in some individuals with biallelic (e.g. 4 subjects in the study by Münch et al, 1 additional case reported by Calloni et al) or monoallelic ROBO1 variants (e.g. P2 in the study by Huang et al, with a diagnosis of EOEE due to a neomorphic variant).

Consider amber rating pending further review.

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Huang et al (2022 - PMID: 35348658) Monoallelic & Biallelic
Novel dominant and recessive variants in human ROBO1 cause distinct neurodevelopmental defects through different mechanisms.

Münch et al (2022 - PMID: 35227688) Biallelic
Biallelic pathogenic variants in roundabout guidance receptor 1 associate with syndromic congenital anomalies of the kidney and urinary tract

Woodring et al (2021 - PMID: 34193621) - Probably not relevant (VUS)
Uncertain, Not Unimportant: Callosal Dysgenesis and Variants of Uncertain Significance in ROBO1

Liu et al (2020 - PMID: 31448886) Monoallelic
A Novel Missense Mutation in Human Receptor Roundabout-1 (ROBO1) Gene Associated with Pituitary Stalk Interruption Syndrome.

Dateki et al (2019 - PMID: 30692597) Biallelic - This individual has been incl. in the study by Munch et al
A homozygous splice site ROBO1 mutation in a patient with a novel syndrome with combined pituitary hormone deficiency

Rasmussen et al (2018 - PMID: 29194579) Biallelic
Targeted gene sequencing and whole-exome sequencing in autopsied fetuses with prenatally diagnosed kidney anomalies

Kruszka et al (2017 - PMID: 28592524) Monoallelic
Loss of function in ROBO1 is associated with tetralogy of Fallot and septal defects

Bashamboo et al (2017 - PMID: 28402530) Monoallelic
Mutations in the Human ROBO1 Gene in Pituitary Stalk Interruption Syndrome

Calloni et al (2017 - PMID: 28286008) Biallelic
Compound Heterozygous Variants in ROBO1 Cause a Neurodevelopmental Disorder With Absence of Transverse Pontine Fibers and Thinning of the Anterior Commissure and Corpus Callosum
Sources: Literature
Intellectual disability v3.1568 POLR3B Arina Puzriakova Mode of inheritance for gene: POLR3B was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Intellectual disability v3.1564 BUB1 Konstantinos Varvagiannis gene: BUB1 was added
gene: BUB1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: BUB1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: BUB1 were set to 35044816
Phenotypes for gene: BUB1 were set to Congenital microcephaly; Global developmental delay; Intellectual disability; Abnormal heart morphology; Growth delay
Penetrance for gene: BUB1 were set to Complete
Review for gene: BUB1 was set to AMBER
Added comment: A recent study provides evidence that this gene (biallelic variants) is relevant for inclusion in the DD/ID panel likely with amber / green rating (2 unrelated individuals with similar phenotype, 3 variants, role of this gene, extensive variant studies and demonstrated effects on cohesion and chromosome segregation, similarities with other disorders caused by mutations in mitosis-associated genes at the clinical and cellular level || number of affected subjects/families, different protein levels/kinase activity likely underlying few differences observed, role of monoallelic variants unclear).

This gene could probably be included in other panels e.g. for microcephaly (not added).

There is no BUB1-related phenotype in OMIM, G2P, SysID, PanelApp Australia.

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Carvalhal, Bader et al (2022 - PMID: 35044816) describe the phenotype of 2 unrelated individuals with biallelic BUB1 pathogenic variants and provide evidence for the underlying mechanism for this condition.

Common features comprised congenital microcephaly (2/2 | -2,8 and -2.9 SDs respectively / -7 and -4,9 SDs on last evaluation), DD/ID (2/2 - in one case with formal evaluation mild), some degree of growth retardation (2/2) and cardiovascular findings (2/2 - small ASD type II). Other findings limited to one subject included Pierre-Robin sequence, Axenfeld-Rieger anomaly, choanal stenosis, hypospadias, tracheal stenosis, etc.

Initial genetic testing was normal (incl. CMA in both, metabolic testing and individual genes incl. PITX2, GREM1, FOXD3, FOXC1 for one proband).

Exome sequencing revealed homozygosity for a start-lost variant (NM_004336.4:c.2T>G / p.?) in the first subject (P1). The variant lied within a 14-Mb region of homozygosity (no reported consanguinity). The second individual (P2) was compound htz for a splice-site and a frameshift variant (c.2625+1G>A and c.2197dupG) with Sanger sequencing used for confirmation and segregation studies.

BUB1 encodes BUB1 Mitotic checkpoint serine/threonine kinase (/Budding uninhibited by benzimidazoles 1, s. cerevisiae, homolog of) a multifunctional component of the segregation machinery contributing to multiple mitotic processes. The protein has a kinetochore localization domain, multiple binding motifs and a C-terminal kinase domain (aa 784-1085) this structure allowing both kinase dependent/independent activities.

cDNA sequencing revealed that the splice variant leads to skipping of ex21 and in-frame deletion of 54 residues in the kinase domain (c.2625+1G>A / p.Val822_Leu875del).

Both individuals exhibited normal BUB1 mRNA levels (fibroblasts in both, tracheal tissue in one) but severely reduced protein levels (fibroblasts). A shorter protein product corresponding to the in-frame deletion variant was also detected.

The authors performed additional experiments to confirm small amounts of full-length protein produced by the start-lost variant. This was shown in SV40-transformed fibroblasts from the corresponding individual (treatment with a proteasome inhibitor resulted also in higher levels). Upon generation RPE1 cells using CRISPR for the start-lost variant, again, small amounts of full length protein were detected, which was not the case for complete knockout HAP1 cells. No shorter versions could be detected in the patient cells or RPE1 cells, arguing against utilization of an alternative start codon. (Use of non-AUG start codons discussed based on literature).

In line with small amounts of full-length protein the authors provided evidence for residual kinase activity for the start-loss variant (through proxy of phosphorylation of its substrate and use of a BUB1 kinase inhibitor). Cells from the individual with the frameshift variant and the splice variant had no residual kinase activity.

The authors provide evidence for mitotic defects in cells from both individuals with prolonged mitosis duration and chromosome segregation defects. Some patient-specific findings were thought to be related with BUB1 protein levels (affecting BUB1-mediated kinetochore recruitment of BUBR1, important for chromosome alignment) and others due to residual kinase activity [->phosphorylation of H2A at Threonine 120-> affecting centromeric recruitment of Aurora B, SGO1 (role in protection of centromeric cohesion), TOP2A (a protein preventing DNA breakage during sister chromatid separation), these correlated with high anaphase bridges (in P2), aneuploidy observed in lymphoblasts and primary fibroblasts from P2 but not P2's lymphocytes or lymphocytes from P1) and defective sister chromatid cohesion defects (in primary fibroblasts from P2, milder effect for P1).

Overall the authors provide evidence for overlapping clinical and cellular phenotype for this condition with primary microcephalies (MCPH - mutations in genes for mitotic regulators incl. kinetochore proteins or regulators of chromosome organization), mosaic variegated aneuploidy (biallelic variants in genes for kinetochore proteins, with random aneuploidies occurring in >5% cells of different tissues) and cohesinopathies (mostly Roberts or Warsaw breakage syndromes - characterized by cohesion loss and/or spontaneous railroad chromosomes).

Mouse model: Hmz disruption in mice is lethal shortly after E3.5 (cited PMID: 19772675), while a hypomorphic mutant mouse (lacking exons 2-3, expressing <5% of wt protein levels) is viable but exhibits increased tumorigenesis with aging and aneuploidy (cited PMID: 19117986). Mutant mice that lack kinase activity though with preserved Bub1 protein abundance, did not display increased susceptibility, despite substantial segregation errors and aneuploidies (cited PMID: 23209306).

The authors note that monoallelic germline BUB1 variants have been described in small number of individuals with CRC, exhibiting reduced expression levels and variegated aneuploidy in multiple tissues (cited PMID: 23747338) although the role of BUB1 is debated (cited PMIDs: 27713038, 29448935).

Based on the discussion, complete loss of BUB1 activity is presumed to be embryonically lethal based on the mouse study (PMID: 19772675) and reduced BUB1 expression associated with spontaneous miscarriages (cited PMID: 20643875, to my understanding in this study mRNA levels remained relatively constant despite reduced Bub1 protein levels, mRNA RT-PCR followed by sequencing revealed only 2 synonymous BUB1 variants).
Sources: Literature
Intellectual disability v3.1562 CTR9 Konstantinos Varvagiannis gene: CTR9 was added
gene: CTR9 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CTR9 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CTR9 were set to 35499524; 2815719; 25363760; 27479843; 25099282; 29292210
Phenotypes for gene: CTR9 were set to Delayed speech and language development; Motor delay; Intellectual disability; Behavioral abnormality; Autistic behavior; Failure to thrive; Feeding difficulties; Abnormality of the cardiovascular system
Penetrance for gene: CTR9 were set to unknown
Mode of pathogenicity for gene: CTR9 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: CTR9 was set to AMBER
Added comment: Meuwissen, Verstraeten, Ranza et al (2022 - PMID: 35499524) describe the phenotype of 13 unrelated individuals harboring heterozygous - predominantly de novo - CTR9 missense variants.

Overlapping features included delayed speech and/or motor development (each in 9 cases) with the latter complicated by hypotonia or hyperlaxity in some cases. Balance or coordination problems were also reported in some. Variable degrees of ID ranging from mild to severe were observed in all individuals of relevant age except for 3 who however experienced impairment in other domains and/or learning difficulties (8/11 - 2 individuals were too young for evaluation). Few had evidence of regression. Other features included behavioral abnormalities (incl. ASD in 4), FTT/feeding problems (in 5), cardiovascular findings (in 4 - incl. infantile thoracic aortic aneurysm, VSD, pulm. valve stenosis, SVAS). The authors reported variable/nonspecific dysmorphic features.

WES revealed heterozygous CTR9 missense variants in all cases (NM_014633.5 as RefSeq). The variants occurred de novo in most (11/13) individuals with a one proband having inherited the variant from his affected parent. For one case, a single parental sample was available. Most SNVs were absent from gnomAD with the exception of c.1364A>G/p.Asn455Ser and c.2633G>A/p.Arg878Gln present once in the database (Z-score for CTR9: 4.3 / pLI : 1). The variants affected highly conserved residues with in silico predictions mostly in favor of a deleterious effect.

CTR9 encodes a subunit of the PAF1 complex (PAF1C) with the other subunits encoded by PAF1, LEO1, CDC73, RTF1 and WDR61/SKI8. The complex acts as a transcriptional regulator with CTR9 binding RNA polymerase II. The complex influences gene expression by promoting H2BK123 ubiquitylation, H3K4 and H3K36 methylation. In yeast, Paf1 and Ctr9 appear to mediate involvement of Paf1C in induction of mitophagy (several Refs provided).

In silico modeling: a group of N-terminal variants likely destabilize structure, another group possibly perturbs CTR9-PAF1 interactions and a 3rd class influences interactions with other subunits. p.Glu15Lys did not appear to influence protein stability.

Functional studies: H3K4/H3K36 methylation analysis, mitochondrial quality assessment and RNA-seq studies in fibroblasts did not provide conclusive evidence for downstream consequences of the variants (albeit a brain-specific effect - as demonstrated for other disorders – cannot be excluded).

Animal models: In zebrafish, the Paf1C complex has been shown to play a role in cardiac specification and heart morphogenesis with ctr9 mutants showing severe defects in morphogenesis of primitive heart tube (cited PMID: 21338598). This supports a role of the CTR9 variants in the cardiac abnormalities observed in 4 individuals. Although Paf1C zebrafish homologues are required for Notch-regulated transcription (cited PMID: 17721442), there was no supporting evidence from RNA-seq analyses performed by the authors. In Drosophila, Ctr9 has a key role at multiple stages of nervous system development in Drosophila (cited PMID: 27520958). In rat, Ctr9 is expressed in dopaminergic neurons, with its expression not restricted to the nucleus, regulating dopamine transporter activity (cited PMID: 26048990).

As commented, de novo CTR9 variants have been identified in indivdiduals with developmental disorders in larger cohorts, though without phenotypic details (DDD study - PMID:2815719, De Rubeis et al, 2014 - PMID: 25363760, Lelieveld et al PMID: 27479843) [ https://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=CTR9 ]

Two previous studies (Hanks et al, 2014 - PMID: 25099282, Martins et al 2018, PMID: 29292210) have identified individuals with pLoF variants [in almost all cases leading to skipping of ex9 e.g. NM_014633.4:c.958-9A>G or (RefSeq not provided) c.1194+2T>C, c.1194+3A>C, the single exception being c.106C>T/p.Q36*] in individuals and families with Wilms tumor after exclusion of other genetic causes. Analyses of tumor samples revealed in several of these cases either LOH (most commonly) or truncating variants as second hits. These individuals did not display neurodevelopmental phenotypes (despite detailed clinical information provided in the 2 studies). CTR9 is included in the gene panels for WT and Tumor predisposition - childhood onset with green rating. [In addition few individuals with hyperparathyroidism jaw tumor syndrome due to heterozygous variants in CDC73 - another subunit of the PAF1 complex - have been reported with WT].

Given these reports, commenting on the embryonic lethality of Ctr9 homozygous ko mice (MGI) and the observation of only missense variants in their cohort Meuwissen, Verstraeten, Ranza et al presume that a dominant-negative effect may apply for the variants they report.

Consider inclusion in the current panel with amber (variant effect/underlying mechanism unknown) or green rating (>3 individuals/families/variants, multiple reports, some supporting evidence from animal models).
Sources: Literature
Intellectual disability v3.1561 GLRA2 Konstantinos Varvagiannis reviewed gene: GLRA2: Rating: GREEN; Mode of pathogenicity: Other; Publications: 20531469, 20479760, 26370147, 28588452, 35294868; Phenotypes: Global developmental delay, Intellectual disability, Autism, Behavioral abnormality, Seizures, Microcephaly, Abnormality of eye movement; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1558 SLC35B2 Konstantinos Varvagiannis gene: SLC35B2 was added
gene: SLC35B2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SLC35B2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: SLC35B2 were set to 35325049
Phenotypes for gene: SLC35B2 were set to Abnormality of the skeletal system; Short long bone; Short stature; Abnormality of epiphysis morphology; Scoliosis; Multiple joint dislocation; Global develpmental delay; Intellectual disability; CNS hypomyelination; Abnormality of the corpus callosum; Cerebral atrophy; Abnormality of the amniotic fluid
Penetrance for gene: SLC35B2 were set to Complete
Review for gene: SLC35B2 was set to AMBER
Added comment: 2 unrelated individuals with biallelic SLC35B2 variants have been reported. DD and ID were part of the phenotype.

There is currently no associated phenotype in OMIM/G2P/SysID. The gene has amber rating in the leukodystrophies panel of PanelApp Australia.

Consider inclusion in the current panel (or other possibly relevant ones eg. for skeletal disorders, short stature, white matter disorders, corpus callosum, etc) with amber rating.

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Guasto et al (2022 - PMID:35325049) report 2 unrelated individuals with biallelic SLC35B2 variants.

SLC35B2 encodes solute carrier family 35 (3'-phosphoadenosine 5'-phosphosulfate (PAPS) transporter), member B2.

The protein is located in the Golgi membrane and serves as transporter of the activated nucleotide sulfate PAPS from the cytosol, where it is synthesized to the Golgi lumen. Another PAPS transporter is encoded by SLC35B3. In the Golgi apparatus PAPS serves as substrate of sulfotransferases for the addition sulfate to the covalently attached GAG chains of proteoglycans (PGs).

The phenotype corresponded to a chondrodysplasia manifesting as severe pre- and postnatal growth retardation (height <-4 SD and -8 SD), early scoliosis, multiple joint dislocations (in one). There was severe DD affecting motor and expressive language development with associated ID. Brain imaging was suggestive of hypomyelinating leukodystrophy with thin corpus callosum and cerebral atrophy. One individual had a cleft palate in the context of Pierre Robin sequence.

Both individuals were investigated with exome sequencing.

The first individual - born to consanguineous parents - was homozygous for an in-frame del (NM_178148.3:c.1218_1220del, p.Leu407del) with Sanger sequencing confirming the variants, and heterozygosity in parents and 2 unaffected sibs. There was an initially identified hmz CUL7 variant (for 3M syndrome), which was not felt sufficient to explain the severity of the phenotype and notably ID.

The 2nd proband was homozygous for a fs variant (c.1224_1225delAG / p.Arg408SerfsTer18 - leading to loss of the last 8 amino acids) occurring in the context of uniparental isodisomy [iUPD(6)] spanning the complete chr6 based on the exome data.

Among the evidence presented for SLC35B2 and the variants :
- SLC35B2 has high mRNA expression in fetal and adult mouse brain and other tissues.
- Upon qPCR analysis of mRNA expression in human brain samples, the gene had expression across the brain (frontal lobe grey matter, subcortical frontal white matter/cerebellum).
- High expression was shown upon analysis of mouse brain single cell RNA data (EMBL) in oligodendrocytes and microglial cells.
- RT-PCR on mRNA from skin fibroblasts (both individuals) revealed significant decrease of SCL35B2 mRNA levels compared to controls.
- Transfection of C-terminal c-myc tagged wt or mutant proteins in HEK293F cells, followed by western blotting did not reveal significant difference at the protein level. Wt SLC35B2 localized at the Golgi apparatus as suggested by colocalization with GM130 marker. The 2 variants however displayed only partial colocalization (/loss of localization specificity) with diffuse signal in the cell.
- Chondroitin sulfate disaccharide sulfation was decreased upon HPLC disaccharide analysis in patient fibroblasts and bikunin (a circulating proteoglycan in blood) electrophoretic pattern in patient sera.
- Disorders due to variants in genes implicated in proteoglycan biogenesis (e.g. XYLT1, B3GALT6, CHSY1) are associated with skeletal/connective tissue manifestations with DD/ID.
- C-elegans model lacking pst-1 (SLC35B2 ortholog) provides support that the protein is required for migration, axonal guidance, and presynaptic development in a subset of neurons.
- dsm-1 - the rat ortholog - is expressed in rat brain in D-serine and NMDA receptor rich regions. When expressed in Xenopus oocytes it accelerated the efflux of D-serine (a co-agonist for NMDA receptor).
- Variants in other members of SLC superfamily (e.g. SLC17A5, SLC35A3, SLC29A3, SLC35A2) have been associated with brain-bone phenotypes.
Sources: Literature
Intellectual disability v3.1556 FBXW7 Konstantinos Varvagiannis gene: FBXW7 was added
gene: FBXW7 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: FBXW7 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: FBXW7 were set to 33057194; 35395208; 30885698; 26482194; 19963109; 20332316
Phenotypes for gene: FBXW7 were set to Neurodevelopmental abnormality; Global developmental delay; Intellectual disability; Macrocephaly; Microcephaly; Abnormality of brain morphology; Abnormality of the corpus callosum; Abnormality of the cerebellum; Abnormality of the cardiovascular system; Seizures; Strabismus; Abnormality of the palate
Penetrance for gene: FBXW7 were set to unknown
Review for gene: FBXW7 was set to AMBER
Added comment: While Kaplanis et al (2020 - Ref1), identified FBXW7 among 285 genes significantly associated with developmental disorders, a recent study by Stephenson et al (2022 - Ref2) describes the neurodevelopmental phenotype of 35 individuals making this gene relevant to the current panel. There are previous reports of dn/inh germline variants in individuals (likely 7) with tumor predisposition although a neurodevelopmental phenotype was not reported in most cases.

There is currently no FBXW7-related phenotype in OMIM.

The gene is included in the DD panel of G2P [associated with: FBXW7-related developmental disorder (monoallelic), confidence: definitive, citing the study by Kaplanis et al]. SysID lists FBXW7 among the candidate ID genes (same Ref.). The gene has a green rating for ID in PanelApp Australia (VCGS participating in the recent publication).

Consider inclusion with amber/green rating. Also consider inclusion in other panels that may be relevant(macro/microcephaly, seizures, CHD, corpus callosum / cerebellar abnormalities, cleft palate, WT, etc).

[1]------------
Kaplanis et al (2020 - PMID: 33057194), by combining exome data from 31,058 parent offspring trios from the DDD study, Radboudumc and GeneDx, identified 285 genes significantly associated with developmental disorders, 28 of which (incl. FBXW7) not previously robustly associated with these disorders.

[2]------------
Stephenson et al (2022 - PMID: 35395208) provide clinical information on 35 individuals harboring germline monoallelic FBXW7 variants or chromosomal deletions spanning this gene.

The phenotype corresponded to a phenotypically variable NDD characterized by hypotonia (in about 2/3), neurodevelopmental abnormality (34/35 - as discussed later), seizures (8/35), abnormal brain morphology (13/17 - in 7/17 abnormal CC, in 5/17 abn. cerebellum, etc), head circumference (macrocephaly in 10/35, microcephaly in 2/35). Additional features included abnormal palate or uvula morphology (10/35 - cleft palate in 3 from 2 families while 1 individual from a 3rd family had bifid uvula) or abnormal heart morphology (11/35), ophthalmologic features (e.g. strabismus in 5/35) or hearing impairment (2/35). There was no recognizable gestalt (deeply set eyes with upper eyelid fullness in 9/35).

As for the DD/ID this ranged from borderline to severe, characterized as mild-moderate in 27/35, severe in 3/35. One individual did not present neurodevelopmental abnormality 1/35.

FBXW7 encodes F-box and WD40 domain protein 7 which is part of the SCF E3 ligase complex (SKP1/CUL1/F-box protein) exerting a role of recognition and binding of target proteins for degradation by the ubiquitin proteasome system. In this way FBWX7 participates in regulating a network of proteins involved in cell division, growth, differentiation (as summarized by Roversi et al - Ref2).

Most individuals were investigated by trio-WES/WGS (few with singleton WES or CMA only). 28 germline FBXW7 variants were identified incl. missense (N=21), pLoF (predicted or not to undergo NMD) and 2 deletions encompassing but not limited to FBXW7.

Additional SNVs/CNVs (e.g. an inh intragenic DPP6 dup in one individual (#9) with deletion, other de novo 4q CNVs (#10), an inh 22q spanning partially an ISCA TS region, a CACNA1A and KMT2D SNV, etc) were reported in few individuals.

Most variants arose dn (N=30) with two individuals displaying mosaicism (2/30) and three individuals having inherited the variant from their affected parent. CNVs had occurred dn.

3 missense SNVs were recurrent in unrelated individuals.

All variants identified affected all FBXW7 isoforms.

As the authors comment missense variants clustered at the C-terminal half of the protein with most (16/21) occurring within the WD40 domain. [The N-terminal part commented in the literature to affect localization].

The crystal structure of FBXW7 and SKP1 complex has been determined with CYCLIN E1/DISC1 as substrates, and in silico modeling revealed that all missense variants aligned with residues required for this interaction, or adjacent ones.

All were absent from gnomAD, while missense variants from gnomAD (N=78) were not predicted have significant effect on the binding affinity.

Variant studies revealed that most missense variants (6/7 tested - Arg689Gln being the exception) are unlikely to cause protein instability or degradation in vivo.

Co-expression of these missense variants with CYCLIN E1 / E2, known FBXW7 substrates revealed that variants were less efficient at degrading the substrate with variants in the WD40 domain having greater impact (in some cases E1 / E2 - specific).

Elav-Gal4 mediated neuronal knockdown of the Drosophila ortholog archipelago (ago) using 2 RNAi-s with different efficiency was shown to affect learning or compromise neuronal function (also related to the level of knockdown).

The authors summarize results from animal models for the role of this gene in development and the nervous system.

KO mice die in utero at E10.5 manifesting abn. of hematopoietic or vascular development and heart-chamber maturation(*). Some htz knock-in for human cancer variants, display perinatal lethality, abn lung, cleft palate (30%)(*),etc. Conditional gut specific deletion results in impaired differentiation of intestinal goblet cells (*)(constipation in 16/35 in cohort). KO limited to CNS and PNS results in defective sucking and morphological brain abnormalities. Haploinsufficiency in the nervous system was associated with impaired differentiation of neural stem cells (possibly through a Notch-mediated mechanism). KO in Schwann cells of the peripheral nervous system resulted in enhanced myelination.

Excessive oligodendrocyte cells and hypermyelination (as a result of elevated Notch & mTOR signaling) are observed in homozygous mutant zebrafish or after morpholino-mediated fbxw7 knockdown.

Overall, the authors propose haploinsufficiency or loss-of-function as the underlying mechanism.

Finally, as the authors comment, FBXW7 is a tumor suppressor among the most commonly mutated genes in human cancer (3.5%). Germline variants have been previously reported in individuals with cancer (Wilms tumor, rhabdoid, etc - most summarized below). However, none of the 35 individuals in this cohort (oldest 44 y.o.) had any history of cancer.

Reports of individuals with germline variants causing (monoallelic) disruption of FBXW7 - cases without DD/ID:

[3]------------
Mahamdallie et al (2019 - PMID: 30885698) investigated with WES a cohort of 890 individuals with Wilms tumor (799 non-familial disease, 91 from WT pedigrees). In this context they identified 4 individuals having developed WT (ages: 28-76m) with FBXW7 dn or inherited LoF variants (710G>A / p.Trp237* dn - 1972C>T / p.Arg658* - inh:NA, 1017_1021del5, 670C>T - paternal / p.Arg224* inh:NA - RefSeq not provided). One additional individual with a missense variant (1753A>T / p.Ser585Cys - dn) had developed rhabdoid tumor. While the authors mentioned additional features for other subjects in their cohort, among the 5 individuals with FBXW7 variants, only one had hypotonia (ID_0592) and another (ID_7520) had two febrile convulsions.

[4]------------
Roversi et al (2015 - PMID: 26482194) described the phenotype of a 34 y.o. female with syndromic presentation (macrocephaly, nephrotic syndrome due to FSGS, Hodgkin's lymphoma, Wilms tumor, ovarian cystadenoma, breast carcinoma) harboring a 157 kb deletion of 4q31.3.

Eventual DD/ID was not reported despite detailed clinical description.

The deletion spanned almost the entire FBXW7 gene and a pseudogene (hg19 - chr4:153205202-153362047). The authors provided evidence that the del affected the maternal allele as dn event (maternal mosaicism excluded). Expression of FBXW7 in patient-derived EBV lymphoblastoid cell line revealed decreased levels of expression compared to controls. At somatic level, the authors looked for eventual 2nd hit in tumor tissue (which was not the case) while they demonstrated decreased FBXW7 expression in a WT sample compared to normal renal tissue. Previously, variants in other genes candidate for the phenotype were ruled out (Sanger & MLPA for TP53, BRCA1/2, PALB2, WT1, 11p15 MS-MLPA, std karyotype).

[5]------------
Kuiper et al (2015 - PMID: 19963109), in a 58 y.o. patient with recurrence of RCC, identified a constitutional translocation [t(3;4)(q21;q31)]. Using long-range PCR they defined the breakpoints at 3q21.3 (128379059 - hg18) between the PLXNA1 and C3orf56 genes while the chr4 breakpoint was located within the second intron of FBXW7 (pos. 153500813 - hg18). There were no additional phenotypes reported.

[6]------------
Williams et al (2010 - PMID: 20332316) reported a patient with WT harboring germline variants in WT1 and FBXW7. While the phenotype was sufficiently explained by a germline stopgain WT1 variant with a frameshift WT1 variant (as 2nd hit) confined to the tumor, the authors identified a germline in-frame FBXW7 insertion in the same individual (c.45_46insCCT / p.Thr15_Gly16insPro - RefS : NA) [if correct corresponding to: https://gnomad.broadinstitute.org/variant/4-153332910-C-CAGG - 345/281696 alleles in gnomAD].
Sources: Literature
Intellectual disability v3.1544 DTYMK Konstantinos Varvagiannis gene: DTYMK was added
gene: DTYMK was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DTYMK was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DTYMK were set to Global developmental delay; Intellectual disability; Microcephaly; Seizures; Global brain atrophy; Cardiorespiratory arrest
Phenotypes for gene: DTYMK were set to 31271740; 34918187; 35346037
Penetrance for gene: DTYMK were set to Complete
Review for gene: DTYMK was set to GREEN
Added comment: 4 individuals (from 3 families) harboring biallelic DTYMK pathogenic variants have been reported.

Consider inclusion in the current panel with green rating given consistent and relevant phenotype and evidence provided to date [effect of variants (LoF), pathogenesis, similar phenotypes in zebrafish model, etc].

Relevant studies are summarized below.
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Lam et al (2019 - PMID: 31271740) described two siblings aged 25m and 7y, harboring biallelic DTYMK variants.

The phenotype consisted of hypotonia, congenital microcephaly, DD, severe ID. Other shared features included raised serum lactate, pyruvate and alanine. The phenotype was more pronounced in the younger one (epilepticus during febrile illness, epilepsy on multiple anti-convulsants, evidence of regression, etc). Brain MRI revealed marked cerebral atrophy among the findings while a lactate peak was present in spectroscopy. The elder brother developed an episode of sudden onset coma with respiratory failure at the age of 7y.

Quartet WES identified compound heterozygosity for a fs and a missense DTYMK variant (NM_012145.3:c.287_320del / p.Asp96Valfs*8 - c.295G>A / p.Ala99Thr). There were no additional findings. Previous genetic panel analysis for epilepsy was unremarkable for the 1st sib.

There are two pathways for synthesis of dNTPs, the de novo pathway operating in the cytosol only and the salvage operating in both cytosol and mitochondria. DTYMK encodes (deoxy)thymidylate kinase which catalyzes conversion (phosphorylation) of dTMP to dTDP - a step right after convergence of both pathways - in the dTTP synthesis pathway.

Mutations in TK2, an enzyme phosphorylating thymidine in mitochondria to dTMP have been associated with mitochondrial DNA depletion syndrome (MDDS).

Given this and as the 2 sibs had raised serum lactate and pyruvate, the authors performed in silico analyses to calculate mtDNA/nDNA ratio dividing the respective read depths for mitochondrial and nuclear DNA obtained from WGS data of the two sibs (blood).

This ratio was shown to be reduced in the more severely affected sib (65.5% of control) although this was not the case for the mildly affected brother (114.6%). As a control a non-MDDS mitochondrial cytopathy sample (corresponding to m.8993T>G) was used. The respective ratio which was calculated for a known POLG-related MDDS case was 15.6%.
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Vanoevelen et al (2022 - PMID: 34918187) describe two unrelated children with hypotonia, absence of developmental progress, microcephaly, seizures (recurrent febrile seizures/myoclonic jerks). Severe cerebral atrophy (with unaffected cerebellum) was observed upon brain imaging. Other findings included puffy body/extremities. Both had complications following respiratory illness leading to demise. CNS pathology in the 1st individual revealed massive neuronal dropout, with sparing of dentate nucleus and brainstem.

CMA in both cases was normal. This was also the case for extensive metabolic investigations (which provided no evidence of eventual mitochondrial dysfunction).

WES revealed compound heterozygosity for 2 missense variants in the first individual (NM_012145.3:c.382G>A - p.Asp128Asn and c.242C>T - p.Pro81Leu). The second individual, born to consanguineous parents, was homozygous for c.242C>T / p.Pro81Leu.

In silico predictions varied although each variant were (mostly) suggestive of a deleterious effect.

Variants were both ultrarare without homozygotes in ExAC,.

The authors generated a dtymk ko zebrafish model (hmz for a frameshift variant). Zebrafish exhibited markedly smaller eyes and pericardiac edema (3dpf-), twitching movements somewhat reminiscent of epilepsy (at 3dpf), prominent edema of brain and intestine. Head size was significantly smaller at a timepoint prior to brain edema (also after correction for length). Histology provided evidence of empty spaces in brain, suggestive of neurodegeneration, with high amounts of apoptotic cells.

dTMPK activity was measured in zebrafish (at 5dpf) as well as in fibroblasts from one individual and in both cases, it was barely detectable and significantly lower compared to wt/htz zebrafish or to the activity in fibroblasts from the parents of the individual tested.

In fibroblasts from the same individual with comparison to his parents, the authors demonstrated that DNA replication was impaired (using pulse-EdU staining to quantify cells in S-phase).

Assessment of cell proliferation in the brain of dtymk ko zebrafish using phospo-Ser10-Histone H3 (pH3) staining was suggestive of severe proliferation defects in forebrain.

Impaired biosynthesis of nucleotides for DNA synthesis/repair would be predicted to result in nucleotide pool imbalance, leading to incorporation of ribonucleotides in genomic DNA with - in turn - impairment of DNA replication and genomic instability (sensitivity to strand breakage).

In line with this, genomic DNA of ko zebrafish following alkaline hydrolysis and alkaline gel electrophoresis was shown to migrate at lower position and to be more fragmented indicating increased sensitivity (due to incorporation of ribonucleotides).

Visualization of DNA breakage by γH2AX staining, following UV-irradiation of zebrafish embryos revealed persistence of elevated γH2AX levels and DNA damage response signaling, interpreted as increase in unrepaired DNA breaks.

mtDNA copy numbers in fibroblasts from the affected individual was somewhat but not significantly lower compared to his parents. Importantly, the copy numbers were similar to controls (N=5) which overall does not support mtDNA depletion as a consequence of DTYMK deficiency.

Integrity of mtDNA did not appear to be compromised , with the mitochondrial genome migrating at the expected length of 16,5 kb with no indications of mtDNA deletions for both affected individual and his parents.

Activity of the mitochondrial respiratory complexes I-V in fibroblasts from the affected individual was comparable to that of his parents.

Overall, there was no evidence for mtDNA depletion (although not studied in muscle biopsy) while functional studies failed to demonstrate mitochondrial dysfunction.

The authors discuss other disorders of impaired dTTP metabolism due to mutations in TYMP, RRM2B or CAD.
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In a recent study using zebrafish model, Hu Frisk et al (2022 - PMID: 35346037) further demonstrate that Dtymk is essential for neurodevelopment providing evidence for expression of a compensatory thymidylate kinase-like enzyme at later stages of development (explaining survival of ko dtymk zebrafish despite the central role of this enzyme in dTTP generation). [Not further reviewed]
Sources: Literature
Intellectual disability v3.1538 GDAP1 Arina Puzriakova Mode of inheritance for gene: GDAP1 was changed from BIALLELIC, autosomal or pseudoautosomal to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.1520 PAN2 Konstantinos Varvagiannis gene: PAN2 was added
gene: PAN2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PAN2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PAN2 were set to 29620724; https://doi.org/10.1038/s41431-022-01077-y
Phenotypes for gene: PAN2 were set to Global developmental delay; Intellectual disability; Sensorineural hearing impairment; Abnormality of the genitourinary system; Abnormality of the cardiovascular system; Abnormality of blood and blood-forming tissues; EEG abnormality; Seizures; Anorectal anomaly; Abnormality of the skeletal system; Abnormality of the eye; Abnormality of head or neck
Penetrance for gene: PAN2 were set to Complete
Review for gene: PAN2 was set to AMBER
Added comment: 1.
Maddirevula et al (2018 - PMID: 29620724) first reported on the phenotype associated with biallelic pathogenic variants in PAN2.

This concerned a male (15DG2222) born to consanguineous parents and exhibiting MCA, dysmorphic features and global DD (age of 34 m). Features incl. imperforate anus, metopic craniosynostosis, scoliosis, CHD (PFO, PDA, VSD), renal anomalies (duplicated collecting system) and abnormalities of the eye (posterior embryotoxon, maculopathy).

As the other 411 individuals from the cohort, the child had 1st-tier testing genetic testing using a dysmorphology/skeletal dysplasia panel of 296 genes.

Subsequent autozygome analysis (Axiom genotyping platform) was used to identify ROH (authors state "segregating within the family", in pedigree the proband was the single affected person and single child).

WES revealed a PAN2 indel. [NM_001166279.1:c.3162delC / p.(Ser1055Profs*4)].

There were no additional studies.

Role of PAN2 and animal models discussed as below.
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2.
Reuter et al. (2022 - https://doi.org/10.1038/s41431-022-01077-y) describe the phenotype of 5 additional individuals - from 3 unrelated families (2 consanguineous) - harboring biallelic PAN2 variants. The authors review the phenotype of the previously described case.

Features included DD (6/6), ID (4/5 with relevant age in the mild-moderate range, 1/5 had borderline IF), sensorineural hearing loss (5/6) and incompletely penetrant congenital anomalies of the heart (4/6 - TOF, septal defects, Ao root dilat), urinary malformations (4/6 - hypoplasia/agenesis, anovesical fistula), ophthalmological anomalies (2/6 - Rieger, posterior embryotoxon, etc). EEG anomalies or seizures were noted in 4/6. Craniofacial feat. in >=2/6 included cleft palate/bifid uvula, ptosis, hypertelorism, abn. of the nose, low-set ears, short neck. There was no comprehensive evaluation for skeletal dysplasia despite short stature/skeletal anomalies in multiple individuals. Hematological anomalies were reported in 2, possibly explained by another concurrent diagnosis (of GSD) in one individual.

WGS was performed for 1 individual, and WES for 4 members of the 2nd family and the proband in the 3rd. ROH identified in all 3 families (1 non-consanguineous but from the same region of Italy) are mentioned in the suppl. Sanger sequencing for parents and affected/unaffected sibs was mentioned for the 2 families with solo WGS/WES. One individual had a dual - previously established - diagnosis (of SLC37A4-related GSD) not related to his NDD. There were no other candidate variants except for VUS or variants in 'genes of uncertain significance'.

The majority of mammalian mature mRNAs have polyA tails, added during RNA processing. PAN2 encodes a subunit of the Pan2-Pan3 deadenylation complex which shortens mRNA 3' polyA tails, regulating mRNA stability/translation efficiency.

Specifically Pan2 is the catalytic subunit, while the interaction with Pan3 mediates efficient mRNA binding. Deadenylation in cytoplasm is mostly carried out by the Pan2-Pan3 or Ccr4-Not compexes. While perturbations of mRNA metabolism/decay are established causes of NDD and ID. In particular, monoallelic variants in genes of Ccr4-Not complex (inc. CNOT1/2/3) already causative of NDDs.

All affected individuals were homozygous for pLoF PAN2 variants, namely (NM_001166279.2): c.2335G>T / p.(Glu779*) [Fam1], c.3408dupT / p.(Glu1137*) [Fam2], c.574-2A>G / p.? [Fam3].

Variants were absent from gnomAD (where PAN2 has a pLI:0.94, o/e:0.19).

There were no variant studies performed. The splicing variant is predicted in silico to abolish the splice-acceptor site, with in-frame skippling of ex5 which codes a repeat within the WD40 domain. Previous studies in yeast have shown that this domain is important for sensing the length of the polyA tail, with absence of this domain resulting in impaired deadenylation of 90A tails (similarly to complete Pan2 del) [cited PMID: 31104843].

Overall PAN2 loss-of-function is thought to be the underlying disease mechanism.

Partial functional redundancy of Pan2/Pan3 (initiation of deadenylation) and Ccr4-Not complexes (further shortening of polyA) is speculated to mitigate consequences of PAN2 LoF in humans.

In yeast Pan2Δ, Ccr4Δ and Pan2Δ/Ccr4Δ have been studied with more severe phenotypes in double mutants where ability to shorten mRNA polyA tails was abolished [cited PMID:11239395]. In yeast extracts lacking Pan2p and Pan3p, transcripts were polyadenylated to >90-200 adenosines [cited PMID: 9774670]

Mouse mutants (MGI:1918984) had increased heart weight, increased eosinophil cell number while homozygosity for a stopgain allele (by ENU mutagenesis) was shown to result in embyonic lethality.

Finally, given the presence of thrombocytopenia and anemia in 3 individuals (2 families) as well as the link between mRNA deadenylation and telomere disease, telomere length analyses from WGS data were performed (TelSeq/Expansion Hunter dn), but there was no evidence for telomeric shortening.
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Currently, there is no PAN2-related phenotype in OMIM/G2P/SysID/PanelApp Australia.
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Consider inclusion in the ID panel with amber rating [>3 individuals/families/variants, though variant studies not performed (NMD/splicing) and authors of 2nd study recognize possibility of additional/concurrent diagnoses in individuals from consanguineous families, possibility of missed dn variants due to singleton WGS/WES in 2 fam. Also the presumed deadenylation defect not studied to date].

Please consider adding this gene to other panels - eg. for sens. hearing loss (5/6 - 3 fam), urinary tract anomalies (4/6 - 4 fam), congenital (4/6 - 3fam), anorectal malformations (2/6 - 2 families, incl. fistula or imperforate anus), clefting (2/6 - 1 fam), hematological disorders, etc.

For the time being, not added in epilepsy panel as some individuals had only EEG anomalies, few had also clinical seizures not necessarily requiring treatment.
Sources: Literature
Intellectual disability v3.1520 HIST1H4D Konstantinos Varvagiannis gene: HIST1H4D was added
gene: HIST1H4D was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: HIST1H4D was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: HIST1H4D were set to 35202563
Phenotypes for gene: HIST1H4D were set to Global developmental delay; Intellectual disability; Microcephaly; Growth abnormality; Abnormality of the face
Penetrance for gene: HIST1H4D were set to Complete
Mode of pathogenicity for gene: HIST1H4D was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: HIST1H4D was set to AMBER
Added comment: Histone H4 is a core component of the nucleosome, the basic repeating unit of eukaryotic chromatin. Each nucleosome consists of ~150 bp of DNA wrapped around a histone octamer. Each histone octamer is composed of 2 copies of each of the histones H2A, H2B, H3, H4. This organization is important for DNA replication, transcription and repair.

There are 14 canonical histone H4 genes in the human genome, which despite being different at the nucleotide level encode an identical protein. These cluster in 3 genomic loci. Their transcription is independently regulated with differing expression during brain development and in human tissues.

Histone H4 forms a dimer with H3 (which however has variant isoforms linked to specific cellular processes).

Pathogenic variants in genes encoding H4 have been reported in several individuals. Irrrespective of the gene for H4 involved, all patients presented with highly overlapping features, DD and ID being universal. Available reports to date concern :
- H4C3/HIST1H4C (9 subjects - PMID: 28920961, 35202563),
- H4C11/HIST1H4J (1 subject - PMID: 31804630, 35202563),
- H4C4/HIST1H4D (1 subject - PMID:35202563),
- H4C5/HIST1H4E (17 subjects - PMID: 35202563),
- H4C6/HIST1H4F (1 subject - PMID: 35202563),
- H4C9/HIST1H4I (3 subjects - PMID: 35202563).

Variants in all cases were missense SNVs, occurring (in almost all cases) as dn variants and affecting the same residue in the same and/or different H4 genes (details for clusters below). Eg. Arg45Cys was a recurrent variant for H4C5 (>=7 subjects), while variants affecting Arg40 have been reported in H4C4, H4C5, H4C9, H4C11 (7 subjects overall).

Zebrafish studies for all genes reported have included most - if not all - patient variants and recapitulate features observed in affected individuals (head size/structure and growth).

Additional studies specificaly for H4C3/HIST1H4C have been performed in patient fibroblasts (demonstrating among others transcriptional dysregulation) and zebrafish (accumulation of DSBs, increased apoptosis in head/tail, abn. cell cycle progression).

Note that the nomenclature for variants - at the protein level - used in literature commonly takes into consideration cleavage of Met1, thus the numbering may not correspond to the HGVS one.

Relevant entries exist in OMIM, G2P and SysID only for H4C3/HIST1H4C (Tessadori-van Haaften neurodevelopmental syndrome 1, #619758) and H4C11/HIST1H4J (?Tessadori-van Haaften neurodevelopmental syndrome 2, #619759) but not for other genes.

Rating in PanelApp Australia - ID Panel : HIST1H4C Green, H4J Amber, H4D Amber, H4E Green, H4F Amber, H4I Green.

Please consider inclusion in other possibly relevant panels (microcephaly, short stature/FTT, etc).

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Initial work from Tessadori et al (incl. DDD study, 2017 - PMID:28920961) identified monoallelic missense SNVs affecting the same residue of H4C3 (HIST1H4C), in 3 individuals from 2 families. [c.274A>C/ HGVS p.(Lys92Gln) dn in 1 subject and c.275A>C/ HGVS p.(Lys92Arg) inherited from unaffected mosaic parent].

Individuals from both families having relevant age had intellectual disability (2/2 - 2 families). Other features incl. growth delay (3/3) and microcephaly (3/3).

Expression of the variants in zebrafish severely affected structural development recapitulating the patient phenotypes (microcephaly and short stature).

RNA sequencing in fibroblasts from 2 unrelated patients and a control, revealed that expression of H4C3 variants was similar to wt. The authors estimated that ~8% of H4 cDNA molecules contained the variant. LC-MS/MS analysis suggested that the mutant protein was present in nucleosomes at a level of 1-2% while RNA-seq identified 115 differential expressed genes, with enrichment for relevant procedures (chr. organization, histone binding, DNA packaging, nucleosomal organization, cell cycle).

Post-translational modifications of Lys92 (H4K91) are highly conserved and have been previously associated with processes from chromatin assembly , DNA damage sensitivity, etc. Post-translational marks on Lys92 (K91) were absent in patient derived cells as a result of each variant.

Zebrafish models for both variants were suggestive for accumulation of double strand breaks (DSBs) more visible in heads and tails of larvae. Embryos expressing mutants displayed increased apoptosis in head and tail. Additional studies in larvae were suggestive of abnormal cell cycle progression (rel. increase in cellls in S/G2/M phase, increased occurrence of activated CHK2 with p53 stabilization) applying to both variants studied.

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In a subsequent publication, Tessadori et al. (2020 - PMID: 31804630) described the phenotype of a 14 y.o. boy harboring a dn heterozygous missense H4C11 (HIST1H4J) variant following trio-ES [c.274A>G / HGVS p.(Lys92Glu)]. Features incl. profound ID, microcephaly, short stature with some dysmorphic features (uplsanting p-f, hypertelorism, etc). Previous work-up was normal/non-diagnostic and incl. FMR1, MECP2 and a CMA showing an inherited 207 kb CNV involving KCNV1. Upon mRNA microinjection in zebrafish embryos - either for wt or for Lys92Glu HIST1H4J - effect for wt was very mild. Lys92Glu expression led to defective development of head structures (brain, eyes), faulty body axis growth and dysmorphic tail reproducing the microcephaly and short stature phenotype. This was similar to previous zebrafish studies for HIS1H4C variants (above).

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Tessadori et al. (2022 - PMID: 35202563) describe 29 *additional individuals with de novo missense variants in genes encoding H4, namely:
- H4C3 (HIST1H4C/N=6 subjects),
- H4C11 (HIST1H4J/N=1),
- H4C4 (HIST1H4D/N=1),
- H4C5 (HIST1H4E/N=17),
- H4C6 (HIST1H4F/N=1),
- H4C9 (HIST1H4I/N=3).

All individuals, exhibited DD and ID (29/29). Other features incl. hypotonia (10/29), seizures (5/29), autism (5/29), ataxia (4/29). Abnormal growth incl. progressive microcephaly (2/19 prenatal, 20/29 postnatal onset), short stature/FTT (each 11/29). Few had skeletal features (craniosynostosis 2/29, abn. digits 4/29, vertebral 4/29). Some had visual (17/28) or hearing impairment (7/29). Facial features incl. hypertelorism (5/29), upslanting p-f (3/29), broad nasal tip (11/29), thin upper lip (4/29) and teeth anomalies (6/29 - notably gap between central incisors).

The authors state that the cohort was collected with trio WES but also after data sharing via Genematcher / DECIPHER.

Identified variants were in all cases missense and de novo, the latter either by trio WES or Sanger sequencing of parents.

Previous work-up or presence of additional variants are not discussed.

At the protein level 10 aa were affected, 6 of which recurrently within the same gene (Arg45, His75, Lys91, Tyr98) as well among several genes for H4 (Pro32, Arg40). Variants lied within two clusters, one corresponding to the α-helix of H4 (reported variants affected Lys31 - Arg45) important for DNA contacts, interactions with H3 and histone chaperones. The other within the core of nucleosome (reported patient variants : His75-Tyr98) with important strucural contact between H3-H4 dimer and histone chaperones.

There were no detectable genotype-phenotype patterns separating individual H4 genes or protein regions. Of note, variability was observed even among 7 individuals with the same dn H4C5 variant (Arg45Cys).

All variants were absent from control databases incl. gnomAD and affected residues conserved through to S. cerevisiae. Substitutions affecting Arg45 and Gly94 and His75 have been studied previously with effect in growth/fitness/chromatin remodeling/DNA damage repair depending on variant (5 studies cited).

Zebrafish embryos at the 1 cell stage were injected with mRNA encoding either wt or identified variants, the latter inducing significant developmental defects with the exception of Pro32Ala (H4C3) and Arg40Cys (H4C5, H4C11).

For Pro32Ala and Arg40Cys however, the strong recurrence in this cohort supports pathogenicity. A dosage dependent effect was observed for 2 variants.

H4 genes appear to be tolerant to both missense and loss-of-function variation (the latter even in homozygous form) suggesting a dominant effect of the variants.

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[RefSeqs : H4C3/HIST1H4C - NM_0035242.4 | H4C4/HIST1H4D - NM_003539.4 | H4C5/HIST1H4E - NM_003545.3 | H4C6/HIST1H4F - NM_003540.4 | H4C9/HIST1H4I - NM_003495.2 | H4C11/HIST1H4J - NM_021968.4 // Variants at the protein level above are according to the HGVS nomenclature. However as the N-terminal methionine is cleaved, numbering relative to the mature peptide has also been used in publications eg. p.Pro33Ala HGVS corresponding to Pro32Ala]
Sources: Literature
Intellectual disability v3.1520 HIST1H4E Konstantinos Varvagiannis gene: HIST1H4E was added
gene: HIST1H4E was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: HIST1H4E was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: HIST1H4E were set to 35202563
Phenotypes for gene: HIST1H4E were set to Global developmental delay; Intellectual disability; Microcephaly; Growth abnormality; Abnormality of the face
Penetrance for gene: HIST1H4E were set to unknown
Mode of pathogenicity for gene: HIST1H4E was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: HIST1H4E was set to GREEN
Added comment: Histone H4 is a core component of the nucleosome, the basic repeating unit of eukaryotic chromatin. Each nucleosome consists of ~150 bp of DNA wrapped around a histone octamer. Each histone octamer is composed of 2 copies of each of the histones H2A, H2B, H3, H4. This organization is important for DNA replication, transcription and repair.

There are 14 canonical histone H4 genes in the human genome, which despite being different at the nucleotide level encode an identical protein. These cluster in 3 genomic loci. Their transcription is independently regulated with differing expression during brain development and in human tissues.

Histone H4 forms a dimer with H3 (which however has variant isoforms linked to specific cellular processes).

Pathogenic variants in genes encoding H4 have been reported in several individuals. Irrrespective of the gene for H4 involved, all patients presented with highly overlapping features, DD and ID being universal. Available reports to date concern :
- H4C3/HIST1H4C (9 subjects - PMID: 28920961, 35202563),
- H4C11/HIST1H4J (1 subject - PMID: 31804630, 35202563),
- H4C4/HIST1H4D (1 subject - PMID:35202563),
- H4C5/HIST1H4E (17 subjects - PMID: 35202563),
- H4C6/HIST1H4F (1 subject - PMID: 35202563),
- H4C9/HIST1H4I (3 subjects - PMID: 35202563).

Variants in all cases were missense SNVs, occurring (in almost all cases) as dn variants and affecting the same residue in the same and/or different H4 genes (details for clusters below). Eg. Arg45Cys was a recurrent variant for H4C5 (>=7 subjects), while variants affecting Arg40 have been reported in H4C4, H4C5, H4C9, H4C11 (7 subjects overall).

Zebrafish studies for all genes reported have included most - if not all - patient variants and recapitulate features observed in affected individuals (head size/structure and growth).

Additional studies specificaly for H4C3/HIST1H4C have been performed in patient fibroblasts (demonstrating among others transcriptional dysregulation) and zebrafish (accumulation of DSBs, increased apoptosis in head/tail, abn. cell cycle progression).

Note that the nomenclature for variants - at the protein level - used in literature commonly takes into consideration cleavage of Met1, thus the numbering may not correspond to the HGVS one.

Relevant entries exist in OMIM, G2P and SysID only for H4C3/HIST1H4C (Tessadori-van Haaften neurodevelopmental syndrome 1, #619758) and H4C11/HIST1H4J (?Tessadori-van Haaften neurodevelopmental syndrome 2, #619759) but not for other genes.

Rating in PanelApp Australia - ID Panel : HIST1H4C Green, H4J Amber, H4D Amber, H4E Green, H4F Amber, H4I Green.

Please consider inclusion in other possibly relevant panels (microcephaly, short stature/FTT, etc).

------
Initial work from Tessadori et al (incl. DDD study, 2017 - PMID:28920961) identified monoallelic missense SNVs affecting the same residue of H4C3 (HIST1H4C), in 3 individuals from 2 families. [c.274A>C/ HGVS p.(Lys92Gln) dn in 1 subject and c.275A>C/ HGVS p.(Lys92Arg) inherited from unaffected mosaic parent].

Individuals from both families having relevant age had intellectual disability (2/2 - 2 families). Other features incl. growth delay (3/3) and microcephaly (3/3).

Expression of the variants in zebrafish severely affected structural development recapitulating the patient phenotypes (microcephaly and short stature).

RNA sequencing in fibroblasts from 2 unrelated patients and a control, revealed that expression of H4C3 variants was similar to wt. The authors estimated that ~8% of H4 cDNA molecules contained the variant. LC-MS/MS analysis suggested that the mutant protein was present in nucleosomes at a level of 1-2% while RNA-seq identified 115 differential expressed genes, with enrichment for relevant procedures (chr. organization, histone binding, DNA packaging, nucleosomal organization, cell cycle).

Post-translational modifications of Lys92 (H4K91) are highly conserved and have been previously associated with processes from chromatin assembly , DNA damage sensitivity, etc. Post-translational marks on Lys92 (K91) were absent in patient derived cells as a result of each variant.

Zebrafish models for both variants were suggestive for accumulation of double strand breaks (DSBs) more visible in heads and tails of larvae. Embryos expressing mutants displayed increased apoptosis in head and tail. Additional studies in larvae were suggestive of abnormal cell cycle progression (rel. increase in cellls in S/G2/M phase, increased occurrence of activated CHK2 with p53 stabilization) applying to both variants studied.

------
In a subsequent publication, Tessadori et al. (2020 - PMID: 31804630) described the phenotype of a 14 y.o. boy harboring a dn heterozygous missense H4C11 (HIST1H4J) variant following trio-ES [c.274A>G / HGVS p.(Lys92Glu)]. Features incl. profound ID, microcephaly, short stature with some dysmorphic features (uplsanting p-f, hypertelorism, etc). Previous work-up was normal/non-diagnostic and incl. FMR1, MECP2 and a CMA showing an inherited 207 kb CNV involving KCNV1. Upon mRNA microinjection in zebrafish embryos - either for wt or for Lys92Glu HIST1H4J - effect for wt was very mild. Lys92Glu expression led to defective development of head structures (brain, eyes), faulty body axis growth and dysmorphic tail reproducing the microcephaly and short stature phenotype. This was similar to previous zebrafish studies for HIS1H4C variants (above).

------
Tessadori et al. (2022 - PMID: 35202563) describe 29 *additional individuals with de novo missense variants in genes encoding H4, namely:
- H4C3 (HIST1H4C/N=6 subjects),
- H4C11 (HIST1H4J/N=1),
- H4C4 (HIST1H4D/N=1),
- H4C5 (HIST1H4E/N=17),
- H4C6 (HIST1H4F/N=1),
- H4C9 (HIST1H4I/N=3).

All individuals, exhibited DD and ID (29/29). Other features incl. hypotonia (10/29), seizures (5/29), autism (5/29), ataxia (4/29). Abnormal growth incl. progressive microcephaly (2/19 prenatal, 20/29 postnatal onset), short stature/FTT (each 11/29). Few had skeletal features (craniosynostosis 2/29, abn. digits 4/29, vertebral 4/29). Some had visual (17/28) or hearing impairment (7/29). Facial features incl. hypertelorism (5/29), upslanting p-f (3/29), broad nasal tip (11/29), thin upper lip (4/29) and teeth anomalies (6/29 - notably gap between central incisors).

The authors state that the cohort was collected with trio WES but also after data sharing via Genematcher / DECIPHER.

Identified variants were in all cases missense and de novo, the latter either by trio WES or Sanger sequencing of parents.

Previous work-up or presence of additional variants are not discussed.

At the protein level 10 aa were affected, 6 of which recurrently within the same gene (Arg45, His75, Lys91, Tyr98) as well among several genes for H4 (Pro32, Arg40). Variants lied within two clusters, one corresponding to the α-helix of H4 (reported variants affected Lys31 - Arg45) important for DNA contacts, interactions with H3 and histone chaperones. The other within the core of nucleosome (reported patient variants : His75-Tyr98) with important strucural contact between H3-H4 dimer and histone chaperones.

There were no detectable genotype-phenotype patterns separating individual H4 genes or protein regions. Of note, variability was observed even among 7 individuals with the same dn H4C5 variant (Arg45Cys).

All variants were absent from control databases incl. gnomAD and affected residues conserved through to S. cerevisiae. Substitutions affecting Arg45 and Gly94 and His75 have been studied previously with effect in growth/fitness/chromatin remodeling/DNA damage repair depending on variant (5 studies cited).

Zebrafish embryos at the 1 cell stage were injected with mRNA encoding either wt or identified variants, the latter inducing significant developmental defects with the exception of Pro32Ala (H4C3) and Arg40Cys (H4C5, H4C11).

For Pro32Ala and Arg40Cys however, the strong recurrence in this cohort supports pathogenicity. A dosage dependent effect was observed for 2 variants.

H4 genes appear to be tolerant to both missense and loss-of-function variation (the latter even in homozygous form) suggesting a dominant effect of the variants.

------
[RefSeqs : H4C3/HIST1H4C - NM_0035242.4 | H4C4/HIST1H4D - NM_003539.4 | H4C5/HIST1H4E - NM_003545.3 | H4C6/HIST1H4F - NM_003540.4 | H4C9/HIST1H4I - NM_003495.2 | H4C11/HIST1H4J - NM_021968.4 // Variants at the protein level above are according to the HGVS nomenclature. However as the N-terminal methionine is cleaved, numbering relative to the mature peptide has also been used in publications eg. p.Pro33Ala HGVS corresponding to Pro32Ala]
Sources: Literature
Intellectual disability v3.1520 HIST1H4F Konstantinos Varvagiannis gene: HIST1H4F was added
gene: HIST1H4F was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: HIST1H4F was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: HIST1H4F were set to 35202563
Phenotypes for gene: HIST1H4F were set to Global developmental delay; Intellectual disability; Microcephaly; Growth abnormality; Abnormality of the face
Penetrance for gene: HIST1H4F were set to unknown
Mode of pathogenicity for gene: HIST1H4F was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: HIST1H4F was set to AMBER
Added comment: Histone H4 is a core component of the nucleosome, the basic repeating unit of eukaryotic chromatin. Each nucleosome consists of ~150 bp of DNA wrapped around a histone octamer. Each histone octamer is composed of 2 copies of each of the histones H2A, H2B, H3, H4. This organization is important for DNA replication, transcription and repair.

There are 14 canonical histone H4 genes in the human genome, which despite being different at the nucleotide level encode an identical protein. These cluster in 3 genomic loci. Their transcription is independently regulated with differing expression during brain development and in human tissues.

Histone H4 forms a dimer with H3 (which however has variant isoforms linked to specific cellular processes).

Pathogenic variants in genes encoding H4 have been reported in several individuals. Irrrespective of the gene for H4 involved, all patients presented with highly overlapping features, DD and ID being universal. Available reports to date concern :
- H4C3/HIST1H4C (9 subjects - PMID: 28920961, 35202563),
- H4C11/HIST1H4J (1 subject - PMID: 31804630, 35202563),
- H4C4/HIST1H4D (1 subject - PMID:35202563),
- H4C5/HIST1H4E (17 subjects - PMID: 35202563),
- H4C6/HIST1H4F (1 subject - PMID: 35202563),
- H4C9/HIST1H4I (3 subjects - PMID: 35202563).

Variants in all cases were missense SNVs, occurring (in almost all cases) as dn variants and affecting the same residue in the same and/or different H4 genes (details for clusters below). Eg. Arg45Cys was a recurrent variant for H4C5 (>=7 subjects), while variants affecting Arg40 have been reported in H4C4, H4C5, H4C9, H4C11 (7 subjects overall).

Zebrafish studies for all genes reported have included most - if not all - patient variants and recapitulate features observed in affected individuals (head size/structure and growth).

Additional studies specificaly for H4C3/HIST1H4C have been performed in patient fibroblasts (demonstrating among others transcriptional dysregulation) and zebrafish (accumulation of DSBs, increased apoptosis in head/tail, abn. cell cycle progression).

Note that the nomenclature for variants - at the protein level - used in literature commonly takes into consideration cleavage of Met1, thus the numbering may not correspond to the HGVS one.

Relevant entries exist in OMIM, G2P and SysID only for H4C3/HIST1H4C (Tessadori-van Haaften neurodevelopmental syndrome 1, #619758) and H4C11/HIST1H4J (?Tessadori-van Haaften neurodevelopmental syndrome 2, #619759) but not for other genes.

Rating in PanelApp Australia - ID Panel : HIST1H4C Green, H4J Amber, H4D Amber, H4E Green, H4F Amber, H4I Green.

Please consider inclusion in other possibly relevant panels (microcephaly, short stature/FTT, etc).

------
Initial work from Tessadori et al (incl. DDD study, 2017 - PMID:28920961) identified monoallelic missense SNVs affecting the same residue of H4C3 (HIST1H4C), in 3 individuals from 2 families. [c.274A>C/ HGVS p.(Lys92Gln) dn in 1 subject and c.275A>C/ HGVS p.(Lys92Arg) inherited from unaffected mosaic parent].

Individuals from both families having relevant age had intellectual disability (2/2 - 2 families). Other features incl. growth delay (3/3) and microcephaly (3/3).

Expression of the variants in zebrafish severely affected structural development recapitulating the patient phenotypes (microcephaly and short stature).

RNA sequencing in fibroblasts from 2 unrelated patients and a control, revealed that expression of H4C3 variants was similar to wt. The authors estimated that ~8% of H4 cDNA molecules contained the variant. LC-MS/MS analysis suggested that the mutant protein was present in nucleosomes at a level of 1-2% while RNA-seq identified 115 differential expressed genes, with enrichment for relevant procedures (chr. organization, histone binding, DNA packaging, nucleosomal organization, cell cycle).

Post-translational modifications of Lys92 (H4K91) are highly conserved and have been previously associated with processes from chromatin assembly , DNA damage sensitivity, etc. Post-translational marks on Lys92 (K91) were absent in patient derived cells as a result of each variant.

Zebrafish models for both variants were suggestive for accumulation of double strand breaks (DSBs) more visible in heads and tails of larvae. Embryos expressing mutants displayed increased apoptosis in head and tail. Additional studies in larvae were suggestive of abnormal cell cycle progression (rel. increase in cellls in S/G2/M phase, increased occurrence of activated CHK2 with p53 stabilization) applying to both variants studied.

------
In a subsequent publication, Tessadori et al. (2020 - PMID: 31804630) described the phenotype of a 14 y.o. boy harboring a dn heterozygous missense H4C11 (HIST1H4J) variant following trio-ES [c.274A>G / HGVS p.(Lys92Glu)]. Features incl. profound ID, microcephaly, short stature with some dysmorphic features (uplsanting p-f, hypertelorism, etc). Previous work-up was normal/non-diagnostic and incl. FMR1, MECP2 and a CMA showing an inherited 207 kb CNV involving KCNV1. Upon mRNA microinjection in zebrafish embryos - either for wt or for Lys92Glu HIST1H4J - effect for wt was very mild. Lys92Glu expression led to defective development of head structures (brain, eyes), faulty body axis growth and dysmorphic tail reproducing the microcephaly and short stature phenotype. This was similar to previous zebrafish studies for HIS1H4C variants (above).

------
Tessadori et al. (2022 - PMID: 35202563) describe 29 *additional individuals with de novo missense variants in genes encoding H4, namely:
- H4C3 (HIST1H4C/N=6 subjects),
- H4C11 (HIST1H4J/N=1),
- H4C4 (HIST1H4D/N=1),
- H4C5 (HIST1H4E/N=17),
- H4C6 (HIST1H4F/N=1),
- H4C9 (HIST1H4I/N=3).

All individuals, exhibited DD and ID (29/29). Other features incl. hypotonia (10/29), seizures (5/29), autism (5/29), ataxia (4/29). Abnormal growth incl. progressive microcephaly (2/19 prenatal, 20/29 postnatal onset), short stature/FTT (each 11/29). Few had skeletal features (craniosynostosis 2/29, abn. digits 4/29, vertebral 4/29). Some had visual (17/28) or hearing impairment (7/29). Facial features incl. hypertelorism (5/29), upslanting p-f (3/29), broad nasal tip (11/29), thin upper lip (4/29) and teeth anomalies (6/29 - notably gap between central incisors).

The authors state that the cohort was collected with trio WES but also after data sharing via Genematcher / DECIPHER.

Identified variants were in all cases missense and de novo, the latter either by trio WES or Sanger sequencing of parents.

Previous work-up or presence of additional variants are not discussed.

At the protein level 10 aa were affected, 6 of which recurrently within the same gene (Arg45, His75, Lys91, Tyr98) as well among several genes for H4 (Pro32, Arg40). Variants lied within two clusters, one corresponding to the α-helix of H4 (reported variants affected Lys31 - Arg45) important for DNA contacts, interactions with H3 and histone chaperones. The other within the core of nucleosome (reported patient variants : His75-Tyr98) with important strucural contact between H3-H4 dimer and histone chaperones.

There were no detectable genotype-phenotype patterns separating individual H4 genes or protein regions. Of note, variability was observed even among 7 individuals with the same dn H4C5 variant (Arg45Cys).

All variants were absent from control databases incl. gnomAD and affected residues conserved through to S. cerevisiae. Substitutions affecting Arg45 and Gly94 and His75 have been studied previously with effect in growth/fitness/chromatin remodeling/DNA damage repair depending on variant (5 studies cited).

Zebrafish embryos at the 1 cell stage were injected with mRNA encoding either wt or identified variants, the latter inducing significant developmental defects with the exception of Pro32Ala (H4C3) and Arg40Cys (H4C5, H4C11).

For Pro32Ala and Arg40Cys however, the strong recurrence in this cohort supports pathogenicity. A dosage dependent effect was observed for 2 variants.

H4 genes appear to be tolerant to both missense and loss-of-function variation (the latter even in homozygous form) suggesting a dominant effect of the variants.

------
[RefSeqs : H4C3/HIST1H4C - NM_0035242.4 | H4C4/HIST1H4D - NM_003539.4 | H4C5/HIST1H4E - NM_003545.3 | H4C6/HIST1H4F - NM_003540.4 | H4C9/HIST1H4I - NM_003495.2 | H4C11/HIST1H4J - NM_021968.4 // Variants at the protein level above are according to the HGVS nomenclature. However as the N-terminal methionine is cleaved, numbering relative to the mature peptide has also been used in publications eg. p.Pro33Ala HGVS corresponding to Pro32Ala]
Sources: Literature
Intellectual disability v3.1520 HIST1H4I Konstantinos Varvagiannis gene: HIST1H4I was added
gene: HIST1H4I was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: HIST1H4I was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: HIST1H4I were set to 35202563
Phenotypes for gene: HIST1H4I were set to Global developmental delay; Intellectual disability; Microcephaly; Growth abnormality; Abnormality of the face
Penetrance for gene: HIST1H4I were set to unknown
Mode of pathogenicity for gene: HIST1H4I was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: HIST1H4I was set to GREEN
Added comment: Histone H4 is a core component of the nucleosome, the basic repeating unit of eukaryotic chromatin. Each nucleosome consists of ~150 bp of DNA wrapped around a histone octamer. Each histone octamer is composed of 2 copies of each of the histones H2A, H2B, H3, H4. This organization is important for DNA replication, transcription and repair.

There are 14 canonical histone H4 genes in the human genome, which despite being different at the nucleotide level encode an identical protein. These cluster in 3 genomic loci. Their transcription is independently regulated with differing expression during brain development and in human tissues.

Histone H4 forms a dimer with H3 (which however has variant isoforms linked to specific cellular processes).

Pathogenic variants in genes encoding H4 have been reported in several individuals. Irrrespective of the gene for H4 involved, all patients presented with highly overlapping features, DD and ID being universal. Available reports to date concern :
- H4C3/HIST1H4C (9 subjects - PMID: 28920961, 35202563),
- H4C11/HIST1H4J (1 subject - PMID: 31804630, 35202563),
- H4C4/HIST1H4D (1 subject - PMID:35202563),
- H4C5/HIST1H4E (17 subjects - PMID: 35202563),
- H4C6/HIST1H4F (1 subject - PMID: 35202563),
- H4C9/HIST1H4I (3 subjects - PMID: 35202563).

Variants in all cases were missense SNVs, occurring (in almost all cases) as dn variants and affecting the same residue in the same and/or different H4 genes (details for clusters below). Eg. Arg45Cys was a recurrent variant for H4C5 (>=7 subjects), while variants affecting Arg40 have been reported in H4C4, H4C5, H4C9, H4C11 (7 subjects overall).

Zebrafish studies for all genes reported have included most - if not all - patient variants and recapitulate features observed in affected individuals (head size/structure and growth).

Additional studies specificaly for H4C3/HIST1H4C have been performed in patient fibroblasts (demonstrating among others transcriptional dysregulation) and zebrafish (accumulation of DSBs, increased apoptosis in head/tail, abn. cell cycle progression).

Note that the nomenclature for variants - at the protein level - used in literature commonly takes into consideration cleavage of Met1, thus the numbering may not correspond to the HGVS one.

Relevant entries exist in OMIM, G2P and SysID only for H4C3/HIST1H4C (Tessadori-van Haaften neurodevelopmental syndrome 1, #619758) and H4C11/HIST1H4J (?Tessadori-van Haaften neurodevelopmental syndrome 2, #619759) but not for other genes.

Rating in PanelApp Australia - ID Panel : HIST1H4C Green, H4J Amber, H4D Amber, H4E Green, H4F Amber, H4I Green.

Please consider inclusion in other possibly relevant panels (microcephaly, short stature/FTT, etc).

------
Initial work from Tessadori et al (incl. DDD study, 2017 - PMID:28920961) identified monoallelic missense SNVs affecting the same residue of H4C3 (HIST1H4C), in 3 individuals from 2 families. [c.274A>C/ HGVS p.(Lys92Gln) dn in 1 subject and c.275A>C/ HGVS p.(Lys92Arg) inherited from unaffected mosaic parent].

Individuals from both families having relevant age had intellectual disability (2/2 - 2 families). Other features incl. growth delay (3/3) and microcephaly (3/3).

Expression of the variants in zebrafish severely affected structural development recapitulating the patient phenotypes (microcephaly and short stature).

RNA sequencing in fibroblasts from 2 unrelated patients and a control, revealed that expression of H4C3 variants was similar to wt. The authors estimated that ~8% of H4 cDNA molecules contained the variant. LC-MS/MS analysis suggested that the mutant protein was present in nucleosomes at a level of 1-2% while RNA-seq identified 115 differential expressed genes, with enrichment for relevant procedures (chr. organization, histone binding, DNA packaging, nucleosomal organization, cell cycle).

Post-translational modifications of Lys92 (H4K91) are highly conserved and have been previously associated with processes from chromatin assembly , DNA damage sensitivity, etc. Post-translational marks on Lys92 (K91) were absent in patient derived cells as a result of each variant.

Zebrafish models for both variants were suggestive for accumulation of double strand breaks (DSBs) more visible in heads and tails of larvae. Embryos expressing mutants displayed increased apoptosis in head and tail. Additional studies in larvae were suggestive of abnormal cell cycle progression (rel. increase in cellls in S/G2/M phase, increased occurrence of activated CHK2 with p53 stabilization) applying to both variants studied.

------
In a subsequent publication, Tessadori et al. (2020 - PMID: 31804630) described the phenotype of a 14 y.o. boy harboring a dn heterozygous missense H4C11 (HIST1H4J) variant following trio-ES [c.274A>G / HGVS p.(Lys92Glu)]. Features incl. profound ID, microcephaly, short stature with some dysmorphic features (uplsanting p-f, hypertelorism, etc). Previous work-up was normal/non-diagnostic and incl. FMR1, MECP2 and a CMA showing an inherited 207 kb CNV involving KCNV1. Upon mRNA microinjection in zebrafish embryos - either for wt or for Lys92Glu HIST1H4J - effect for wt was very mild. Lys92Glu expression led to defective development of head structures (brain, eyes), faulty body axis growth and dysmorphic tail reproducing the microcephaly and short stature phenotype. This was similar to previous zebrafish studies for HIS1H4C variants (above).

------
Tessadori et al. (2022 - PMID: 35202563) describe 29 *additional individuals with de novo missense variants in genes encoding H4, namely:
- H4C3 (HIST1H4C/N=6 subjects),
- H4C11 (HIST1H4J/N=1),
- H4C4 (HIST1H4D/N=1),
- H4C5 (HIST1H4E/N=17),
- H4C6 (HIST1H4F/N=1),
- H4C9 (HIST1H4I/N=3).

All individuals, exhibited DD and ID (29/29). Other features incl. hypotonia (10/29), seizures (5/29), autism (5/29), ataxia (4/29). Abnormal growth incl. progressive microcephaly (2/19 prenatal, 20/29 postnatal onset), short stature/FTT (each 11/29). Few had skeletal features (craniosynostosis 2/29, abn. digits 4/29, vertebral 4/29). Some had visual (17/28) or hearing impairment (7/29). Facial features incl. hypertelorism (5/29), upslanting p-f (3/29), broad nasal tip (11/29), thin upper lip (4/29) and teeth anomalies (6/29 - notably gap between central incisors).

The authors state that the cohort was collected with trio WES but also after data sharing via Genematcher / DECIPHER.

Identified variants were in all cases missense and de novo, the latter either by trio WES or Sanger sequencing of parents.

Previous work-up or presence of additional variants are not discussed.

At the protein level 10 aa were affected, 6 of which recurrently within the same gene (Arg45, His75, Lys91, Tyr98) as well among several genes for H4 (Pro32, Arg40). Variants lied within two clusters, one corresponding to the α-helix of H4 (reported variants affected Lys31 - Arg45) important for DNA contacts, interactions with H3 and histone chaperones. The other within the core of nucleosome (reported patient variants : His75-Tyr98) with important strucural contact between H3-H4 dimer and histone chaperones.

There were no detectable genotype-phenotype patterns separating individual H4 genes or protein regions. Of note, variability was observed even among 7 individuals with the same dn H4C5 variant (Arg45Cys).

All variants were absent from control databases incl. gnomAD and affected residues conserved through to S. cerevisiae. Substitutions affecting Arg45 and Gly94 and His75 have been studied previously with effect in growth/fitness/chromatin remodeling/DNA damage repair depending on variant (5 studies cited).

Zebrafish embryos at the 1 cell stage were injected with mRNA encoding either wt or identified variants, the latter inducing significant developmental defects with the exception of Pro32Ala (H4C3) and Arg40Cys (H4C5, H4C11).

For Pro32Ala and Arg40Cys however, the strong recurrence in this cohort supports pathogenicity. A dosage dependent effect was observed for 2 variants.

H4 genes appear to be tolerant to both missense and loss-of-function variation (the latter even in homozygous form) suggesting a dominant effect of the variants.

------
[RefSeqs : H4C3/HIST1H4C - NM_0035242.4 | H4C4/HIST1H4D - NM_003539.4 | H4C5/HIST1H4E - NM_003545.3 | H4C6/HIST1H4F - NM_003540.4 | H4C9/HIST1H4I - NM_003495.2 | H4C11/HIST1H4J - NM_021968.4 // Variants at the protein level above are according to the HGVS nomenclature. However as the N-terminal methionine is cleaved, numbering relative to the mature peptide has also been used in publications eg. p.Pro33Ala HGVS corresponding to Pro32Ala]
Sources: Literature
Intellectual disability v3.1519 FAR1 Sarah Leigh reviewed gene: FAR1: Rating: GREEN; Mode of pathogenicity: None; Publications: 25439727, 30561787; Phenotypes: ; Mode of inheritance: BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.1519 POLR3B Ivone Leong Source NHS GMS was added to POLR3B.
Mode of inheritance for gene POLR3B was changed from BIALLELIC, autosomal or pseudoautosomal to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1519 PHF6 Ivone Leong Source NHS GMS was added to PHF6.
Mode of inheritance for gene PHF6 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1519 MED12 Ivone Leong Source NHS GMS was added to MED12.
Mode of inheritance for gene MED12 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1519 HCCS Ivone Leong Source NHS GMS was added to HCCS.
Mode of inheritance for gene HCCS was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1518 CPSF3 Konstantinos Varvagiannis gene: CPSF3 was added
gene: CPSF3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CPSF3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CPSF3 were set to 35121750
Phenotypes for gene: CPSF3 were set to Failure to thrive; Abnormal muscle tone; Global developmental delay; Intellectual disability; Microcephaly; Seizures
Penetrance for gene: CPSF3 were set to Complete
Review for gene: CPSF3 was set to AMBER
Added comment: Arnadottir (2022 - PMID: 35121750) describe the phenotype associated with biallelic CPSF3 pathogenic variants.

Based on WGS of 56,969 Icelanders and imputing the genotype of another 153,054 chip-genotyped Icelanders, the authors identified missense variants with a deficit of homozygous carriers to what would be expected based on AF. (For variants with MAF>0.4%, for which >=3 hmz carriers would be expected by H-W equilibrium, no identified hmz carriers within this cohort/dataset). A total of 114 such missense variants was identified.

5 of these SNVs, among which a CPSF3 one (NM_016207.3:c.1403G>A / p.Gly468Glu), were however observed in a series of 764 individuals investigated with clinical WGS at the National University Hospital.

The CPSF3 variant with a MAF of 0.41% (3 hmz expected but none observed in the population set) was found in homozygosity in 2 closely related individuals, both investigated for FTT, severe DD, ID, microcephaly, seizures but remaining unresolved following WGS with no other candidate variants.

Using genealogical information from the db of deCODE genetics, the authors identified 3 couples from the 153k genotyped Icelanders where both partners were htz carriers for this SNV. These 3 couples had 10 offspring, 4 of whom deceased but with the same phenotypic features as above (hypotonia 4/4, ID 4/4, seizures 3/4, microcephaly 2/4). Paraffin embedded samples of 2 of these children and WG & Sanger sequencing confirmed hmz for Gly468Glu in 2 sibs, without other candidate variants. Samples of the 2 other individuals were N/A.

Through GeneMatcher 2 additional first-cousin patients from Mexico were identified, being hmz for another CPSF3 variant (c.1061T>C/p.Ile354Thr) and having overlapping phenotype of abnormal muscle tone, ID, seizures and microcephaly. There were no other variants in WES analysis.

mRNA studies in WBCs from Gly468Glu htz carriers did not reveal reduced levels and W.Blot of lymphocytes from a hmz individual confirmed expression, overall suggesting that the variant does not affect the protein levels but presumably the function.

CPSF3 encodes cleavage and polyadenylation specificity factor 3, a 684 aa protein, subunit of the cleavage and polyadenylation specificity factor compex. As discussed, cleavage and polyadenylation of the 3' of pre-mRNAs is necessary before transport out of the nucleus with CPSF playing a crucial role in the process of cleavage.

CPSF3 ko mice exhibit embryonic lethality, while in yeast mutations in key residues of the CPSF3 homolog are lethal.

In gnomAD, CPSF3 has a pLI of 0, z-score of 3.61 with no homozygotes for pLoF variants in 141k individuals (or ~57k WGS Icelanders).

The 2 missense variants concerned highly conserved residues (GERP ~5.8). Both are hypothesized to affect the ability of the protein to bind other factors involved in pre-mRNA cleavage.

Overall the authors speculate that not only complete loss of CPSF3 would result in drastic phenotypic effects - as in the murine model - but also variants altering its enzymatic function.

There is currently no CPSF3-related phenotype in OMIM, G2P, SysID, The gene is included with green rating in the ID, epilepsy and microcephaly panels in PanelApp Australia.

Consider inclusion probably with amber rating (Highly consistent phenotype, biological function, evidence from animal models. 2 identified variants, authors state that follow-up functional studies are needed). Also consider inclusion in other possibly relevant panels.
Sources: Literature
Intellectual disability v3.1518 NRCAM Konstantinos Varvagiannis gene: NRCAM was added
gene: NRCAM was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: NRCAM was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: NRCAM were set to 35108495
Phenotypes for gene: NRCAM were set to Hypotonia; Hypertonia; Spasticity; Global developmental delay; Intellectual disability; Microcephaly; Behavioral abnormality; Neuropathy; Hearing abnormality; Abnormality of the eye; Abnormality of the skeletal system; Scoliosis; Abnormality of the face
Penetrance for gene: NRCAM were set to Complete
Review for gene: NRCAM was set to GREEN
Added comment: Kurolap et al (2022 - PMID: 35108495) describe the phenotype of 10 individuals (from 8 families) with biallelic variants in NRCAM.

Features included tone abnormalities (hypotonia in 4/10, hypertonia/spasticity in 4/10), DD (8/10 - 7 families) and cognitive impairment (in 7/10 - 6 fam), neuropathy (4/10 - incl. 2 sibs without DD/ID). Other phenotypes incl. FTT (2/8), microcephaly (3/6), variable behavioral issues (3/5), abnormalities from the eyes/vision (6/8 - cataract in 2), abnormal hearing (3/7) or skeletal findings (8/9 - incl. scoliosis in 5). Nonspecific facial features were reported in 5/8.

Previous metabolic, genetic (incl. karyotype or CMA, FMR1, testing for Steinert disease or SMA) or other work-up (e.g. muscle biopsy) is reported for several subjects but was normal/non-diagnostic.

All were investigated by WES/WGS which revealed biallelic NRCAM variants. Sanger sequencing was used for confirmation and segregation analyses, with compatible results in several affected/unaffected sibs tested. There were no alternative explanations for the NDD phenotype with the exception of one subject with a mosaic functionally characterized LP KRAS variant suspected to contribute to his phenotype.

NRCAM encodes neuronal cell adhesion molecule (CAM). CAMs are membrane bound proteins with important role in tissue morphogenesis and maintenance. They mediate interactions between neighboring cells or cells and the extracellular matrix. The L1 subgroup of immunoglobulin CAMS - consisting of L1CAM, neurofascin, NRCAM, CHL1 - is the most abundant in the CNS with several critical functions in CNS development, among others in neural cell differentiation, axonal growth and guidance, myelination, synapse formation. Pathogenic L1CAM (XL) and NFASC variants (AR) are associated with NDD.

Different missense (N=7), stopgain/frameshift (N=3), a splice variant (NM_001037132.2:c.2647-2A>G) as well as a deep intronic one (c.230+824G>C / rs575851831). Variants occurred in different domains with a cluster (42%) in the fibronectin III domain.

Missense SNVs were ultrarare or not present in gnomAD, occurred in conserved residues, with several in silico predictions in favor of a deleterious effect. Structural modelling suggested that all substitutions occurred at residues exposed to solvent and possible abrogated interaction with other proteins.

There were no expression studies performed at the mRNA/protein level. The splice variant is predicted to cause ex22 skipping leading to frameshift. The deep intronic variant is predicted to disrupt a site for spl. regulator SC35 and may cause activation of a cryptic acceptor site with inclusion of a cryptic exon.

The zebrafish nrcama gene is the sole ortholog of human NRCAM, with another gene proposed as possible ortholog (nrcamb) mapping upon BLAST analysis to cntn1a. The authors performed CRISPR-Cas9 mutagenesis in zebrafish introducing a partial deletion of ex18 and 19. Mutant zebrafish were viable, displayed altered axonal projections and abnormal swimming behavior (increased movement in darkness).

Currently, there is no NRCAM-associated phenotype in OMIM/G2P/SysID. PanelApp Australia includes NRCAM in its ID panel with green rating.

Consider inclusion probably with green (>3 individuals/families/variants, segregation, gene in the L1-Ig CAM family causing NDD, zebrafish model) or amber rating (ID not a universal feature, variant effect not studied).
Sources: Literature
Intellectual disability v3.1518 TIAM1 Konstantinos Varvagiannis gene: TIAM1 was added
gene: TIAM1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TIAM1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TIAM1 were set to 35240055; 33328293
Phenotypes for gene: TIAM1 were set to Delayed speech and language development; Global developmental delay; Intellectual disability; Seizures; Behavioral abnormality; Abnormality of the endocrine system; Hypothyroidism; Abnormality of nervous system morphology
Penetrance for gene: TIAM1 were set to Complete
Review for gene: TIAM1 was set to AMBER
Added comment: Lu et al (2022 - PMID: 35240055) describe 5 individuals (from 4 families) with biallelic TIAM1 missense variants.

The phenotype overall corresponded to a neurodevelopmental disorder with DD (5/5), ID (4/4 individuals of relevant age - 3 families), speech delay (5/5), seizures (5/5 - onset: 2m-13y) and behavioral abnormalities (2/2, sibs with autism and ADHD). Several subjects had endocrine symptoms, namely hypothyroidism (N=3 - 2 families), Addison's disease (1) or hypomagnesemia (1). Non-consistent abnormalities were reported in (3/3) subjects who had a brain MRI.

Previous investigations were mentioned for 3 individuals (incl. 2 sibs) and included normal CMA and/or metabolic workup.

Singleton or trio exome sequencing (in one family) revealed biallelic missense TIAM1 variants.

6 different missense variants were reported, all ultra-rare or not present in gnomAD (also o/e:0.2, pLI:0.96), with CADD scores in favor of deleterious effect (NM_001353694.2): c.67C>T/p.Arg23Cys*, c.2584C>T/p.Leu862Phe*, c.983G>T/p.Gly328Val*, c.4640C>A/p.Ala1547Glu, c.1144G>C/p.Gly382Arg, c.4016C>T/p.Ala1339Val.

TIAM1 encodes a RAC1-specific guanine exchange factor (GEF), regulating RAC1 signaling pathways that in turn affect cell shape, migration, adhesion, growth, survival, and polarity, and influence actin cytoskeletal organization, endocytosis, and membrane trafficking. RAC1 signaling plays important role in control of neuronal morphogenesis and neurite outgrowth (based on the summary by Entrez and authors).

TIAM1 is highly expressed in human brain (GTEx).

The authors provide evidence that sif, the Drosophila ortholog, is expressed primarily in neurons of the fly CNS (but not in glia). Using different sif LoF mutant flies they demonstrate that loss of sif impairs viability. Surviving flies exhibited climbing defects and seizure-like behaviors, both significantly rescued upon UAS-sif expression. Neuronal specific sif knockdown resulted in similar phenotypes to ubiquitous knockdown, while glial knockdown did not result in climbing defects.

The semi-lethal phenotype could be fully rescued by expression of the fly sif cDNA, but only partially by human TIAM1 cDNA reference. Upon expression, 3 patient-variants (R23C, L862F, G328V) had variable rescue abilities similar to or lower (R23C) than TIAM1 Ref. TIAM1 Ref and variants could not rescue the neurological phenotypes though. Higher/ectopic expression of sif or TIAM1 Ref was toxic, which was also observed to a lesser extent for variants.

Overall, the evidence provided suggests that the 3 variants tested induce partial LoF.

In a recent study cited (PMID: 33328293), Tiam1 KO mice had simplified dendritic arbors, reduced spine density and diminished excitatory transmission in dentate gyrus. The authors comment that this mouse model presented only subtle behavioral abnormalities which they speculate may be secondary to GEF redundancy (eg. Tiam2).

There is no TIAM1-associated phenotype in OMIM/G2P/SysID. TIAM1 is included in PanelApp Australia in the ID and epilepsy panels with green rating.

Consider inclusion in the current panel with amber rating [As authors discuss: some phenotypic features differed in their small cohort and the contribution of other recessive conditions in 2 consanguineous families cannot be excluded. Also: in fig S1 only status of parents but not of affected/unaffected sibs is specified with the exception of Fam1].
Sources: Literature
Intellectual disability v3.1512 NUS1 Arina Puzriakova Mode of inheritance for gene: NUS1 was changed from MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.1496 CSTF2 Zornitza Stark reviewed gene: CSTF2: Rating: AMBER; Mode of pathogenicity: None; Publications: 32816001; Phenotypes: Intellectual disability; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1475 PHF6 Ivone Leong reviewed gene: PHF6: Rating: ; Mode of pathogenicity: None; Publications: 24092917, 25099957; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1463 HCCS Ivone Leong reviewed gene: HCCS: Rating: ; Mode of pathogenicity: None; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1371 ZC4H2 Ivone Leong reviewed gene: ZC4H2: Rating: ; Mode of pathogenicity: None; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1369 AP1S2 Arina Puzriakova Mode of inheritance for gene: AP1S2 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1367 FAAH2 Dmitrijs Rots reviewed gene: FAAH2: Rating: GREEN; Mode of pathogenicity: None; Publications: PMID: 34645488; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1335 ZDHHC15 Zornitza Stark reviewed gene: ZDHHC15: Rating: RED; Mode of pathogenicity: None; Publications: 34345675; Phenotypes: Mental retardation, X-linked 91, 300577, cerebral palsy, intellectual disability, autism spectrum disorder, epilepsy; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1332 KIF4A Zornitza Stark reviewed gene: KIF4A: Rating: GREEN; Mode of pathogenicity: None; Publications: 24812067, 34346154; Phenotypes: Mental retardation, X-linked 100, MIM# 300923; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1315 MED12 Eleanor Williams Mode of inheritance for gene: MED12 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1313 MED12 Eleanor Williams reviewed gene: MED12: Rating: ; Mode of pathogenicity: None; Publications: ; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1298 CLCN3 Arina Puzriakova Mode of inheritance for gene: CLCN3 was changed from BOTH monoallelic and biallelic, autosomal or pseudoautosomal to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.1272 GNB1 Sarah Leigh Added comment: Comment on mode of pathogenicity: Gen2Phen entry for GNB1 (https://www.ebi.ac.uk/gene2phenotype/gfd?dbID=2121) lists the mutation consequence summary as Activating
Intellectual disability v3.1233 KDM5C Arina Puzriakova Mode of inheritance for gene: KDM5C was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1222 RNF220 Konstantinos Varvagiannis gene: RNF220 was added
gene: RNF220 was added to Intellectual disability. Sources: Literature,Other
Mode of inheritance for gene: RNF220 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: RNF220 were set to 33964137; 10881263
Phenotypes for gene: RNF220 were set to Leukodystrophy; CNS hypomyelination; Ataxia; Intellectual disability; Sensorineural hearing impairment; Elevated hepatic transaminases; Hepatic fibrosis; Dilated cardiomyopathy; Spastic paraplegia; Dysarthria; Abnormality of the corpus callosum
Penetrance for gene: RNF220 were set to Complete
Review for gene: RNF220 was set to GREEN
Added comment: Sferra et al (2021 - PMID: 33964137) provide extensive evidence that biallelic RNF220 mutations cause a disorder characterized by hypomyelinating leukodystrophy, ataxia (9/9 - onset 1-5y), borderline intellectual functioning (3/9) / intellectual disability (5/9 - in most cases mild), sensorineural deafness (9/9) with complete hearing loss in the first decade of life, hepatopathy (9/9) with associated periportal fibrosis, and dilated cardiomyopathy (9/9) which was fatal.

Other neurologic manifestations apart from ataxia incl. hyperreflexia (8/8), spastic paraplegia (9/9), dysarthria (9/9), peripheral neuropathy (4/9), seizures in one case (1/9). Upon brain MRI there was thin corpus callosum (9/9) or cerebellar atrophy in some (2/9).

The authors identified homozygosity for 2 recurrent missense RNF220 variants in affected members belonging to these 5 broad consanguineous pedigrees (7 families), namely NM_018150.4:c.1094G>A / p.Arg365Gly in 4 Roma families in the context of a shared haplotype (/founder effect) as well as c.1088G>A / p.Arg363Gly in a large pedigree from southern Italy initially reported by Leuzzi et al (2000 - PMID: 10881263).

Extensive segregation analyses were carried out including several affected and unaffected members.

RNF220 encodes ring finger protein 220, which functions as an E3 ubiquitin ligase. Previous studies have shown among others a role in modulation of Sonic hedgehog/GLI signaling and cerebellar development

Evidence for the role of RNF220 included relevant expression, localization within the cell, interaction partners (lamin B1, 20S proteasome), similarities with other laminopathies in terms of phenotype, etc :
*RNF220 has a relevant expression pattern in CNS (based on qRT-PCR analyses in human brain, cerebellum, cerebral cortex / mRNA levels in human fetal CNS with higher expression in cerebellum, spinal cord and cortex / previous GTEx data / protein levels in mouse CNS)
*The protein displays nuclear localization based on iPSC cells differentiated to motor neurons (also supported by data from the Human Protein Atlas). Transfection of COS-1 cells demonstrated localization primarily to the nucleus (as also previously demonstrated in HEK293T cells) in vesicle like structures with ASF2/SF2 colocalization suggesting enrichment in nuclear speckles. There was also partial co-distribution with the 20S proteasome. R363Q and R365Q additionally coalesced in the cytoplasm forming protein aggregates/inclusions.
*Immunofluorescence studies in patient fibroblasts also confirmed abnormal increase of the protein in the cytoplasm and increased fluorescence with the 20S proteasome.
*Proteomic identification of RNF220-interacting proteins in transfected HEK293T cells demonstrated enrichment for all members of the lamin protein family (incl . lamin B1, AC, B2).
*RNAi-mediated downregulation of RNF222 in Drosophila suggested altered subcellular localization and accumulation of the fly orthologue for human lamin B1.
*Immunoprecipitation of lamin B1 from the nuclear matrix of cerebellar cells suggested significant interaction of endogenous lamin B1 with RNF220, while transfection studies in HEK293T cells for wt/mt suggested reduced binding to endogenous lamin B1 for RNF220 mt compared to wt (more prominent for R365Q). RNF220 mutants also reduced ubiquitination of nuclear lamin B1 compared to wt.
*Patient fibroblasts immunostained with different nuclear envelope markers displayed abnormal nuclear shapes with multiple invaginations and lobulations, findings also observed in laminopathies.

There is currently no associated phenotype in OMIM or G2P. SysID includes RNF220 among the current primary ID genes.

Consider inclusion in panels for leukodystrophies, childhood onset ataxia, sensorineural hearing loss, corpus callosum anomalies, cardiomyopathies, hepatopathies, etc in all cases with green rating.
Sources: Literature, Other
Intellectual disability v3.1220 ARF3 Konstantinos Varvagiannis gene: ARF3 was added
gene: ARF3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: ARF3 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: ARF3 were set to 34346499
Phenotypes for gene: ARF3 were set to Global developmental delay; Intellectual disability; Seizures; Morphological abnormality of the central nervous system
Penetrance for gene: ARF3 were set to unknown
Review for gene: ARF3 was set to AMBER
Added comment: Sakamoto et al (2021 - PMID: 34346499) provide some evidence that monoallelic ARF3 pathogenic variants may be associated with a NDD with brain abnormality.

Using trio exome sequencing, the authors identified 2 individuals with NDD harboring de novo ARF3 variants, namely: NM_001659.2:c.200A>T / p.Asp67Val and c.296G>T / p.Arg99Leu.

Individual 1 (with Asp67Val / age : 4y10m), appeared to be more severelely affected with prenatal onset progressive microcephaly, severe global DD, epilepsy. Upon MRI there was cerebellar and brainstem atrophy. Individual 2 (Arg99Leu / 14y) had severe DD and ID (IQ of 23), epilepsy and upon MRI cerebellar hypoplasia. This subject did not exhibit microcephaly. Common facial features incl. broad nose, full cheeks, small philtrum, strabismus, thin upper lips and abnormal jaw. There was no evidence of systemic involvement in both.

ARF3 encodes ADP-ribosylation factor 3. Adenosine diphosphate ribosylation factors (ARFs) are key proteins for regulation of cargo sorting at the Golgi network, with ARF3 mainly working at the trans-Golgi network. ARFs belong to the small GTP-binding protein (G protein) superfamily. ARF3 switches between an active GTP-bound form and an inactive GDP-bound form, regulated by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs) respectively.

Members of the ARF superfamily regulate various aspects of membrane traffic, among others in neurons.

There are 5 homologs of ARF families, divided in 3 classes. ARF3 and ARF1 belong to class I. Monoallelic ARF1 mutations are associated with Periventricular nodular heterotopia 8 (MIM 618185).

In vivo, in vitro and in silico studies for the 2 variants suggest that both impair the Golgi transport system although each variant most likely exerts a different effect (gain-of-function for Arg99Leu vs loss-of-function/dominant-negative for Asp67Val).

This was also reflected in somewhat different phenotype of the subjects with the respective variants. Common features included severe DD, epilepsy and brain abnormalities although Asp67Val was associated with diffuse brain atrophy as well as congenital microcephaly and Arg99Leu with cerebellar hypoplasia.

Evidence to support the effect of each variant include:

Arg99Leu:
Had identical Golgi localization to that of wt
Had increased binding activity with GGA1, a protein recruited by the GTP-bound active form of ARF3 to the TGN membrane (supporting GoF)
In silico structural analysis suggested it may fail to stabilize the conformation of Asp26, resulting in impaired GTP hydrolysis (GoF).
In transgenic fruit flies, evaluation of the ARF3 variant toxicity using the rough eye phenotype this variant was associated with increased severity of the r-e phenotype similar to a previously studied GoF variant (Gln71Leu)

Asp67Val:
Did not show a Golgi-like pattern of localization (similar to Thr31Asn a previously studied dominant-negative variant)
Displayed decreased protein stability
In silico structural analysis suggested that Asp67Val may lead to compromised binding of GTP or GDP (suggestive of LoF)
In transgenic Drosophila eye-specific expression of Asp67Val (similar to Thr31Asn, a known dominant-negative variant) was lethal possibly due to high toxicity in very small amounts in tissues outside the eye.

There is no associated phenotype in OMIM, G2P or SysID.
Sources: Literature
Intellectual disability v3.1220 VPS50 Konstantinos Varvagiannis gene: VPS50 was added
gene: VPS50 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: VPS50 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: VPS50 were set to 34037727
Phenotypes for gene: VPS50 were set to Neonatal cholestatic liver disease; Failure to thrive; Profound global developmental delay; Postnatal microcephaly; Seizures; Abnormality of the corpus callosum
Penetrance for gene: VPS50 were set to Complete
Review for gene: VPS50 was set to AMBER
Added comment: Schneeberger et al (2021 - PMID: 34037727) describe the phenotype of 2 unrelated individuals with biallelic VPS50 variants.

Common features included transient neonatal cholestasis, failure to thrive, severe DD with failure to achieve milestones (last examination at 2y and 2y2m respectively), postnatal microcephaly, seizures (onset at 6m and 25m) and irritability. There was corpus callosum hypoplasia on brain imaging.

Both individuals were homozygous for variants private to each family (no/not known consanguinity applying to each case). The first individual was homozygous for a splicing variant (NM_017667.4:c.1978-1G>T) and had a similarly unaffected sister deceased with no available DNA for testing. The other individual was homozygous for an in-frame deletion (c.1823_1825delCAA / p.(Thr608del)).

VPS50 encodes a critical component of the endosome-associated recycling protein (EARP) complex, which functions in recycling endocytic vesicles back to the plasma membrane [OMIM based on Schindler et al]. The complex contains VPS50, VPS51, VPS52, VPS53, the three latter also being components of GARP (Golgi-associated-retrograde protein) complex. GARP contains VPS54 instead of VPS50 and is required for trafficking of proteins to the trans-golgi network. Thus VPS50 (also named syndetin) and VPS54 function in the EARP and GARP complexes, to define directional movement of their endocytic vesicles [OMIM based on Schindler et al]. The VPS50 subunit is required for recycling of the transferrin receptor.

As discussed by Schneeberger et al (refs provided in text):
- VPS50 has a high expression in mouse and human brain as well as throughout mouse brain development.
- Mice deficient for Vps50 have not been reported. vps50 knockdown in zebrafish results in severe developmental defects of the body axis. Knockout mice for other proteins of the EARP/GARP complex (e.g. Vps52, 53 and 54) display embryonic lethality.

Studies performed by Schneeberger et al included:
- Transcript analysis for the 1st variant demonstrated skipping of ex21 (in patient derived fabriblasts) leading to an in frame deletion of 81 bp (r.1978_2058del) with predicted loss of 27 residues (p.Leu660_Leu686del).
- Similar VPS50 mRNA levels but significant reduction of protein levels (~5% and ~8% of controls) were observed in fibroblasts from patients 1 and 2. Additionally, significant reductions in the amounts of VPS52 and VPS53 protein levels were observed despite mRNA levels similar to controls. Overall, this suggested drastic reduction of functional EARP complex levels.
- Lysosomes appeared to have similar morphology, cellular distribution and likely unaffected function in patient fibroblasts.
- Transferrin receptor recycling was shown to be delayed in patient fibroblasts suggestive of compromise of endocytic-recycling function.

As the authors comment, the phenotype of both individuals with biallelic VPS50 variants overlaps with the corresponding phenotype reported in 15 subjects with biallelic VPS53 or VPS51 mutations notably, severe DD/ID, microcephaly and early onset epilepsy, CC anomalies. Overall, for this group, they propose the term "GARP and/or EARP deficiency disorders".

There is no VPS50-associated phenotype in OMIM or G2P. SysID includes VPS50 among the ID candidate genes.

Consider inclusion in other relevant gene panels (e.g. for neonatal cholestasis, epilepsy, microcephaly, growth failure in early infancy, corpus callosum anomalies, etc) with amber rating pending further reports.
Sources: Literature
Intellectual disability v3.1217 PIDD1 Konstantinos Varvagiannis changed review comment from: There is enough evidence to include this gene in the current panel with green rating.

Biallelic PIDD1 pathogenic variants have been reported in 26 individuals (11 families) with DD (all), variable degrees of ID (mild to severe), behavioral (eg. aggression/self-mutilation in several, ADHD) and/or psychiatric abnormalities (ASD, psychosis in 5 belonging to 3 families), well-controlled epilepsy is some (9 subjects from 6 families) and MRI abnormalities notably abnormal gyration pattern (pachygyria with predominant anterior gradient) as well as corpus callosum anomalies (commonly thinning) in several. Dysmorphic features have been reported in almost all, although there has been no specific feature suggested.

The first reports on the phenotype associated with biallelic PIDD1 mutations were made by Harripaul et al (2018 - PMID: 28397838) and Hu et al (2019 - PMID: 29302074) [both studies investigating large cohorts of individuals with ID from consanguineous families].

Sheikh et al (2021 - PMID: 33414379) provided details on the phenotype of 15 individuals from 5 families including those from the previous 2 reports and studied provided evidence on the role of PIDD1 and the effect of variants.

Zaki et al (2021 - PMID: 34163010) reported 11 additional individuals from 6 consanguineous families, summarize the features of all subjects published in the literature and review the neuroradiological features of the disorder.

PIDD1 encodes p53-induced death domain protein 1. The protein is part of the PIDDosome, a multiprotein complex also composed of the bipartite linker protein CRADD (also known as RAIDD) and the proform of caspase-2 and induces apoptosis in response to DNA damage.

There are 5 potential PIDD1 mRNA transcript variants with NM_145886.4 corresponding to the longest. Similar to the protein encoded by CRADD, PIDD1 contains a death domain (DD - aa 774-893). Constitutive post-translational processing gives PIDD1-N, PIDD1-C the latter further processed into PIDD1-CC (by auto-cleavage). Serine residues at pos. 446 and 588 are involved in this autoprocessing generating PIDD1-C (aa 446-910) and PIDD1-CC (aa 774-893). The latter is needed for caspase-2 activation.

Most (if not all) individuals belonged to consanguineous families of different origins and harbored pLoF or missense variants.

Variants reported so far include : c.2587C>T; p.Gln863* / c.1909C>T ; p.Arg637* / c.2443C>T / p.Arg815Trp / c.2275-1G>A which upon trap assay was shown to lead to skipping of ex15 with direct splicing form exon14 to the terminal exon 16 (resulting to p.Arg759Glyfs*1 with exlcusion of the entire DD) / c.2584C>T; p.Arg862Trp / c.1340G>A; p.Trp447* / c.2116_2120del; p.Val706His*, c.1564_1565del; p.Gly602fs*26

Evidence so far provided includes:
- Biallelic CRADD variants cause a NDD disorder and a highly similar gyration pattern.
- Confirmation of splicing effect (eg. for c.2275-1G>A premature stop in position 760) or poor expression (NM_145886.3:c.2587C>T; p.Gln863*). Arg815Trp did not affect autoprocessing or protein stability.
- Abnormal localization pattern, loss of interaction with CRADD and failure to activate caspase-2 (MDM2 cleavage assay) [p.Gln863* and Arg815Trp]
- Available expression data from GTEx (PIDD1 having broad expression in multiple tissues, but higher in brain cerebellum) as well as BrainSpan and PsychEncode studies suggesting high coexpression of PIDD1, CRADD and CASP2 in many regions in the developing human brain.
- Variants in other genes encoding proteins interacting with PIDD1 (MADD, FADD, DNAJ, etc) are associated with NDD.

Pidd-1 ko mice (ex3-15 removal) lack however CNS-related phenotypes. These show decreased anxiety but no motor anomalies. This has also been the case with Cradd-/- mice displaying no significant CNS phenotypes without lamination defects.

There is currently no associated phenotype in OMIM, PanelApp Australia. PIDD1 is listed in the DD panel of G2P (PIDD1-relared NDD / biallelic / loss of function / probable) . SysID includes PIDD1 among the current primary ID genes.

Overall the gene appears to be relevant for the epilepsy panel, panels for gyration and/or corpus callosum anomalies etc.
Sources: Literature, Other; to: There is enough evidence to include this gene in the current panel with green rating.

Biallelic PIDD1 pathogenic variants have been reported in 26 individuals (11 families) with DD (all), variable degrees of ID (mild to severe), behavioral (eg. aggression/self-mutilation in several, ADHD) and/or psychiatric abnormalities (ASD, psychosis in 5 belonging to 3 families), well-controlled epilepsy is some (9 subjects from 6 families) and MRI abnormalities notably abnormal gyration pattern (pachygyria with predominant anterior gradient) as well as corpus callosum anomalies (commonly thinning) in several. Dysmorphic features have been reported in almost all, although there has been no specific feature suggested.

The first reports on the phenotype associated with biallelic PIDD1 mutations were made by Harripaul et al (2018 - PMID: 28397838) and Hu et al (2019 - PMID: 29302074) [both studies investigating large cohorts of individuals with ID from consanguineous families].

Sheikh et al (2021 - PMID: 33414379) provided details on the phenotype of 15 individuals from 5 families including those from the previous 2 reports and studied provided evidence on the role of PIDD1 and the effect of variants.

Zaki et al (2021 - PMID: 34163010) reported 11 additional individuals from 6 consanguineous families, summarize the features of all subjects published in the literature and review the neuroradiological features of the disorder.

PIDD1 encodes p53-induced death domain protein 1. The protein is part of the PIDDosome, a multiprotein complex also composed of the bipartite linker protein CRADD (also known as RAIDD) and the proform of caspase-2 and induces apoptosis in response to DNA damage.

There are 5 potential PIDD1 mRNA transcript variants with NM_145886.4 corresponding to the longest. Similar to the protein encoded by CRADD, PIDD1 contains a death domain (DD - aa 774-893). Constitutive post-translational processing gives PIDD1-N, PIDD1-C the latter further processed into PIDD1-CC (by auto-cleavage). Serine residues at pos. 446 and 588 are involved in this autoprocessing generating PIDD1-C (aa 446-910) and PIDD1-CC (aa 774-893). The latter is needed for caspase-2 activation.

Most (if not all) individuals belonged to consanguineous families of different origins and harbored pLoF or missense variants.

Variants reported so far include : c.2587C>T; p.Gln863* / c.1909C>T ; p.Arg637* / c.2443C>T / p.Arg815Trp / c.2275-1G>A which upon trap assay was shown to lead to skipping of ex15 with direct splicing form exon14 to the terminal exon 16 (resulting to p.Arg759Glyfs*1 with exlcusion of the entire DD) / c.2584C>T; p.Arg862Trp / c.1340G>A; p.Trp447* / c.2116_2120del; p.Val706His*, c.1564_1565del; p.Gly602fs*26

Evidence so far provided includes:
- Biallelic CRADD variants cause a NDD disorder and a highly similar gyration pattern.
- Confirmation of splicing effect (eg. for c.2275-1G>A premature stop in position 760) or poor expression (NM_145886.3:c.2587C>T; p.Gln863*). Arg815Trp did not affect autoprocessing or protein stability.
- Abnormal localization pattern, loss of interaction with CRADD and failure to activate caspase-2 (MDM2 cleavage assay) [p.Gln863* and Arg815Trp]
- Available expression data from GTEx (PIDD1 having broad expression in multiple tissues, but higher in brain cerebellum) as well as BrainSpan and PsychEncode studies suggesting high coexpression of PIDD1, CRADD and CASP2 in many regions in the developing human brain.
- Variants in other genes encoding proteins interacting with PIDD1 (MADD, FADD, DNAJ, etc) are associated with NDD.

Pidd-1 ko mice (ex3-15 removal) lack however CNS-related phenotypes. These show decreased anxiety but no motor anomalies. This has also been the case with Cradd-/- mice displaying no significant CNS phenotypes without lamination defects.

There is currently no associated phenotype in OMIM, PanelApp Australia. PIDD1 is listed in the DD panel of G2P (PIDD1-related NDD / biallelic / loss of function / probable) . SysID includes PIDD1 among the current primary ID genes.

Overall the gene appears to be relevant for the epilepsy panel, panels for gyration and/or corpus callosum anomalies etc.
Sources: Literature, Other
Intellectual disability v3.1217 PIDD1 Konstantinos Varvagiannis gene: PIDD1 was added
gene: PIDD1 was added to Intellectual disability. Sources: Literature,Other
Mode of inheritance for gene: PIDD1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PIDD1 were set to 28397838; 29302074; 33414379; 34163010
Phenotypes for gene: PIDD1 were set to Global developmental delay; Intellectual disability; Seizures; Autism; Behavioral abnormality; Psychosis; Pachygyria; Lissencephaly; Abnormality of the corpus callosum
Penetrance for gene: PIDD1 were set to Complete
Review for gene: PIDD1 was set to GREEN
Added comment: There is enough evidence to include this gene in the current panel with green rating.

Biallelic PIDD1 pathogenic variants have been reported in 26 individuals (11 families) with DD (all), variable degrees of ID (mild to severe), behavioral (eg. aggression/self-mutilation in several, ADHD) and/or psychiatric abnormalities (ASD, psychosis in 5 belonging to 3 families), well-controlled epilepsy is some (9 subjects from 6 families) and MRI abnormalities notably abnormal gyration pattern (pachygyria with predominant anterior gradient) as well as corpus callosum anomalies (commonly thinning) in several. Dysmorphic features have been reported in almost all, although there has been no specific feature suggested.

The first reports on the phenotype associated with biallelic PIDD1 mutations were made by Harripaul et al (2018 - PMID: 28397838) and Hu et al (2019 - PMID: 29302074) [both studies investigating large cohorts of individuals with ID from consanguineous families].

Sheikh et al (2021 - PMID: 33414379) provided details on the phenotype of 15 individuals from 5 families including those from the previous 2 reports and studied provided evidence on the role of PIDD1 and the effect of variants.

Zaki et al (2021 - PMID: 34163010) reported 11 additional individuals from 6 consanguineous families, summarize the features of all subjects published in the literature and review the neuroradiological features of the disorder.

PIDD1 encodes p53-induced death domain protein 1. The protein is part of the PIDDosome, a multiprotein complex also composed of the bipartite linker protein CRADD (also known as RAIDD) and the proform of caspase-2 and induces apoptosis in response to DNA damage.

There are 5 potential PIDD1 mRNA transcript variants with NM_145886.4 corresponding to the longest. Similar to the protein encoded by CRADD, PIDD1 contains a death domain (DD - aa 774-893). Constitutive post-translational processing gives PIDD1-N, PIDD1-C the latter further processed into PIDD1-CC (by auto-cleavage). Serine residues at pos. 446 and 588 are involved in this autoprocessing generating PIDD1-C (aa 446-910) and PIDD1-CC (aa 774-893). The latter is needed for caspase-2 activation.

Most (if not all) individuals belonged to consanguineous families of different origins and harbored pLoF or missense variants.

Variants reported so far include : c.2587C>T; p.Gln863* / c.1909C>T ; p.Arg637* / c.2443C>T / p.Arg815Trp / c.2275-1G>A which upon trap assay was shown to lead to skipping of ex15 with direct splicing form exon14 to the terminal exon 16 (resulting to p.Arg759Glyfs*1 with exlcusion of the entire DD) / c.2584C>T; p.Arg862Trp / c.1340G>A; p.Trp447* / c.2116_2120del; p.Val706His*, c.1564_1565del; p.Gly602fs*26

Evidence so far provided includes:
- Biallelic CRADD variants cause a NDD disorder and a highly similar gyration pattern.
- Confirmation of splicing effect (eg. for c.2275-1G>A premature stop in position 760) or poor expression (NM_145886.3:c.2587C>T; p.Gln863*). Arg815Trp did not affect autoprocessing or protein stability.
- Abnormal localization pattern, loss of interaction with CRADD and failure to activate caspase-2 (MDM2 cleavage assay) [p.Gln863* and Arg815Trp]
- Available expression data from GTEx (PIDD1 having broad expression in multiple tissues, but higher in brain cerebellum) as well as BrainSpan and PsychEncode studies suggesting high coexpression of PIDD1, CRADD and CASP2 in many regions in the developing human brain.
- Variants in other genes encoding proteins interacting with PIDD1 (MADD, FADD, DNAJ, etc) are associated with NDD.

Pidd-1 ko mice (ex3-15 removal) lack however CNS-related phenotypes. These show decreased anxiety but no motor anomalies. This has also been the case with Cradd-/- mice displaying no significant CNS phenotypes without lamination defects.

There is currently no associated phenotype in OMIM, PanelApp Australia. PIDD1 is listed in the DD panel of G2P (PIDD1-relared NDD / biallelic / loss of function / probable) . SysID includes PIDD1 among the current primary ID genes.

Overall the gene appears to be relevant for the epilepsy panel, panels for gyration and/or corpus callosum anomalies etc.
Sources: Literature, Other
Intellectual disability v3.1216 CLCN3 Zornitza Stark gene: CLCN3 was added
gene: CLCN3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CLCN3 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: CLCN3 were set to 34186028
Phenotypes for gene: CLCN3 were set to Neurodevelopmental disorder
Mode of pathogenicity for gene: CLCN3 was set to Other
Review for gene: CLCN3 was set to GREEN
gene: CLCN3 was marked as current diagnostic
Added comment: 11 individuals reported, 9 that carried 8 different rare heterozygous missense variants in CLCN3, and 2 siblings that were homozygous for an NMD-predicted frameshift variant likely abolishing ClC-3 function. All missense variants were confirmed to be de novo in eight individuals for whom parental data was available.

The 11 individuals in the cohort share clinical features of variable severity. All 11 have GDD or ID and dysmorphic features, and a majority has mood or behavioural disorders and structural brain abnormalities:
- Structural brain abnormalities on MRI (9/11) included partial or full agenesis of the corpus callosum (6/9), disorganized cerebellar folia (4/9), delayed myelination (3/9), decreased white matter volume (3/9), pons hypoplasia (3/9), and dysmorphic dentate nuclei (3/9). Six of those with brain abnormalities also presented with seizures.
- Nine have abnormal vision, including strabismus in four and inability to fix or follow in the two with homozygous loss-of-function variants.
- Hypotonia ranging from mild to severe was reported in 7 of the 11 individuals.
- Six have mood or behavioural disorders, particularly anxiety (3/6).
- Consistent dysmorphic facial features included microcephaly, prominent forehead, hypertelorism, down-slanting palpebral fissures, full cheeks, and micrognathia.

The severity of disease in the two siblings with homozygous disruption of ClC-3 is consistent with the drastic phenotype seen in Clcn3 KO mice. The disease was more severe in two siblings carrying homozygous loss-of-function variants with the presence of GDD, absent speech, seizures, and salt and pepper fundal pigmentation in both individuals, with one deceased at 14 months of age. The siblings also had significant neuroanatomical findings including diffusely decreased white matter volume, thin corpora callosa, small hippocampi, and disorganized cerebellar folia. Supporting biallelic inheritance for LoF variants, disruption of mouse Clcn3 results in drastic neurodegeneration with loss of the hippocampus a few months after birth and early retinal degeneration. Clcn3−/− mice display severe neurodegeneration, whereas heterozygous Clcn3+/− mice appear normal.

Patch-clamp studies were used to investigate four of the missense variants. These suggested a gain of function in two variants with increased current in HEK cells, however they also showed reduced rectification of voltage and a loss of transient current, plus decreased current amplitude, glycosylation and surface expression when expressed in oocytes, and were suspected to interfere with channel gating and a negative feedback mechanism. These effects were also shown to vary depending on pH levels. The current of the remaining two variants did not differ from WT. For heterozygous missense variants, the disruption induced may be at least partially conferred to mutant/WT homodimers and mutant/ClC-4 heterodimers.

Both loss and gain of function in this gene resulted in the same phenotype.

Green for mono-allelic variants, Amber/Red for bi-allelic.
Sources: Literature
Intellectual disability v3.1201 CAMK4 Konstantinos Varvagiannis gene: CAMK4 was added
gene: CAMK4 was added to Intellectual disability. Sources: Literature,Other
Mode of inheritance for gene: CAMK4 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CAMK4 were set to 30262571; 33098801; 33211350
Phenotypes for gene: CAMK4 were set to Global developmental delay; Intellectual disability; Autism; Behavioral abnormality; Abnormality of movement; Dystonia; Ataxia; Chorea; Myoclonus
Penetrance for gene: CAMK4 were set to Complete
Review for gene: CAMK4 was set to GREEN
Added comment: 3 publications by Zech et al (2018, 2020 - PMIDs : 30262571, 33098801, 33211350) provide clinical details on 3 individuals, each harboring a private de novo CAMK4 variant.

Overlapping features included DD, ID, behavoral issues, autism and abnormal hyperkinetic movements. Dystonia and chorea in all 3 appeared 3-20 years after initial symptoms.

CAMK4 encodes Calcium/Calmodulin-dependent protein kinase IV, an important mediator of calcium-mediated activity and dynamics, particularly in the brain. It is involved in neuronal transmission, synaptic plasticity, and neuronal gene expression required for brain development and neuronal homeostasis (summary by OMIM based on Zech et al, 2018).

The 473 aa enzyme has a protein kinase domain (aa 46-300) and a C-terminal autoregulatory domain (aa 305-341) the latter comprising an autoinhibitory domain (AID / aa 305-321) and a calmodulin-binding domain (CBD / aa 322-341) [NP_001735.1 / NM_001744.4 - also used below].

Variants in all 3 subjects were identified following trio-WES and were in all cases protein-truncating, mapping to exon 10 or exon 10-intron 10 junction, expected to escape NMD and cause selective abrogation of the autoinhibitory domain (aa 305-321) leading overall to gain-of-function.

Variation databases include pLoF CAMK4 variants albeit in all cases usptream or downstream of this region (pLI of this gene in gnomAD: 0.51). Variants leading to selective abrogation of the autoregulatory domain have not been reported.

Extensive evidence for the GoF effect of the variant has been provided in the first publication. Several previous studies have demonstrated that abrogation of the AID domain leads to consitutive activation (details below).

Mouse models - though corresponding to homozygous loss of function - support a role for CAMKIV in cognitive and motor symptoms. Null mice display tremulous and ataxic movements, deficiencies in balance and sensorimotor performance associated with reduced number of Purkinje neurons (Ribar et al 2000, PMID: 11069976 - not reviewed). Wei et al (2002, PMID: 12006982 - not reviewed) provided evidence for alteration in hippocampal physiology and memory function.

Heterozygous mutations in other genes for calcium/calmodulin-dependent protein kinases (CAMKs) e.g. CAMK2A/CAMK2B (encoding subunits of CAMKII) have been reported in individuals with ID.

---

The proband in the first publication (PMID: 30262571) was a male with DD, ID, behavioral difficulties (ASD, autoaggression, stereotypies) and hyperkinetic movement disorder (myoclonus, chorea, ataxia) with severe generalized dystonia (onset at the age of 13y). Brain MRI demonstrated cerebellar atrophy.

Extensive work-up incl. karyotyping, CMA, DYT-TOR1A, THAP1, GCH1, SCA1/2/3/6/7/8/12/17, Friedreich's ataxia and FMR1 analysis was negative.F

Trio WES identified a dn splice site variant (c.981+1G>A) in the last exon-intron junction. RT-PCR followed by gel electrophoresis and Sanger in fibroblasts from an affected and control subject revealed that the proband had - as predicted by the type/location of the variant - in equal amount 2 cDNA products, a normal as well as a truncated one.

Sequencing of the shortest revealed utilization of a cryptic donor splice site upstream of the mutated donor leading to a 77bp out-of-frame deletion and introduction of a premature stop codon in the last codon (p.Lys303Serfs*28). Western blot in fibroblast cell lines revealed 2 bands corresponding to the normal protein product as well as to the p.Lys303Serfs*28 although expression of the latter was lower than that of the full length protein.

Several previous studies have shown that mutant CAMKIV species that lack the autoinhibitory domain are consitutively active (several Refs provided). Among others Chatila et al (1996, PMID: 8702940) studied an in vitro-engineered truncation mutant (Δ1-317 - truncation at position 317 of the protein) with functionally validated gain-of-function effect.

To prove enhanced activity of the splicing variant, Zech et al assessed phosphorylation of CREB (cyclic AMP-responsive element binding protein), a downstream substrate of CAMKIV. Immunobloting revealed significant increase of CREB phosphorylation in patient fibroblasts compared to controls. Overactivation of CAMKIV signaling was reversed when cells were treated with STO-609 an inhibitor of CAMKK, the ustream activator of CAMKIV.

Overall the authors demonstrated that loss of CAMKIV autoregulatory domain due to this splice variant had a gain-of-function effect.

----

Following trio-WES, Zech et al (2020 - PMID: 33098801) identified another relevant subject within cohort of 764 individuals with dystonia. This 12-y.o. male, harboring a different variant affecting the same donor site (c.981+1G>T), presented DD, ID, dystonia (onset at 3y) and additional movement disorders (myoclonus, ataxia) as well as similar behavior (ASD, autoaggression, stereotypies). [Details in suppl. p20].

----

Finally Zech et al (2020 - PMID: 33211350) reported on a 24-y.o. woman with adolescence onset choreodystonia. Other features included DD, moderate ID, absence seizures in infancy, OCD with anxiety and later diagnosis of ASD. Trio WES revealed a dn stopgain variant (c.940C>T; p.Gln314*).

----

There is no associated phenotype in OMIM, G2P, PanelApp AUS.

In SysID CAMK4 is listed among the current primary ID genes.

----

Please consider inclusion in other relevant panels.
Sources: Literature, Other
Intellectual disability v3.1201 ATP9A Konstantinos Varvagiannis gene: ATP9A was added
gene: ATP9A was added to Intellectual disability. Sources: Literature,Other
Mode of inheritance for gene: ATP9A was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: ATP9A were set to Global developmental delay; Intellectual disability; Postnatal microcephaly; Failure to thrive; Abnormality of the abdomen
Penetrance for gene: ATP9A were set to Complete
Review for gene: ATP9A was set to AMBER
Added comment: Vogt, Verheyen et al (2021 - http://dx.doi.org/10.1136/jmedgenet-2021-107843) report 3 affected individuals from 2 unrelated consanguineous families.

Features included DD, variable ID (Fam1: sib1-mild, sib2-possible, Fam2: severe), postnatal microcephaly (-2.33 to -3.58 SD), failure to thrive as well as gastrointestinal symptoms (nausea, vomiting, GE reflux).

These subjects were homozygous for pLoF ATP9A variants private to each family.

Previous investigations incl. karyotype, aCGH and transferrin electophoresis (CDGs) and were unremarkable.

Diagnosis was made by exome sequencing and homozygosity mapping. Affected sibs from the first family were homozygous for a stopgain variant [NM_006045.3:c.868C>Τ / p.(Arg290*)]. The subject from the second family was homozygous for a variant affecting the consensus (donor) splice site [c.642+1G>A - same RefSeq]. Both variants were absent from gnomAD. Sanger sequencing was used to confirm variants, carrier status of the parents and unaffected sibs in both families.

Sequencing of cDNA from the individual homozygous for the splicing variant demonstrated skipping of exon 7 with the variant likely leading to frameshift and introduction of a premature stop codon.

qPCR in dermal fibroblasts from affected individuals from both families revealed expression downregulation of ATP9A (14% and 4% respectively for the stopgain and splice variant). Study at the protein level was not possible due to absence of antibody against endogenous ATP9A.

ATP9A encodes ATPase phospholipid transporting 9A (similarly to ATP9B) belonging to the subclass 2 of the P4-ATPase family. As the authors comment, the protein is mainly expressed in the brain although the precise function or subcellular distribution of endogenous ATP9A are unknown.

A previous study showed that overexpressed ATP9A in HeLa cells localizes to early/recycling endosomes and the trans-Golgi network, being required for endocytic recycling of the transferrin receptor to the plasma membrane. ATP9A (in complex with DOP1B and MON2) functionally interacts with the SNX3-retromer. A previous ATP9A knockdown cell line suggested dysregulation of >100 genes with ARPC3 (actin-related protein 2/3 complex subunit 3) being strongly upregulated.

Overall ATP9A appears to have a role in endosome trafficking pathways as well as to inhibit secretion of exosomes at the plasma membrane likely due to alteration of the actin cytoskeleton.

In line with the role of APT9A in early/recycling endosomes and identified interactions, the authors demonstrated overexpression of ARPC3 and SNX3. Study of genes encoding other known interacting proteins was not possible due to poor expression in fibroblasts.

As the authors note, mutations in genes encoding proteins of the Golgi and endosomal trafficking are important for brain development and have been associated with postnatal microcephaly.

In OMIM, G2P, SysID there is no associated phenotype.

The gene is included in the ID panel of PanelApp AUS with amber rating.
Sources: Literature, Other
Intellectual disability v3.1167 ACSL4 Ivone Leong changed review comment from: ACSL4 is said to be X-linked dominant in OMIM.

PMID: 12525535 - a family with 4 affected males, 1 unaffected male, 2 carrier females and 1 non-carrier female. All affected males full scale IQ (FSIQ) ranged from 43-71, unaffected male FSIQ is 116, carrier females ranged from 74-83 and non-carrier female is 133. All carrier females showed 100% skewed inactivation.

PMID: 11889465 - Family MRX63, all carrier females showed complete skewed X-inactivation. All affected males showed non-specific, non-progressive mental deficiency (moderate - severe). Carrier females showed highly variable cognitive capacities (normal to moderate).

Based on the available evidence the MOI should be changed from "X-LINKED: hemizygous mutation in males, biallelic mutations in females" to "X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)".; to: ACSL4 is said to be X-linked dominant in OMIM.

PMID: 12525535 - a family with 4 affected males, 1 unaffected male, 2 carrier females and 1 non-carrier female. All affected males full scale IQ (FSIQ) ranged from 43-71, unaffected male FSIQ is 116, carrier females ranged from 74-83 and non-carrier female is 133. All carrier females showed 100% skewed inactivation.

PMID: 11889465 - Family MRX63, all carrier females showed complete skewed X-inactivation. All affected males showed non-specific, non-progressive mental deficiency (moderate - severe). Carrier females showed highly variable cognitive capacities (normal to moderate).

As there are only 2 cases where carrier females have a phenotype, the MOI should be kept as "X-LINKED: hemizygous mutation in males, biallelic mutations in females".
Intellectual disability v3.1167 RING1 Eleanor Williams gene: RING1 was added
gene: RING1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: RING1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: RING1 were set to 29386386
Phenotypes for gene: RING1 were set to microcephaly; intellectual disability
Review for gene: RING1 was set to RED
Added comment: Not associated with any phenotype in OMIM.

PMID: 29386386 - Pierce et al 2018 - report a 13 yo female with a de novo RING1 p.R95Q variant and syndromic neurodevelopmental disabilities. Early motor and language development were normal but were delayed after the first year of life. Cognitive testing showed a verbal IQ of 55 and a visual performance IQ of 63. Head circumference at birth was -4.9 SD, and -4.2 SD at age 13 which falls into the severe microcephaly category. C. elegans with either the missense mutation or complete knockout of spat-3 (the suggested RING1 ortholog) were defective in monoubiquitylation of histone H2A and had defects in neuronal migration and axon guidance.
Sources: Literature
Intellectual disability v3.1156 ACSL4 Ivone Leong reviewed gene: ACSL4: Rating: ; Mode of pathogenicity: None; Publications: 12525535, 11889465; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1154 ARHGEF9 Arina Puzriakova edited their review of gene: ARHGEF9: Changed mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.1154 ARHGEF9 Arina Puzriakova Mode of inheritance for gene: ARHGEF9 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.1094 UFSP2 Konstantinos Varvagiannis changed review comment from: Ni et al (2021 - PMID: 33473208) describe the phenotype of 8 children (belonging to 4 families - 2 of which consanguineous) homozygous for a UFSP2 missense variant [NM_018359.5:c.344T>A; p.(Val115Glu)].

Members of a broader consanguineous pedigree from Pakistan with 3 affected children with epilepsy and DD and ID underwent exome sequencing. All affected individuals were homozygous for the specific SNV with their parents (2 parent pairs, in both cases first cousins) being heterozygous. An unaffected sib was homozygous for the wt allele. Through genematching platforms 3 additional families with similarly affected individuals and homozygosity for the same variant were recruited. These additional families were from Pakistan (1/3) and Afganistan (2/3).

Based on ROH analysis from the broader first pedigree and an additional family the authors concluded on a single shared region of homozygosity on chr 4q. Lack of ES data did not allow verification of whether 2/4 families shared the same haplotype with the other 2.

The authors calculated the probability of the genotype-phenotype cosegragation occurring by chance (0.009) and this was lower than the recommended criterion (0.06) for strong evidence of pathogenicity.

Shared features included abnormal tone in most (hypotonia 6/8, limb hypertonia 1/8), seizures (8/8 - onset 2d - 7m), severe DD with speech delay/absent speech (8/8), ID (8/8), strabismus (6/8).

UFSP2 encodes UFM1-specific protease 2 involved in UFmylation, a post-translational protein modification. As summarized by the authors the cysteine protease encoded by this gene (as is also the case for UFSP1) cleaves UFM1 in the initial step of UFMylation. Apart from producing mature UFM1, the 2 proteases have also the ability to release UFM1 from UFMylated proteins, in the process of de-UFMylation. [several refs. provided]

UFMylation is important in brain development with mutations in genes encoding other components of the pathway reported in other NDD disorders (incl. UFM1, UBA5, UFC1).

Additional studies were carried to provide evidence for pathogenicity of this variant.

Skin biopsies from 3 individuals were carried out to establish fibroblast cultures. Immunoblotting revealed reduced UFSP2 levels relative to controls. mRNA levels measured by qRT-PCR revealed no differences compared to controls altogether suggesting normal mRNA but reduced protein stability.

The authors demonstrated increased levels of UFM1-conjugated proteins (incl. DDRGK1, or TRIP4). Ectopic expression of wt UFSP2 normalized the levels of UFMylated proteins in the fibroblasts which was not the case for the V115E variant. Further the variant was difficult to detect by immunoblotting consistent with an effect on protein destabilization.

Although disruption of UFMylation induces ER stress, this was not shown to occur in patient fibroblast lines, when assessed for ER stress markers.

Evaluation of data from the GTEx project, concerning UFSP2 as well as well as DDRGK1 or TRIP4 - an UFMylation target - revealed relevant expression in multiple regions of the human brain.

Overall the authors provide evidence for defective de-UFMylation in patient fibroblasts (presence of increased UFMylation marks). The authors stress out that the effect of the variant in UFMylation in brain is unknown, as UFSP1 or other enzymes might compensate in the presence of hypomorphic UFSP2 mutants.

Biallelic UFSP2 variants have previously been reported in 2 skeletal dysplasias [# 142669. BEUKES HIP DYSPLASIA; BHD and # 617974. SPONDYLOEPIMETAPHYSEAL DYSPLASIA, DI ROCCO TYPE; SEMDDR]. These disorders are not characterized by neurological dysfunction or epilepsy. The authors underscore the fact that variants identified in these disorders (Y290H, D526A, H428R) localize within the C-terminal catalytic (peptidase) domain [aa 278 – 461] while the variant here identified lies in the N-terminal substrate binding domain affecting protein stability/abundance.

In OMIM, only the 2 aforementioned disorders are currently associated with biallelic UFSP2 mutations. There is no associated phenotype in G2P. SysID includes UFSP2 among the primary ID genes.

You may consider inclusion in the current panel with amber/green rating.
Sources: Literature; to: Ni et al (2021 - PMID: 33473208) describe the phenotype of 8 children (belonging to 4 families - 2 of which consanguineous) homozygous for a UFSP2 missense variant [NM_018359.5:c.344T>A; p.(Val115Glu)].

Members of a broader consanguineous pedigree from Pakistan with 3 affected children with epilepsy and DD and ID underwent exome sequencing. All affected individuals were homozygous for the specific SNV with their parents (2 parent pairs, in both cases first cousins) being heterozygous. An unaffected sib was homozygous for the wt allele. Through genematching platforms 3 additional families with similarly affected individuals and homozygosity for the same variant were recruited. These additional families were from Pakistan (1/3) and Afganistan (2/3).

Based on ROH analysis from the broader first pedigree and an additional family the authors concluded on a single shared region of homozygosity on chr 4q. Lack of ES data did not allow verification of whether 2/4 families shared the same haplotype with the other 2.

The authors calculated the probability of the genotype-phenotype cosegragation occurring by chance (0.009) and this was lower than the recommended criterion (0.06) for strong evidence of pathogenicity.

Shared features included abnormal tone in most (hypotonia 6/8, limb hypertonia 1/8), seizures (8/8 - onset 2d - 7m), severe DD with speech delay/absent speech (8/8), ID (8/8), strabismus (6/8).

UFSP2 encodes UFM1-specific protease 2 involved in UFmylation, a post-translational protein modification. As summarized by the authors the cysteine protease encoded by this gene (as is also the case for UFSP1) cleaves UFM1 in the initial step of UFMylation. Apart from producing mature UFM1, the 2 proteases have also the ability to release UFM1 from UFMylated proteins, in the process of de-UFMylation. [several refs. provided]

UFMylation is important in brain development with mutations in genes encoding other components of the pathway reported in other NDD disorders (incl. UFM1, UBA5, UFC1).

Additional studies were carried to provide evidence for pathogenicity of this variant.

Skin biopsies from 3 individuals were carried out to establish fibroblast cultures. Immunoblotting revealed reduced UFSP2 levels relative to controls. mRNA levels measured by qRT-PCR revealed no differences compared to controls altogether suggesting normal mRNA but reduced protein stability.

The authors demonstrated increased levels of UFM1-conjugated proteins (incl. DDRGK1, or TRIP4). Ectopic expression of wt UFSP2 normalized the levels of UFMylated proteins in the fibroblasts which was not the case for the V115E variant. Further the variant was difficult to detect by immunoblotting consistent with an effect on protein destabilization.

Although disruption of UFMylation induces ER stress, this was not shown to occur in patient fibroblast lines, when assessed for ER stress markers.

Evaluation of data from the GTEx project, concerning UFSP2 as well as well as DDRGK1 or TRIP4 - an UFMylation target - revealed relevant expression in multiple regions of the human brain.

Overall the authors provide evidence for defective de-UFMylation in patient fibroblasts (presence of increased UFMylation marks). The authors stress out that the effect of the variant in UFMylation in brain is unknown, as UFSP1 or other enzymes might compensate in the presence of hypomorphic UFSP2 mutants.

**Monoallelic** (correction to previous review) UFSP2 variants have previously been reported in 2 skeletal dysplasias [# 142669. BEUKES HIP DYSPLASIA; BHD and # 617974. SPONDYLOEPIMETAPHYSEAL DYSPLASIA, DI ROCCO TYPE; SEMDDR]. These disorders are not characterized by neurological dysfunction or epilepsy. The authors underscore the fact that variants identified in these disorders (Y290H, D526A, H428R) localize within the C-terminal catalytic (peptidase) domain [aa 278 – 461] while the variant here identified lies in the N-terminal substrate binding domain affecting protein stability/abundance.

In OMIM, only the 2 aforementioned disorders are currently associated with biallelic UFSP2 mutations. There is no associated phenotype in G2P. SysID includes UFSP2 among the primary ID genes.

You may consider inclusion in the current panel with amber/green rating.
Sources: Literature
Intellectual disability v3.1092 UFSP2 Konstantinos Varvagiannis gene: UFSP2 was added
gene: UFSP2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: UFSP2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: UFSP2 were set to 33473208
Phenotypes for gene: UFSP2 were set to Abnormal muscle tone; Seizures; Global developmental delay; Delayed speech and language development; Intellectual disability; Strabismus
Penetrance for gene: UFSP2 were set to Complete
Added comment: Ni et al (2021 - PMID: 33473208) describe the phenotype of 8 children (belonging to 4 families - 2 of which consanguineous) homozygous for a UFSP2 missense variant [NM_018359.5:c.344T>A; p.(Val115Glu)].

Members of a broader consanguineous pedigree from Pakistan with 3 affected children with epilepsy and DD and ID underwent exome sequencing. All affected individuals were homozygous for the specific SNV with their parents (2 parent pairs, in both cases first cousins) being heterozygous. An unaffected sib was homozygous for the wt allele. Through genematching platforms 3 additional families with similarly affected individuals and homozygosity for the same variant were recruited. These additional families were from Pakistan (1/3) and Afganistan (2/3).

Based on ROH analysis from the broader first pedigree and an additional family the authors concluded on a single shared region of homozygosity on chr 4q. Lack of ES data did not allow verification of whether 2/4 families shared the same haplotype with the other 2.

The authors calculated the probability of the genotype-phenotype cosegragation occurring by chance (0.009) and this was lower than the recommended criterion (0.06) for strong evidence of pathogenicity.

Shared features included abnormal tone in most (hypotonia 6/8, limb hypertonia 1/8), seizures (8/8 - onset 2d - 7m), severe DD with speech delay/absent speech (8/8), ID (8/8), strabismus (6/8).

UFSP2 encodes UFM1-specific protease 2 involved in UFmylation, a post-translational protein modification. As summarized by the authors the cysteine protease encoded by this gene (as is also the case for UFSP1) cleaves UFM1 in the initial step of UFMylation. Apart from producing mature UFM1, the 2 proteases have also the ability to release UFM1 from UFMylated proteins, in the process of de-UFMylation. [several refs. provided]

UFMylation is important in brain development with mutations in genes encoding other components of the pathway reported in other NDD disorders (incl. UFM1, UBA5, UFC1).

Additional studies were carried to provide evidence for pathogenicity of this variant.

Skin biopsies from 3 individuals were carried out to establish fibroblast cultures. Immunoblotting revealed reduced UFSP2 levels relative to controls. mRNA levels measured by qRT-PCR revealed no differences compared to controls altogether suggesting normal mRNA but reduced protein stability.

The authors demonstrated increased levels of UFM1-conjugated proteins (incl. DDRGK1, or TRIP4). Ectopic expression of wt UFSP2 normalized the levels of UFMylated proteins in the fibroblasts which was not the case for the V115E variant. Further the variant was difficult to detect by immunoblotting consistent with an effect on protein destabilization.

Although disruption of UFMylation induces ER stress, this was not shown to occur in patient fibroblast lines, when assessed for ER stress markers.

Evaluation of data from the GTEx project, concerning UFSP2 as well as well as DDRGK1 or TRIP4 - an UFMylation target - revealed relevant expression in multiple regions of the human brain.

Overall the authors provide evidence for defective de-UFMylation in patient fibroblasts (presence of increased UFMylation marks). The authors stress out that the effect of the variant in UFMylation in brain is unknown, as UFSP1 or other enzymes might compensate in the presence of hypomorphic UFSP2 mutants.

Biallelic UFSP2 variants have previously been reported in 2 skeletal dysplasias [# 142669. BEUKES HIP DYSPLASIA; BHD and # 617974. SPONDYLOEPIMETAPHYSEAL DYSPLASIA, DI ROCCO TYPE; SEMDDR]. These disorders are not characterized by neurological dysfunction or epilepsy. The authors underscore the fact that variants identified in these disorders (Y290H, D526A, H428R) localize within the C-terminal catalytic (peptidase) domain [aa 278 – 461] while the variant here identified lies in the N-terminal substrate binding domain affecting protein stability/abundance.

In OMIM, only the 2 aforementioned disorders are currently associated with biallelic UFSP2 mutations. There is no associated phenotype in G2P. SysID includes UFSP2 among the primary ID genes.

You may consider inclusion in the current panel with amber/green rating.
Sources: Literature
Intellectual disability v3.1056 HTT Eleanor Williams changed review comment from: PMID: 33432339 - Jung et al 2021 - further characterisation of the family previously reported in PMID: 27329733 (Rodan et al 2016) - using WGS they confirm they are the most likely cause of the LOMARS phenotype and clarify their locations as NM_002111.8(HTT): c.8157T>A (p.Phe2719Leu) and NM_002111.8(HTT)c.4469+1G>A (Note there are incorrect Clinvar entries). Functional studies show them each to be a hypomorphic mutation, resulting in severe deficiency of huntingtin in compound heterozygotes.; to: PMID: 33432339 - Jung et al 2021 - further characterisation of the family previously reported in PMID: 27329733 (Rodan et al 2016) - using WGS they confirm they are the most likely cause of the LOMARS phenotype and clarify their locations as NM_002111.8(HTT): c.8157T>A (p.Phe2719Leu) and NM_002111.8(HTT)c.4469+1G>A (Note there are incorrect Clinvar entries). Functional studies show them each to be a hypomorphic mutation, resulting in severe deficiency of huntingtin in compound heterozygotes.

Still only 2 cases reported to date (PMID: 27329733/33432339 and 26740508) with biallelic LOF variants in HTT associated with the LOMARS phenotype although this study add further weight with some functional data.
Intellectual disability v3.1037 JMJD1C Zornitza Stark gene: JMJD1C was added
gene: JMJD1C was added to Intellectual disability. Sources: Expert Review
Mode of inheritance for gene: JMJD1C was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: JMJD1C were set to 26181491; 32996679
Phenotypes for gene: JMJD1C were set to Intellectual disability
Review for gene: JMJD1C was set to GREEN
gene: JMJD1C was marked as current diagnostic
Added comment: Reported in ID cohort (with Rett-like phenotypic overlap) with supporting functional studies (PMID: 26181491). 7 individuals with rare variants identified, and variants demonstrated to be de novo in 2, one with a Rett-like phenotype and the other with ID. Functional study of the JMJD1C mutant Rett syndrome patient demonstrated that the altered protein had abnormal subcellular localization, diminished activity to demethylate the DNA damage-response protein MDC1, and reduced binding to MECP2. JMJD1C protein shown to be widely expressed in brain regions and that its depletion compromised dendritic activity.

Splice-disrupting JMJD1C variant reported in association with learning disability and myoclonic epilepsy (PMID 32996679).

Disruption of gene due to balanced translocation (PMID 33591602) implicated in autism spectrum disease phenotype.
Sources: Expert Review
Intellectual disability v3.1034 NEUROD2 Arina Puzriakova gene: NEUROD2 was added
gene: NEUROD2 was added to Intellectual disability. Sources: Literature
Q2_21_rating tags were added to gene: NEUROD2.
Mode of inheritance for gene: NEUROD2 was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: NEUROD2 were set to 16504944; 30323019; 33438828
Phenotypes for gene: NEUROD2 were set to Developmental and epileptic encephalopathy 72, OMIM:618374
Review for gene: NEUROD2 was set to GREEN
Added comment: NEUROD2 is associated with a relevant phenotype in OMIM (MIM# 618374), but is not yet listed in Gene2Phenotype.

- PMID: 30323019 (2019) - Two unrelated children with refractory early-infantile epileptic encephalopathy. Developmental delay (DD) preceded onset of seizures in both cases, with signs of DD becoming evident at 2-4 months and seizures arising at 5 months of age. Patient 1 became seizure-free after introducing a ketogenic diet at 16 months; however, an EEG at 22 months remained abnormal and she continues to have severe GDD with no independent sitting, walking or speaking at the chronological age of 3 years and 2 months. Patient 2 became seizure-free when a vagal nerve stimulator (VNS) was placed at 16 months of age. He displayed significant improvement on EEG and subsequently began regaining neurodevelopmental milestones.
WES revealed different de novo variants in the NEUROD2 gene (P1: c.388G>C, p.E130Q; P2: c.401T>C, p.M134T, respectively). Knockdown of the neurod2 in Xenopus tropicalis tadpoles resulted in abnormal swimming behaviour and progressive seizures followed by periods of immobility. Overexpression of wild-type human NEUROD2 in tadpoles induced non-neuronal cells to differentiate into neurons - on the other hand, overexpression of the mutant alleles failed to to cause any (p.E130Q) or a comparable degree (p.M134T) of ectopic neuronal induction as seen with the wild-type protein.

- Conference poster (Genomics of Rare Disease 2021) - 'Neuronal Differentiation Factor 2 (NEUROD2) Pathogenic Variant as a Molecular Aetiology of Infantile Spasm ' by Sakpichaisakul et al, QSNICH, Thailand -
In a 15 month-old female with infantile spasm, trio exome sequencing revealed a de novo variant in NEUROD2 (c.388G>C, p.E130Q). She was born of non-consanguineous healthy parents with no family history of epilepsy. Poor eye contact and no social smile were noted in the first few months, followed by the first infantile spasm at 5 months of age. This was initially controlled by combined vigabatrin and prednisolone therapy - however relapsing seizures were detected at 15 months. Sequential treatment with vigabatrin following prednisolone resulted in cessation of seizures, and subsequently regaining of neurodevelopmental milestones (sitting without support, grabbing objects without pincer grasp and speaking one single word)

----- Cases without seizures -

- PMID: 33438828 (2021) - Adolescent (14 yrs old) with GDD but without seizures who was found to have a novel de novo NEUROD2 missense variant (c.488 T > C, p.L163P). An additional individual (12 yrs) with DD and a different missense NEUROD2 (c.703G>A, p.A235T) was also identified, but lacking parental samples for segregation analysis.
Functional analysis in Xenopus laevis revealed that injection of the p.L163P mRNA variant resulted in a defective ability to induce ectopic neurons in tadpoles as compared with wild-type NEUROD2 mRNA, while the p.A235T variant functioned similarly to wild-type.
Sources: Literature
Intellectual disability v3.976 SIAH1 Arina Puzriakova gene: SIAH1 was added
gene: SIAH1 was added to Intellectual disability. Sources: Literature
Q2_21_rating tags were added to gene: SIAH1.
Mode of inheritance for gene: SIAH1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: SIAH1 were set to 32430360
Phenotypes for gene: SIAH1 were set to Developmental delay; Infantile hypotonia; Dysmorphic features; Laryngomalacia
Review for gene: SIAH1 was set to GREEN
Added comment: - PMID: 32430360 (2021) - Five unrelated individuals with shared features of developmental delay, infantile hypotonia, dysmorphic features and laryngomalacia. All had speech delay and where cognitive assessment was age appropriate individuals exhibited learning difficulties. Trio WES revealed distinct de novo variants in SIAH1. In vitro assays demonstrated that SIAH1 mutants induce loss of Wnt stimulatory activity.
Sources: Literature
Intellectual disability v3.761 PIGF Zornitza Stark gene: PIGF was added
gene: PIGF was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PIGF was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PIGF were set to 33386993
Phenotypes for gene: PIGF were set to Glycosylphosphatidylinositol deficiency, onychodystrophy, osteodystrophy, intellectual disability, and seizures
Review for gene: PIGF was set to RED
Added comment: The same homozygous missense variant identified in 2 individuals from different families from the same region of India. Individuals had a phenotype similar to DOORS syndrome without deafness. Impaired glycosylphosphatidylinositol (GPI) biosynthesis was demonstrated.

Rated Red as the two families are likely to be related (founder mutation?).
Sources: Literature
Intellectual disability v3.751 VPS4A Evan Reid changed review comment from: Multiple families (now 10) described with a consistent phenotype (we have termed it CIMDAG as an acronym for the major features). All have de novo heterozygous missense mutations of VPS4A, with a distinct mutational hotspot (R284) in many families. Mechanism is likely dominant negative. Haplo-insufficiency of VPS4A is tolerated and present in general population databases, so loss of function mutations likely do not cause this disease.
Sources: Literature, Research; to: Multiple families (now 10) described with a consistent phenotype (termed CIMDAG as an acronym for the major features). All have de novo heterozygous missense mutations of VPS4A, with a distinct mutational hotspot (R284) in many families. Mechanism is likely dominant negative. Haplo-insufficiency of VPS4A is tolerated and present in general population databases, so loss of function mutations likely do not cause this disease.
Sources: Literature, Research
Intellectual disability v3.751 VPS4A Evan Reid gene: VPS4A was added
gene: VPS4A was added to Intellectual disability. Sources: Literature,Research
Mode of inheritance for gene: VPS4A was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: VPS4A were set to (PMID: 33186545; 33186543; 33460484)
Phenotypes for gene: VPS4A were set to developmental delay; intellectual disability; cerebellar hypoplasia; pontine hypoplasia; thin corpus callosum; microcephaly; growth retardation; congenital anaemia; dyserythropeoitic anaemia; dystonia; congenital cataracts; deafness
Penetrance for gene: VPS4A were set to Complete
Mode of pathogenicity for gene: VPS4A was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: VPS4A was set to GREEN
Added comment: Multiple families (now 10) described with a consistent phenotype (we have termed it CIMDAG as an acronym for the major features). All have de novo heterozygous missense mutations of VPS4A, with a distinct mutational hotspot (R284) in many families. Mechanism is likely dominant negative. Haplo-insufficiency of VPS4A is tolerated and present in general population databases, so loss of function mutations likely do not cause this disease.
Sources: Literature, Research
Intellectual disability v3.749 OTUD5 Zornitza Stark gene: OTUD5 was added
gene: OTUD5 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: OTUD5 was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Publications for gene: OTUD5 were set to 33131077
Phenotypes for gene: OTUD5 were set to X-linked severe neurodevelopmental delay, hydrocephalus, and early lethality
Review for gene: OTUD5 was set to RED
Added comment: 13 male patients from a single family with three generations affected. Patients presented prenatally or during the neonatal period with IUGR, ventriculomegaly, hydrocephalus, hypotonia, congenital heart defects, hypospadias, and severe neurodevelopmental delay. The disease is typically fatal during infancy, mainly due to sepsis (pneumonias). Female carriers are asymptomatic. WGS in four individuals identified a unique candidate variant in the OTUD5 gene (NM_017602.3:c.598G > A, p.Glu200Lys). The variant cosegregated with the disease in 10 tested individuals.
Sources: Literature
Intellectual disability v3.724 FGF13 Arina Puzriakova Mode of inheritance for gene: FGF13 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.702 NUS1 Eleanor Williams Added comment: Comment on mode of inheritance: The mode of inheritance should be considered for change to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal in line with its classification on the Genetic Epilepsy Syndromes panel.
Intellectual disability v3.694 FGF13 Zornitza Stark gene: FGF13 was added
gene: FGF13 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: FGF13 was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Publications for gene: FGF13 were set to 33245860
Phenotypes for gene: FGF13 were set to Intellectual disability; epilepsy
Mode of pathogenicity for gene: FGF13 was set to Other
Review for gene: FGF13 was set to GREEN
gene: FGF13 was marked as current diagnostic
Added comment: Two sibling pairs and three unrelated males reported who presented in infancy with intractable focal seizures and severe developmental delay. The variants were located in the N-terminal domain of the A isoform of FGF13/FHF2 (FHF2A). The X-linked FHF2 gene (also known as FGF13) has alternative first exons which produce multiple protein isoforms that differ in their N-terminal sequence. The variants were located at highly conserved residues in the FHF2A inactivation particle that competes with the intrinsic fast inactivation mechanism of Nav channels. Functional characterization of mutant FHF2A co-expressed with wild-type Nav1.6 (SCN8A) revealed that mutant FHF2A proteins lost the ability to induce rapid-onset, long-term blockade of the channel while retaining pro-excitatory properties. These gain-of-function effects are likely to increase neuronal excitability consistent with the epileptic potential of FHF2 variants.
Sources: Literature
Intellectual disability v3.574 TFE3 Arina Puzriakova Mode of inheritance for gene: TFE3 was changed from to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.515 MAPRE2 Arina Puzriakova Mode of inheritance for gene: MAPRE2 was changed from BIALLELIC, autosomal or pseudoautosomal to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.513 MAPRE2 Arina Puzriakova edited their review of gene: MAPRE2: Changed mode of inheritance: BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.484 PRKACB Konstantinos Varvagiannis gene: PRKACB was added
gene: PRKACB was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PRKACB was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: PRKACB were set to 33058759
Phenotypes for gene: PRKACB were set to Postaxial hand polydactyly; Postaxial foot polydactyly; Common atrium; Atrioventricular canal defect; Narrow chest; Abnormality of the teeth; Intellectual disability
Penetrance for gene: PRKACB were set to unknown
Mode of pathogenicity for gene: PRKACB was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: PRKACB was set to AMBER
Added comment: ID was a feature in 2/4 individuals with PRKACB pathogenic variant reported to date.

Please consider inclusion of PRKACB (and PRKACA) in other relevant gene panels e.g. for polydactyly, congenital heart defects. The disorder may be considered in the DD of ciliopathies.

-----


Palencia-Campos et al (2020 - PMID: 33058759) report on the phenotype of 3 individuals heterozygous for PRKACA and 4 individuals heterozygous for PRKACB pathogenic variants.

The most characteristic features in all individuals with PRKACA/PRKACB mutation, included postaxial polydactyly of hands (6/7 bilateral, 1/7 unilateral) and feet (4/7 bilateral, 1/7 unilateral), brachydactyly and congenital heart defects (CHD 5/7) namely a common atrium or AVSD. Two individuals with PRKACA variant who did not have CHD had offspring with the same variant and an AVSD.

Other variably occurring features included short stature, limbs, narrow chest, abnormal teeth, oral frenula, nail dysplasia. One individual with PRKACB variant presented tumors.

Intellectual disability was reported in 2/4 individuals with PRKACB variant (1/4: mild, 1/4: severe). The 3 individuals with PRKACA variant did not present ID.

As the phenotype was overall suggestive of Ellis-van Creveld syndrome (or the allelic Weyers acrofacial dysostosis), although these diagnoses were ruled out following analysis of EVC and EVC2 genes.

WES was carried out in all.

PRKACA : A single heterozygous missense variant was identified in 3 individuals from 3 families (NM_002730.4:c.409G>A / p.Gly137Arg) with 1 of the probands harboring the variant in mosaic state (28% of reads) and having 2 similarly affected offspring. The variant was de novo in one individual and inherited in a third one having a similarly affected fetus (narrow thorax, postaxial polyd, AVSD).

PRKACB : 4 different variants were identified (NM_002731.3: p.His88Arg/Asn, p.Gly235Arg, c.161C>T - p.Ser54Leu). One of the individuals was mosaic for the latter variant, while in all other cases the variant had occurred de novo.

Protein kinase A (PKA) is a tetrameric holoenzyme formed by the association of 2 catalytic (C) subunits with a regulatory (R) subunit dimer. Activation of PKA is achieved through binding of 2 cAMP molecules to each R-subunit, and unleashing(/dissociation) of C-subunits to engage substrates. PRKACA/B genes encode the Cα- and Cβ-subunits while the 4 functionally non-redundant regulatory subunits are encoded by PRKAR1A/1B/2A/2B genes.

The authors provide evidence that the variants confer increased sensitivity of PKA holoenzymes to activation by cAMP (compared to wt).

By performing ectopic expression of wt or mt PRKACA/B (variants studied : PRKACA p.Gly137Arg / PRKACB p.Gly235Arg) in NIH 3T3 fibroblasts, the authors demonstrate that inhibition of hedgehog signaling likely underlyies the developmental defects observed in affected individuals.

As for PRKACA, the authors cite another study where a 31-month old female with EvC syndrome diagnosis was found to harbor the aforementioned variant (NM_001304349.1:c.637G>A:p.Gly213Arg corresponding to NM_002730.4:c.409G>A / p.Gly137Arg) as a de novo event. Without additional evidence at the time, the variant was considered to be a candidate for this subject's phenotype (Monies et al 2019 – PMID: 31130284).
Sources: Literature
Intellectual disability v3.410 NEDD4L Eleanor Williams changed review comment from: Associated with Periventricular nodular heterotopia 7 #617201 (AD) in OMIM.

PMID: 27694961 - Broix et al 2016 - report 4 different de novo missense changes in NEDD4L in a total of five unrelated patients with periventricular nodular heterotopia and neurodevelopmental delay, and in a additional familial case with a similar phenotype and a previously found missense variant. In the familial case, two affected siblings were found to be heterozygous for the variant, the father and an unaffected sibling did not carry the variant, and the mother was found to show somatic mosaicism of NEDD4L variant. Functional studies showed a sensitivity of PNH-associated mutants to proteasome degradation.; to: Associated with Periventricular nodular heterotopia 7 #617201 (AD) in OMIM.

PMID: 27694961 - Broix et al 2016 - report 4 different de novo missense changes in NEDD4L in a total of five unrelated patients with periventricular nodular heterotopia and neurodevelopmental delay, and in a additional familial case with a similar phenotype and a previously found missense variant. In the familial case, two affected siblings were found to be heterozygous for the variant, the father and an unaffected sibling did not carry the variant, and the mother was found to show somatic mosaicism of NEDD4L variant. Functional studies showed a sensitivity of PNH-associated mutants to proteasome degradation. Seizures were reported in some but not all affected individuals.
Intellectual disability v3.401 GPSM2 Eleanor Williams changed review comment from: Associated with Chudley-McCullough syndrome604213 in OMIM

Summary: From 19 reported families, 3 individuals from 2 families showed cognitive delay.

PMID: 27180139 - Hemzeh et al 2016 - report two brothers from a Yemeni family who were diagnosed clinically with CMS then tested for GPSM2 mutations using Sanger sequencing. A homozygous mutation in GPSM2 was found in both brothers (c.1055C > A) leading to a truncating protein change; (p.Ser352*). The 12 year old brother showed cognitive delay, noted by the inability to tell the time in minutes, or to follow complex commands. The 11 year old brother could speak in sentences but with poor articulation, and could not respond to complex commands.

PMID: 23494849 - Almomani et al 2013 - report three patients from two unrelated Dutch families with CMS were investigated in which the same c.1473delG variant observed in 4 of the Menonite families by Doherty et al was observed. All three patients had normal cognitive abilities.

PMID: 22578326 - Doherty et al 2012 - report on 5 Menonite, 1 European-American, 1 Dutch and 1 Mexican-American family in which probands had severe/profound hearing loss and ventriculomegaly (total of 12 affected individuals). They also look again at the patients reported with autosomal recessive nonsyndromic deafness (DFNB82) by Walsh et al 2010 (PMID: 20602914, 1 proband ina Pakistani family) and Yariz et al 2012 (PMID: 21348867, 3 probands in a Turkish family) who they found had brain abnormalities consistent with with a diagnosis of Chudley-McCullough syndrome.
Oout of the 16 patients reported, only one had developmental issues beyond what is typically seen in individuals with severe hearing loss.



- -; to: Associated with Chudley-McCullough syndrome604213 in OMIM

Summary: From 19 reported families, 3 individuals from 2 families showed cognitive delay.

PMID: 27180139 - Hemzeh et al 2016 - report two brothers from a Yemeni family who were diagnosed clinically with CMS then tested for GPSM2 mutations using Sanger sequencing. A homozygous mutation in GPSM2 was found in both brothers (c.1055C > A) leading to a truncating protein change; (p.Ser352*). The 12 year old brother showed cognitive delay, noted by the inability to tell the time in minutes, or to follow complex commands. The 11 year old brother could speak in sentences but with poor articulation, and could not respond to complex commands. The poor articulation was thought to be due to late cochlear implant surgery.

PMID: 23494849 - Almomani et al 2013 - report three patients from two unrelated Dutch families with CMS were investigated in which the same c.1473delG variant observed in 4 of the Menonite families by Doherty et al was observed. All three patients had normal cognitive abilities.

PMID: 22578326 - Doherty et al 2012 - report on 5 Menonite, 1 European-American, 1 Dutch and 1 Mexican-American family in which probands had severe/profound hearing loss and ventriculomegaly (total of 12 affected individuals). They also look again at the patients reported with autosomal recessive nonsyndromic deafness (DFNB82) by Walsh et al 2010 (PMID: 20602914, 1 proband ina Pakistani family) and Yariz et al 2012 (PMID: 21348867, 3 probands in a Turkish family) who they found had brain abnormalities consistent with with a diagnosis of Chudley-McCullough syndrome.
Oout of the 16 patients reported, only one had developmental issues beyond what is typically seen in individuals with severe hearing loss.



- -
Intellectual disability v3.382 CTNND1 Eleanor Williams gene: CTNND1 was added
gene: CTNND1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CTNND1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CTNND1 were set to 32196547
Review for gene: CTNND1 was set to GREEN
Added comment: PMID: 32196547 - Alharatani et al 2020 - report an expanded phenotype for CTNND1 patients. They report 13 individuals from nine families with novel protein-truncating variants in CTNND1 identified by WES. The mutations were not previously described in blepharocheilodontic (BCD), orofacial cleft cases nor in gnomAD. 8 patients had de novo variants, 2 inherited from affected parents, 2 participants inherited a variant from a parent with a mild phenotype. 8/13 patients showed cleft palate. Additional phenotypic features seen include mild limb phenotypes (9/13), cardiovascular anomalies (6/13) and Developmental delay and other neurodevelopmental problems (8/13)
Sources: Literature
Intellectual disability v3.369 NEMF Konstantinos Varvagiannis changed review comment from: Martin et al (2020 - PMID:32934225) report on 8 individuals from 6 families with a juvenile neuromuscular disease due to biallelic NEMF variants. (In one of these 8 cases it could not be ruled out that a de novo and maternally inherited variant were on the same allele, as phase was not determined). A ninth individual with similar presentation was found to harbor a single NEMF missense SNV as de novo event (due to a speculated dominant-negative effect). This individual had a similar presentation.

Features incl. hypotonia (4/8 with biallelic variant (B) | 1/1 monoallelic (M) ), DD/ID (7/8B | 0/1M) with speech delay as universal feature (8/8B | 1/1M), axonal neuropathy (3/3B | 1/1M), ataxia (3/8B | 0/1M). Other findings included tremor (1/7B | 1/1M), abnormal brain imaging (2/6B / ?/1M), kyphosis/scoliosis (4/8B | 0/1M), respiratory distress (1/8B | 0/1M).

NEMF (Rqc2 in yeast) encodes the nuclear export mediator factor, a component of the Ribosome-associated Quality Control (RCQ) complex which is involved in proteolytic targeting of incomplete polypeptides prodduced by ribosome stalling. NEMF facilitates the recruitment of E3 ligase Listerin (LTN1) which ubiquitinates nascent polypeptide chains for subsequent proteasomal degradation.

The author provide evidence that mice homozygous for Nemf missense mutations display progressive motor phenotypes, exhibit neurogenic atrophy and progressive axonal degeneration. A further NEMF-null mouse model displayed more severe phenotype (with heterozygous mice being unaffected).

Equivalent mutations (of those in the above mouse model) in yeast (Rqc2) were shown to interfere with its ability to modify aberrant translation products with C-terminal tails which assist RQC-mediated protein degradation.

Mutation of Ltn1 (belonging to the same protein control pathway) has been also shown to lead to neurodegeneration im mice.

Overall NEMF is thought to play a role in neuronal translational homeostasis and the disorder to be mediated by dysfunction of the RQC pathway (normally protecting neurons against degeneration).
Sources: Literature; to: Martin et al (2020 - PMID:32934225) report on 8 individuals from 6 families with a juvenile neuromuscular disease due to biallelic NEMF variants. (In one of these 8 cases it could not be ruled out that a de novo and maternally inherited variant were on the same allele, as phase was not determined). A ninth individual with similar presentation was found to harbor a single NEMF missense SNV as de novo event (due to a speculated dominant-negative effect). This individual had a similar presentation.

Features incl. hypotonia (4/8 with biallelic variant (B) | 1/1 monoallelic (M) ), DD/ID (7/8B | 0/1M) with speech delay as universal feature (8/8B | 1/1M), axonal neuropathy (3/3B | 1/1M), ataxia (3/8B | 0/1M). Other findings included tremor (1/7B | 1/1M), abnormal brain imaging (2/6B / ?/1M), kyphosis/scoliosis (4/8B | 0/1M), respiratory distress (1/8B | 0/1M).

NEMF (Rqc2 in yeast) encodes the nuclear export mediator factor, a component of the Ribosome-associated Quality Control (RCQ) complex which is involved in proteolytic targeting of incomplete polypeptides produced by ribosome stalling. NEMF facilitates the recruitment of E3 ligase Listerin (LTN1) which ubiquitinates nascent polypeptide chains for subsequent proteasomal degradation.

The author provide evidence that mice homozygous for Nemf missense mutations display progressive motor phenotypes, exhibit neurogenic atrophy and progressive axonal degeneration. A further NEMF-null mouse model displayed more severe phenotype (with heterozygous mice being unaffected).

Equivalent mutations (of those in the above mouse model) in yeast (Rqc2) were shown to interfere with its ability to modify aberrant translation products with C-terminal tails which assist RQC-mediated protein degradation.

Mutation of Ltn1 (belonging to the same protein control pathway) has been also shown to lead to neurodegeneration in mice.

Overall NEMF is thought to play a role in neuronal translational homeostasis and the disorder to be mediated by dysfunction of the RQC pathway (normally protecting neurons against degeneration).
Sources: Literature
Intellectual disability v3.369 NEMF Konstantinos Varvagiannis changed review comment from: Martin et al (2020 - PMID:32934225) report on 8 individuals from 6 families with a juvenile neuromuscular disease due to biallelic NEMF variants. (In one of these 8 cases it could be ruled out that the de novo and maternally inherited variants were on the same allele, as phase was not been determined). A ninth individual with similar presentation was found to harbor a single NEMF missense SNV as de novo event (due to a speculated dominant-negative effect). This individual had a similar presentation.

Features incl. hypotonia (4/8 with biallelic variant (B) | 1/1 monoallelic (M) ), DD/ID (7/8B | 0/1M) with speech delay as universal feature (8/8B | 1/1M), axonal neuropathy (3/3B | 1/1M), ataxia (3/8B | 0/1M). Other findings included tremor (1/7B | 1/1M), abnormal brain imaging (2/6B / ?/1M), kyphosis/scoliosis (4/8B | 0/1M), respiratory distress (1/8B | 0/1M).

NEMF (Rqc2 in yeast) encodes the nuclear export mediator factor, a component of the Ribosome-associated Quality Control (RCQ) complex which is involved in proteolytic targeting of incomplete polypeptides prodduced by ribosome stalling. NEMF facilitates the recruitment of E3 ligase Listerin (LTN1) which ubiquitinates nascent polypeptide chains for subsequent proteasomal degradation.

The author provide evidence that mice homozygous for Nemf missense mutations display progressive motor phenotypes, exhibit neurogenic atrophy and progressive axonal degeneration. A further NEMF-null mouse model displayed more severe phenotype (with heterozygous mice being unaffected).

Equivalent mutations (of those in the above mouse model) in yeast (Rqc2) were shown to interfere with its ability to modify aberrant translation products with C-terminal tails which assist RQC-mediated protein degradation.

Mutation of Ltn1 (belonging to the same protein control pathway) has been also shown to lead to neurodegeneration im mice.

Overall NEMF is thought to play a role in neuronal translational homeostasis and the disorder to be mediated by dysfunction of the RQC pathway (normally protecting neurons against degeneration).
Sources: Literature; to: Martin et al (2020 - PMID:32934225) report on 8 individuals from 6 families with a juvenile neuromuscular disease due to biallelic NEMF variants. (In one of these 8 cases it could not be ruled out that a de novo and maternally inherited variant were on the same allele, as phase was not determined). A ninth individual with similar presentation was found to harbor a single NEMF missense SNV as de novo event (due to a speculated dominant-negative effect). This individual had a similar presentation.

Features incl. hypotonia (4/8 with biallelic variant (B) | 1/1 monoallelic (M) ), DD/ID (7/8B | 0/1M) with speech delay as universal feature (8/8B | 1/1M), axonal neuropathy (3/3B | 1/1M), ataxia (3/8B | 0/1M). Other findings included tremor (1/7B | 1/1M), abnormal brain imaging (2/6B / ?/1M), kyphosis/scoliosis (4/8B | 0/1M), respiratory distress (1/8B | 0/1M).

NEMF (Rqc2 in yeast) encodes the nuclear export mediator factor, a component of the Ribosome-associated Quality Control (RCQ) complex which is involved in proteolytic targeting of incomplete polypeptides prodduced by ribosome stalling. NEMF facilitates the recruitment of E3 ligase Listerin (LTN1) which ubiquitinates nascent polypeptide chains for subsequent proteasomal degradation.

The author provide evidence that mice homozygous for Nemf missense mutations display progressive motor phenotypes, exhibit neurogenic atrophy and progressive axonal degeneration. A further NEMF-null mouse model displayed more severe phenotype (with heterozygous mice being unaffected).

Equivalent mutations (of those in the above mouse model) in yeast (Rqc2) were shown to interfere with its ability to modify aberrant translation products with C-terminal tails which assist RQC-mediated protein degradation.

Mutation of Ltn1 (belonging to the same protein control pathway) has been also shown to lead to neurodegeneration im mice.

Overall NEMF is thought to play a role in neuronal translational homeostasis and the disorder to be mediated by dysfunction of the RQC pathway (normally protecting neurons against degeneration).
Sources: Literature
Intellectual disability v3.369 NEMF Konstantinos Varvagiannis changed review comment from: Martin et al (2020 - PMID:32934225) report on 8 individuals from 6 families with a juvenile neuromuscular disease due to biallelic NEMF variants. A ninth individual with similar presentation was found to harbor a single NEMF missense SNV as de novo event (due to a speculated dominant-negative effect). This individual had a similar presentation.

Features incl. hypotonia (4/8 with biallelic variant (B) | 1/1 monoallelic (M) ), DD/ID (7/8B | 0/1M) with speech delay as universal feature (8/8B | 1/1M), axonal neuropathy (3/3B | 1/1M), ataxia (3/8B | 0/1M). Other findings included tremor (1/7B | 1/1M), abnormal brain imaging (2/6B / ?/1M), kyphosis/scoliosis (4/8B | 0/1M), respiratory distress (1/8B | 0/1M).

NEMF (Rqc2 in yeast) encodes the nuclear export mediator factor, a component of the Ribosome-associated Quality Control (RCQ) complex which is involved in proteolytic targeting of incomplete polypeptides prodduced by ribosome stalling. NEMF facilitates the recruitment of E3 ligase Listerin (LTN1) which ubiquitinates nascent polypeptide chains for subsequent proteasomal degradation.

The author provide evidence that mice homozygous for Nemf missense mutations display progressive motor phenotypes, exhibit neurogenic atrophy and progressive axonal degeneration. A further NEMF-null mouse model displayed more severe phenotype (with heterozygous mice being unaffected).

Equivalent mutations (of those in the above mouse model) in yeast (Rqc2) were shown to interfere with its ability to modify aberrant translation products with C-terminal tails which assist RQC-mediated protein degradation.

Mutation of Ltn1 (belonging to the same protein control pathway) has been also shown to lead to neurodegeneration im mice.

Overall NEMF is thought to play a role in neuronal translational homeostasis and the disorder to be mediated by dysfunction of the RQC pathway (normally protecting neurons against degeneration).
Sources: Literature; to: Martin et al (2020 - PMID:32934225) report on 8 individuals from 6 families with a juvenile neuromuscular disease due to biallelic NEMF variants. (In one of these 8 cases it could be ruled out that the de novo and maternally inherited variants were on the same allele, as phase was not been determined). A ninth individual with similar presentation was found to harbor a single NEMF missense SNV as de novo event (due to a speculated dominant-negative effect). This individual had a similar presentation.

Features incl. hypotonia (4/8 with biallelic variant (B) | 1/1 monoallelic (M) ), DD/ID (7/8B | 0/1M) with speech delay as universal feature (8/8B | 1/1M), axonal neuropathy (3/3B | 1/1M), ataxia (3/8B | 0/1M). Other findings included tremor (1/7B | 1/1M), abnormal brain imaging (2/6B / ?/1M), kyphosis/scoliosis (4/8B | 0/1M), respiratory distress (1/8B | 0/1M).

NEMF (Rqc2 in yeast) encodes the nuclear export mediator factor, a component of the Ribosome-associated Quality Control (RCQ) complex which is involved in proteolytic targeting of incomplete polypeptides prodduced by ribosome stalling. NEMF facilitates the recruitment of E3 ligase Listerin (LTN1) which ubiquitinates nascent polypeptide chains for subsequent proteasomal degradation.

The author provide evidence that mice homozygous for Nemf missense mutations display progressive motor phenotypes, exhibit neurogenic atrophy and progressive axonal degeneration. A further NEMF-null mouse model displayed more severe phenotype (with heterozygous mice being unaffected).

Equivalent mutations (of those in the above mouse model) in yeast (Rqc2) were shown to interfere with its ability to modify aberrant translation products with C-terminal tails which assist RQC-mediated protein degradation.

Mutation of Ltn1 (belonging to the same protein control pathway) has been also shown to lead to neurodegeneration im mice.

Overall NEMF is thought to play a role in neuronal translational homeostasis and the disorder to be mediated by dysfunction of the RQC pathway (normally protecting neurons against degeneration).
Sources: Literature
Intellectual disability v3.369 NEMF Konstantinos Varvagiannis gene: NEMF was added
gene: NEMF was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: NEMF was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: NEMF were set to 32934225
Phenotypes for gene: NEMF were set to Hypotonia; Global developmental delay; Intellectual disability; Axonal neuropathy; Ataxia; Abnormal brain imaging; Kyphosis; Scoliosis; Tremor; Respiratory distress
Penetrance for gene: NEMF were set to Complete
Review for gene: NEMF was set to GREEN
Added comment: Martin et al (2020 - PMID:32934225) report on 8 individuals from 6 families with a juvenile neuromuscular disease due to biallelic NEMF variants. A ninth individual with similar presentation was found to harbor a single NEMF missense SNV as de novo event (due to a speculated dominant-negative effect). This individual had a similar presentation.

Features incl. hypotonia (4/8 with biallelic variant (B) | 1/1 monoallelic (M) ), DD/ID (7/8B | 0/1M) with speech delay as universal feature (8/8B | 1/1M), axonal neuropathy (3/3B | 1/1M), ataxia (3/8B | 0/1M). Other findings included tremor (1/7B | 1/1M), abnormal brain imaging (2/6B / ?/1M), kyphosis/scoliosis (4/8B | 0/1M), respiratory distress (1/8B | 0/1M).

NEMF (Rqc2 in yeast) encodes the nuclear export mediator factor, a component of the Ribosome-associated Quality Control (RCQ) complex which is involved in proteolytic targeting of incomplete polypeptides prodduced by ribosome stalling. NEMF facilitates the recruitment of E3 ligase Listerin (LTN1) which ubiquitinates nascent polypeptide chains for subsequent proteasomal degradation.

The author provide evidence that mice homozygous for Nemf missense mutations display progressive motor phenotypes, exhibit neurogenic atrophy and progressive axonal degeneration. A further NEMF-null mouse model displayed more severe phenotype (with heterozygous mice being unaffected).

Equivalent mutations (of those in the above mouse model) in yeast (Rqc2) were shown to interfere with its ability to modify aberrant translation products with C-terminal tails which assist RQC-mediated protein degradation.

Mutation of Ltn1 (belonging to the same protein control pathway) has been also shown to lead to neurodegeneration im mice.

Overall NEMF is thought to play a role in neuronal translational homeostasis and the disorder to be mediated by dysfunction of the RQC pathway (normally protecting neurons against degeneration).
Sources: Literature
Intellectual disability v3.332 MECP2 Arina Puzriakova reviewed gene: MECP2: Rating: GREEN; Mode of pathogenicity: None; Publications: 32469049; Phenotypes: Rett syndrome, 312750; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.332 UPF3B Arina Puzriakova reviewed gene: UPF3B: Rating: GREEN; Mode of pathogenicity: None; Publications: 32667670; Phenotypes: Mental retardation, X-linked, syndromic 14, 300676; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.315 ZMYM2 Konstantinos Varvagiannis gene: ZMYM2 was added
gene: ZMYM2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: ZMYM2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: ZMYM2 were set to 32891193
Phenotypes for gene: ZMYM2 were set to Abnormality of the urinary system; Global developmental delay; Intellectual disability; Microcephaly; Abnormality of the cardiovascular system; Autism; Seizures; Abnormality of the head or neck; Abnormality of the nail; Small hand; Short foot; Clinodactyly
Penetrance for gene: ZMYM2 were set to unknown
Review for gene: ZMYM2 was set to AMBER
Added comment: Heterozygous pathogenic (pLoF) ZMYM2 variants have been reported in individuals with syndromic presentation including CAKUT (in several cases) and variable neurological manifestations among extra-renal features. DD and ID were reported in some of the families described to date as summarized below. You might consider inclusion with green/amber rating in the ID panel and green in the panel for CAKUT.

--

Connaughton et al (2020 - PMID: 32891193) report on 19 individuals (from 15 unrelated families) with heterozygous pathogenic ZMYM2 variants. [Article not reviewed in detail].

Affected individuals from 7 families presented with CAKUT while all of them displayed extra-renal features. Neurological manifestations were reported in 16 individuals from 14 families (data not available for 1 fam), among others hypotonia (3/14 fam), speech delay (4/14 fam), global DD (9/14 fam), ID (4/14 fam), microcephaly (4/14 fam). ASD was reported in 4 fam (4 indiv). Seizures were reported in 2 fam (2 indiv). Variable other features included cardiac defects, facial dysmorphisms, small hands and feet with dys-/hypo-plastic nails and clinodactyly.

14 pLoF variants were identified, in most cases as de novo events (8 fam). In 2 families the variant was inherited from an affected parent. Germline mosaicism occurred in 1 family.

The human disease features were recapitulated in a X. tropicalis morpholino knockdown, with expression of truncating variants failing to rescue renal and craniofacial defects. Heterozygous Zmym2-deficient mice also recapitulated the features of CAKUT.

ZMYM2 (previously ZNF198) encodes a nuclear zinc finger protein localizing to the nucleus (and PML nuclear body).

It has previously been identified as transcriptional corepressor interacting with nuclear receptors and the LSD1-CoREST-HDAC1 complex. It has also been shown to interact with FOXP transcription factors.

The authors provide evidence for loss of interaction of the truncated ZMYM2 with FOXP1 (mutations in the latter having recently been reported in syndromic CAKUT).
Sources: Literature
Intellectual disability v3.314 LMNB1 Konstantinos Varvagiannis gene: LMNB1 was added
gene: LMNB1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: LMNB1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: LMNB1 were set to 32910914
Phenotypes for gene: LMNB1 were set to Global developmental delay; Intellectual disability; Microcephaly; Short stature; Seizures; Abnormality of the corpus callosum; Cortical gyral simplification; Feeding difficulties; Scoliosis
Penetrance for gene: LMNB1 were set to unknown
Mode of pathogenicity for gene: LMNB1 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: LMNB1 was set to GREEN
Added comment: Cristofoli et al (2020 - PMID: 32910914) report 7 individuals (from 5 families) harboring mostly de novo LMNB1 variants.

The common phenotype consisted of primary microcephaly (7/7 ranging from -4.4 to -10 SD), DD/ID (7/7), relative short stature in most (+0.7 to -4 SD). Additional features included brain MRI abnormalities (abnormal CC in 3, simplified gyral pattern in 3, small structurally normal brain, etc), seizures (4 individuals from 2 families), limb spasticity (1/7), cortical visual impairment (in 3), feeding difficulties (5/7), scoliosis (4/7). Non-overlapping dysmorphic features were reported in some.

Variants were identified by WES or custom-designed gene panel and included 3 missense variants, 1 in-frame deletion and a splice variant. The in-frame deletion was inherited from a similarly affected parent in whom the variant occurred as a dn event. The splice SNV(NM_005573.3:c.939+1G>A) occurred in 3 sibs and was present as mosaic variant (15%) in the parent. This variant was predicted to result to extension of exon 5 by 6 amino-acids (samples were unavailable for mRNA studies).

LMNB1 encodes a B-type lamin (the other being encoded by LMNB2). A- and B- type lamins are major components of the nuclear lamina. As the authors comment, LMNB1 is expressed in almost all cell types beginning at the earliest stages of development.

Lamin-deficient mouse models support an essential role of B-type lamins in organogenesis, neuronal migration, patterning during brain development.

Functional studies performed, demonstrated impaired formation of LMNB1 nuclear lamina in LMNB1-null HeLa cells transfected with cDNAs for 3 missense variants.

Two variants (Lys33Glu/Arg42Trp) were shown to result in decreased nuclear localization with increased abundance in the cytosolic fraction. In patient derived LCLs these variants led to abnormal nuclear morphology. A missense variant in another domain (Ala152Gly - 1st coil domain) resulted also in lower abundance of lamin B1, irregular lamin A/C nuclear lamina, as well as more condensed nuclei (HeLa cells).

LMNB1 duplications or missense mutations increasing LMNB1 expression are associated with a different presentation of AD leuodystrophy. A variant previously associated with leukodystrophy (Arg29Trp) was shown to behave differently (present in the nuclear extract but not in the cytosol, lamin B1 to A/C ratio in nuclear extract was not significantly altered compared to wt as was the case for Arg42Trp, Lys33Glu).

Given the pLI score of 0.55 as well as the phenotype of individuals with deletions (not presenting microcephaly) the authors predict that a dominant-negative effect applies (rather than haploinsufficiency).

Consider inclusion in the following panels : DD/ID (green), epilepsy (amber - 4 of 7 patients belonging to 2 families), primary microcephaly (green), callosome (amber/green - 3 individuals belonging to 3 families), mendeliome (green), etc.
Sources: Literature
Intellectual disability v3.281 PAK3 Arina Puzriakova reviewed gene: PAK3: Rating: ; Mode of pathogenicity: None; Publications: 31943058; Phenotypes: Intellectual disability; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.280 TRAPPC2L Arina Puzriakova gene: TRAPPC2L was added
gene: TRAPPC2L was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TRAPPC2L was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TRAPPC2L were set to 30120216; 32843486
Phenotypes for gene: TRAPPC2L were set to Encephalopathy, progressive, early-onset, with episodic rhabdomyolysis, 618331
Review for gene: TRAPPC2L was set to AMBER
Added comment: Gene is associated with Encephalopathy, progressive, early-onset, with episodic rhabdomyolysis in OMIM, but not in G2P.

PMID: 30120216 (2018) - Two unrelated probands with an identical homozygous missense (c.109G>T, p.Asp37Tyr) variant in TRAPPC2L. Both individuals presented neurodevelopmental delay, febrile illness-induced encephalopathy, and episodic rhabdomyolysis, followed by developmental arrest, seizures and tetraplegia. The variant segregated with the phenotype in each family, and haplotype analysis suggested a founder effect.

The mutant protein was expressed in patient fibroblasts, but displayed membrane trafficking delays. Studies in yeast showed that the variant impaired interaction with TRAPPC10, and increased levels of the active RAB11.


PMID: 32843486 (2020) - In an Ashkenazi Jewish family with three affected sibs with GDD/ID, WGS revealed a segregating homozygous missense variant (c.5G>C, p.Ala2Gly) in the TRAPPC2L gene. No seizures, brain MRI abnormalities, or illness provoked regression were documented in this family.

Comparable to the previous study, the variant resulted in delayed ER-to-Golgi trafficking and elevated levels of active RAB11. Studies using yeast and in vitro binding, showed that the variant disrupted interaction with another core TRAPP protein, TRAPPC6a.
Sources: Literature
Intellectual disability v3.239 FAM50A Konstantinos Varvagiannis gene: FAM50A was added
gene: FAM50A was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: FAM50A was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for gene: FAM50A were set to 32703943
Phenotypes for gene: FAM50A were set to Mental retardation syndrome, X-linked, Armfield type (MIM #300261)
Penetrance for gene: FAM50A were set to unknown
Review for gene: FAM50A was set to GREEN
Added comment: Lee et al (2020 - PMID: 32703943) provide evidence that Armfield X-Linked intellectual disability syndrome is caused by monoallelic FAM50A pathogenic variants. The current review is based only on this reference.

The authors provide clinical details on 6 affected individuals from 5 families.

Features included postnatal growth delay, DD and ID (6/6 - also evident for those without formal IQ assesment), seizures (3/6 from 2 families), prominent forehead with presence of other facial features and variable head circumference (5th to >97th %le), ocular anomalies (5/6 - strabismus/nystagmus/Axenfeld-Rieger), cardiac (3/6 - ASD/Fallot) and genitourinary anomalies (3/6).

In the first of these families (Armfield et al 1999 - PMID: 10398235), linkage analysis followed by additional studies (Sanger, NGS of 718 genes on chrX, X-exome NGS - several refs provided) allowed the identification of a FAM50A variant. Variants in other families were identified by singleton (1 fam) or trio-ES (3 fam).

In affected individuals from 3 families, the variant had occurred de novo. Carrier females in the other families were unaffected (based on pedigrees and/or the original publication). XCI was rather biased in most obligate carrier females from the 1st family (although this ranged from 95:5 to 60:40).

Missense variants were reported in all affected subjects incl. Trp206Gly, Asp255Gly, Asp255Asn (dn), Glu254Gly (dn), Arg273Trp (dn) (NM_004699.3).

Previous studies have demonstrated that FAM50A has ubiquitous expression in human fetal and adult tissues (incl. brain in fetal ones).

Immunostaining suggests a nuclear localization for the protein (NIH/3T3 cells). Comparison of protein levels in LCLs from affected males and controls did not demonstrate significant differences. Protein localization for 3 variants (transfection of COS-7 cells) was shown to be similar to wt.

Complementation studies in zebrafish provided evidence that the identified variants confer partial loss of function (rescue of the morpholino phenotype with co-injection of wt but not mt mRNA). The zebrafish ko model seemed to recapitulate the abnormal development of cephalic structures and was indicative of diminished/defective neurogenesis. Transcriptional dysregulation was demonstrated in zebrafish (altered levels and mis-splicing). Upregulation of spliceosome effectors was demonstrated in ko zebrafish.

Similarly, mRNA expression and splicing defects were demonstrated in LCLs from affected individuals. FAM50A pulldown followed by mass spectrometry in transfected HEK293T cells demonstrated enrichment of binding proteins involved in RNA processing and co-immunoprecipitation assays (transfected U-87 cells) suggested that FAM50A interacts with spliceosome U5 and C-complex proteins.

Overall aberrant spliceosome C-complex function is suggested as the underlying pathogenetic mechanism.

Several other neurodevelopmental syndromes are caused by variants in genes encoding C-complex affiliated proteins (incl. EFTUD2, EIF4A3, THOC2, etc.).

Please consider inclusion in the ID panel with green rating and epilepsy panel with amber (seizures in individuals from 2 families).
Sources: Literature
Intellectual disability v3.222 PAM16 Arina Puzriakova Added comment: Comment on list classification: Three unrelated cases, but two share the same founder mutation - Rating Amber until further cases are reported (added to watchlist).
Intellectual disability v3.219 NARS Konstantinos Varvagiannis changed review comment from: [Please note that HGNC Approved Gene Symbol for this gene is NARS1]

Manole et al (2020 - PMID: 32738225) provide evidence that both biallelic and monoallelic (de novo) pathogenic NARS1 variants cause a neurodevelopmental disorder. In total 32 individuals from 21 families are reported, with biallelic variants identified in individuals from 13 families and de novo in 8 families.

Similar features were reported for AR/AD occurrences of the disorder and included of microcephaly (90% - most often primary), epilepsy (23/32 or 74% - variable semiology incl. partial/myoclonic/generalized tonic-clonic seizures), DD and ID (as a universal feature), abnormal tone in several (hypotonia/spasticity), ataxia, demyelinating peripheral neuropathy (in 3 or more for each inheritance mode - or a total of 25%). Some individuals had dysmorphic features.

NARS1 encodes an aminoacyl-tRNA synthetase (ARS) [asparaginyl-tRNA synthetase 1]. Aminoacyl-tRNA synthetases constitute a family of enzymes catalyzing attachment of amino-acids to their cognate tRNAs. As the authors comment, mutations in genes encoding several other ARSs result in neurological disorders ranging from peripheral neuropathy to severe multi-systemic NDD. Dominant, recessive or both modes for inheritance for mutations in the same gene (e.g. AARS1, YARS1, MARS1, etc) have been reported.

Some variants were recurrent, e.g. the c.1600C>T / p.Arg534* which occurred in 6 families as a de novo event or c.1633C>T p.Arg545Cys (homozygous in 6 families). 3 different variants were reported to have occured de novo (c.965G>T - p.Arg322Leu, c.1525G>A - p.Gly509Ser, p.Arg534*) with several other variants identified in hmz/compound htz individuals. A single SNV (c.1067A>C - p.Asp356Ala) was suggested to be acting as modifier and pathogenic only when in trans with a severe variant. [NM_004539.4 used as RefSeq for all].

The authors provide several lines of evidence for a partial loss-of-function effect (e.g. reduction in mRNA expression, enzyme levels and activity in fibroblasts or iNPCs) underlying pathogenicity of the variants identified in individuals with biallelic variants. A gain-of-function (dominant-negative) effect is proposed for de novo variants (such effect also demonstrated for the p.Arg534* in a zebrafish model).

As also Manole et al suggest, NARS1 can be considered for inclusion in gene panels for DD/ID, epilepsy and/or demyelinating neuropathy.
Sources: Literature; to: [Please note that HGNC Approved Gene Symbol for this gene is NARS1]

Manole et al (2020 - PMID: 32738225) provide evidence that both biallelic and monoallelic (de novo) pathogenic NARS1 variants cause a neurodevelopmental disorder. In total 32 individuals from 21 families are reported, with biallelic variants identified in individuals from 13 families and de novo in 8 families.

Similar features were reported for AR/AD occurrences of the disorder and included microcephaly (90% - most often primary), epilepsy (23/32 or 74% - variable semiology incl. partial/myoclonic/generalized tonic-clonic seizures), DD and ID (as a universal feature), abnormal tone in several (hypotonia/spasticity), ataxia, demyelinating peripheral neuropathy (in 3 or more for each inheritance mode - or a total of 25%). Some individuals had dysmorphic features.

NARS1 encodes an aminoacyl-tRNA synthetase (ARS) [asparaginyl-tRNA synthetase 1]. Aminoacyl-tRNA synthetases constitute a family of enzymes catalyzing attachment of amino-acids to their cognate tRNAs. As the authors comment, mutations in genes encoding several other ARSs result in neurological disorders ranging from peripheral neuropathy to severe multi-systemic NDD. Dominant, recessive or both modes for inheritance for mutations in the same gene (e.g. AARS1, YARS1, MARS1, etc) have been reported.

Some variants were recurrent, e.g. the c.1600C>T / p.Arg534* which occurred in 6 families as a de novo event or c.1633C>T p.Arg545Cys (homozygous in 6 families). 3 different variants were reported to have occured de novo (c.965G>T - p.Arg322Leu, c.1525G>A - p.Gly509Ser, p.Arg534*) with several other variants identified in hmz/compound htz individuals. A single SNV (c.1067A>C - p.Asp356Ala) was suggested to be acting as modifier and pathogenic only when in trans with a severe variant. [NM_004539.4 used as RefSeq for all].

The authors provide several lines of evidence for a partial loss-of-function effect (e.g. reduction in mRNA expression, enzyme levels and activity in fibroblasts or iNPCs) underlying pathogenicity of the variants identified in individuals with biallelic variants. A gain-of-function (dominant-negative) effect is proposed for de novo variants (such effect also demonstrated for the p.Arg534* in a zebrafish model).

As also Manole et al suggest, NARS1 can be considered for inclusion in gene panels for DD/ID, epilepsy and/or demyelinating neuropathy.
Sources: Literature
Intellectual disability v3.219 NARS Konstantinos Varvagiannis gene: NARS was added
gene: NARS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: NARS was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: NARS were set to 32738225
Phenotypes for gene: NARS were set to Abnormal muscle tone; Microcephaly; Global developmental delay; Intellectual disability; Seizures; Ataxia; Abnormality of the face; Demyelinating peripheral neuropathy
Penetrance for gene: NARS were set to Complete
Review for gene: NARS was set to GREEN
Added comment: [Please note that HGNC Approved Gene Symbol for this gene is NARS1]

Manole et al (2020 - PMID: 32738225) provide evidence that both biallelic and monoallelic (de novo) pathogenic NARS1 variants cause a neurodevelopmental disorder. In total 32 individuals from 21 families are reported, with biallelic variants identified in individuals from 13 families and de novo in 8 families.

Similar features were reported for AR/AD occurrences of the disorder and included of microcephaly (90% - most often primary), epilepsy (23/32 or 74% - variable semiology incl. partial/myoclonic/generalized tonic-clonic seizures), DD and ID (as a universal feature), abnormal tone in several (hypotonia/spasticity), ataxia, demyelinating peripheral neuropathy (in 3 or more for each inheritance mode - or a total of 25%). Some individuals had dysmorphic features.

NARS1 encodes an aminoacyl-tRNA synthetase (ARS) [asparaginyl-tRNA synthetase 1]. Aminoacyl-tRNA synthetases constitute a family of enzymes catalyzing attachment of amino-acids to their cognate tRNAs. As the authors comment, mutations in genes encoding several other ARSs result in neurological disorders ranging from peripheral neuropathy to severe multi-systemic NDD. Dominant, recessive or both modes for inheritance for mutations in the same gene (e.g. AARS1, YARS1, MARS1, etc) have been reported.

Some variants were recurrent, e.g. the c.1600C>T / p.Arg534* which occurred in 6 families as a de novo event or c.1633C>T p.Arg545Cys (homozygous in 6 families). 3 different variants were reported to have occured de novo (c.965G>T - p.Arg322Leu, c.1525G>A - p.Gly509Ser, p.Arg534*) with several other variants identified in hmz/compound htz individuals. A single SNV (c.1067A>C - p.Asp356Ala) was suggested to be acting as modifier and pathogenic only when in trans with a severe variant. [NM_004539.4 used as RefSeq for all].

The authors provide several lines of evidence for a partial loss-of-function effect (e.g. reduction in mRNA expression, enzyme levels and activity in fibroblasts or iNPCs) underlying pathogenicity of the variants identified in individuals with biallelic variants. A gain-of-function (dominant-negative) effect is proposed for de novo variants (such effect also demonstrated for the p.Arg534* in a zebrafish model).

As also Manole et al suggest, NARS1 can be considered for inclusion in gene panels for DD/ID, epilepsy and/or demyelinating neuropathy.
Sources: Literature
Intellectual disability v3.219 ZNF407 Konstantinos Varvagiannis gene: ZNF407 was added
gene: ZNF407 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: ZNF407 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: ZNF407 were set to 24907849; 32737394; 23195952
Phenotypes for gene: ZNF407 were set to Global developmental delay; Intellectual disability
Penetrance for gene: ZNF407 were set to unknown
Review for gene: ZNF407 was set to AMBER
Added comment: You may consider inclusion of this gene probably with amber rating (or green if the evidence for biallelic variants is considered sufficient).

Biallelic variants:

- Kambouris et al. (2014 - PMID: 24907849) described 2 brothers with severe DD and ID, born to first cousin parents. Homozygosity mapping, following other non-diagnostic investigations (incl. aCGH), revealed 4 major homozygosity intervals. Exome sequencing in one identified 5 variants within these intervals, ZNF407 (c.5054C>G, p.Ser1685Trp) being the best candidate, supported also by segregation studies. The authors commented that zinc finger proteins act as transcriptional regulators, with mutations in genes encoding for other zinc finger proteins interfering with normal brain development.

- Zahra et al. (2020 - PMID: 32737394) report on 7 affected individuals (from 3 families) homozygous or compound heterozygous for ZNF407 variants. Features included hypotonia, DD and ID (in all) and variable occurrence of short stature (6/6), microcephaly (in at least 5), behavioural, visual problems and deafness. Linkage analysis in the first family revealed a 4.4 Mb shared homozygosity region and exome (30x) revealed a 3-bp duplication, confirmed by Sanger sequencing and segregating with the disease (NM_001146189:c.2814_2816dup, p.Val939dup). Affected subjects from the 2 other families were each found to be homozygous (c.2405G>T) or compound heterozygous (c.2884C>G, c.3642G>C) for other variants. Segregation was compatible in all families. Other studies were not performed. The authors comment than only the 3-bp duplication fulfilled ACMG criteria for classification as LP, the other variants being all formally classified as VUS (also due to in silico predictions predicting a LB effect). In addition, while several features such as DD/ID and short stature appeared to be frequent among all patients reported, Zahra et all comment that there was partial clinical overlap with the sibs described by Kambouris et al (additional variants?).


Monoallelic disruption of ZNF407:

- Ren et al (2013 - PMID: 23195952) described an 8 y.o. boy with ID and ASD. The boy was found to harbor a de novo translocation between chromosomes 3 and 18 [46,XY,t(3;18)(p13;q22.3)]. Array CGH did not reveal any P/LP CNV. Delineation of the breakpoints (FISH, long-range PCR) revealed that the chr18 breakpoint disrupted intron 3 of ZNF407 (isoform 1) with the other breakpoint within a gene-free region of exon 3. There was a loss of 4-8 nt in chr18 and 2-6 in chr3. Sequencing of ZNF407 did not reveal additional variants. RNA isolation in blood followed by RT-PCR studied expression of all 3 ZNF407 isoforms (the intronic region being shared by isoforms 1 and 2). Expression of isoform 1 was shown to be significantly reduced compared to controls. Isoform 2 was undetectable (in blood) while isoform 3 expression was similar to controls. Sequencing of 105 additional patients with similar clinical presentation (ID & ASD) revealed 2 further individuals with de novo missense variants.

- Based on the discussion by Kambouris et al (PMID: 24907849 - cited literature not here reviewed) ZNF407 may be deleted in patients with congenital aural atresia due to deletion of a critical region of 18q22.3 (though TSHZ1 is responsible for this phenotype) or 18q- although such deletions span several other genes (cited PMID: 16639285). In one case the breakpoint was shown to be disrupting ZNF407 (cited PMID: 24092497).

- The denovo db and Decipher (research variant tab) list few individuals with de novo ZNF407 SNVs although these do not seem to allow conclusions.

https://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=ZNF407
https://decipher.sanger.ac.uk/search/ddd-research-variants/results?q=znf407
Sources: Literature
Intellectual disability v3.219 MAPK1 Konstantinos Varvagiannis gene: MAPK1 was added
gene: MAPK1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: MAPK1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: MAPK1 were set to 32721402
Phenotypes for gene: MAPK1 were set to Global developmental delay; Intellectual disability; Behavioral abnormality; Growth delay; Abnormality of the face; Abnormality of the neck; Abnormality of the cardiovascular system; Abnormality of the skin
Penetrance for gene: MAPK1 were set to unknown
Mode of pathogenicity for gene: MAPK1 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: MAPK1 was set to GREEN
Added comment: Motta et al (2020 - PMID: 32721402) report on 7 unrelated individuals harboring de novo missense MAPK1 pathogenic variants.

The phenotype corresponded to a neurodevelopmental disorder and - as the authors comment - consistently included DD, ID , behavioral problems. Postnatal growth delay was observed in approximately half. Hypertelorism, ptosis, downslant of palpebral fissures, wide nasal bridge as low-set/posteriorly rotated ears were among the facial features observed (each in 3 or more subjects within this cohort). Together with short/webbed neck and abnormalities of skin (lentigines / CAL spots) and growth delay these led to clinical suspicion of Noonan s. or disorder of the same pathway in some. Congenital heart defects (ASD, mitral valve insufficiency, though not cardiomyopathy) occurred in 4/7. Bleeding diathesis and lymphedema were reported only once.

MAPK1 encodes the mitogen-activated protein kinase 1 (also known as ERK2) a serine/threonine kinase of the RAS-RAF-MEK-(MAPK/)ERK pathway.

MAPK1 de novo variants were identified in all individuals following trio exome sequencing (and extensive previous genetic investigations which were non-diagnostic).

The distribution of variants, as well as in silico/vitro/vivo studies suggest a GoF effect (boosted signal through the MAPK cascade. MAPK signaling also upregulated in Noonan syndrome).

The authors comment that screening of 267 additional individuals with suspected RASopathy (without mutations in previously implicated genes) did not reveal other MAPK1 variants.

Overall this gene can be considered for inclusion in the ID panel with green rating.
Sources: Literature
Intellectual disability v3.209 EEF1A2 Eleanor Williams changed review comment from: PMID: 32160274 - Davies et al 2020 - several reports of de novo missense mutations in EEF1A2 associated with neurodevelopmental disorders but no clear loss of function mutations. They created mice with a missense mutation in EEF1A2 (D252H) in both heterozygous and homozygous state and EEF1AS null mutant mice and analysed using behavioural and motor phenotyping alongside molecular modelling and analysis of binding partners. They found the D252H homozygous mice were more severely affected than null homozygotes on the same genetic background. The results suggest that the D252H mutation results in a gain of function.; to: PMID: 32160274 - Davies et al 2020 - several reports of de novo missense mutations in EEF1A2 associated with neurodevelopmental disorders but no clear loss of function mutations. They created mice with a missense mutation in EEF1A2 (D252H) in both heterozygous and homozygous state and EEF1A2 null mutant mice and analysed using behavioural and motor phenotyping alongside molecular modelling and analysis of binding partners. They found the D252H homozygous mice were more severely affected than null homozygotes on the same genetic background. The results suggest that the D252H mutation results in a gain of function.
Intellectual disability v3.205 EXOSC8 Arina Puzriakova Added comment: Comment on list classification: Three unrelated cases, but two share the same founder mutation - Rating Amber until further cases are reported (added to watchlist).
Intellectual disability v3.202 ATP6AP1 Arina Puzriakova reviewed gene: ATP6AP1: Rating: AMBER; Mode of pathogenicity: None; Publications: 27231034; Phenotypes: Immunodeficiency, 300972, Hepatopathy, Intellectual disability, Cutis laxa, Epilepsy; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.201 LARS Konstantinos Varvagiannis gene: LARS was added
gene: LARS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: LARS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: LARS were set to 32699352
Phenotypes for gene: LARS were set to Infantile liver failure syndrome 1, MIM# 615438
Penetrance for gene: LARS were set to Complete
Review for gene: LARS was set to GREEN
Added comment: Please consider inclusion with amber/green rating in the current panel.

Biallelic pathogenic LARS1 variants cause Infantile liver failure syndrome 1, MIM# 615438.

Lenz et al (2020 - PMID: 32699352) review the phenotype of 25 affected individuals from 15 families.

Seizures occurred in 19/24 and were commonly associated with infections. Encephalopathic episodes (in 13 patients) accompanied by seizures up to status epilepticus occurred independently of hepatic decompensation.

In addition 22/24 presented with neurodevelopmental delay. The authors comment that cognitive impairment was present in 13/17 individuals (mild-severe) whereas most presented with learning disabilities.

These patients will be most likely investigated for their liver disease (although presentation was highly variable and/or very mild in few).

The gene encodes a cytoplasmic amino-acyl tRNA synthetase (ARS) with neurologic manifestations observed in almost all patients (and seizures / DD and ID common to other disorders due to mutations in other genes encoding for ARSs).

Please note that the HGNC approved symbol for this gene is LARS1.
Sources: Literature
Intellectual disability v3.195 LIPT1 Arina Puzriakova changed review comment from: Associated with phenotype in OMIM and probable for Leigh syndrome with secondary deficiency for pyruvate and alpha-ketoglutarate dehydrogenase in G2P. LIPT1 deficiency, resulting from bi-allelic variants, is associated with developmental delay, epilepsy, and broad metabolic abnormalities. To date, five unrelated families have been reported with at least one affected child. PMID: 24341803 (2013) - In a boy with LIPT1 deficiency, exome sequencing revealed two heterozygous mutations (c.875C>G and c.535A>G). Psychomotor development was delayed from birth, but sudden further regression occurred at 18 months.; to: Associated with phenotype in OMIM and probable for Leigh syndrome with secondary deficiency for pyruvate and alpha-ketoglutarate dehydrogenase in G2P.

LIPT1 deficiency, resulting from biallelic variants, is associated with developmental delay, epilepsy, and broad metabolic abnormalities. To date, five unrelated families have been reported with at least one affected child.

PMID: 24341803 (2013) - In a boy with LIPT1 deficiency, exome sequencing revealed two compound heterozygous variants (c.875C>G and c.535A>G). Psychomotor development was delayed from birth, but sudden further regression occurred at 18 months. He could not speak but understood simple orders. He was otherwise fully conscious, alert, and he could smile, laugh and follow with eyes. Supporting functional data, including a yeast model.

PMID: 29681092 (2018) – Compound heterozygous variants (c.212C>T and c.539T>C) identified in a male with seizures, severe lactic acidosis, and failure to thrive. Initially he was reportedly developmentally normal; however, due to subsequent neurodevelopmental regression, he had global developmental delays by 21-months-of-age.

PMID 31042466 (2019) – In an 8-year-old female with developmental delay, seizures, and lactic acidosis, WES revealed two compound heterozygous variants (c.875C>G, c.131A>G). Two older sibs died of a similar condition at 7 months and 3 years. Sequencing was not possible in these individuals; however, a healthy sibling did not carry either variant. Functional analysis in patient-derived fibroblasts and mice confirmed LIPT1 deficiency.

In two unrelated families, the phenotype resulted in early infant death, and therefore ID could not be assessed:
PMID: 24256811 (2014) – compound heterozygous missense variants (c.212C>T and c.292C>G) were identified in a female that died on the ninth day of life.
PMID: 27247813 (2016) – compound heterozygous nonsense variants (c.806G>A and c.980T>G) detected in two sibs who both died on the first day of life. A third sibling, who did not harbour these variants, was healthy and thriving at 12 months of life.
Intellectual disability v3.191 GPC4 Arina Puzriakova Mode of inheritance for gene: GPC4 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.183 GPC4 Arina Puzriakova reviewed gene: GPC4: Rating: GREEN; Mode of pathogenicity: ; Publications: 30982611; Phenotypes: Keipert syndrome, 301026; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.170 CNPY3 Konstantinos Varvagiannis gene: CNPY3 was added
gene: CNPY3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CNPY3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CNPY3 were set to 29394991; 30237576
Phenotypes for gene: CNPY3 were set to Epileptic encephalopathy, early infantile, 60 (MIM 617929)
Penetrance for gene: CNPY3 were set to Complete
Review for gene: CNPY3 was set to GREEN
Added comment: Biallelic CNPY3 mutations cause Epileptic encephalopathy, early infantile, 60 (MIM 617929).

The phenotype including among others hypotonia, intractable seizures, DD and ID has been first reported by Mutoh et al (2018 - PMID: 29394991) in 3 subjects from 2 families. Evidence was provided for the role of the gene (incl. mouse model) and pathogenicity of the identified variants (resulting in LoF).

Another subject with similar features of hypotonia, DD, intractable epilepsy, feeding problems has been described briefly by Maddirevula et al (2019 - PMID: 30237576).
Sources: Literature
Intellectual disability v3.170 PAX1 Konstantinos Varvagiannis gene: PAX1 was added
gene: PAX1 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: PAX1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PAX1 were set to 29681087; 23851939; 28657137
Phenotypes for gene: PAX1 were set to Otofaciocervical syndrome 2, 615560
Penetrance for gene: PAX1 were set to Complete
Review for gene: PAX1 was set to AMBER
Added comment: Biallelic PAX1 pathogenic variants cause Otofaciocervical syndrome 2 (OMIM 615560).

Brief review of the literature suggests 3 relevant publications to date (04-07-2020).

2 individuals with DD and ID have been reported (Patil et al, 2018 - PMID: 29681087 and Pohl et al, 2013 - PMID: 23851939). Other subjects reported were only evaluated as newborns(mostly)/infants [Paganini et al, 2017 - PMID: 28657137, Patil et al, 2018 - PMID: 29681087].

While the first report by Pohl et al identified a homozygous missense variant supported by functional studies [NM_006192.5:c.497G>T - p.(Gly166Val)] subsequent ones identified homozygosity for pLoF mutations [Patil et al: NM_006192.4:c.1173_1174insGCCCG / Paganini et al: NM_006192:c.1104C>A - p.(Cys368*)].

As discussed by Pohl et al:

PAX1 encodes a transcription factor with critical role in pattern formation during embryogenesis. Study of the mouse Gly157Val (equivalent to human Gly166Val) Pax1 variant suggested reduced binding affinity (reduced transactivation of a regulatory sequence of the Nkx3-2 promoter) and hypofunctional nature of this variant.

Mouse models seem to recapitulate features of the disorder (skeletal, immunodeficiency) while the role of Pax1 in hearing process was thought to be supported by early expression (P6) in mouse cochlea.

Overall this gene can be considered for inclusion in the ID panel with amber/green rating.
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v3.170 EXOC2 Konstantinos Varvagiannis gene: EXOC2 was added
gene: EXOC2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: EXOC2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: EXOC2 were set to 32639540
Phenotypes for gene: EXOC2 were set to Global developmental delay; Intellectual disability; Abnormality of the face; Abnormality of brain morphology
Penetrance for gene: EXOC2 were set to Complete
Review for gene: EXOC2 was set to AMBER
Added comment: Van Bergen et al (2020 - PMID: 32639540) report on 3 individuals from 2 families, harboring biallelic EXOC2 mutations.

Clinical presentation included DD, ID (severe in 2 subjects from fam1, borderline intellectual functioning in fam2), dysmorphic features and brain abnormalities. Cerebellar anomalies were common to all with a molar tooth sign observed in one (1/3). Other findings limited to subjects from one family included acquired microcephaly, congenital contractures, spastic quadriplegia (each observed 2/3).

Previous investigations were in all cases non-diagnostic. WES identified biallelic EXOC2 mutations in all affected individuals.

EXOC2 encodes an exocyst subunit. The latter is an octameric complex, component of the membrane transport machinery, required for tethering and fusion of vesicles at the plasma membrane. As discussed ,vesicle transport is important for the development of brain and the function of neurons and glia. Exocyst function is also important for delivery of Arl13b to the primary cilium (biallelic ARL13B mutations cause Joubert syndrome 8) and ciliogenesis.

Affected subjects from a broader consanguineous family (fam1) were homozygous for a truncating variant. Fibroblast studies revealed mRNA levels compatible with NMD (further restored in presence of CHX) as well as reduced protein levels. The female belonging to the second non-consanguineous family was found to harbor 2 missense variants in trans configuration.

An exocytosis defect was demonstrated in fibroblasts from individuals belonging to both families. Ciliogenesis appeared to be normal, however Arl13b localization/recruitment to the cilia was reduced compared with control cells with the defect rescued upon exogenous expression of wt EXOC2.

Mutations in other genes encoding components of the exocyst complex have been previously reported in individuals with relevant phenotypes (e.g. EXOC8 in a boy with features of Joubert s. or EXOC4 in nephrotic syndrome).

The authors discuss on the essential role of EXOC2 based on model organism studies (e.g. impaired neuronal membrane traffic, failure of neuronal polarization and neuromuscular junction expansion seen in Drosophila Sec5 (EXOC2) null mutants).
Sources: Literature
Intellectual disability v3.127 CAPZA2 Eleanor Williams gene: CAPZA2 was added
gene: CAPZA2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CAPZA2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CAPZA2 were set to 32338762
Review for gene: CAPZA2 was set to AMBER
Added comment: Not associated with a disease phenotype in OMIM.

PMID: 32338762 - Huang et al 2020 - report 2 unrelated families (Chinese and European) in which a de novo heterozygous variant has been identified in CAPZA2 in paediatric probands that present with global motor development delay, speech delay, intellectual disability, hypotonia. One proband had seizures at 7 months but these were controlled with medication and did not repeat. The other proband at age one had an atypical febrile seizure that was controlled without medication. Functional studies in Drosophila suggest that these variants are mild loss of function mutations but that they can act as dominant negative variants in actin polymerization in bristles.
Sources: Literature
Intellectual disability v3.126 PDCD6IP Zornitza Stark gene: PDCD6IP was added
gene: PDCD6IP was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PDCD6IP was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PDCD6IP were set to 32286682
Phenotypes for gene: PDCD6IP were set to microcephaly; Intellectual disability
Review for gene: PDCD6IP was set to AMBER
Added comment: One consanguineous family with 2 affected sibs with primary microcephaly (-4SD), intellectual disability and short stature (-5/6SD), and homozygous frameshift variant in PDCD6IP. The homozygous variant was confirmed in both affected sibs, while the four healthy siblings and parents were heterozygous. The clinical features observed in the patients were similar to the phenotypes observed in mouse and zebrafish models of PDCD6IP mutations in previous studies.
Sources: Literature
Intellectual disability v3.87 DSCR3 Zornitza Stark gene: DSCR3 was added
gene: DSCR3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DSCR3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DSCR3 were set to 31845315
Phenotypes for gene: DSCR3 were set to Intellectual disability, no OMIM # yet
Review for gene: DSCR3 was set to RED
Added comment: 1 family/2 cousins with cognitive impairment, growth failure, skeletal abnormalities, and distinctive facial features. Both shared the homozygous nonsense variant c.178G>T (p.Glu60*) in the VPS26C gene. This gene encodes VPS26C, a member of the retriever integral membrane protein recycling pathway. The nature of the variant which is predicted to result in loss‐of‐function, expression studies revealing significant reduction in the mutant transcript, and the co‐segregation of the homozygous variant with the phenotype in two affected individuals.
Sources: Literature
Intellectual disability v3.83 SATB1 Eleanor Williams changed review comment from: Conference talk/abstract from ESHG 2020 - Mutation-specific pathophysiological mechanisms in a new SATB1-associated neurodevelopmental disorder - Den Hoed et al - report f26 individuals with SATB1 variants, 17 of which have missense variants and 9 have truncating variants. 21 of 26 variants (80%) were confirmed to be de novo in origin. Patients showed a broad phenotypic spectrum, including ID and/or neurodevelopmental delay, epilepsy, dental abnormalities and aspecific brain MRI findings. Additionally, patients with missense variants are more severely affected than those with truncating variants.
No peer reviewed publication was found in PubMed relating to these results so recommend Amber rating for now.
Sources: Other; to: Conference talk/abstract from ESHG 2020 - Mutation-specific pathophysiological mechanisms in a new SATB1-associated neurodevelopmental disorder - Den Hoed et al - report 26 individuals with SATB1 variants, 17 of which have missense variants and 9 have truncating variants. 21 of 26 variants (80%) were confirmed to be de novo in origin. Patients showed a broad phenotypic spectrum, including ID and/or neurodevelopmental delay, epilepsy, dental abnormalities and aspecific brain MRI findings. Additionally, patients with missense variants are more severely affected than those with truncating variants.
No peer reviewed publication was found in PubMed relating to these results so recommend Amber rating for now.
Sources: Other
Intellectual disability v3.83 SATB1 Eleanor Williams gene: SATB1 was added
gene: SATB1 was added to Intellectual disability. Sources: Other
Mode of inheritance for gene: SATB1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Phenotypes for gene: SATB1 were set to intellectual disability
Review for gene: SATB1 was set to AMBER
Added comment: Conference talk/abstract from ESHG 2020 - Mutation-specific pathophysiological mechanisms in a new SATB1-associated neurodevelopmental disorder - Den Hoed et al - report f26 individuals with SATB1 variants, 17 of which have missense variants and 9 have truncating variants. 21 of 26 variants (80%) were confirmed to be de novo in origin. Patients showed a broad phenotypic spectrum, including ID and/or neurodevelopmental delay, epilepsy, dental abnormalities and aspecific brain MRI findings. Additionally, patients with missense variants are more severely affected than those with truncating variants.
No peer reviewed publication was found in PubMed relating to these results so recommend Amber rating for now.
Sources: Other
Intellectual disability v3.78 TTC5 Konstantinos Varvagiannis gene: TTC5 was added
gene: TTC5 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TTC5 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TTC5 were set to 29302074; 32439809
Phenotypes for gene: TTC5 were set to Central hypotonia; Global developmental delay; Intellectual disability; Abnormality of nervous system morphology; Microcephaly; Abnormality of the face; Behavioral abnormality; Abnormality of the genitourinary system
Penetrance for gene: TTC5 were set to Complete
Review for gene: TTC5 was set to GREEN
Added comment: Hu et al (2019 - PMID: 29302074) reported briefly on 3 individuals from 2 consanguineous families (from Turkey and Iran) with biallelic TTC5 variants. Features included DD (3/3), ID (severe in 2/2 with relevant age), microcephaly (3/3), brain abnormalities, etc. A nonsense and a variant affecting splice site were identified by WES/WGS.

---

In a recent report, Rasheed et al (2020 - PMID: 32439809) report on the phenotype of 8 individuals - belonging to 5 consanguineous families - all 8 harboring homozygous TTC5 mutations.

Frequent features included hypotonia (6/8), motor and speech delay, moderate to severe ID (10/10 of relevant age - inclusion of less severely affected subjects was not considered by study design), brain MRI abnormalities (8/8). Other findings included microcephaly in some (6/11), behavioral abnormalities in few (autistic behavior in 2/8, aggression in 2/8), genitourinary anomalies (2/8), seizures (1/11). Facial phenotype incl. thin V-shaped upper lip, low-set ears (in most) and/or additional features.

TTC5 encodes a 440 aa protein, functioning as a scaffold to stabilise p300-JMY interactions. Apart from this role in nucleus, it has functions in the cytoplasm (inhibiting actin nucleataion, autophagosome formation, etc).

The gene has ubiquitous expression, highest in brain.

All variants were identified following WES - as the best candidates - in affected individuals with compatible Sanger studies in all affected family members and carrier parents.

2 missense and 2 nonsense variants were identified with the 2 missense SNVs localizing within TPR domains. qRT-PCR studies for a nonsense variant localizing 19 nt before the last exon, revealed fourfold decreased expression in affected individuals compared to carriers.

Families from Egypt shared a homozygous ~6.3 Mb haplotype block spanning TTC5, suggesting that p.(Arg263Ter) is likely a founder mutation.

The authors underscore some phenotypic (though not facial) similarities with Rubinstein-Taybi syndrome 2 due to EP300 mutations (in line with the role of TTC5).

Biallelic variants in genes encoding other members of the TTC family (containing a TPR motif), e.g. TTC8 or TTC15 cause disorders with neurologic manifestations (and DD/ID).
Sources: Literature
Intellectual disability v3.77 AGMO Rebecca Foulger changed review comment from: PMID:27000257 (2016) Alrayes et al., 2016 enrolled a consanguineous family from Saudi Arabia presenting with primary microcephaly, developmental delay, short stature and intellectual disability. They identified a novel homozygous deletion mutation (c.967delA; p.Glu324Lysfs12*) in exon 10 of the alkylglycerol monooxygenase (AGMO) gene in 2 brothers. Population screening of 178 ethnically matched control chromosomes and consultation of the ExAC database confirmed that this variant was not present outside the family. Epilepsy is not mentioned amongst their phenotypes.; to: PMID:27000257 (2016) Alrayes et al., 2016 enrolled a consanguineous family from Saudi Arabia presenting with primary microcephaly, developmental delay, short stature and intellectual disability. They identified a novel homozygous deletion mutation (c.967delA; p.Glu324Lysfs12*) in exon 10 of the alkylglycerol monooxygenase (AGMO) gene in 2 brothers. Population screening of 178 ethnically matched control chromosomes and consultation of the ExAC database confirmed that this variant was not present outside the family.
Intellectual disability v3.72 CXorf56 Rebecca Foulger Mode of inheritance for gene: CXorf56 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.55 EXT2 Rebecca Foulger commented on gene: EXT2: PMID:30075207. In 2 brothers, born of consanguineous Syrian parents, with MIM:616682 El-Bazzal et al. (2019) identified a homozygous missense mutation in the EXT2 gene (p.Ser4Leu). Psychomotor delay was noted for both at the age of 3 months.
Intellectual disability v3.55 EXT2 Rebecca Foulger commented on gene: EXT2: PMID:26246518: In 4 siblings, born of consanguineous parents in the Old Order Mennonite community, with seizures, scoliosis, and macrocephaly/microcephaly syndrome (MIM:616682), Farhan et al. (2015) identified homozygosity for 2 missense mutations in EXT2 (M87R and R95C). All siblings had moderate ID and a seizure disorder.
Intellectual disability v3.35 CDC42BPB Konstantinos Varvagiannis gene: CDC42BPB was added
gene: CDC42BPB was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CDC42BPB was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CDC42BPB were set to 32031333
Phenotypes for gene: CDC42BPB were set to Central hypotonia; Global developmental delay; Intellectual disability; Seizures; Autistic behavior; Behavioral abnormality
Penetrance for gene: CDC42BPB were set to unknown
Review for gene: CDC42BPB was set to GREEN
Added comment: Chilton et al (2020 - PMID: 32031333) report on 14 individuals with missense and loss-of-function CDC42BPB variants.

Features included hypotonia (8/11), DD (12/13 - the 14th was a fetus), ID (7/13), ASD (8/12), clinical seizures (in 3 - a 4th had abnormal EEG without seizures), behavioral abnormalities. Variable non-specific dysmorphic features were reported in some (sparse hair being the most frequent - 4/8). Additional features were observed in few (=<4) incl. cryptorchidism, ophthalmological issues, constipation, kidney abnormalities, micropenis, etc.

All individuals had non-diagnostic prior genetic testing (incl. CMA, FMR1, MECP2, Angelman/Prader-Willi methylation studies, autism gene panel - suggesting relevance to the current panel) or metabolic testing.

Variants were identified following clinical exome sequencing with Sanger confirmation. Most occurred as de novo events (11/14) while inheritance was not available for few (3/14). Missense variants did not display (particular) clustering.

Almost all variants were absent from gnomAD and were predicted to be deleterious in silico (among others almost all had CADD scores >25).

As the authors comment, CDC42BPB encodes myotonic dystrophy-related Cdc42-binding kinase β (MRCKβ) a serine/threonine protein kinase playing a role in regulation of cytoskeletal reorganization and cell migration in nonmuscle cells (through phosporylation of MLC2).

Previous studies have demonstrated that it is ubiquitously expressed with prenatal brain expression.

The gene appears to be intolerant to pLoF (pLI of 1) as well as to missense variants (Z-score of 3.66).

CDC42BPB is a downstream effector of CDC42. Mutations of the latter cause Takenouchi-Kosaki syndrome with DD/ID and some further overlapping features (with CDC42BPB-associated phenotypes).

Homozygous Cdc42bpb KO in mouse appears to be nonviable (MGI:2136459). Loss of gek in the eyes of Drosophila results in disrupted growth cone targeting to the lamina (gek is the fly CDC42BPB ortholog).

Please consider inclusion with amber / green rating in the ID panel (>=4 relevant individuals / variants) and other panels (e.g. for epilepsy, ASD).
Sources: Literature
Intellectual disability v3.34 ADAM22 Rebecca Foulger commented on gene: ADAM22: PMID:27066583. Muona et al., 2016 report a Finnish proband-parent-trio with intractable seizures and ID. Compound het variants c.1202G>A, p.Cys401Tyr and c.2396delG, p.Ser799IlefsTer96 were found in ADAM22. Functional assays showed that mutant proteins failed to form the LGI1-ADAM22 ligand-receptor complex. The variants are unlikely to be full LOF.
Intellectual disability v3.29 NRROS Zornitza Stark gene: NRROS was added
gene: NRROS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: NRROS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: NRROS were set to 32100099; 32197075
Phenotypes for gene: NRROS were set to neurodegeneration; intracranial calcification; epilepsy
Review for gene: NRROS was set to GREEN
Added comment: Normal development or mild developmental delay until onset of regression around age of 1 concurrent with epilepsy
Biallelic LOF mutations with functional evidence of pathogenicity reported in 6 unrelated families. Suggest also add to Epilepsy panel, possibly others.
Sources: Literature
Intellectual disability v3.23 RNF13 Sarah Leigh changed review comment from: Associated with relevant phenotype in OMIM and as probable Gen2Phen gene. At least 2 variants reported in 3 unrelated cases, together with supportive functional studies.; to: Associated with relevant phenotype in OMIM and as probable Gen2Phen gene. At least 2 variants reported in 3 unrelated cases, together with supportive functional studies.

Gain-of-function mechanism has been reported, therefore the mutational spectrum may be limited and is still to be determined through further cases or further functional studies (view of Helen Britain, GeL Clincial Fellow).
Intellectual disability v3.3 CXorf56 Zornitza Stark reviewed gene: CXorf56: Rating: GREEN; Mode of pathogenicity: None; Publications: 29374277, 31822863; Phenotypes: Mental retardation, X-linked 107, MIM# 301013; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females; Current diagnostic: yes
Intellectual disability v3.3 MAPRE2 Zornitza Stark reviewed gene: MAPRE2: Rating: GREEN; Mode of pathogenicity: None; Publications: 26637975; Phenotypes: Symmetric circumferential skin creases, congenital, 2, MIM# 616734; Mode of inheritance: BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Intellectual disability v3.3 ZIC3 Zornitza Stark reviewed gene: ZIC3: Rating: RED; Mode of pathogenicity: None; Publications: ; Phenotypes: Heterotaxy, visceral, 1, X-linked 306955, Congenital heart defects, nonsyndromic, 1, X-linked, 306955, VACTERL association, X-linked, 314390; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.3 TRAPPC2 Zornitza Stark reviewed gene: TRAPPC2: Rating: RED; Mode of pathogenicity: None; Publications: ; Phenotypes: Spondyloepiphyseal dysplasia tarda, MIM# 313400; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.3 TBX22 Zornitza Stark reviewed gene: TBX22: Rating: RED; Mode of pathogenicity: None; Publications: ; Phenotypes: Abruzzo-Erickson syndrome, MIM# 302905, Cleft palate with ankyloglossia, MIM# 303400; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.3 TASP1 Zornitza Stark gene: TASP1 was added
gene: TASP1 was added to Intellectual disability. Sources: Expert list
Mode of inheritance for gene: TASP1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TASP1 were set to 31209944; 31350873
Phenotypes for gene: TASP1 were set to Developmental delay; microcephaly; dysmorphic features; congenital abnormalities
Review for gene: TASP1 was set to GREEN
gene: TASP1 was marked as current diagnostic
Added comment: Four unrelated families reported; two with founder mutation. Protein interacts with KMT2A and KMT2D. Another de novo missense variant reported in a single infant with multiple congenital abnormalities, insufficient evidence for mono allelic disease at present.
Sources: Expert list
Intellectual disability v3.3 SLC9A7 Zornitza Stark gene: SLC9A7 was added
gene: SLC9A7 was added to Intellectual disability. Sources: Expert list
Mode of inheritance for gene: SLC9A7 was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Publications for gene: SLC9A7 were set to 30335141
Phenotypes for gene: SLC9A7 were set to Intellectual developmental disorder, X-linked 108; OMIM #301024
Review for gene: SLC9A7 was set to AMBER
Added comment: 6 males from 2 unrelated families with hemizygous missense mutation in the SLC9A7 gene. The mutation segregated with the disorder in the family. In vitro functional expression studies in CHO cells (AP-1 cells) showed that the mutation caused decreased levels of protein expression and reduced oligosaccharide maturation/glycosylation compared to wildtype, indicating impaired posttranslational processing. Subcellular localization studies indicated that protein trafficking was unaffected by the mutation. However, examination of the trans-Golgi compartment suggested a gain-of-function effect and a perturbation of glycosylation of secretory cargo. Serum transferrin studies in 1 patient suggested a glycosylation defect. One to watch.
Sources: Expert list
Intellectual disability v3.3 SOX3 Zornitza Stark reviewed gene: SOX3: Rating: AMBER; Mode of pathogenicity: None; Publications: 29175558, 30125608, 12428212, 15800844; Phenotypes: Mental retardation, X-linked, with isolated growth hormone deficiency, MIM#300123, Panhypopituitarism, X-linked, MIM#312000; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.0 LMAN2L Zornitza Stark gene: LMAN2L was added
gene: LMAN2L was added to Intellectual disability. Sources: Expert list
Mode of inheritance for gene: LMAN2L was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: LMAN2L were set to 31020005; 26566883
Phenotypes for gene: LMAN2L were set to Intellectual disability; epilepsy
Review for gene: LMAN2L was set to AMBER
Added comment: 1 consanguineous family with 7 individuals with ID and epilepsy, with homozygous LMAN2L missense mutation. Segregated with disease in family, and unaffected family members were heterozygous variant carriers. No functional studies.

1 non-consanguineous family with 4 affected with heterozygous frameshift LMAN2L mutation. Segregates in family. Mutation eliminates LMAN2L's endoplasmic reticulum retention signal and mislocalizes the protein from that compartment to the plasma membrane.

Amber or Red.
Sources: Expert list
Intellectual disability v3.0 LAS1L Zornitza Stark reviewed gene: LAS1L: Rating: GREEN; Mode of pathogenicity: None; Publications: 25644381, 25644381; Phenotypes: Wilson-Turner syndrome, MIM# 309585; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females; Current diagnostic: yes
Intellectual disability v3.0 GPC4 Zornitza Stark gene: GPC4 was added
gene: GPC4 was added to Intellectual disability. Sources: Expert list
Mode of inheritance for gene: GPC4 was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for gene: GPC4 were set to 30982611
Phenotypes for gene: GPC4 were set to Keipert syndrome OMIM# 301026
Review for gene: GPC4 was set to GREEN
gene: GPC4 was marked as current diagnostic
Added comment: 10 individuals from 6 families reported, functional studies in mice. Mild to moderate ID part of the phenotype.
Sources: Expert list
Intellectual disability v3.0 FAAH2 Zornitza Stark reviewed gene: FAAH2: Rating: RED; Mode of pathogenicity: None; Publications: 25885783; Phenotypes: Neuropsychiatric disorder; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.0 CHRDL1 Zornitza Stark reviewed gene: CHRDL1: Rating: RED; Mode of pathogenicity: None; Publications: ; Phenotypes: Megalocornea 1, X-linked, MIM# 309300; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.0 CHM Zornitza Stark reviewed gene: CHM: Rating: RED; Mode of pathogenicity: None; Publications: ; Phenotypes: Choroideremia, MIM# 303100; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.0 EBP Zornitza Stark reviewed gene: EBP: Rating: GREEN; Mode of pathogenicity: None; Publications: ; Phenotypes: Chondrodysplasia punctata, X-linked dominant MIM#302960, Conradi-Hunermann syndrome, MEND syndrome, MIM#300960; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males); Current diagnostic: yes
Intellectual disability v3.0 BGN Zornitza Stark reviewed gene: BGN: Rating: RED; Mode of pathogenicity: None; Publications: ; Phenotypes: Meester-Loeys syndrome, MIM# 300989, Spondyloepimetaphyseal dysplasia, X-linked, MIM#300106; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females
Intellectual disability v3.0 BCORL1 Zornitza Stark reviewed gene: BCORL1: Rating: GREEN; Mode of pathogenicity: None; Publications: 24123876, 30941876; Phenotypes: Shukla-Vernon syndrome, MIM# 301029; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females; Current diagnostic: yes
Intellectual disability v3.0 ATP6AP1 Zornitza Stark gene: ATP6AP1 was added
gene: ATP6AP1 was added to Intellectual disability. Sources: Expert list
Mode of inheritance for gene: ATP6AP1 was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Publications for gene: ATP6AP1 were set to 27231034
Phenotypes for gene: ATP6AP1 were set to Immunodeficiency 47, MIM#300972
Review for gene: ATP6AP1 was set to GREEN
gene: ATP6AP1 was marked as current diagnostic
Added comment: 11 males from 6 unrelated families with primarily an immunodeficiency disorder; six patients from 3 families who carried the same variant (E346K) had neurologic features, including seizures, mild intellectual disability, and behavioral abnormalities
Sources: Expert list
Intellectual disability v3.0 SUPT16H Konstantinos Varvagiannis gene: SUPT16H was added
gene: SUPT16H was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SUPT16H was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: SUPT16H were set to http://dx.doi.org/10.1136/jmedgenet-2019-106193
Phenotypes for gene: SUPT16H were set to Global developmental delay; Intellectual disability; Abnormality of the corpus callosum
Penetrance for gene: SUPT16H were set to Complete
Review for gene: SUPT16H was set to AMBER
Added comment: Bina et al (2020 - http://dx.doi.org/10.1136/jmedgenet-2019-106193) report on 4 unrelated individuals with heterozygous SNVs affecting SUPT16H as well as 1 further with microdeletion spanning this gene.

The phenotype consisted of DD with subsequent ID in a subset of them (ages of the cohort: 2y-14y), autistic features in few, abnormalities of the corpus callosum (for 3 with available MRI images), variable gastrointestinal problems in some, and possibly minor dysmorphic features.

SUPT16H encodes a subunit of the FACT (facilitates chromatin transcription) complex, a chromatin-specific factor required for transcription elongation as well as for DNA replication and repair (OMIM citing Belotserkovskaya et al. 2003 - PMID: 12934006). The 2 subunits of the complex [Spt16 (encoded by SUPT16H) and SSRP1] are essential for histone regulation. As the authors note, Spt16 interacts with the histone dimer H2A-H2B during transcription to allow RNA polymerase access to previously coiled DNA [cited PMIDs : 9489704, 10421373 / A recent study by Liu et al 2019 (PMID: 31775157) appears highly relevant].

SUPT16H has a Z-score of 5.1 in gnomAD and a pLI of 1 (%HI of 22.56 in Decipher).

SNVs :
4 de novo missense SNVs were identified following exome sequencing (NM_007192.3:c.484A>G or I162V / L432P / N571S / R734W), all absent from gnomAD and mostly predicted to be deleterious (I162V predicted benign, tolerated, disease-causing by PolyPhen2, SIFT, MutationTaster respectively and had a CADD score of 13.61). Prior work-up for these individuals (incl. CMA in some / MS-MLPA for Angelman s. in 1 / metabolic investigations) had (probably) not revealed an apparent cause, with small CNVs inherited from healthy parents (a 4q13.3 dup / 20q13.2 del - coordinates not provided).

There were no studies performed for the identified variants.

CNVs :
A 5th individual reported by Bina et al was found to harbor a 2.05 Mb 14q11.2 deletion spanning SUPT16H. The specific deletion also spanned CHD8 while the same individual harbored also a 30.17 Mb duplication of 18p11.32q12.1.

CNVs spanning SUPT16H reported to date, also span the (very) proximal CHD8. [Genomic coordinates (GRCh38) for SUPT16H and CHD8 as provided by OMIM : 14:21,351,471-21,384,018 / 14:21,385,198-21,456,122]. Haploinsufficiency of CHD8 is associated with a distinctive syndrome with overgrowth and ID (Douzgou et al 2019 - PMID: 31001818). The phenotype of SUPT16H-CHD8 duplications is discussed in other studies/reviews. [Smol et al 2020 - PMID: 31823155 / Smyk et al 2016 - PMID: 26834018].

Animal models were not commented on by Bina et al (possibly not available for mouse : http://www.informatics.jax.org/marker/MGI:1890948 / https://www.mousephenotype.org/data/genes/MGI:1890948 ).
Sources: Literature
Intellectual disability v3.0 TET3 Konstantinos Varvagiannis gene: TET3 was added
gene: TET3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TET3 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: TET3 were set to https://doi.org/10.1016/j.ajhg.2019.12.007
Phenotypes for gene: TET3 were set to Global developmental delay; Intellectual disability; Macrocephaly; Growth abnormality; Seizures; Autistic behavior; Abnormality of movement; Abnormality of the face
Penetrance for gene: TET3 were set to Complete
Review for gene: TET3 was set to GREEN
Added comment: Beck et al (2020 - DOI: https://doi.org/10.1016/j.ajhg.2019.12.007) report on individuals with monoallelic de novo or biallelic pathogenic TET3 variants.

For both inheritance modes (AR/AD) DD/ID were among the observed features (mild-severe - individuals from families 2, 4 and 6 for whom presence of ID was not commented, relevance to the current panel is suggested from the developmental milestones in the supplement. One individual presented DD without ID). Other features included hypotonia (in 8), ASD/autistic features (in 5), seizures (2 unrelated subjects for each inheritance mode). Postnatal growth abnormalities were observed in many, in most cases involving head size (with/without abnormal stature) and few presented abnormal prenatal growth. Variable movement disorders were observed in some. Some facial features appeared to be more common (eg. long face, tall forehead, etc).

Most were referred for their DD. Extensive prior genetic investigations had (mostly) come out normal (with possible contribution of a 16p11.2 dup in an individual with monoallelic variant or a 16q22 dup in another with biallelic TET3 variants). Monoallelic / biallelic variants in all subjects were identified following exome sequencing.

TET3 encodes a methylcytosine dioxygenase (the TET family consisting of 3 enzymes, TET1, TET2, TET3). These enzymes are involved in DNA demethylation through a series of reactions beginning with the conversion of 5-methyl cytosine [5mc] to 5-hydromethylcytosine [5hmC].

5 individuals from 3 families (1/3 consanguineous) harbored biallelic missense variants. 5 different missense variants were observed. Heterozygous parents appeared to be mildly affected (eg. having learning difficulties, etc).

6 individuals from 5 families harbored monoallelic variants [3 truncating (of which 2 localizing in the last exon), 2 missense SNVs]. In one family the variant was inherited from a similarly affected parent. In all other cases the variant had occured de novo. No additional TET3 variants were identified, with the limitations of WES.

All missense mutations, whether observed in individuals with biallelic or monoallelic variants, were located within the catalytic domain or - for a single variant (NM_001287491.1:c.2254C>T / p.Arg752Cys) - adjacent to it.

Functional studies were carried out only for (all) missense variants observed in individuals with biallelic variants. Conversion of 5mC to 5hmC is the first step in DNA demethylation. In HEK293 cells overexpressing either wt or variants, production of 5hmc was measured. 4/5 missense variants evaluated demonstrated a defect in converting 5mC to 5hmC, Arg752Cys being an exception (as also predicted by its localization).

DD/ID and abnormal growth are also features of disorders of the epigenetic machinery (DNA methylation machinery, histone machinery, chromatin remodelers, other chromatin-associated proteins). Similarly to TET3, both monoallelic and biallelic variants in KDM5B, encoding for another component of the epigenetic machinery, have been identified in individuals with ID.

Mouse models discussed by the authors [several Refs provided though not here reviewed] : The gene has been shown to be highly expressed in oocytes, zygotes and neurons and to play a role in demethylation of the paternal genome after fertilization. (From the MGI: 'mice inheriting a null allele from a germ cell conditional null mother display impaired reprogramming of the paternal genome resulting in reduced embryo viability'). Beck et al also note that Tet3 inhibition or depletion in differentiated neurons can impact synaptic function [PMIDs cited: 25915473, 24757058, 26711116].
Sources: Literature
Intellectual disability v3.0 NUS1 Konstantinos Varvagiannis edited their review of gene: NUS1: Added comment: Please consider upgrading this gene (NUS1 is also rated Green in the epilepsy panel).

Den et al (2019 - PMID: 31656175) reported on 2 additional unrelated individuals (aged 17 and 59y) both presenting intellectual disability, epilepsy , involuntary movements, ataxia and scoliosis. Both were found to harbor the same splicing variant in NUS1 (NM_138459.4:c.691+1C>A) following exome sequencing. Using lymphoblastoid cell lines from both individuals it was demonstrated that the variant creates a new splice donor site in exon 3 further creating a new reading frame and producing a premature termination codon [c.601_691del or p.(Arg202Glnfs*9)]. Using cyclohexamide, it was further shown that the mutant mRNA is partially subjected to NMD. [Additional variants identified by exome for the 2 subjects were non diagnostic (/VUS). An SPTAN1 nonsense variant identified in one was inherited from an unaffected parent (dominant-negative mechanism listed in G2P for this gene / in ClinVar all pLoF variants are submitted as VUS)].
-----; Changed rating: GREEN; Changed publications: 25066056, 29100083, 24824130, 30348779, 31656175
Intellectual disability v3.0 RNF113A Konstantinos Varvagiannis reviewed gene: RNF113A: Rating: GREEN; Mode of pathogenicity: None; Publications: 25612912, 31880405, 31793730, 29133357, 30506991, 15256591, 24026126, 23555887; Phenotypes: ; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v3.0 MTHFS Konstantinos Varvagiannis changed review comment from: Biallelic pathogenic MTHFS variants cause Neurodevelopmental disorder with microcephaly, epilepsy, and hypomyelination (# 618367).

The gene encodes 5,10-Methenyltetrahydrofolate synthetase which catalyzes conversion of 5-formyltetrahydrofolate (5-FTHF or folinic acid) to 5,10-methenyltetrahydrofolate (5,10-MTHF).

At least 3 unrelated individuals have been reported. The phenotype appears to be relevant to both epilepsy and ID gene panels and the role of variants/the gene supported by enzymatic activity studies, 5-FTHF accumulation, 5,10-MTHF levels (low/low-normal), the role of folate metabolism pathway overall and some supporting (metabolic) evidence from the mouse model.
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Rodan et al (2018 - PMID: 30031689) reported on 2 individuals both presenting with microcephaly, severe global DD, epilepsy, progressive spasticity and cerebral hypomyelination upon MRI imaging. Short stature was also feature in both.

The 1st patient was an 8-year-old male who following exome sequencing was found to harbor 2 missense variants each inherited from a carrier parent. (NM_006441.3:c.434G>A / p.R145Q and c.107T>C / p.L36P). A further AFG3L2 indel was not felt to fit with his phenotype (and the onset of the related disorder appears to occur later).

Previous investigations included extensive metabolic testing, CMA, Angelman syndrome methylation analysis, GFAP, POLG1, TYMP sequencing, mitochondrial genome analysis and an XL-ID gene panel (further suggesting relevance of this gene to the current panel) were all non-diagnostic.

CSF 5-MTHF levels were initially on the low-normal range, subsequently found to be decreased (upon folinic acid supplementation) and later normalized upon use of another regimen.

MTHFS activity was measured in control fibroblasts as well as fibroblasts from this individual, with the latter demonstrating no enzyme activity. Accumulation (30x elevation) of 5-FTHF (the substrate of MTHFS) was demonstrated in patient fibroblasts.

The 2nd patient was a 11-year-old male with similar features incl. global DD (standing/walking/single words at/after 4 years of age, limited vocabulary and articulation upon last examination).

Extensive metabolic work-up as well as genetic testing for an epilepsy panel, vanishing white matter disease gene panel, mitochondrial genome as well as specific gene sequencing (LAMA2, POLR3A, POLR3B) were all non-diagnostic. Trio exome revealed 2 MTHFS variants in trans configuration (c.484C>T / p.Q162X and c.434G>A / p.R145Q).
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Romero et al (2019 - PMID: 31844630) reported on a 4-year-old female with congenital microcephaly, severe global DD (nonverbal/nonambulatory at the age of 4), spasticity, epilepsy and cerebral hypomyelination.

Extensive investigations prior to exome sequencing revealed macrocytic anemia, decreased CSF 5-MTHF and elevated neopterin, 2 CNVs of uncertain significance upon CMA with additional long ROH on chr15. Methylation studies were negative. The child was homozygous for c.220C>T / p.R74X (RefSeq is probably NM_006441.3. MTHFS lies on chr15. The parents were unrelated but came from the same town). There were no other candidate variants from the exome analysis.

Both articles discuss extensively the role of the folate metabolism pathway overall in nucleic acid synthesis, AA metabolism, neurotransmitter synthesis, methylation as well as 5-FTHF / 5,10-MTHF in particular in myelin stabilization and DNA synthesis (eg. according to Romero et al. a defect in MTHFS would impair myelin production and also lead to decreased myelin stability).
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A book chapter cited by Rodan et al (in N. Blau et al. (eds.), Physician’s Guide to the Diagnosis, Treatment, and Follow-Up of Inherited Metabolic Diseases - DOI: 10.1007/978-3-642-40337-8_10) included limited details on a patient with 'MTHFS gene mutation'. This individual had early speech delay, seizures beginning in infancy, ID, autistic features, recurrent infections and was found to have very low CSF 5-MTHF levels. [Details in p169 and table 10.6 - p173].
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In a mouse model reported by Field et al (2011 - PMID: 22303332), Mthfs was disrupted through insertion of a gene trap vector between the first 2 exons. Heterozygous [Mthfs(gt/+)] mice were fertile and viable. Mthfs protein levels were slightly but not statistically significantly reduced in tissues measured. No homozygous embryos were recovered following intercrosses of heterozygous mice, suggesting that Mthfs is an essential gene. Mouse embryonic fibroblasts from heterozygous mice [Mthfs (gt/+)] exhibited reduced de novo purine biosynthesis, but did not exhibit altered de novo thymidylate biosynthesis. Plasma folate levels were altered in heterozygous mice on a standard (/control) diet.
Sources: Literature; to: Biallelic pathogenic MTHFS variants cause Neurodevelopmental disorder with microcephaly, epilepsy, and hypomyelination (# 618367).

The gene encodes 5,10-Methenyltetrahydrofolate synthetase which catalyzes conversion of 5-formyltetrahydrofolate (5-FTHF or folinic acid) to 5,10-methenyltetrahydrofolate (5,10-MTHF).

At least 3 unrelated individuals have been reported. The phenotype appears to be relevant to both epilepsy and ID gene panels and the role of variants/the gene supported by enzymatic activity studies, 5-FTHF accumulation, 5,10-MTHF levels (low/low-normal), the role of folate metabolism pathway overall and some supporting (metabolic) evidence from the mouse model.
---
Rodan et al (2018 - PMID: 30031689) reported on 2 individuals both presenting with microcephaly, severe global DD, epilepsy, progressive spasticity and cerebral hypomyelination upon MRI imaging. Short stature was also feature in both.

The 1st patient was an 8-year-old male who following exome sequencing was found to harbor 2 missense variants each inherited from a carrier parent. (NM_006441.3:c.434G>A / p.R145Q and c.107T>C / p.L36P). A further AFG3L2 indel was not felt to fit with his phenotype (and the onset of the related disorder appears to occur later).

Previous investigations included extensive metabolic testing, CMA, Angelman syndrome methylation analysis, GFAP, POLG1, TYMP sequencing, mitochondrial genome analysis and an XL-ID gene panel (further suggesting relevance of this gene to the current panel) were all non-diagnostic.

CSF 5-MTHF levels were initially on the low-normal range, subsequently found to be decreased (upon folinic acid supplementation) and later normalized upon use of another regimen.

MTHFS activity was measured in control fibroblasts as well as fibroblasts from this individual, with the latter demonstrating no enzyme activity. Accumulation (30x elevation) of 5-FTHF (the substrate of MTHFS) was demonstrated in patient fibroblasts.

The 2nd patient was a 11-year-old male with similar features incl. global DD (standing/walking/single words at/after 4 years of age, limited vocabulary and articulation upon last examination).

Extensive metabolic work-up as well as genetic testing for an epilepsy panel, vanishing white matter disease gene panel, mitochondrial genome as well as specific gene sequencing (LAMA2, POLR3A, POLR3B) were all non-diagnostic. Trio exome revealed 2 MTHFS variants in trans configuration (c.484C>T / p.Q162X and c.434G>A / p.R145Q).
---
Romero et al (2019 - PMID: 31844630) reported on a 4-year-old female with congenital microcephaly, severe global DD (nonverbal/nonambulatory at the age of 4), spasticity, epilepsy and cerebral hypomyelination.

Extensive investigations prior to exome sequencing revealed macrocytic anemia, decreased CSF 5-MTHF and elevated neopterin, 2 CNVs of uncertain significance upon CMA with additional long ROH on chr15. Methylation studies were negative. The child was homozygous for c.220C>T / p.R74X (RefSeq is probably NM_006441.3. MTHFS lies on chr15. The parents were unrelated but came from the same town). There were no other candidate variants from the exome analysis.

Both articles discuss extensively the role of the folate metabolism pathway overall in nucleic acid synthesis, AA metabolism, neurotransmitter synthesis, methylation as well as 5-FTHF / 5,10-MTHF in particular in myelin stabilization and DNA synthesis (eg. according to Romero et al. a defect in MTHFS would impair myelin production and also lead to decreased myelin stability).
---
A book chapter cited by Rodan et al (in N. Blau et al. (eds.), Physician’s Guide to the Diagnosis, Treatment, and Follow-Up of Inherited Metabolic Diseases - DOI: 10.1007/978-3-642-40337-8_10) included limited details on a patient with 'MTHFS gene mutation'. This individual had early speech delay, seizures beginning in infancy, ID, autistic features, recurrent infections and was found to have very low CSF 5-MTHF levels. [Details in p169 and table 10.6 - p173].
---
In a mouse model reported by Field et al (2011 - PMID: 22303332), Mthfs was disrupted through insertion of a gene trap vector between the first 2 exons. Heterozygous [Mthfs(gt/+)] mice were fertile and viable. Mthfs protein levels were slightly but not statistically significantly reduced in tissues measured. No homozygous embryos were recovered following intercrosses of heterozygous mice, suggesting that Mthfs is an essential gene. Mouse embryonic fibroblasts from heterozygous mice [Mthfs (gt/+)] exhibited reduced de novo purine biosynthesis, but did not exhibit altered de novo thymidylate biosynthesis. Plasma folate levels were altered in heterozygous mice on a standard (/control) diet.

[Please consider inclusion in other possibly relevant panels e.g. for metabolic disorders]
Sources: Literature
Intellectual disability v3.0 MTHFS Konstantinos Varvagiannis gene: MTHFS was added
gene: MTHFS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: MTHFS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: MTHFS were set to 30031689; 31844630; 22303332; https://doi.org/10.1007/978-3-642-40337-8_10
Phenotypes for gene: MTHFS were set to Neurodevelopmental disorder with microcephaly, epilepsy, and hypomyelination, 618367
Penetrance for gene: MTHFS were set to Complete
Review for gene: MTHFS was set to GREEN
Added comment: Biallelic pathogenic MTHFS variants cause Neurodevelopmental disorder with microcephaly, epilepsy, and hypomyelination (# 618367).

The gene encodes 5,10-Methenyltetrahydrofolate synthetase which catalyzes conversion of 5-formyltetrahydrofolate (5-FTHF or folinic acid) to 5,10-methenyltetrahydrofolate (5,10-MTHF).

At least 3 unrelated individuals have been reported. The phenotype appears to be relevant to both epilepsy and ID gene panels and the role of variants/the gene supported by enzymatic activity studies, 5-FTHF accumulation, 5,10-MTHF levels (low/low-normal), the role of folate metabolism pathway overall and some supporting (metabolic) evidence from the mouse model.
---
Rodan et al (2018 - PMID: 30031689) reported on 2 individuals both presenting with microcephaly, severe global DD, epilepsy, progressive spasticity and cerebral hypomyelination upon MRI imaging. Short stature was also feature in both.

The 1st patient was an 8-year-old male who following exome sequencing was found to harbor 2 missense variants each inherited from a carrier parent. (NM_006441.3:c.434G>A / p.R145Q and c.107T>C / p.L36P). A further AFG3L2 indel was not felt to fit with his phenotype (and the onset of the related disorder appears to occur later).

Previous investigations included extensive metabolic testing, CMA, Angelman syndrome methylation analysis, GFAP, POLG1, TYMP sequencing, mitochondrial genome analysis and an XL-ID gene panel (further suggesting relevance of this gene to the current panel) were all non-diagnostic.

CSF 5-MTHF levels were initially on the low-normal range, subsequently found to be decreased (upon folinic acid supplementation) and later normalized upon use of another regimen.

MTHFS activity was measured in control fibroblasts as well as fibroblasts from this individual, with the latter demonstrating no enzyme activity. Accumulation (30x elevation) of 5-FTHF (the substrate of MTHFS) was demonstrated in patient fibroblasts.

The 2nd patient was a 11-year-old male with similar features incl. global DD (standing/walking/single words at/after 4 years of age, limited vocabulary and articulation upon last examination).

Extensive metabolic work-up as well as genetic testing for an epilepsy panel, vanishing white matter disease gene panel, mitochondrial genome as well as specific gene sequencing (LAMA2, POLR3A, POLR3B) were all non-diagnostic. Trio exome revealed 2 MTHFS variants in trans configuration (c.484C>T / p.Q162X and c.434G>A / p.R145Q).
---
Romero et al (2019 - PMID: 31844630) reported on a 4-year-old female with congenital microcephaly, severe global DD (nonverbal/nonambulatory at the age of 4), spasticity, epilepsy and cerebral hypomyelination.

Extensive investigations prior to exome sequencing revealed macrocytic anemia, decreased CSF 5-MTHF and elevated neopterin, 2 CNVs of uncertain significance upon CMA with additional long ROH on chr15. Methylation studies were negative. The child was homozygous for c.220C>T / p.R74X (RefSeq is probably NM_006441.3. MTHFS lies on chr15. The parents were unrelated but came from the same town). There were no other candidate variants from the exome analysis.

Both articles discuss extensively the role of the folate metabolism pathway overall in nucleic acid synthesis, AA metabolism, neurotransmitter synthesis, methylation as well as 5-FTHF / 5,10-MTHF in particular in myelin stabilization and DNA synthesis (eg. according to Romero et al. a defect in MTHFS would impair myelin production and also lead to decreased myelin stability).
---
A book chapter cited by Rodan et al (in N. Blau et al. (eds.), Physician’s Guide to the Diagnosis, Treatment, and Follow-Up of Inherited Metabolic Diseases - DOI: 10.1007/978-3-642-40337-8_10) included limited details on a patient with 'MTHFS gene mutation'. This individual had early speech delay, seizures beginning in infancy, ID, autistic features, recurrent infections and was found to have very low CSF 5-MTHF levels. [Details in p169 and table 10.6 - p173].
---
In a mouse model reported by Field et al (2011 - PMID: 22303332), Mthfs was disrupted through insertion of a gene trap vector between the first 2 exons. Heterozygous [Mthfs(gt/+)] mice were fertile and viable. Mthfs protein levels were slightly but not statistically significantly reduced in tissues measured. No homozygous embryos were recovered following intercrosses of heterozygous mice, suggesting that Mthfs is an essential gene. Mouse embryonic fibroblasts from heterozygous mice [Mthfs (gt/+)] exhibited reduced de novo purine biosynthesis, but did not exhibit altered de novo thymidylate biosynthesis. Plasma folate levels were altered in heterozygous mice on a standard (/control) diet.
Sources: Literature
Intellectual disability v3.0 PUM1 Konstantinos Varvagiannis commented on gene: PUM1: 5 unrelated individuals with de novo pathogenic PUM1 variants have been reported in the literature. DD (5/5), ID (4/5 - relevant severity to the current panel), seizures (4/4 - absence/tonic-clonic, abnormal EEG) and variable other features (incl. facial dysmorphism, ataxia, cryptorchidism) appear to be part of the phenotype. 9 individuals with deletions spanning PUM1 and proximal genes presented similar features.

[1] PMID: 29474920 - Gennarino et al (2018)
[2] PMID: 30903679 - Bonnemason-Carrere et al (2019)
[3] PMID: 31859446 - Voet et al (2019) [with review of the literature]

SNVs in relevant individuals were identified by exome sequencing and were in all cases de novo.

Arg1147Trp was a recurrent variant reported in 3 unrelated subjects with ID and seizures (Refs 1,2,3 / NM_001020658.1:c.3439C>T). A nonsense variant was reported in an additional one with DD, ID, seizures and additional features (c.2509C>T / p.Arg837* - Ref3). One individual with a de novo missense variant (c.3416G>A / p.Arg1139Trp) with DD and ataxia, though without ID was reported in Ref1.

Details on 9 individuals with 0.3 - 5.6 Mb deletions spanning PUM1 and other genes are provided in Ref1. Features also included DD, ID, seizures, ataxia, etc.

Extensive initial investigations were reported for individuals in Refs 2 and 3 (various investigations incl. karyotype, SNP-array, targeted sequencing of OPHN1, KANSL1 or of a small panel of ID genes, biopsies and/or metabolic work-up) to rule out alternative causes. These only revealed a likely benign CNV and a GRIA3 SNV of uncertain significance in the case of an individual harboring the recurrent Arg1147Trp variant [Ref2].

Role of the gene (from OMIM):
Pumilio proteins, such as PUM1, negatively regulate gene expression by repressing translation of mRNAs to which they bind (Lee et al., 2016). A clinically significant PUM1 target is ataxin (ATXN1; 601556), mutation in which causes spinocerebellar ataxia-1 (SCA1; 601556).

Variant studies:
- Arg1147Trp was shown to be associated with normal PUM1 mRNA levels, but reduced (to ~43%) PUM1 protein levels in patient fibroblasts. ATXN1 mRNA and protein levels, as well as protein and/or mRNA levels of other PUM1 targets were shown to be increased (Ref1).
- In Ref1, in vitro transfection assays with wt or mt PUM1 were performed in HEK293T cells to evaluate repression of ATXN1 and E2F3. While overexpression of wt and Arg1147Trp were able to reduce ATXN1 and E2F3 levels, Arg1139Trp was not able to repress ATXN1 or E2F3.
- Upon overexpression in mouse hippocampal neurons, PUM1 missense mutations (among others Arg1139Trp and Arg1147Trp) were shown to alter neuronal morphology.

Overall haploinsufficiency is the proposed mechanism for the disorder for which the acronym PADDAS is used (Pumilio1-associated developmental disability, ataxia and seizure).

Milder mutations reducing PUM1 levels by 25% are associated with adult-onset ataxia without ID (PRCA or Pumilio1-related cerebellar ataxia) [Ref1].

Mouse models:
The role of PUM1 was first suggested in mouse models where Pum1 mutations were shown to lead to a SCA1-like phenotype (PMID cited : 12086639 - Watase et al 2002) further shown to be caused by increased Atxn1 mRNA and protein levels (PMID cited : 25768905 - Gennarino et al 2015).
The mouse model seems to recapitulate several of the features observed in affected individuals : Pum1 homozygous ko mice display among others hyperactivity, progressive cerebellar signs, spontaneous seizures as also observed in affected individuals (PMID cited : 25768905 - Gennarino et al 2015). Cryptorchidism was observed in 2 patients similar to testicular hypoplasia reported in Pum1 ko mice (PMID cited : 22342750 - Chen et al 2012).
- Heterozygous mice were evaluated in Ref1 with 69% or 75% exhibiting spontaneous seizures by the end of 30 or 35 wks respectively, with abnormal EEG activity already by 16 wks.

Additional individuals with PUM1 variants and a relevant phenotype of ID with or without seizures have been reported as part of the DDD study or as external submissions to Decipher and ClinVar :

https://decipher.sanger.ac.uk/search?q=PUM1#research-variants/results [ DDD4K.01387 participant ]
https://decipher.sanger.ac.uk/search?q=pum1#consented-patients/results [ external submission(s) ]
https://www.ncbi.nlm.nih.gov/clinvar/variation/431110/ [ splice-site variant in an individual with ID submitted prior to the 1st publication on the disorder ]
Intellectual disability v3.0 DLL1 Konstantinos Varvagiannis gene: DLL1 was added
gene: DLL1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DLL1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: DLL1 were set to 31353024
Phenotypes for gene: DLL1 were set to Global developmental delay; Intellectual disability; Morphological abnormality of the central nervous system; Seizures; Behavioral abnormality; Autism; Scoliosis
Penetrance for gene: DLL1 were set to unknown
Review for gene: DLL1 was set to GREEN
Added comment: Heterozygous DLL1 pathogenic variants cause Neurodevelopmental disorder with nonspecific brain abnormalities and with or without seizures (# 618709).

Fischer-Zirnsak et al (2019 - PMID: 31353024) reported on 15 affected individuals from 12 unrelated families.

Most common features included DD/ID (12/14), ASD (6/14 - belonging to 6 families) or other behavioral abnormalities, seizures (6/14 - from 6 unrelated families) and various brain MRI abnromalities. As commented by OMIM (based on the same ref) "Cognitive function ranges from severely impaired to the ability to attend schools with special assistance". Among other features, scoliosis was observed in 4. The authors could not identify a distinctive facial gestalt.

Variable initial investigations (where discussed/performed - also suggesting relevance to the current panel) included CMA, FMR1, FLNA, mitochondrial DNA analysis and metabolic work-up but had not revealed an alternative cause.

The DLL1 variants were identified by WES (with the exception of a 122-kb microdeletion spanning DLL1 and FAM120B detected by CMA). Nonsense, frame-shift, splice-site variants in positions predicted to result to NMD were identified in most. One individual was found to harbor a missense variant (NM_005618.3:c.536G>T / p.Cys179Phe) and another the aforementioned microdeletion.

The variant in several individuals had occurred as a de novo event. In 2 families, it was inherited from an also affected parent (an unaffected sib was non-carrier) while in 3 families parental studies were not possible/complete.

In frame insertion of 4 residues was demonstrated for a splice site variant, from LCLs of the corresponding individual. For another individual, material was unavailable for mRNA studies. The missense variant affected a cysteine (of the DSL domain) conserved in all Notch ligands while AA changes affecting the same position of JAG1 (another Notch ligand) have been described in patients with Alagille s.

Based on the variants identified and reports of deletions spanning DLL1 in the literature, haploinsufficiency is the proposed underlying mechanism. The gene has also a pLI of 1 and %HI of 4.65.

DLL1 encodes the Delta-like canonical Notch ligand 1. Notch signaling is an established pathway for brain morphogenesis. Previous in vivo and in vitro studies have demonstrated the role of DLL1 in CNS. The gene is highly expressed in neuronal precursor cells during embryogenesis. Expression of Dll1 (and other molecules of the Notch signalling pathway) in an oscillatory/sustained pattern and cell-cell interactions important for this pathway have been demonstrated to play a role in neuronal differentiation. [Most discussed by Fischer-Zirnsak et al with several refs provided / also Gray et al., 1999 - PMID: 10079256 & OMIM].

Animal models as summarized by the authors:
[Mouse] Loss of Dll1 in mice has been shown to increase neuronal differentiation, cause CNS hyperplasia and increased number of neurons (PMIDs cited: 9109488, 12397111, 20081190). Reduced Dll1 expression was associated with scoliosis and mild vertebral defects (cited PMIDs: 19562077, 14960495, 22484060 / among others Dll1 haploinsufficiency and dominant negative models studied). Scoliosis and vertebral segmentation defects were features in 4 and 1 individual, respectively in the cohort of 15.
[Zebrafish] Homozygous mutations in dlA, the zebrafish ortholog, disrupted the Delta-Notch signaling and led to patterning defects in the hindbrain and overproduction of neurons (cited: 15366005).

Please consider inclusion in other possibly relevant panels e.g. for ASD.
Sources: Literature
Intellectual disability v3.0 MN1 Konstantinos Varvagiannis gene: MN1 was added
gene: MN1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: MN1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: MN1 were set to 31834374; 31839203; 15870292
Phenotypes for gene: MN1 were set to Central hypotonia; Feeding difficulties; Global developmental delay; Intellectual disability; Hearing impairment; Abnormality of facial skeleton; Craniosynostosis; Abnormality of the face; Abnormality of the cerebellum; Abnormality of the corpus callosum; Polymicrogyria
Penetrance for gene: MN1 were set to Complete
Review for gene: MN1 was set to GREEN
Added comment: Two studies by Mak et al (2019 - PMID: 31834374 / Ref1) and Miyake et al (2019 - PMID: 31839203 / Ref2) provide sufficient evidence for heterozygous MN1 C-terminal truncating variants (predicted to escape NMD - localizing within the last nucleotides of exon 1 or in exon 2) being associated with a distinctive phenotype and DD and ID among the features.

Mak et al also discuss on the phenotype of individuals with variants causing N-terminal truncation or with MN1 deletions (discussed at the end of this review).

Overlapping features for C-terminal truncating variants included hypotonia, feeding difficulties, global DD and ID, hearing loss, cranial shape defects (/craniosynostosis in few), highly suggestive/distinctive facial features (eg. frontal bossing, hypertelorism, downslanting palpebral-fissures, shallow orbits, short upturned nose, low-set/posteriorly rotated/dysplastic ears, etc) and brain MRI abnormalities (eg. rhomboencephalosynapsis or cerebellar dysplasia, polymicrogyria, dysplastic CC).

The majority of the affected individuals were investigated by WES/WGS with a single one tested by targeted MN1 Sanger sequencing due to highly suggestive features. Variable previous investigations incl. CMA in several, gene panel testing (Rasopathies, hearing loss, craniofacial panels, FMR1, etc) and metabolic work were normal in most. In a single case a likely pathogenic ACSL4 also explained part of the phenotype (Ref2). In the majority of these individuals, the variant had occured as a de novo event. Two sibs had inherited the truncating variant from a milder affected mosaic parent. A parental sample was not available for an additional individual.

p.(Arg1295*) or NM_002430.2:c.3883C>T was a recurrent variant, seen in several individuals and in both studies.

Several lines of evidence are provided for the MN1 variants and the role of the gene including:
- For few individuals for whom cell lines were available, variants were shown to escape NMD by cDNA/RT-PCR/RNA-seq [Ref1 & 2].
- The gene has a high expression in fetal brain [Ref2 / fig S2]
- MN1 (* 156100 - MN1 protooncogene, transcriptional regulator) has been proposed to play a role in cell proliferation and shown to act as transcription cofactor (increasing its transactivation capacity in synergy with coactivators EP300 and RAC3) [Discussion and Refs provided in Ref2].
- In vitro studies suggested increased protein stability (upon transfection of wt/mut constructs in HEK293T cells), enhanced MN1 aggregation in nuclei (when wt/mut GFP-tagged MN1 was expressed in HeLa cells), increased inhibitory effect on cell growth (MG63 cells - role of MN1 in cell proliferation discussed above) and retained transactivation activity (upon transient MN1 overexpression of wt/mt MN1 in HEK293T cells) for the variants. These seem to support a gain-of-function effect for the C-terminal truncating variants [Ref2].
- The truncating variants are proposed to raise the fraction of Intrinsically disordered regions (IDRs = regions without fixed tertiary structure) probably contributing to the above effects [Ref2].
- Expression of FLAG-tagged MN1 wt/mut MN1 followed by immunoprecipitation and mass spectrometry analysis (mCAT-Hela cells), provided evidence that MN1 is involved in transcriptional regulation: a. through binding ZBTB24 and RING1 E3 ubiquitin ligase (with mutant MN1 displaying impaired interaction with ZBTB24 and no binding to RING1) and/or b. through interaction with DNA-binding transcription factors PBX1 and PKNOX1. Proper MN1 degradation is proposed to mediate precise transcriptional regulation. [Ref2]
- Transcriptome analysis in LCLs from an affected individual suggested dysregulation of genes relevant to neuronal development (eg. LAMP, ITGA, etc) and GO analysis suggested enrichment for pathways possibly linked to the observed phenotypes [Ref2].
- Discussed in both Refs1/2, homozygous Mn1-ko mice display abnormal skull bone development and die at/shortly after birth as a result of cleft palate. Heterozygous Mn1-ko mice display hypoplastic membranous bones of the cranial skeleton and cleft palate (CP), the latter with incomplete penetrance [Meester-Smoor et al 2005 - PMID: 15870292]. This is thus compatible with the cranial shape defects observed in C-terminal truncations (while CP has been reported in gene deletions, bifid uvula was reported once in C-terminal and N-terminal truncating variants, in the latter case with submucous CP).
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The phenotype of other MN1 variants is discussed by Mak et al (Ref1) :
- 3 individuals with MN1 N-terminal truncating variants (eg. Ser179*, Pro365Thrfs*120, Ser472*) presented speech delay, mild conductive hearing loss and facial features different from C-terminal truncations. None of these individuals had significant ID.
- Microdeletions: One individual (#27) with 130 kb deletion harboring only MN1, presented microcephaly, DD and ID and mildly dysmorphic facial features. Deletions spanning MN1 and other genes (eg a 1.17 Mb deletion in ind. #28) and relevant cases from the literature reviewed, with mild DD/ID, variable palatal defects and/or facial dysmorphisms (distinct from the C-terminal truncating variants) among the frequent findings.

[Please consider inclusion in other possibly relevant gene panels eg. for hearing loss (conductive/sensorineural in 16/20 reported by Mak et al) or craniosynostosis, etc].
Sources: Literature
Intellectual disability v3.0 CXorf56 Konstantinos Varvagiannis gene: CXorf56 was added
gene: CXorf56 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: CXorf56 was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for gene: CXorf56 were set to 29374277; 31822863
Phenotypes for gene: CXorf56 were set to ?Mental retardation, X-linked 107, 301013
Penetrance for gene: CXorf56 were set to unknown
Review for gene: CXorf56 was set to AMBER
Added comment: Verkerk et al (2018 - PMID: 29374277) reported on a three-generation family with five males and one female presenting mild non-syndromic ID. Segregation was compatible with X-linked inheritance.

Multipoint linkage analysis with XL microsatellite markers demonstrated a linkage peak at Xq23-24 with LOD score of 3.3. Haplotype analysis and utilization of additional STR markers allowed narrowing to a region of 7.6 Mb containing 92 genes.

WGS in 3 affected males (spanning 3 generations) and 1 unaffected male and application of relevant filters for rare protein affecting variants within this region - present only in affected but absent in the unaffected individual - suggested a CXorf56 frameshift variant in exon 2 [NM_022101.3:c.159_160insTA / p.(Asp54*)] as the only relevant for this phenotype.

Sanger sequencing was performed for 25 family members with all 5 affected males and 1 affected female harboring this insertion and 8 unaffected females (also) shown to be carriers.

X-chromosome inactivation studies demonstrated that unaffected females had skewed inactivation (76-93%) of the variant allele, while the single affected female did not have a skewed XCI pattern (54%).

In EBV-transformed lymphoblasts grown with/without cycloheximide, mRNA levels were shown to be significantly lower in the affected female compared to unaffected ones (and corrected upon treatment with cycloheximide). mRNA levels were also significantly lower in cell lines from an affected male, with expression showing significant increase after treatment with cycloheximide. These results confirmed that nonsense-mediated decay applies.

The variant was absent from ExAC (where CXorf56 has a pLI of 0.93) and 188 healthy Dutch individuals.

The function of CXorf56 is not known. The gene appears to be expressed in brain and a (broad) range of other tissues [ https://gtexportal.org/home/gene/CXORF56 ].

Immunostaining in 8-week old murine brain, showed that the protein is present in the nucleus and cell soma of most neurons in brain cortex and cerebellum. Upon transfection of human CXorf56 cDNA in mouse primary hippocampal neurons, the protein localized in the nucleus, dendrites (co-localizing with Map2) and dendritic spines. As the authors note, the latter may suggest a role in synaptic function.

Overexpression in HEK293T cells demonstrated predominantly nuclear localization.

Mouse : Based on MGI (and an article by Cox et al. - PMID: 20548051 / both cited by the authors) male chimeras hemizygous for a gene trapped allele have abnormal midbrain-hindbrain boundary morphology, decreased forebrain size, while a subset hemizygous for a different gene trapped allele show growth delay [ http://www.informatics.jax.org/marker/MGI:1924894 ].

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Rocha et al (2019 - PMID: 31822863) report on 9 affected individuals with mild to severe ID belonging to 3 unrelated families. Additional features in this cohort - observed in some - included abnormal reflexes, fine tremor, seizures (in 3), abnormal gait, etc.

In the 1st family, 3 males presented with (severe/severe/moderate) ID and 2 females with mild ID. Following a normal CMA and FMR1 testing, trio plus exome sequencing revealed a CXorf56 in-frame deletion [NM_022101.3:c.498_503del / p.(Glu167_Glu168del)]. Sanger sequencing in 9 members, confirmed presence of the variant in one unaffected mother, all her affected sons (2) and daughers(2) and an affected grandson and absence in 2 remaining unaffected daughters. Skewing of XCI was seen in blood cells from affected females (97 and 83%) while the unaffected mother had complete inactivation of the carrier X-chromosome. The authors commented that even minor reductions in CXorf56 (suggested by XCI in affected females) may be detrimental and/or that inactivation for this gene may be different than that of AR gene (which was studied instead) or in other tissues.

In family 2, an affected mother (with learning difficulties) and her 2 sons - the most severely affected presenting moderate ID - harbored a frameshift variant [c.303_304delCTinsACCC / p.(Phe101Leufs*20)].

A male with ID belonging to a 3rd family, for which no further information was available, was found to harbor the c.498_503del variant (also discussed above) as a de novo event.

It has been commented that individuals with Xq24 deletions spanning CXorf56 present with ID, although (all) such deletions reported in the literature also span the neighboring UBE2A gene, associated with Mental retardation, X-linked syndromic, Nascimento-type (MIM #300860).

-----

In OMIM, the CXorf56-related phenotype is ?Mental retardation, X-linked 107 (# 301013), based only on the report by Verkerk et al.

This gene is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc).

-----

Overall, CXorf56 can be considered for inclusion in the ID panel either with amber (function of the gene unknown, skewed XCI also in affected females in the 2nd reference) or with green rating (several individuals from 4 families, compatible segregation studies and females presenting a milder phenotype than males or unaffected, LOD score in the 1st report, studies confirming lower mRNA levels and NMD, gene expressed in human brain, expression in mouse brain cortex and cerebellum, evidence from transfection studies in mouse hippocampal neurons).

[Note : penetrance was here set to unknown / It was complete for males, incomplete for females].
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v3.0 UGP2 Konstantinos Varvagiannis gene: UGP2 was added
gene: UGP2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: UGP2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: UGP2 were set to 31820119
Phenotypes for gene: UGP2 were set to Seizures; Global developmental delay; Intellectual disability; Feeding difficulties; Abnormality of vision; Abnormality of the face
Penetrance for gene: UGP2 were set to Complete
Review for gene: UGP2 was set to GREEN
Added comment: Perenthaler et al. (2019 - PMID: 31820119) provide evidence that homozygosity for a variant abolishing the start codon of the UGP2 transcript (NM_001001521.1) encoding the predominant (short) protein isoform in brain, leads to a severe epileptic encephalopathy.

This variant (chr2:64083454A>G / NM_001001521.1:c.1A>G - p.?) is also predicted to result in a substitution of a methionine at position 12 by a valine of the longer UGP2 transcript (NM_006759.3:c.34A>G - p.Met12Val).

The 2 isoforms differ only by 11 amino acids at the N-terminal and are otherwise expected to be functionally equivalent.

The authors provide details on 22 individuals from 15 families (some of which consanguineous).

Features included intractable seizures (in all), absence of developmental milestones (in all), progressive microcephaly, visual impairment. The authors reported also presence of somewhat similar facial features. Some of these individuals passed away early.

Previous work-up in several of them (incl. SNP-array, gene panel testing and metabolic investigations) had not revealed any abnormality, apart from ROH in some individuals. In all cases, the homozygous UGP2 SNV was the only P/LP variant for the neurodevelopmental phenotype following exome/genome sequencing. Segregation studies in affected/unaffected family members were compatible.

Families came from the Netherlands (but mostly from) India, Pakistan and Iran. Presence of a region of homozygosity shared between individuals from different families suggested that the variant might represent a mutation that originated several generations ago (in the area of Balochistan). The variant is present 15x in gnomAD, only in heterozygous state (in Asian mostly, reported once in Ashkenazi Jewish or Europeans) [ https://gnomad.broadinstitute.org/variant/2-64083454-A-G ].

UGP2 encodes UDP-glucose pyrophosphorylase which is an essential enzyme in sugar metabolism, catalyzing conversion of glucose-1-phosphate to UDP-glucose. UDP-glucose, in turn, serves as precursor for production of glycogen by glycogen synthase.

The authors provide several lines of evidence for a the role of the gene in the CNS as well as for the deleterious effect of the specific variant :
- In patient fibroblasts total UGP2 levels were not signifficantly different compared to parent / control fibroblasts, the longer isoform being upregulated (and stable) when the shorter is missing. Immunocytochemistry demonstrated similar localization of UGP2 in the case of mutant or wt cells. Enzymatic activity (/capacity to produce UDP-glucose) was similar between homozygous mut, heterozygous and wt fibroblasts.
- In H9-derived neural stem cells, Western Blot, RT-PCR and qRT-PCR suggested that the short isoform is the predominant one. (In embryonic stem cells, or fibroblasts the ratio between short and long isoform was lower).
- Analysis of RNA-seq data from human fetal tissues suggested that the short isoform is the predominant in brain.
- UGP2 was detected upon immunohistochemistry in fetal brain tissues from first to third trimester of pregnancy while Western Blot confirmed preferential expression of the shorter isoform.
- Homozygous embryonic (ESC) or neural stem cells (NSC) for the variant (knock-in/KI) or for a frameshift variant (knock-out/KO) were generated. Study of NSCs demonstrated reduced total UGP2 protein expression upon Western Blot in the case of KI cells and depleted in KO ones. Transcriptome analysis did not show major transcriptome alterations in KI/KO ESCs compared to wt. In NSC KI/KO cells transcriptome alterations were observed compared to wt with upregulation among others of genes for synaptic processes and genes implicated in epilepsy.
- The absence of UGP2 was shown to result in reduced ability of KO/KI NSCs to produce UDP-glucose, reduced capacity to synthesize glycogen under hypoxia (rescued in the case of KO cells by overexpression of wt or long isoform), defects of protein glycosylation as well as in increased unfolded protein response (/susceptibility to ER stress). These alterations are commented to be possibly implicated in pathogenesis of epilepsy, progressive microcephaly, etc.
- A CRISPR-Cas9 zebrafish model leading with loss of ugp2a and hypomorphic ugp2b (the zebrafish homologs of UGP2) demonstrated abnormal behavior, reduced eye movements and increased frequency/duration of movements upon stimulation with a potent convulsant (suggestive of increased seizure susceptibility).
- UGP knockout in drosophila is lethal while flies compound heterozygous for hypomorphic alleles are viable but show a movement defects due to altered synaptogenesis secondary to glycosylation defects (cited PMID: 27466186).
- The authors make speculations as for the occurrence of a single variant (and not others) eg. absence of UGP2 (in the case of LoF variants affecting both isoforms) would possibly be incompatible with life, Met12Val being tolerable for the long transcript not affecting stability/enzymatic activity (which may not be the case for other substitutions affecting Met12), etc.
Sources: Literature
Intellectual disability v3.0 KAT8 Konstantinos Varvagiannis gene: KAT8 was added
gene: KAT8 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: KAT8 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: KAT8 were set to 31794431
Phenotypes for gene: KAT8 were set to Global developmental delay; Intellectual disability; Seizures; Abnormality of vision; Feeding difficulties; Abnormality of the cardiovascular system; Autism
Penetrance for gene: KAT8 were set to unknown
Review for gene: KAT8 was set to GREEN
Added comment: Heterozygous pathogenic missense KAT8 variants have been reported in individuals with DD, ID and epilepsy. Variants occurred as de novo events within the chromobarrel or the acetyltransferase domain and were all shown to affect H4K16 acetylation, as would be predicted by the gene's function (lysine acetyltransferase). Evidence from brain specific Kat8 knockout in mouse, supports the role of the gene in brain development. One similarly affected individual compound heterozygous for a nonsense and a missense variant (the former affecting subnuclear localization and the latter H4K16ac) was also reported, with carrier relatives being unaffected. Mutations in genes of the MSL/NSL complexes (with which KAT8 forms multisubunit complexes) or genes in other acetyltransferases of the same subfamily (MYST) as KAT8 cause neurodevelopmental disorders [Details provided below].
-----
Li et al. (2019 - PMID: 31794431) report on 8 unrelated individuals with heterozygous de novo pathogenic KAT8 variants, as well as an additional one compound heterozygous for a nonsense and a missense one.

Overlapping phenotype consisted of DD/ID (8/8), seizures/epilepsy (6/8), brain MRI anomalies as well as presence of variable facial dysmorphic features. Less frequent features included abnormal vision (5/8), feeding difficulties (3/8), cardiac anomalies (3/8), autism (in 1).

The (9th) individual with biallelic variants had similar phenotype of DD/ID, epilepsy, autism and dysmorphic facial features. Heterozygous parents and sister, the latter carrier for the missense variant, were all unaffected.

All individuals had undergone exome sequencing, while extensive other investigations for at least 7/9 had only revealed variants of uncertain significance/contribution to the phenotype or were normal.

KAT8 encodes lysine acetyltransferase 8, which acetylates histone H4 at lysine 16 (H4K16). It belongs to the MYST subfamily of lysine acetyltransferases, the other members of which include KAT6A, KAT6B (both involved in neurodevelopmental disorders) and KAT5.

KAT8 forms two stoichiometric multisubunitcomplexes, one with the MSL complex and the other with the NSL. Mutations in genes encoding for subunits of the NSL or MSL complex (eg. KANSL1 and MSL3) are associated with neurodevelopmental disorders.

Overall 6 missense SNVs were reported among the heterozygous patients, p.Tyr90Cys (NM_032188.2:c.269A>G) being a recurrent one seen in 3. The compound heterozygous patient had a missense (c.973C>T / p.Arg325Cys) and a nonsense variant (c.523A>T / p.Lys175*). All missense variants lied either in the chromobarrel domain or the acetyltransferase domain. Variants in the latter domain localized within the KAT8/Mof-specific region or - in the case of the compound heterozygous individual - within the acetyl-CoA binding motif.

FLAG-tagged KAT8 (either wt or for all missense SNVs) was transfected in HEK293 cells with vectors for HA-tagged MSL proteins. While the nonsense variant was difficult to express, missense SNVs were expressed to similar levels to wt, promoted expression of MSL proteins but resulted in defective H4K16 acetylation and to a lesser extent H4K5 acetylation. As a result all missense variants impaired acetylation. This was also the case for chromobarrel domain variants, while expression of a KAT8 lacking the chromobarrel domain confirmed its ability to form complex with the MSL proteins and the impairment of H4K16 acetylation.

The nonsense variant demonstrated abnormal subnuclear localization.

The mouse model provides extensive evidence for the involvement of KAT8 in cerebral development. Cerebrum-specific Kat8 knockout mice presented postnatal growth retardation, hyperactivity/irritability, pre-weaning lethality, and cerebral hypoplasia upon autopsy. Loss of Kat8 reduced the number of neural stem and progenitor cells available for embryonic cerebrocortical development, impaired cell proliferation and stimulated apoptosis. The article also provides additional evidence from mouse model.
Sources: Literature
Intellectual disability v3.0 RARS Konstantinos Varvagiannis gene: RARS was added
gene: RARS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: RARS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: RARS were set to 31814314; 28905880; 24777941
Phenotypes for gene: RARS were set to Cerebral hypomyelination; Global developmental delay; Intellectual disability; Seizures; Cerebral atrophy; Nystagmus; Ataxia; Feeding difficulties
Penetrance for gene: RARS were set to Complete
Review for gene: RARS was set to GREEN
Added comment: Biallelic pathogenic RARS1 variants cause Leukodystrophy, hypomyelinating, 9 (# 616140).

The current review was based primarily on PMID: 31814314 (Mendes et al, 2019) providing details on 20 affected individuals from 15 families. 5 of these patients were included in a previous publication (Wolf et al, 2014 - PMID: 24777941) sharing authors with this study.

Clinical presentation and severity can be highly variable. However, among the 15 patients of relevant age (5/20 deceased at an early age), ID was observed in 13 (in 6/13 mild-moderate, in 7/13 severe/profound). Epilepsy was reported in half (10/20) with seizures being refractory to treatment in most and the phenotype corresponding to an infantile epileptic encephalopathy. DD and seizures were the presenting feature in 7 and 5 patients respectively, while in other cases presenting features were less specific (eg. failure to thrive in 1/20, irritabilty in 2/20). As a result the gene appears to be relevant to both DD/ID and epilepsy panels.

RARS1 encodes the cytoplasmic arginyl-tRNA synthetase 1, which is a component of the aminoacyl-tRNA synthetase complex (OMIM and Wolf et al, 2014 - PMID: 24777941). Aminoacyl-tRNA synthetases catalyze the aminoacylation ('charging') of tRNA by (with) their cognate amino acid.

Utilisation of alternative initiation codons, from a single mRNA transcript, results in translation of a long and a short protein isoform (Zheng et al 2006 - PMID: 16430231). The long isoform is needed for the formation of the multi-synthetase complex (MSC), while the short is free in the cytoplasm and does not have any interaction with the MSC. The long isoform appears to be essential for protein synthesis (discussed with several refs provided in PMID: 28905880 - Nafisinia et al, 2017).

The role of variants has been supported in several patients by additional studies - among others :
[PMID 31814314] Impaired Arginyl-tRNA synthetase activity was demonstrated in fibroblasts from 3 patients. Activity was normal in one additional individual compound heterozygous for a variant affecting initiation codon and a missense one. Western blot however demonstrated presence mainly of the short protein isoform. The authors suggest that this isoform possibly contributed to enzymatic activity. The long isoform which is needed for the MSC complex was only represented by a faint band in the Western Blot of the same individual.
[PMID: 28905880] Using fibroblasts from an affected subject homozygous for a missense variant (NM_002887.3:c.5A>G / p.Asp2Gly) and controls, a 75% reduction of the long isoform was shown upon WB. The short isoform was present at similar levels. As the N-terminus (of the long isoform) mediates interaction with the MSC (and AIMP1), assembly of the latter was 99% reduced in patient fibroblasts. Proliferation of patient fibroblasts was significantly reduced when cultured in a medium with limited arginine, a finding which was thought to reflect inefficient protein synthesis.

Mutations in other genes encoding for aminoacyl-tRNA synthetases (eg. AARS1, VARS1) or scaffolding proteins of the multisynthetase complex (eg. AIMP1 and AIMP2) lead to neurodevelopmental disorders with overlapping phenotype [most genes rated green in both the ID and epilepsy panel].
Sources: Literature
Intellectual disability v3.0 SUZ12 Konstantinos Varvagiannis changed review comment from: ID can be a feature in individuals heterozygous for SUZ12 pathogenic variants. 13 affected individuals (from 12 families) have been reported:

[1] PMID 28229514 (Imagawa et al, 2017) : 1 individual
[2] PMID 30019515 (Imagawa et al, 2018) : 2 further unrelated subjects
[3] PMID 31736240 (Cyrus et al, 2019) : 10 additional subjects (from 9 families)

Reviewed by Cyrus et al, features observed in more than half of the (13) affected individuals included prenatal and/or postnatal overgrowth (in some only prenatal, others only postnatal, others did not manifest overgrowth at all), some suggestive facial features (eg. prominent forehead, hypertelorism, downslanting palpebral fissures, round face, broad/low nasal bridge), DD and ID (the latter in 7/13, in most cases mild), advanced bone age, musculoskeletal abnormalities and cryptorchidism. Less frequent features included brain MRI abnormalities (eg. CC hypoplasia/agenesis, etc.), umbilical hernias, respiratory abnormalities, cardiac anomalies (in one).

All were diagnosed with WES/WGS/panel testing, with few having additional findings upon this or prior testing (eg. CNVs/SNVs).

SUZ12 encodes one of the 4 core proteins of the PRC2 complex (the 3 other being encoded by EZH1/2, EED and RBBP4/7). The complex has a methyltransferase activity, catalyzing addition of up to 3 methyl groups on histone 3 at lysine residue 27 (H3K27), leading to chromatin compaction and further to gene silencing.

Mutations in genes encoding 2 other core components of the PRC2 complex - namely EZH2 and EED - cause Weaver and Cohen-Gibson syndrome with overlapping phenotype incl. overgrowth, advanced bone age, craniofacial features and DD/ID.

The SET domain of EZH1/2 and EED as well as the VEFS domain of SUZ12 are contributing to the catalytic activity.

SUZ12 variants reported to date include missense and pLoF variants (frameshift, nonsense, splice site ones) predicted to disrupt or eliminate the VEFS-box domain [almost all missense within this domain with the exception of one proximal to it (Arg535Gln) / pLoF causing truncation prior or within this domain (Arg654Ter might be an exception)] {NP_056170.2}.

Variants either occurred de novo or were inherited (~1/3), on some occasions from a mildly affected parent. Parental mosaicism has also been reported (eg. in ref1, and one or possibly two additional families in ref3).

Some preliminary assumptions on possible genotype-phenotype correlations (for overgrowth and ID related to missense/pLoF variants) are discussed in ref3.

SUZ12 is also be deleted in some patients with NF1 deletion (and a diagnosis of neurofibromatosis type 1). Deletion of SUZ12 has been proposed to contribute to the phenotype of these individuals (eg. overgrowth, cognitive development, facial features). [Discussed in ref1].

Functional studies have been carried out only in the first report (ref1) and demonstrated decreased trimethylation of H3K27 in the case of a missense variant. Overall a partial loss-of-function mechanism has been proposed for the variants.

Mouse models: A study by Pasini et al (PMID: 15385962) did not report phenotypic differences between wt and heterozygous Suz12 knockout mice (gene-trap vector) as for size, morphology and fertility. Total knockout resulted in embryonic lethality, significant growth retardation and several developmental defects. Loss of Suz12 was shown to result in absence of di- and tri-methylated H3K27 in the ko embryos. In another study cited (Miro et al - PMID: 19535498) heterozygous mice (replacement of exons 12-16 with a lacZ gene and neo cassette) displayed variable CNS defects with incomplete penetrance.

The role of the PRC2 complex and the phenotypes related to mutations in genes encoding its core components, are discussed in PMID: 31724824 (also by Cyrus et al, 2019).

SUZ12 is not associated with any phenotype in OMIM. In G2P it is included in the DD panel associated with Weaver-like overgrowth syndrome (disease confidence : confirmed). The gene is also included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
Sources: Literature; to: ID can be a feature in individuals heterozygous for SUZ12 pathogenic variants. 13 affected individuals (from 12 families) have been reported:

[1] PMID 28229514 (Imagawa et al, 2017) : 1 individual
[2] PMID 30019515 (Imagawa et al, 2018) : 2 further unrelated subjects
[3] PMID 31736240 (Cyrus et al, 2019) : 10 additional subjects (from 9 families)

Reviewed by Cyrus et al, features observed in more than half of the (13) affected individuals included prenatal and/or postnatal overgrowth (in some only prenatal, others only postnatal, others did not manifest overgrowth at all), some suggestive facial features (eg. prominent forehead, hypertelorism, downslanting palpebral fissures, round face, broad/low nasal bridge), DD and ID (the latter in 7/13, in most cases mild), advanced bone age, musculoskeletal abnormalities and cryptorchidism. Less frequent features included brain MRI abnormalities (eg. CC hypoplasia/agenesis, etc.), umbilical hernias, respiratory abnormalities, cardiac anomalies (in one).

All were diagnosed with WES/WGS/panel testing, with few having additional findings upon this or prior testing (eg. CNVs/SNVs).

SUZ12 encodes one of the 4 core proteins of the PRC2 complex (the 3 other being encoded by EZH1/2, EED and RBBP4/7). The complex has a methyltransferase activity, catalyzing addition of up to 3 methyl groups on histone 3 at lysine residue 27 (H3K27), leading to chromatin compaction and further to gene silencing.

Mutations in genes encoding 2 other core components of the PRC2 complex - namely EZH2 and EED - cause Weaver and Cohen-Gibson syndrome with overlapping phenotype incl. overgrowth, advanced bone age, craniofacial features and DD/ID.

The SET domain of EZH1/2 and EED as well as the VEFS domain of SUZ12 are contributing to the catalytic activity.

SUZ12 variants reported to date include missense and pLoF variants (frameshift, nonsense, splice site ones) predicted to disrupt or eliminate the VEFS-box domain [almost all missense within this domain with the exception of one proximal to it (Arg535Gln) / pLoF causing truncation prior or within this domain (Arg654Ter might be an exception)] {NP_056170.2}.

Variants either occurred de novo or were inherited (~1/3), on some occasions from a mildly affected parent. Parental mosaicism has also been reported (eg. in ref1, and one or possibly two additional families in ref3).

Some preliminary assumptions on possible genotype-phenotype correlations (for overgrowth and ID related to missense/pLoF variants) are discussed in ref3.

SUZ12 may also be deleted in some patients with NF1 deletion (and a diagnosis of neurofibromatosis type 1). Deletion of SUZ12 has been proposed to contribute to the phenotype of these individuals (eg. overgrowth, cognitive development, facial features). [Discussed in ref1].

Functional studies have been carried out only in the first report (ref1) and demonstrated decreased trimethylation of H3K27 in the case of a missense variant. Overall a partial loss-of-function mechanism has been proposed for the variants.

Mouse models: A study by Pasini et al (PMID: 15385962) did not report phenotypic differences between wt and heterozygous Suz12 knockout mice (gene-trap vector) as for size, morphology and fertility. Total knockout resulted in embryonic lethality, significant growth retardation and several developmental defects. Loss of Suz12 was shown to result in absence of di- and tri-methylated H3K27 in the ko embryos. In another study cited (Miro et al - PMID: 19535498) heterozygous mice (replacement of exons 12-16 with a lacZ gene and neo cassette) displayed variable CNS defects with incomplete penetrance.

The role of the PRC2 complex and the phenotypes related to mutations in genes encoding its core components, are discussed in PMID: 31724824 (also by Cyrus et al, 2019).

SUZ12 is not associated with any phenotype in OMIM. In G2P it is included in the DD panel associated with Weaver-like overgrowth syndrome (disease confidence : confirmed). The gene is also included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
Sources: Literature
Intellectual disability v3.0 SUZ12 Konstantinos Varvagiannis changed review comment from: ID can be a feature in individuals heterozygous for SUZ12 pathogenic variants. 13 affected individuals (from 12 families) have been reported:

[1] PMID 28229514 (Imagawa et al, 2017) : 1 individual
[2] PMID 30019515 (Imagawa et al, 2018) : 2 further unrelated subjects
[3] PMID 31736240 (Cyrus et al, 2019) : 10 newly diagnosed subjects (from 9 families)

Reviewed by Cyrus et al, features observed in more than half of the (13) affected individuals included prenatal and/or postnatal overgrowth (in some only prenatal, others only postnatal, others did not manifest overgrowth at all), some suggestive facial features (eg. prominent forehead, hypertelorism, downslanting palpebral fissures, round face, broad/low nasal bridge), DD and ID (the latter in 7/13, in most cases mild), advanced bone age, musculoskeletal abnormalities and cryptorchidism. Less frequent features included brain MRI abnormalities (eg. CC hypoplasia/agenesis, etc.), umbilical hernias, respiratory abnormalities, cardiac anomalies (in one).

All were diagnosed with WES/WGS/panel testing, with few having additional findings upon this or prior testing (eg. CNVs/SNVs).

SUZ12 encodes one of the 4 core proteins of the PRC2 complex (the 3 other being encoded by EZH1/2, EED and RBBP4/7). The complex has a methyltransferase activity, catalyzing addition of up to 3 methyl groups on histone 3 at lysine residue 27 (H3K27), leading to chromatin compaction and further to gene silencing.

Mutations in genes encoding 2 other core components of the PRC2 complex - namely EZH2 and EED - cause Weaver and Cohen-Gibson syndrome with overlapping phenotype incl. overgrowth, advanced bone age, craniofacial features and DD/ID.

The SET domain of EZH1/2 and EED as well as the VEFS domain of SUZ12 are contributing to the catalytic activity.

SUZ12 variants reported to date include missense and pLoF variants (frameshift, nonsense, splice site ones) predicted to disrupt or eliminate the VEFS-box domain [almost all missense within this domain with the exception of one proximal to it (Arg535Gln) / pLoF causing truncation prior or within this domain (Arg654Ter might be an exception)] {NP_056170.2}.

Variants either occurred de novo or were inherited (~1/3), on some occasions from a mildly affected parent. Parental mosaicism has also been reported (eg. in ref1, and one or possibly two additional families in ref3).

Some preliminary assumptions on possible genotype-phenotype correlations (for overgrowth and ID related to missense/pLoF variants) are discussed in ref3.

SUZ12 is also be deleted in some patients with NF1 deletion (and a diagnosis of neurofibromatosis type 1). Deletion of SUZ12 has been proposed to contribute to the phenotype of these individuals (eg. overgrowth, cognitive development, facial features). [Discussed in ref1].

Functional studies have been carried out only in the first report (ref1) and demonstrated decreased trimethylation of H3K27 in the case of a missense variant. Overall a partial loss-of-function mechanism has been proposed for the variants.

Mouse models: An study by Pasini et al (PMID: 15385962) did not report phenotypic differences between wt and heterozygous Suz12 knockout mice (gene-trap vector) as for size, morphology and fertility. Total knockout resulted in embryonic lethality, significant growth retardation and several developmental defects. Loss of Suz12 was shown to result in absence of di- and tri-methylated H3K27 in the ko embryos. In another study cited (Miro et al - PMID: 19535498) heterozygous mice (replacement of exons 12-16 with a lacZ gene and neo cassette) displayed variable CNS defects with incomplete penetrance.

The role of the PRC2 complex and the phenotypes related to mutations in genes encoding its core components, are discussed in PMID: 31724824 (also by Cyrus et al, 2019).

SUZ12 is not associated with any phenotype in OMIM. In G2P it is included in the DD panel associated with Weaver-like overgrowth syndrome (disease confidence : confirmed). The gene is also included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
Sources: Literature; to: ID can be a feature in individuals heterozygous for SUZ12 pathogenic variants. 13 affected individuals (from 12 families) have been reported:

[1] PMID 28229514 (Imagawa et al, 2017) : 1 individual
[2] PMID 30019515 (Imagawa et al, 2018) : 2 further unrelated subjects
[3] PMID 31736240 (Cyrus et al, 2019) : 10 additional subjects (from 9 families)

Reviewed by Cyrus et al, features observed in more than half of the (13) affected individuals included prenatal and/or postnatal overgrowth (in some only prenatal, others only postnatal, others did not manifest overgrowth at all), some suggestive facial features (eg. prominent forehead, hypertelorism, downslanting palpebral fissures, round face, broad/low nasal bridge), DD and ID (the latter in 7/13, in most cases mild), advanced bone age, musculoskeletal abnormalities and cryptorchidism. Less frequent features included brain MRI abnormalities (eg. CC hypoplasia/agenesis, etc.), umbilical hernias, respiratory abnormalities, cardiac anomalies (in one).

All were diagnosed with WES/WGS/panel testing, with few having additional findings upon this or prior testing (eg. CNVs/SNVs).

SUZ12 encodes one of the 4 core proteins of the PRC2 complex (the 3 other being encoded by EZH1/2, EED and RBBP4/7). The complex has a methyltransferase activity, catalyzing addition of up to 3 methyl groups on histone 3 at lysine residue 27 (H3K27), leading to chromatin compaction and further to gene silencing.

Mutations in genes encoding 2 other core components of the PRC2 complex - namely EZH2 and EED - cause Weaver and Cohen-Gibson syndrome with overlapping phenotype incl. overgrowth, advanced bone age, craniofacial features and DD/ID.

The SET domain of EZH1/2 and EED as well as the VEFS domain of SUZ12 are contributing to the catalytic activity.

SUZ12 variants reported to date include missense and pLoF variants (frameshift, nonsense, splice site ones) predicted to disrupt or eliminate the VEFS-box domain [almost all missense within this domain with the exception of one proximal to it (Arg535Gln) / pLoF causing truncation prior or within this domain (Arg654Ter might be an exception)] {NP_056170.2}.

Variants either occurred de novo or were inherited (~1/3), on some occasions from a mildly affected parent. Parental mosaicism has also been reported (eg. in ref1, and one or possibly two additional families in ref3).

Some preliminary assumptions on possible genotype-phenotype correlations (for overgrowth and ID related to missense/pLoF variants) are discussed in ref3.

SUZ12 is also be deleted in some patients with NF1 deletion (and a diagnosis of neurofibromatosis type 1). Deletion of SUZ12 has been proposed to contribute to the phenotype of these individuals (eg. overgrowth, cognitive development, facial features). [Discussed in ref1].

Functional studies have been carried out only in the first report (ref1) and demonstrated decreased trimethylation of H3K27 in the case of a missense variant. Overall a partial loss-of-function mechanism has been proposed for the variants.

Mouse models: A study by Pasini et al (PMID: 15385962) did not report phenotypic differences between wt and heterozygous Suz12 knockout mice (gene-trap vector) as for size, morphology and fertility. Total knockout resulted in embryonic lethality, significant growth retardation and several developmental defects. Loss of Suz12 was shown to result in absence of di- and tri-methylated H3K27 in the ko embryos. In another study cited (Miro et al - PMID: 19535498) heterozygous mice (replacement of exons 12-16 with a lacZ gene and neo cassette) displayed variable CNS defects with incomplete penetrance.

The role of the PRC2 complex and the phenotypes related to mutations in genes encoding its core components, are discussed in PMID: 31724824 (also by Cyrus et al, 2019).

SUZ12 is not associated with any phenotype in OMIM. In G2P it is included in the DD panel associated with Weaver-like overgrowth syndrome (disease confidence : confirmed). The gene is also included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
Sources: Literature
Intellectual disability v3.0 SUZ12 Konstantinos Varvagiannis gene: SUZ12 was added
gene: SUZ12 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SUZ12 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: SUZ12 were set to 28229514; 30019515; 31736240; 15385962; 19535498; 31724824
Phenotypes for gene: SUZ12 were set to Overgrowth; Global developmental delay; Intellectual disability; Accelerated skeletal maturation; Abnormality of the skeletal system; Abnormality of the genitourinary system; Abnormality of the corpus callosum; Abnormality of the respiratory system; Abnormality of the abdominal wall
Penetrance for gene: SUZ12 were set to unknown
Review for gene: SUZ12 was set to GREEN
Added comment: ID can be a feature in individuals heterozygous for SUZ12 pathogenic variants. 13 affected individuals (from 12 families) have been reported:

[1] PMID 28229514 (Imagawa et al, 2017) : 1 individual
[2] PMID 30019515 (Imagawa et al, 2018) : 2 further unrelated subjects
[3] PMID 31736240 (Cyrus et al, 2019) : 10 newly diagnosed subjects (from 9 families)

Reviewed by Cyrus et al, features observed in more than half of the (13) affected individuals included prenatal and/or postnatal overgrowth (in some only prenatal, others only postnatal, others did not manifest overgrowth at all), some suggestive facial features (eg. prominent forehead, hypertelorism, downslanting palpebral fissures, round face, broad/low nasal bridge), DD and ID (the latter in 7/13, in most cases mild), advanced bone age, musculoskeletal abnormalities and cryptorchidism. Less frequent features included brain MRI abnormalities (eg. CC hypoplasia/agenesis, etc.), umbilical hernias, respiratory abnormalities, cardiac anomalies (in one).

All were diagnosed with WES/WGS/panel testing, with few having additional findings upon this or prior testing (eg. CNVs/SNVs).

SUZ12 encodes one of the 4 core proteins of the PRC2 complex (the 3 other being encoded by EZH1/2, EED and RBBP4/7). The complex has a methyltransferase activity, catalyzing addition of up to 3 methyl groups on histone 3 at lysine residue 27 (H3K27), leading to chromatin compaction and further to gene silencing.

Mutations in genes encoding 2 other core components of the PRC2 complex - namely EZH2 and EED - cause Weaver and Cohen-Gibson syndrome with overlapping phenotype incl. overgrowth, advanced bone age, craniofacial features and DD/ID.

The SET domain of EZH1/2 and EED as well as the VEFS domain of SUZ12 are contributing to the catalytic activity.

SUZ12 variants reported to date include missense and pLoF variants (frameshift, nonsense, splice site ones) predicted to disrupt or eliminate the VEFS-box domain [almost all missense within this domain with the exception of one proximal to it (Arg535Gln) / pLoF causing truncation prior or within this domain (Arg654Ter might be an exception)] {NP_056170.2}.

Variants either occurred de novo or were inherited (~1/3), on some occasions from a mildly affected parent. Parental mosaicism has also been reported (eg. in ref1, and one or possibly two additional families in ref3).

Some preliminary assumptions on possible genotype-phenotype correlations (for overgrowth and ID related to missense/pLoF variants) are discussed in ref3.

SUZ12 is also be deleted in some patients with NF1 deletion (and a diagnosis of neurofibromatosis type 1). Deletion of SUZ12 has been proposed to contribute to the phenotype of these individuals (eg. overgrowth, cognitive development, facial features). [Discussed in ref1].

Functional studies have been carried out only in the first report (ref1) and demonstrated decreased trimethylation of H3K27 in the case of a missense variant. Overall a partial loss-of-function mechanism has been proposed for the variants.

Mouse models: An study by Pasini et al (PMID: 15385962) did not report phenotypic differences between wt and heterozygous Suz12 knockout mice (gene-trap vector) as for size, morphology and fertility. Total knockout resulted in embryonic lethality, significant growth retardation and several developmental defects. Loss of Suz12 was shown to result in absence of di- and tri-methylated H3K27 in the ko embryos. In another study cited (Miro et al - PMID: 19535498) heterozygous mice (replacement of exons 12-16 with a lacZ gene and neo cassette) displayed variable CNS defects with incomplete penetrance.

The role of the PRC2 complex and the phenotypes related to mutations in genes encoding its core components, are discussed in PMID: 31724824 (also by Cyrus et al, 2019).

SUZ12 is not associated with any phenotype in OMIM. In G2P it is included in the DD panel associated with Weaver-like overgrowth syndrome (disease confidence : confirmed). The gene is also included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
Sources: Literature
Intellectual disability v2.1143 AFF3 Konstantinos Varvagiannis changed review comment from: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb affecting only AFF3 (LAF4) and removing also this sequence.

The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy].

9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13.

AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development.

Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot.

Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study].

Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects.

Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant.

Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3.
----
Shimizu et al. (8/2019 - PMID: 31388108) describe an additional individual with de novo AFF3 missense variant. The phenotype overlaps with that summarized by Voisin et al. incl. mesomelic dysplasia with additional skeletal anomalies, bilateral kidney hypoplasia and severe DD at the age of 2.5 years. Seizures and pulmonary problems were not observed. Although a different RefSeq is used the variant is among those also reported by Voisin et al. [NM_002285.2:c.697G>A (p.Ala233Thr) corresponding to NM_001025108.1:c.772G>A (p.Ala258Thr)].
----
In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM.
Some diagnostic laboratories include AFF3 in their ID panel (eg. among the many co-authors' affiliations GeneDx and Victorian Clinical Genetics - which was already listed as source for AFF3 in the current panel).
----
As a result this gene can be considered for upgrade to green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article).

[Review modified to add additional reference/case report]; to: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb deletion affecting only AFF3 (LAF4) and removing also this sequence.

The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy].

9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13.

AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development.

Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot.

Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study].

Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects.

Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant.

Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3.
----
Shimizu et al. (8/2019 - PMID: 31388108) describe an additional individual with de novo AFF3 missense variant. The phenotype overlaps with that summarized by Voisin et al. incl. mesomelic dysplasia with additional skeletal anomalies, bilateral kidney hypoplasia and severe DD at the age of 2.5 years. Seizures and pulmonary problems were not observed. Although a different RefSeq is used the variant is among those also reported by Voisin et al. [NM_002285.2:c.697G>A (p.Ala233Thr) corresponding to NM_001025108.1:c.772G>A (p.Ala258Thr)].
----
In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM.
Some diagnostic laboratories include AFF3 in their ID panel (eg. among the many co-authors' affiliations GeneDx and Victorian Clinical Genetics - which was already listed as source for AFF3 in the current panel).
----
As a result this gene can be considered for upgrade to green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article).

[Review modified to add additional reference/case report]
Intellectual disability v2.1140 CSF2RA Rebecca Foulger Mode of inheritance for gene: CSF2RA was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to BIALLELIC, autosomal or pseudoautosomal
Intellectual disability v2.1135 TRAPPC4 Konstantinos Varvagiannis gene: TRAPPC4 was added
gene: TRAPPC4 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TRAPPC4 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TRAPPC4 were set to 31794024
Phenotypes for gene: TRAPPC4 were set to Feeding difficulties; Progressive microcephaly; Intellectual disability; Seizures; Spastic tetraparesis; Abnormality of the face; Scoliosis; Cortical visual impairment; Hearing impairment
Penetrance for gene: TRAPPC4 were set to Complete
Review for gene: TRAPPC4 was set to GREEN
Added comment: Van Bergen et al. (2019 - PMID: 31794024) report on 7 affected individuals from 3 famillies (only 1 of which consanguineous), all homozygous for a TRAPPC4 splicing variant.

Overlapping features included feeding difficulties, progressive microcephaly, severe to profound developmental disability (7/7 - DD also prior to the onset of seizures / regression also reported in 3), epilepsy (7/7 - onset in the first year), spastic quadriparesis. Other findings in some/few incl. scoliosis, cortical visual and hearing impairment. Some facial features were shared (eg. bitemporal narrowing, long philtrum, open mouth with thin tented upper lip, pointed chin, etc). Brain imaging demonstrated abnormalities in those performed (among others cerebral with/without cerebellar atrophy).

Work-up prior to exome sequencing was normal (highly variable incl. metabolic testing, CMA, MECP2, CDKL5, mitochondrial depletion studies, etc).

Exome of affected individuals (and parents +/- affected sibs in some families) revealed a homozygous TRAPPC4 splicing variant [NM_016146.5:c.454+3A>G / chr11:g.118890966A>G (hg19)]. Sanger sequencing confirmed variant in affecteds, heterozygosity in parents and compatible genotypes with disease status in sibs/other members.

Families were of Caucasian/Turkish and French-Canadian ethnicities. SNP array to compare haplotypes between affecteds in 2 families did not reveal a shared haplotype (/founder effect) and the variant is present in gnomAD (68/281054 - no hmz) in many populations (European/Asian/African/Latino) [https://gnomad.broadinstitute.org/variant/11-118890966-A-G].

mRNA studies in fibroblasts from an affected individual confirmed the splicing defect (2 RT-PCR products corresponding to wt and a shorter due to skipping of exon 3, the latter further confirmed by Sanger sequencing. The shorter transcript is not present in controls). qPCR revealed that the normal transript in patient fibroblasts was present at 6% of the level observed in control fibroblasts (or 54% in the case of a heterozygote parent compared to controls).

Western blot in patient fibroblasts, revealed presence of full-length protein in significantly reduced levels compared to fibroblasts from carrier parents or controls. There was no band using an antibody targeting the N-terminal region of the protein prior to exon 3, suggesting that NMD applies (skipping of ex3 is also predicted to lead to frameshift).

TRAPPC4 encodes one of the core proteins of the TRAPP complex. Use of different accessory proteins leads to formation of 2 distinct complexes (TRAPPII / III). The complex has an important role in intracellular trafficking. Both TRAPPII & TRAPPIII have a function in the secretory pathway, while complex III has a role also in autophagy. Core proteins are important for the complex stability. The TRAPP complex serves as a GEF for Ypt/Rab GTPases [several refs in article].

Mutations in genes for other proteins of the complex lead to neurodevelopmental disorders with associated ID ('TRAPPopathies' used by the authors / TRAPPC12, C6B, C9 green in the current panel).

Western blot suggested that levels of other TRAPP subunits (TRAPPC2 or C12) under denaturing conditions, although PAGE/size exclusion chromatography suggested that the levels of fully-assembled TRAPP complexes were lower in affected individuals.

Studies in patient fibroblasts showed a secretory defect (between ER, Golgi and the plasma membrane) which was restored upon lentiviral transduction with wt TRAPPC4 construct. Basal and starvation-induced autophagy were also impaired in patient fibroblasts (increased LC3 marker and LC3-positive structures / impaired co-localization with lysosomes) partly due to defective autophagosome formation (/sealing).

TRAPPC4 is the human orthologue of the yeast Trs23. In a yeast model of reduced Trs23 (due to temperature instability) the authors demonstrated impaired assembly of the TRAPP core. The yeast model recapitulated the autophagy as well as well as the secretory defect observed in patient fibroblasts.
Sources: Literature
Intellectual disability v2.1135 SNX27 Konstantinos Varvagiannis gene: SNX27 was added
gene: SNX27 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SNX27 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: SNX27 were set to 25894286; 31721175; 21300787; 23524343
Phenotypes for gene: SNX27 were set to Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures
Penetrance for gene: SNX27 were set to Complete
Review for gene: SNX27 was set to GREEN
gene: SNX27 was marked as current diagnostic
Added comment: Evidence from 2 publications suggests that DD, ID and seizures are part of the phenotype of individuals with biallelic SNX27 pathogenic variants :
---------
Damseh, Danson et al (2015 - PMID: 25894286) first reported on a consanguineous family with 4 affected sibs, homozygous for an SNX27 pathogenic variant. Features incl. hypotonia soon after birth, failure to thrive, severely delayed psychomotor development with no milestone acquisition, occurrence of myoclonic seizures with 3 individuals deceased early. Exome sequencing in one revealed a few candidate variants, with an SNX27 frameshift one [NM_030918.6:c.515_516del - p.(His172Argfs*6) / absent from ExAC] being the only retained following Sanger segregation studies. Using fibroblasts from an affected individual, Western blot with an antibody which would also bind prior to the truncation site, was consistent with dramatically reduced/absent SNX27 truncated mutant protein. Protein levels of VPS35, a component of the retromer responsible for direct cargo binding (not mediated by a cargo adaptor as SNX27), were normal.
---------
Parente et al (2019 - PMID: 31721175) reported on a 13-year-old male with motor and language delay, ADHD, ID (kindergarten academic level at the age of 13) and seizures with onset at the age of 9 years (GTC, with abnormal EEG and postical SV tachycardia). Variable physical findings were reported. White matter hyperintesities were noted upon initial brain MRI (but were less marked in subsequent ones). Initial genetic testing (Alexander's disease, CMA, FMR1) was normal. Exome revealed compound heterozygosity for 2 SNX27 variants (NM_030918.5/NM_001330723.1 both apply c.510C>G - p.Tyr170* and c.1295G>A - p.Cys432Tyr) each inherited from healthy carrier parents. There were no other potentially causative variants. A parental history of - isolated - late onset seizures was reported (so this individual may not be considered for the seizure phenotype here).

The authors also reported on a further 31-year old affected male. This individual had infantile hypotonia, poor eye contact with subsequent significant DD, seizures (febrile/afebrile T-C with onset at the age of 14m) and ID estimated in the severe range. Variable - though somewhat different - physical findings were reported. Initial work-up included basic metabolic testing, standard karyotype, FISH for 15q11 and subtelomeric regions and PHF6 genetic testing - all normal. Exome (and subsequent Sanger confirmation/parental studies) revealed compound heterozygosity for a missense and a frameshift variant (c.989G>A / p.Arg330His and c.782dupT / p.Leu262Profs*6 same in NM_001330723.1, NM_030918.6).
---------
SNX27 encodes sorting nexin 27, a cargo adaptor for the retromer. The latter is a multi-protein complex essential for regulating the retrieval and recycling of transmembrane cargos from endosomes to the trans-Golgi network or the plasma membrane [Lucas et al 2016 - PMID: 27889239 / McNally et al 2018 - PMID: 30072228].

As summarized by Parente et al, the encoded protein by regulating composition of the cell surface influences several processes eg. neuronal excitability, synaptic plasticity, Wnt signaling etc. It has been shown to interact with surface receptors and their ligands including GIRK channels, 5-HT4, ionotropic glutamate receptors (incl. NMDA- and AMPA-type receptors) and mGluR5 [several refs. provided].

Knockout of Snx27 in mice resulted in embryonic lethality (16% hmz of the 25% expected), severe postnatal growth retardation and death within the first 3 weeks. Snx27(+/-) mice have normal neuroanatomy but exhibit cognitive deficits (in learning and memory) and defects in synaptic function/plasticity with reduced amounts of NMDA and AMPA receptors (Cai et al - PMID: 21300787, Wang et al - PMID: 23524343).
---------
The gene is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx) and a current primary ID gene in SysID. There is no associated phenotype in OMIM/G2P.
Sources: Literature
Intellectual disability v2.1135 SLC5A6 Konstantinos Varvagiannis changed review comment from: SLC5A6 encodes the sodium dependent multivitamin transporter (SMVT), a transporter of biotin, pantothenate and lipoate. The transporter has a major role in vitamin uptake in the digestive system (among others is the sole transporter for intestinal uptake of biotin which is not synthesized and but must be obtained from exogenous sources) as well as transport across the blood-brain barrier (SMVT being responsible for 89% of biotin transport) [several refs provided by Subramanian et al and Byrne et al].

4 affected individuals from 3 families have been reported.

Subramanian et al (2017 - PMID: 27904971) et al reported on a girl with feeding difficulties and failure to thrive (requiring nasogastric tube placement), microcephaly, DD (at 15m developmental age corresponding to 6m with features suggestive of spastic cerebral palsy), occurrence of multiple infections, osteoporosis and pathologic bone fractures. MRIs suggested brain atrophy, thin CC and hypoplasia of the pons. Metabolic (AA, OA) investigations and array-CGH were normal. Whole exome sequencing revealed presence of a missense (Arg123Leu - RefSeq not provided) and a nonsense (Arg94Ter) SLC5A6 variant. Serum biotin was normal although - at the time - the child was on parenteral and G-T nutrition. Following administration of biotin, pantothenic acid and lipoic acid the child demonstrated among others improved motor and verbal skills, head growth and normalization of immunoglobulin levels. Transfection of mutants in human derived intestinal HuTu-80 cells and brain U87 cells was carried out and a 3H-biotin assay showed no induction in biotin uptake confirming impaired functionality of the transporter. While wt protein displayed normal expression/membrane localization, Arg94Ter was poorly expressed with ectopic localization (cytoplasm). Arg123Leu was retained predominantly intracellularly, probably in the ER as was further supported by colocalization with DsRed-ER. Evidence from the literature is provided that deficiencies of the specific vitamins explain the clinical features (DD, microcephaly, immunological defect, osteopenia, etc).

Schwantje et al (2019 - PMID: 31392107) described a girl with severe feeding problems, vomiting with blood (suspected Mallory-Weiss syndrome), poor weight gain and delayed gross motor development. The child presented an episode of gastroenteritis associated with reduced consciousness, circulatory insufficiency and metabolic derangement (hypoglycemia, severe metabolic acidosis, hyperammonemia, mild lactate elevation, ketonuria). Investigations some months prior to the admission (?) were suggestive of a metabolic disorder due to elevated plasma C3-carnitine, C5-OH-carnitine and elevated urinary excretion of 3-OH-isovaleric acid (biotinidase deficiency was considered in the DD but enzymatic activity was only marginally decreased). Biotin supplementation was initiated. Trio-exome sequencing (at 3yrs) demonstrated compound heterozygosity for 2 frameshift variants [NM_021095.2:c.422_423del / p.(Val141Alafs*34) and c.1865_1866del]. Following this result, increase of biotin supplementation and introduction of pantothenic acid, GI symptoms (incl. chronic diarrhea) resolved and the child displayed improved appetite and growth, yet a stable motor delay. The authors cite previous studies of conditional ko mice, displaying intestinal mucosal abnormalities and growth defects (similar to the child's problems), prevented by biotin and pantothenic acid supplementation.

Byrne et al (2019 - PMID: 31754459) reported on a sibling pair with severe motor/speech developmental regression following a plateau (at 12m and 14m), development of ataxia and dyskinetic movements (both), seizures (one). Feeding difficulties, reflux and failure to thrive required N-G/gastrostomy feeding while both presented GI hemorrhage (in the case of the older sib, lethal). Other features in the youngest sib included brain MRI abnormalities (cerebral/cerebellar atrophy, thin CC, etc) and IgG deficiency. Biochemical, single-gene testing and mtDNA sequencing were not diagnostic. Exome in one, revealed presence of a frameshift [c.422_423del as above] and a missense variant (Arg400Thr). Sanger sequencing confirmed variants in both sibs and heterozygosity in parents. HeLa cells transfected with empty vector, wt or mut expression constructs confirmed significantly decreased 3H-biotin uptake for mut constructs compared to wt (and similar to empty vector). Parenteral triple vitamin replacement at the age of ~7 years resulted in improved overall condition, regain of some milestones, attenuation of vomiting, and resolution of peripheral neuropathy. Seizure were well-controlled (as was the case before treatment) despite persistence of epileptiform discharges. Again the authors cite studies of conditional (intestine-specific) SLC5A6 ko mice, with those viable (~1/3) demonstrating growth retardation, decreased boned density and GI abnormalities (similar to affected individuals). The phenotype could be rescued by oversupplementation of biotin and pantothenic acid (PMIDs cited: 23104561, 29669219).

[Please consider inclusion in other relevant panels eg. metabolic disorders]
Sources: Literature; to: SLC5A6 encodes the sodium dependent multivitamin transporter (SMVT), a transporter of biotin, pantothenate and lipoate. The transporter has a major role in vitamin uptake in the digestive system (among others is the sole transporter for intestinal uptake of biotin which is not synthesized but must be obtained from exogenous sources) as well as transport across the blood-brain barrier (SMVT being responsible for 89% of biotin transport) [several refs provided by Subramanian et al and Byrne et al].

4 affected individuals from 3 families have been reported.

Subramanian et al (2017 - PMID: 27904971) et al reported on a girl with feeding difficulties and failure to thrive (requiring nasogastric tube placement), microcephaly, DD (at 15m developmental age corresponding to 6m with features suggestive of spastic cerebral palsy), occurrence of multiple infections, osteoporosis and pathologic bone fractures. MRIs suggested brain atrophy, thin CC and hypoplasia of the pons. Metabolic (AA, OA) investigations and array-CGH were normal. Whole exome sequencing revealed presence of a missense (Arg123Leu - RefSeq not provided) and a nonsense (Arg94Ter) SLC5A6 variant. Serum biotin was normal although - at the time - the child was on parenteral and G-T nutrition. Following administration of biotin, pantothenic acid and lipoic acid the child demonstrated among others improved motor and verbal skills, head growth and normalization of immunoglobulin levels. Transfection of mutants in human derived intestinal HuTu-80 cells and brain U87 cells was carried out and a 3H-biotin assay showed no induction in biotin uptake confirming impaired functionality of the transporter. While wt protein displayed normal expression/membrane localization, Arg94Ter was poorly expressed with ectopic localization (cytoplasm). Arg123Leu was retained predominantly intracellularly, probably in the ER as was further supported by colocalization with DsRed-ER. Evidence from the literature is provided that deficiencies of the specific vitamins explain the clinical features (DD, microcephaly, immunological defect, osteopenia, etc).

Schwantje et al (2019 - PMID: 31392107) described a girl with severe feeding problems, vomiting with blood (suspected Mallory-Weiss syndrome), poor weight gain and delayed gross motor development. The child presented an episode of gastroenteritis associated with reduced consciousness, circulatory insufficiency and metabolic derangement (hypoglycemia, severe metabolic acidosis, hyperammonemia, mild lactate elevation, ketonuria). Investigations some months prior to the admission (?) were suggestive of a metabolic disorder due to elevated plasma C3-carnitine, C5-OH-carnitine and elevated urinary excretion of 3-OH-isovaleric acid (biotinidase deficiency was considered in the DD but enzymatic activity was only marginally decreased). Biotin supplementation was initiated. Trio-exome sequencing (at 3yrs) demonstrated compound heterozygosity for 2 frameshift variants [NM_021095.2:c.422_423del / p.(Val141Alafs*34) and c.1865_1866del]. Following this result, increase of biotin supplementation and introduction of pantothenic acid, GI symptoms (incl. chronic diarrhea) resolved and the child displayed improved appetite and growth, yet a stable motor delay. The authors cite previous studies of conditional ko mice, displaying intestinal mucosal abnormalities and growth defects (similar to the child's problems), prevented by biotin and pantothenic acid supplementation.

Byrne et al (2019 - PMID: 31754459) reported on a sibling pair with severe motor/speech developmental regression following a plateau (at 12m and 14m), development of ataxia and dyskinetic movements (both), seizures (one). Feeding difficulties, reflux and failure to thrive required N-G/gastrostomy feeding while both presented GI hemorrhage (in the case of the older sib, lethal). Other features in the youngest sib included brain MRI abnormalities (cerebral/cerebellar atrophy, thin CC, etc) and IgG deficiency. Biochemical, single-gene testing and mtDNA sequencing were not diagnostic. Exome in one, revealed presence of a frameshift [c.422_423del as above] and a missense variant (Arg400Thr). Sanger sequencing confirmed variants in both sibs and heterozygosity in parents. HeLa cells transfected with empty vector, wt or mut expression constructs confirmed significantly decreased 3H-biotin uptake for mut constructs compared to wt (and similar to empty vector). Parenteral triple vitamin replacement at the age of ~7 years resulted in improved overall condition, regain of some milestones, attenuation of vomiting, and resolution of peripheral neuropathy. Seizure were well-controlled (as was the case before treatment) despite persistence of epileptiform discharges. Again the authors cite studies of conditional (intestine-specific) SLC5A6 ko mice, with those viable (~1/3) demonstrating growth retardation, decreased boned density and GI abnormalities (similar to affected individuals). The phenotype could be rescued by oversupplementation of biotin and pantothenic acid (PMIDs cited: 23104561, 29669219).

[Please consider inclusion in other relevant panels eg. metabolic disorders]
Sources: Literature
Intellectual disability v2.1135 SLC5A6 Konstantinos Varvagiannis gene: SLC5A6 was added
gene: SLC5A6 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SLC5A6 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: SLC5A6 were set to 27904971; 31392107; 31754459; 23104561; 29669219
Phenotypes for gene: SLC5A6 were set to Feeding difficulties; Failure to thrive; Global developmental delay; Developmental regression; Intellectual disability; Seizures; Microcephaly; Cerebral atrophy; Abnormality of the corpus callosum; Vomiting; Chronic diarrhea; Gastrointestinal hemorrhage; Abnormal immunoglobulin level; Osteopenia; Abnormality of metabolism/homeostasis
Penetrance for gene: SLC5A6 were set to Complete
Review for gene: SLC5A6 was set to GREEN
Added comment: SLC5A6 encodes the sodium dependent multivitamin transporter (SMVT), a transporter of biotin, pantothenate and lipoate. The transporter has a major role in vitamin uptake in the digestive system (among others is the sole transporter for intestinal uptake of biotin which is not synthesized and but must be obtained from exogenous sources) as well as transport across the blood-brain barrier (SMVT being responsible for 89% of biotin transport) [several refs provided by Subramanian et al and Byrne et al].

4 affected individuals from 3 families have been reported.

Subramanian et al (2017 - PMID: 27904971) et al reported on a girl with feeding difficulties and failure to thrive (requiring nasogastric tube placement), microcephaly, DD (at 15m developmental age corresponding to 6m with features suggestive of spastic cerebral palsy), occurrence of multiple infections, osteoporosis and pathologic bone fractures. MRIs suggested brain atrophy, thin CC and hypoplasia of the pons. Metabolic (AA, OA) investigations and array-CGH were normal. Whole exome sequencing revealed presence of a missense (Arg123Leu - RefSeq not provided) and a nonsense (Arg94Ter) SLC5A6 variant. Serum biotin was normal although - at the time - the child was on parenteral and G-T nutrition. Following administration of biotin, pantothenic acid and lipoic acid the child demonstrated among others improved motor and verbal skills, head growth and normalization of immunoglobulin levels. Transfection of mutants in human derived intestinal HuTu-80 cells and brain U87 cells was carried out and a 3H-biotin assay showed no induction in biotin uptake confirming impaired functionality of the transporter. While wt protein displayed normal expression/membrane localization, Arg94Ter was poorly expressed with ectopic localization (cytoplasm). Arg123Leu was retained predominantly intracellularly, probably in the ER as was further supported by colocalization with DsRed-ER. Evidence from the literature is provided that deficiencies of the specific vitamins explain the clinical features (DD, microcephaly, immunological defect, osteopenia, etc).

Schwantje et al (2019 - PMID: 31392107) described a girl with severe feeding problems, vomiting with blood (suspected Mallory-Weiss syndrome), poor weight gain and delayed gross motor development. The child presented an episode of gastroenteritis associated with reduced consciousness, circulatory insufficiency and metabolic derangement (hypoglycemia, severe metabolic acidosis, hyperammonemia, mild lactate elevation, ketonuria). Investigations some months prior to the admission (?) were suggestive of a metabolic disorder due to elevated plasma C3-carnitine, C5-OH-carnitine and elevated urinary excretion of 3-OH-isovaleric acid (biotinidase deficiency was considered in the DD but enzymatic activity was only marginally decreased). Biotin supplementation was initiated. Trio-exome sequencing (at 3yrs) demonstrated compound heterozygosity for 2 frameshift variants [NM_021095.2:c.422_423del / p.(Val141Alafs*34) and c.1865_1866del]. Following this result, increase of biotin supplementation and introduction of pantothenic acid, GI symptoms (incl. chronic diarrhea) resolved and the child displayed improved appetite and growth, yet a stable motor delay. The authors cite previous studies of conditional ko mice, displaying intestinal mucosal abnormalities and growth defects (similar to the child's problems), prevented by biotin and pantothenic acid supplementation.

Byrne et al (2019 - PMID: 31754459) reported on a sibling pair with severe motor/speech developmental regression following a plateau (at 12m and 14m), development of ataxia and dyskinetic movements (both), seizures (one). Feeding difficulties, reflux and failure to thrive required N-G/gastrostomy feeding while both presented GI hemorrhage (in the case of the older sib, lethal). Other features in the youngest sib included brain MRI abnormalities (cerebral/cerebellar atrophy, thin CC, etc) and IgG deficiency. Biochemical, single-gene testing and mtDNA sequencing were not diagnostic. Exome in one, revealed presence of a frameshift [c.422_423del as above] and a missense variant (Arg400Thr). Sanger sequencing confirmed variants in both sibs and heterozygosity in parents. HeLa cells transfected with empty vector, wt or mut expression constructs confirmed significantly decreased 3H-biotin uptake for mut constructs compared to wt (and similar to empty vector). Parenteral triple vitamin replacement at the age of ~7 years resulted in improved overall condition, regain of some milestones, attenuation of vomiting, and resolution of peripheral neuropathy. Seizure were well-controlled (as was the case before treatment) despite persistence of epileptiform discharges. Again the authors cite studies of conditional (intestine-specific) SLC5A6 ko mice, with those viable (~1/3) demonstrating growth retardation, decreased boned density and GI abnormalities (similar to affected individuals). The phenotype could be rescued by oversupplementation of biotin and pantothenic acid (PMIDs cited: 23104561, 29669219).

[Please consider inclusion in other relevant panels eg. metabolic disorders]
Sources: Literature
Intellectual disability v2.1134 OXR1 Konstantinos Varvagiannis gene: OXR1 was added
gene: OXR1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: OXR1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: OXR1 were set to https://doi.org/10.1016/j.ajhg.2019.11.002
Phenotypes for gene: OXR1 were set to Central hypotonia; Global developmental delay; Delayed speech and language development; Intellectual disability; Seizures; Abnormality of the cerebellum
Penetrance for gene: OXR1 were set to Complete
Review for gene: OXR1 was set to GREEN
Added comment: Wang et al (2019 - https://doi.org/10.1016/j.ajhg.2019.11.002 ) report on 5 individuals (from 3 families) with biallelic OXR1 LoF variants.

Common features included hypotonia (4/5), severe global DD (5/5) and speech delay (5/5), ID (5/5), epilepsy (5/5) with cerebellar dysplasia/atrophy (5/5) and in some scoliosis.

All were investigated by exome sequencing and were found to harbor biallelic loss-of-function variants (2 splice-site, a stopgain and a frameshift one) either in homozygosity (2 consanguineous families) or in compound heterozygosity. In all cases parental segregation studies were compatible and in one family, an unaffected sib shown to be carrier.

Althouhgh OXR1 has been shown to affect several processes (among others DNA lesions induced by oxidative stress in E.coli, neuronal maintenance, mitochondrial morphology and DNA maintenance, etc), its mechanism of action is still not well defined. There are 6 RefSeq transcripts, the longest (NM_018002.3) encoding 3 protein domains (LysM, GRAM, TLDc). The TLDc domain is encoded by all transcripts.

Identified variants affected (probably all - fig1D) transcripts expressed in the CNS, namely NM_018002.3, NM_001198532.1, NM_181354.4. The 3 transcripts not expressed in the CNS are NM_001198533.1, NM_001198534.1 and NM_001198535.1.

Western blot with 2 different antibodies which would bind upstream of the truncation site failed to detect presence of truncated proteins in 2 affected individuals from 2 families.

The Drosophila homolog of OXR is mustard (mtd). The authors provide evidence that loss of mtd is lethal. This was however rescued by expression of an 80kb fly BAC clone covering mtd, or the fly mtd-RH isoform cDNA, or a short human OXR1 cDNA containing only the TLDc domain or a human NCOA7 cDNA. The latter is another human mtd homolog which also contains the TLDc domain. As a result the TLDc domain compensated sufficiently for loss of mtd.

Flies that survived displayed bang sensitivity and climbing defects the former assay being suggestive of susceptibility to seizures and the latter of impaired neurological/muscular function.

The authors provided evidence that mtd is broadly expressed in the fly CNS. RNAi mediated mtd knockdown specific to neurons (elav/nSyb-GAL4 expression of mtd RNAi) led to lethal eclosion defects for RNAis targeting most (18)/all(23) mtd isoforms. Lifespan was increased upon expression of human OXR1 cDNA. Neuronal loss and vacuolization was demonstrated and additional experiments in R7 photoreceptors showed presence of aberrant lysosomal structures (autolysosomes, autophagosomes and/or endolysosomes).

Aberrant lysosomal structures were also observed in fibroblasts from affected individuals (accumulation of lysosomes and/or presence of highly aberrant compartments with content typical of lysosomal dysfunction).

Overall the data presented suggest a critical role for OXR1 in lysosomal biology.

Although previous reports suggested that OXR1 is involved in oxidative stress resistance, studies performed by the authors suggested that oxidative stress is probably not the driver of the mutant fly defects.
Sources: Literature
Intellectual disability v2.1122 TMX2 Konstantinos Varvagiannis edited their review of gene: TMX2: Added comment: A recent report by Vandervore, Schot et al. following the previous review (Am J Hum Genet. 2019 Nov 12 - PMID: 31735293), provides further evidence that biallelic TMX2 mutations cause malformations of cortical development, microcephaly, DD and ID and epilepsy.

As a result this gene should probably be considered for inclusion in the ID/epilepsy panels with green rating.

Overall, 14 affected subjects from 10 unrelated families are reported in the aforementioned study. The majority had severe DD/ID (failure to achieve milestones, absent speech/ambulation and signs of cerebral palsy) with few having a somewhat milder impairment. 12 (of the 14) presented with epilepsy (spasms, myoclonic seizures, focal seizures with/without generalization or generalized tonic-clonic seizures) with onset most often in early infancy. Upon brain MRI (in 12 individuals), 5 presented polymicrogyria, 2 others pachygyria, 4 with brain atrophy, etc.

All individuals were found to harbor biallelic TMX2 mutations by exome sequencing while previous investigations in several had ruled out alternative causes (infections, metabolic or chromosomal anomalies). Missense variants, an in-frame deletion as well as pLoF (stopgain/frameshift) variants were reported. [NM_015959.3 used as ref below].

The effect of variants was supported by mRNA studies, eg. RT-qPCR/allele specific RT-qPCR. The latter proved reduced expression for a frameshift variant (c.391dup / p.Leu131Profs*6) most likely due to NMD. Total mRNA levels were also 23% lower in an individual compound htz for a missense variant and a stopgain one localized in the last exon (c.757C>T / p.Arg253*). As for the previously reported c.614G>A (p.Arg205Gln), affecting the last nucleotide of exon 6, total mRNA in skin fibroblasts from a homozygous individual was not significantly decreased. RNA-Seq however demonstrated the presence of 4 different transcripts (roughly 25% each), one representing the regular mRNA, one with intron 6 retention (also present at low levels in healthy individuals), one with loss of 11 nucleotides within exon 6 and a fourth one due to in-frame skipping of exon 6.

*To the best of my understanding :

Thioredoxin (TRX)-related transmembrane proteins (TMX) belong to the broader family of oxidoreductases of protein disulfide isomerase (PDI) having an important role in protein folding.

Study of the data from the Allen Human Brain Atlas suggest relevant fetal expression also increasing during postnatal life.

As RNA-seq was carried out for 2 individuals, GO analysis suggested that the most deregulated clusters of genes are implicated in post-translational protein modifications (as would be expected for PDIs), membranes and synapse while pathway analysis suggested that relevant categories were inhibited eg. nervous system development/function and cell growth/proliferation/survival.

Upon transfection of HEK293T cells, exogenous TMX2 was shown to co-localize with calnexin (CNX) to the (ER) mitochondria-associated-membrane. Mass-spectrometry based analysis of co-immunoprecipitated proteins confirmed interaction with CNX but also other regulators of calcium homeostasis, mitochondrial membrane components and respiratory chain NADH dehydrogenase.

Study of the mitochondrial activity of TMX2-deficient fibroblasts suggested reduced respiratory reserve capacity, compensated by increased glycolytic activity.

TMX2 occurs in both reduced and oxidized monomeric form. It also forms (homo)dimers with the ratio of dimers/monomers increasing under conditions of oxidative stress. Variant TMX2 increased propensity to form dimers, thus mimicking increased oxidative state. This was observed under stress but also under native conditions.

---------; Changed rating: GREEN
Intellectual disability v2.1107 VAMP7 Eleanor Williams Mode of inheritance for gene: VAMP7 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1106 SPRY3 Eleanor Williams Mode of inheritance for gene: SPRY3 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1105 SLC25A6 Eleanor Williams Mode of inheritance for gene: SLC25A6 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1104 P2RY8 Eleanor Williams Mode of inheritance for gene: P2RY8 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1103 PLCXD1 Eleanor Williams Mode of inheritance for gene: PLCXD1 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1102 DMXL2 Konstantinos Varvagiannis changed review comment from: This gene can be considered for upgrade to green rating (ID and epilepsy with >=4 relevant individuals/families/variants and >=2 studies, role of the protein, effect of variants in most cases demonstrated, phenotypic similarities with other disorders affecting autophagy, some evidence from animal models, etc).

Rare heterozygous variants disrupting DMXL2 (intragenic losses/gains, SNVs, CNVs affecting also additional genes) have been reported in individuals with variable neurodevelopmental disorders (ASD and ID) or psychiatric phenotypes [Costain et al. 2019 - PMID: 30732576 - summarized in Table 1]. (Highly) variable expressivity and possibly incomplete penetrance were proposed in the respective study. As a result evidence for ID/seizures due to monoallelic variants appears to be relatively limited.

DD, ID and (probably) epilepsy appear however to be features in several individuals with biallelic pathogenic variants as summarized in the studies below.

OMIM recently added a relevant entry with the DMXL2-associated phenotypes being the following:
- Epileptic encephalopathy, early infantile, 81; EIEE81 - 618663 (AD) [based on refs 2,3]
- ?Deafness, autosomal dominant 71 - 617605 (AD) [DD/ID/seizures are not part of the phenotype]
- ?Polyendocrine-polyneuropathy syndrome - 616113 (AR) [based on ref1]

DMXL2 is not associated with any phenotype in G2P. In SysID it is listed as a candidate ID gene based on the report by Tata et al (ref1). This gene is included in some gene panels for ID.

[1] Tata el al. (2014 - PMID: 25248098) reported on 3 sibs born to consanguineous Senegalese parents, presenting with a progressive endocrine and neurodevelopmental disorder. Features incl. incomplete puberty, central hypothyroidism, abnormal glucose regulation, moderate ID (3/3) and peripheral polyneuropathy. Seizures were not part of the phenotype. Linkage analysis suggested 2 candidate regions on chromosomes 13 and 15 with a LOD score of 2.5. High throughput sequencing of genes within these regions (~500) in an affected member and parent revealed a 15 bp in-frame deletion of DMXL2 (NM_015263.4:c.5827_5841del / p.Asp1943_Ser1947del). Sanger sequencing of other affected and unaffected members supported AR inheritance. RT-qPCR demonstrated that DMXL2 mRNA levels in blood lymphocytes were significantly lower in homozygous patients compared to heterozygous or wt family members or controls. The authors demonstrated that the encoded protein (rabconnectin-3a) is a synaptic protein (expressed in exocytosis vesicles) at the ends of axons of GnRH producing neurons. Neuron-specific deletion of one allele in mice resulted in delayed puberty and very low fertility. Adult mice had lower number of GnRH neurons in hypothalamus. siRNA-mediated downregulation of Dmxl2 expression in an insulin-secreting cell line resulted in only slight insulin secretion in response to augmenting concentrations of glucose, providing evidence of involvement of the protein in control of regulated insulin secretion.
-----------
[2] Maddirevula et al. (2019 - PMID: 30237576) reported briefly on a 36 months old boy, born to consanguineous parents, homozygous for a frameshift DMXL2 variant [individual 17-3220 | NM_001174117.1:c.4349_4350insTTACATGA or p.(Glu1450Aspfs*23)]. Features included focal seizures (onset at the age of 3m) with subsequent global DD, absent eye contact, cerebral atrophy and macrocephaly. This individual was identified following re-evaluation of exome data in a database of ~1550 exomes specifically for homozygous variants that would have been classified earlier as LP/P if the respective gene had sufficient evidence for association with a disorder. The family was not reported to have other affected members. As the authors noted, the boy was not known to have the multi-endocrine abnormalities reported by Tata et al. There are no additional information provided (eg. on confirmation of variants, etc).
-----------
[3] Esposito et al. (2019 - PMID: 31688942) report on 3 sibling pairs (all 3 families unrelated) with biallelic DMXL2 mutations and summarize previous evidence on the gene and the DMXL2-related phenotypes.

All presented a highly similar phenotype of Ohtahara syndrome (seizures with onset in the first days of life, tonic/myoclonic/occasionaly focal, burst-suppression upon EEG), profound DD/ID, quadriparesis, sensorineural hearing loss and presence of dysmorphic features. Sibs from 2 families presented evidence of peripheral polyneuropathy. Early brain MRIs revealed thin CC and hypomyelination in all, with later scans suggestive of gray and white matter shrinkage with leukoencephalopathy. None achieved developmental skills following birth with 5/6 deceased by the age of 9 years.

Exome sequencing revealed biallelic DMXL2 variants in all, with compatible parental segregation studies (NM_015263.3):
- Fam1 (2 sibs) : c.5135C>T (p.Ala1712Val) in trans with c.4478C>G (p.Ser1493*)
- Fam2 (2 sibs) : homozygosity for c.4478C>A (p.Ser1493*)
- Fam3 (2 sibs) : homozygosity for c.7518-1G>A

Heterozygous parents (aged 39-59) did not exhibit hearing impairment [report of a single multigenerational family by Chen et al (2017 - PMID: 27657680) where a heterozygous missense variant segregated with hearing loss - respective OMIM entry: ?Deafness, autosomal dominant 71 - 617605].

In patients' fibroblasts, effect of the variants on mRNA/protein expression was demonstrated with mRNA expressed only in a patient from family 1, and degraded/absent for the 2 stopgain SNVs affecting codon 1493. Skipping of ex31 leading to frameshift/introduction of a PTC was shown for the splice variant (p.Trp2508Argfs*4 secondary to c.7518-1G>A). Protein was also absent upon western-blot.

DMXL2 encodes a vesicular protein, DmX-Like protein 2 or rabconnectin-3a (cited Tata et al).

The gene is expressed in brain ( https://www.gtexportal.org/home/gene/DMXL2 ).

As Esposito et al comment, it is known to regulate the trafficking and activity of v-ATPase the latter having a role in acidifying intracellular organelles and promoting endosomal maturation (cited PMIDs : 25248098, 19758563, 22875945, 24802872).

In line with this, staining of patients' fibroblasts using the acidotropic dye LysoTracker demonstrated increased signal, reversed by re-expression of DMXL2 protein. Overall an acidic shift in pH with impairment of lysosomal structures and function was suggested. The authors provided additional evidence for altered lysosomal function and associated autophagy with accumulation of autophagy receptors (eg p62) and substrates (polyubiquitinated proteins). Vacuolization and accumulation of atypical fusion-like structures was shown upon ultrastractural analysis.

shRNA-mediated downregulation/silencing of Dmxl2 in mouse hippocampal neurons resulted also in altered lysosomal structures and defective autophagy. The neurons exhibited impaired neurite elongation and synapse formation.

The authors suggest similarities with Vici syndrome, where biallelic EPG5 mutations result in autophagic defects and clinical manifestations of DD/ID/epilepsy.

Dmxl2 homozygous ko mice display embryonic lethality with heterozygous mice displaying macrocephaly and corpus callosum dysplasia (cited PMIDs: 25248098, 30735494) .; to: This gene can be considered for upgrade to green rating (ID and epilepsy with >=4 relevant individuals/families/variants and >=2 studies, role of the protein, effect of variants in most cases demonstrated, phenotypic similarities with other disorders affecting autophagy, some evidence from animal models, etc).

Rare heterozygous variants disrupting DMXL2 (intragenic losses/gains, SNVs, CNVs affecting also additional genes) have been reported in individuals with variable neurodevelopmental disorders (ASD and ID) or psychiatric phenotypes [Costain et al. 2019 - PMID: 30732576 - summarized in Table 1]. (Highly) variable expressivity and possibly incomplete penetrance were proposed in the respective study. As a result evidence for ID/seizures due to monoallelic variants appears to be relatively limited.

DD, ID and (probably) epilepsy appear however to be features in several individuals with biallelic pathogenic variants as summarized in the studies below.

OMIM recently added a relevant entry with the DMXL2-associated phenotypes being the following:
- Epileptic encephalopathy, early infantile, 81; EIEE81 - 618663 (AR) [based on refs 2,3]
- ?Deafness, autosomal dominant 71 - 617605 (AD) [DD/ID/seizures are not part of the phenotype]
- ?Polyendocrine-polyneuropathy syndrome - 616113 (AR) [based on ref1]

DMXL2 is not associated with any phenotype in G2P. In SysID it is listed as a candidate ID gene based on the report by Tata et al (ref1). This gene is included in some gene panels for ID.

[1] Tata el al. (2014 - PMID: 25248098) reported on 3 sibs born to consanguineous Senegalese parents, presenting with a progressive endocrine and neurodevelopmental disorder. Features incl. incomplete puberty, central hypothyroidism, abnormal glucose regulation, moderate ID (3/3) and peripheral polyneuropathy. Seizures were not part of the phenotype. Linkage analysis suggested 2 candidate regions on chromosomes 13 and 15 with a LOD score of 2.5. High throughput sequencing of genes within these regions (~500) in an affected member and parent revealed a 15 bp in-frame deletion of DMXL2 (NM_015263.4:c.5827_5841del / p.Asp1943_Ser1947del). Sanger sequencing of other affected and unaffected members supported AR inheritance. RT-qPCR demonstrated that DMXL2 mRNA levels in blood lymphocytes were significantly lower in homozygous patients compared to heterozygous or wt family members or controls. The authors demonstrated that the encoded protein (rabconnectin-3a) is a synaptic protein (expressed in exocytosis vesicles) at the ends of axons of GnRH producing neurons. Neuron-specific deletion of one allele in mice resulted in delayed puberty and very low fertility. Adult mice had lower number of GnRH neurons in hypothalamus. siRNA-mediated downregulation of Dmxl2 expression in an insulin-secreting cell line resulted in only slight insulin secretion in response to augmenting concentrations of glucose, providing evidence of involvement of the protein in control of regulated insulin secretion.
-----------
[2] Maddirevula et al. (2019 - PMID: 30237576) reported briefly on a 36 months old boy, born to consanguineous parents, homozygous for a frameshift DMXL2 variant [individual 17-3220 | NM_001174117.1:c.4349_4350insTTACATGA or p.(Glu1450Aspfs*23)]. Features included focal seizures (onset at the age of 3m) with subsequent global DD, absent eye contact, cerebral atrophy and macrocephaly. This individual was identified following re-evaluation of exome data in a database of ~1550 exomes specifically for homozygous variants that would have been classified earlier as LP/P if the respective gene had sufficient evidence for association with a disorder. The family was not reported to have other affected members. As the authors noted, the boy was not known to have the multi-endocrine abnormalities reported by Tata et al. There are no additional information provided (eg. on confirmation of variants, etc).
-----------
[3] Esposito et al. (2019 - PMID: 31688942) report on 3 sibling pairs (all 3 families unrelated) with biallelic DMXL2 mutations and summarize previous evidence on the gene and the DMXL2-related phenotypes.

All presented a highly similar phenotype of Ohtahara syndrome (seizures with onset in the first days of life, tonic/myoclonic/occasionaly focal, burst-suppression upon EEG), profound DD/ID, quadriparesis, sensorineural hearing loss and presence of dysmorphic features. Sibs from 2 families presented evidence of peripheral polyneuropathy. Early brain MRIs revealed thin CC and hypomyelination in all, with later scans suggestive of gray and white matter shrinkage with leukoencephalopathy. None achieved developmental skills following birth with 5/6 deceased by the age of 9 years.

Exome sequencing revealed biallelic DMXL2 variants in all, with compatible parental segregation studies (NM_015263.3):
- Fam1 (2 sibs) : c.5135C>T (p.Ala1712Val) in trans with c.4478C>G (p.Ser1493*)
- Fam2 (2 sibs) : homozygosity for c.4478C>A (p.Ser1493*)
- Fam3 (2 sibs) : homozygosity for c.7518-1G>A

Heterozygous parents (aged 39-59) did not exhibit hearing impairment [report of a single multigenerational family by Chen et al (2017 - PMID: 27657680) where a heterozygous missense variant segregated with hearing loss - respective OMIM entry: ?Deafness, autosomal dominant 71 - 617605].

In patients' fibroblasts, effect of the variants on mRNA/protein expression was demonstrated with mRNA expressed only in a patient from family 1, and degraded/absent for the 2 stopgain SNVs affecting codon 1493. Skipping of ex31 leading to frameshift/introduction of a PTC was shown for the splice variant (p.Trp2508Argfs*4 secondary to c.7518-1G>A). Protein was also absent upon western-blot.

DMXL2 encodes a vesicular protein, DmX-Like protein 2 or rabconnectin-3a (cited Tata et al).

The gene is expressed in brain ( https://www.gtexportal.org/home/gene/DMXL2 ).

As Esposito et al comment, it is known to regulate the trafficking and activity of v-ATPase the latter having a role in acidifying intracellular organelles and promoting endosomal maturation (cited PMIDs : 25248098, 19758563, 22875945, 24802872).

In line with this, staining of patients' fibroblasts using the acidotropic dye LysoTracker demonstrated increased signal, reversed by re-expression of DMXL2 protein. Overall an acidic shift in pH with impairment of lysosomal structures and function was suggested. The authors provided additional evidence for altered lysosomal function and associated autophagy with accumulation of autophagy receptors (eg p62) and substrates (polyubiquitinated proteins). Vacuolization and accumulation of atypical fusion-like structures was shown upon ultrastractural analysis.

shRNA-mediated downregulation/silencing of Dmxl2 in mouse hippocampal neurons resulted also in altered lysosomal structures and defective autophagy. The neurons exhibited impaired neurite elongation and synapse formation.

The authors suggest similarities with Vici syndrome, where biallelic EPG5 mutations result in autophagic defects and clinical manifestations of DD/ID/epilepsy.

Dmxl2 homozygous ko mice display embryonic lethality with heterozygous mice displaying macrocephaly and corpus callosum dysplasia (cited PMIDs: 25248098, 30735494) .
Intellectual disability v2.1102 IL3RA Eleanor Williams Mode of inheritance for gene: IL3RA was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1101 DHRSX Eleanor Williams Mode of inheritance for gene: DHRSX was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1100 CRLF2 Eleanor Williams Mode of inheritance for gene: CRLF2 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1099 AKAP17A Eleanor Williams Mode of inheritance for gene: AKAP17A was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to Unknown
Intellectual disability v2.1098 CNOT2 Konstantinos Varvagiannis gene: CNOT2 was added
gene: CNOT2 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: CNOT2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CNOT2 were set to 31512373; 31145527; 28135719; 28159701; 30768759; 21505450; 18076123; 22247066
Phenotypes for gene: CNOT2 were set to Intellectual developmental disorder with nasal speech, dysmorphic facies, and variable skeletal anomalies, MIM 618608
Penetrance for gene: CNOT2 were set to unknown
Review for gene: CNOT2 was set to GREEN
gene: CNOT2 was marked as current diagnostic
Added comment: Heterozygous pathogenic CNOT2 variants cause Intellectual developmental disorder with nasal speech, dysmorphic facies, and variable skeletal anomalies (MIM 618608 - recently added disorder in OMIM). Larger 12q15 deletions, spanning CNOT2 have been reported in patients with similar phenotype.

Relevant individuals - most discussed below - include 2 patients with truncating de novo mutation, 1 with de novo intragenic deletion, few with small deletions spanning also 2-3 additional proximal genes and others with larger 12q15 deletions encompassing CNOT2 and several other genes.

Overall the phenotype - summarized by Uehara et al. (Ref1 - below) - seems to consist of language delay, mild motor delay (in most), some suggestive facial features (upslanted palpebral fissures, anteverted nares, thin upper lip and micrognathia). Nasal speech has also been reported in some individuals.

As commented by Uehara et al. (Ref1), CNOT2 (CCR4-NOT transcription complex subunit 2) is a member of the carbon catabolite repressor 4 complex (CCR4-NOT), the latter having an important role in deadenylation of mRNA and global mRNA expression. Disruption of the complex - which can be caused by loss of one of its components - results in various human disorders incl. neural diseases. siRNA CNOT2 depletion has been shown to induce CCR4-NOT disruption (cited PMIDs: 16284618, 29438013, 31006510, 21299754).

The type of variants (truncating, intragenic deletion, larger deletions) and the highly overlapping phenotypes in the respective patients suggest happloinsufficiency as the underlying mechanism. CNOT2 has also a pLI of 1 in gnomAD (o/e =0.06) and a %HI in Decipher of 4.39.

The gene appears to have relevant expression (https://www.proteinatlas.org/ENSG00000111596-CNOT2/tissue).
Animal models have not been discussed (or phenotypes possibly not sufficiently studied - MGI for Cnot2 : http://www.informatics.jax.org/marker/MGI:1919318).

CNOT2 is not associated with any phenotype in G2P. It is listed among the ID candidate genes in SysID.
This gene is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc).

Overall CNOT2 could be considered for inclusion in the ID panel with amber (DD although outcome is not known, presumed dysfunction of the CCR4-NOT complex, variant studies or animal models not available) or green rating (sufficient cases and variants, consistent phenotype).
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Individuals with CNOT2-only disruption:
[1] PMID: 31512373 (Uehara et al., 2019) - A 6 y.o. male investigated for hypotonia, feeding problems, DD (speech and motor), macrocephaly (+3 SD) and some possibly suggestive facial/other features was found to harbor a de novo stopgain variant (NM_001199302.1: c.946A>T, p.Lys316Ter) after trio exome sequencing. The variant and its de novo occurrence were confirmed by Sanger sequencing. NMD was the predicted effect (variant in ex11 of 21 / effect not further studied). Previous metabolic work-up and chromosomal testing had not revealed an alternative diagnosis.
[2] PMID: 31145527 (Alesi et al. 2019) - A 13 y.o. boy with hypotonia, failure to thrive, DD and following a specific schooling program for children with learning difficulties is reported. The authors comment on the facial phenotype (incl. upslanted p-f, anteverted nares, etc). Other features included valvular/supravalvular pulm. stenosis, mid aortic insufficiency, renal anomalies/failure, skeletal anomalies. Speech was nasal. CMA revealed an 85-kb 12q15 deletion spanning only CNOT2 (exons 3-15). Real-time PCR in proband and parents confirmed the variant and its de novo occurrence.
[3] PMID: 28135719 (DDD study, 2017) - An individual with developmental disorder and a de novo (validated) frameshift variant was identified [DDD4K.00807 - NM_014515.5:c.1158del / p.(L387Sfs*3)]. Phenotype in Decipher incl. abnormality of head/neck, nervous, skeletal system and growth. [https://decipher.sanger.ac.uk/ddd/research-variant/16b4f7866652f08e25a194f65535b4c5#overview].

Individuals with disruption of additional proximal genes due to CNVs:
[4] PMID: 28159701 (Alesi et al. 2017) - The authors report on a 29 y.o. individual with history of DD, learning difficulties, ID (WAIS-R IQ of 48 at the age of 17 y), some dysmorphic facial features. Additional features incl. recurrent infections, nasal voice as well as skeletal anomalies. CMA revealed a 742 kb microdeletion spanning CNOT2, KCNMB4 and PTPRB. Real-time PCR confirmed deletion and it's de novo occurrence in the proband.
[5] PMID: 30768759 (Uehara et al. 2019) - A female investigated among others for global DD (walking/1st words at 24m), mild ID, submucosal cleft palate with some distinctive facial features (upslanted p-f, micrognathia, etc) was found to harbor a 1.32-Mb deletion of 12q15 encompassing CNOT2 and 14 other genes. Given the phenotypic resemblance to patients with 12q15 deletions, the previously defined smallest region of overlap (ref 4,6), the LoF SNV in Decipher the authors suggested that CNOT2 is the critical gene for the phenotype of 12q15 deletion syndrome.

Larger deletions defining the smallest region of overlap
[6] PMID: 21505450 (Vergult et al. 2011) - 3 patients with de novo microdeletions of ~ 2.5 Mb in size with a 1.34 MB common region of overlap are reported. Learning diability, DD, nasal speech and hypothyroidism were among the common features.
[7] PMID: 18076123 (Schluth et al. 2008) - A girl with large (~10 Mb) de novo deletion of 12q15 - q21.2 identified by BAC array was described. The phenotype consisted of hypotonia, DD, moderate ID, growth delay and facial dysmorphic features.
[8] PMID: 22247066 (Lopez et al. 2012) - A patient with ID and features of Floating-Harbor syndrome was found to harbor a 4.7 Mb de novo 12q15-q21.1 deletion spanning CNOT2 and 18 additional genes.
[..]
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.1098 TMX2 Konstantinos Varvagiannis gene: TMX2 was added
gene: TMX2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TMX2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TMX2 were set to 31586943; 31270415
Phenotypes for gene: TMX2 were set to Global developmental delay; Intellectual disability; Seizures; Microcephaly; Abnormal cortical gyration
Penetrance for gene: TMX2 were set to Complete
Review for gene: TMX2 was set to AMBER
Added comment: PMID: 31586943 - Ghosh et al. 2019 - reported on 8 individuals from 4 consanguineous families from the Middle East and Central Asia, all with a phenotype of DD/ID, seizures and microcephaly with lissencephaly (microlissencephaly is the term applying to the combination of two) upon brain MRI.

All patients were investigated by exome sequencing and the variant localized within a region of ROH which was common to all 4 families. All were homozygous for a TMX2 missense variant (NM_001144012.2:c.500G>A or p.Arg167Gln / NM_015959.4:c.614G>A p.Arg205Gln or hg38 - Chr11:g.57739039G>A). The variant was considered to be the best candidate, upon review of all other homozygous ones.

Sanger sequencing confirmed homozygosity for the variant in affected subjects, with additional compatible segregation studies including parents in all families as well as unaffected sibs (in two families).

Despite presence of the same mutation in all, several proximal to this variant SNPs did not appear to be shared among the families studied, thus suggesting that the variant had arisen within different haplotype blocks.

The authors comment that the variant was not previously identified in public databases. (The variant seems to correspond to rs370455806, present in 10 htz individuals in gnomAD, as well as in the GME database [GME Genotype Count 992:0:1 (hmz?) | Allele Count: 2,1984] . GME includes primarily - although not necessarily - healthy individuals).

This SNV affecting the last nucleotide of an exon of several transcripts (correct ref. is NM_001144012.2 as appears in the supplement / using NM_001347898.1 as in the fig./text the variant would lie within an intron), an eventual splicing effect was studied. mRNA transcript levels were assessed following RT-PCR using different sets of primers. There was no evidence of novel splice isoforms but mRNA levels were reduced compared to controls (15-50% in affected individuals, to a lesser level in carriers). This led to the hypothesis that NMD of an aberrantly spliced mRNA might apply, although this was not proven.

TMX2 encodes a protein disulfide isomerase (PDI). PDIs are transmembrane ER proteins which have a critical role in protein folding (PMID cited: 12670024). There were no relevant studies carried out in the article.

As for animal models, the authors comment that mice homozygous for null mutations display preweaning lethality with complete penetrance.(http://www.informatics.jax.org/diseasePortal/popup?isPhenotype=true&markerID=MGI:1914208&header=mortality/aging).
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Previously, Schot el al. (ESHG Conference 2018 Oral Presentation - Mutations in the thioredoxin related gene TMX2 cause primary microcephaly, polymicrogyria and severe neurodegeneration with impaired mitochondrial energy metabolism - available in PMID: 31270415 / https://www.nature.com/articles/s41431-019-0407-4 ) reported on 7 individuals from 5 unrelated families with biallelic TMX2 mutations. A newborn with microcephaly, polymicrogyria who died of refractory epilepsy, was compound heterozygous for 2 TMX2 variants. 6 additional individuals (from 4 unrelated families) with similar phenotype were found to harbor biallelic TMX2 mutations. It was commented that TMX2 is enriched in mitochondria-associated membrane of the ER with a role in ER stress protection and regulation of neuronal apoptosis. In line with this, fibroblasts from 2 unrelated patients showed secondary OXPHOS deficiency and increased glycolytic activity (the latter possibly as a compensatory mechanism).
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There is no associated phenotype in OMIM/G2P/SysID.
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Overall this gene could be considered for inclusion in the ID/epilepsy panel probably with amber (/red) rating pending further evidence.
Sources: Literature
Intellectual disability v2.1098 NSF Konstantinos Varvagiannis gene: NSF was added
gene: NSF was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: NSF was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: NSF were set to 31675180
Phenotypes for gene: NSF were set to Seizures; EEG with burst suppression; Global developmental delay; Intellectual disability
Penetrance for gene: NSF were set to unknown
Mode of pathogenicity for gene: NSF was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: NSF was set to AMBER
Added comment: Suzuki et al. (2019 - PMID: 31675180) report on 2 unrelated individuals with de novo missense NSF variants. Overall the phenotype corresponded to an early infantile epileptic encephalopathy. The first patient developed vomiting and tonic seizures immediately after birth, with burst-suppression pattern upon EEG. Trio exome sequencing, followed by Sanger sequencing of proband and parents, revealed a de novo missense variant (NM_006178.3:c.1375G>A / p.Ala459Thr), absent from public databases and predicted in silico to be deleterious (CADD score of 30). The girl died 36 days after birth due to respiratory failure. Another subject, having necessitated mechanical ventilation due to absence of spontaneous respiration after birth, developed myoclonic seizures. EEG showed a burst-suppression pattern. At the age of 3, she was noted to have persistence of seizures and profound ID. Trio exome sequencing identified a missense NSF variant (c.1688C>T / p.Pro563Leu) also confirmed and shown to be de novo by Sanger sequencing. Again the variant was absent from public datasets and had a CADD score of 34. While expression of wt NSF allele in the developing eye of Drosophila had no effect, expression of mutants severely affected eye development - suggesting a dominant negative effect. NSF encodes a homo-hexameric AAA ATPase, which is recruited by SNAPs (Soluble NSF Attachment Proteins) - and the latter by SNAREs (SNAP REceptors) - thus having a role in vesicular transport and membrane fusion. There is currently no associated phenotype in OMIM/G2P. Overall, this gene could be considered for inclusion probably with amber/red rating pending further evidence (eg. additional work-up or alternative causes/explanations not discussed).
Sources: Literature
Intellectual disability v2.1098 SCAMP5 Konstantinos Varvagiannis gene: SCAMP5 was added
gene: SCAMP5 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SCAMP5 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: SCAMP5 were set to 31439720; 20071347
Phenotypes for gene: SCAMP5 were set to Global developmental delay; Intellectual disability; Seizures; Abnormality of nervous system morphology; Behavioral abnormality
Penetrance for gene: SCAMP5 were set to unknown
Mode of pathogenicity for gene: SCAMP5 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: SCAMP5 was set to AMBER
Added comment: PMID: 31439720 (Hubert et al. 2019) reported on 2 unrelated individuals with severe ID, seizures behavioral and brain MRI abnormalities (white matter hyperintensity and mesial temporal sclorosis), both harboring the same missense SCAMP5 mutation as a de novo event (NM_001178111.1:c.538G>T or p.Gly180Trp).

Previously aCGH +/- metabolic workup were non diagnostic.

The occurrence of the same de novo variant in both as well as the similar presentation (incl. MRI images) suggested SCAMP5 as the most probable candidate gene, despite presence of few other variants in both.

SCAMP5 is highly expressed in brain (https://www.proteinatlas.org/ENSG00000198794-SCAMP5) and previous studies have suggested a role in synaptic vesicle trafficking (PMIDs cited: 29562188, 25057210, etc).

Cultured skin fibroblasts from affected individuals failed to express SCAMP5.

Scamp is the Drosophila orthologue, with previous studies having demonstrated that mutants display defects in climbing, olfactory-assisted memory and susceptibility to heat induced seizures (PMIDs cited: 25478561, 19144841). Expression of the Scamp Gly302Trp variant in Drosophila ('equivalent' to the SCAMP5 Gly180Trp) revealed strongly reduced levels for the variant compared with wt upon Western Blot, either due to reduced expression or due to increased turnover. Overall the effect of Gly302Trp expression was similar to Scamp knockdown by RNAi (eg. rough eye phenotype, reduced ability to climb the walls of a graded tube after tapping, less/no flies reaching adult stage) but significantly different compared to wt.

As a result, a dominant-negative effect was presumed.
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PMID: 20071347 (Castermans et al. 2010) is cited as a previous report of a relevant affected individual. In this study a 40 y.o. male with early DD, mild ID (IQ of 63) and ASD was found to harbor a de novo apparently balanced t(1;15) translocation affecting CLIC4 and PPCDC (both not associated with ID). [1-Mb resolution aCGH revealed no relevant CNVs].

Studies were however focused on SCAMP5 given that the gene is located downstream of / proximal to PPCDC, has brain-enriched expression as well as involvement in synaptic trafficking and demonstrated:
- Less than 50% expression upon quantitative RT-PCR in patients leukocytes, compared to control.
- Silencing and overexpression of Scamp5 in mouse β-TC3 cells resulted in increased and suppressed respectively secretion of large dense-core vesicles (LDCVs).
- Given conservation of some components involved in secretion of dense core granules (DCGs) in platelets and LDCVs in neuronal cells, study of patient platelets - where SCAMP5 was confirmed to be expressed - suggested an altered pattern of DCGs.
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SCAMP5 is not associated with any phenotype in OMIM/G2P/SysID and not commonly included in gene panels for ID.
----------
Overall, this gene could be considered for inclusion in the ID and epilepsy panels probably with amber (# of unrelated individuals, 1 recurrent de novo variant and 1 regulatory effect, gene expressed in brain with a role in synaptic vesicle trafficking) or red rating (pending further evidence).
Sources: Literature
Intellectual disability v2.1098 PCYT2 Konstantinos Varvagiannis gene: PCYT2 was added
gene: PCYT2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PCYT2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PCYT2 were set to 31637422
Phenotypes for gene: PCYT2 were set to Global developmental delay; Developmental regression; Intellectual disability; Spastic paraparesis; Seizures; Spastic tetraparesis; Cerebral atrophy; Cerebellar atrophy
Penetrance for gene: PCYT2 were set to Complete
Review for gene: PCYT2 was set to GREEN
Added comment: Vaz et al. (2019 - PMID: 31637422 - DDD study among the co-authors) report on 5 individuals - from 4 families - with biallelic PCYT2 mutations.

The phenotype corresponded to a complex hererditary paraplegia with global DD, regression (4/5), ID (mild in 3/5, severe in 2/5), spastic para-/tetraparesis, epilepsy (5/5 - variable onset 2-16 yrs - focal or tonic-clonic seizures) and progressive cerebral and cerebellar atrophy.

Exome sequencing in all revealed biallelic PCYT2 variants, confirmed with Sanger s. in probands and their parents (NM_001184917.2 - corresponding to the canonical transcript used as Ref below):
- P1 (Fam1) : 2 missense SNVs in trans configuration, c.730C>T or p.His244Tyr and c.920C>T or p.Pro307Leu
- P2 (Fam2 - consanguineous of White British origin), P3 (Fam3 - Consanguineous of Turkish origin), P4,5 (Fam4 - consanguineous, unspecified origin) : homozygosity for c.1129C>T or p.Arg377Ter) affecting the last exon of 8/12 transcripts, including the canonical one.

Individuals with the same genotype displayed variable degrees of ID (eg P3 - severe / P2, P4,5 - mild ID).

For sibs in Fam4, homozygosity for a missense SACS variant led to consideration of the respective disorder (AR spastic ataxia of Charlevoix-Saguenay) though the variant was predicted to be tolerated in silico and notably the MRI images not suggestive.

All variants were absent from / had extremely low AF in public databases, with no homozygotes.

Posphatidylethanolamine (PE) is a membrane lipid, particularly enriched in human brain (45% of phospholypid fraction). PE is synthesized either via the CDP-ethanolamine pathway or by decarboxylation of phosphatidylserine in mitochondria. PCYT2 encodes CTP:phosophoethanolamine cytidyltransferase (ET) which is an ubiquitously expressed rate-limiting enzyme for PE biosynthesis in the former pathway.

In silico, the 2 missense variants - localizing in the CTP catalytic domain 2 - were predicted to be damaging, as well as to affect protein stability.

Fibroblasts of 3 patients (P1, P2, P3) representing all variants were studied:
- Enzymatic activity was shown to be significantly reduced (though not absent) compared to controls. Abnormalities were noted upon Western Blot incl. absence in all 3 patients studied of one of the 2 bands normally found in controls (probably representing the longer isoform), reduced intensity in all 3 of another band probably corresponding to a shorter isoform, and presence of an additional band of intermediate molec. mass in patients with the truncating variant.
- RT-PCR on mRNA from patient fibroblasts did not reveal (significant) reduction compared to controls.
- Lipidomic profile of patient fibroblasts was compatible with the location of the block in the phospholipid biosynthesis pathway and different from controls.

The lipidomic profile had similarities with what has been reported for EPT1 deficiency, the enzyme directly downstream of ET. The SELENO1-related phenotype (/EPT1 deficiency) is also highly overlapping.

CRISPR-Cas9 was used to generate pcyt2 partial or complete knockout (ko) zebrafish, targeting either the final (ex13) or another exon (ex3) respectively. mRNA expression was shown to be moderately reduced in the first case and severely reduced/absent in the second, compared to wt. Similarly, complete-ko (ex3) led to significantly lower survival, with impaired though somewhat better survival of partial-ko (ex13) zebrafish.

Complete knockout of Pcyt2 in mice is embryonically lethal (PMID cited: 17325045) while heterozygous mice develop features of metabolic syndrome (PMID cited: 22764088).

Given lethality in knockout zebrafish / mice and the residual activity (15-20%) in patient fibroblasts, the variants reported were thought to be hypomorphic and complete loss of function possibly incompatible with life.

PCYT2 is not associated with any phenotype in OMIM/G2P/SysID and not commonly included in gene panels for ID.

As a result this gene could included in the ID / epilepsy panels with green (~/>3 indiv/fam/variants with the nonsense found in different populations, consistent phenotype, lipidomics, in silico/in vitro/in vivo evidence) or amber rating.

[Please consider inclusion in other possibly relevant panels eg. for metabolic disorders, etc].
Sources: Literature
Intellectual disability v2.1098 PDE6D Konstantinos Varvagiannis gene: PDE6D was added
gene: PDE6D was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PDE6D was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PDE6D were set to 24166846; 30423442
Phenotypes for gene: PDE6D were set to ?Joubert syndrome 22 - MIM 615665
Penetrance for gene: PDE6D were set to Complete
Review for gene: PDE6D was set to AMBER
gene: PDE6D was marked as current diagnostic
Added comment: Thomas et al. (2014 - PMID: 24166846) reported on a consanguineous Pakistani family with 3 members presenting variable polydactyly, brain anomalies (incl. molar tooth sign), microphthalmia/coloboma with retinal disease, renal hypoplasia suggestive of Joubert syndrome.

Genotyping with a SNP array identified a unique 17-Mb region of homozygosity on chr2 with LOD score of 2.6. The region contained 208 genes, of which 15 present in ciliary gene databases. A homozygous splicing variant appeared to be the only relevant, PDE6D being a ciliary gene within this region [NM_002601.4:c.140-1G>A]. Status of all affected members, parents and 2 unaffected sibs was verified with Sanger sequencing.

PDE6D encodes a phosphodiesterase that binds to prenyl groups and has a critical role in ciliogenesis (Humbert et al. - PMID: 23150559 and OMIM).
Several lines of evidence provided support a role for PDE6D and the reported variants :
- Study of PDE6D expression during human embryogenesis suggests ubiquitous localization and highest levels in organs affected in ciliopathies (CNS, kidney tubules, respiratory tract epitherlial cells).
- RT-PCR of mRNA from control/patient fibroblasts and sequencing confirmed the splicing defect leading to an in-frame deletion of exon 3.
- Wt and mutant protein both localized in the basal body of primary cilia (patient/control fibroblasts). Cilia in both cases had normal morphology.
- Experiments in RPE cells confirmed that INPP5E (involved in Joubert/MORM syndrome) interacts (/is probably a cargo of) PDE6D, a process dependent on prenylation.
- Exon 3 deletion was confirmed to disrupt PDE6D binding to INPP5E.
- Analysis by immunofluoresence of INPP5E localization using control/patient fibroblasts and renal tissue showed absence of INPP5E from primary cilia in the case of patient cells (but not controls) suggesting that PDE6D is important for trafficking INPP5E to the cilium.
- Previous study in mice suggested altered photoreceptor physiology in Pde6d (-/-) animals, resulting in a slowly progressing rod/cone dystrophy. The effect was however limited to the eye. (PMID cited : 17496142 - Zhang et al., 2007).
- Morpholino knockdown of pde6d resulted in pericardial edema, eye abnormalities (microphthalmia and disorganized retinal cell layers) and kidney morphogenesis defects (distended, blocked pronephric openings and proximal tubule cysts). Edema was rescued upon coinjection of morpholino with wt (but not mutant) mRNA. Similarly coinjection led to complete or partial rescue of eye development in the case of wt and mutant mRNA respectively supporting pathogenicity and (partial) loss-of-function effect for the variant.
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Mégarbané et al. (2019 - PMID: 30423442) reported on an affected 6 month-old boy born to Lebanese first-cousin parents. Features included hypotonia, developmental delay, microcephaly, oculomotor apraxia, postaxial polydactyly of hands and feet and presence of a molar tooth sign upon brain MRI. Renal and retinal anomalies were absent (also given his age). Exome sequencing revealed homozygosity for a frameshift PDE6D variant [NM_002601.3:c.367_368insG or p.(Leu123Cysfs*13)]. Sanger sequencing confirmed presence of the variant in the proband and carrier status of the parents. The variant affected the penultimate exon (note : present in only this longest transcript) and was not predicted to trigger NMD but rather lead to elimination of a highly conserved PDZ-interaction domain.
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The phenotype associated with biallelic PDE6D variants in OMIM is ?Joubert syndrome 22 - MIM 615665 based only on the 1st report ('delayed psychomotor development' among the features). There is no relevant entry in G2P. PDE6D is listed as a Current primary (/confirmed) ID gene in SysID (the aforementioned PMIDs cited).

This gene is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
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Overall PDE6D could be considered for inclusion in the ID panel probably with amber rating (2 families/variants, DD but outcome otherwise unknown - evidence for the the gene causing JS seems however sufficient).
Sources: Literature
Intellectual disability v2.1098 AP1B1 Konstantinos Varvagiannis gene: AP1B1 was added
gene: AP1B1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: AP1B1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: AP1B1 were set to 31630788; 31630791
Phenotypes for gene: AP1B1 were set to Failure to thrive; Abnormality of the skin; Hearing abnormality; Abnormality of copper homeostasis; Global developmental delay; Intellectual disability
Penetrance for gene: AP1B1 were set to Complete
Review for gene: AP1B1 was set to AMBER
Added comment: Boyden et al. (2019 - PMID: 31630788) and Alsaif et al (2019 - PMID: 31630791) report on the phenotype related to biallelic AP1B1 mutations.

Common features included failure to thrive, ichthyosis (with variable palmoplantar keratoderma/erythroderma/abnormal hair) and hearing loss. Each study focused on different additional features eg. thrombocytopenia or photophobia in all individuals reported by Boyden et al, while Alsaif et al. focused on abnormal copper metabolism (low plasma copper and ceruloplasmin) observed in all 3 affected individuals and enteropathy/hepatopathy observed in 2 sibs.

DD was observed in all 3 individuals (2 families) reported by Alsaif et al. and patient 424 reported by Boyden et al. ID was noted in all individuals of relevant age (2 from 2 families) in the study by Alsaif. Boyden commented that ID is not part of the phenotype. The adult (424) - despite his early DD - was noted to have normal intellect and had graduated college. The other patient (1325) was last followed up at 11 months (still DD was not reported).

AP1B1 encodes one of the large subunits (β1) of the adaptor protein complex 1. Each of the AP complexes is a heterotetramer composed of two large (one of γ, α, δ, ε and β1-β4 for AP-1 to AP-4 respectively), one medium (μ1-μ4) and one small (σ1-σ4) adaptin subunit. The complex is involved in vesicle-mediated transport.

Variants were confirmed in probands and carrier parents (NM_001127.3):
Boyden Pat424 (33y) : c.430T>C (p.Cys144Arg) in trans with c.2335delC (p.Leu779Serfs*26)
Boyden Pat1325 (11m) [consanguineous Ashkenazi Jewish family] : homozygosity for c.2374G>T (p.Glu792*)
Alsaif sibs P1,P2 (4y4m, 1y5m) [consanguineous - Pakistani origin] : homozygous for a chr22 75 kb deletion spanning only the promoter and ex1-2 of AP1B1
Alsaif P3 (4y6m) [consanguineous - Saudi origin] : homozygous for a c.38-1G>A

Variant / additional studies :
22q 75-kb deletion: PCR deletion mapping and Sanger delineated the breakpoints of the 22q12.2 del to chr22:29758984-29815476 (hg?). Complete absence of transcript upon RT-PCR (mRNA from fibrolasts).
Splicing variant (c.38-1G>A): RT-PCR confirmed replacement of the normal transcript by an aberrant harboring a 1 bp deletion (r.40del).
Stopgain variant (c.2374G>T): Western blot demonstrated loss of AP1B1 (and marked reduction also for AP1G1) in cultured keratinocytes of the homozygous patient.

Loss-of-function is the effect predicted by variants. Vesicular defects were observed in keratinocytes of an affected individual (homozygous for the nonsense variant). Rescue of these vesicular defects upon transduction with wt AP1B1 lentiviral construct confirmed the LoF effect. [Boyden et al.]

ATP7A and ATP7B, two copper transporters, have been shown to depend on AP-1 for their trafficking. Similar to MEDNIK syndrome, caused by mutations in AP1S1 and having an overlapping phenotype with AP1B1 (also including hypocupremia and hypoceruloplasminemia), fibroblasts from 2 affected individuals (from different families) demonstrated abnormal ATP7A trafficking. [Alsaif et al.]

Proteomic analysis of clathrin coated vesicles (2 ind from 2 fam) demonstrated that AP1B1 was the only AP1/AP2 CCV component consistently reduced in 2 individuals (from 2 families). [Alsaif et al.]

Boyden et al. provided evidence for abnormal differentiation and proliferation in skin from an affected individual. In addition E-cadherin and β-catenin were shown to be mislocalized in keratinocytes from this affected individual.

Loss of ap1b1 in zebrafish is not lethal but lead to auditory defects (/vestibular deficits). The inner ears appear to develop normally, although there is progressive degeneration of ear epithelia. There are no behavioral/neurological phenotypes listed for mouse models. [ http://www.informatics.jax.org/marker/MGI:1096368 ].

AP1B1 is not associated with any phenotype in OMIM/G2P/SysID.

Overall this gene could be considered for inclusion in the ID panel probably with amber rating.
Sources: Literature
Intellectual disability v2.1098 IQSEC1 Konstantinos Varvagiannis gene: IQSEC1 was added
gene: IQSEC1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: IQSEC1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: IQSEC1 were set to 31607425
Phenotypes for gene: IQSEC1 were set to Central hypotonia; Global developmental delay; Intellectual disability; Behavioral abnormality; Short stature
Penetrance for gene: IQSEC1 were set to Complete
Review for gene: IQSEC1 was set to AMBER
Added comment: Ansar et al. (2019 - PMID: 31607425) reported on 5 individuals with biallelic IQSEC1 variants.

Common features included hypotonia, DD, speech impairment, severe ID, behavioral problems as well as short stature. Early-onset seizures were observed in 3 sibs (for whom there was also a paternal family history of seizures).

These subjects belonging to 2 consanguineous families from Pakistan and S. Arabia were found to harbor homozygous missense variants private to each family (Fam1: NM_001134382.2:c.1028C>T or p.Thr354Met following SNP genotyping of several members and exome of the proband | Fam2: c.962G>A or p.Arg321Gln following exome in 2 affected members). Sanger confirmation and study of parents (+/- sibs) were compatible.

The homozygous variant was the only candidate in the 1st family (also following exclusion of other causes of ID/short stature), and most likely/compatible with the patient's phenotype in the 2nd.

As the authors note, IQSEC1-3 encode guanine exchange factors (GEFs) for the ARF family of GTPases. IQSEC2 is a known XLID gene, while biallelic IQSEC3 mutations in ID have been recently reported (PMID: 31130284), all presenting phenotypic similarities (ID, short stature, speech defect).

Previous studies cited had shown that IQSEC1 & 2 are concentrated at the postsynaptic density of glutamatergic synapses in mammalian brain, playing a role in actin-dependent processes incl. AMPA receptor trafficing at synapses (all refs in article).

Drosophila model: The ortholog of IQSEC1, 2 and 3 is schizo and the phenotype associated with its loss is a growth cone guidance defect through dysregulation of the Slit-Robo pathway (all refs in article). The authors studied overexpression of either reference IQSEC1 cDNA or variant cDNAs in wt flies, the former only being toxic/lethal. Loss of schizo was also embryonically lethal but was partially rescued by expression of reference IQSEC1 cDNA. Expression of cDNA for the 2 variants did not rescue lethality. As a result LoF appears to be the underlying effect of both variants. The authors provided evidence that schizo is localized in glia and neurons at various stages of development and is important for proper axon guidance in both CNS and PNS. In Drosophila, schizo is also localized in photoreceptors and RNAi-mediated knockdown resulted in severely impaired sight (also observed in 1 patient).

Mouse model: Through generation of Iqsec1-floxed mice, it was demonstrated that targeted depletion of Iqsec1 in the cortex resulted in increased density/immature morphology of dendritic spines.

IQSEC1 is not associated with any phenotype in OMIM / G2P / SysID and not commonly included in gene panels for ID.

As a result, this gene could be considered for inclusion in the ID panel as probably as amber (2 families/variants).
Sources: Literature
Intellectual disability v2.1091 NKAP Catherine Snow Added comment: Comment on list classification: NKAP reviewed by Konstantinos Varvagiannis following publication by Fiordaliso et al. (PMID:31587868) who identified 10 males from 8 unrelated families with missense mutations in NKAP (on Xq24) Hypotonia and tall stature with Marfanoid habitus was predominant phenotype. One variant (NM_024528:c.988G>A / p.Arg333Gln) was seen in 4 families and although origin was not provided for all families this variant was seen in brothers with parents from Slovakia and an individual with parents from Japan.
NKAP is not currently in OMIM or Gene2Phenotype.
Rating NKAP as Green as consistent phenotype observed, >3 unrelated individuals and some functional work in Zebrafish.
Intellectual disability v2.1062 TDP2 Konstantinos Varvagiannis gene: TDP2 was added
gene: TDP2 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: TDP2 was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: TDP2 were set to 24658003; 30109272; 31410782
Phenotypes for gene: TDP2 were set to Spinocerebellar ataxia, autosomal recessive 23, 616949)
Penetrance for gene: TDP2 were set to unknown
Review for gene: TDP2 was set to GREEN
gene: TDP2 was marked as current diagnostic
Added comment: Biallelic pathogenic TGP2 variants cause Spinocerebellar ataxia, autosomal recessive 23 (MIM 616949). At least 6 affected individuals from 4 families have been reported, in all cases homozygous for LoF variants (3 different). ID, epilepsy and ataxia are consistent features of the disorder.

TDP2 encodes a phosphodiesterase that is required for efficient repair of double strand breaks (DSBs) produced by abortive topoisomerase II (TOP2) activity.

The gene is expressed in fetal and adult human brain.

Evidence at the variant level (mRNA, protein levels) and additional studies for impairment of TOP2-induced DSB repair support a role.

Animal models (primarily mice) reproduce the DSB repair defect, provide some histopathological evidence, show transcriptional dysregulation of genes (in line with the role of TOP2 in transcription). They have however failed to reproduce relevant neurological phenotypes.

Published studies are summarized below.

TDP2 is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc and GeneDx). There is no associated phenotype in G2P. TDP2 is listed among the current primary ID genes in SysID.

Overall, this gene could be considered for inclusion in the ID and epilepsy panels probably as green (>=3 patients/families/variants, relevant ID and seizures in all, expression in brain, mRNA/protein levels tested, impaired activity) or amber (absence of neurological phenotypes in mouse model).
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[1] - PMID: 24658003 (Gómez-Herreros et al. 2014):
Reports 3 individuals from a consanguineous Irish family. Features included seizures (onset by 2m, 6m and 12y), ID (3/3) and ataxia (3/3).

A splicing variant (NM_016614.3:c.425+1G>A) was found in a 9.08-Mb region of homozygosity shared by all. A further ZNF193 missense variant localizing in the same region was thought unlikely to contribute to the phenotype (evidence also provided in subsequent study).

The effect of the specific variant was proven by abnormal mRNA size, lower mRNA levels due to NMD (corrected upon cyclohexamide treatment), loss of TDP2 protein upon WB, loss of protein activity in lymphoblastoid cells from affected individuals, decreased repair of DSBs and increased cell death upon addition of etoposide (which promotes TOP2 abortive activity).

The authors report very briefly on a further patient (from Egypt), with ID, 'reports of fits' and ataxia. This individual, with also affected sibs, was homozygous LoF (c.413_414delinsAA / p.Ser138*). Again, the authors were not able to detect TDP2 activity in blood from this subject.

As also commented:
- TDP2 has relevant expression in human (particularly adult) brain.
- Mouse model : Tdp2 is expressed in relevant tissues, absence of Tdp2 activity was observed in neural tissue of mice homoyzgous for an ex1-3 del, with impairment of DSB repair. The authors were unable to detect a neurological phenotype with behavioral analyses, preliminary assesment of seizure propensity. Mice did not show developmental defects. Histopathology however, revealed ~25% reduction in the density of interneurons in cerebellum (a 'hallmark of DSB repair' and associated with seizures and ataxia). Transcription of several genes was shown to be disregulated.
- Knockdown in zebrafish appears to affect left-right axis detremination (cited PMID: 18039968).

[2] - PMID: 30109272 (Zagnoli-Vieira et al. 2018):
A 6 y.o. male with seizures (onset by 5m), hypotonia, DD and ID, microcephaly and some additional clinical features and testing (ETC studies on muscle biopsy, +lactate, +(lactate/pyruvate) ratio) which could be suggestive of mitochondrial disorder. This individual from the US was homozygous for the c.425+1G>A variant but lacked the ZNF193 one (despite a shared haplotype with the Irish patients). Again absence of the protein was shown upon WB in patient fibroblasts, also supported by its activity. Complementation studies restored the DSB repair defect. The defect was specific to TOP2-induced DSBs as suggested by hypersensitivity to etoposide but not to ionizing radiation. CRISPR/Cas9 generated mutant human A549 cells demonstrated abnormal DSB repair. Fibroblasts / edited A549 cells failed to show mitochondrial defects (which were noted in muscle).

[3] - PMID: 31410782 (Ciaccio et al. 2019):
A girl born to consanguineous Italian parents, presented with moderate/severe ID, seizures (onset at 12y) and - among others - gait ataxia, tremor and dysmetria. MRI at the age of 12, demonstrated cerebellar atrophy (although previous exams were N). WES revealed a homozygous nonsense variant (c.400C>T / p.Arg134Ter) for which each parent was found to be carrier. Previous investigations included aCGH, NGS testing for epilepsy and metabolic testing.
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.1062 NKAP Konstantinos Varvagiannis reviewed gene: NKAP: Rating: GREEN; Mode of pathogenicity: None; Publications: DOI: 10.1016/j.ajhg.2019.09.009; Phenotypes: Global developmental delay, Intellectual disability, Tall stature, Scoliosis, Pectus excavatum, Pectus carinatum, Arachnodactyly, Camptodactyly, Abnormality of the cardiovascular system, Abnormality of the genitourinary system, Abnormality of the face, Obesity; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.1062 APC2 Konstantinos Varvagiannis gene: APC2 was added
gene: APC2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: APC2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: APC2 were set to 31585108; 25753423; 19759310; 22573669
Phenotypes for gene: APC2 were set to Global developmental delay; Intellectual disability; Seizures; Morphological abnormality of the central nervous system
Penetrance for gene: APC2 were set to Complete
Review for gene: APC2 was set to GREEN
gene: APC2 was marked as current diagnostic
Added comment: Probably 14 individuals from 9 families (8 consanguineous) with biallelic APC2 LoF variants have been reported.

ID and brain abnormalities were features in all, although the presentation was quite different between sibs in the first report (PMID: 25753423 - mild/mod ID, ventriculomegaly and CC anomalies, macrocephaly with variable height, Sotos-like facial features) and 12 subsequently described patients (PMID: 31585108 - severe ID, P>A lissencephaly/CC anomalies/ventriculomegaly/paucity of white matter in (almost) all, gT-C/myoclonic seizures in 8/12 with onset 3m-6y, OFC in the low percentiles).

In all cases relevant alternative diagnoses (eg. macrocephaly/overgrowth syndromes - 1st report, mutations in other lissencephaly genes, metabolic disorders - 2nd) were ruled out.

APC2 encodes Adenomatous polyposis coli protein 2, expressed in the CNS.

All variants reported to date were LoF (stopgain/frameshift/splicing) and were supported by parental-only studies. Mutations in the 1st report as well as 4/8 variants from the 2nd report localized within the last exon (NM_005883.2 / longest of >=3 isoforms), although the 2nd report did not observe obvious genotype-phenotype correlations.

Despite a pLI of 1 in gnomAD, Lee et al. comment that heterozygous carriers did not have any noticeable phenotype. They further note that carriers were not examined by brain MRI, though. 27 heterozygous high-confidence variants appear in individuals in gnomAD. Finally as commented on, APC2 is not mutated in colon cancer.

Animal models: Apc -/- mice displayed disrupted neuronal migration, with defects of lamination of cerebral cortex and cerebellum supporting the observed brain abnormalities. In addition Apc2-deficient mice also presented impaired learning and memory abilities. Extensive additional studies have shown Apc2 co-localization with microtubules affecting their stabilization, distribution along actin fibers (all supporting a role in cytoskeletal organization) and regulation of Rac1 (a Rho GTPase). Generation of Neuro2a cells demonstrated abnormal localization mainly in cell bodies of mutant hAPC2 proteins (due to frameshift in the last exon / deletion of the C-terminal part) - different from wt (neurites, growth cones, cell bodies). The first patient report also provided evidence for Apc2 being a downstream effector of Nsd1, with Nsd1 knockdown brains displaying impaired migration / laminar positioning of cortical neurons (similar to Apc2-/- model) and rescued by forced expression of Apc2.

Relevant articles:
PMIDs: 19759310 and 22573669 (Shintani et al. 2009 & 2012) [mouse model]
PMID: 25753423 (Almuriekhi et al. 2015) [2 individuals + mouse model]
PMID: 31585108 (Lee et al. 2019) [12 individuals from 8 families]
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In OMIM, the APC2-related phenotype is ?Sotos syndrome 3 (MIM 617169 - AR). G2P does not have any associated phenotype for this gene. In SysID, APC2 belongs to the Current primary ID genes.
APC2 is included in gene panels for ID offered by some diagnostic laboratories (eg. Radboudumc, GeneDx).
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Overall, this gene could be considered for inclusion in the ID panel probably as green (>3 individuals/families/variants, highly specific pattern of lissencephaly in 12/14, mouse model supporting migration defects and impaired learning/memory) rather than amber (differences between the 1st and the other families reported as for the OFC and presence of lissencephaly).
Sources: Literature
Intellectual disability v2.1062 CDH2 Konstantinos Varvagiannis changed review comment from: Accogli et al. (2019 - PMID: 31585109) report on 9 individuals with de novo pathogenic CDH2 variants.

Overlapping features included axon pathfinding defects (corpus callosum agenesis/hypoplasia, mirror movements, Duane anomaly), cardiac, ocular and genital anomalies. Neurodevelopmental phenotypes included DD (8/9), ID (2/8 mild and 2/8 moderate, the remaining had either low-average/borderline int. functioning (2), did not present ID (2) or did not have relevant age for evaluation) and ASD (in 2).

CDH2 encodes cadherin-2 (N-cadherin) with high expression in neural tissue. As the authors note, the gene has important role in neural development, incl. proliferation and differentiation of neural progenitor cells, neural tube formation, synaptogenesis, neuronal migration and axon elongation. N-cadherin, similar to other classical cadherins has an extracellular domain with 5 extracellular cadherin (EC) domain repeats that mediate cell adhesion either in cis or in trans (between molecules of the same / different cells).

Mutations in other cadherins have been associated among others with neurodevelopmental disorders (eg. PCDH19, PCDH12, etc).

Variants in all cases were de novo, identified following trio-WES. 7 missense variants (6 of which clustering within the EC4-EC5 linker region or the EC5 domain - calculated p=1.37x10-4) and 2 frameshift ones predicted not to lead to NMD were identified.

One individual had an additional DNM1 variant, formally fulfilling ACMG criteria for pathogenic. The authors however felt that presentation of the specific subject (low-average/borderline int. functioning, absence of seizures and microcephaly) was not compatible with the phenotype of DNM1-encephalopathy .

Missense SNVs within the EC4-EC5 region, were shown to impair cell-cell adhesion by affecting both self-binding and trans adhesion to wt N-cadherin (in L cells studied). This supported a possible dominant-negative effect. A single variant in the EC2 domain - previously shown to be critical for adhesion - was thought to have a similar effect. The authors speculated that truncating variants may also act in a dominant-negative manner (as has been demonstrated for other cadherins) although LoF remains possible.

Cdh2 knockout in mice is embryonically lethal. Mouse with conditional inactivation of Cdh2 in the cerebral cortex leads to cortical disorganization and CCA similar to the human phenotypes (PMIDs cited: 9015265, 17222817). Other animal studies (mouse, zebrafish, chicken, dog, etc) are also cited to link with specific defects.

Heterozygous CDH2 variants affecting the ectodomain have been associated with ARVC (2 variants, one of which segregated with the disorder in a 3-generation family, the other identified in two unrelated families with several affecteds - refs. provided in the article). Cardiac abnormalities were noted in several subjects (incl. electrical activity in 2). [Amber rating of this gene in Arrhythmogenic cardiomyopathy panel].
------
The gene is not associated with any phenotype in OMIM / G2P / SysID and not commonly included in panels for ID.
------
As a result CDH2 could be considered for inclusion in the ID panel probably as amber (mild/moderate ID in 4/8, uncertainty regarding the underlying effect of some variants or additional phenotypes (ARVC)) or green (>3 individuals/variants/families, ID is a feature and in some cases of moderate degree).
Sources: Literature; to: Accogli et al. (2019 - PMID: 31585109) report on 9 individuals with de novo pathogenic CDH2 variants.

Overlapping features included axon pathfinding defects (corpus callosum agenesis/hypoplasia, mirror movements, Duane anomaly), cardiac, ocular and genital anomalies. Neurodevelopmental phenotypes included DD (8/9), ID (2/8 mild and 2/8 moderate, the remaining had either low-average/borderline int. functioning (2), did not present ID (2) or did not have relevant age for evaluation) and ASD (in 2).

CDH2 encodes cadherin-2 (N-cadherin) with high expression in neural tissue. As the authors note, the gene has important role in neural development, incl. proliferation and differentiation of neural progenitor cells, neural tube formation, synaptogenesis, neuronal migration and axon elongation. N-cadherin, similar to other classical cadherins has an extracellular domain with 5 extracellular cadherin (EC) domain repeats that mediate cell adhesion either in cis or in trans (between molecules of the same / different cells).

Mutations in other cadherins have been associated among others with neurodevelopmental disorders (eg. PCDH19, PCDH12, etc).

Variants in all cases were de novo, identified following trio-WES. 7 missense variants (6 of which clustering within the EC4-EC5 linker region or the EC5 domain - calculated p=1.37x10-4) and 2 frameshift ones predicted not to lead to NMD were identified.

One individual had an additional DNM1 variant, formally fulfilling ACMG criteria for pathogenic. The authors however felt that presentation of the specific subject (low-average/borderline int. functioning, absence of seizures and microcephaly) was not compatible with the phenotype of DNM1-encephalopathy .

Missense SNVs within the EC4-EC5 region, were shown to impair cell-cell adhesion by affecting both self-binding and trans adhesion to wt N-cadherin (in L cells studied). This supported a possible dominant-negative effect. A single variant in the EC2 domain - previously shown to be critical for adhesion - was thought to have a similar effect. The authors speculated that truncating variants may also act in a dominant-negative manner (as has been demonstrated for other cadherins) although LoF remains possible.

Cdh2 knockout in mice is embryonically lethal. Conditional inactivation of Cdh2 in the cerebral cortex leads to cortical disorganization and CCA similar to the human phenotypes (PMIDs cited: 9015265, 17222817). Other animal studies (mouse, zebrafish, chicken, dog, etc) are also cited to link with specific defects.

Heterozygous CDH2 variants affecting the ectodomain have been associated with ARVC (2 variants, one of which segregated with the disorder in a 3-generation family, the other identified in two unrelated families with several affecteds - refs. provided in the article). Cardiac abnormalities were noted in several subjects (incl. electrical activity in 2). [Amber rating of this gene in Arrhythmogenic cardiomyopathy panel].
------
The gene is not associated with any phenotype in OMIM / G2P / SysID and not commonly included in panels for ID.
------
As a result CDH2 could be considered for inclusion in the ID panel probably as amber (mild/moderate ID in 4/8, uncertainty regarding the underlying effect of some variants or additional phenotypes (ARVC)) or green (>3 individuals/variants/families, ID is a feature and in some cases of moderate degree).
Sources: Literature
Intellectual disability v2.1062 CDH2 Konstantinos Varvagiannis gene: CDH2 was added
gene: CDH2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CDH2 was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: CDH2 were set to 31585109; 9015265; 17222817
Phenotypes for gene: CDH2 were set to Abnormality of the corpus callosum; Abnormality of neuronal migration; Bimanual synkinesia; Duane anomaly; Abnormality of cardiovascular system; Abnormality of the eye; Abnormality of the genital system; Global developmental delay; Intellectual disability
Penetrance for gene: CDH2 were set to unknown
Review for gene: CDH2 was set to AMBER
Added comment: Accogli et al. (2019 - PMID: 31585109) report on 9 individuals with de novo pathogenic CDH2 variants.

Overlapping features included axon pathfinding defects (corpus callosum agenesis/hypoplasia, mirror movements, Duane anomaly), cardiac, ocular and genital anomalies. Neurodevelopmental phenotypes included DD (8/9), ID (2/8 mild and 2/8 moderate, the remaining had either low-average/borderline int. functioning (2), did not present ID (2) or did not have relevant age for evaluation) and ASD (in 2).

CDH2 encodes cadherin-2 (N-cadherin) with high expression in neural tissue. As the authors note, the gene has important role in neural development, incl. proliferation and differentiation of neural progenitor cells, neural tube formation, synaptogenesis, neuronal migration and axon elongation. N-cadherin, similar to other classical cadherins has an extracellular domain with 5 extracellular cadherin (EC) domain repeats that mediate cell adhesion either in cis or in trans (between molecules of the same / different cells).

Mutations in other cadherins have been associated among others with neurodevelopmental disorders (eg. PCDH19, PCDH12, etc).

Variants in all cases were de novo, identified following trio-WES. 7 missense variants (6 of which clustering within the EC4-EC5 linker region or the EC5 domain - calculated p=1.37x10-4) and 2 frameshift ones predicted not to lead to NMD were identified.

One individual had an additional DNM1 variant, formally fulfilling ACMG criteria for pathogenic. The authors however felt that presentation of the specific subject (low-average/borderline int. functioning, absence of seizures and microcephaly) was not compatible with the phenotype of DNM1-encephalopathy .

Missense SNVs within the EC4-EC5 region, were shown to impair cell-cell adhesion by affecting both self-binding and trans adhesion to wt N-cadherin (in L cells studied). This supported a possible dominant-negative effect. A single variant in the EC2 domain - previously shown to be critical for adhesion - was thought to have a similar effect. The authors speculated that truncating variants may also act in a dominant-negative manner (as has been demonstrated for other cadherins) although LoF remains possible.

Cdh2 knockout in mice is embryonically lethal. Mouse with conditional inactivation of Cdh2 in the cerebral cortex leads to cortical disorganization and CCA similar to the human phenotypes (PMIDs cited: 9015265, 17222817). Other animal studies (mouse, zebrafish, chicken, dog, etc) are also cited to link with specific defects.

Heterozygous CDH2 variants affecting the ectodomain have been associated with ARVC (2 variants, one of which segregated with the disorder in a 3-generation family, the other identified in two unrelated families with several affecteds - refs. provided in the article). Cardiac abnormalities were noted in several subjects (incl. electrical activity in 2). [Amber rating of this gene in Arrhythmogenic cardiomyopathy panel].
------
The gene is not associated with any phenotype in OMIM / G2P / SysID and not commonly included in panels for ID.
------
As a result CDH2 could be considered for inclusion in the ID panel probably as amber (mild/moderate ID in 4/8, uncertainty regarding the underlying effect of some variants or additional phenotypes (ARVC)) or green (>3 individuals/variants/families, ID is a feature and in some cases of moderate degree).
Sources: Literature
Intellectual disability v2.1047 METTL5 Konstantinos Varvagiannis gene: METTL5 was added
gene: METTL5 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: METTL5 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: METTL5 were set to 29302074; http://doi.org/10.1016/j.ajhg.2019.09.007; https://imgc2019.sciencesconf.org/data/abstract_book_complete.pdf
Phenotypes for gene: METTL5 were set to Delayed speech and language development; Intellectual disability; Microcephaly; Behavioral abnormality
Penetrance for gene: METTL5 were set to Complete
Review for gene: METTL5 was set to GREEN
Added comment: [1] - PMID: 29302074 :
In a WES/WGS study of 404 consanguineous families with two or more offspring affected by ID, Hu et al. identified two sibs homozygous for a METTL5 missense variant [NM_014168:c.182G>A / p.Gly61Asp]. These 2 subjects, born to first cousin parents from Iran, presented with early learning impairment, aggressive behaviour, severe microcephaly (-7SD and -8SD) and ID formally evaluated to be in the severe range. Sanger confirmation of variants and segregation studies were performed for all available and informative members in families participating in the study. In silico predictions were all in favour of a deleterious effect (PolyPhen2, MutationTaster, SIFT, CADD) and the variant was absent from ExAC. The effect of the specific variant was studied in ref. 2 (below).

[2] - DOI: 10.1016/j.ajhg.2019.09.007 :
Richard et al. (2019) reported on 5 additional individuals from 2 consanguineous families. Common phenotype consisted of speech delay, moderate/severe ID (4/4), microcephaly (4/4 - though milder than in the first report), behavioral problems (ADHD, aggressiveness, autistic feat.) and possibly some overlapping facial features (nose and ear abnormalities). 3 sibs from the 1st family, from Pakistan, were homozygous for a frameshift variant (NM_014167.2:c.344_345delGA / p.Arg115Asnfs*19) while sibs from the 2nd family, from Yemen, were homozygous for p.Lys191Valfs*1 (c.571_572delAA). Confirmation and segregation studies supported a role for the variants.

The authors performed additional studies for METTL5 and all 3 variants reported to date, notably:
- Based on RNA-seq data from the Allen Brain Atlas, METTL5 is expressed in the developing and adult human brain (incl. cerebellar cortex, hippocampus and striatum).
- Immunostaining in mouse brain demonstrated ubiquitous expression (postnatal day 30).
- In rat hippocampal neurons, enrichment of METTL5 was found in the soma, the nucleus and pre- and post- synaptic regions.
- Myc-/GFP-tagged METTL5 wt or mutants were transiently expressed in COS7 cells, and were found in the cytoplasm and nucleus. Levels of the 2 frameshift variants were significantly reduced compared with wt, although this was not the case for Gly61Asp.
- Upon transfection of rat hippocampal neurons, METTL5-GFP tagged wt and mt proteins showed similar localicalization in nucleus and dendrites.
- Western blot on HEK293T cells transfected with Myc-METTL5 wt or mt constructs demonstrated decreased amounts for the frameshift (but not the missense) variants while comparison after addition of a proteasome inhibitor or cyclohexamide suggested that this is not probably due to decreased mutant protein - rather than mRNA (NMD) - stability.
- In zebrafish, morpholino knockdown of mettl5 led to reduced head size and head/body ratio (reproducing the microcephaly phenotype) and curved tails. Forebrain and midbrain sizes were also significantly reduced.

Based on the ACMG criteria, Gly61Asp is classified as VUS (PM2, PP1, PP3) and the frameshift ones as pathogenic (PS3, PM2, PM4, PP1, PP3).

The authors comment that METTL5 is an uncharacterized member of the methyltransferase superfamily (of 33 METTL proteins). Variants in other methyltransferase-like genes (mainly METTL23) have been associated with ID, while various histone-/DNA-/tRNA-/rRNA- methyltransferases such as EHMT1, DNMT3A, NSUN2, FTSJ1, etc have been implicated in ID. Given the role of methyltransferases in neurodevelopment and neuroplasticity, homology comparisons suggesting presence of relevant domain in METTL5 and accumulation of the protein in the nucleus, a role as epigenetic regulator is proposed (see also ref. 3).

[3] - Conference abstract by Helmut et al. ["A novel m6A RNA methyltransferase in mammals - characterization of Mettl5 mutant mice in the German Mouse Clinic" - Oral presentation in the 33rd International Mammalian Genome Conference Sept. 2019 - available at : https://imgc2019.sciencesconf.org/data/abstract_book_complete.pdf ]
The group using an in vitro methyltransferase assay, identified METTL5 as a m6A RNA methyltransferase. Generation of Mettl5-knockout mice using the CRISPR/Cas technology, suggested that homozygous mice are subviable, with lower body mass and abnormal growth of nasal bones in half. Homozygous mice were hypoactive and hypoexploratory during an open field test at the age of 8 weeks, while further alterations were observed in neurological functions. Phenotypic deviations were absent or very mild in heterozygous animals. As a result, the mouse model appeared to recapitulate relevant human phenotypes (microcephaly, ID and growth retardation).

----
There is no associated entry in OMIM (neither for the gene nor for a related disorder). G2P does not list any phenotype for this gene, either.

METTL5 is included in the SysID database as a current primary ID gene (cited: 27457812, 28097321 / Given the shared co-authors with the study by Richard et al. as well as the overlapping variants, these articles probably report on the same individuals recently described in more detail).

The gene is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).
----

Overall, METTL5 could be considered for inclusion in the ID panel probably as green (3 families, 3 variants, segregation, suggested role of the gene, relevant expression patterns, some evidence at the variant-level, zebrafish and mouse models) or amber (underlying effect of Gly61Asp unknown and variant classified as VUS).
Sources: Literature
Intellectual disability v2.1047 CSDE1 Konstantinos Varvagiannis gene: CSDE1 was added
gene: CSDE1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CSDE1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CSDE1 were set to http://doi.org/10.1126/sciadv.aax2166
Phenotypes for gene: CSDE1 were set to Autism; Global developmental delay; Intellectual disability
Penetrance for gene: CSDE1 were set to unknown
Review for gene: CSDE1 was set to GREEN
Added comment: Guo et al. (2019 - DOI: 10.1126/sciadv.aax2166) report on 18 individuals from 18 unrelated families, with heterozygous likely gene disrupting (stopgain/frameshift/spice-site) CSDE1 variants.

Initial sequencing with MIPs found in 3 individuals from an autism cohort (4045 probands), while subsequent targeted sequencing of a larger cohort (autism spectrum/ID network) led to identification of 5 additional relevant individuals and Genematcher/collaborations a further 10 (the latter by WES).

Consistent phenotypes included ASD (10 of 15 formally evaluated), DD (motor: 15/17 - speech: 17/17) and ID (mild to severe in 14 of 16 assessed, in further 2 in the below-average range). Recurrent seizures or epilepsy were reported for 7 of 16 patients. Other variable features were anxiety or ADHD, increased OFC, ocular, hand and MRI anomalies.

The study was mainly focused on LGD variants with p.R123* (NM_001242891.1:c.367C>T) being a reccurrent one, found in 3 families.

8 of these variants were de novo, 8 further inherited (often from a less severely affected parent, although parental neuropsychiatric status was not available for individuals from all 3 groups). In 2 cases inheritance was unknown (only 1 parental sample available).

3 individuals with de novo missense variants were also identified. Features in those individuals also included ASD and/or DD and ID (2/3) [Table S1].

Arguments to support involvement of the CSDE1 variants included the:
- role of the gene encoding an RNA binding protein implicated in neuronal migration/differentiation (cited : 24012837, 29129916),
- statistically significant burden of the variants in the cohorts examined,
- relevant CSDE1 intolerance scores (pLI of 1 and %RVIS of 6.18),
- relevant human (mRNA) / mouse (protein) spatial and temporal expression patterns,
- exclusion of apparent alternative diagnoses to the extent possible in many subjects with CNVs/SNVs/ROH of uncertain significance in very few,
- cosegregation with rather similar neuropsychiatric phenotypes in case of carrier parents,
- enrichment of ASD-related genes (and FMRP targets) among CSDE1-binding targets,
- suppression of Ctnnb1 expression (at the protein level) affecting Wnt/β-catenin signalling,
- effect of knockdown and/or mutants in mouse (shRNA) and Drosophila (mt and siRNA) models affecting synapse formation and synaptic transmission,
- rescue of many of the previous phenotypes by expression of human CSDE1 (mice), expression of stabilized β-Catenin (mice) or RNAi-stable-dUNR (Drosophila) [also supporting LoF as the underlying effect of variants].

CSDE1 is not commonly included in gene panels for ID offered by diagnostic laboratories. There is no associated phenotype in OMIM/G2P.

Overall, this gene could be considered for inclusion in the ID panel probably as green (or amber).
Sources: Literature
Intellectual disability v2.1046 PMPCB Konstantinos Varvagiannis changed review comment from: Biallelic pathogenic PMPCB variants cause, Multiple mitochondrial dysfunctions syndrome 6 (MIM 617954).

5 relevant individuals from 4 unrelated families (in one case consanguineous) have been reported by Vögtle et al. (2018 - PMID: 29576218).

Onset of symptoms (eg. hypotonia) often preceded a period of developmental regression/stagnation which was common in all individuals and occurred within the first 2 years of life, usually following febrile illness. In all cases neurological features were severe (lack of ambulation/speech). Seizures were observed in 4 individuals from 3 families, with onset at the age of 11-24m. MRI images demonstrated T2 signal hyperintensities of the basal ganglia with cerebellar and cerebral atrophy in some. Deterioration with early death was reported on three occasions, though some years after symptom onset.

Following exclusion of other diagnoses in some cases (eg. aCGH, epilepsy panel), WES identified biallelic PMPCB missense variants, supported by Sanger confirmation and segregation studies. The following variants were reported (NM_004279.2):
- c.523C>T (p.Arg175Cys) in trans with c.601G>C (p.Ala201Pro) [Fam A and B]
- c.524G>A (p.Arg175His) in trans with c.530T>G (p.Val177Gly) [Fam C]
- c.1265T>C (p.Ile422Thr) in homozygous state [Fam D with 2 affected sibs]

The gene encodes the catalytic (beta) subunit of the mitochondrial processing protease (MPP) which is responsible for the cleavage/maturation of nuclear-encoded mitochondrial precursor proteins after their import in mitochondria. The alpha subunit is encoded by PMPCA (green rating proposed for this panel).

Extensive studies demonstrated (perhaps a better summary provided by OMIM):
- Reduced PMPCB protein levels in mitochondria isolated from patient fibroblasts or patient-derived pluripotent stem cells.
- Frataxin maturation was impaired with accumulation of the intermediate form and lower amounts of mature FXN, indicating decrease in MPP activity.
- Analysis of the homologous Mas1 S. cerevisiae mutants was carried out, with the exception of Ile422Thr (corresponding to Mas1 - Ile398Thr), the introduction of which did not yield viable yiest strains. Homologous mutations led to a temperature-sensitive phenotype with accumulation of immature/unprocessed precursor proteins and decrease of mature/processed forms both in vivo or in organello (following isolation of mitochondria). Under conditions of heat stress, Mas1 mutations decreased biogenesis of Fe-S clusters.
- Respiratory chain complexes I-III contain Fe-S clusters. In muscle biopsy from an affected individual, complex II activity was significantly reduced (although this was not the case in fibroblasts or liver biopsy). Dysfunction of mitochondrial and cytosolic Fe-S cluster-dependent enzymes (eg. aconitase) was also shown in muscle tissue.

Regression/stagnation with seizures/non-achievement of milestones may justify testing for an ID / epilepsy gene panel. In addition, metabolic studies or mitochondrial respiratory chain complex studies were sometimes non-informative (lactate elevated in 3/5 subjects) or not carried out at all / in relevant tissues (muscle biopsy in 2 individuals, fibroblasts/liver biopsy did not demonstrate reduced complex activity when tested).

PMPCB is included in the ID gene panel of Radboudumc, as well as the SysID database. The gene is included in the DD panel of G2P associated with "Neurodegeneration in Early Childhood" (disease confidence : probable).

As a result, PMPCB can be considered for inclusion in both epilepsy and ID panels as green (or amber).
Sources: Literature, Radboud University Medical Center, Nijmegen; to: Biallelic pathogenic PMPCB variants cause, Multiple mitochondrial dysfunctions syndrome 6 (MIM 617954).

5 relevant individuals from 4 unrelated families (in one case consanguineous) have been reported by Vögtle et al. (2018 - PMID: 29576218).

Onset of symptoms (eg. hypotonia) often preceded a period of developmental regression/stagnation which was common in all individuals and occurred within the first 2 years of life, usually following febrile illness. In all cases neurological features were severe (lack of ambulation/speech). Seizures were observed in 4 individuals from 3 families, with onset at the age of 11-24m. MRI images demonstrated T2 signal hyperintensities of the basal ganglia with cerebellar and cerebral atrophy in some. Deterioration with early death was reported on three occasions, though some years after symptom onset.

Following exclusion of other diagnoses in some cases (eg. aCGH, epilepsy panel), WES identified biallelic PMPCB missense variants, supported by Sanger confirmation and segregation studies. The following variants were reported (NM_004279.2):
- c.523C>T (p.Arg175Cys) in trans with c.601G>C (p.Ala201Pro) [Fam A and B]
- c.524G>A (p.Arg175His) in trans with c.530T>G (p.Val177Gly) [Fam C]
- c.1265T>C (p.Ile422Thr) in homozygous state [Fam D with 2 affected sibs]

The gene encodes the catalytic (beta) subunit of the mitochondrial processing protease (MPP) which is responsible for the cleavage/maturation of nuclear-encoded mitochondrial precursor proteins after their import in mitochondria. The alpha subunit is encoded by PMPCA (green rating proposed for this panel).

Extensive studies demonstrated (perhaps a better summary provided by OMIM):
- Reduced PMPCB protein levels in mitochondria isolated from patient fibroblasts or patient-derived pluripotent stem cells.
- Frataxin maturation was impaired with accumulation of the intermediate form and lower amounts of mature FXN, indicating decrease in MPP activity.
- Analysis of the homologous Mas1 S. cerevisiae mutants was carried out, with the exception of Ile422Thr (corresponding to Mas1 - Ile398Thr), the introduction of which did not yield viable yeast strains. Homologous mutations led to a temperature-sensitive phenotype with accumulation of immature/unprocessed precursor proteins and decrease of mature/processed forms both in vivo or in organello (following isolation of mitochondria). Under conditions of heat stress, Mas1 mutations decreased biogenesis of Fe-S clusters.
- Respiratory chain complexes I-III contain Fe-S clusters. In muscle biopsy from an affected individual, complex II activity was significantly reduced (although this was not the case in fibroblasts or liver biopsy). Dysfunction of mitochondrial and cytosolic Fe-S cluster-dependent enzymes (eg. aconitase) was also shown in muscle tissue.

Regression/stagnation with seizures/non-achievement of milestones may justify testing for an ID / epilepsy gene panel. In addition, metabolic studies or mitochondrial respiratory chain complex studies were sometimes non-informative (lactate elevated in 3/5 subjects) or not carried out at all / in relevant tissues (muscle biopsy in 2 individuals, fibroblasts/liver biopsy did not demonstrate reduced complex activity when tested).

PMPCB is included in the ID gene panel of Radboudumc, as well as the SysID database. The gene is included in the DD panel of G2P associated with "Neurodegeneration in Early Childhood" (disease confidence : probable).

As a result, PMPCB can be considered for inclusion in both epilepsy and ID panels as green (or amber).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.1046 PMPCB Konstantinos Varvagiannis gene: PMPCB was added
gene: PMPCB was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: PMPCB was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: PMPCB were set to Multiple mitochondrial dysfunctions syndrome 6, 617954
Penetrance for gene: PMPCB were set to Complete
Review for gene: PMPCB was set to GREEN
gene: PMPCB was marked as current diagnostic
Added comment: Biallelic pathogenic PMPCB variants cause, Multiple mitochondrial dysfunctions syndrome 6 (MIM 617954).

5 relevant individuals from 4 unrelated families (in one case consanguineous) have been reported by Vögtle et al. (2018 - PMID: 29576218).

Onset of symptoms (eg. hypotonia) often preceded a period of developmental regression/stagnation which was common in all individuals and occurred within the first 2 years of life, usually following febrile illness. In all cases neurological features were severe (lack of ambulation/speech). Seizures were observed in 4 individuals from 3 families, with onset at the age of 11-24m. MRI images demonstrated T2 signal hyperintensities of the basal ganglia with cerebellar and cerebral atrophy in some. Deterioration with early death was reported on three occasions, though some years after symptom onset.

Following exclusion of other diagnoses in some cases (eg. aCGH, epilepsy panel), WES identified biallelic PMPCB missense variants, supported by Sanger confirmation and segregation studies. The following variants were reported (NM_004279.2):
- c.523C>T (p.Arg175Cys) in trans with c.601G>C (p.Ala201Pro) [Fam A and B]
- c.524G>A (p.Arg175His) in trans with c.530T>G (p.Val177Gly) [Fam C]
- c.1265T>C (p.Ile422Thr) in homozygous state [Fam D with 2 affected sibs]

The gene encodes the catalytic (beta) subunit of the mitochondrial processing protease (MPP) which is responsible for the cleavage/maturation of nuclear-encoded mitochondrial precursor proteins after their import in mitochondria. The alpha subunit is encoded by PMPCA (green rating proposed for this panel).

Extensive studies demonstrated (perhaps a better summary provided by OMIM):
- Reduced PMPCB protein levels in mitochondria isolated from patient fibroblasts or patient-derived pluripotent stem cells.
- Frataxin maturation was impaired with accumulation of the intermediate form and lower amounts of mature FXN, indicating decrease in MPP activity.
- Analysis of the homologous Mas1 S. cerevisiae mutants was carried out, with the exception of Ile422Thr (corresponding to Mas1 - Ile398Thr), the introduction of which did not yield viable yiest strains. Homologous mutations led to a temperature-sensitive phenotype with accumulation of immature/unprocessed precursor proteins and decrease of mature/processed forms both in vivo or in organello (following isolation of mitochondria). Under conditions of heat stress, Mas1 mutations decreased biogenesis of Fe-S clusters.
- Respiratory chain complexes I-III contain Fe-S clusters. In muscle biopsy from an affected individual, complex II activity was significantly reduced (although this was not the case in fibroblasts or liver biopsy). Dysfunction of mitochondrial and cytosolic Fe-S cluster-dependent enzymes (eg. aconitase) was also shown in muscle tissue.

Regression/stagnation with seizures/non-achievement of milestones may justify testing for an ID / epilepsy gene panel. In addition, metabolic studies or mitochondrial respiratory chain complex studies were sometimes non-informative (lactate elevated in 3/5 subjects) or not carried out at all / in relevant tissues (muscle biopsy in 2 individuals, fibroblasts/liver biopsy did not demonstrate reduced complex activity when tested).

PMPCB is included in the ID gene panel of Radboudumc, as well as the SysID database. The gene is included in the DD panel of G2P associated with "Neurodegeneration in Early Childhood" (disease confidence : probable).

As a result, PMPCB can be considered for inclusion in both epilepsy and ID panels as green (or amber).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.1046 PMPCA Konstantinos Varvagiannis gene: PMPCA was added
gene: PMPCA was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: PMPCA was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PMPCA were set to 25808372; 26657514; 27148589; 30617178
Phenotypes for gene: PMPCA were set to Spinocerebellar ataxia, autosomal recessive 2 (MIM 213200)
Penetrance for gene: PMPCA were set to Complete
Review for gene: PMPCA was set to GREEN
gene: PMPCA was marked as current diagnostic
Added comment: Biallelic pathogenic PMPCA variants cause Spinocerebellar ataxia, autosomal recessive 2 (SCAR2 - MIM 213200). More than 20 individuals from several unrelated families have been reported. At least 6 different pathogenic variants have been identified. Loss of PMPCA function is the suggested mechanism. ID is a feature of the disorder.

PMPCA encodes the α-subunit of mitochondrial processing peptidase (αMPP), a heterodimeric enzyme responsible for the cleavage of nuclear-encoded mitochondrial precursor proteins after import in the mitochondria (summary by Jobling et al and OMIM).

Arguments for involvement of the gene include the highly similar phenotype, segregation studies, expression of the gene in fetal and relevant adult tissues (in brain/cerebellum/cerebellar vermis), lower protein levels demonstrated for some variants, abnormal processing of frataxin (in line with the role of αMPP) demonstrated in most cases, rescue of the maturation defect upon transduction of wt PMPCA cDNA, disruption of REDOX balance in patient cells, etc.

Relevant studies are summarized below.

PMPCA is included in gene panels for ID offered by several diagnostic laboratories (incl. Radboud UMC, GeneDx, etc) and listed as a confirmed ID gene in SysID. It is not associated with any phenotype in G2P.

As a result, this gene can be considered for inclusion in the current panel probably as green (or amber).

----

[1] - Jobling et al. (2015 - PMID: 25808372) described the phenotype of 17 individuals from 4 families, all presenting with non-progressive cerebellar ataxia and the majority with ID of variable severity (15/17 - relevant to the current panel). Individuals from 3 of the families - all of Lebanese origin - were homozygous for NM_015160.3:c.1129G>A (p.Ala377Thr). A further similarly affected subject was compound heterozygous for c.287C>T (p.Ser96Leu) and c.1543G>A (p.Gly515Arg).

The homozygous variant in the first family was found within a 2.85 Mb linkage region on chr 9q34. An additional variant within this region (in CAMSAP1) was discarded following results in other families of the same origin.

Semi-quantitative RT-PCR demonstrated fetal expression of the PMPCA as well as relatively higher expression in adult brain, cerebellum and cerebellar vermis.

As for Ala377Thr, protein levels were shown to be lowest in affected individuals (LCLs, fibroblasts) and low - though somewhat higher - in carrier parents (LCL) compared to controls. RT-PCR on total RNA from LCLs did not show evidence of abnormal transcripts/additional splicing defect. Localization of mutant protein and morphology of mitochondrial reticulum was similar to controls. Maturation of frataxin - the protein depleted in Friedreich ataxia - was shown to be abnormal in patient lymphoblasts, compatible with the role of αMPP. In line with abnormal mitochondrial function, REDOX balance was increased in patient cells.

[2] - Choquet et al. (2016 - PMID: 26657514) reported on 2 sibs - born to distantly related parents. The authors noted a phenotype corresponding to SCAR2 although the presentation was somewhat milder, intellectual disability was not a feature (despite some learning difficulties in one) and ataxia was progressive. WES demonstrated homozygosity for NM_015160:c.766G>A (p.Val256Met). Western blot in patient lymphoblasts showed αMPP levels similar to carriers and controls. Abnormal maturation (accumulation of specific isoforms) was shown for frataxin.

[3] - Joshi et al. (2016 - PMID: 27148589) described the phenotype of 2 cousins belonging to a large Lebanese pedigree. Presentation in both was compatible with multisystem involvement incl. profound global DD, severe hypotonia, weakness, respiratory insufficiency, blindness suggestive of mitochondrial disorder. mtDNA, analyses of mitochondrial focused nuclear gene panel and aCGH were non-diagnostic. Both subjects were compound heterozygous for NM_015160.3:c.1066G>A (p.Gly356Ser) and c.1129G>A (p.Ala377Thr) following WES, with compatible segregation studies within the family. Western blot revealed PMPCA levels similar to control. Reduction of PMPCA staining and abnormally enlarged mitochondria were observed upon immunofluorescence in patient fibroblasts. Frataxin processing was abnormal. Lentiviral transduction of patient fibroblasts with wt PMPCA cDNA, led to increased PMPCA levels and correction of frataxin processing.

[4] - Rubegni et al. (2019 - PMID: 30617178) report on a 7-y.o. boy with global DD, spastic-ataxic gait and 'low IQ'. MRI images were suggestive of cerebellar atrophy with hyperintensity in the striatum. The child was homozygous for c.553C>T / p.Arg185Trp (reference not specified, although the variant would be compatible with NM_015160.3).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.1022 CACNA2D2 Konstantinos Varvagiannis gene: CACNA2D2 was added
gene: CACNA2D2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CACNA2D2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CACNA2D2 were set to 23339110; 24358150; 30410802; 29997391; 31402629; 11487633; 11756448; 4177347; 14660671; 15331424
Phenotypes for gene: CACNA2D2 were set to Cerebellar atrophy with seizures and variable developmental delay (MIM 618501)
Penetrance for gene: CACNA2D2 were set to Complete
Review for gene: CACNA2D2 was set to AMBER
gene: CACNA2D2 was marked as current diagnostic
Added comment: Gene reviewed for the epilepsy panel. Due to the phenotype of EE, with variable GDD (severe in many cases) and/or ID (either specifically commented on or inferred in some cases, although not universal) this gene might also be relevant for the current panel. CACNA2D2 is also included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx) as well as the SysID database. There is no associated phenotype in G2P.

Copied from the epilepsy panel:

Biallelic pathogenic CACNA2D2 variants cause Cerebellar atrophy with seizures and variable developmental delay (MIM 618501).

A recent OMIM update, a subsequent relevant publication by Punatha et al. as well as several additional LP/P variants in ClinVar for the phenotype of epileptic encephalopathy, support possible upgrade to green.

The following affected individuals appear to be relevant [NM_006030.3 used as RefSeq unless otherwise specified]:

[1] Edvardson et al. (PMID: 23339110) - 3 sibs born to consanguineous parents with EIEE, severe GDD / ID (inferred from the descritpion, at least for the oldest one), cerebellar atrophy and movement abnormalities. A CACNA2D2 variant (c.3137T>C / p.Leu1046Pro) was found in affected individuals by SNP-arrays and WES in one of them. Functional studies (reduction in current density of calcium channels in Xenopus laevis oocytes) supported the deleterious effect of the variant. A role of a rare hmz CESLR3 variant could not be ruled out.

[2] Pippucci et al. (PMID: 24358150) - 1 individual born to consanguineous parents, presenting with EE (onset at 1-2 m), severe GDD, cerebellar atrophy and choreiform movements. Homozygosity for a LoF variant (c.1294delA - p.Asn432fs) was found by WES. The role of the variant was further supported by expression studies (80% reduced mRNA levels, protein levels estimated at 3% of control / milder effect in htz parents). The proband was also hmz for a CESLR3 variant. Previous studies incl. 'high-resolution karyotype' and metabolic investigations.

[3] Butler et al. (PMID: 30410802) - A 5 y.o. male, with EE (seizure onset at 7m / GDD) and cerebellar atrophy. Compound heterozygosity for c.782C>T (p.Pro261Leu) and c.3137T>C (p.Leu1046Pro) was demonstrated by WES and supported by segregation studies.

[4] Valence et al. (PMID: 29997391) - Reported on a 20 y.o. male belonging to a cohort of 20 individuals with congenital ataxia, all from consaguineous families. This individual, who had cerebellar atrophy, ataxia, a single episode of febrile seizures and normal cognitive impairment was homozygosity for c.2971G>A (p.Asp991Asn). RT-PCR revealed presence of a normal length transcript as well as an additional, longer one, due to a concurrent splicing effect (activation of a cryptic donor splice site and retention of 4 bases of intronic sequence). Presence of both nl/abn length transcripts was presumed to explain the mild phenotype (variability also commented in OMIM).

[5] Punatha et al. (PMID: 31402629) - 3 affected individuals from 2 consanguineous families presenting with early onset EE (onset 1-7m), GDD/ID, cerebelar atrophy and ataxia. Sibs from the first family were homozygous for c.1778G>C (p.Arg593Pro). An affected 5 y.o. child from the 2nd family was homozygous for c.485_486delAT (p.Tyr162Ter). Mutations were found by WES in regions of AOH.

The following variants - not reported in the literature - have been submitted in ClinVar as LP / P for EE:
[VCV000645106.1] NM_006030.4:c.1389+2T>C - EIEE with suppression bursts - Likely Pathogenic (Invitae)
[VCV000570589.1] NM_006030.4:c.1956_1960del (p.Asn652fs) - EIEE - Pathogenic (Invitae)
[VCV000578284.1] NM_006030.4:c.1555C>T (p.Gln519Ter) - EIEE - Pathogenic (Invitae)
[VCV000653393.1] NM_006030.4:c.851dup (p.Ala286fs) - EIEE with suppression bursts - Pathogenic (Invitae)
[VCV000411003.1] NM_006030.4:c.485_486del (p.Tyr161_Tyr162insTer) - EIEE - Pathogenic (Invitae)

Additional ones have been reported as LP / P although the condition is not specified.
[VCV000620551.1] NM_006030.4:c.1023C>A (p.Cys341Ter) - Likely pathogenic (GeneDx)
[VCV000373439.2] NM_006030.4:c.1846-1G>A - Likely pathogenic (GeneDx)
[VCV000423330.2] NM_006030.4:c.200dup (p.His68fs) - Pathogenic (GeneDx).

The aforementioned laboratories include CACNA2D2 in gene panels for epilepsy (Invitae) and/or ID (GeneDx).

A role for the CACNA2D2 is supported by :
- The highly overlapping features (with the exception of the milder phenotype reported by Valence et al.) incl. early onset of seizures, GDD, cerebellar atrophy in all (9/9 incl. the individual reported by Valence, as evaluated Punatha et al). Ataxia was a feature in many (with movement abnormalities also in the remaining ones).
- The role of the gene encoding the alpha-2-delta-2 auxiliary subunit of high voltage-gated calcium channels. Auxiliary subunits modulate calcium current and channel activation and inactivation kinetics, and may be involved in proper assembly and membrane localization of the channels (summary by Edvardson and OMIM).
- Functional / expression studies for some of the variants (as in Refs 1,2,4).
- Relevant expression patterns (notably in cerebellum) [GTEx project]
- Mouse models recapitulating the human phenotypes (summarized by Edvardson et al) : The 'ducky' mouse model (due to biallelic Cacna2d2 mutations) presenting absence epilepsy, spike-wave seizures and ataxia. Dysgenesis of the cerebellum is among the neuropathological findings (PMIDs cited : 11487633, 11756448, 4177347). The 'entla' mouse model (also AR due to an in-frame duplication) presents also epilepsy and ataxia (PMID : 14660671). Targeted knockout in another mouse model resulted also in ataxic gait, seizure susceptibility and cerebellar anomalies/degeneration (PMID: 15331424).

[Please consider inclusion in other relevant panels eg. for cerebellar anomalies / ataxia].
Sources: Literature
Intellectual disability v2.1022 GABRA2 Konstantinos Varvagiannis changed review comment from: Heterozygous pathogenic GABRA2 variants cause Epileptic encephalopathy, early infantile, 78 (MIM 618557) [new OMIM entry].

At least 8 relevant individuals have been reported to date in the following studies:
- Orenstein et al. (2018 - PMID: 29422393) - 1 individual
- Butler et al. (2018 - PMID: 29961870) - 1 subject
- Maljevic et al. (2019 - PMID: 31032849 - 3 unrelated children as well as 2 affected sibs
- Sanchis-Juan et al. (2019 - bioRxiv / https://doi.org/10.1101/678219) - 1 further patient

In all affected individuals the variants were missense and - in almost all cases - had occurred as de novo events. The 2 sibs reported by Maljevic however, had inherited a missense variant from their unaffected mosaic parent.

Clinical descriptions for individuals from the 3 studies are provided in OMIM and also summarized in the suppl. table 1 by Sanchis-Juan et al. (https://www.biorxiv.org/content/biorxiv/early/2019/06/21/678219/DC2/embed/media-2.xlsx). Seizures, DD and ID (relevant to the current panel) are among the reported features. Functional studies have been performed for most of the variants and are summarized for each one in the OMIM entry for GABRG2 and the aforementioned table as well.

The following variants have been reported (NM_000807.2): c.1003A>C - p.Asn335His (dn) / c.875C>A - Thr292Lys (dn) / c.871C>G - p.Leu291Val (dn) / c.788T>C - p.Met263Thr (dn) / c.851T>C - p.Val284Ala (dn) / c.975C>A - p.Phe325Leu (inherited from mosaic parent) / c.839C>T - p.Pro280Leu (dn - Sanchis-Juan et al).

As commented by Jenkins and Escayg (2019 - PMID: 31032848 / both among the authors of the 1st report) as well as by Sanchis-Juan et al., both loss- and gain- of function effects explain the pathogenicity of the various mutations reported to date. [In gnomAD GABRA2 has a Z-score for missense variants of 3.13 as well as a pLI of 1].
------
GABRA2 is not associated with any phenotype in G2P.
This gene is not commonly included in gene panels for ID offered by diagnostic laboratories.
------
As a result, GABRA2 can be considered for inclusion in the epilepsy and ID panels probably as green (several relevant individuals, several reported variants with supporting functional studies for most, etc.).

[Consider inclusion in other possibly relevant gene panels eg. for ASD which was feature in some patients at relevant age and/or among those evaluated].; to: Heterozygous pathogenic GABRA2 variants cause Epileptic encephalopathy, early infantile, 78 (MIM 618557) [new OMIM entry].

At least 8 relevant individuals have been reported to date in the following studies:
- Orenstein et al. (2018 - PMID: 29422393) - 1 individual
- Butler et al. (2018 - PMID: 29961870) - 1 subject
- Maljevic et al. (2019 - PMID: 31032849 - 3 unrelated children as well as 2 affected sibs
- Sanchis-Juan et al. (2019 - bioRxiv / https://doi.org/10.1101/678219) - 1 further patient

In all affected individuals the variants were missense and - in almost all cases - had occurred as de novo events. The 2 sibs reported by Maljevic however, had inherited a missense variant from their unaffected mosaic parent.

Clinical descriptions for individuals from the 3 studies are provided in OMIM and also summarized, Maljevic - Table 1 (7 patients) and/or in the suppl. table 1 by Sanchis-Juan et al. (8 patients) (https://www.biorxiv.org/content/biorxiv/early/2019/06/21/678219/DC2/embed/media-2.xlsx). Seizures, DD and ID (relevant to the current panel) are among the reported features. Functional studies have been performed for most of the variants and are summarized for each one in the OMIM entry for GABRG2 and the aforementioned table as well.

The following variants have been reported (NM_000807.2): c.1003A>C - p.Asn335His (dn) / c.875C>A - Thr292Lys (dn) / c.871C>G - p.Leu291Val (dn) / c.788T>C - p.Met263Thr (dn) / c.851T>C - p.Val284Ala (dn) / c.975C>A - p.Phe325Leu (inherited from mosaic parent) / c.839C>T - p.Pro280Leu (dn - Sanchis-Juan et al).

As commented by Jenkins and Escayg (2019 - PMID: 31032848 / both among the authors of the 1st report) as well as by Sanchis-Juan et al., both loss- and gain- of function effects explain the pathogenicity of the various mutations reported to date. [In gnomAD GABRA2 has a Z-score for missense variants of 3.13 as well as a pLI of 1].
------
GABRA2 is not associated with any phenotype in G2P.
This gene is not commonly included in gene panels for ID offered by diagnostic laboratories.
------
As a result, GABRA2 can be considered for inclusion in the epilepsy and ID panels probably as green (several relevant individuals, several reported variants with supporting functional studies for most, etc.).

[Consider inclusion in other possibly relevant gene panels eg. for ASD which was feature in some patients at relevant age and/or among those evaluated].
Intellectual disability v2.1022 GABRA2 Konstantinos Varvagiannis gene: GABRA2 was added
gene: GABRA2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: GABRA2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: GABRA2 were set to 29422393; 29961870; 31032849; 31032848; doi.org/10.1101/678219
Phenotypes for gene: GABRA2 were set to Epileptic encephalopathy, early infantile, 78 (MIM 618557)
Penetrance for gene: GABRA2 were set to unknown
Review for gene: GABRA2 was set to GREEN
Added comment: Heterozygous pathogenic GABRA2 variants cause Epileptic encephalopathy, early infantile, 78 (MIM 618557) [new OMIM entry].

At least 8 relevant individuals have been reported to date in the following studies:
- Orenstein et al. (2018 - PMID: 29422393) - 1 individual
- Butler et al. (2018 - PMID: 29961870) - 1 subject
- Maljevic et al. (2019 - PMID: 31032849 - 3 unrelated children as well as 2 affected sibs
- Sanchis-Juan et al. (2019 - bioRxiv / https://doi.org/10.1101/678219) - 1 further patient

In almost all affected individuals, the variants were missense and had occurred as de novo events. The 2 sibs reported by Maljevic however, had inherited a missense variant from their unaffected mosaic parent.

Clinical descriptions for individuals from the 3 studies are provided in OMIM and also summarized in the suppl. table 1 by Sanchis-Juan et al. (https://www.biorxiv.org/content/biorxiv/early/2019/06/21/678219/DC2/embed/media-2.xlsx?download=true). Seizures, DD and ID (relevant to the current panel) are among the reported features. Functional studies have been performed for most of the variants and are summarized for each one in the OMIM entry for GABRG2 and the aforementionned table as well.

The following variants have been reported (NM_000807.2): c.1003A>C - p.Asn335His (dn) / c.875C>A - Thr292Lys (dn) / c.871C>G - p.Leu291Val (dn) / c.788T>C - p.Met263Thr (dn) / c.851T>C - p.Val284Ala (dn) / c.975C>A - p.Phe325Leu (inherited from mosaic parent) / c.839C>T - p.Pro280Leu (dn - Sanchis-Juan et al).

As commented by Jenkins and Escayg (2019 - PMID: 31032848 / both among the authors of the 1st report) as well as by Sanchis-Juan et al., both loss- and gain- of function effects explain the pathogenicity of the various reported (all) missense mutations. [In gnomAD GABRA2 has a Z-score for missense variants of 3.13 as well as a pLI of 1].
------
GABRA2 is not associated with any phenotype in G2P.
This gene is not commonly included in gene panels for ID offered by diagnostic laboratories.
------
As a result, GABRA2 can be considered for inclusion in the epilepsy and ID panels probably as green (several relevant individuals, several reported variants with supporting functional studies for most, etc.).

[Consider inclusion in other possibly relevant gene panels eg. for ASD which was feature in some patients at relevant age and/or among those evaluated].
Sources: Literature
Intellectual disability v2.1022 PIGP Konstantinos Varvagiannis gene: PIGP was added
gene: PIGP was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PIGP was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PIGP were set to 28334793; 31139695
Phenotypes for gene: PIGP were set to Generalized hypotonia; Global developmental delay; Seizures; Intellectual disability; Feeding difficulties; Cortical visual impairment
Penetrance for gene: PIGP were set to Complete
Review for gene: PIGP was set to GREEN
gene: PIGP was marked as current diagnostic
Added comment: Johnstone et al. (2017 - PMID: 28334793) report on 2 sibs born to non-consanguineous parents of French-Irish ancestry. Both presented with seizures (onset at the age of 2 and 7 weeks respectively), hypotonia and profound DD. Other features included CVI and feeding difficulties. Extensive metabolic testing as well as prior genetic testing (ARX, STXBP1, MECP2, aCGH) in the family were non-diagnostic. WES suggested the presence of 2 PIGP variants with Sanger sequencing used for confirmation and segregation studies.

PIGP encodes a subunit of the enzyme that catalyzes the first step of glycophosphatidylinositol (GPI) anchor biosynthesis. Mutations in other genes whose proteins are in complex with PIGP (PIGA, PIGC, PIGQ, PIGY, DPM2) lead to similar phenotypes. The phenotype overall was also overlapping with the inherited GPI deficiencies (belonging to the broader group of CDGs).

PIGP has 2 isoforms, which differ by 24 amino acids due to utilization of alternative start codons [corresponding to NM_153681.2 (158 aa) and NM_153682.2 (134 aa)].

The variants identified affected both transcripts with the first SNV leading either to loss of the start codon (NM_153682.2:c.2T>C - p.Met1Thr) or to substitution of a methionine at position 25(NM_153681.2:c.74T>C;p.Met25Thr). The second variant led to frameshift in the last exon of both transcripts predicting a longer protein product (NM_153681.2:c.456delA / p.Glu153AsnfsTer34 or NM_153682.2:c.384delA / p.Glu129AsnfsTer34).

Overall extensive studies demonstrated decreased levels of PIGP mRNA in patient fibroblast, decreased amounts of mutant protein in transfected HEK293 cells. The decreased levels of GPI-APs further supported the effect of variants :

- mRNA levels in patient fibroblasts were reduced compared to controls. Conclusions could not be drawn from Western blot, since no antibodies could specifically detect PIGP. HEK293 cells transfected of mt or wt HA-tagged PIGP cDNA led to undetectable amounts for the first variant (both M1T/M25T) and a protein product of increased molecular weight for the frameshift one.
- Flow cytometry of patient granulocytes indicated reduced signal of CD16 (a GPI-anchored protein) and FLAER (binding directly to the GPI anchor).
- Reduced levels of GPI-APs were also observed in PIGP deficient HAP1 cells transfected with either wt, or mutant PIGP cDNA (of both isoforms for the M1T/M25T or isoform 2 for the frameshift mutation).

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Krenn et al. (2019 - PMID: 31139695) described a patient born to non-consanguineous Polish parents. Features were highly similar to those reported by Johnstone et al. and incl. intractable infantile seizures (onset at 7m), hypotonia, severe DD and feeding difficulties. Metabolic work-up failed to identify an alternative diagnosis. WES revealed homozygosity for the frameshift variant reported by Johnstone et al. Sanger sequencing confirmed the variant and carrier state in both parents. Identified ROH of less than 7 Mb in the WES data, suggested a founder mutation rather than unreported consanguinity. The variant is present 9 times in gnomAD (AF of 3.2e-5 / no homozygotes). Flow cytometry of patient granulocytes, revealed markedly reduced expression of GPI-APs (CD157, CD59, FLAER) compared to parents/controls.

ALP was normal in all aforementioned individuals (probably in line with PIGP being involved in the 1st step of the GPI anchor biosynthesis).

--------

A further individual with phenotype of EIEE-55;GPIBD-14 is reported in LOVD [Individual #00246132]. This individual, born to consanguineous parents, was tested by WES and found to be homozygous for a frameshift variant, also affecting the last exon in both transcripts (NM_153681.2:c.384delA (p.Glu129ArgfsTer7) / NM_153682.2:c.312delA (p.Glu105ArgfsTer7). This was probably in agreement with segregation studies according to the respective entry. The specific variant is reported as pathogenic [variant ID #0000500090].

--------

?Epileptic encephalopathy, early infantile, 55 (MIM 617599) is the corresponding phenotype in OMIM. There is no relevant G2P entry.
PIGP is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx).

--------

As a result, PIGP can be considered for inclusion in the ID/epilepsy panels probably as green (3 individuals, role of the gene and similarity to other inherited GPI deficiencies, extensive supporting studies) or amber.

(Please consider inclusion in other possibly relevant panels eg. CDGs, etc).
Sources: Literature
Intellectual disability v2.1021 MED25 Konstantinos Varvagiannis changed review comment from: Please consider the 2 additional articles by Nair et al. (2019 - DOI: 10.1159/000494465 - PMID: 30800049 & DOI: 10.1159/000501114 - PMID: NA) reporting on 3 individuals from 2 consanguineous Lebanese families. All affected individuals were homozygous for a MED25 missense variant [NM_030973.3:c.518T>C / p.Ile173Thr], possibly a founder mutation in the Lebanese population. The phenotype presented some similarities with the previously described patients. The variant has a very low AF in gnomAD (0.00003470) and was also absent from the Saudi Variant Database. In silico predictions from PolyPhen2, PROVEAN, MutationTaster were suggestive of a probably damaging effect. The individual from the first report (PMID: 30800049) had an additional homozygous COQ8A variant, with some features fitting with the phenotype of AR primary CoQ10 deficiency type 4 and others negating this diagnosis.

MED25 is included in gene panels for ID offered by several diagnostic laboratories (incl. Radboudumc, Victorian Clinical Genetics and many others). It is not however included in the DD panel of G2P.; to: Please consider the 2 additional articles by Nair et al. (2019 - DOI: 10.1159/000494465 - PMID: 30800049 & DOI: 10.1159/000501114 - PMID: NA) reporting on 3 individuals from 2 consanguineous Lebanese families. All affected individuals were homozygous for a MED25 missense variant [NM_030973.3:c.518T>C / p.Ile173Thr], possibly a founder mutation in the Lebanese population. The phenotype presented some similarities with the previously described patients. The variant has a very low AF in gnomAD (0.00003470) and was also absent from the Saudi Variant Database. In silico predictions from PolyPhen2, PROVEAN, MutationTaster were suggestive of a probably damaging effect. The individual from the first report (PMID: 30800049) had an additional homozygous COQ8A variant, with some features fitting with the phenotype of AR primary CoQ10 deficiency type 4 and others negating this (possibly concurrent) diagnosis.

MED25 is included in gene panels for ID offered by several diagnostic laboratories (incl. Radboudumc, Victorian Clinical Genetics and many others). It is not however included in the DD panel of G2P.
Intellectual disability v2.1021 KATNB1 Konstantinos Varvagiannis gene: KATNB1 was added
gene: KATNB1 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: KATNB1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: KATNB1 were set to 25521378; 25521379; 26640080
Phenotypes for gene: KATNB1 were set to Lissencephaly 6, with microcephaly (MIM 616212)
Penetrance for gene: KATNB1 were set to Complete
Review for gene: KATNB1 was set to GREEN
gene: KATNB1 was marked as current diagnostic
Added comment: Biallelic pathogenic KATNB1 variants cause Lissencephaly 6, with microcephaly (MIM 616212). At least 13 affected individuals from 9 (mostly consanguineous) families have probably been reported in the following articles:

- Mishra-Gorur et al. (2014 - PMID: 25521378) [7 individuals from 5 unrelated families]
- Hu et al. (2014 - PMID: 25521379) [5 individuals from 3 families]
- Yigit el al. (2016 - PMID: 26640080) [1 subject born to consanguineous parents]

The phenotype appears to be relevant to the current panel. Several different variants have been reported to date. Extensive studies as for the impact of mutations at the cellular level as well as animal models (zebrafish, mouse, drosophila) support involvement of KATNB1. These arguments, provided mainly by the first two studies, are summarized in the respective OMIM entry for the disorder : https://omim.org/entry/616212 (variants and their effect are discussed in the entry for KATNB1 - https://omim.org/entry/602703).

The individual reported by Yigit el al. was a 5 year-old girl with - among others - severely delayed psychomotor development. The child was found to harbor a homozygous splice site variant (removing the acceptor AG signature). Confirmation of the variant and segregation studies were performed with Sanger sequencing. cDNA studies were carried out and demonstrated aberrant splicing.

KATNB1 is not associated with any disorder in G2P.
The gene is included in panels for ID offered by several diagnostic laboratories (incl. Radboudumc).

As a result, this gene can be considered for inclusion in the current panel probably as green (or amber).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.1021 MED13 Konstantinos Varvagiannis changed review comment from: Snijders Blok et al. (2018 - PMID: 29740699) report on 13 individuals with MED13 mutations.

Features included DD with speech difficulties (both universal) and motor delay in some. ID was observed in at least 9/13 and in most cases was in the borderline/mild range (moderate ID reported for 1 individual). Other features were ASD (5/13), ADHD, eye/vision abnormalities and in few individuals obstipation or congenital heart anomalies. Some possibly overlapping facial characteristics were also noted.

MED13 and MED13L are mutually exclusive components of the CDK8 kinase module that regulates the activity of the Mediator complex. The Mediator transmits signals from various transcription factors to RNA polymerase II (Pol II). Reversible binding of the CDK8 kinase controls Mediator - Pol II interaction (prevents Pol II recruitment) and thus acts as a molecular switch in Pol II - mediated transcription. DD and ID are features of the MED13L- and CDK8- related disorders.

3 stopgain, 2 frameshift, 6 missense variants and 1 in-frame deletion were reported. In 11 cases, the variants had occurred as de novo events, while 1 individual had inherited a nonsense variant from a similarly affected mother (unknown inheritance in her case).

Effect of a stopgain variant was studied with similar (total) transcript levels between the affected patient and his parents/controls upon qPCR. Sanger sequencing of cDNA amplicons was suggestive of the presence of an aberrant transcript at ~70% levels relative to the normal transcript. Truncated protein was undetectable by Western Blot in mononuclear blood cells from affected subjects. Total MED13 protein levels were not clearly different when comparing an affected individual with his unaffected parent (?).

Missense variants and the inframe deletion clustered either in the N- or the C-terminal domain, with the N-terminal ones all (T326I, T326del, P327S, P327Q / NM_005121.2 - NP_005112.2) affecting positions of a known phosphodegron sequence, important for the protein's ubiquitination and degradation. Another previously studied variant (T326A) had been shown to prevent degradation. As a result, the variants affecting aa 326-327 might lead to altered (increased) levels of MED13.

The remaining missense variants affected the C-terminal portion (Q2060L, A2064V).

As a result the impact of the different subcategories of variants remains unclear/inconclusive.

MED13 is not associated with any phenotype in OMIM. This gene is part of the DD panel of G2P, associated with "MED13 - Neurodevelopment disorder" (dis. confidence : probable / mutation consequence : LoF / GDD, speech/language delay, ID, autistic behavior among the assigned phenotypes).

MED13 is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc).

ID is part of the phenotype of MED13-related disorder, however as the severity in most individuals - when present - was in the borderline/mild range (not relevant for the present panel) and/or the underlying effect of mutations remains unclear, amber rating can probably be considered for this gene.
Sources: Radboud University Medical Center, Nijmegen, Literature; to: Snijders Blok et al. (2018 - PMID: 29740699) report on 13 individuals with MED13 mutations.

Features included DD with speech difficulties (both universal) and motor delay in some. ID was observed in at least 9/13 and in most cases was in the borderline/mild range (moderate ID reported for 1 individual). Other features were ASD (5/13), ADHD, eye/vision abnormalities and in few individuals obstipation or congenital heart anomalies. Some possibly overlapping facial characteristics were also noted.

MED13 and MED13L are mutually exclusive components of the CDK8 kinase module that regulates the activity of the Mediator complex. The Mediator transmits signals from various transcription factors to RNA polymerase II (Pol II). Reversible binding of the CDK8 kinase controls Mediator - Pol II interaction (prevents Pol II recruitment) and thus acts as a molecular switch in Pol II - mediated transcription. DD and ID are features of the MED13L- and CDK8- related disorders.

3 stopgain, 2 frameshift, 6 missense variants and 1 in-frame deletion were reported. In 11 cases, the variants had occurred as de novo events, while 1 individual had inherited a nonsense variant from a similarly affected mother (unknown inheritance in her case).

Effect of a stopgain variant was studied with similar (total) transcript levels between the affected patient and his parents/controls upon qPCR. Sanger sequencing of cDNA amplicons was suggestive of the presence of an aberrant transcript at ~70% levels relative to the normal transcript. Truncated protein was undetectable by Western Blot in mononuclear blood cells from affected subjects. Total MED13 protein levels were not clearly different when comparing an affected individual with his unaffected parent (?).

Missense variants and the inframe deletion clustered either in the N- or the C-terminal domain, with the N-terminal ones all (T326I, T326del, P327S, P327Q / NM_005121.2 - NP_005112.2) affecting positions of a known phosphodegron sequence, important for the protein's ubiquitination and degradation. Another previously studied variant (T326A) had been shown to prevent degradation. As a result, the variants affecting aa 326-327 might lead to altered (increased) levels of MED13.

The remaining missense variants affected the C-terminal portion (Q2060L, A2064V).

As a result the impact of the different subcategories of variants remains unclear/inconclusive.

MED13 is not associated with any phenotype in OMIM. This gene is part of the DD panel of G2P, associated with "MED13 - Neurodevelopment disorder" (dis. confidence : probable / mutation consequence : LoF / GDD, speech/language delay, ID, autistic behavior among the assigned phenotypes).

MED13 is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc).

ID is part of the phenotype of MED13-related disorder. However as the severity in most individuals - when present - was in the borderline/mild range (not relevant for the present panel) and/or the underlying effect of mutations remains unclear, amber rating seems more appropriate.
Sources: Radboud University Medical Center, Nijmegen, Literature
Intellectual disability v2.1021 MED13 Konstantinos Varvagiannis gene: MED13 was added
gene: MED13 was added to Intellectual disability. Sources: Radboud University Medical Center, Nijmegen,Literature
Mode of inheritance for gene: MED13 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: MED13 were set to 29740699
Phenotypes for gene: MED13 were set to Delayed speech and language development; Motor delay; Intellectual disability; Autistic behavior; Attention deficit hyperactivity disorder; Abnormality of the eye; Constipation
Penetrance for gene: MED13 were set to unknown
Review for gene: MED13 was set to AMBER
gene: MED13 was marked as current diagnostic
Added comment: Snijders Blok et al. (2018 - PMID: 29740699) report on 13 individuals with MED13 mutations.

Features included DD with speech difficulties (both universal) and motor delay in some. ID was observed in at least 9/13 and in most cases was in the borderline/mild range (moderate ID reported for 1 individual). Other features were ASD (5/13), ADHD, eye/vision abnormalities and in few individuals obstipation or congenital heart anomalies. Some possibly overlapping facial characteristics were also noted.

MED13 and MED13L are mutually exclusive components of the CDK8 kinase module that regulates the activity of the Mediator complex. The Mediator transmits signals from various transcription factors to RNA polymerase II (Pol II). Reversible binding of the CDK8 kinase controls Mediator - Pol II interaction (prevents Pol II recruitment) and thus acts as a molecular switch in Pol II - mediated transcription. DD and ID are features of the MED13L- and CDK8- related disorders.

3 stopgain, 2 frameshift, 6 missense variants and 1 in-frame deletion were reported. In 11 cases, the variants had occurred as de novo events, while 1 individual had inherited a nonsense variant from a similarly affected mother (unknown inheritance in her case).

Effect of a stopgain variant was studied with similar (total) transcript levels between the affected patient and his parents/controls upon qPCR. Sanger sequencing of cDNA amplicons was suggestive of the presence of an aberrant transcript at ~70% levels relative to the normal transcript. Truncated protein was undetectable by Western Blot in mononuclear blood cells from affected subjects. Total MED13 protein levels were not clearly different when comparing an affected individual with his unaffected parent (?).

Missense variants and the inframe deletion clustered either in the N- or the C-terminal domain, with the N-terminal ones all (T326I, T326del, P327S, P327Q / NM_005121.2 - NP_005112.2) affecting positions of a known phosphodegron sequence, important for the protein's ubiquitination and degradation. Another previously studied variant (T326A) had been shown to prevent degradation. As a result, the variants affecting aa 326-327 might lead to altered (increased) levels of MED13.

The remaining missense variants affected the C-terminal portion (Q2060L, A2064V).

As a result the impact of the different subcategories of variants remains unclear/inconclusive.

MED13 is not associated with any phenotype in OMIM. This gene is part of the DD panel of G2P, associated with "MED13 - Neurodevelopment disorder" (dis. confidence : probable / mutation consequence : LoF / GDD, speech/language delay, ID, autistic behavior among the assigned phenotypes).

MED13 is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc).

ID is part of the phenotype of MED13-related disorder, however as the severity in most individuals - when present - was in the borderline/mild range (not relevant for the present panel) and/or the underlying effect of mutations remains unclear, amber rating can probably be considered for this gene.
Sources: Radboud University Medical Center, Nijmegen, Literature
Intellectual disability v2.1021 PAK1 Konstantinos Varvagiannis changed review comment from: Horn et al. (2019 - doi.org/10.1093/brain/awz264) report on 4 additional individuals with de novo missense PAK1 pathogenic variants. ID, seizures and macrocephaly and walking difficulties were observed in all (4/4). ASD was reported in 3 (but was not among the features in the study by Harms et al).

PAK1 encodes p21 protein-activated kinase 1. The protein has 2 major domains, an autoregulatory and a protein kinase domain. Homodimerization masks the active site of the kinase, leading to autoinhibition (inactive form). PAK1 is activated by dissociation into monomers upon binding of the GTP-bound forms of the Rho GTPases CDC42 and RAC1. TRIO and HACE1 are indirect regulators of PAK1, via RAC1. PAK1 in turn, activates LIMK1 which plays a critical role in dendritic spine morphogenesis and brain function.

CDC42, RAC1, TRIO, HACE1 are all associated with neurodevelopmental disorders. Activation of RAC-PAK1-LIMK1 pathway has been demonstrated for Fragile-X syndrome (sharing ID, macrocephaly and seizures).

Mutations in PAK3, another member of the group I PAK subfamily with similar activation mechanism to PAK1 (by CDC42 / RAC1), cause Mental retardation, X-linked 30/47 (MIM 300558) (Green rating in the current panel).

4 additional missense variants - further to the 2 previously described ones - were found, all as de novo events:
c.397T>C (p.Ser133Pro) / c.361C>T p.(Pro121Ser) / c.328T>A p.(Ser110Thr) / c.1409T>G (p.Leu470Arg) [For the specific variants, cDNA and aa change are the same for both NM_001128620.1 and NM_002576].

The 3 former variants located within the autoinhibitory domain while the latter in the protein kinase domain though - again - close to the autoinhibitory one (in tertiary structure). A gain of function effect by reduced ability of autoinhibition (leading to autophosphorylation) and activation of PAK1 is the suggested mechanism. Gain of function is also supported by the fact that Pak1-/- do not exhibit neurodevelopmental anomalies / abnormal head size. PAK1 is not particularly intolerant to LoF variants as suggested by its pLI of 0.67.

The corresponding phenotype in OMIM is Intellectual developmental disorder with macrocephaly, seizures, and speech delay (MIM 618158). The gene is part of the DD panel of G2P, associated with "Neurodevelopmental Disorder" (monoallelic, activating / disease confidence : probable).

PAK1 is included in the gene panel for ID offered by Radboudumc.; to: Based on a further recent study, PAK1 can probably be upgraded to green in both ID and epilepsy gene panels:

Horn et al. (2019 - doi.org/10.1093/brain/awz264) report on 4 additional individuals with de novo missense PAK1 pathogenic variants. ID, seizures and macrocephaly and walking difficulties were observed in all (4/4). ASD was reported in 3 (but was not among the features in the study by Harms et al).

PAK1 encodes p21 protein-activated kinase 1. The protein has 2 major domains, an autoregulatory and a protein kinase domain. Homodimerization masks the active site of the kinase, leading to autoinhibition (inactive form). PAK1 is activated by dissociation into monomers upon binding of the GTP-bound forms of the Rho GTPases CDC42 and RAC1. TRIO and HACE1 are indirect regulators of PAK1, via RAC1. PAK1 in turn, activates LIMK1 which plays a critical role in dendritic spine morphogenesis and brain function.

CDC42, RAC1, TRIO, HACE1 are all associated with neurodevelopmental disorders. Activation of RAC-PAK1-LIMK1 pathway has been demonstrated for Fragile-X syndrome (sharing ID, macrocephaly and seizures).

Mutations in PAK3, another member of the group I PAK subfamily with similar activation mechanism to PAK1 (by CDC42 / RAC1), cause Mental retardation, X-linked 30/47 (MIM 300558) (Green rating in the current panel).

4 additional missense variants - further to the 2 previously described ones - were found, all as de novo events:
c.397T>C (p.Ser133Pro) / c.361C>T p.(Pro121Ser) / c.328T>A p.(Ser110Thr) / c.1409T>G (p.Leu470Arg) [For the specific variants, cDNA and aa change are the same for both NM_001128620.1 and NM_002576].

The 3 former variants located within the autoinhibitory domain while the latter in the protein kinase domain though - again - close to the autoinhibitory one (in tertiary structure). A gain of function effect by reduced ability of autoinhibition (leading to autophosphorylation) and activation of PAK1 is the suggested mechanism. Gain of function is also supported by the fact that Pak1-/- do not exhibit neurodevelopmental anomalies / abnormal head size. PAK1 is not particularly intolerant to LoF variants as suggested by its pLI of 0.67.

The corresponding phenotype in OMIM is Intellectual developmental disorder with macrocephaly, seizures, and speech delay (MIM 618158). The gene is part of the DD panel of G2P, associated with "Neurodevelopmental Disorder" (monoallelic, activating / disease confidence : probable).

PAK1 is included in the gene panel for ID offered by Radboudumc.

(Previous review below)
Intellectual disability v2.1021 PAK1 Konstantinos Varvagiannis edited their review of gene: PAK1: Added comment: Horn et al. (2019 - doi.org/10.1093/brain/awz264) report on 4 additional individuals with de novo missense PAK1 pathogenic variants. ID, seizures and macrocephaly and walking difficulties were observed in all (4/4). ASD was reported in 3 (but was not among the features in the study by Harms et al).

PAK1 encodes p21 protein-activated kinase 1. The protein has 2 major domains, an autoregulatory and a protein kinase domain. Homodimerization masks the active site of the kinase, leading to autoinhibition (inactive form). PAK1 is activated by dissociation into monomers upon binding of the GTP-bound forms of the Rho GTPases CDC42 and RAC1. TRIO and HACE1 are indirect regulators of PAK1, via RAC1. PAK1 in turn, activates LIMK1 which plays a critical role in dendritic spine morphogenesis and brain function.

CDC42, RAC1, TRIO, HACE1 are all associated with neurodevelopmental disorders. Activation of RAC-PAK1-LIMK1 pathway has been demonstrated for Fragile-X syndrome (sharing ID, macrocephaly and seizures).

Mutations in PAK3, another member of the group I PAK subfamily with similar activation mechanism to PAK1 (by CDC42 / RAC1), cause Mental retardation, X-linked 30/47 (MIM 300558) (Green rating in the current panel).

4 additional missense variants - further to the 2 previously described ones - were found, all as de novo events:
c.397T>C (p.Ser133Pro) / c.361C>T p.(Pro121Ser) / c.328T>A p.(Ser110Thr) / c.1409T>G (p.Leu470Arg) [For the specific variants, cDNA and aa change are the same for both NM_001128620.1 and NM_002576].

The 3 former variants located within the autoinhibitory domain while the latter in the protein kinase domain though - again - close to the autoinhibitory one (in tertiary structure). A gain of function effect by reduced ability of autoinhibition (leading to autophosphorylation) and activation of PAK1 is the suggested mechanism. Gain of function is also supported by the fact that Pak1-/- do not exhibit neurodevelopmental anomalies / abnormal head size. PAK1 is not particularly intolerant to LoF variants as suggested by its pLI of 0.67.

The corresponding phenotype in OMIM is Intellectual developmental disorder with macrocephaly, seizures, and speech delay (MIM 618158). The gene is part of the DD panel of G2P, associated with "Neurodevelopmental Disorder" (monoallelic, activating / disease confidence : probable).

PAK1 is included in the gene panel for ID offered by Radboudumc.; Changed rating: GREEN; Changed publications: 30290153, doi.org/10.1093/brain/awz264; Set current diagnostic: yes
Intellectual disability v2.1015 DDX6 Konstantinos Varvagiannis gene: DDX6 was added
gene: DDX6 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DDX6 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: DDX6 were set to 31422817
Phenotypes for gene: DDX6 were set to Generalized hypotonia; Global developmental delay; Intellectual disability; Unsteady gait; Abnormality of the cardiovascular system; Abnormality of the genitourinary system; Abnormality of limbs
Penetrance for gene: DDX6 were set to unknown
Review for gene: DDX6 was set to GREEN
Added comment: Balak et al. (2019 - PMID: 31422817) report on 5 individuals with de novo likely pathogenic DDX6 variants.

Clinical details are provided for 4. Frequent features included hypotonia, DD, ID (4/4), gait instability, cardiac, genitourinary as well anomalies of the extremities.

DDX6 belongs to the DEAD box family of RNA helicases. This helicase is an essential component of processing bodies (P-bodies / PBs), which are mebrane-less organelles involved in storage of mRNAs and proteins related to mRNA decay thus playing an important role in translational repression/post-transcriptional regulation (PMID: 29381060).

All 5 variants had occurred as de novo events, clustered in exon 11 (NM_004397.5) and affected residues 372-373 of the QxxR motif (c.1115A>G or p.His372Arg / c.1118G>A or p.Arg373Gln) or 390-391 of the V motif (c.1168T>C or p.Cys390Arg / c.1171A>C or p.Thr391Pro / c.1172C>T or p.Thr391Ile). The specific motifs (and RecA-2 domain) are involved in RNA binding, helicase activity and protein-partner binding.

Fibroblasts from 2 individuals were studied. Patient cells contained fewer PBs compared to cells from relatives/control-subjects, despite similar amounts of DDX6 protein upon immunobloting. Additional studies suggested that DDX6 variants caused impaired binding of other DDX6 protein partners involved in PB formation / translation repression (eg. LSM14A, 4E-T, etc) thus resulting in defective PB assembly.

Transcriptome analysis in fibroblasts from one affected individual revealed (significant) differential expression of >1000 genes, enriched for genes related to protein translation, ribosome and RNA processing.

As the authors discuss, given the residual PB assembly, haploinsufficiency is favored over a dominant-negative effect which would result in complete suppression of PBs (as sugested by a previous study of a dominant-negative DDX6 variant - PMID cited: 19297524). [In gnomAD, DDX6 has a Z-score for missense variants of 3.78 and a pLI of 1].

DDX6 is not associated with any phenotype in OMIM.
In G2P it is associated with ID (disease confidence : probable / mutations : all missense/in frame).

As a result, this gene can be considered for inclusion in the ID panel as green (sufficient cases, relevant phenotype, functional studies) or amber.
Sources: Literature
Intellectual disability v2.1007 FRMPD4 Rebecca Foulger Mode of inheritance for gene: FRMPD4 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.998 PIGU Rebecca Foulger commented on gene: PIGU: PMID:31353022 (Knaus et al. 2019) report two homozygous missense mutations (c.209T>A [p.Ile70Lys] and c.1149C>A [p.Asn383Lys]) in 5 individuals from 3 unrelated families. All individuals presented with global DD severe-to-profound ID, muscular hypotonia, seizures, brain anomalies, scoliosis, and mild facial dysmorphism. Sequencing confirmed that all parents were healthy carriers. c.209T>A has not been observed in gnomAD while c.1149C>A has been observed only in the heterozygous state (7/277194).
Intellectual disability v2.996 POLR2A Konstantinos Varvagiannis gene: POLR2A was added
gene: POLR2A was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: POLR2A was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: POLR2A were set to 31353023
Phenotypes for gene: POLR2A were set to Generalized hypotonia; Global developmental delay; Feeding difficulties
Penetrance for gene: POLR2A were set to unknown
Review for gene: POLR2A was set to GREEN
gene: POLR2A was marked as current diagnostic
Added comment: Haijes et al. (2019 - PMID: 31353023) report on 16 individuals with heterozygous de novo POLR2A variants.

DD in all domains was observed in all individuals, ranging from mild to severe (in 8/16 moderate or more severe). The developmental scores were stable over time (as for eventual catch-up/decline) supporting relevance to the current panel.

POLR2A encodes RPB1, the largest subunit of RNA polymerase II (pol II). Pol II is responsible for the transcription of all protein coding genes as well as several long/short non-coding RNA genes.

Missense, in-frame deletions as well as truncating mutations were observed. POLR2A has a pLI of 1 and a Z-score for missense variants of 7.13 (one of the highest ones). The reported variants did not cluster in specific domains of the protein although many were in regions relatively depleted in benign variants in gnomAD (stretches of desert Z-scores). Measures such as the CADD scores did not discriminate between deleterious ones and those in gnomAD.

Different layers of structural analyses, functional analyses (impaired growth in S. cerevisiae in genetic background lacking transcr. factors Dst1 / Sub1 - suggesting reduced transcriptional fidelity / reduced HeLa cell viability) or phenotypic overlap were used to classify variants in probably disease causing (11), possibly disease causing (4 - only based on phenotypic overlap) or of unknown effect (1 variant - due to unavailable/incomplete phenotype).

Some variants were predicted to act by haploinsufficiency while others (missense ones) by a dominant-negative mechanism, the latter being more likely to result in severe phenotypes.

Mutations in genes encoding subunits of pol III (responsible for tRNA synthesis) are associated with leukodystrophy phenotypes with some limited overlap with POLR2A (delayed myelination/white-matter loss/tooth misalignment). Mutations in genes encoding other subunits of pol II (other than RPB1 encoded by POLR2A) have not been implicated in disease though.

POLR2A is not associated with any phenotype in OMIM/G2P. This gene is included in panels for ID offered by some diagnostic laboratories [eg. Utrecht UMC - affiliation of many co-authors of this study or GeneDx].

As a result, this gene can be considered for inclusion in the ID panel probably as green, or amber.
Sources: Literature
Intellectual disability v2.996 AFF3 Konstantinos Varvagiannis changed review comment from: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb affecting only AFF3 (LAF4) and removing also this sequence.

The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy].

9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13.

AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development.

Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot.

Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study].

Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects.

Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant.

Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3.
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In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM.
Some diagnostic laboratories include AFF3 in their ID panel (eg. among the many co-authors' affiliations GeneDx and Victorian Clinical Genetics - which was already listed as source for AFF3 in the current panel).
----
As a result this gene can be considered for upgrade to green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article).; to: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb affecting only AFF3 (LAF4) and removing also this sequence.

The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy].

9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13.

AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development.

Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot.

Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study].

Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects.

Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant.

Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3.
----
Shimizu et al. (8/2019 - PMID: 31388108) describe an additional individual with de novo AFF3 missense variant. The phenotype overlaps with that summarized by Voisin et al. incl. mesomelic dysplasia with additional skeletal anomalies, bilateral kidney hypoplasia and severe DD at the age of 2.5 years. Seizures and pulmonary problems were not observed. Although a different RefSeq is used the variant is among those also reported by Voisin et al. [NM_002285.2:c.697G>A (p.Ala233Thr) corresponding to NM_001025108.1:c.772G>A (p.Ala258Thr)].
----
In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM.
Some diagnostic laboratories include AFF3 in their ID panel (eg. among the many co-authors' affiliations GeneDx and Victorian Clinical Genetics - which was already listed as source for AFF3 in the current panel).
----
As a result this gene can be considered for upgrade to green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article).

[Review modified to add additional reference/case report]
Intellectual disability v2.996 PIGU Konstantinos Varvagiannis gene: PIGU was added
gene: PIGU was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PIGU was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PIGU were set to 31353022
Phenotypes for gene: PIGU were set to Global developmental delay; Intellectual disability; Seizures; Cerebral atrophy; Cerebellar hypoplasia; Scoliosis
Penetrance for gene: PIGU were set to Complete
Review for gene: PIGU was set to GREEN
Added comment: Knaus et al. (2019 - PMID: 31353022) report on 5 affected individuals (from 3 unrelated families) with biallelic pathogenic PIGU variants.

Common features included tone abnormalities, global DD, ID, seizures, CNS anomalies (cerebral atrophy and/or cerebellar hypoplasia), scoliosis. Affected individuals presented also with facial similarities. DD/ID were universal features and their severity appears to be relevant to the panel. Seizures were also reported in all individuals (myoclonic in 3, for whom this was specified). ALP was normal in all.

Three individuals from 2 non-consanguineous families (one from Norway, the other not specified) were homozygous for a missense variant NM_080476.4:c.1149C>A (or p.Asn383Lys) present with an AF of 7/277197 in Europeans. Two individuals born to consanguineous parents from Turkey were homozygous for another missense variant (c.209T>A or p.Ile70Lys - same RefSeq).

Segregation analyses in parents and unaffected sibs were carried out.

PIGU encodes a subunit of the GPI transaminidase, a heteropentameric complex (other subunits encoded by PIGK, PIGS, PIGT and GPAA1) that mediates attachment in the endoplasmic reticulum of glycosylphosphatidylinositol (GPI) to the C-termini of proteins which are subsequently anchored to the cell surface.

Pathogenic variants in 18 of 29 genes implicated in biosynthesis of the GPI anchor have been identified as a cause of GPI biosynthesis disorders, with ID and seizures as principal features. Mutations in other genes encoding components of the GPI transaminidase complex (GPAA1, PIGT and PIGS) lead to neurodevelopmental disorders.

Functional impairment of PIGU was supported by flow-cytometric analysis showing significant reduction of cell surface expression of GPI anchored proteins (mainly FLAER, CD16 and CD24) on granulocytes from affected individuals. In addition accumulation of free GPI anchors on the cell surface of B cells from affected individuals further suggested deficiency of the GPI transaminidase.

Transient expression of mutant (Asn383Lys) protein failed to rescue expression of GPI-APs to the same extent as wt in a CHO cell line deficient for PIGU.

Feature analysis demonstrated similarities among individuals with mutations in other genes of the GPI transamidase complex (GPAA1 and PIGT) as well as with GPI biosynthesis disorders. Facial analysis was also suggestive of facial similarities between individuals with GPAA1 and PIGU mutations.

PIGU is not associated with any phenotype in OMIM or G2P.

As a result this gene can be considered for inclusion in the ID and epilepsy panels probably as green (3 families, ID of relevant severity and seizures in all affected individuals, known group of disorders and supportive evidence) or amber.
Sources: Literature
Intellectual disability v2.996 WDR37 Konstantinos Varvagiannis gene: WDR37 was added
gene: WDR37 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: WDR37 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: WDR37 were set to 31327510; 31327508
Phenotypes for gene: WDR37 were set to Global developmental delay; Intellectual disability; Seizures; Abnormality of the eye; Abnormality of nervous system morphology; Hearing abnormality; Abnormality of the cardiovascular system; Abnormality of the skeletal system; Abnormality of the genitourinary system
Penetrance for gene: WDR37 were set to unknown
Review for gene: WDR37 was set to GREEN
Added comment: Two concurrent publications by Reis et al. and Kanca et al. (2019 - PMIDs: 31327510, 31327508) report on the phenotype of individuals with de novo WDR37 mutations.

The study by Reis et al. provides clinical details on 4 affected individuals, while 5 further are described by Kanca et al.

4 different de novo variants were reported in these individuals who appear to be unrelated in (and between) the 2 studies [NM_014023.3]:
- c.356C>T (p.Ser119Phe) [Reis indiv. 1 - 3y, Kanca proband 3 - 5m2w]
- c.389C>T (p.Thr130Ile) [Reis indiv. 2 - 22m , Kanca proband 5 - 6w]
- c.374C>T (p.Thr125Ile) [Reis indiv. 3 - 8y , Kanca proband 1 - 7y]
- c.386C>G (p.Ser129Cys) [Reis indiv. 4 - unkn age, Kanca probands 2 and 4, 6.5y and 19y]

Common features included DD/ID (severity relevant for the current panel), seizures (9/9), ocular anomalies (corneal opacity/Peters anomaly, coloboma, microphthalmia etc.) and variable brain, hearing, cardiovascular, skeletal and genitourinary anomalies. Some facial and/or other dysmorphic features (incl. excess nuchal skin / webbed neck) were also frequent among affected individuals. Feeding difficulties and growth deficiency were also among the features observed.

The function of WDR37 is not known. Variants demonstrated comparable protein levels and cellular localization compared to wt.

Reis et al. provide evidence using CRISPR-Cas9 mediated genome editing in zebrafish, to introduce the Ser129Cys variant observed in affected individuals as well as novel missense and frameshift variants. Poor growth (similar to the human phenotype) and larval lethality were noted for missense variants. Head size was proportionately small. Ocular (coloboma/corneal) or craniofacial anomalies were not observed. Zebrafish heterozygous for LoF variants survived to adulthood.

Based on these a dominant-negative mechanism was postulated for missense alleles.

RNA-seq analysis in zebrafish showed upregulation of cholesterol biosynthesis pathways (among the most dysregulated ones).

Previous data in mice, suggest a broad expression pattern for Wdr37 with enrichment in ocular and brain tissues, significant associations in homozygous mutant mice for decreased body weight, grip strength, skeletal anomalies and possible increase (p =< 0.05) in ocular (lens/corneal) and other anomalies [BioGPS and International Mouse Phenotyping Consortium cited].

CG12333 loss (the Drosophila WDR37 ortholog) causes increased bang sensitivity in flies (analogous to the human epilepsy phenotype), defects in copulation and grip strength, phenotypes that were rescued by human reference but not variant cDNAs.

As discussed by Kanca et al. based on data from Drosophila and mice, limited phenotypic similarity of CNVs spanning WDR37 and adjacent genes with the reported individuals and the presence of LoF variants in control populations haploinsufficiency appears unlikely. Gain-of-function is also unlikely, as expression of human variants in flies did not exacerbate the observed phenotypes. A dominant-negative effect is again proposed.

WDR37 is not associated with any phenotype in OMIM/G2P.

As a result WDR37 can be considered for inclusion in the ID and epilepsy panels with green (relevant phenotype, sufficient cases, animal models) or amber rating.
Sources: Literature
Intellectual disability v2.979 EMC1 Catherine Snow Mode of inheritance for gene EMC1 was changed from BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal to BIALLELIC, autosomal or pseudoautosomal
Intellectual disability v2.977 KIF2A Catherine Snow changed review comment from: Three further cases identified in the literature.
PMID:27747449 (Cavallin et al 2017) detected two de novo p.Ser317Asn and p.His321Pro mutations in KIF2A in two patients with lissencephaly and microcephaly. Case 1 had DD, no epilepsy but was only 9 months old at last reporting. Case 2 had neonatal seizures and severe DD.
PMID:27896282 (Tian et al 2016) report a patient with lissencephaly, developmental delay, and infantile spasms, due to de novo heterozygous variant in KIF2A (p.Thr320Ile).

Therefore upgrading rating from Amber to Green as now sufficient (>3) unrelated cases.; to: Three further cases identified in the literature.
PMID:27747449 (Cavallin et al 2017) detected two de novo p.Ser317Asn and p.His321Pro mutations in KIF2A in two patients with lissencephaly and microcephaly. Case 1 had DD, no epilepsy but was only 9 months old at last reporting. Case 2 had neonatal seizures and severe DD.
PMID:27896282 (Tian et al 2016) report a patient with lissencephaly, developmental delay, and infantile spasms, due to de novo heterozygous variant in KIF2A (p.Thr320Ile).
Most cases identified have epilepsy first however as one individual did not have seizures KIF2A is relevant for the ID panel.
Therefore upgrading rating from Amber to Green as now sufficient (>3) unrelated cases.
Intellectual disability v2.969 GRIA2 Catherine Snow changed review comment from: GRIA2 has been associated with ID in PMID: 31300657. The authors identified 28 unrelated individuals who had heterozygous de novo GRIA2 mutations. All individuals had experienced DD and moderate to severe ID, except 2 who had died at a young age. Epilepsy was identified in at least 10 individuals.
Multiple de-novo intragenic variants including missense (n = 15), splice-site (n = 2), in-frame deletion (n = 1), stop-gain (n = 1) and frameshift (n = 2) variants were reported. In all patients with intragenic variants they were first identified by WES, WGS or massively parallel targeted sequencing and confirmed as de-novo by trio Sanger sequencing. Also a further three patients were identified with a microdeletion involving GRIA2 using micro array analysis.

GRIA2 is currently not associated with a disease in OMIM or Gene2Phenotype and this is the first time that GRIA2 has been reported to be associated with ID but other AMPA receptors, GRIA3, and GRIA4 are Green on the ID panel.
Therefore there is not sufficient number of unrelated individuals and evidence to make GRIA2 Green.; to: GRIA2 has been associated with ID in PMID: 31300657. The authors identified 28 unrelated individuals who had heterozygous de novo GRIA2 mutations. All individuals had experienced DD and moderate to severe ID, except 2 who had died at a young age. Epilepsy was identified in at least 10 individuals.
Multiple de-novo intragenic variants including missense (n = 15), splice-site (n = 2), in-frame deletion (n = 1), stop-gain (n = 1) and frameshift (n = 2) variants were reported. In all patients with intragenic variants they were first identified by WES, WGS or massively parallel targeted sequencing and confirmed as de-novo by trio Sanger sequencing. Also a further three patients were identified with a microdeletion involving GRIA2 using micro array analysis.

GRIA2 is currently not associated with a disease in OMIM or Gene2Phenotype and this is the first time that GRIA2 has been reported to be associated with ID but other AMPA receptors, GRIA3, and GRIA4 are Green on the ID panel.
Therefore there is now sufficient number of unrelated individuals and evidence to make GRIA2 Green.
Intellectual disability v2.959 ATRX Rebecca Foulger Added comment: Comment on mode of inheritance: Changed Mode of inheritance from XLR to XLD: Alpha-thalassemia/mental retardation syndrome, 301040 is listed as XLD in OMIM (in addition to Mental retardation-hypotonic facies syndrome, X-linked, 309580 listed as XLR). Although PMID:17503331 report that nearly all female carriers of ATRX syndrome have highly skewed X-chromosome inactivation in favour of cells expressing the normal ATRX allele and are essentially phenotypically normal, PMID:16955409 report a female carrier where the chromosome carrying the mutant allele was active and she therefore showed a phenotype.
Intellectual disability v2.959 ATRX Rebecca Foulger Mode of inheritance for gene: ATRX was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.954 SLC9A6 Rebecca Foulger Mode of inheritance for gene: SLC9A6 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.953 PIGB Konstantinos Varvagiannis gene: PIGB was added
gene: PIGB was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PIGB was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PIGB were set to 31256876
Phenotypes for gene: PIGB were set to Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures; Hearing abnormality; Abnormality of vision; Elevated alkaline phosphatase; Abnormality of the head; Abnormality of the hand; Abnormality of the foot
Penetrance for gene: PIGB were set to Complete
Review for gene: PIGB was set to GREEN
Added comment: Murakami et al. (2019 - PMID: 31256876) provide detailed information on 14 individuals from 10 families (4 of which consanguineous) with biallelic pathogenic PIGB variants.

Overlapping features included DD/ID (13/13), epilepsy (14/14), deafness (7/14), ophthalmological or brain anomalies, hand and feet anomalies as well as presence of dysmorphic features. ID was common, in those individuals with appropriate age. Some had a previous diagnosis of DOORS syndrome (deafness/onychodystrophy/osteodystrophy,retardation, seizures) and few showed 2-oxoglutatic aciduria which can also be seen in DOORS s.

PIGB encodes phosphatidylinositol glycan anchor biosynthesis class B protein.

Overall the phenotype was similar to other inherited glycosylphosphatidylinositol (GPI) deficiencies (IGDs). As happens to be the case in some other GPI deficiencies alkaline phosphatase was also elevated in those tested (8/9).

8 missense, 1 stopgain as well as an intronic SNV are reported. All variants were either absent or ultra-rare and with no homozygotes in gnomAD.

Affected individuals from 4 families, harbored an intronic SNV in the homozygous state. For this variant - with MAF of 0.0001592 or 6.51x10-5 in ExAC and gnomAD - activation of an aberrant splice acceptor site was shown [NM_004855.4:c.847-10A>G or p.Gln282_Trp283insArgCysGln].

Flow cytometric analysis of blood cells or fibroblasts showed decreased levels for various GPI-AP (GPI-anchored protein) markers in affected individuals. These levels were rescued upon transduction with a PIGB-encoding-Lx304 lentiviral vector of fibroblasts from one affected individual, suggesting that the PIGB defect was responsible.

The effect of the variants was evaluated using PIGB-deficient CHO cells, transfected with wt or mutant PIGB cDNAs. FACS analysis and immunoblotting demonstrated that variants were able to restore only slightly/partially - if at all - the surface presence of GPI-APs in the case of variants while the levels of mutant protein were reduced.

PIGB is not associated with any phenotype in OMIM/G2P. This gene is not commonly included in gene panels for ID offered by diagnostic laboratories.

As a result, this gene can be considered for inclusion in the ID and epilepsy panels probably as green (or amber).
Sources: Literature
Intellectual disability v2.951 POU3F3 Konstantinos Varvagiannis gene: POU3F3 was added
gene: POU3F3 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: POU3F3 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: POU3F3 were set to https://doi.org/10.1016/j.ajhg.2019.06.007; 24550763
Phenotypes for gene: POU3F3 were set to Generalized hypotonia; Delayed speech and language development; Global developmental delay; Intellectual disability; Autistic behavior
Penetrance for gene: POU3F3 were set to unknown
Review for gene: POU3F3 was set to GREEN
gene: POU3F3 was marked as current diagnostic
Added comment: Snijders Blok et al. (2019, DOI: https://doi.org/10.1016/j.ajhg.2019.06.007) report on 19 individuals with heterozygous POU3F3 variants.

Features included hypotonia in some, DD/ID (19/19) with impairment in speech and language skills, and autism-like symptoms with formal ASD diagnosis in 7(/19). Epilepsy was reported for 2 individuals. Overlapping facial features were noted among these individuals.

POU3F3 encodes a member of the class III POU family of transcription factors expressed in the central nervous system (Sumiyama et al. 1996, PMID: 8703082 cited in OMIM) and as the authors comment holds a role in regulation of key processes, eg. cortical neuronal migration, upper-layer specification and production and neurogenesis (PMIDs cited: 11859196, 12130536, 22892427, 17141158).

In almost all subjects (17/19) the variant had occurred as a de novo event, while one individual had inherited the variant from a similarly affected parent.

In total 12 nonsense/frameshift variants, 5 missense ones as well as 1 in-frame deletion were identified following (mostly) trio exome sequencing. All variants were absent from gnomAD, with in silico predictions in favour of pathogenicity.

The few missense variants and the in-frame deletion were found either in the POU-specific (NM_006236.2:c.1085G>T / p.Arg362Leu found in 2 subjects) or the POU-homeobox domain (where 2 variants affected the same residue, namely p.Arg407Gly/Leu, the other variant was p.Asn456Ser).

POU3F3 is an intronless gene and as a result truncating variants are not subject to NMD. The gene appears to be intolerant to LoF variants (pLI of 0.89 in gnomAD).

Western blot analysis of YFP-tagged POU3F3 variants (in HEK293 cell lysates) showed that the YFP-fusion proteins were expressed and had the expected molecular weights.

For several truncating variants tested as well as the in-frame deletion, aberrant subcellular localization pattern was demonstrated although this was not the case for 4 missense variants.

In vitro studies were carried out and suggested that POU3F3, as is known to be the case for POU3F2, is able to activate an intronic binding site in FOXP2. Using a luciferase assay, transcriptional activation was severely impaired for truncating variants tested, significantly lower for many missense ones with the exception of those affecting Arg407 in which case luciferase expression was either similar to wt (for Arg407Gly) or even increased in the case of Arg407Leu.

As the authors comment, both loss- and gain- of function mechanisms may underly pathogenicity of variants.

The ability of mutant proteins to form dimers either with wt or themselves was tested. Dimerization capacity was intact for most missense variants but was lost/decreased for truncating variants. The in-frame deletion resulted in impaired dimerization with wt, although homo-dimerization was found to be normal.
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Dheedene et al. (2014 - PMID: 24550763) had previously reported on a boy with ID. aCGH had demonstrated a de novo 360-kb deletion of 2q12.1 spanning only POU3F3 and MRPS9 the latter encoding a mitochondrial ribosomal protein (which would be most compatible with a - yet undescribed - recessive inheritance pattern / disorder).
---
POU3F3 is not associated with any phenotype in OMIM/G2P.
The gene is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc, among the principal authors of the study).
---
As a result POU3F3 seems to fulfill criteria for inclusion in the current panel probably as green [DD/ID was a universal feature - severity of ID was relevant in 5/10 individuals for whom details were available, functional evidence provided] or amber.
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.950 NEXMIF Rebecca Foulger Mode of inheritance for gene: NEXMIF was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.938 CTBP1 Konstantinos Varvagiannis changed review comment from: 12 individuals with a recurrent missense variant in CTBP1 have been reported, all summarized in the last article:
- Beck et al. 2016 (PMID: 27094857) : 4 individuals
- Sommerville et al. 2017 (PMID: 28955726) : 1 subject
- Beck et al. 2019 (PMID: 31041561) : 7 further individuals

Features included hypotonia, DD/ID, ataxia and tooth enamel defects. The degree of ID - when present - appeared to be highly variable based at least on the first two reports (3 individuals with severe ID, 1 with borderline-normal intellectual functioning, 1 did not exhibit ID) where this feature was further commented on.

A recurrent missense variant was found in all 12 affected individuals [NM_001328.2:c.1024C>T - p.(Arg342Trp) or NM_001012614.1:c.991C>T - p.(Arg331Trp)]. De novo occurrence this SNV was shown for (almost) all individuals, although in one case maternal sequencing reads were compatible with low-level somatic mosaicism (4/75 reads) not detected by Sanger sequencing. The mother of this individual was phenotypically normal. The variant is absent from gnomAD. Several in silico predictions (SIFT, PolyPhen2, MutationTaster, etc) suggest a deleterious effect.

Given recurrence of this specific variant, and presence of LoF ones in healthy individuals (pLI of 0.98 though in gnomAD) Beck et al. suggested a dominant negative or a gain-of-function effect rather than a loss of function mechanism.

Exclusion of alternative causes: was mainly discussed for the subject reported by Sommerville et al., due to the primary suspicion of a mitochondrial disorder (sequencing and research for mtDNA rearrangements, additional analysis of nuclear genes for mitochondrial disorders).

Expression: CTBP1 encodes C-terminal binding protein 1, with expression among others in brain and cerebellum (https://gtexportal.org/home/gene/CTBP1).

Role and Functional studies:
- The major nuclear isoform of CTBP1 (corresponding to NM_001328.2) and of its paralog CTBP2 function as transcriptional regulators (corepressors). The PLDLS(Pro-Leu-Asp-Leu-Ser)-binding cleft domain where this variant lies, acts as a high-affinity protein-binding interface to recruit DNA-binding repressors and chromatin modifying enzymes (PMID: 17967884).
- In a human glioblastoma cell line interaction of various cofactors with (Flag-tagged) CTBP1 was studied by immunoprecitipation with the Flag antibody and subsequent proteomic (LC-MS) analysis. This demonstrated reduced interaction in the case of R342W (compared to wt) with Zn-finger transcription factors, histone deacetylases, histone methyltransferases, histone H3-K4 demethylase etc. Western blot analyses also revealed reduced interaction of the R342W with several CTBP cofactors.
- RNA-seq analysis in glioblastoma cell line revealed similar overall transcriptional profiles between wt and R342W though multiple RNA species showed significant differences (eg. genes involved in the biological processes of mitotic nuclear division, DNA repair, transcription and regulation of transcription among those that were most upregulated and genes involved in brain development among the most downregulated).
- Patient fibroblasts under conditions of glucose deprivation exhibited strikingly more cell death compared to control fibroblasts. Study of mRNA levels of pro-apoptotic genes by q-RT-PCR revealed that Noxa expression under glucose deprivation vs under normal glucose was 8 to 10-fold enhanced for control fibroblasts, but more than 30-fold enhanced in the case patient fibroblasts. Western blot analyses were also in line with this.
- Mitochondrial dysfunction (probably secondary) with evidence of decreased complex I (and complex IV) activities in skeletal muscle was the case for 2 individuals among multiple patients who had muscle biopsies.

Animal models:
- Beck et al. discuss previously published mouse models where Ctbp1/2 both play overlapping transcriptional roles during development. Homozygous deletion of Ctbp2 is embryonically lethal (>E10.5). Homozygous deletion of Ctbp1 results in viable mice with reduced size and lifespan (Cited: Hildebrand et al. 2002 - PMID: 12101226)
- As commented on by Sommerville et al., Ctbp1 knockout in mouse embryonic fibroblasts resulted in elongated mitochondria, abnormal mitochondrial cristae, diminished ATP and O2 consumption and mitochondrial membrane potential.

----
CTBP1 is associated with Hypotonia, ataxia, developmental delay, and tooth enamel defect syndrome (617915) in OMIM. It is not associated with any phenotype in G2P.
Some diagnostic laboratories (eg. GeneDx participating in the first study and others) include this gene in panels for intellectual disability.
----

As a result, CTBP1 can be added in the current panel probably as green.; to: 12 individuals with a recurrent missense variant in CTBP1 have been reported, all summarized in the last article:
- Beck et al. 2016 (PMID: 27094857) : 4 individuals
- Sommerville et al. 2017 (PMID: 28955726) : 1 subject
- Beck et al. 2019 (PMID: 31041561) : 7 further individuals

Features included hypotonia, DD/ID, ataxia and tooth enamel defects. The degree of ID - when present - appeared to be highly variable based at least on the first two reports (3 individuals with severe ID, 1 with borderline-normal intellectual functioning, 1 did not exhibit ID) where this feature was further commented on.

A recurrent missense variant was found in all 12 affected individuals [NM_001328.2:c.1024C>T - p.(Arg342Trp) or NM_001012614.1:c.991C>T - p.(Arg331Trp)]. De novo occurrence this SNV was shown for (almost) all individuals, although in one case maternal sequencing reads were compatible with low-level somatic mosaicism (4/75 reads) not detected by Sanger sequencing. The mother of this individual was phenotypically normal. The variant is absent from gnomAD. Several in silico predictions (SIFT, PolyPhen2, MutationTaster, etc) suggest a deleterious effect.

Given recurrence of this specific variant, and presence of LoF ones in healthy individuals (pLI of 0.98 though in gnomAD) Beck et al. suggested a dominant negative or a gain-of-function effect rather than a loss of function mechanism.

Exclusion of alternative causes: was mainly discussed for the subject reported by Sommerville et al., due to the primary suspicion of a mitochondrial disorder (sequencing and research for mtDNA rearrangements, additional analysis of nuclear genes for mitochondrial disorders).

Expression: CTBP1 encodes C-terminal binding protein 1, with expression among others in brain and cerebellum (https://gtexportal.org/home/gene/CTBP1).

Role and Functional studies:
- The major nuclear isoform of CTBP1 (corresponding to NM_001328.2) and of its paralog CTBP2 function as transcriptional regulators (corepressors). The PLDLS(Pro-Leu-Asp-Leu-Ser)-binding cleft domain where this variant lies, acts as a high-affinity protein-binding interface to recruit DNA-binding repressors and chromatin modifying enzymes (PMID: 17967884).
- In a human glioblastoma cell line interaction of various cofactors with (Flag-tagged) CTBP1 was studied by immunoprecitipation with the Flag antibody and subsequent proteomic (LC-MS) analysis. This demonstrated reduced interaction in the case of R342W (compared to wt) with Zn-finger transcription factors, histone deacetylases, histone methyltransferases, histone H3-K4 demethylase etc. Western blot analyses also revealed reduced interaction of the R342W with several CTBP cofactors.
- RNA-seq analysis in glioblastoma cell line revealed similar overall transcriptional profiles between wt and R342W though multiple RNA species showed significant differences (eg. genes involved in the biological processes of mitotic nuclear division, DNA repair, transcription and regulation of transcription among those that were most upregulated and genes involved in brain development among the most downregulated).
- Patient fibroblasts under conditions of glucose deprivation exhibited strikingly more cell death compared to control fibroblasts. Study of mRNA levels of pro-apoptotic genes by q-RT-PCR revealed that Noxa expression under glucose deprivation vs under normal glucose was 8 to 10-fold enhanced for control fibroblasts, but more than 30-fold enhanced in the case patient fibroblasts. Western blot analyses were also in line with this.
- Mitochondrial dysfunction (probably secondary) with evidence of decreased complex I (and complex IV) activities in skeletal muscle was the case for 2 individuals among multiple patients who had muscle biopsies.

Animal models:
- Beck et al. discuss previously published mouse models where Ctbp1/2 both play overlapping transcriptional roles during development. Homozygous deletion of Ctbp2 is embryonically lethal (>E10.5). Homozygous deletion of Ctbp1 results in viable mice with reduced size and lifespan (Cited: Hildebrand et al. 2002 - PMID: 12101226)
- As commented on by Sommerville et al., Ctbp1 knockout in mouse embryonic fibroblasts resulted in elongated mitochondria, abnormal mitochondrial cristae, diminished ATP and O2 consumption and mitochondrial membrane potential (Cited: Kim and Youn 2009 - PMID: 19136938).

----
CTBP1 is associated with Hypotonia, ataxia, developmental delay, and tooth enamel defect syndrome (617915) in OMIM. It is not associated with any phenotype in G2P.
Some diagnostic laboratories (eg. GeneDx participating in the first study and others) include this gene in panels for intellectual disability.
----

As a result, CTBP1 can be added in the current panel probably as green.
Intellectual disability v2.938 CTBP1 Konstantinos Varvagiannis changed review comment from: 12 individuals with a recurrent missense variant in CTBP1 have been reported, all summarized in the last article:
- Beck et al. 2016 (PMID: 27094857) : 4 individuals
- Sommerville et al. 2017 (PMID: 28955726) : 1 subject
- Beck et al. 2019 (PMID: 31041561) : 7 further individuals

Features included hypotonia, DD/ID, ataxia and tooth enamel defects. The degree of ID - when present - appeared to be highly variable based at least on the first two reports (3 individuals with severe ID, 1 with borderline-normal intellectual functioning, 1 did not exhibit ID) where this feature was further commented on.

A recurrent missense variant was found in all 12 affected individuals [NM_001328.2:c.1024C>T - p.(Arg342Trp) or NM_001012614.1:c.991C>T - p.(Arg331Trp)]. De novo occurrence this SNV was shown for (almost) all individuals, although in one case maternal sequencing reads were compatible with low-level somatic mosaicism (4/75 reads) not detected by Sanger sequencing. The mother of this individual was phenotypically normal. The variant is absent from gnomAD. Several in silico predictions (SIFT, PolyPhen2, MutationTaster, etc) suggest a deleterious effect.

Given recurrence of this specific variant, and presence of LoF ones in healthy individuals (pLI of 0.98 though in gnomAD) Beck et al. suggested a dominant negative or a gain-of-function effect rather than a loss of function mechanism.

Exclusion of alternative causes: was mainly discussed for the subject reported by Sommerville et al., due to the primary suspicion of a mitochondrial disorder (sequencing and research for mtDNA rearrangements, additional analysis of nuclear genes for mitochondrial disorders).

Expression: CTBP1 encodes C-terminal binding protein 1, with expression among others in brain and cerebellum (https://gtexportal.org/home/gene/CTBP1 ).

Role and Functional studies:
- The major nuclear isoform of CTBP1 (corresponding to NM_001328.2) and of its paralog CTBP2 function as transcriptional regulators (corepressors). The PLDLS(Pro-Leu-Asp-Leu-Ser)-binding cleft domain where this variant lies, acts as a high-affinity protein-binding interface to recruit DNA-binding repressors and chromatin modifying enzymes (PMID: 17967884).
- In a human glioblastoma cell line interaction of various cofactors with (Flag-tagged) CTBP1 was studied by immunoprecitipation with the Flag antibody and subsequent proteomic (LC-MS) analysis. This demonstrated reduced interaction in the case of R342W (compared to wt) with Zn-finger transcription factors, histone deacetylases, histone methyltransferases, histone H3-K4 demethylase etc. Western blot analyses also revealed reduced interaction of the R342W with several CTBP cofactors.
- RNA-seq analysis in glioblastoma cell line revealed similar overall transcriptional profiles between wt and R342W though multiple RNA species showed significant differences (eg. genes involved in the biological processes of mitotic nuclear division, DNA repair, transcription and regulation of transcription among those that were most upregulated and genes involved in brain development among the most downregulated).
- Patient fibroblasts under conditions of glucose deprivation exhibited strikingly more cell death compared to control fibroblasts. Study of mRNA levels of pro-apoptotic genes by q-RT-PCR revealed that Noxa expression under glucose deprivation vs under normal glucose was 8 to 10-fold enhanced for control fibroblasts, but more than 30-fold enhanced in the case patient fibroblasts. Western blot analyses were also in line with this.
- Mitochondrial dysfunction (probably secondary) with evidence of decreased complex I (and complex IV) activities in skeletal muscle was the case for 2 individuals among multiple patients who had muscle biopsies.

Animal models:
- Beck et al. discuss previously published mouse models where Ctbp1/2 both play overlapping transcriptional roles during development. Homozygous deletion of Ctbp2 is embryonically lethal (>E10.5). Homozygous deletion of Ctbp1 results in viable mice with reduced size and lifespan (Cited: Hildebrand et al. 2002 - PMID: 12101226)
- As commented on by Sommerville et al., Ctbp1 knockout in mouse embryonic fibroblasts resulted in elongated mitochondria, abnormal mitochondrial cristae, diminished ATP and O2 consumption and mitochondrial membrane potential.

----
CTBP1 is associated with Hypotonia, ataxia, developmental delay, and tooth enamel defect syndrome (617915) in OMIM. It is not associated with any phenotype in G2P.
Some diagnostic laboratories (eg. GeneDx participating in the first study and others) include this gene in panels for intellectual disability.
----

As a result, CTBP1 can be added in the current panel probably as green.
Sources: Literature; to: 12 individuals with a recurrent missense variant in CTBP1 have been reported, all summarized in the last article:
- Beck et al. 2016 (PMID: 27094857) : 4 individuals
- Sommerville et al. 2017 (PMID: 28955726) : 1 subject
- Beck et al. 2019 (PMID: 31041561) : 7 further individuals

Features included hypotonia, DD/ID, ataxia and tooth enamel defects. The degree of ID - when present - appeared to be highly variable based at least on the first two reports (3 individuals with severe ID, 1 with borderline-normal intellectual functioning, 1 did not exhibit ID) where this feature was further commented on.

A recurrent missense variant was found in all 12 affected individuals [NM_001328.2:c.1024C>T - p.(Arg342Trp) or NM_001012614.1:c.991C>T - p.(Arg331Trp)]. De novo occurrence this SNV was shown for (almost) all individuals, although in one case maternal sequencing reads were compatible with low-level somatic mosaicism (4/75 reads) not detected by Sanger sequencing. The mother of this individual was phenotypically normal. The variant is absent from gnomAD. Several in silico predictions (SIFT, PolyPhen2, MutationTaster, etc) suggest a deleterious effect.

Given recurrence of this specific variant, and presence of LoF ones in healthy individuals (pLI of 0.98 though in gnomAD) Beck et al. suggested a dominant negative or a gain-of-function effect rather than a loss of function mechanism.

Exclusion of alternative causes: was mainly discussed for the subject reported by Sommerville et al., due to the primary suspicion of a mitochondrial disorder (sequencing and research for mtDNA rearrangements, additional analysis of nuclear genes for mitochondrial disorders).

Expression: CTBP1 encodes C-terminal binding protein 1, with expression among others in brain and cerebellum (https://gtexportal.org/home/gene/CTBP1).

Role and Functional studies:
- The major nuclear isoform of CTBP1 (corresponding to NM_001328.2) and of its paralog CTBP2 function as transcriptional regulators (corepressors). The PLDLS(Pro-Leu-Asp-Leu-Ser)-binding cleft domain where this variant lies, acts as a high-affinity protein-binding interface to recruit DNA-binding repressors and chromatin modifying enzymes (PMID: 17967884).
- In a human glioblastoma cell line interaction of various cofactors with (Flag-tagged) CTBP1 was studied by immunoprecitipation with the Flag antibody and subsequent proteomic (LC-MS) analysis. This demonstrated reduced interaction in the case of R342W (compared to wt) with Zn-finger transcription factors, histone deacetylases, histone methyltransferases, histone H3-K4 demethylase etc. Western blot analyses also revealed reduced interaction of the R342W with several CTBP cofactors.
- RNA-seq analysis in glioblastoma cell line revealed similar overall transcriptional profiles between wt and R342W though multiple RNA species showed significant differences (eg. genes involved in the biological processes of mitotic nuclear division, DNA repair, transcription and regulation of transcription among those that were most upregulated and genes involved in brain development among the most downregulated).
- Patient fibroblasts under conditions of glucose deprivation exhibited strikingly more cell death compared to control fibroblasts. Study of mRNA levels of pro-apoptotic genes by q-RT-PCR revealed that Noxa expression under glucose deprivation vs under normal glucose was 8 to 10-fold enhanced for control fibroblasts, but more than 30-fold enhanced in the case patient fibroblasts. Western blot analyses were also in line with this.
- Mitochondrial dysfunction (probably secondary) with evidence of decreased complex I (and complex IV) activities in skeletal muscle was the case for 2 individuals among multiple patients who had muscle biopsies.

Animal models:
- Beck et al. discuss previously published mouse models where Ctbp1/2 both play overlapping transcriptional roles during development. Homozygous deletion of Ctbp2 is embryonically lethal (>E10.5). Homozygous deletion of Ctbp1 results in viable mice with reduced size and lifespan (Cited: Hildebrand et al. 2002 - PMID: 12101226)
- As commented on by Sommerville et al., Ctbp1 knockout in mouse embryonic fibroblasts resulted in elongated mitochondria, abnormal mitochondrial cristae, diminished ATP and O2 consumption and mitochondrial membrane potential.

----
CTBP1 is associated with Hypotonia, ataxia, developmental delay, and tooth enamel defect syndrome (617915) in OMIM. It is not associated with any phenotype in G2P.
Some diagnostic laboratories (eg. GeneDx participating in the first study and others) include this gene in panels for intellectual disability.
----

As a result, CTBP1 can be added in the current panel probably as green.
Sources: Literature
Intellectual disability v2.938 CTBP1 Konstantinos Varvagiannis gene: CTBP1 was added
gene: CTBP1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CTBP1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CTBP1 were set to 27094857; 28955726; 31041561
Phenotypes for gene: CTBP1 were set to Generalized hypotonia; Global developmental delay; Intellectual disability; Ataxia; Abnormality of dental enamel
Penetrance for gene: CTBP1 were set to unknown
Mode of pathogenicity for gene: CTBP1 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: CTBP1 was set to GREEN
gene: CTBP1 was marked as current diagnostic
Added comment: 12 individuals with a recurrent missense variant in CTBP1 have been reported, all summarized in the last article:
- Beck et al. 2016 (PMID: 27094857) : 4 individuals
- Sommerville et al. 2017 (PMID: 28955726) : 1 subject
- Beck et al. 2019 (PMID: 31041561) : 7 further individuals

Features included hypotonia, DD/ID, ataxia and tooth enamel defects. The degree of ID - when present - appeared to be highly variable based at least on the first two reports (3 individuals with severe ID, 1 with borderline-normal intellectual functioning, 1 did not exhibit ID) where this feature was further commented on.

A recurrent missense variant was found in all 12 affected individuals [NM_001328.2:c.1024C>T - p.(Arg342Trp) or NM_001012614.1:c.991C>T - p.(Arg331Trp)]. De novo occurrence this SNV was shown for (almost) all individuals, although in one case maternal sequencing reads were compatible with low-level somatic mosaicism (4/75 reads) not detected by Sanger sequencing. The mother of this individual was phenotypically normal. The variant is absent from gnomAD. Several in silico predictions (SIFT, PolyPhen2, MutationTaster, etc) suggest a deleterious effect.

Given recurrence of this specific variant, and presence of LoF ones in healthy individuals (pLI of 0.98 though in gnomAD) Beck et al. suggested a dominant negative or a gain-of-function effect rather than a loss of function mechanism.

Exclusion of alternative causes: was mainly discussed for the subject reported by Sommerville et al., due to the primary suspicion of a mitochondrial disorder (sequencing and research for mtDNA rearrangements, additional analysis of nuclear genes for mitochondrial disorders).

Expression: CTBP1 encodes C-terminal binding protein 1, with expression among others in brain and cerebellum (https://gtexportal.org/home/gene/CTBP1 ).

Role and Functional studies:
- The major nuclear isoform of CTBP1 (corresponding to NM_001328.2) and of its paralog CTBP2 function as transcriptional regulators (corepressors). The PLDLS(Pro-Leu-Asp-Leu-Ser)-binding cleft domain where this variant lies, acts as a high-affinity protein-binding interface to recruit DNA-binding repressors and chromatin modifying enzymes (PMID: 17967884).
- In a human glioblastoma cell line interaction of various cofactors with (Flag-tagged) CTBP1 was studied by immunoprecitipation with the Flag antibody and subsequent proteomic (LC-MS) analysis. This demonstrated reduced interaction in the case of R342W (compared to wt) with Zn-finger transcription factors, histone deacetylases, histone methyltransferases, histone H3-K4 demethylase etc. Western blot analyses also revealed reduced interaction of the R342W with several CTBP cofactors.
- RNA-seq analysis in glioblastoma cell line revealed similar overall transcriptional profiles between wt and R342W though multiple RNA species showed significant differences (eg. genes involved in the biological processes of mitotic nuclear division, DNA repair, transcription and regulation of transcription among those that were most upregulated and genes involved in brain development among the most downregulated).
- Patient fibroblasts under conditions of glucose deprivation exhibited strikingly more cell death compared to control fibroblasts. Study of mRNA levels of pro-apoptotic genes by q-RT-PCR revealed that Noxa expression under glucose deprivation vs under normal glucose was 8 to 10-fold enhanced for control fibroblasts, but more than 30-fold enhanced in the case patient fibroblasts. Western blot analyses were also in line with this.
- Mitochondrial dysfunction (probably secondary) with evidence of decreased complex I (and complex IV) activities in skeletal muscle was the case for 2 individuals among multiple patients who had muscle biopsies.

Animal models:
- Beck et al. discuss previously published mouse models where Ctbp1/2 both play overlapping transcriptional roles during development. Homozygous deletion of Ctbp2 is embryonically lethal (>E10.5). Homozygous deletion of Ctbp1 results in viable mice with reduced size and lifespan (Cited: Hildebrand et al. 2002 - PMID: 12101226)
- As commented on by Sommerville et al., Ctbp1 knockout in mouse embryonic fibroblasts resulted in elongated mitochondria, abnormal mitochondrial cristae, diminished ATP and O2 consumption and mitochondrial membrane potential.

----
CTBP1 is associated with Hypotonia, ataxia, developmental delay, and tooth enamel defect syndrome (617915) in OMIM. It is not associated with any phenotype in G2P.
Some diagnostic laboratories (eg. GeneDx participating in the first study and others) include this gene in panels for intellectual disability.
----

As a result, CTBP1 can be added in the current panel probably as green.
Sources: Literature
Intellectual disability v2.903 CSNK2B Rebecca Foulger commented on gene: CSNK2B: PMID:30655572: Nakashima et al, 2019 describe 4 patients with ID, DD and seizures. Two of the patients had variants in CSNK2B: c.533_534insGT, p.(Pro179Tyrfs*49) in Malaysian Patient 3, and c.494A>G, p.(His165Arg) in Japanese Patient 4. Both had seizures within 2 months of age. Both variants occurred de novo. In each patient, only 1 likely candidate variant was proposed. Functional assays suggested that Pro179Tyrfs*49 mutant protein was produced but showed disrupted interaction with CSNK2A1.
Intellectual disability v2.857 MED12L Konstantinos Varvagiannis gene: MED12L was added
gene: MED12L was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: MED12L was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: MED12L were set to 31155615
Phenotypes for gene: MED12L were set to Motor delay; Delayed speech and language development; Intellectual disability; Behavioral abnormality; Abnormality of the abdomen; Seizures; Abnormality of the corpus callosum
Penetrance for gene: MED12L were set to unknown
Review for gene: MED12L was set to AMBER
Added comment: Nizon et al. (2019 - PMID: 31155615) report on 7 unrelated individuals with nucleotide or copy-number variants in MED12L.

Features included motor delay (4/7), speech impairment (7/7) with ID of variable degrees (7/7 - mild to severe). Variable behavioral abnormalities (ASD in 4/7, aggressive behavior, ADHD, etc), functional GI anomalies, corpus callosum abnormalities and seizures were among other features noted in some/few. There was no recognizable facial phenotype.

Nucleotide variants included 1 stopgain, 1 frameshift and 2 splice site variants. 3 CNVs were reported (two 3q25.1 microduplications of 460- and 147-kb respectively and one microdeletion of 291-kb) although all spanned also other genes.

De novo occurrence was shown for 2 CNVs and 2 SNVs, as parental samples were unavailable for 3 of the subjects.

Contribution of other genetic (eg. an inherited 22q11.2 microduplication, VUS in other genes) or environmental factors could not be ruled out for few individuals.

Among the arguments provided:

MED12L encodes a subunit of the kinase module of the mediator complex, a complex required for transcription by RNA polymerase II. Mutations in other subunits of the kinase module (eg. MED12, MED13L, etc) have been implicated in intellectual disability.

The protein is localized in the nucleus. The gene is mainly expressed in the brain.

The functional effect of 2 CNVs was evaluated using the recovery of RNA synthesis assay, an assay reflecting global transcriptional activity. Fibrobast studies from one individual with microdeletion and one further subject with microduplication demonstrated decreased RNA synthesis compared to controls. Decreased RNA synthesis was also observed in cell lines from individuals with mutations in other genes for subunits of the mediator complex (eg. MED12 or MED13L) or from individuals with Cockayne syndrome.

Therefore haploinsufficiency is suggested to underly the transcriptional defect. (MED12L also appears to be intolerant to LoF variation with a pLI score of 1).

Some features appear to be common among the disorders caused by pathogenic variants in MED12L or other subunits of the kinase module (MED12, MED13, MED13L) eg. ID, abnormal behaviour or autistic features.

Animal models are not discussed / (probably not) available (MGI for Med12l : http://www.informatics.jax.org/marker/MGI:2139916).

MED12L is not associated with any phenotype in OMIM or G2P. The gene is not commonly included in gene panels for ID offered by diagnostic laboratories.

As a result, this gene can be considered for inclusion in the ID panel, probably as amber (4 variants affecting only MED12L, segregation studies performed for 2, degree of ID reported mild on 2 occasions) pending further reports.
Sources: Literature
Intellectual disability v2.854 BCORL1 Rebecca Foulger Mode of inheritance for gene: BCORL1 was changed from Unknown to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.853 ALKBH8 Konstantinos Varvagiannis gene: ALKBH8 was added
gene: ALKBH8 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: ALKBH8 was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: ALKBH8 were set to Global developmental delay; Intellectual disability; Seizures
Penetrance for gene: ALKBH8 were set to Complete
Review for gene: ALKBH8 was set to AMBER
Added comment: Monies et al. (2019 - PMID: 31079898) report on 7 individuals from 2 different consanguineous Saoudi families, harboring homozygous truncating ALKBH8 pathogenic variants. The same individuals are included in another concurrent publication from the same group (Monies et al. 2019 - PMID: 31130284).

All presented with DD and ID (Fam1 : moderate in the proband, degree not commented on for his 3 sibs / Fam2 : mild in the proband, severe in all his 3 sibs). Epilepsy was reported for 6/7 individuals although the type has not been commented on (onset 9-12 months to 2 years). Variable other features were noted in few.

Affected subjects from the first family were homozygous for a stopgain variant (NM_001301010.1:c.1660C>T or p.Arg554Ter) while individuals from the second family were homozygous for a frameshift one (c.1794delC or p.Trp599Glyfs*19). The variants affected in both cases the last exon of ALKBH8 and RT-PCR confirmed that they escape NMD.

Alternative causes were ruled out, at least for the proband from the second family (chromosomal analysis, SNP-array, metabolic investigations).

Linkage analysis of both families confirmed linkage to the same autozygous interval of chr11q22.3 with a LOD score of 6.

Segregation analyses in both families, confirmed homozygosity for the truncating variants in affected members and heterozygosity in their parents (or several unaffected sibs, none of those studied was homozygous for the ref. allele).

In mouse or human cells, ALKBH8 has previously been shown to be involved in tRNA modifications of the wobble uridines of specific tRNAs (PMIDs cited: 20308323, 20583019, 21653555).

LC-MS/MS analyses of tRNA extracted from LCLs derived from affected individuals, unaffected relatives (UR) and independent controls (IC) revealed that wobble nucleotide modifications were completely absent (or dramatically decreased in the case of mcm5U) in affected individuals but readily detected in UR/IC. As specific modifications were absent, substantial amounts of precursors (eg. cm5U - the precursor of mcm5U) were detected in affected individuals but not in unaffected ones.

Absence of wobble modifications (eg. mchm5U) has equally been observed in Alkbh8 knockout mice. Alkbh8-deficient mice show similar increases in precursors. Alkbh8 KO mice are however phenotypically normal (the authors comment that eventual cognitive defects were not formally evaluated and might have been missed - PMIDs cited: 20123966, 21285950).

As a result, the studies carried out confirmed the loss-of-function effect and were in line with previous functional studies in animal models, although the pathogenesis of ID remains unclear.

The expression profile of ALKBH8 is also unclear (wide profile of expression suggested developmentally, the authors studied LCLs, other studies suggest that embryonic expression is broad but becomes progressively more restricted to specific neuronal cells).

Mutations in other genes involved in tRNA modification (eg. ADAT3, PUS3, PUS7) have been shown underlie disorders affecting the CNS, with ID as a feature.

ALKBH8 is not currently associated with any phenotype in OMIM / G2P.

As a result, this gene can be considered for inclusion in the ID/epilepsy panels as amber pending further evidence.
Sources: Literature
Intellectual disability v2.853 AP2M1 Konstantinos Varvagiannis gene: AP2M1 was added
gene: AP2M1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: AP2M1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: AP2M1 were set to 31104773
Phenotypes for gene: AP2M1 were set to Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures; Ataxia; Autistic behavior
Penetrance for gene: AP2M1 were set to Complete
Review for gene: AP2M1 was set to GREEN
Added comment: Helbig et al. (2019 - PMID: 31104773) report on 4 individuals with developmental and epileptic encephalopathy due to a recurrent de novo AP2M1 missense variant (NM_004068.3:c.508C>T or p.Arg170Trp). Seizure types included atonic, myoclonic-atonic, absence seizures (with or without eyelid myoclonia), tonic-clonic etc. Hypotonia, developmental delay (prior to the onset of seizures at 1y 3m to 4y) and intellectual disability were observed in all four. Other features included ataxia (3/4) or autism spectrum disorder (2/4).

AP2M1 encodes the μ-subunit of the adaptor protein complex 2 (AP-2). AP2M1 is highly expressed in the CNS. The AP-2 complex is involved in clathrin-mediated endocytosis at the plasma mebrane of neurons and non-neuronal cells. This mechanism is important for recycling synaptic vesicle components at mammalian central synapses. Previous evidence suggests regulation of GABA and/or glutamate receptors at the neuronal surface by AP-2 (several references provided by Helbig et al.).

The authors provide evidence for impaired (reduced) clathrin-mediated endocytosis of transferrin in AP-2μ-depleted human HeLa cells upon plasmid-based re-expression of the Arg170Trp variant compaired to re-expression of WT. A similar defect was demonstrated upon comparison of the same process when WT and Arg170Trp re-expression was studied in primary astrocytes from conditional AP-2μ knockout mice.

Expression levels, protein stability, membrane recruitment and localization of the AP-2 complex in clathrin-coated pits were similar for the Arg170Trp variant and WT. As a result, the effect of the specific variant is suggested to be mediated by alteration of the AP-2 complex function (/impaired recognition of cargo membrane proteins) rather than haploinsufficiency.

AP2M1 is highly intolerant to missense / LoF variants with z-score and pLI in ExAC of 5.82 and 0.99 respectively.

As the authors discuss, heterozygous Ap2m1 mutant mice do not have an apparent phenotype. Homozygous mutant mice die before day 3.5 postcoitus, suggesting a critical role in early embryonic development (PMID 16227583 cited)

AP2M1 is currently not associated with any phenotype in OMIM / G2P.

As a result, this gene can be considered for inclusion in the epilepsy and ID panels probably as green (4 individuals with highly similar phenotype of DEE, relevance of phenotype and/or degree of ID, functional studies, etc) rather than amber (single recurrent variant - although this is also the case for other genes rated green).
Sources: Literature
Intellectual disability v2.847 DYNC1I2 Konstantinos Varvagiannis gene: DYNC1I2 was added
gene: DYNC1I2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DYNC1I2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DYNC1I2 were set to 31079899
Phenotypes for gene: DYNC1I2 were set to Microcephaly; Intellectual disability; Abnormality of nervous system morphology; Abnormality of head or neck
Penetrance for gene: DYNC1I2 were set to Complete
Review for gene: DYNC1I2 was set to AMBER
Added comment: Ansar et al. (2019 - PMID: 31079899) report on five individuals from 3 families, with biallelic likely pathogenic DYNC1I2 variants.

The phenotype consisted of microcephaly, intellectual disability, cerebral malformations and suggestive facial features. 2/5 individuals, from different families presented seizures.

Affected individuals from a consanguineous Pakistani family were homozygous for a splicing variant (c.607+1G>A - RNA was unavailable for further studies). One individual from a futher family was compound heterozygous for a missense variant (c.740A>G or p.Tyr247Cys) and a 374 kb deletion encompassing DYNC1I2 as well as 3 other genes (DCAF17, CYBRD1, SLC25A12). Another individual was found to harbor c.740A>G (p.Tyr247Cys) in trans with c.868C>T (p.Gln290*). [NM_001378.2 used as reference].

DYNC1I2 encodes Dynein Cytoplasmic 1 intermediate chain 2, a component of the cytoplasmic dynein 1 complex. This complex is involved in retrograde cargo transport within the cytoplasmic microtubule network. Emerging evidence suggests a critical role of this complex in neurodevelopment and homeostasis (PMIDs cited by the authors: 25374356, 28395088). Mutations in other genes encoding components of the complex (principally DYNC1H1) give rise to neurological disorders, some of which with ID as a principal feature (eg. Mental retardation, autosomal dominant 13 - MIM 614563).

In zebrafish, DYNC1I2 has 2 orthologs - dync1i2a and dync1i2b. The former is suggested to be the functionally relevant DYNC1I2 ortholog as CRISPR-Cas9 dync1i2a disruption and/or suppression with morpholinos resulted in altered craniofacial patterning and reduction in head size (similar to the microcephaly phenotype reported in affected individuals).

In vivo complementation studies suggested a loss of function effect for the p.Tyr247Cys variant, similar to the p.Gln290* one.

Evidence is provided for a role of increased apoptosis, probably secondary to altered cell cycle progression (prolonged mitosis due to abnormal spindle morphology), to explain the reduced head size/microcephaly phenotype.

There is no associated phenotype in OMIM/G2P.

As a result, DYNC1I2 could be considered for inclusion in the ID panel probably as amber (ID reported for 5 individuals from 3 families, severity of ID not specified for all, eg. fam. 2 for whom the deletion was also spanning other genes which might contribute to the phenotype).
Sources: Literature
Intellectual disability v2.845 ACTL6B Rebecca Foulger commented on gene: ACTL6B: Bell et al., 2019 (PMID:31031012) identified 11 individuals (from 10 families) with biallelic variants in ACTL6B and global developmental delay, epileptic encephalopathy, and spasticity. They also identified 10 unrelated individuals with de novo heterozygous variants with ID, developmental delay, hypotonia, Rett-like stereotypies (e.g. handwringing), and minor facial dysmorphisms: 9/10 of these individuals had the identical de novo c.1027G>A (p.Gly343Arg) mutation. Engineered knock-out of ACTL6B in wild-type human neurons resulted in profound deficits in dendrite development.
Intellectual disability v2.834 UFM1 Rebecca Foulger commented on gene: UFM1: In 4 patients with profound global developmental delay from 2 Sudanese families, Nahorski et al, 2018 (PMID:29868776) identified a homozygous misense variant in the UFM1 gene (R81C). Functional assays showed the mutated protein had decreased ability to form a complex with UBA5 and UFC1, and suggested that a complete LOF allele would be embryonic lethal. Although the Sudanese families were not known to be related, they originate from the same village in Sudan, and families shared a haplotype, suggesting a founder effect. Nahorski et al, 2018 included a comparison of the phenotypes and UFM1 variants from the Hamilton et al., 2017 (PMID:28931644) in Table 2.
Intellectual disability v2.821 TRAF7 Rebecca Foulger Added comment: Comment on list classification: TRAF7 was added to the panel and rated Green by Konstantinos Varvagiannis based on PMID:29961569 (Tokita et al, 2018) who report four different heterozygous missense mutations in the TRAF7 gene in 7 unrelated patients with MIM:618164. The variants were de novo in at least six of the patients. Motor and/or speech delay were present to a variable degree in 5 of the 5 subjects for whom this outcome could be assessed (The remaining two subjects were 1 week old and 3 weeks old). After discussion with Louise Daugherty, I have rated TRAF7 as Amber: PMID:29961569 assayed motor delay and speech delay as indicators of developmental delay- the authors don't refer to global DD, and motor/speech delay are not directly linked to ID. Additional evidence comes from an ID cohort study (PMID:27479843, Lelieveld et al, 2016) and the DDD study (PMID:28135719). Rated Amber with a 'watchlist' tag, awaiting further evidence.
Intellectual disability v2.800 ZNF142 Konstantinos Varvagiannis gene: ZNF142 was added
gene: ZNF142 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: ZNF142 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: ZNF142 were set to 31036918
Phenotypes for gene: ZNF142 were set to Global developmental delay; Intellectual disability; Seizures; Tremor; Dystonia
Penetrance for gene: ZNF142 were set to unknown
Review for gene: ZNF142 was set to GREEN
Added comment: Khan et al. (2019 - PMID: 31036918) describe the phenotype of 7 females from 4 families, harboring biallelic likely pathogenic ZNF142 variants.

Overlapping features included cognitive impairment (ID in 6/7 from 3 families, borderline intellectual functioning was reported one occasion), speech impairement and motor impairment (7/7), and variably penetrant seizures (5/7), tremor (4/7) and dystonia (3/7). Most individuals (5/7) had experienced at least one episode of seizures (tonic-clonic) though seizures were recurrent in 3 sibs.

Other disorders with ID (eg. Angelman syndrome, Rett syndrome, chromosomal disorders) or movement disorders as a feature were previously ruled out for many subjects.

6 individuals were homozygous or compound heterozygous for LoF (stopgain or frameshift) variants. One individual harbored 2 missense SNVs in the compound heterozygous state. Variants reported include (NM_001105537.2): c. 817_818delAA (p.Lys273Glufs*32), c.1292delG (p.Cys431Leufs*11), c.3175C>T (p.Arg1059*), c.4183delC (p.Leu1395*), c.3698G>T (p.Cys1233Phe), c.4498C>T (p.Arg1500Trp) with the LoF variants predicted to result in NMD. Expression or functional studies were not carried out.

ZNF142 encodes a C2H2 domain-containing transcription factor. Mutations in other zinc finger proteins (ZNF/zfp) have been reported in several neurodevelopmental disorders impacting the CNS (eg. ZBTB20 and ZBTB11 heterozygous and biallelic mutations, respectively) and/or presenting with movement disorders among their manifestations (eg. YY1).

As the authors comment, homozygous ablation of the orthologous (Zfp142) locus in mice results in behavioral and neurological phenotypes [MGI ref.ID: J:211773 cited - http://www.informatics.jax.org/marker/reference/J:211773 (though Zfp142 or its locus do not seem to appear in the list)].

ZNF142 is not - at least commonly - included in gene panels for ID offered by diagnostic laboratories. It is not associated with any phenotype in OMIM, nor in G2P.

As a result, this gene can be considered for inclusion in the current panel as probably as green (individuals from 3 families, appropriate degree of ID for the current panel) or amber (if further evidence would be required).
Sources: Literature
Intellectual disability v2.800 POLA1 Konstantinos Varvagiannis reviewed gene: POLA1: Rating: GREEN; Mode of pathogenicity: None; Publications: 31006512; Phenotypes: Global developmental delay, Intellectual disability, Microcephaly, Growth abnormality, Hypogonadism; Mode of inheritance: X-LINKED: hemizygous mutation in males, biallelic mutations in females; Current diagnostic: yes
Intellectual disability v2.800 SNAP25 Konstantinos Varvagiannis gene: SNAP25 was added
gene: SNAP25 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: SNAP25 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: SNAP25 were set to 29491473; 28135719; 29100083; 25381298; 25003006
Phenotypes for gene: SNAP25 were set to ?Myasthenic syndrome, congenital 18, 616330
Penetrance for gene: SNAP25 were set to Complete
Review for gene: SNAP25 was set to GREEN
gene: SNAP25 was marked as current diagnostic
Added comment: Probably 9 individuals with heterozygous SNAP25 pathogenic variants have been reported to date, most summarized in the first reference (NM_130811.2 used as reference for all variants below):
- Fukuda et al. (2018 - PMID: 29491473) 2 sibs (~11 and 2.5 y.o) with seizures and cerebellar ataxia but not ID. harboring c.176G>C (p.Arg59Pro) variant which was inherited from a mosaic unaffected parent.
- DDD study (2017 - PMID: 28135719) [also in Heyne et al. 2018 - PMID: 29942082] 3 inividuals (11 m - 7 y of age) with DD and seizures due to c.118A>G (p.Lys40Glu), c.127G>C (p.Gly43Arg) and c.520C>T (p.Gln174*) de novo variants.
- Hamdan et al. (2017 - PMID: 29100083) a 23 y.o. male with epilepsy and ID and c.496G>T (p.Asp166Tyr) de novo variant
- Shen et al. (2014 - PMID: 25381298) a 11 y.o. female with epilepsy and ID and c.200T>A (p.Ile67Asn) de novo variant
- Rohena et al. (2013 - PMID: 25003006) a 15 y.o. female with epilepsy and ID and c.142G>T (p.Val48Phe) de novo variant
- Decipher patient 292139, a male with c.212T>C (p.Met71Thr) with hypotonia, DD, poor coordination and additional features (epilepsy not reported).

Seizures of variable type [absence seizures, generalized tonic-clonic (most), focal clonic, myoclonic, etc] have been reported for most (8/9) of these individuals. DD was a feature in several subjects and intellectual outcome has been specifically commented on for 5 (2 without and 3 with ID - moderate/severe/not further specified).

SNAP25 encodes a (t-)SNARE protein essential for synaptic vesicle exocytosis. Mutations in genes for other components of the SNARE complex (eg. STXBP1) have been associated with epilepsy and/or ID.

SNAP25a and SNAP25b are the 2 major protein isoforms [corresponding transcripts: ENST00000304886 (NM_003081) and ENST00000254976 (NM_130811) respectively]. These isoforms are produced by utilization of alternative exons 5 (5a or 5b) though the amino-acid sequence encoded by these exons appears to be identical except for 9 residues. Most variants reported to date affect both transcripts (and protein isoforms) although 2 were specific for ENST00000254976 (or SNAP25b isoform - Fukuda et al. and Shen et al.).

Mouse Snap25 has also 2 isoforms. Both are predominantly localized in embryonic and adult mouse brains. Snap25a is produced before Snap25b though the latter becomes the major isoform early postnatally (by the second week) [PMIDs cited: 7878010, 21526988].

Based on the phenotype of some individuals with chromosome 20 deletions in Decipher (note: only 3 deletions spanning SNAP25 however appear currently, the phenotype is not specified and 2 of them are >4.5Mb) or the pLI of 0.96 in gnomAD, haploinsufficiency has been proposed as a likely mechanism. A dominant-negative effect was however suggested for the Ile67Asn studied by Shen et al. Functional studies have not been performed for other variants.

Animal models discussed:
- Snap25 null drosophila show complete loss of synaptic transmission upon electroretinogram recordings (PMID cited: 12242238).
- In mice, elimination of Snap25b expression resulted in developmental defects, seizures and impaired short-term synaptic plasticity (PMID cited: 19043548).
- Mice with a 4.6 Mb deletion encompassing 12 genes (incl. Snap25) display seizure predisposition (PMID cited: 23064108).
- Heterozygosity for Ile67Thr in (blind-drunk mutant) mice results in impaired vesicle trafficking, impaired sensorimotor gating and ataxia (PMID cited:17283335).

In OMIM, heterozygous SNAP25 mutations are associated with ?Myasthenic syndrome, congenital, 18 (with intellectual disability and ataxia). SNAP25 is part of the DD panel, associated with "Epilepsy and intellectual disability" (disease confidence: probable).

This gene is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc). SNAP25 is among the genes discussed by Erger et al. (PMID: 30914295) as associated with ID in OMIM/HPO/G2P/SysID but not included in the current panel.

As a result SNAP25 can be considered for inclusion in the ID panel probably as green (3 individuals with ID, role of SNARES in "synaptopathies", supportive animal models) or amber (if functional studies for individual variants would be required).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.800 CACNA1B Konstantinos Varvagiannis gene: CACNA1B was added
gene: CACNA1B was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CACNA1B was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: CACNA1B were set to Global developmental delay; Developmental regression; Seizures; Intellectual disability; Abnormality of movement
Penetrance for gene: CACNA1B were set to Complete
Review for gene: CACNA1B was set to GREEN
Added comment: Gorman et al. (2019 - doi.org/10.1016/j.ajhg.2019.03.005) report on 6 individuals from 3 unrelated families, with biallelic LoF CACNA1B variants. The phenotype corresponds to a developmental epilepic encephalopathy with hyperkinetic movement disorder (ID was a universal feature, DD and/or regression occurred prior to the onset of seizures in several individuals) .

CACNA1B encodes calcium channel, voltage-dependent N type, α-1B subunit (Ca v2.2). As commented by the authors, Ca v2.1 and v2.2 are important for SNARE-mediated release of neurotransmitters through modulation of Ca+2 levels. In addition, Ca v2.2 has been postulated to have a role in synaptic plasticity, synaptogenesis, migration of immature neurons, etc. It is thought to have a crucial role in neurotransmission in the early postnatal period (Ca v2.2 channels are subsequently replaced by Ca v2.1 in mature synapses within the thalamus, cerebellum and auditory brainstem). Knockout mice display neurodevelopmental abnormalities including impaired locomotor activity and memory impairment (all ref. cited within the article).

3 sibs, born to 1st cousin parents, harbored p.Leu1222Argfs*29 (NM_000718.4:c.3665del) in the homozygous state. One additional individual was homozygous for p.Arg383*. Compound heterozygosity for a frameshift and a splicing variant (p,Gly1192Cysfs* and c.4857+1G>C) was identified in 2 sibs from a 3rd family.

Expression/functional studies have not been performed for any of the variants reported.

In OMIM, monoallelic CACNA1B pathogenic variants are associated with ?Dystonia 23 (MIM 614860) based on the identification of a heterozygous missense (R1389H) mutation in members of a Dutch with myoclonus-dystonia syndrome (Groen et al. 2015 - PMID: 25296916).

As a result, this gene can be considered for inclusion in the epilepsy and ID panels as green (or amber).
Sources: Literature
Intellectual disability v2.800 BCORL1 Konstantinos Varvagiannis reviewed gene: BCORL1: Rating: AMBER; Mode of pathogenicity: None; Publications: 24123876, 30941876; Phenotypes: Global developmental delay, Intellectual disability, Autism, Behavioral abnormality; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males); Current diagnostic: yes
Intellectual disability v2.800 ISCA-37468-Loss Louise Daugherty Mode of inheritance for Region: ISCA-37468-Loss was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.799 ISCA-37468-Loss Louise Daugherty Mode of inheritance for Region: ISCA-37468-Loss was changed from MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.798 P4HTM Konstantinos Varvagiannis gene: P4HTM was added
gene: P4HTM was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: P4HTM was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: P4HTM were set to 30940925; 25078763
Phenotypes for gene: P4HTM were set to Central hypotonia; Muscular hypotonia; Global developmental delay; Intellectual disability; Seizures; Abnormality of the eye; Hypoventilation; Sleep apnea; Dysautonomia
Penetrance for gene: P4HTM were set to Complete
Review for gene: P4HTM was set to GREEN
Added comment: Rahikkala et al. (2019 - PMID: 30940925) report on 13 individuals from 5 families with biallelic pathogenic P4HTM variants. 6 of these individuals from a large consanguineous family from Finland were previously reported by the same group, although studies at the time had revealed a 11.5 Mb region of homozygosity with 3 genes within this interval considered to be candidate for the patients' phenotype (P4HTM, TKT, USP4) [Kaasinen et al. - PMID: 25078763].

Common features included Hypotonia (13/13), DD and ID (the latter present in 12/13 individuals with appropriate age for evaluation) and Eye Abnormalities, reason why the acronym HIDEA is suggested for the disorder. Epilepsy was observed in 10 individuals (10/13). Hypoventilation, sleep apnea and dysautonomia were additional features reported.

Muscle biopsies from 4 individuals had variable findings suggestive of disruption of normal mitochondrial function.

Finnish patients were homozygous for a SNV - possibly a founder variant in this population - predicted to lead to a missense change in the canonical transcript (NM_177938.2:c.1073G>A) but causing an in-frame loss of the complete exon 6 of another transcript (NM_177939.2).

The latter transcript (encoding a 502 aa protein) is the prevalent one in fibroblasts/myoblasts instead of the canonical one (563 aa). It is not known whether the canonical transcript is the prevalent in brain tissue although northern blot analysis in a previous study suggested presence of a 2.3 kb mRNA in brain instead of a 1.8 kb observed in other tissues, a finding which may be suggestive of expression of the canonical transcript. [Reviewer's note: In gnomAD based on the pext values from the GTEx, the noncanonical transcript appears to be prevalent in brain regions - https://gnomad.broadinstitute.org/gene/ENSG00000178467]

All variants reported in affected both transcripts. All 5 variants have been submitted to LOVD ( https://databases.lovd.nl/shared/variants/P4HTM?search_var_status=%3D%22Marked%22%7C%3D%22Public%22 - the first author appearing as the submitter).

Overexpression of wt and 3 mutants (His161Pro, Gln352*and Exon6del) in insect cells followed by analysis with SDS-PAGE and western blot revealed severly reduced/abolished fraction of soluble protein for the 3 studied variants suggesting improper protein folding.

Knockout of the gene in mice leads to retinal defects and/or visual impairment in line with eye abnormalites (nystagmus, strabismus, achromic retinal fundi or cortical blindness) being a prominent feature in affected individuals. Mouse studies suggest that this gene is also important for renal function, although kidney problems were not reported in any affected individual.

Overall loss-of-function is suggested to be the underlying mechanism.

P4HTM is not associated with any phenotype in OMIM, nor in G2P. This gene is not (at least commonly) included in gene panels for ID offered by diagnostic laboratories.

As a result P4HTM can be considered for inclusion in the ID and epilepsy panels probably as green (several affected individuals, degree of ID relevant) or amber.
Sources: Literature
Intellectual disability v2.798 VAMP2 Konstantinos Varvagiannis gene: VAMP2 was added
gene: VAMP2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: VAMP2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: VAMP2 were set to 30929742
Phenotypes for gene: VAMP2 were set to Generalized hypotonia; Global developmental delay; Intellectual disability; Autistic behavior; Stereotypic behavior; Seizures; Abnormality of movement; Cortical visual impairment
Penetrance for gene: VAMP2 were set to unknown
Review for gene: VAMP2 was set to GREEN
gene: VAMP2 was marked as current diagnostic
Added comment: Salpietro et al. (2019 - PMID: 30929742 - DDD study among the co-authors) report on 5 individuals each with private heterozygous de novo variants in VAMP2.

The overlapping phenotype consisted among others of hypotonia with DD, moderate/severe ID and ASD (all in 5/5). Other features included the presence of clinical seizures (3/5 - EEG anomalies observed in all individuals), variable Rett-like stereotypies, hyperkinetic movements, central visual impairment. OFC was normal in all subjects.

VAMP2 encodes the vesicular SNARE protein synaptobrevin-2 which - along with its partners (syntaxin-1A and synaptosomal-associated protein 25) - mediates fusion of synaptic vesicles for the release of neurotransmitters. A number of synaptic proteins involved in Ca+2-regulated neurotransmitter release (eg. Munc18 encoded by STXBP1) regulate the fusion of synaptic vesicles, although SNAREs alone are sufficient for this process.

All variants localized in the v-SNARE domain (aa 31-91 - of 116 total residues - NP_0055047.2) with some phenotypic differences between variants localizing in the C-terminal end of the v-SNARE domain compared to those localizing in its proximal part. The following 3 missense variants and 2 in-frame deletions were reported (using NM_014232 as reference): c.223T>C or p.Ser75Pro - c.233A>C or p.Glu78Ala - c.230T>C or p.Phe77Ser - c.128_130delTGG or p.Val43del and c.135_137delCAT or p.Ile45del.

Functional studies were performed for 2 missense variants and were suggestive of impairment in vesicle fusion for the Ser75Pro variant. The fusion profile for Glu78Ala was however similar to wt. Upon Munc18-activated conditions, wt vesicle fusion was 2-fold increased, in contrast to a >90% loss-of-function effect which was observed for the Ser75Pro variant. Munc18 was however able to activate vesicle fusion mediated by the Glu78Ala variant. When using mixed v-liposomes (50:50 Wildtype:Ser75Pro mutant) the fusion profile was identical to the profile of homogeneous samples containing only the mutant protein which was suggestive of dominant interference of the mutant with wildtype.

In gnomAD, VAMP2 has a (low) Z-score and pLI of 1.41 and 0.89 respectively.

The authors comment that mutations in other genes encoding presynaptic proteins involved in Ca+2-regulated neurotransmitter release (eg SNAP25, STXBP1, etc) have been identified in other neurological disorders (with ID as a feature).

VAMP2 is not associated with any phenotype in OMIM or G2P. This gene is included in gene panels for ID offered by some diagnostic laboratories.

As a result, VAMP2 can be considered for inclusion in the ID panel probably as green (5 individuals, degree of ID relevant) or amber.
Sources: Literature
Intellectual disability v2.787 CDK8 Konstantinos Varvagiannis commented on gene: CDK8: Calpena et al. (2019 - PMID: 30905399 - DDD study among the co-authors) report on 12 unrelated individuals with pathogenic CDK8 missense variants.

Common features included hypotonia and DD (universal feature). Older children displayed variable degrees of ID (2 mild, 5 moderate, 2 moderate-severe). Other features included feeding difficulties, behavioral disorders, CHD, epilepsy (2 individuals), impaired vision and hearing problems in few.

CDK8 (alternatively CDK19) serves a one of the four subunits of a kinase module that reversibly binds to the mediator complex to regulate its activity (in turn, regulation of transcription). Mutations in other genes coding for the 3 other subunits of the kinase module (eg. MED12 or MED13L) lead to syndromic neurodevelopmental disorders.

8 missense CDK8 variants were reported in total. Ser62Leu (NM_001260.2:c.185C>T) was recurrent, observed in 5 subjects. The variants had occurred as de novo events in all cases (10 individuals) where parental samples were available.

All variants clustered in the kinase domain (residues 21-335 - of 464 total) around the ATP binding pocket. A thermal stability assay did not reveal gross protein instability in the presence or absence of ATP while the ability to bind ATP was retained for most/all variants. Study of STAT1 phosphorylation was suggestive of attenuated kinase activity for all variants, though to a lesser degree for 2 of them. Given the type of variants (all missense) and the pLI of 0.38 haploinsufficiency appears to be unlikely. A dominant-negative mechanism is favoured.

CDK8 is not associated with any phenotype in G2P.

As a result, CDK8 can be considered for upgrade to green or amber (if the degree of ID is relevant for the current panel).
Intellectual disability v2.787 ARHGEF6 Richard Scott commented on gene: ARHGEF6: Literature review identifies lack of clarity about published data on this gene. As per note in OMIM entry:

ARHGEF6, IVS1AS, T-C, -11 (rs140322310)
RCV000012185
This variant, formerly titled MENTAL RETARDATION, X-LINKED 46, has been reclassified based on a review of the ExAC database by Hamosh (2018).
In affected males in a large Dutch family with nonspecific X-linked mental retardation (MRX46; 300436), Kutsche et al. (2000) identified a mutation in the ARHGEF6 gene. The base change IVS1-11T-C had a marginal effect on the predicted splicing efficiency but was not detected in 170 control chromosomes. In affected males, RT-PCR amplification demonstrated products of 2 different sizes: a larger amplicon corresponding to the wildtype fragment, and a smaller amplicon in which exon 1 was spliced to exon 3. Thus, all mentally retarded males in the MRX46 family exhibited enhanced skipping of exon 2.
Hamosh (2018) found that the IVS1-11T-C variant (rs140322310) was present in 53 hemizygotes in the ExAC database (November 21, 2018), suggesting that the variant is not pathogenic
Intellectual disability v2.784 BRSK2 Konstantinos Varvagiannis gene: BRSK2 was added
gene: BRSK2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: BRSK2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: BRSK2 were set to https://doi.org/10.1016/j.ajhg.2019.02.002
Phenotypes for gene: BRSK2 were set to Global developmental delay; Intellectual disability; Autism; Behavioral abnormality
Penetrance for gene: BRSK2 were set to unknown
Review for gene: BRSK2 was set to GREEN
gene: BRSK2 was marked as current diagnostic
Added comment: Hiatt et al. (2019 - https://doi.org/10.1016/j.ajhg.2019.02.002) report on 9 individuals, each with private heterozygous BRSK2 variant.

Features included among others speech or motor delay, ID (8/9), ASD and variable behavioral anomalies.

6 variants predicted LoF (stopgain, frameshift or affecting splice-site) while 3 additional ones were missense (2 in the protein kinase domain and 1 in the kinase-associated 1 domain). In 6 individuals the variant had occurred as a de novo event while for 3 others parental samples were unavailable. Given the unknown inheritance, a single variant did not meet sufficient ACMG criteria to be classified as P/LP.

All variants had in silico predictions supporting a deleterious effect and were absent from bravo database and gnomAD, where the gene appears to be relatively intolerant to protein-altering variation.

As the authors note BRSK2 encodes a serine/threonine protein kinase involved in axonogenesis and polarization of cortical neurons. Although Brsk2- (or Brsk1-) knockout mice appear to be healthy and fertile, double knockouts for these genes resulted in pups with decreased spontaneous movement, poor response to tactile stimulation that died shortly after birth. In mice Brsk2 (and Brsk1) expression is restricted to the nervous system (PMID cited by the authors: 15705853) while in humans this gene is most highly expressed in brain (PMID cited: 23715323 - GTEx project).

BRSK2 has been shown to interact with other neurodevelopmental genes eg. TSC2, PTEN, WDR45.

Within the cohort of individuals studied, there was statistically significant enrichment for de novo BRSK2 variants when compared to the estimated backround mutation rate.

Two further BRSK2 de novo protein-altering variants were previously reported in individuals with neurodevelopmental disorders (Iossifov et al. - PMID: 25363768 and DDD study - PMID: 28135719) although the missense variant in the latter study is also present in gnomAD database.

BRSK2 is not associated with any phenotype in OMIM, nor in G2P.
The gene is included in gene panels for ID offered by some diagnostic laboratories (eg. among those participating in the study).

As a result, this gene can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature
Intellectual disability v2.783 TRRAP Konstantinos Varvagiannis gene: TRRAP was added
gene: TRRAP was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TRRAP was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: TRRAP were set to 30827496
Phenotypes for gene: TRRAP were set to Global developmental delay; Intellectual disability; Autism; Microcephaly; Abnormal heart morphology; Abnormality of the urinary system; Seizures
Penetrance for gene: TRRAP were set to unknown
Mode of pathogenicity for gene: TRRAP was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: TRRAP was set to GREEN
gene: TRRAP was marked as current diagnostic
Added comment: Cogné et al. (DDD study among the co-authors - PMID: 30827496) report on 24 individuals with pathogenic TRRAP variants.

17 different variants were reported. All variants were missense SNVs and on most occasions had occurred as de novo or apparently de novo events (paternity and maternity not checked). On one occasion, a parent was not unavailable although the respective grand-parents were not found to harbor the variant. Parental germline mosaicism explained the occurence of a variant in 2 sibs.

The authors suggest a strong genotype-phenotype correlation. Individuals whose variant localized within the residues 1031-1159 (NM_001244580.1) presented with a syndromic form of ID with additional malformations. ID was a universal feature in this group (for those subjects evaluated). For variants outside this cluster of residues the phenotype was rather that of ASD without ID or isolated ID with or without ASD, albeit with some exceptions (eg. F860L also associated with a syndromic presentation). ID was a feature in the majority of individuals belonging to the latter group (67% - all with DD) or overall irrespective of the variant localization (85% for those evaluated - all with DD).

Epilepsy was a feature in 4 individuals (4/24) belonging to either group.

All 17 variants were absent from gnomAD with CADD scores supporting a deleterious effect (SIFT/PolyPhen2 (both) predicted a tolerated/benign effect for some eg. Ala1043Thr). A few variants were recurrent, namely Ala1043Thr (5 individuals), Glu1106Lys (2), Gly1883Arg (2), Pro1932Leu (in 2 sibs).

6 further subjects (individuals 25-30, reported separately in the supplement) harbored 6 additional variants with lesser evidence for pathogenicity.

TRRAP is among the 5 most intolerant genes to missense mutations (z-score of 10.1 in ExAC) while it is also intolerant to LoF variants (pLI of 1). No deletions have been reported in DECIPHER and no LoF were identified in the study. Given type of variants and their clustering rather a gain-of-function effect or dominant-negative effect is suggested. As the authors note a LoF effect of non-clustering variants, associated with a milder phenotype cannot excluded. [Mode of pathogenicity to change if thought to be useful].

TRRAP encodes a protein involved in the recruitment to chromatin of histone acetyltransferases. The latter control the process of acetylation of lysine residues in histones and other DNA-binding proteins thus playing a major role in regulation of gene expression. In line with this, RNA sequencing analysis in skin fibroblasts from affected subjects demonstrated dysregulation of expression for several genes implicated in neuronal function and ion transport.

As summarized by the authors: In mice, Trapp knockout is embryonically lethal. Brain-specific knockout leads to premature differentiation of neural progenitors and abnormal brain development. Brain atrophy and microcephaly are observed (microcephaly was a feature in some affected individuals as well, primarily those with variants affecting residues 1031-1159). [PMIDs cited: 11544477, 24792116].

De novo TRRAP variants have been reported also in individuals with neuropsychiatric disorders (PMIDs: 21822266, 23042115, 28392909, 30424743) while TRRAP has been classified among the prenatally-biased genes relevant to its brain expression (PMID:23042115).

A de novo missense variant (c.11270G>A or p.R3757Q) was also previously reported in a study of 264 individuals with epileptic encephalopathy (Epi4K Consortium - PMID: 23934111 - indiv. ND29352).
-----------
TRRAP is not associated with any phenotype in OMIM, nor in G2P.
The gene is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx participating in the current study).
-----------
As a result, this gene can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature
Intellectual disability v2.782 CARS Konstantinos Varvagiannis gene: CARS was added
gene: CARS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CARS was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: CARS were set to Microcephaly; Neurodevelopmental delay; Brittle hair; Fragile nails
Penetrance for gene: CARS were set to Complete
Review for gene: CARS was set to GREEN
Added comment: Kuo et al. (2019 - doi.org/10.1016/j.ajhg.2019.01.006) report on 4 individuals from 3 families with biallelic pathogenic CARS variants.

Common features included microcephaly, DD, brittle hair and nails. All 4 were adults and presented with motor, language and cognitive disabilities.

Reported genotypes (and variants) included [NM_001751.5 and NP_001742.1]:
- c.1138C>T (p.Gln380*) and c.1022G>A (p.Arg341His) (1 individual)
- c.1076C>T (p.Ser359Leu) and c.1199T>A (p.Leu400Gln) (2 sibs)
- c.2061dup (p.Ser688Glnfs ∗2) in homozygous state (1 individual - no reported consanguinity)

Segregation studies confirmed the in trans occurrence of the variants in affected individuals and carrier state in unaffected parents or other family members.

CARS encodes Cysteinyl-tRNA synthetase an aminoacyl-tRNA synthetase (ARS). ARSs are a group of enzymes responsible for ligating amino acids to cognate tRNA molecules. CARS responsible for charging cysteine to tRNA molecules in the cytoplasm (CARS2 is responsible for charging cysteine to tRNA molecules in mitochondria).

Mutations in several ARSs have been linked to disorders with features overlapping to CARS-related phenotype.

Studies included:
- Western blot (pat. fibroblasts) confirmed expression of stable truncated p.Ser688Glnfs ∗2 but absence of the predicted truncating p.Gln380*. Expression in fibroblasts from the individual with compound heteroz. for the missense variants was similar to controls.
- Subcellular localization did not appear to be affected.
- Aminocacylation was significantly reduced (~40-80%) using protein lysates from affected individual fibroblasts (all families) supporting a LoF effect.
- A yeast complementation assay suggested LoF/hypomorphic effect with no or reduced yeast cell growth depending on the variant tested (hypomorphic variants: Arg341His and Ser359Leu). Aminoacylation assays (in yeast) showed reduced activity (by 50% and 84% respectively) for the 2 hypomorphic variants (compatible with the observations in patient fibroblasts).
- Conservation and the presumed effect of individual variants (in catalytic domain, truncation upstream of anticodon-binding domain or in a region affecting binding specificity of CARS and tRNA-cys) also supported pathogenicity.

All individuals demonstrated strikingly similar hair-shaft anomalies upon polarized light microscopy (eg. trichorrhexis/tiger-tail patterns/abnormal shaft diameter) in line with macroscopical observations of fine brittle hair suggesting a common underlying genetic cause (presumably explained by high cysteine content of keratins).
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CARS is not associatated with any phenotype in OMIM, nor in G2P.
The gene is not - at least commonly - included in gene panels for ID offered by diagnostic laboratories.
-------
As a result, this gene can be considered for inclusion in the current panel as green (or amber).
Sources: Literature
Intellectual disability v2.782 NUS1 Eleanor Williams Mode of inheritance for gene: NUS1 was changed from BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Intellectual disability v2.768 STAG2 Rebecca Foulger Mode of inheritance for gene: STAG2 was changed from X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.742 WARS2 Konstantinos Varvagiannis gene: WARS2 was added
gene: WARS2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: WARS2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: WARS2 were set to 28236339; 28650581; 28905505; 29783990; 29120065
Phenotypes for gene: WARS2 were set to Neurodevelopmental disorder, mitochondrial, with abnormal movements and lactic acidosis, with or without seizures, 617710
Penetrance for gene: WARS2 were set to unknown
Review for gene: WARS2 was set to GREEN
gene: WARS2 was marked as current diagnostic
Added comment: Several individuals with biallelic pathogenic WARS2 variants have been published to date. DD and ID have been reported among others in most of the affected individuals (only the respective features are commented on below):

PMID: 28236339 (Musante et al. 2017) : 2 sibs compound heterozygous for NM_201263.2:c.325delA (p.Ser109Alafs*159) and c.37T>G (p.Trp13Gly). DD with ID were features in both.

PMID: 28650581 (Theisen et al. 2017) : The authors report on 1 individual with DD, ID and seizures was found to harbor in the compound heterozygous state NM_0158360.3:c.938A>T (p.K313M) and c.298_300delCTT (p.L100del).

PMID: 28905505 (Wortmann et al. 2017) : Details on 6 individuals from 5 unrelated families are provided. DD and ID were observed in 5 of these individuals (Fam 2-5). Severe, neonatal presentation was the case for an additional subject. Confirmed occurrence of epilepsy was reported for 3 individuals from 2 families (and suspected in a further one). Using NM_0158360.3 variants were the following :
Fam1 : c.91-8725_348+27113del36096 (p.Lys31_Glndel116) in trans with c.1045G>C (p.Val349Leu)
Fam2 : c.797del (p.Pro266Argfs*10) in trans with c.938A>T (p.Lys313met) [in 2 individuals]
Fam3 : c.231C>G (p.His77Gln) in trans with c.1054G>A (p.Glu352Lys)
Fam4 : c.532G>C (p.Val178Leu) in homozygous state
Fam5 : c.134G>T (p.Gly45Val) in trans with c.938A>T (p.Lys313Met)

PMID: 29783990 (Vantroys et al. 2018) : The authors report on 1 individual with DD, ID and seizures (among other features), compound heterozygous for c.797del (p.Pro266Argfs*10) and c.938A>T (p.Lys313met), similar to subjects from family 2 in PMID: 28905505.

PMID: 29120065 (Burke et al. 2018) : One 17-year-old boy with infantile-onset Parkinsonism but not DD/ID is described in this study. This individuals was found to harbor in the following variants in the compound heterozygous state: NM_015836.3: c.37T>G (p.Trp13Gly) and c.683C>G (p.Ser228Trp).

Probably 7 missense variants, 3 frameshift ones and an intragenic deletion have been reported in individuals with DD/ID (overview in fig 4. - in PMID: 29783990).
- p.Pro266Argfs*10 is located in the last exon of the gene (NM_015836.3).
- p.Trp13Gly (c.37T>G using either NM_201263.2 or NM_015836.3 as ref) has been commented to be a functional polymorphism 'uncovered' by the presence of a LoF allele in trans in affected individuals (AF : 0.003265 and 6 homozygotes in gnomAD)
- p.Lys313Met is possibly the most frequently reported variant as discussed by Vantroys et al.

WARS2 encodes mitochondrial tryptophanyl-tRNA synthetase (a cytoplasmic form is encoded by WARS). As commented in most of the articles, aminoacyl-tRNA synthetases (ARS) are a group of enzymes responsible for ligating amino acids to cognate tRNA molecules. Mutations in mitochondrial ARSs lead to impaired intramitochondrial translation affecting OXPHOS complexes (with mitochondrial-encoded subunits). Mutations in all 19 mitochondrial ARSs have been linked to disorders affecting different organ systems with variable severity and phenotypic presentation (summarized by Vantroys et al.).

Several lines of evidence have been provided to support a role for specific variants (eg. reduced WARS2 amounts upon Western blot, or impaired mitochondrial localization depending on the different variants and their effect) or WARS2 (expression in brain, impaired aminoacylation, abnormalities in OXPHOS enzymes/biosynthesis , etc).

Alternative causes (disorders of the differential diagnosis) have been ruled out on most - if not all - occasions.

As commented by Wortmann et al. the clinical spectrum appears to be broad as for the age of onset, features and clinical course (as happens to be the case for some other disorders due deficiencies of other ARSs). The same authors state that apart from elevated lactate which is suggestive of mitochondrial dysfunction, no specific metabolite was found to be altered in affected individuals.

Phenotypic variability even between individuals with the same genotype has been reported. Eg. severe neonatal presentation with lactic acidosis/hypoglycaemia was the case for 2 sibs in family 2 from Wortmann et al. but the clinical course was different for the subject reported by Vantroys et al. (DD/ID with seizure onset at the age of 6 yrs).

As a result, investigations (and selection of gene panel) may not be straightforward.

In addition consideration of this gene in the epilepsy panel seems to be relevant given that seizures were noted in at least 5 individuals (from 4 families - 28650581, 28905505, 29783990) and severe adverse effects of valproate administration occurred in the subject reported by Vantroys et al.
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The associated phenotype in OMIM is Neurodevelopmental disorder, mitochondrial, with abnormal movements and lactic acidosis, with or without seizures (# 617710). WARS2 is not associated with any disorder in G2P.
This gene is included in panels for ID offered by some diagnostic laboratories.
-----------
As a result, WARS2 can be considered for inclusion in the ID and epilepsy panels as green (or amber).
Sources: Literature
Intellectual disability v2.725 FRMPD4 Louise Daugherty Mode of inheritance for gene: FRMPD4 was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.706 ASNS Louise Daugherty Added comment: Comment on list classification: New gene added by external expert and reviewed by curation team, enough evidence to support gene-disease association and relevance to this panel to rate this gene Green. From PMID: 29375865 (2018) A. Abhyankar et al. summarised Ruzzo et al. (PMID:24139043) studied nine children from four families presenting with similar phenotypes and reported two missense mutations‐c.1084T>G (p.F362V; NM_183356) and c.1648C>T (p.R550C; NM_183356) in the asparagine synthetase domain that dramatically reduce ASNS protein abundance. The authors concluded that accumulation of aspartate/glutamate secondary to ASNS depletion in the brain resulted in the neurologic impairment. One of the two mutations reported in that study, c.1084T>G (p.F362V; NM_183356), is four residues upstream of NP_001664.3:p.Gly366Glu seen in our patient. HEK293 cells expressing c.1084T>G (p.F362V; NM_183356) mutant allele showed dramatic reduction in protein abundance. Additionally, Ruzzo et al. reported a hypomorphic ASNS mouse knockout with structural brain abnormalities and deficits in learning/memory. Subsequently, eight more cases of ASNSD have been reported in the literature PMID: 2566342,27422383, 27469131, 27743885.
Intellectual disability v2.654 CUX1 Konstantinos Varvagiannis gene: CUX1 was added
gene: CUX1 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: CUX1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CUX1 were set to 30014507; 20510857; 25059644
Phenotypes for gene: CUX1 were set to Global developmental delay with or without impaired intellectual development, 618330
Penetrance for gene: CUX1 were set to unknown
Review for gene: CUX1 was set to GREEN
gene: CUX1 was marked as current diagnostic
Added comment: Heterozygous pathogenic variants in CUX1 cause Global developmental delay with or without impaired intellectual development (MIM 618330).

Platzer et al. (2018 - PMID: 30014507) report on 9 individuals from 7 families with heterozygous null-allele variants in CUX1.

All individuals displayed DD (speech delay 9/9 - motor delay 7/9 - hypotonia 3/7 for whom this information was available). Mild/moderate ID was a feature in 5/8. Catch up was observed in 3/8 individuals who - despite a history of previous significant DD - displayed a normal age-related intelligence. For 1/9 individual (Decipher 338131) information on eventual ID was unavailable. Overall the phenotype was compatible with non-syndromic DD with possible ID.

CUX1 encodes Cut homebox-1 transcription factor.

5 LoF variants (Gln21*, Gln800Argfs*19, Gln873*, Ala1067Cysfs*3, Leu1262Argfs*10) and 2 intragenic deletions (deletion of exons 9-24 in one subject and 3-24 in another) are reported.

In 6/9 individuals the variant (SNV/CNV) had occurred as a de novo event. Mosaic de novo intragenic deletion was reported for the subject from Decipher. In one family 2 sibs with mild ID had inherited a LoF variant from their affected mother with moderate ID (origin of the variant unknown in her case).

Leu1262Argfs*10 lies in the penultimate exon (NM_001202543.1 used as ref.) and is presumed to escape NMD.

Expression studies (or functional studies) are not performed for any of the variants.

As Gln800Argfs*19, found in one subject with mild ID in the present study, has been reported once in gnomAD, and given the presence of 12 individuals overall with LoF variants in the specific database, plausible explanations are discussed (among others : mild phenotype, incomplete penetrance, somatic mosaicism, exclusion of individuals with severe early-onset disorders in gnomAD, etc).

Given the reported variants, the probability of LoF intolerance (pLI:1.00), and the haploinsufficiency score (% HI) of 7.19, haploinsufficiency is thought to be the underlying mechanism. CUX1 however appears to be intolerant also to missense SNVs (z-score : 5.05).

Mouse models suggest a role for Cux1 in brain development and signaling. As the authors note, Cux1 (similar to its paralog, Cux2) is selectively expressed in layer II to IV cortical neurons. In Cux1-deficient mice, dendrites display a simpler morphology with decrease in dendritic length and number of branches (PMIDs cited: 20510857, 25059644). (MGI db for Cux1 - http://www.informatics.jax.org/marker/MGI:88568 : "Homozygotes for a targeted null mutation exhibit delayed lung development and neonatal mortality. Survivors show growth retardation and hair defects. Homozygotes for a partially deleted protein have curly hair, and females tend to lose their litters").

Finally, heterozygous mutations in CUX2, encoding cut-like homeobox-2 transcription factor, cause Epileptic encephalopathy, early infantile, 67 (MIM 618141 - in all cases reported to date due to a recurrent missense variant. Gene rated green in the current panel).
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CUX1 is not associated with any phenotype in G2P.
This gene is included in panels for ID offered by diagnostic laboratories (incl. Radboudumc).
-------
As a result, CUX1 can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.632 LSS Konstantinos Varvagiannis gene: LSS was added
gene: LSS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: LSS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: LSS were set to 30723320; 30401459
Phenotypes for gene: LSS were set to Alopecia; Abnormality of the skin; Hypotonia; Global developmental delay; Intellectual disability; Seizures; Abnormality of the genital system; Microcephaly
Penetrance for gene: LSS were set to Complete
Review for gene: LSS was set to GREEN
Added comment: DD and ID seem to be among the features observed in some individuals with biallelic LSS mutations, although the clinical presentation appears to be highly variable.

PMID: 30723320 [Besnrard et al, 2019] reports on 10 individuals from 6 unrelated families with biallelic LSS variants. One additional subject from a seventh family was found to harbor only a missense SNV (in the maternal allele) while the transcript corresponding to the other (/paternal) allele was less expressed upon RNA studies from patient fibroblasts. The allelic imbalance and the phenotypic overlap with the other individuals of the study were thought to be explained by an LSS defect.

The phenotype consisted of total alopecia (11/11) with additional dermatological features in most (9/11), hypotonia (7/11), DD with variable degrees of ID (11/11 both), epilepsy (8/11), microcephaly and genital anomalies in few. Cataracts were not noted in any individuals. The authors suggest that the phenotype corresponds to that observed in a neuroectodermal syndrome previously known as APMR (alopecia with mental retardation - other genes or loci earlier proposed).

Variants included: 7 missense SNVs, 1 nonsense, 1 frameshift, 2 splice variants (c.1109+2T>C / c.1194+5G>A - using NM_002340.5).

Using a minigene assay the latter variants were confirmhed (both) to affect splicing, at least to some important extent. However the splicing defect for one SNV (c.1194+5G>A - skipping of exon 12) was not confirmed upon RNA studies from blood samples of the respective individuals but an allelic balance in favor of the other allele instead (due to presumed utilisation of an alternative splice site, introduction of a premature stop codon and NMD).

Allelic imbalance is discussed for the individual with the single LSS variant but not shown.

Variants did not show clustering (also upon 3D modelling).

Lanosterol synthase converts (S)-2,3-oxidosqualene to lanosterol in the cholesterol biosynthesis pathway. Quantification of cholesterol and its precursors in affected individuals did not however reveal any important imbalance.

As most individuals harbored an allele with missense variant, and mice homozygous for an allele with absent LSS activity show variable lethality, residual LSS activity is suggested for the individuals studied.

Several other disorders affecting cholesterol biosynthesis present overlapping features eg. DD/ID in Lathosterolosis, Desmosterolosis, Smith-Lemli-Opitz syndrome (in this case also genital anomalies), etc or cutaneous anomalies in others.

A neurodevelopmental phenotype in animal models for LSS deficiency is not commented.
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Based on the discussion of the current article (and OMIM):

Earlier studies [PMIDs : 26200341, 29016354 - Zhao et al 2015 and Chen and Liu 2017 respectively] found biallelic missense in individuals with congenital cataracts. DD/ID were not commented/observed. The subject reported by Chen had baldness and genital defects. Shumiya cataract rats due to mutation in Lss gene recapitulate the specific human phenotype [PMID: 16440058 and OMIM]. Cataract was not a feature in any of the individuals of the present study. The corresponding entry for this phenotype in OMIM is Cataract 44 (#616509).

PMID: 30401459 [Romano et al, 2018] reported biallelic LSS mutations in 3 unrelated families with hypotrichosis. Intellectual disability was a feature in 2 sibs from 1 non-consanguineous family (among the three). ID was considered to be coincidental by the authors. The respective entry in OMIM is Hypotrichosis 14 (#618275).
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LSS is not included in the DD panel of G2P, nor in gene panels for ID offered by diagnostic laboratories.
-----
As a result this gene can be considered for inclusion in this panel as green (or amber).
Sources: Literature
Intellectual disability v2.621 NECAP1 Konstantinos Varvagiannis gene: NECAP1 was added
gene: NECAP1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: NECAP1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: NECAP1 were set to 24399846; 30525121; 30626896
Phenotypes for gene: NECAP1 were set to ?Epileptic encephalopathy, early infantile 21, 615833
Penetrance for gene: NECAP1 were set to Complete
Review for gene: NECAP1 was set to GREEN
gene: NECAP1 was marked as current diagnostic
Added comment: Biallelic pathogenic variants in NECAP1 cause ?Epileptic encephalopathy, early infantile, 21 (MIM 615833).
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PMID: 24399846 (Alazami et al. 2014) report on 6 individuals from an multigenerational family from Saudi Arabia with biallelic NECAP1 nonsense variant. The common phenotype consisted of hypotonia, profound global developmental delay preceding the onset of intractable seizures (fragmented multifocal clonic and tonic) in early infancy. Initial workup excluded metabolic causes.

4 of these individuals were born to first cousins once removed, while 2 additional affected subjects from the broader pedigree were born to seemingly unrelated parents from the same region. All affected individuals shared a single autozygous 4.78-Mb interval on chromosome 12p. Linkage analysis confirmed involvement of this locus (LOD score : 5.0447). Exome sequencing demonstrated homozygosity for a nonsense variant (NM_015509.3:c.142C>T - p.R48*). mRNA levels in lymphoblast cell lines from affected subjects were significantly reduced when compared to controls, probably due to NMD.

Necap1 was shown to be strongly expressed in the developing (E14.5) mouse brain and spinal cord, upon immunohistochemical analysis (part of the current study).

NECAP1 has been previously shown to have a functional role in Clathrin-mediated encocytocis (CME), a process which plays a critical role at the site of synapsis (in synaptic vesicle recycling).
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PMID: 30525121 (Alsahli et al. 2018) report on a 41-month-old girl with hypotonia, profound global developmental delay and onset of seizures at the age of 3 months (generalized tonic and clonic / flexor hemispasms). Initial workup was negative for an eventual metabolic origin. The girl was born to consanguineous Saudi parents and was found to harbor the p.R48* variant in the homozygous state, following trio-WES.
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PMID: 30626896 (Mizuguchi et al. 2019) report on a 16-month-old boy, born to consanguineous parents from Malaysia. This individual presented with axial hypotonia and profound developmental delay and developed generalized tonic-clonic and clonic seizures at the (corrected) age of 3 months. EEG demonstrated a burst suppression pattern and a clinical diagnosis of Ohtahara syndrome was retained. Metabolic workup was normal.

Homozygosity for a splice-site NECAP1 variant (NM_015509.3:c.301+1G>A) was demonstrated following exome sequencing. The variant was shown to result in inclusion of a 44-bp intron, resulting in frameshift and introduction of a premature termination codon (p.Gly101Aspfs*45). The level of abnormal transcript was 2-fold increased in lymphoblast cells trated with cycloheximide when compared to cells treated with DMSO, suggesting involvement of NMD.

As also in PMID: 30525121, the present study suggests similarities with the DNM1-related phenotype (Epileptic encephalopathy, early infantile, 31 - #616346 - DNM1 is rated green in the ID panel) as DNM1 also participates in vesicle recycling. The authors of the present study also note that mutations in CLTC (encoding clathrin heavy chain) cause hypotonia with DD/ID with or without epilepsy (Mental retardation, autosomal dominant 56 - #617854 - CLTC is rated green in the ID panel).
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NECAP1 is not associated with any phenotype in G2P.
This gene is included in gene panels for ID offered by some diagnostic laboratories.
----
As a result this gene can be considered for inclusion in this panel as green (or amber).
Sources: Literature
Intellectual disability v2.617 FRMPD4 Konstantinos Varvagiannis reviewed gene: FRMPD4: Rating: GREEN; Mode of pathogenicity: None; Publications: 29267967, 25644381; Phenotypes: Mental retardation, X-linked 104, 300983; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males); Current diagnostic: yes
Intellectual disability v2.611 CYFIP2 Konstantinos Varvagiannis gene: CYFIP2 was added
gene: CYFIP2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CYFIP2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CYFIP2 were set to 29534297; 29667327; 30664714; 25432536; 27524794; 12818175; 20537992
Phenotypes for gene: CYFIP2 were set to Epileptic encephalopathy, early infantile 65, 618008
Penetrance for gene: CYFIP2 were set to unknown
Review for gene: CYFIP2 was set to GREEN
gene: CYFIP2 was marked as current diagnostic
Added comment: Heterozygous pathogenic variants in CYFIP2 cause Epileptic encephalopathy, early infantile, 65 (MIM 618008)
--------------
[Apologies for any eventual mistakes esp.as for the functional evidence]:

Nakashima et al. (2018 - PMID: 29534297) report on 4 unrelated individuals with early-onset epileptic encephalopathy due to de novo missense CYFIP2 variants.

The phenotype consisted of early-onset intractable seizures (diagnosis of West syndrome in 2, Ohtahara syndrome in further individuals) with hypotonia (3/4), DD/ID (4/4) and microcephaly (3/4).

All variants affected Arg87 residue (NM_001037333.2:c.259C>T or p.Arg87Cys in 2 individuals, the 2 other subjects harbored Arg87Leu and Arg87Pro respectively).

CYFIP2 encodes the cytoplasmic FMRP interacting protein 2. CYFIP2 (similar to CYFIP1) is a component of the WAVE regulatory complex (WRC) which has been shown to play a role in actin remodeling, axon elongation, dendritic morphogenesis and synaptic plasticity (several PMIDs cited).

In the inactive state of the WRC complex, CYFIP2 binds to the VCA domain of WAVE. GTP-bound Rac1 (GTPase) leads to release of the VCA domain from CYFIP2 which allows binding of this domain to the Arp2/3 complex (active WRC state) and in turn stimulates actin polymerization and lamellipodia formation.

Using lymphoblastoid cell lines from affected individuals and healthy controls and CYFIP2 expression was evaluated by Western Blot and was found to be similar between the 2 groups.

Additional studies suggested weaker binding of the WAVE1 VCA domain to mutant CYFIP2 compared to WT CYFIP2 (upon transfection of HEK293T cells). This could possibly favor activation of WRC (/the WAVE signalling pathway).

As a result a gain-of-function effect on the WAVE signalling pathway is suggested as a possible mechanism.

Using B16F1 mouse melanoma cells lamellipodia formation (process in which CYFIP2 has previously been implicated) was not shown to be impaired in the case of mutant CYFIP2. However aberrant accumulation of F-actin (and co-localization with mutant CYFIP2) was observed in the present study.

Only large 5q deletions spanning CYFIP2 (and several other genes) have been described to date.

Cyfip2 heterozygous knockout in mice results in abnormal behavior and memory loss. WAVE activity was enhanced (despite reduced WAVE protein production). Homozygous Cyfip2 loss is lethal (PMIDs cited by the authors: 25432536, 27524794). Impaired axonal growth, guidance and branching is noted in Drosophila mutants (CYFIP1/2 ortholog) (PMID cited: 12818175). The authors comment that Cyfip2 (nev) mutant zebrafish show a similar phenotype to mutant flies (PMID cited: 20537992).
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Peng et al. (2018 - PMID: 29667327) in a study of 56 Chinese families with West Syndrome (epileptic/infantile spasms, hypsarrhytmia and ID) identified 1 individual with the Arg87Cys CYFIP2 variant as a de novo occurrence.
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Zweier et al. (2019 - DDD study among the co-authors - PMID: 30664714) report on 12 unrelated subjects with heterozygous pathogenic de novo CYFIP2 variants.

The common phenotype consisted of tone abnormalities (12/12), DD/ID (12/12) and seizures (12/12 though a single individual had experienced a single episode of febrile seizure). Absolute or relative microcephaly and/or additional features were also noted in several individuals.

7 missense variants (4 occurrences of the Arg87Cys variant) as well as splice variant (shown to lead to exon skipping) are reported, as de novo events in these individuals. The splice variant was expected to escape NMD producing a truncating protein.

Although the variants are distantly located in the primary structure, spatial clustering (in the tertiary structure) is suggested by in silico modelling (all in proximity at the CYFIP2-WAVE1 interface).

CYFIP2 appears to be intolerant to both missense and LoF variants (Z-score of 6.15 and pLI of 1 respectively in ExAC).

The authors comment that haploinsufficiency as a mechanism is rather unlikely given the absence of small CNVs or variants predicted to lead to NMD. Again, a gain-of-function effect of these variants on WAVE activation (partial-loss-of function in terms of WRC stabilization and/or conformation of the VCA region in the inactive state) is proposed.
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CYFIP2 is not associated with any phenotype in G2P.
The gene is included in gene panels for intellectual disability offered by some diagnostic laboratories (eg. participants in these studies).
--------------
As a result this gene could be considered for inclusion in this panel as green.
Sources: Literature
Intellectual disability v2.602 ISCA-37494-Gain Louise Daugherty Region: ISCA-37494-Gain was added
Region: ISCA-37494-Gain was added to Intellectual disability. Sources: Expert list
Mode of inheritance for Region: ISCA-37494-Gain was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for Region: ISCA-37494-Gain were set to 25927380; 21984752; 24357492
Phenotypes for Region: ISCA-37494-Gain were set to Chromosome Xq28 duplication syndrome, 300815; X linked intellectual disability (XLID); PMID: 25927380 cognitive impairment, behavioral problems, distinctive facial features; duplication affects males with a recognizable syndrome, females exhibiting milder phenotypes; PMID:21984752 behavioural abnormalities (hyperactivity and aggressiveness), characteristic facial features (high forehead, upper eyelid fullness, broad nasal bridge and thick lower lip); PMID:24357492 Cognitive impairment in male patients
Review for Region: ISCA-37494-Gain was set to GREEN
Added comment: Sources: Expert list
Intellectual disability v2.601 ISCA-37494-Loss Louise Daugherty Region: ISCA-37494-Loss was added
Region: ISCA-37494-Loss was added to Intellectual disability. Sources: Expert list
Mode of inheritance for Region: ISCA-37494-Loss was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for Region: ISCA-37494-Loss were set to 25927380; 21984752
Phenotypes for Region: ISCA-37494-Loss were set to PMID: 25927380 cognitive impairment, behavioral problems, distinctive facial features; deletion results in skewed chromosome X inactivation and no clinical phenotype in females; PMID: 21984752 in utero male lethality with deletions
Review for Region: ISCA-37494-Loss was set to GREEN
Added comment: Sources: Expert list
Intellectual disability v2.600 ISCA-46299-Gain Louise Daugherty Region: ISCA-46299-Gain was added
Region: ISCA-46299-Gain was added to Intellectual disability. Sources: Expert list
Mode of inheritance for Region: ISCA-46299-Gain was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for Region: ISCA-46299-Gain were set to 22840365; 20655035; 26692240
Phenotypes for Region: ISCA-46299-Gain were set to X linked intellectual disability (XLID); PMID: 26692240 Mild‐profound intellectual disability, speech delay, failure to thrive, hand abnormalities, motor delay, abnormal palate; PMID:22840365 Mild intellectual disability; PMID:26692240 Region 2 (53,160,114–53,713,154 bp Within Chromosome Xp11.22)
Review for Region: ISCA-46299-Gain was set to GREEN
Added comment: Sources: Expert list
Intellectual disability v2.597 PLEKHG2 Konstantinos Varvagiannis gene: PLEKHG2 was added
gene: PLEKHG2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PLEKHG2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: PLEKHG2 were set to 26539891; 26573021; 24001768
Phenotypes for gene: PLEKHG2 were set to Leukodystrophy and acquired microcephaly with or without dystonia, 616763
Penetrance for gene: PLEKHG2 were set to unknown
Review for gene: PLEKHG2 was set to AMBER
gene: PLEKHG2 was marked as current diagnostic
Added comment: Karaca et al. (2015 - PMID: 26539891) in a study of 128 - mostly consanguineous - families with neurogenetic disorders and brain malformations, identified an individual homozygous for a PLEKHG2 missense variant (NM_022835.2:c.1708G>A or p.Gly570Arg). This individual (BAB4830) had a similarly affected sib. Features included hypotonia, intellectual disability, microcephaly, cerebellar atrophy and nystagmus (description provided in supplement - Table S1). This variant has been submitted in ClinVar as likely pathogenic by the corresponding laboratory (SCV000537940.1).
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Edvardson et al. (2016 - PMID: 26573021) reported on 5 individuals from 2 unrelated consanguineous Palestinian families, harboring a missense variant in the homozygous state (NM_022835.2:c.610C>T or p.Arg204Trp - 1/5 was unavailable for testing).
Unaffected relatives here either heterozygous for this variant or homozygous for the reference allele.

Common features included hypotonia (5/5), DD/ID (5/5), postnatal microcephaly (5/5), dystonia (3/5), nystagmus (2/5) or seizures (1/5) [many of these similar to those reported by Karaca et al]. Brain MRI images were consistent with leukodystrophy and prolonged relaxation of dorsal tegmental tracts (similar findings were not commented by Karaca et al).

PLEKHG2 encodes a Rho guanine exchange factor (RhoGEF). RhoGEFs activate RhoGTPases through release of GDP and binding of GTP. Mutations in other RhoGEFs have been associated with neurodevelopmental disorders.

PLEKHG2 activity was shown to be significantly decreased in HEK293A cells transfected with R204W-PLEKHG2 when compared to tranfection with wt. Western blotting suggested that this was not the result of defective expression.

Using lymphoblastoid cell lines from peripheral B lymphocytes from individuals homozygous for R204W and controls, similar levels of expression were shown between the 2 groups.

As the authors note, PLEKHG2 is required for Rac- and Cdc42-stimulated actin polymerization in leukocytes (PMID cited: 24001768).

SDF1a-stimulated actin polymerization was studied in patient cells and was shown to be significantly impaired. In line with this actin polymerization was also impaired upon siRNA-mediated downregulation of PLEKHG2 expression in control cells.
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A subsequent submission of the Gly570Arg variant in ClinVar (2017 - SCV000609979.1 - same variant as the one reported by Karaca et al) reports this as a VUS.
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PLEKHG2 is associated with Leukodystrophy and acquired microcephaly with or without dystonia (616763) in OMIM.
This gene is not associated with any phenotype in G2P.
PLEKHG2 is included in gene panels for ID offered by some diagnostic laboratories.
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As a result, this gene could be considered for inclusion in this panel probably as amber (or green if the current evidence is considered to be sufficient).
Sources: Literature
Intellectual disability v2.597 DHPS Konstantinos Varvagiannis gene: DHPS was added
gene: DHPS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DHPS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DHPS were set to 21389784; 21850436
Phenotypes for gene: DHPS were set to Abnormal muscle tone; Global developmental delay; Intellectual disability; Seizures; EEG abnormality; Behavioral abnormality; Abnormality of head or neck
Penetrance for gene: DHPS were set to Complete
Review for gene: DHPS was set to GREEN
Added comment: Ganapathi et al. (doi.org/10.1016/j.ajhg.2018.12.017 - PMID : NA) report on 5 individuals from 4 unrelated families with biallelic pathogenic variants in DHPS.

The phenotype consisted of DD/ID (5/5), tone abnormalities (hypotonia/hypertonia/spasticity - 5/5), seizures (5/5 - in one case though unclear staring spells) with EEG abnormalities (5/5). Additionally most individuals displayed behavioral issues, or some common facial features.

Several other disorders had been ruled prior to the diagnosis, in all cases by exome sequencing.

All individuals harbored a specific missense variant (c.518A>G or p.Asn173Ser) in trans with various other variants incl. a splice site mutation (c.1014+1G>A), an in-frame deletion of 2 amino acids (c.912_917delTTACAT or p.Tyr305_Ile306del) or a variant abolishing the translation initiation codon (c.1A>G or p.Met1?) [All variants using NM_001930.3 as a reference].

Deoxyhypusine synthase (encoded by DHPS) is an enzyme participating in the first step of hypusine synthesis, an amino-acid which is specific to eukaryotic initiation factor 5A (eIF5A) and its homolog (eIF5A2).

eIF5A, its hypusinated form and DHPS have all been previously implicated in cellular proliferation/differentiation. eIF5A has also been proposed to be a mRNA translation elongation factor. A role of eIF5A in neuronal growth and survival has been proposed previously (all ref. in present article).

Neither eIF5A, nor DHPS or DOHH (an enzyme required for the second step of hypusination) have been associated to any disorders previously. Mutations in genes encoding other eukaryotic elongator factors (eg. EEF1A2, EEF2) have been associated with neurodevelopmental disorders.

Concerning the DHPS variants reported:

cDNA studies suggested that the c.1014+1G>A variant is translated but results in aberrant splicing and truncation of the protein before its active site.

The in-frame deletion as well as the missense variant were shown to have absent or partial (20%) enzyme activity in vitro respectively compared to wild-type (following expression in E.coli BL21(DE3) cells).

In line with this, reduced hypusination of eIF5A was observed for these 2 variants when compared to wild-type DHPS, upon co-transfection of constructs overexpressing DHPS (wt or mut.) and eIF5A in HEK293T cells.

Absence of homozygous DHPS LoF variants in population databases might suggest that complete deficiency is incompatible with normal embryonic development. Mice heterozygous for Dhps deletion do not demonstrate severe phenotypes, though homozygosity is embryonically lethal (PMIDs: 21389784, 21850436).
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DHPS is not associated with any phenotype in G2P, nor in OMIM.
This gene is not - at least commonly - included in gene panels for ID offered by diagnostic laboratories.
---------
As a result, DHPS can be considered for inclusion in this panel as green (or amber).
Sources: Literature
Intellectual disability v2.597 SOX4 Konstantinos Varvagiannis gene: SOX4 was added
gene: SOX4 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SOX4 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Phenotypes for gene: SOX4 were set to Global developmental delay; Intellectual disability; Growth delay; Clinodactyly of the 5th finger; Abnormality of head or neck
Penetrance for gene: SOX4 were set to unknown
Review for gene: SOX4 was set to GREEN
Added comment: Zawerton et al. (DDD study among the co-authors - doi.org/10.1016/j.ajhg.2018.12.014 - PMID:NA) report on 4 unrelated individuals with de novo SOX4 pathogenic variants. The common phenotype consisted of DD/ID (4/4 - very mild to severe), overlapping facial features as well as digital anomalies (5th finger clinodactyly in 4/4).

SOX4 is a member of the SOX family of transcription factors, all presenting at least 50% identity with SRY (the first identified member of this family) in the HMG (DNA-binding) domain. Most SOX genes have important roles in cell fate / differentiation. Mutations in other genes of this family (eg. SRY, SOX9, SOX10, SOX5) are associated with severe human syndromes.

SOX4 is highly expressed in human brain during gestation - particularly in areas of active neurogenesis - with progressive decrease thereafter until the 3rd - 4th decade of life.

Knockdown of the SOX4 ortholog in Xenopus laevis embryos resulted in smaller head size, microphthalmia, shorter body length and underdevelopment of fore- and mid-brain. (Growth deficiency was a common feature in affected individuals, and microcephaly in 2/4).

Sox4-null mice die in utero due to heart septation defects, while such abnormalities were not reported in heterozygous mice. One affected subject had a VSD. Sox4 inactivation in mice results in impaired skeletal growth (similarly to the patients).

All 4 different missense variants clustered in the HMG domain (aa 58-133) which appears relatively (more) depleted in missense variants (only 12 missense HMG-domain variants in gnomAD). [Overall the Z-score for missense variants is 3.72. pLI = 0.38. %HI in DECIPHER : 24.67%].

The 4 missense variants presented impaired DNA binding and transcription activation in COS-1 transfected cells which appeared to distinguish them from the 12 gnomAD ones. Synthesis, stability and nuclear translocation appeared to be similar to wt.

Other parameters eg. residue conservation in the SOX family, presence of "equivalent" known disease causing mutations in other SOX genes or in silico analyses suggesting structural consequences were supportive of a deleterious effect for the 4 variants (but also for some of the 12 gnomAD ones).

SOX4 and SOX11 have almost identical DNA-binding domains, while the mechanism of mutations reported and the phenotypes appear to be relatively similar, as commented by the authors.
--------------
SOX4 is not associated with any phenotype in G2P, nor in OMIM.
This gene is not - at least commonly - included in gene panels for ID offered by diagnostic laboratories.
--------------
As a result SOX4 can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature
Intellectual disability v2.595 NUS1 Konstantinos Varvagiannis gene: NUS1 was added
gene: NUS1 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: NUS1 was set to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Publications for gene: NUS1 were set to 25066056; 29100083; 24824130; 30348779
Phenotypes for gene: NUS1 were set to #617082 - ?Congenital disorder of glycosylation, type 1aa; #617831 - Mental retardation, autosomal dominant 55, with seizures; Abnormality of extrapyramidal motor function
Penetrance for gene: NUS1 were set to unknown
Review for gene: NUS1 was set to AMBER
gene: NUS1 was marked as current diagnostic
Added comment: Mutations in NUS1 have been implicated in recessive as well as dominant forms of ID (1 and 3 unrelated individuals respectively). The latter individuals presented with a developmental and epileptic encephalopathy with ID. At least 2 of these individuals had tremor and other movement disorders. A recent study proposes that NUS1 variants contribute to Parkinson's disease (1 individual with de novo variant affecting the canonical splice site, 26 additional individuals with missense variants - for which segregation studies where not however performed). ID is not commented on for these individuals.

NUS1 is included in the DD panel of G2P, associated with "Epilepsy and intellectual disability". (Monoallelic LoF variants / Disease confidence : probable). This gene is included in gene panels for ID offered by diagnostic laboratories (incl. Radboudumc). Associated phenotypes in OMIM and others discussed in the literature are summarized below (to my understanding).

As a result, NUS1 can be considered for inclusion in the ID panel probably as amber.
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Recessive - [MIM #617082 - ?Congenital disorder of glycosylation, type 1aa] :

Park et al. (2014 - PMID: 25066056) report on an individual homozygous for a NUS1 missense variant (R290H) and suggest that biallelic variants cause a congenital disorder of glycosylation.

The authors based in studies in yeast, mice and man provide evidence that NUS1 encodes the Nogo-B receptor (NgBR), a subunit of cis-prenyltransferase (cis-PTase), important for its activation. cis-PTase catalyzes one of the reactions for dolichol biosynthesis. Dolichol, in turn, is a carrier of glycans for N-linked glycosylation, O-mannosylation and GPI anchor biosynthesis.

Genetic defects in the dolichol biosynthetic pathway have been linked to other forms of CDG and/or other recessive or dominant neurodevelopmental disorders (eg. SRD5A3- and DHDDS-related disorders).

Similarities are provided at the cellular level between different organisms. Heterozygous knockout mice appear normal. Homozygosity is associated with embryonic lethality before E6.5. Conditional knockout in mouse embryonic fibroblasts led to accumulation of free cholesterol, decreased cis-PTase activity, and mannose incorporation in protein (the first & third rescued by transduction with lentiviral human NgBR).

In patient fibroblasts protein levels appeared similar to controls. Interaction with Nogo-B (and hCIT - the product of DHDDS) was not affected. As in mice, accumulation of free cholesterol was observed in cells, with decreased cis-PTase activity and mannose incorporation. LAMP-1 and ICAM-1 were hypoglycosylated in patient fibroblasts. Altered dolichol profiles in serum and urine were observed in carriers of the NUS1 variant, similarly to what described in individuals with DHDDS LoF variants.
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Dominant - [MIM #617831 - Mental retardation, autosomal dominant 55, with seizures].

Hamdan et al. (2017 - PMID: 29100083) report on 3 unrelated individuals with developmental and epileptic encephalopathy (onset: 10m - 2.5y) and ID. Two individuals harbored de novo LoF variants while a third subject had a deletion of exon 2. Movement disorders were noted in all 3 and included tremor (2 subjects) or ataxia (1 additional subject).

The authors cite a previous study on 6q22.1 deletions the critical region of which encompassed only NUS1 and the promoter of SLC35F1 (Szafranski et al. - PMID: 24824130). Haploinsufficiency is discussed as a possible mechanism (pLI of 0.87). A more severe phenotype due to dramatic reduction of NUS1 activity is proposed for the previously reported patient with CDG.
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Other:
Guo et al. (2018 - PMID: 30348779) suggest that NUS1 pathogenic variants contribute to Parkinson's disease. By performing WES in 39 individuals with early onset Parkinson's disease and their unaffected patients (and sibs) the authors identified 1 individual with de novo insertion affecting a NUS1 canonical splice site. RT-PCR demonstrated increased mRNA levels compared with controls. Skipping of 91 bp of exon 3 was demonstrated.

Study in 2 large sporadic PD-patient (N=1852+3237)/control cohorts (N=1565+2858) suggested association between NUS1 non-synonymous variants and PD (P=1.01e-5, OR:11.3). Other genetic causes of PD were excluded in 26 additional individuals with NUS1 missense variants.

Phenotypes of all 27 individuals are provided in Dataset_S04.

NUS1 has been found to be differentially expressed in PD mouse models.

RNAi-mediated knockdown of Tango14 (the Drosophila NUS1) resulted in impaired climbing activity, reduction in brain dopamine levels and abnormal apoptotic signals in brain.
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.595 STAG2 Konstantinos Varvagiannis gene: STAG2 was added
gene: STAG2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: STAG2 was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for gene: STAG2 were set to 29263825; 28296084; 30158690; 30447054; 19449417; 26443594; 25677961; 23637084; 25450604
Phenotypes for gene: STAG2 were set to Global developmental delay; Intellectual disability; Abnormality of head or neck; Microcephaly; Growth delay; Hearing impairment; Abnormal heart morphology
Penetrance for gene: STAG2 were set to unknown
Review for gene: STAG2 was set to GREEN
gene: STAG2 was marked as current diagnostic
Added comment: Several affected individuals (from at least 8 unrelated) families have been reported in the literature. The phenotype consists - among others - of DD/ID. STAG2 is located on long arm of chromosome X (Xq25). Based on these reports, both males and females can be affected.

Soardi et al. (2017 - PMID: 29263825) report an affected male belonging to a large pedigree with 4 other similarly affected males. The disorder in this pedigree followed a typical X-linked inheritance pattern. All affected males were hemizygous for a missense variant (NM_001042749.1:c.980G>A or p.Ser327Asn). Common phenotype consisted of moderate ID, short stature, sensory hearing loss and some similar facial features. Unaffected males did not harbor the variant. Heterozygous females were not affected. Co-segragation of the variant with the affected status under an X-linked model, appeared unlikely to have occurred by chance (probability of 1/131,072 - logarithm of odds score of 5.12).

Mullegama et al. (2017 - PMID: 28296084) report on an 8-year-old girl harboring a de novo nonsense variant in STAG2 (NM_001042749.1:c.205C>T or p.Arg69Ter). This individual presented - among others with - DD, microcephaly, growth delay, digit anomalies, particular facial features, and anomalies of other systems (eg. hearing loss, cardiac defect, etc). The authors summarize the features of 2 subjects from the DDD study as available in DECIPHER, without additional details. [Variants of these individuals NM_001042749.1:c.1913_1922del10 or p.(A638Vfs*10) / NM_001042749.1:c.1811G>A p.(R604Q)].

Yuan et al. (2018 - PMID: 30158690) report on 4 females with de novo LoF STAG2 variants as well as 1 male subject with a de novo missense one. DD (5/5) and ID (4/4) were features in all individuals for whom this information was available. One additional female had an intragenic STAG2 deletion, although this subject was not reported to have DD or ID (table S6 : microcephaly, seizures and facial phenotype). It is not known whether the deletion was inherited or had occurred as a de novo event. All variants from this study have been submitted in ClinVar (phenotype : STAG2-related disorder).

Mullegama et al. (2018 - PMID: 30447054) report on a 4-year-old male with DD, microcephaly, growth delay, digit anomalies due to a de novo missense STAG2 variant (c.3027A>T or p.Lys1009Asn). As discussed by the authors at the time of the study 33 males with Xq25 duplications and ID had been reported (PMIDs cited: 19449417, 26443594, 25677961, 23637084, 25450604).

Discussed in these articles :

STAG2 (or STAG1) is one of the 4 core proteins of the cohesin complex, the other 3 being SMC1A, SMC3 and RAD21. Mutations in genes encoding these proteins or their interactors (eg. NIBPL, HDAC8, ESCO2, etc) have been associated cohesinopathies, a group of multisystem developmental disorders (eg. Cornelia de Lange syndrome, Roberts/SC phocomelia, etc).

It has been commented that the phenotype of STAG2-related disorder presents overlap with other cohesinopathies (eg. DD, microcephaly and growth retardation, craniofacial features, anomalies of the digits, etc).

Decreased proportion of nuclei with premature sister chromatid separation compared to controls was found on one occasion (suggestive of tighter sister chromatid cohesion) [Mullegama-A]. Sister chromatid cohesion was not affected in another report [Soardi et al.].

Western blot demonstrated significant reduction of STAG2 levels for a nonsense variant [Mullegama-A]. Levels were not perturbed for a missense variant [Soardi et al.].

Upon immunofluorescence STAG2 presented normal (nuclear) localization for a missense variant for which this was studied [Soardi et al.].

Perturbation of the cell cycle profile (higher percentage of G2/M cells) was demonstrated for patient fibroblasts compared to controls on one occasion where this was studied. [Soardi et al.].

Microarray expression studies in patient fibroblasts demonstrated altered transcription (upregulation) of genes implicated in cell division, mitosis and DNA replication upon comparison with normal fibroblasts [Soardi et al.].

The effect of a missense variant on STAG2 binding to other cohesin subunits (SCC1, SMC1 and SMC3) and regulators was studied. Binding was found to be reduced in vivo (in HeLa cells) for SCC1 (its direct binding partner) as well as SMC1, SMC3 (possibly indirectly). Reduced STAG2 binding to cohesin regulators was also shown in vivo. However, in vitro studies were not suggestive of impaired binding of STAG2 to SCC1 (a finding difficult to explain) [Soardi et al.].

STAG2 appears to be intolerant to LoF variants (pLI of 1 in ExAC). Z-Score for missense variants is 5.11.

Mullegama et al. (B) comment that Xq25 duplications in males may be associated with milder phenotypes compared to intragenic variants. They further hypothesize that males are able to survive less damaging variants while females are able to survive more deleterious (eg. LoF) ones though with more severe phenotypes (similarity to the MECP2 model is discussed).
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STAG2 is not associated with any phenotype in OMIM.
In G2P this gene is associated with STAG2-related developmental delay with microcephaly and congenital anomalies (disease confidence : confirmed / Both DD and ID among the phenotypes assigned to this entry).
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STAG2 is included in gene panels for ID offered by some diagnostic laboratories.
----------
As a result, this gene can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature
Intellectual disability v2.588 MAPK8IP3 Konstantinos Varvagiannis gene: MAPK8IP3 was added
gene: MAPK8IP3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: MAPK8IP3 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Phenotypes for gene: MAPK8IP3 were set to 25363768; 28213671; 28135719
Penetrance for gene: MAPK8IP3 were set to unknown
Review for gene: MAPK8IP3 was set to GREEN
Added comment: Platzer et al. (doi.org/10.1016/j.ajhg.2018.12.008) report on 13 unrelated individuals with de novo pathogenic variants in MAPK8IP3.

The phenotype consisted - among others - of DD with ID (13/13) as well as variable brain anomalies (incl. cerebral or cerebellar atrophy, corpus callosum anomalies, perisylvian polymicrogyria, etc). Microcephaly, seizures, ataxia, ASD were features seen in fewer individuals.

The variants reported included 2 nonsense, 1 frameshift as well as 6 missense mutations (3 missense variants were found - each - in 2 or more individuals).

All three LoF variants were located in the first exon. (mRNA levels were not studied for these variants although NMD is presumed). The brain anomalies were more consistent for missense variants.

MAPK8IP3 appears intolerant to LoF variants (pLI of 1) with constraint also for missense variants (Z-score of 4.06).

In silico structural modeling was possible for 4 missense variants based on available crystal structures and different mechanisms were presumed (disruption of contacts between Leu444 of adjacent subunits, altered interaction between proximal residues at positions 461 and 466, or disruption of protein protein interactions).

The C.elegans MAPK8IP3 ortholog is encoded by the unc-16 gene. Impaired clearance and accumulation of organelles (incl. lysosomes) in axons is observed in unc-16 mutants (recessive phenotype).

For 6 variants, also conserved in C.elegans, mutants were engineered using CRISPR genome editing. The observed mutant phenotypes (increased axonal lysosomal density compared to controls for 2 variants, sluggish locomotion with lower swimming cycle rate for 1 nonsense and 4 missense variants) were rescued upon CRISPR reverse engineering of each mutant allele back to its wild-type sequence.

The authors cite 3 previous studies, in which individuals investigated for neurodevelopmental disorders where found to harbor de novo MAPK8IP3 variants, namely:
- PMID 25363768 (Iossifov et al.) : p.Tyr94Cys [ASD without ID]
- PMID 28213671 (Berger et al.) : p.Glu461Gly [Smith-Magenis-like phenotype)
- PMID 28135719 (DDD study) p.Arg1146Cys [This variant was found in 3 individuals in the study by Platzer et al.]
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A few additional individuals with neurodevelopmental disorders appear in the denovo-db after filtering for coding variants:
http://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=MAPK8IP3
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NM_015133.4:c.111C>G (p.Tyr37Ter) has been submitted in ClinVar by the Undiagnosed Diseases Network (NIH) as likely pathogenic, associated with MAPK8IP3-related disorder (hypotonia, DD, EEG anomalies among the phenotypes). It is not clear whether this subject corresponds to individual #3 reported by the previous study (possibly not the case).
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MAPK8IP3 is not associated with any phenotype in OMIM, nor in G2P.
This gene is not commonly included in gene panels for ID.
------------
As a result, MAPK8IP3 can be considered for inclusion in this panel as green (rather than amber).
Sources: Literature
Intellectual disability v2.588 ZNF462 Konstantinos Varvagiannis gene: ZNF462 was added
gene: ZNF462 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: ZNF462 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: ZNF462 were set to 28513610; 29427787; 14564155; 12825074
Phenotypes for gene: ZNF462 were set to Ptosis; Prominent metopic ridge; Craniosynostosis; Global developmental delay; Intellectual disability; Autistic behavior
Penetrance for gene: ZNF462 were set to unknown
Review for gene: ZNF462 was set to AMBER
gene: ZNF462 was marked as current diagnostic
Added comment: Weiss et al. (PMID: 28513610) report on 8 individuals (from 6 unrelated families) with heterozygous pathogenic variants affecting ZNF462.

Frequent features included ptosis metopic ridging, craniosynostosis, dysgenesis of corpus callosum. DD (with or without ASD) was a feature in 4 (4/8), one of whom was reported to present mild ID.

4 LoF mutations as well as 2 9q31.2 deletions spanning also other genes are reported [NM_021224.4]:
Fam. 1 - c.3787C>T p.(Arg1263*) (familial) - Normal development in all 3 family members
Fam. 2 - c.2979_2980delinsA p.(Val994Trpfs*147) (de novo) - DD
Fam. 3 - c.4263delA p.(Glu1422Serfs*6) (de novo) - DD
Fam. 4 - Chr9:g.(108940763-110561397)del (hg19) (de novo) - Normal development
Fam. 5- Chr9:g(108464368-110362345)del (hg19) (de novo) - DD with mild ID
Fam. 6 - c.5145delC p.(Tyr1716Thrfs*28) (de novo) - DD

There were no expression/functional studies performed although haploinsufficiency can be presumed based on these variants (ZNF462 has a pLI of 1 in ExAC).
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Cosemans et al. (PMID: 29427787) report on an individual investigated - among others - for mild ID and ASD. This individual harbored a de novo (complex) translocation disrupting ZNF462 and KLF12.

As this subject presented similar features to those reported by Weiss et al. (eg. craniofacial anomalies, abn. development, ASD) and given that KLF12 is not associated with any disorder, the phenotype of this individual was thought to be secondary to disruption of ZNF462.

Details on this patient - before delineation of the translocation breakpoints - were provided previously by Fryns and Hendrickx ( PMID:9297446).
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Cited by the previous article, a further case of ZNF462 disruption due to translocation was previously published in the literature (same individual - Talisetti et al. PMID: 14564155 / Ramocki et al. PMID: 12825074). Profound ID was among the features of this individual although the translocation disrupted also a further ID gene (ASXL2).
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In ClinVar 8 variants have been submitted as pathogenic/likely pathogenic although a phenotype is provided only for 3 variants published by Weiss et al.(submitting lab participating in PMID: 28513610 / SCV000494060.1 corresp. to Fam.1 / SCV000494061.1 - Fam.2 / SCV000494062.1 - Fam. 3).
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Several individuals with de novo coding variants in ZNF462 have been reported in the context of larger cohorts (some with ID as a principal feature).
http://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=ZNF462
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In Decipher apart from the DDD study participants DDD4K.03663 and DDD4K.03792 (appearing in the denovo-db) with LoF and abnormality of the nervous system, several further individuals have been submitted.

2 of these subjects, harbored a de novo LoF (submitted as pathogenic) and had ID as a feature.
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ZNF462 is included in the DD panel of G2P, associated with Craniofacial anomalies, corpus callosum dysgenesis, ptosis, and developmental delay [Disease confidence: probable / Global DD (but not ID) among the phenotypes assigned to this entry].

This gene is not associated with any phenotype in OMIM.
----------
ZNF462 is included in gene panels for ID offered by diagnostic laboratories (incl. Radboudumc).
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As a result this gene can be considered for inclusion in the ID panel probably as amber (or green if the current evidence is thought to be sufficient).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.588 TBC1D20 Konstantinos Varvagiannis gene: TBC1D20 was added
gene: TBC1D20 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: TBC1D20 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TBC1D20 were set to 24239381; 26063829
Phenotypes for gene: TBC1D20 were set to Warburg Micro syndrome 4 (MIM 615663)
Penetrance for gene: TBC1D20 were set to Complete
Review for gene: TBC1D20 was set to GREEN
gene: TBC1D20 was marked as current diagnostic
Added comment: Biallelic pathogenic variants in TBC1D20 cause Warburg Micro syndrome 4 (MIM 615663).
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Liegel et al. (PMID: 24239381) report on 7 individuals from 5 unrelated families. ID was a universal feature along with opthalmological, endocrine and other neurological features of the disorder. Seizures were noted in 4 individuals from 2 families. Table S4 of this article provides clinical details on each subject.

All affected individuals were homozygous for LoF variants, private to each family. 3 nonsense variants, 1 frameshift one as well as an intragenic deletion (exons 2-8) were identified.

These subjects belonged to a cohort of 77 individuals with suspected Warburg Micro syndrome (WMS) or disorders of the same spectrum (eg. Martsof syndrome).

Screening for TBC1D20 mutations in these individuals was performed after identification of a homozygous LoF Tbc1d20 mutation in blind sterile mice, presenting a phenotype somewhat similar to WMS (congenital cataracts and testicular anomalies).

Alternative causes of WM (eg. pathogenic variants in RAB3GAP1, RAB3GAP2 and RAB18) had previously been excluded in this cohort.

The authors demonstrated aberrant lipid droplet formation in embryonic fibroblasts from blind sterile mice as well as in fibroblasts from individuals with a diagnosis of WMS due to mutations in either of TBC1D20, RAB18 and RAB3GAP1.
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TBC1D20 is included in the DD panel of G2P, associated with Warburg micro syndrome 4 (Disease confidence: probable / ID among the phenotypes assigned to this entry).

This gene is included in gene panels for ID offered by different diagnostic laboratories (incl. Radboudumc).
---------
As a result, TBC1D20 can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.588 PPP2CA Konstantinos Varvagiannis gene: PPP2CA was added
gene: PPP2CA was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PPP2CA was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: PPP2CA were set to 29274472; 30030003
Phenotypes for gene: PPP2CA were set to Feeding difficulties; Muscular hypotonia; Global developmental delay; Intellectual disability; Language impairment; Seizures; Abnormality of nervous system morphology
Penetrance for gene: PPP2CA were set to unknown
Review for gene: PPP2CA was set to GREEN
Added comment: Reynhout et al. (doi.org/10.1016/j.ajhg.2018.12.002 - PMID not available) report on 16 individuals with heterozygous pathogenic PPP2CA variants.

Frequent features included feeding difficulties, hypotonia, developmental delay (16/16) with intellectual disability (probably 15/16 - a single individual developped cognitive dysfunction following a psychotic episode), language impairment, behavioral problems, seizures (10/16), brain abnormalities and variable other features.

The variants reported included 3 nonsense mutations, 1 frameshift, 1 duplication of one amino acid, 9 missense variants (of which one was observed twice and 2 affected Asp223) as well as a partial gene deletion (spanning also CDKL3).

Various mechanisms seemed to explain the effect of the different variants - among others - haploinsufficiency for some or a dominant negative effect for others, etc.

Type 2A protein phosphatases (PP2As) comprise 3 subunits, a catalytic C-type subunit (PPP2CA encodes the Cα subunit), a scaffolding A-type subunit as well as a regulatory B-type subunit important for their function. Impairment of PP2A-B56δ (encoded by PPP2R5D) binding/functionality was suggested for most of the variants. Similar dysfunction has been observed - among others - upon loss of one functional allele of PPP2R1A.

The effect of 2 variants affecting Asp223 (Asp223Val and Asp233His) was unclear as they largely behaved similar to wild-type in various functional assays. The authors argue that contribution of mutations in other genes could not be ruled out for the individuals harboring these variants, as could also be the case for the subject with disruption of (also) CDKL3.

The authors note overlapping phenotype with PPP2R1A and PPP2R5D-related ID (MIM 616362 and 616355 respectively - genes rated green in this panel).

Brain-specific Ppp2ca knockout in mice (PMID: 29274472) resulted in morphological and behavioral abnormalities partly overlapping with features observed in individuals with PPP2CA mutations. However mice heterozygous for null mutations have not been phenotypically examined (PMID: 30030003).
---------
PPP2CA is not associated with any phenotype in OMIM, nor in G2P.
This gene is not commonly included in gene panels for ID offered by diagnostic laboratories.
---------
As a result, PPP2CA can be considered for inclusion in this panel as green.
Sources: Literature
Intellectual disability v2.588 CTNNA2 Konstantinos Varvagiannis gene: CTNNA2 was added
gene: CTNNA2 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CTNNA2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CTNNA2 were set to 30013181
Phenotypes for gene: CTNNA2 were set to Cortical dysplasia, complex, with other brain malformations 9 (MIM 618174)
Penetrance for gene: CTNNA2 were set to Complete
Review for gene: CTNNA2 was set to AMBER
Added comment: Biallelic loss-of-function mutations in CTNNA2 cause cortical dysplasia, complex, with other brain malformations 9 (MIM 618174).
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Schaffer et al. (PMID: 30013181) report on 7 individuals from 3 unrelated consanguineous families. All individuals presented with profoundly impaired motor and cognitive development (severe ID in 6/7 for whom this information was available, all 6 from 2 families - a further individual from the 3rd family was non-ambulatory with absent speech at the age of 28 months), with acquired microcephaly and intractable seizures (7/7 - onset: 6m-3y - atonic/myoclonic/infantile spasms). Pachygyria without posterior-anterior gradient or focal dysplasias was common to all.

CTNNA2 encodes αN-catenin. It is expressed in human fetal brain, mainly in regions expressing migration markers DCX and TUJ1. Reduced migration was shown for iPSC-derived neural progenitor cells from an affected individual, compared to controls. The protein contains a putative actin-binding domain (ABD) at its C terminus. Several lines of evidence are provided that this domain is critical for the process of neuronal migration.
-------
CTNNA2 is included in the DD panel of G2P associated with disordered cortical neuronal migration (Disease confidence: probable / ID and seizures among the phenotypes assigned to this entry).

This gene is not commonly included in gene panels for intellectual disability.
-------
As a result CTNNA2 could be considered for inclusion in this panel as amber or possibly green.
Sources: Literature
Intellectual disability v2.588 TSEN15 Konstantinos Varvagiannis gene: TSEN15 was added
gene: TSEN15 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: TSEN15 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TSEN15 were set to 27392077; 25558065
Phenotypes for gene: TSEN15 were set to Pontocerebellar hypoplasia, type 2F (MIM 617026)
Penetrance for gene: TSEN15 were set to Complete
Review for gene: TSEN15 was set to GREEN
gene: TSEN15 was marked as current diagnostic
Added comment: Biallelic pathogenic variants in TSEN15 cause Pontocerebellar hypoplasia, type 2F (MIM 617026).

Four individuals with molecular confirmation of the diagnosis, from 3 unrelated consanguineous families have been reported by Breuss et al. (PMID: 27392077). One of these individuals was previously included in a study of neurogenetic disorders in consanguineous families (Alazami et al. - PMID: 25558065). A similarly affected sib (possibly not tested) was reported for one patient.

DD with variable degrees of ID (mild to severe), progressive microcephaly were common to all. Seizures were noted in 2 individuals. MRI images (for the feature of pontocerebellar hypoplasia - PCH) were only available for 2 families.

Affected subjects were homozygous for missense variants private to each family, namely:
- NM_052965.3:c.226T>G (p.Trp76Gly)
- NM_052965.3:c.346C>T (p.His116Tyr)
- NM_052965.3:c.455A>G (p.Tyr152Cys)

Trp76Gly and Tyr152Cys resulted in reduced protein abundance while His116Tyr did not have an effect on TSEN15 expression levels.

TSEN15 is part of the tRNA splicing endonuclease complex, the 3 other components of which (TSEN2, TSEN34, TSEN54) have already been associated with PCH. The complex interacts with an RNA kinase encoded by CLP1.

All 3 variants resulted in altered stoichiometry (/relative abundance) of the 3 other subunits of the complex as well as the relative levels of CLP1.

Almost complete loss of in vitro tRNA cleavage activity was the case for purified complexes from all 3 mutants.
------
TSEN15 is included in the DD panel of G2P associated with Pontocerebellar Hypoplasia and Progressive Microcephaly (Disease confidence: probable). ID is among the assigned phenotypes.

This gene is included in gene panels for ID offered by diagnostic laboratories (incl. Radboudumc).
------
As a result, TSEN15 could be considered for inclusion in this panel as green (or amber).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.588 RAB11A Konstantinos Varvagiannis gene: RAB11A was added
gene: RAB11A was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: RAB11A was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: RAB11A were set to 29100083
Phenotypes for gene: RAB11A were set to Global developmental delay; Intellectual disability
Penetrance for gene: RAB11A were set to unknown
Review for gene: RAB11A was set to AMBER
gene: RAB11A was marked as current diagnostic
Added comment: PMID: 29100083 (by Hamdan et al.) is a study on de novo mutations in individuals with developmental and epileptic encephalopathies (DEE).

One subject from this study was found to harbor a de novo missense RAB11A variant [NM_004663.4:c.244C>T or p.(Arg82Cys)]. This individual presented with epilepsy, developmental regression and severe ID.

In their cohort the authors also identified an additional individual with a de novo missense variant [(c.71A>G or p.(Lys24Arg)] who had moderate ID and abnormal EEG albeit without seizures.

De novo variants in RAB11A had previously been identified in 3 DDD study participants with ID.

The authors obtained clinical details on the 2 individuals with the p.(Ser154Leu) variant [NM_004663.4:c.461C>T]. One of them had moderate ID without seizures while the other had moderate global DD at the age of 4 years, also without seizures.

A third DDD study participant harbored another missense variant p.(Lys13Asn) [NM_004663.4:c.39A>C] as a de novo occurence. The authors did not manage to obtain clinical details although this patient was reported to have abnormalities of the nervous system in Decipher.

The features of all 4 individuals for whom clinical details were available are summarized in table 7.

Previous studies suggest that RAB11A has a role in NTRK2 and AMPA receptor recycling at the post-synaptic membrane of neurons and - as a result - in regulation of synaptic plasticity.
-----------
RAB11A is not associated with any phenotype in OMIM.

This gene is included in the DD panel of G2P, associated with epilepsy and intellectual disability (disease confidence: probable).

It is also included in gene panels for ID offered by some diagnostic laboratories.
-----------
As a result, it can be considered for inclusion in this panel as amber or possibly green (3 unrelated individuals with ID, 1 further with DD at a young age).
Sources: Literature
Intellectual disability v2.588 SLC35A3 Konstantinos Varvagiannis gene: SLC35A3 was added
gene: SLC35A3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: SLC35A3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: SLC35A3 were set to 24031089; 28328131; 28777481; 16344554
Phenotypes for gene: SLC35A3 were set to ?Arthrogryposis, mental retardation, and seizures (MIM 615553)
Penetrance for gene: SLC35A3 were set to Complete
Review for gene: SLC35A3 was set to GREEN
gene: SLC35A3 was marked as current diagnostic
Added comment: Biallelic pathogenic variants in SLC35A3 cause Arthrogryposis, mental retardation, and seizures (MIM 615553).
--------
Edvardson et al. (PMID: 24031089) report on 8 affected individuals from 3 nuclear Ashkenazi Jewish families. All harbored a nonsense [NM_012243.1:c.514C>T / p.(Gln172*)] as well as a missense variant [NM_012243.1:c.886A>G / p.(Ser296Gly)] in the compound heterozygous state. Most of the parents, who were heterozygous for the one or the other variant, were distantly related.

Common features included ASD (8/8), arthrogryposis (8/8), seizures (6/8) and intellectual disability (6/8 - variable degrees).

Upon cDNA studies, the (predicted) missense variant led to skipping of exon 8 and there was no normal size transcript (as would be expected for a variant of this type). Introduction of a premature stop codon due to this variant as well instability of the mRNA from the Gln172Ter allele was presumed to lead to absence of functional SLC35A3 protein.

Testing of 2045 Ashkenazi Jewish individuals revealed a carrier frequency of 1/205 for the missense variant in this community (with no occurrence of the nonsense variant).

SLC35A3 is a nucleotide sugar transporter that transports (uniquely) UDP-N-acetylglucosamine (UDP-GlcNAc) from the cytoplasm where it is synthesized to its site of use in the Golgi. Proper function of such transporters is essential for biosynthesis of glycoproteins, glycolipids and proteoglycans.

Although the transport of UDP-GlcNAc is mediated also by other less specific transporters, members of the SLC35 family, reduced transport was shown in patient fibroblasts compared to controls. In addition an abnormal N-glycan profile was shown in patient fibroblasts (but was not the case in serum).

Biallelic SLC35A3 mutations in cattle were previously shown to cause a Complex Vertebral Malformation (CVM) syndrome characterized by abnormal growth, vertebral and heart malformations as well as arthrogryposis (Thomsen et al. - PMID: 16344554). Arthrogryposis as well as some skeletal features observed in patients were similar to those of the animal model.
--------
Marini et al. (PMID: 28328131) report on 2 sibs compound heterozygous for a missense and a frameshift variant [NM_012243.2:c.73C>T or p.(Arg25Cys) and c.899_900delTTinsA or p.(Leu300Glnfs*6)]. Hypotonia, DD with ID, early-onset seizures and arthrogryposis were features in both. Severe scoliosis was also noted in the younger sib.
---------
Edmondson et al. (PMID: 28777481) report on a neonate (follow-up till the 21st day of life) with extensive vertebral anomalies (butterfly vertebrae, hemibertebrae, sagittal clefts, scoliosis), heart defects (PFO, PDA) and arthrogryposis. Presence of hypotonia or other neurologic features (eg. seizures) is not commented on. Conventional caryotype and SNP-array analysis were normal apart from the presence of ROH regions due to parental consanguinity. Exome sequencing revealed only a homozygous missense SNV [c.74G>T or p.(Arg25Leu) - NP_036375.1] which was supported by an abnormal N-glycan profile. As proposed for the bovine model (PMID: 16344554) and discussed in this article, similarity of the skeletal/congenital heart defects with those observed in Alagille syndrome might be due to some of the Notch functions being dependent upon N-acetylglucosamine modification.
---------
In ClinVar :

There is a further submission of p.Ser296Gly as pathogenic (SCV000699337.1 - 2016) apart from the submission by OMIM (SCV000108589.2 - 2013). The associated condition is Arthrogryposis, mental retardation, and seizures.

A frameshift variant [NM_012243.2(SLC35A3):c.680dup (p.Asp227Glufs)- SCV000826704.1 - April 2018] as well as an intragenic deletion [NC_000001.10:g.(?_100472570)_(100477109_?)del (GRCh37) - SCV000837123.1 - June 2018] have both been submitted as pathogenic, associated with Arthrogryposis, mental retardation, and seizures. (Note: due to the different submission dates, one can presume that these variants were found in different individuals).
---------
SLC35A3 is not associated with any phenotype in OMIM.
It is included in gene panels for ID offered by some diagnostic laboratories.
---------
As a result, this gene can be considered for inclusion in the ID panel probably as green (or amber)
[Consider upgrade of this gene to green in other panels (eg. CDGs, arthrogryposis, IEMs) and/or inclusion in other possibly relevant panels.]
Sources: Literature
Intellectual disability v2.588 HEPACAM Konstantinos Varvagiannis reviewed gene: HEPACAM: Rating: GREEN; Mode of pathogenicity: None; Publications: 21419380; Phenotypes: ; Mode of inheritance: BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal; Current diagnostic: yes
Intellectual disability v2.587 DONSON Konstantinos Varvagiannis gene: DONSON was added
gene: DONSON was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: DONSON was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DONSON were set to 28630177; 28191891
Phenotypes for gene: DONSON were set to Microcephaly, short stature, and limb abnormalities (MIM 617604); Microcephaly-micromelia syndrome (MIM 251230)
Penetrance for gene: DONSON were set to unknown
Review for gene: DONSON was set to AMBER
gene: DONSON was marked as current diagnostic
Added comment: It seems that the phenotypes related to DONSON biallelic mutations (PMIDs: 28630177, 28191891) can be extremely variable with pre-/perinatally lethal cases to variable degrees of microcephaly (-2.4 to -10.7 SD), short stature (several individuals with height within the normal percentiles), limb anomalies (many without such anomalies, or at least significant). Similarly, DD and more specifically ID has been observed in some patients (when it happened to be the case it was most commonly mild).

This is most evident in the supplementary information of PMID: 28191891, specifically the following table:
https://media.nature.com/original/nature-assets/ng/journal/v49/n4/extref/ng.3790-S2.xlsx

Clinical synopses for the DONSON-related phenotypes:
https://www.omim.org/clinicalSynopsis/table?mimNumber=617604,251230

The gene is not associated with any phenotype in G2P.

DONSON is included in gene panels for ID offered by diagnostic laboratories (incl. Radboudumc).

As a result, gene could be considered for inclusion in the ID panel probably as amber (or green) following further review and/or if the phenotype is though to be relevant.

[Consider also inclusion in other relevant panels apart from microcephaly, eg. limb disorders etc.]
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.584 ZBTB11 Konstantinos Varvagiannis gene: ZBTB11 was added
gene: ZBTB11 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: ZBTB11 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: ZBTB11 were set to 29893856; 28382966
Phenotypes for gene: ZBTB11 were set to Intellectual disability
Penetrance for gene: ZBTB11 were set to Complete
Review for gene: ZBTB11 was set to AMBER
Added comment: Fattahi et al. (PMID: 29893856) report on 9 individuals from 2 broader consanguineous pedigrees with biallelic ZBTB11 mutations.

Features in the first family (from Iran) consisted of moderate ID, microcephaly, ataxic gait, and spasticity with MRI findings of cerebellar atrophy and ventriculomegaly.

Individuals from the second family (from Pakistan) presented with moderate ID and variable features.

Homozygosity for missense ZBTB11 variants, private to each family was shown (NM_014415.3:c.2185C>T / p.H729Y and c.2640T>G / p.H880Q for the first and second family respectively).

As the authors note, ZBTB11 is predicted to be a zinc finger transcriptional regulator and one of the hypotheses emitted suggests possible disruption of DNA binding.

Functional studies performed demonstrated that the mutant proteins were excluded from the nucleolus where the (wt) protein localizes.

Previous zebrafish models (PMID: 28382966) suggested CNS degeneration among other phenotypes in Zbtb11 mutants.

Knockdown of the drosophila ZBTB11-ortholog (CkIIα-i1) resulted in recognizable shrinking of the mushroom body with significant reduction in the number of neurons compared to controls.

Other Zinc Finger and BTB Domain-Containing proteins cause disorders with ID as a prominent feature (eg. ZBTB16, ZBTB20, etc.).

ZBTB11 is not associated with any phenotype in OMIM nor in G2P.

As a result, this gene can be considered for inclusion in this panel probably as amber (2 pedigrees only) or green (given the supportive functional studies).
Sources: Literature
Intellectual disability v2.584 AIMP2 Konstantinos Varvagiannis gene: AIMP2 was added
gene: AIMP2 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: AIMP2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: AIMP2 were set to 29215095
Phenotypes for gene: AIMP2 were set to Leukodystrophy, hypomyelinating, 17 (MIM 618006)
Penetrance for gene: AIMP2 were set to Complete
Review for gene: AIMP2 was set to AMBER
gene: AIMP2 was marked as current diagnostic
Added comment: Biallelic pathogenic variants in AIMP2 cause Leukodystrophy, hypomyelinating, 17 (MIM 618006).

3 individuals from 2 unrelated consanguineous families, of Indian origin have been reported (all in PMID: 29215095).

The phenotype consisted of feeding difficulties, lack of development with intellectual disability and seizures as well as brain MRI abnormalities (cerebral and cerebellar atrophy, hypo-intensities of the basal ganglia on T2w sequences). Severe microcephaly was observed in 2 patients for whom this information was available (birth measurements not specified).

All patients described to date were homozygous for a nonsense variant [NM_006303.3:c.105C>A or p.(Tyr35Ter)] which appears to be a founder mutation in this population.

Quantitative reverse transcription PCR demonstrated reduced mRNA levels in peripheral lymphocytes, but this decrease was not significant compared to controls (the authors presume low level of NMD).

Previous mouse models provide some - but not substantial - support.

The authors note marked similarity with the phenotype associated with AIMP1 (Leukodystrophy, hypomyelinating, 3 - MIM 260600), another auxiliary protein of the macromolecular multienzyme multi-tRNA synthetase complex. AIMP1 is listed in the current panel as green.

AIMP2 is not associated with any phenotype in G2P.

This gene is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc).

As a result, AIMP2 can be considered for inclusion in this panel probably as amber.
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.584 VPS11 Konstantinos Varvagiannis gene: VPS11 was added
gene: VPS11 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: VPS11 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: VPS11 were set to 27120463; 26307567; 27473128
Phenotypes for gene: VPS11 were set to Leukodystrophy, hypomyelinating, 12 (MIM 616683)
Penetrance for gene: VPS11 were set to Complete
Review for gene: VPS11 was set to GREEN
gene: VPS11 was marked as current diagnostic
Added comment: Biallelic mutations in VPS11 cause Leukodystrophy, hypomyelinating, 12 (MIM 616683).

PMIDs: 27120463, 26307567, 27473128 all report on this disorder.

The phenotype consists of global DD, ID, (variable) acquired microcephaly with hypomyelination upon brain MRI. Seizures appear to be a feature in several individuals.

Almost all individuals appear to be of Ashkenazi Jewish descent, homozygous for a founder mutation (NM_021729.5:c.2536T>G or p.Cys846Gly). PMIDs: 27120463 and 26307567 report on 13 individuals from 7 Ashkenazi families.

A second variant (p.Leu387_Gly395del) was however found in the homozygous state in 2 sibs born to consanguineous parents.

Pathogenicity is supported by extensive functional studies in all relevant articles.

VPS11 is not associated with any phenotype in G2P.

The gene is included in gene panels for ID offered by diagnostic laboratories (incl. Radboudumc).

As a result, this gene can be considered for inclusion in this panel as green.

[Please consider inclusion in the lysosomal disorders panel as well as in the undiagnosed metabolic disorders panel].
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.584 LINGO1 Konstantinos Varvagiannis gene: LINGO1 was added
gene: LINGO1 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: LINGO1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: LINGO1 were set to 28837161
Phenotypes for gene: LINGO1 were set to Mental retardation, autosomal recessive 64 (MIM 618103)
Penetrance for gene: LINGO1 were set to Complete
Review for gene: LINGO1 was set to AMBER
gene: LINGO1 was marked as current diagnostic
Added comment: Biallelic pathogenic variants in LINGO1 cause Mental retardation, autosomal recessive 64 (MIM 618103).

Ansar et al. (PMID: 28837161) report on 5 individuals from 2 consanguineous Pakistani families.

Affected individuals from both families presented with similar phenotype consisting of global developmental delay (5/5), intellectual disability (5/5), microcephaly (4/5) as well as abnormal behavior (5/5).

Subjects from both families were homozygous for missense variants (private to each family) affecting proximal residues (290 and 288) of the protein (NM_032808.6:c.869G>A or p.Arg290His and c.863A>G or p.Tyr288Cys).

All variants were absent in an ethnically matched control cohort (201 individuals) as well as the relevant subpopulation in gnomAD.

Functional studies were not performed.

LINGO1 is a transmembrane protein predominantly expressed in the CNS. Previous studies suggest that this protein has an important role in myelination, neuronal survival and CNS repair.

LINGO1 is rather intolerant to both missense and LoF variants (Z-score of 4 and pLI of 0.95). According to the authors these variants may be hypomorphic, which might in turn suggest that monoallelic heterozygous LoF mutations could cause ID (although this remains an assumption).

This gene is not associated with any phenotype in G2P but is included in panels for ID offered by diagnostic laboratories (incl. Radboudumc).

As a result, LINGO1 can be considered for inclusion in this panel probably as amber (2 families, no functional studies).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.584 PAK1 Konstantinos Varvagiannis gene: PAK1 was added
gene: PAK1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PAK1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: PAK1 were set to 30290153
Phenotypes for gene: PAK1 were set to Intellectual developmental disorder with macrocephaly, seizures, and speech delay (MIM 618158)
Penetrance for gene: PAK1 were set to unknown
Mode of pathogenicity for gene: PAK1 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: PAK1 was set to AMBER
Added comment: Heterozygous pathogenic PAK1 variants cause Intellectual developmental disorder with macrocephaly, seizures, and speech delay (MIM 618158).

Harms et al. (PMID: 30290153) report on two unrelated individuals with de novo missense mutations in PAK1. Common features included developmental delay with associated intellectual disability, seizures, ataxic gait. Postnatal-onset microcephaly as well as some facial features were also common to both subjects.

Each patient was found to harbour a (private) de novo missense variant [NM_001128620.1:c.392A>G or p.(Tyr131Cys) - c.1286A>G or p.(Tyr429Cys)]. Expression studies demonstrated similar levels for the mutant and wt transcript and Western blot confirmed similar amounts of protein in patient fibroblasts when compared to controls. Functional studies suggest that gain-of-function is the underlying mechanism for both variants.

PAK1 is not associated with any phenotype in G2P.

As a result, this gene can be considered for inclusion in this panel as amber.
Sources: Literature
Intellectual disability v2.584 PTRHD1 Konstantinos Varvagiannis gene: PTRHD1 was added
gene: PTRHD1 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: PTRHD1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PTRHD1 were set to 30398675; 27134041; 29143421; 27753167
Phenotypes for gene: PTRHD1 were set to Parkinsonism; Intellectual disability
Penetrance for gene: PTRHD1 were set to Complete
Review for gene: PTRHD1 was set to AMBER
gene: PTRHD1 was marked as current diagnostic
Added comment: 7 individuals with biallelic PTRHD1 mutations from 3 pedigrees have been reported. The phenotype in all consisted of early-onset Parkinsonism with intellectual disability (overview in Table 1 - PMID: 30398675).

Jaberi et al. (PMID: 27134041) first reported on 2 sibs born to consanguineous Iranian parents. Both presented with parkinsonism with ID. After homozygosity mapping and exome sequencing, one variant in PTRHD1 (NM_001013663.1:c.155G>A or p.Cys52Tyr) as well as another variant in ADORA1 were the only candidates for the patients phenotype. At the time, the authors favored ADORA1 as the causative gene for their patients' phenotype but could not exclude pathogenicity of PTRHD1.

Khodadadi et al. (PMID: 27753167) published on 2 additional sibs from Iran with a similar phenotype. These individuals - born to consanguineous parents - were homozygous for a further PTRHD1 missense variant (p.His53Tyr) which is proximal to the variant reported by Jaberi et al.

This led the authors of the first publication to acknowledge that PTRHD1 was probably responsible for their patients' phenotype (PMID: 29143421). [A recent study of exome sequencing data of a Parkinson disease 1214-patient cohort failed to find any case explained by biallelic ADORA1 mutations - PMID: 27987235].

The variants reported in these 2 publications are classified as VUS in OMIM (last update : 02/23/2017).

Kuipers et al. (PMID: 30398675) report on 3 additional individuals of African origin with identical phenotype. These individuals, whose parents originated from an isolated african community, were homozygous for a frameshift PTRHD1 deletion (c.169_196del or p.Ala57Argfs*26). This variant is rare in gnomAD (MAF of 0.018% overall or 0.15% in the African subpopulation). Alternative causes of PD / parkinsonism were previously excluded.

The phenotype of all reported individuals is summarized in Table 1 of this article.

PTRHD1 is not assocated with any phenotype in OMIM nor in G2P.

This gene is included in the gene panel for ID, offered by Radboudumc.

Therefore, this gene can be considered for inclusion in this panel as amber or green.

[Please consider inclusion of this gene in the Parkinson Disease and Complex Parkinsonism gene panel].
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.583 CCDC47 Konstantinos Varvagiannis gene: CCDC47 was added
gene: CCDC47 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CCDC47 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CCDC47 were set to 30401460
Phenotypes for gene: CCDC47 were set to Woolly hair; Abnormality of the liver; Global developmental delay; Intellectual disability
Penetrance for gene: CCDC47 were set to Complete
Review for gene: CCDC47 was set to GREEN
Added comment: Morimoto el al. (PMID: 30401460) report on 4 individuals from 4 unrelated families with biallelic LoF variants in CCDC47. The phenotype consisted of abnormal (woolly) hair, liver dysfunction, common facial features as well as DD/ID.

The patients were found to harbor the variants in compound heterozygous or more commonly in homozygous state (due to consanguinity and/or common ancestry). 4 loss-of-function variants are reported in total (using NM_020198.2 as a reference):
- c.811C>T or p.(Arg271*) [consanguineous family of Turkish origin]
- c.1145delT or p.(Leu382Argfs*2) [probably a founder mutation in Amish]
- c.1165delT or p.(Ser389Leufs*25)
- c.1189C>T or p.(Arg397*)

Decreased mRNA levels in fibroblasts/lymphoblastoid cells were shown as well as absence of the protein upon Western blot using antibodies recognizing the N and C terminus (thus suggesting NMD).

Localization of CCDC47 in the ER was demonstrated with perturbed Ca+2 homeostasis and signalling in the ER.

Ccdc47-knockout mice present features similar to the human phenotypes eg. growth, neurological as well as heart anomalies. In mice embryonic/neonatal lethality was noted in some cases which might be associated with recurrent miscarriages reported in 3 patient families.

CCDC47 is not associated with any phenotype in G2P or OMIM.

As a result, this gene can be considered for inclusion in this panel as green (or amber).
Sources: Literature
Intellectual disability v2.580 DHDDS Rebecca Foulger gene: DHDDS was added
gene: DHDDS was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: DHDDS was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: DHDDS were set to 29100083; 27343064
Phenotypes for gene: DHDDS were set to Developmental delay and seizures with or without movement abnormalities, 617836
Review for gene: DHDDS was set to GREEN
Added comment: In 5 unrelated patients with developmental delay and seizures with or without movement abnormalities (DEDSM; 617836), Hamdan et al. (2017, PMID:29100083) identified 2 different de novo heterozygous missense mutations in the DHDDS gene (R37H and R211Q). The ID phenotype of patients covers severe/moderate-to-severe ID and global developmental delay.
Sources: Literature
Intellectual disability v2.579 TMEM94 Konstantinos Varvagiannis gene: TMEM94 was added
gene: TMEM94 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: TMEM94 was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: TMEM94 were set to Global developmental delay; Intellectual disability; Abnormal heart morphology; Abnormality of head or neck
Penetrance for gene: TMEM94 were set to Complete
Review for gene: TMEM94 was set to AMBER
Added comment: Stephen et al. (https://doi.org/10.1016/j.ajhg.2018.11.001) report on 10 individuals from 6 unrelated families with bi-allelic truncating TMEM94 variants. The common phenotype consisted of global DD/ID, similar facial features as well as the presence of congenital heart defects (in all but one).

Speech as well as motor delay and learning difficulties were universal features. ID is mentioned in the abstract, explicitly specified for one individual and implied for some of the rest.

Overall 6 different LoF variants are reported. Reduced expression was demonstrated while gene expression microarray and RNA sequencing expression studies demonstrated dysregulation of several essential genes. Using a CRISPR/Cas9 mouse model loss of Tmem94 was shown to be embryonically lethal with craniofacial, cardiac anomalies as well as abnormal neuronal migration pattern observed in homozygous mutant mice embryos.

TMEM94 is not associated with any phenotype in G2P nor in OMIM.

As a result this gene can be considered for inclusion in this panel probably as amber (or green).
Sources: Literature
Intellectual disability v2.579 PUS3 Konstantinos Varvagiannis gene: PUS3 was added
gene: PUS3 was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen
Mode of inheritance for gene: PUS3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PUS3 were set to 27055666; 30308082
Phenotypes for gene: PUS3 were set to Global developmental delay; Intellectual disability; Microcephaly
Penetrance for gene: PUS3 were set to Complete
Review for gene: PUS3 was set to AMBER
gene: PUS3 was marked as current diagnostic
Added comment: PUS3 (Pseudouridylate synthase 3) is proposed as a gene related to ID in a recent publication on PUS7.

Biallelic mutations in this gene are associated in OMIM with ?Mental retardation, autosomal recessive 55 (MIM 617051).

PMID: 27055666 reports on 3 sisters from a consanguineous Saudi Arabian family with failure to thrive, DD/ID, microcephaly and some common (coarse) facial features. These individuals were homozygous for a stopgain mutation in the last exon of the gene. Pseudouridylation appeared to be defective (as has also been the case with other genes related to ID, eg. PUS7).

PMID: 30308082 describes 1 individual born to consanguineous Palestinian parents, homozygous for a further LoF variant. Despite the localisation of this variant (again in the last exon of the gene) qPCR analyses were suggestive of degradation of the abnormal transcript possibly by NMD. The phenotype consisted of DD/ID and microcephaly.

In a further publication (http://dx.doi.org/10.7124/bc.0008D6) Gulkovskyi et al. report on 2 siblings with ID, born to non-consanguineous Ukranian parents. Pathogenicity of the variant is disputed. [NM_031307.4:c.212A>G or p.(Tyr71Cys) is found in an apparent homozygous state in the sibs but was only found in their father. De novo occurence in the maternal allele is proposed although the possibility of microdeletion missed by aCGH or other plausible mechanisms are not considered. This variant has maximum pathogenicity scores in silico (not discussed) and has an allele frequency of 0.00006717 in gnomAD. The authors did not perform studies of pseudouridylation but examined for the presence of hypoproteinemia, observed in some disorders affecting this process).

PUS3 is not associated with any phenotype in G2P but is associated with disease in OMIM.

The gene is included in gene panels for ID offered by various diagnostic laboratories (including Radboudumc). PUS1 is included in the current panel as green and PUS7 has been suggested for inclusion.

As a result, these gene can be considered for inclusion as amber (2 families) or green (given the supportive functional studies and/or the proposed role for the gene).
Sources: Literature, Radboud University Medical Center, Nijmegen
Intellectual disability v2.579 MAST1 Konstantinos Varvagiannis gene: MAST1 was added
gene: MAST1 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: MAST1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: MAST1 were set to 30449657; 28135719; 25666757; 27479843
Phenotypes for gene: MAST1 were set to Global developmental delay, Intellectual disability, Abnormality of the corpus callosum, Cerebellar hypoplasia, Abnormality of the cerebral cortex, Seizures; Global developmental delay, Intellectual disability, Microcephaly, Autism, Seizures
Penetrance for gene: MAST1 were set to unknown
Review for gene: MAST1 was set to GREEN
gene: MAST1 was marked as current diagnostic
Added comment: PMID: 30449657 reports on 6 unrelated individuals with de novo mutations in MAST1. All these 6 individuals were investigated for a strikingly similar phenotype of enlarged corpus callosum (CC), cerebellar hypoplasia, cortical malformation with associated DD/ID. Seizures were a feature in 2/6 (one further had EEG anomalies without clinical seizures).

Three of them harbored an in-frame deletion of 1 amino-acid (3 different indels reported - all in a specific domain) while 3 others had a missense variant (NM_014975.2:c.1549G>A or p.Gly517Ser).

Mast1 has embryonic expression in murine models with postnatal decrease. Similarly qPCR of human fetal brain cDNA demonstrated expression at 13 and 22 gestational weeks. A murine model for L278del recapitulated the brain (incl. CC) and cerebellar phenotype while Mast1 knockout mice do not present similar morphological defects. While Western blot in murine brain lysates demonstrated absence of Mast1 in knockout and reduction in the L278del, Mast1 transcript levels for L278del were similar to wildtype. Other Mast proteins (Mast1 & Mast2) were significantly reduced upon western blot while this was not reflected in their mRNA levels, suggesting a dominant-negative effect, at least for the L278del.

4 additional individuals with somewhat different phenotype consisting DD/ID and microcephaly/autism are described in the supplement. All 4 had de novo missense variants but did not display the CC-cerebral and cerebellar anomalies. Four different (additional to Gly517Ser) missense SNVs were observed.

Several additional individuals exist in the denovo-db (among others DDD participant DDD4K.02310 published in 28135719, 25666757 - McMichael et al. commented in the article, 27479843, etc.). [http://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=Mast1]

Epilepsy was a feature in 4/10 individuals (with an additional one with EEG anomalies without clinical seizures). One further individual from PMID:23934111 (in denovo-db) had seizures.

As the authors comment (and as evident from the 6+4 reported patients) the related neurodevelopmental phenotype may be more complex.

MAST1 is not related to any phenotype in G2P, nor in OMIM.

The gene is included in gene panels for ID offered by different diagnostic laboratories.

As a result, this gene can be considered for inclusion in this panel as green.
Sources: Literature
Intellectual disability v2.579 PUS7 Konstantinos Varvagiannis gene: PUS7 was added
gene: PUS7 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PUS7 was set to BIALLELIC, autosomal or pseudoautosomal
Phenotypes for gene: PUS7 were set to Intellectual disability; Microcephaly; Short stature; Behavioral abnormality
Penetrance for gene: PUS7 were set to Complete
Review for gene: PUS7 was set to GREEN
gene: PUS7 was marked as current diagnostic
Added comment: de Brouwer et al. (https://doi.org/10.1016/j.ajhg.2018.10.026) report on 6 individuals from 3 unrelated families homozygous for truncating variants in PUS7.

The common phenotype consisted of ID with speech delay, microcephaly, short stature as well as aggressive behavior.

One frameshift, one nonsense and one intragenic deletion affecting the penultimate exon of PUS7 were private respectively to each family. qPCR demonstrated reduction of mRNA levels for the two first variants, with absence of the normally sized protein upon Western blot for the first one.

The deletion, not identified due to its small size by aCGH, was found in the exome analysis and confirmed by MAQ. RT-PCR demonstrated the absence of the respective exon in mRNA. The deletion resulted in introduction of a stop codon in the last exon and mRNA expression levels were shown to be normal. Western blot demonstrated absence of a normally sized protein. (As a result, truncating mutations in the last exon may also be deleterious).

Functional studies demonstrated defective tRNA and mRNA pseudouridylation. Drosophila knockouts recapitulated the behavioral phenotype.

Biallelic mutations in PUS1 and PUS3 have been reported in individuals with intellectual disability (as well as some other features noted in PUS7-related disorder).

PUS7 is included in the gene panel for ID offered by Radboud UMC (among the principal authors of the study).

Therefore this gene can be considered for inclusion in this panel as green (rather than amber).
Sources: Literature
Intellectual disability v2.576 PPP1R21 Konstantinos Varvagiannis gene: PPP1R21 was added
gene: PPP1R21 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: PPP1R21 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PPP1R21 were set to 29808498; 28940097
Phenotypes for gene: PPP1R21 were set to Generalized hypotonia; Feeding difficulties; Profound global developmental delay; Abnormality of the face; Abnormality of vision; Abnormal heart morphology; Abnormality of the respiratory system; Hepatosplenomegaly
Penetrance for gene: PPP1R21 were set to Complete
Review for gene: PPP1R21 was set to GREEN
Added comment: Biallelic pathogenic variants in PPP1R21 have been reported so far in 9 individuals from 7 unrelated families. All (7 different) variants reported to date are truncating.

PMID: 29808498 is the first detailed clinical description on the related phenotype. 3 individuals from 3 families are reported. One of these individuals was previously included in a larger patient cohort (in PMID: 28940097).

In a subsequent further publication, Rehman et al. (https://doi.org/10.1002/humu.23694) describe 6 additional patients from 4 unrelated consanguineous families. Again, these individuals were homozygous for truncating mutations. The authors summarize the findings in their patients as well as the previously reported ones.

Common features included feeding difficulties, hypotonia with severe global DD and mildly coarsened facial features (all were observed in 9/9), visual anomalies (8/9), respiratory problems (7/9), cardiac anomalies (4/9) and hepato-/splenomegaly (3/7). Brain MRI anomalies were observed in the majority. DD was severe in all and ID (which is not explicitly mentioned) was evident from the clinical description of several individuals (eg. in PMID: 29808498).

In total 7 loss-of-function variants have been reported. The authors in the first article, underscore the possibility of less severe phenotypes associated to biallelic missense variants (although none has been reported so far).

Functional studies have shown great reduction (but not complete absence) of PPP1R21 mRNA levels in patient fibroblasts compared to controls. A role of PPP1R21 in the endosomal-lysosomal function is demonstrated in line with the presence of myelin figures in patient fibroblasts as well as some phenotypic similarities to neurometabolic/lysosomal storage disorders.

Most variants reported in the most recent publication except one (NM_001135629.2:c.1607dupT) seem to affect all 3 PPP1R21 isoforms (which also seems to be the case for previously published variants). c.1607dupT appears to be the single truncating variant affecting 2 (of 3) isoforms. This variant was however shown to have severely reduced expression in fibroblasts upon qPCR, absent protein staining, and increase in myelin figures.

The protein is expressed in embryonic mouse cortex.

Overall, this gene can be considered for inclusion in this panel as green (or amber).
Sources: Literature
Intellectual disability v2.576 GRIN2D Konstantinos Varvagiannis gene: GRIN2D was added
gene: GRIN2D was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: GRIN2D was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: GRIN2D were set to 27616483; 30280376
Phenotypes for gene: GRIN2D were set to Epileptic encephalopathy, early infantile, 46 (MIM 617162)
Penetrance for gene: GRIN2D were set to unknown
Review for gene: GRIN2D was set to GREEN
gene: GRIN2D was marked as current diagnostic
Added comment: Heterozygous pathogenic variants in GRIN2D cause Epileptic encephalopathy, early infantile, 46 (MIM 617162).

As commented in the previous review, PMID: 27616483 is the first report on 2 unrelated individuals with severe epileptic encephalopathy (onset of seizures at the age of 2 and 4 months). Severe DD with ID was noted in both.

Each of these individuals were heterozygous for the same missense variant (NM_000836.2:c.1999G>A p.Val667Ile) as a de novo event. Functional studies demonstrated a gain-of-function effect.

GRIN2D encodes for an NMDA receptor subunit, and the gain-of-function effect shown for this variant suggests that NMDAR antagonists might be useful as adjuvant therapy (some improvement noted in both individuals).

[The mode of pathogenicity selected here may be modified as more evidence on further variants becomes available. GRIN2D appears to be intolerant also to LoF mutations with a pLI of 1. Both LoF and GoF mutations have been described for genes encoding other NMDAR subunits].

PMID: 30280376 reports on 3 additional unrelated patients with developmental and epileptic encephalopathy and pathogenic or likely pathogenic missense variants in GRIN2D.

Three additional missense variants are reported (Met681Ile, Ser694Arg, Asp449Asn). Parental studies were possible only for the patient with Met681Ile (de novo) as well as for the individual with Ser694Arg (only one parent available though).

Significant developmental delay was evident in all prior to the onset of seizures (1m/2y/3y respectively) and subsequent developmental stagnation/regression with ID.

The phenotype of these 3 individuals as well as of the 2 previously described is summarized in table 1 of the latter article.

GRIN2D is a probable DD gene in G2P and is included in gene panels for ID offered by diagnostic laboratories.

Several other genes for NMDA receptor subunits (eg. GRIN2A, GRIN2B, GRIN1) and relevant/similar phenotypes are included in this panel as green.

As a result, this gene can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature
Intellectual disability v2.574 MCM3AP Konstantinos Varvagiannis gene: MCM3AP was added
gene: MCM3AP was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: MCM3AP was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: MCM3AP were set to 24123876; 28633435; 28969388; 29982295
Phenotypes for gene: MCM3AP were set to Peripheral neuropathy, autosomal recessive, with or without impaired intellectual development (MIM 618124)
Penetrance for gene: MCM3AP were set to Complete
Review for gene: MCM3AP was set to AMBER
gene: MCM3AP was marked as current diagnostic
Added comment: Biallelic mutations in MCM3AP cause Peripheral neuropathy, autosomal recessive, with or without impaired intellectual development (MIM 618124).

All relevant publications [PMIDs: 24123876, 28633435 (first detailed description of a series of patients with functional studies), 28969388, 29982295) are summarized in OMIM.

Overall more than 18 patients from 10 families and at least 8 pathogenic variants have been reported.

Apart from abnormal motor development which may be associated with the sensorimotor neuropathy, intellectual disability was a feature in several individuals (although not a universal one).

Some patients were initially evaluated for their ID while investigations for the neuropathy may be conducted late (as evident in PMID: 28633435).

MCM3AP is included in gene panels for intellectual disability offered by diagnostic laboratories.

As a result, this gene can be considered for inclusion in the ID panel as amber or green (depending on its relevance to the specific panel).
Sources: Literature
Intellectual disability v2.562 CAD Konstantinos Varvagiannis gene: CAD was added
gene: CAD was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: CAD was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: CAD were set to 25678555; 28007989
Phenotypes for gene: CAD were set to Epileptic encephalopathy, early infantile, 50 - MIM 616457
Penetrance for gene: CAD were set to Complete
Review for gene: CAD was set to AMBER
gene: CAD was marked as current diagnostic
Added comment: Biallelic pathogenic variants in CAD cause Epileptic encephalopathy, early infantile, 50 - MIM 616457.

Overall 5 individuals from 4 unrelated families have been reported in detail in PMIDs 25678555 and 28007989 (table 1 in this article provides a summary).

The phenotype consisted of developmental delay which preceded the onset of seizures (6 months to 2 years) and hematologic anomalies (anemia and anisopoikilocytosis). The patients presented developmental stagnation/regression, which in most cases occurred several months following the seizure onset.

CAD is a tri-functional protein catalyzing the first 3 steps of the de novo pyrimidine biosynthesis.

In total, 5 variants have been reported (2 missense, 1 nonsense and 2 splice-site SNVs) with functional studies (cDNA, metabolites) supporting pathogenicity and disruption of this pathway.

CAD mutations have previously been studied in other model organisms.

Mutations in enzymes catalyzing downstream steps of the same pathway are associated with other syndromes.

The disorder appears to be amenable to dietary intervention (uridine supplementation).

CAD is included in gene panels for intellectual disability offered by different diagnostic laboratories.

As a result, this gene can be considered for inclusion in the ID panel as amber or green.
Sources: Literature
Intellectual disability v2.562 RALA Konstantinos Varvagiannis gene: RALA was added
gene: RALA was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: RALA was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Phenotypes for gene: RALA were set to Global developmental delay; Intellectual disability; Seizures; Abnormality of nervous system morphology
Penetrance for gene: RALA were set to unknown
Mode of pathogenicity for gene: RALA was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: RALA was set to GREEN
Added comment: Hiatt et al. (doi.org/10.1371/journal.pgen.1007671) report on 11 individuals (incl. a pair of monozygotic twins) from 10 unrelated families, most (10/11) with de novo mutations in RALA.

DD/ID was a prominent feature (the authors note that ID was specifically noted in 8 but could not be excluded in 3 further individuals who appear to be very young in the table). Structural brain anomalies (9/11), seizures (6/11) and common facial features were also noted.

RALA belongs to the RAS superfamily of small GTPases.

5 different de novo missense variants and 1 in-frame deletion, all within a GTP/GDP binding region of RALA (although appart in the protein primary structure) were observed. 7 occurrences of missense variants concerned Val25 and Lys128 (V25M, V25L, K128R), one Asp130 (D130G) and a further one Ser157 (S157A). The in-frame deletion concerned Ala158.

Missense variants in corresponding positions of RAS proteins (HRAS/KRAS/NRAS) have been reported in RASopathies, while the authors observed some phenotypic overlap with the latter group of disorders (DD/ID, growth delay, macrocephaly, high forehead and position of ears).

Functional studies demonstrated reduction in GTPase activity (for all variants) and altered RALA effector binding (for most reduction - in the case of S157A, increase).

Several lines of evidence are provided to show that alteration of the GTP/GTP-binding rather than a dosage effect is considered the likely mechanism. RALA is depleted in missense mutations in its GTP/GDP binding domain.

For these reasons and others (segregation studies not possible, variant observed 2x in Bravo database, phenotypic differences compared to the rest of the cohort, ROH suggesting parental consanguinity in the specific individual) the single nonsense variant (R176X) reported in the study is considered a VUS.

As a result, this gene can be considered for inclusion in this panel as green.
Sources: Literature
Intellectual disability v2.561 MAB21L1 Konstantinos Varvagiannis gene: MAB21L1 was added
gene: MAB21L1 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: MAB21L1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: MAB21L1 were set to 27103078
Phenotypes for gene: MAB21L1 were set to Global developmental delay; Intellectual disability; Cerebellar hypoplasia; Abnormality of the eye; Abnormality of the genital system
Penetrance for gene: MAB21L1 were set to Complete
Review for gene: MAB21L1 was set to GREEN
gene: MAB21L1 was marked as current diagnostic
Added comment: Bruel et al. (PMID: 27103078) report on a boy, born to consanguineous Algerian parents, homozygous for a frameshift MAB21L1 variant.

Rad et al. (http://dx.doi.org/10.1136/jmedgenet-2018-105623) describe 10 additional individuals from 5 unrelated consanguineous families (from Iran, Lebanon and Turkey). These subjects were homozygous for truncating variants appart from a patient with a missense one [NM_005584.4:c.698A>C or p.(Gln233Pro)].

All 11 individuals presented with a common phenotype consisting of DD/ID (in 9/11 for whom this information was available), cerebellar, ocular and genital anomalies as well as similar facial features.

In total 6 different variants (5 truncating and 1 missense SNV) have been reported. There are no functional studies performed appart from in silico visualisation for the missense variant and protein interaction network analysis for MAB21L1. Previous studies in Mab21l1 knockout mice suggest ocular as well as preputial gland anomalies.

ID appears to be a feature for biallelic mutations in MAB21L2, another member of the male abnormal 21 (MAB21)-like proteins (gene rated green in this panel - associated phenotype : Microphthalmia/coloboma and skeletal dysplasia syndrome, MIM 615877).

MAB21L1 is included in gene panels for intellectual disability offered by some diagnostic laboratoires.

As a result, this gene can be considered for inclusion in this panel as green (or amber)
Sources: Literature, Expert Review
Intellectual disability v2.558 FBXL3 Konstantinos Varvagiannis gene: FBXL3 was added
gene: FBXL3 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: FBXL3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: FBXL3 were set to 30481285
Phenotypes for gene: FBXL3 were set to Intellectual disability; Short stature
Penetrance for gene: FBXL3 were set to Complete
Review for gene: FBXL3 was set to GREEN
Added comment: Ansar et al. (PMID: 30481285) report on 8 individuals from 3 consanguineous families, all homozygous for FBXL3 variants.

The phenotype consisted of mild to severe intellectual disability (8/8), short stature (8/8) with a few common facial features.

In the first family - from Pakistan - all affected individuals were homozygous for a frameshift variant. The 2 sibs from the second family (from Lebanon) were homozygous for a nonsense variant. A further patient, born to distantly related parents from Italy, was found to harbor a missense variant [NM_012158.2:c.1072T>C or p.(Cys358Arg)] in the homozygous state.

FBXL3 is part of an ubiquitin ligase complex that binds the central clock protein cryptochromes (CRY1/2) mediating their degradation. Cys358Arg concerns the same codon as a similar - previously studied - variant (Cys358Ser) reported to affect the mouse circadian rhythm. Disturbance of circadian rhythm was observed in the patient with the Cys358Arg variant.

As previously demonstrated for mutations of the same codon and in line with a pathogenic role for this variant, in silico studies predict impaired interaction of FBXL3 with CRY2. It is proposed that the nonsense and frameshift variants lead to a similar effect due to severe truncation of the protein (upstream of leucine-rich domains important for this interaction).

The authors note that other F-box proteins are implicated in intellectual disability (as in the case of FBXO11 and FBXL4, both rated green in this panel).

As a result, FBXL3 can be considered for inclusion in this panel as green (or amber).
Sources: Literature, Expert Review
Intellectual disability v2.556 DDX59 Konstantinos Varvagiannis gene: DDX59 was added
gene: DDX59 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: DDX59 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DDX59 were set to 23972372; 28711741; 29127725
Phenotypes for gene: DDX59 were set to Orofaciodigital syndrome V, 174300
Penetrance for gene: DDX59 were set to Complete
Review for gene: DDX59 was set to GREEN
Added comment: Biallelic mutations in DDX59 cause Orofaciodigital syndrome V, 174300.

PMID: 23972372 reports on 6 individuals from 2 consanguineous Arab families. All 6 presented with palatal anomalies (cleft palate or bifid uvula), lobulated tongue, facial anomalies (frontal bossing and hypertelorism) as well as intellectual disability.

Individuals from the first family were homozygous for the Val367Gly (NM_001031725.4:c.1100T>G) variant while those from the second were homozygous for Gly534Arg (NM_001031725.4:c.1600G>A), both predicted to be pathogenic in silico. Immunoblot demonstrated reduced levels of the Val367Gly variant in patient fibroblasts (the other variant was probably not tested). Ddx59 was shown to be expressed in lips, palatal shelves and developing limb buds of mouse embryos.

PMID: 28711741 describes 3 further patients (from two consanguineous Pakistani families), presenting the cardinal features of orofaciodigital syndrome (though polydactyly was only reported in one of the three). Developmental delay was reported in all (in the first family one of the sibs had more severe delay with no speech at the age of 7 years, in the patient from the other family speech was limited to 2 words at school age). Affected individuals from both families were found to harbor a SNV leading to loss of a stop codon, thus extending the reading frame by 21 codons.

PMID: 29127725 reports on two sibs with a diagnosis of orofaciodigital syndrome born to non-consanguineous parents. ID was a feature in both. These individuals were homozygous for a frameshift variant. Reverse transcription PCR/semiquantitative PCR demonstrated reduction of the mutant transcript compared to the levels in wt controls (suggestive of incomplete NMD). Functional studies showed possible perturbation of the Sonic Hedgehog pathway. DDX59 expression in CNS from control post-mortem human brains was confirmed to be high (based on data generated in a previous study). Studies in Drosophila suggest reduced lifespan and neuronal defects secondary to mutations in mahe (the Drosophila homolog of DDX59).

As a result this gene can be considered for inclusion in the ID panel as green.
Sources: Literature, Expert Review
Intellectual disability v2.556 DPH1 Konstantinos Varvagiannis gene: DPH1 was added
gene: DPH1 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: DPH1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: DPH1 were set to 25558065; 26220823; 29362492; 29410513
Phenotypes for gene: DPH1 were set to Developmental delay with short stature, dysmorphic features, and sparse hair, 616901
Penetrance for gene: DPH1 were set to Complete
Review for gene: DPH1 was set to GREEN
gene: DPH1 was marked as current diagnostic
Added comment: Biallelic mutations in DPH1 cause Developmental delay with short stature, dysmorphic features, and sparse hair, MIM 616901.

Overall 11 patients from 6 different families have probably been reported in detail. DD/ID is a universal feature.

In PMID 25558065, Alazami et al. identified 1 patient from the same consanguineous Saudi Arabian family (of 8 total similarly affected individuals) homozygous for the Leu234Pro (NM_001383.3:c.701T>C) variant. This individual was part of a large cohort of patients with neurogenetic disorders from consanguineous families. The phenotype is not described in detail.

In PMID 26220823 Louks et al. report on 4 patients from 3 families belonging to the same genetic isolate from North America and provide details on 4 of the individuals identified by Alazami et al.

The individuals identified in this study were homozygous for Met6Lys which was however predicted to be benign and tolerated (by PolyPhen2 and SIFT respectively) in silico.

DD/ID, unusual skull shape, ectodermal anomalies were universal (8/8) with additional features including short stature (7/8), renal (4/6) or cardiac anomalies (3/8). Some facial features appeared to be common, too.

Functional studies were not performed. However Dph1 pathogenic variants in mice result in restricted growth, craniofacial and developmental defects similar to the human phenotypes (PMIDs 14744934 and 24895408 are cited).

PMIDs 29362492 and 29410513 report on 3 further patients with similar (as well as some additional) features including DD/ID. The individual in the first article was compound heterozygous for a missense (Leu164Pro) and a frameshift variant (c.289delG) while 2 sibs born to consanguineous parents in the second article were homozygous for a frameshift variant (c.1227delG).

The phenotype appears to be consistent among all the published patients.

DPH1 is included in gene panels for intellectual disability offered by different diagnostic laboratories.

As a result, this gene can be considered for inclusion in this panel as green.
Sources: Literature, Expert Review
Intellectual disability v2.555 COG6 Konstantinos Varvagiannis gene: COG6 was added
gene: COG6 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: COG6 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: COG6 were set to 26260076; 20605848; 23430903; 23606727; 28139241; 28742265; 29445937; 29709711
Phenotypes for gene: COG6 were set to Congenital disorder of glycosylation, type IIl, 614576; Shaheen syndrome, 615328
Penetrance for gene: COG6 were set to Complete
Review for gene: COG6 was set to GREEN
gene: COG6 was marked as current diagnostic
Added comment: DD/ID is an almost universal feature of individuals with biallelic COG6 mutations, whether this is associated with a type II transferrin IEF pattern (as in Congenital disorder of glycosylation, type IIl, 614576) or not (as in Shaheen syndrome, 615328).

More than 15 patients from several different families have been reported to date.

PMID: 26260076 is a collaborative study reporting on new patients as well as on individuals previously described up to 2015 by Lubbehusen et al. (2010 - PMID: 20605848), Huybrechts et al. (2012 - PMID: 23430903) as well as Shaheen et al. (2013 - PMID: 23606727).

As summarized in table 1 of this article, developmental disability was a feature in 8/10, although for a further 2/10 this was probably not relevant (both deceased too early).

The following articles are additional reports although there might be some overlap (applicable for the Saudi patients) : PMIDs: 28139241 (individuals with diagnosis of CDG from Spain), 28742265 (cohort of CDG patients from Saudi Arabia), 29445937 (case report of Saudi subject), 29709711 (Chinese individual with COG6-CDG).

All types of variants have been observed including missense, stopgain and frameshift ones, as well as variants leading to aberrant splicing [eg. positions -2, -9, -24]. The deep intronic variant (position -24) in the individuals reported by Shaheen and others is considered a founder mutation in the Saudi population.

Individuals homozygous for the latter variant have detectable levels of the normal transcript, although 75% of the produced transcript (upon RT-PCR analysis) correspond to retention of 37 intronic nucleotides leading to frameshift and introduction of a premature stop codon. This was also confirmed with Western blot.

Given the detectable levels of the normal transcript, it has been proposed that Shaheen syndrome represents the mildest end of the spectrum COG6-related disorders.

COG6 is included in gene panels for intellectual disability offered by different diagnostic laboratories.

As a result this gene can be considered for inclusion in this panel as green.
Sources: Literature, Expert Review
Intellectual disability v2.555 TELO2 Konstantinos Varvagiannis gene: TELO2 was added
gene: TELO2 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: TELO2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: TELO2 were set to 27132593; 28944240
Phenotypes for gene: TELO2 were set to You-Hoover-Fong syndrome, MIM 616954
Penetrance for gene: TELO2 were set to Complete
Review for gene: TELO2 was set to GREEN
gene: TELO2 was marked as current diagnostic
Added comment: Biallelic mutations in TELO2 cause You-Hoover-Fong syndrome (MIM 616954). //

PMID: 27132593 reports on 6 patients (from 4 non-consanguineous families) with biallelic TELO2 variants and a similar phenotype.

Intellectual disability and microcephaly were universal features (6/6). Abnormal hearing (3/6), cortical visual impairment (3/6), abnormality of the cardiovascular system (3/6), behavioral problems (laughter outbursts in 3/6) and abnormal balance and movement disorder (6/6) were part of the phenotype. One individual had seizures.

5 missense variants and a complex allele with a stopgain variant localized in cis with a splice-site variant (NM_016111.3:c.514C>T or p.Gln172* in cis with c.2034+1G>A) are reported.

As a result heterozygosity for the complex variant may be confounded with compound heterozygous state until segregation studies are performed.

Functional studies support pathogenicity of the missense variants (reduced protein steady-state levels of TELO2 as well as TTI1 and TTI2 - the 2 other members of the TTT complex) suggesting loss of function.

PMID: 28944240 reports on 2 sisters born to non-consanguineous parents. Both were compound heterozygous for 2 novel variants, a missense and a frameshift one. Severe microcephaly (-8.5 SD and -10.7 SD) and seizures were noted in both. The first sister passed away at the age of 2 months due to a respiratory infection. The other sister demonstrated a compatible, though much more severe phenotype (of ID, dwarfism, retinitis pigmentosa, etc) compared to previously reported patients. //

Biallelic mutations in TTI2 (of the same complex) lead to similar phenotypes (gene rated green in the ID panel). //

TELO2 is included in gene panels for intellectual disability offered by different diagnostic laboratories. //

As a result this gene can be considered for inclusion in this panel as green.
Sources: Literature, Expert Review
Intellectual disability v2.555 BRD4 Konstantinos Varvagiannis gene: BRD4 was added
gene: BRD4 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: BRD4 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: BRD4 were set to 29379197; 30055032; 30302754
Phenotypes for gene: BRD4 were set to Intellectual disability; Microcephaly; Abnormal heart morphology; Abnormality of the face
Penetrance for gene: BRD4 were set to unknown
Review for gene: BRD4 was set to GREEN
gene: BRD4 was marked as current diagnostic
Added comment: PMID: 29379197 reports on 3 unrelated individuals with de novo mutations in BRD4 and a Cornelia de Lange-like phenotype. One of these individuals was a DDD study participant (DDD4K.04273). A further (fourth) individual had a 1.04 Mb deletion encompassing BRD4 (and 28 other genes) and presented with a similar phenotype.

Appart from intellectual disability which was a universal feature common features included a CdLS-like appearance (3/4), microcephaly (3/4) and cardiac malformations (VSD in 2/4).

Review of published patients with multigenic deletions spanning also BRD4 support a CdLS-like phenotype as well as haploinsufficiency as the underlying mechanism.

As the authors note, mice heterozygous for loss-of-function mutations in BRD4 show CdLS like features.
Functional studies performed demonstrated association of BRD4 with NIPBL with colocalization (/shared binding) to super-enhancers and co-regulation of gene expression.

The variants reported in this study included a missense as well as 2 frameshift mutations.

PMIDs: 30055032 and 30302754 report further patients with deletions spanning BRD4 and review the previously published patients.

BRD4 is included in gene panels for intellectual disability offered by different diagnostic laboratories.

As a result this gene can be considered for inclusion in this panel as green.
Sources: Literature, Expert Review
Intellectual disability v2.555 MACF1 Konstantinos Varvagiannis gene: MACF1 was added
gene: MACF1 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: MACF1 was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Phenotypes for gene: MACF1 were set to Intellectual disability; Seizures; Lissencephaly; Brainstem dysplasia
Penetrance for gene: MACF1 were set to unknown
Mode of pathogenicity for gene: MACF1 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: MACF1 was set to GREEN
Added comment: Dobyns et al. (doi.org/10.1016/j.ajhg.2018.10.019) report on 9 individuals (all unrelated appart from a pair of monozygotic twins) with de novo variants in MACF1.

All patients presented lissencephaly and brainstem hypoplasia with associated intellectual disability (9/9) and seizures (9/9).

Seven of these individuals had de novo missense variants within the GAR domain and an eighth had a deletion of several exons also spanning this domain and leading to an in-frame deletion. A further ninth patient had a de novo missense variant in the spectrin repeat domain and was found to have similar features although the brainstem dysplasia was rather subtle.

5 missense variants (4 of which in the GAR domain) and an intragenic deletion are reported in total.

The variants in the GAR domain were predicted to have important effect in the zinc-binding pocket. The spectrin repeat (SR4) is thought to have an important role for the function of MACF1 and further to neuronal migration.

Knockdown of Macf1 in mice has been shown to result in developmental defects similar to the human malformation.

The authors note that several high-confidence loss-of-function mutations are listed in ExAC and as a result this type of variants could be non-pathogenic (or lead to neurodevelopmental disorders with reduced penetrance). Still MACF1 has a pLI of 1.0.

As for the missense variants, the authors suggest either a gain-of-function or dominant negative mechanism.

Caution should be taken when interpreting variants as the ENST00000372915.7 (or MACF1-204) transcript is used for the predicted protein changes, although ENST00000361689.6 or MACF1-203 (corresponding to NM_012090.5) has also been used in some tables or figures.

As a result, this gene can be considered for inclusion in this panel probably as green.
Sources: Literature, Expert Review
Intellectual disability v2.552 SCAPER Louise Daugherty Added comment: Comment on phenotypes: added phenotype and MIM from OMIM : Tatour et al. (2017) PMID: 28794130 describes 4 patients from 3 unrelated families with intellectual disability disorder and retinitis pigmentosa and identified homozygosity or compound heterozygosity for mutations in the SCAPER gene. Noting that the retinal phenotype associated with null SCAPER mutations is not congenital but presents around the second decade of life, the authors suggested that in the retina, SCAPER does not play a developmental role, but rather is important for photoreceptor function and/or maintenance.
Intellectual disability v2.551 NUDT2 Konstantinos Varvagiannis gene: NUDT2 was added
gene: NUDT2 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: NUDT2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: NUDT2 were set to 27431290; 30059600
Phenotypes for gene: NUDT2 were set to Muscular hypotonia; Global developmental delay; Intellectual disability
Penetrance for gene: NUDT2 were set to Complete
Review for gene: NUDT2 was set to AMBER
Added comment: PMID: 27431290 reports briefly on 2 sibs from a consanguineous Saudi family, as part of a cohort of 337 patients investigated for intellectual disability. Both were homozygous for a nonsense NUDT2 mutation [NM_001161.4:c.34C>T or p.Arg12Ter / rs148119952]. The common features included hypotonia, global developmental delay (first words at 2.5 years, sitting at 2-2.5 years,walking achieved by 4 years - valid for both sibs) and intellectual disability. No other candidate variants were found in the exome.

PMID: 30059600 is a further report on 5 individuals from 3 consanguineous families from Saudi Arabia. All presented with low birth weight and height, poor suck, hypotonia, motor and language delay and borderline intelligence. All patients were homozygous for the same nonsense variant (Arg12Ter) which seems to be a founder mutation in Saudi Arabia.

As truncating NUDT2 variants have a combined allele frequency of 0.02% in gnomAD (no homozygotes in the database) the authors comment that most of the other LoF variants observed are in the second - and last - exon of the gene (thus probably escaping NMD) and downstream of its catalytic domain.

As a result this gene can be considered for inclusion in the ID panel probably as amber (single founder mutation - the degree of intellectual disability appears to be more severe in the first report but borderline in the subsequent) or green.
Sources: Literature, Expert Review
Intellectual disability v2.550 UFM1 Konstantinos Varvagiannis gene: UFM1 was added
gene: UFM1 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: UFM1 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: UFM1 were set to 28931644; 29868776
Phenotypes for gene: UFM1 were set to Leukodystrophy hypomyelinating 14, 617899
Penetrance for gene: UFM1 were set to Complete
Review for gene: UFM1 was set to GREEN
Added comment: Biallelic UFM1 mutations cause Leukodystrophy hypomyelinating 14, MIM 617899.

PMID: 28931644 is the first report on 16 individuals from 14 families with shared Roma ethnic background. All subjects were found to harbor a UFM1 promoter 3 basepair deletion in the homozygous state.

All patients demonstrated a severe phenotype including lack of development and severe epileptic encephalopathy while their MRI images demonstrated hypomyelination with atrophy of the basal ganglia and the cerebellum.

The promoter deletion was detected by exome sequencing. Previously a 0.8 Mb homozygous region was identified to be shared by all the patients in whom a SNP array was performed. Alternative causes, notably TUBB4A mutations and deletions/duplications were excluded. 3 individuals had Sanger sequencing of all coding regions within the homozygous interval to rule out other - eventually missed - variants.

PMID: 29868776 reports 4 additional individuals from 2 consanguineous families (one from Ethiopia, for the other this was not specified). All 4 patients were homozygous for the c.241C>T (NM_016617.3) or p.(Arg81Cys) variant which was shown to be hypomorphic upon functional studies.

The phenotype consisted of developmental delay (4/4 or 20/20 including the patients from the previous report with which comparison is made in table 2 of the article) with microcephaly (4/4 or 20/20) and seizures (4/4 or 16/20) as well as MRI abnormalities. Failure to thrive and/or short stature were also among the most common features.

UFM1 (as well as UFC1 also discussed in the same article) participate in ufmylation, with mutations in other enzymes of the same process (notably UBA5 - gene rated Green in the ID and epilepsy panels) having already been described in neurodevelopmental disorders.

As a result, this gene can be considered for inclusion in this panel as green (or amber).
Sources: Literature, Expert Review
Intellectual disability v2.545 UFC1 Konstantinos Varvagiannis gene: UFC1 was added
gene: UFC1 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: UFC1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: UFC1 were set to 29868776
Phenotypes for gene: UFC1 were set to Neurodevelopmental disorder with spasticity and poor growth, 618076
Penetrance for gene: UFC1 were set to Complete
Review for gene: UFC1 was set to GREEN
Added comment: Biallelic UFC1 mutations cause Neurodevelopmental disorder with spasticity and poor growth, MIM 618076.

PMID: 29868776 describes 7 individuals (most) born to consanguineous Saudi families (in one case the parents were not consanguineous but originated from the same tribe) as well as a further individual born to distantly related Swiss parents. One of these patients was previously briefly published by the same authors (PMID: 27431290).

The phenotype consisted of developmental delay (8/8 - usually profound), failure to thrive (8/8), short stature and microcephaly (both observed in 7/8), seizures (4/8) and variable brain MRI anomalies in some of these subjects.

Overall, two UFC1 missense variants are reported [NM_016406.3:c.317C>T or p.(Thr106Ile) and c.68G>A or p.(Arg23Gln) the former in the Saudi individuals]. Functional studies demonstrated the hypomorphic nature of the variants.

UFC1 (as well as UFM1 also discussed in the same article) participate in ufmylation, with mutations in other enzymes of the same process (notably UBA5 - gene rated Green in the ID and epilepsy panels) having already been described in neurodevelopmental disorders.

As a result this gene can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature, Expert Review
Intellectual disability v2.537 GNB5 Konstantinos Varvagiannis gene: GNB5 was added
gene: GNB5 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: GNB5 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: GNB5 were set to 27523599; 27677260; 28697420; 29368331
Phenotypes for gene: GNB5 were set to Intellectual developmental disorder with cardiac arrhythmia, 617173; Language delay and ADHD/cognitive impairment with or without cardiac arrhythmia, 617182
Penetrance for gene: GNB5 were set to Complete
Review for gene: GNB5 was set to GREEN
gene: GNB5 was marked as current diagnostic
Added comment: Biallelic GNB5 pathogenic variants cause Intellectual developmental disorder with cardiac arrhythmia (MIM 617173) or language delay and ADHD/cognitive impairment with or without cardiac arrhythmia (MIM 617182).

PMID: 27523599 is the first report on the associated phenotype. A total of 9 individuals from 6 different families (from various ethnic backgrounds) are described.

The common features included hypotonia (noted in 6 out of 9 patients), intellectual disability (9/9 - in 3 cases mild, in 6 severe), heart rate disturbance (9/9 - in most cases sick sinus syndrome), seizures (4/9), ophthalmological problems (nystagmus in 6 out of 7 for whom this information was available) as well as gastric problems (5/8 with G-E reflux).

The 6 variants (summarized in table S1) included : 2 nonsense mutations, 1 synonymous (demonstrated to affect splicing and leading to retention of 25 intronic bp), 2 further splice variants (positions +1 and +3) and a missense one (S81L).

Nonsense mediated decay was the case for the product of the synonymous/splice variant as well as for a stopgain one.

As noted by the authors, individuals homozygous for the S81L variant had a less severe phenotype - among others - with mild degree of intellectual disability.

Functional studies included knockout of gnb5 in zebrafish, which was able to reproduce the human neurological, cardiac and ophthalmological phenotypes.

Alternative causes for these phenotypes (incl. chromosomal or metabolic disorders) were ruled out.

Affected individuals might benefit interventions for their heart rate disturbance as appears to be the case in the article as well as subsequent studies.

PMID: 27677260 describes an extended consanguineous Saudi family with 5 individuals homozygous for the S81L variant. Common features included severe language delay, ADHD, but normal cognition in those available for evaluation. Seizures were not reported. Pathogenicity of the S81L variant is further supported by functional studies.

PMID: 28697420 describes in detail 2 individuals from a large consanguineous pedigree confirmed to be homozygous for a single nucleotide deletion in GNB5. The phenotype included severe DD/ID, seizures, sinus bradycardia with frequent sinus pauses and ophthalmological problems. Sinus arrhythmia and or seizures were documented in several other relatives deceased and unavailable for testing.

PMID: 28327206 reports on 2 subjects previously included in PMID: 27523599.

PMID: 29368331 describes a child with severe developmental delay, nystagmus and sinus arrhythmia necessitating a pacemaker. EEG was abnormal although no frank seizures were observed. The child was compound heterozygous for a novel missense variant (R246Q) as well a 5 basepair deletion.

GNB5 is included in diagnostic gene panels for intellectual disability offered by different laboratories.

As a result this gene can be considered for inclusion in this panel as green.
Sources: Literature, Expert Review
Intellectual disability v2.535 FUT8 Konstantinos Varvagiannis gene: FUT8 was added
gene: FUT8 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: FUT8 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: FUT8 were set to 29304374
Phenotypes for gene: FUT8 were set to Congenital disorder of glycosylation with defective fucosylation, 618005
Penetrance for gene: FUT8 were set to Complete
Review for gene: FUT8 was set to GREEN
Added comment: PMID: 29304374 reports on 3 unrelated individuals with biallelic pathogenic variants in FUT8.

Two of the patients were born to consanguineous parents and were found to be homozygous for stopgain variants (p.Arg239* in one family and p.Arg315* in the other). A third patient was compound heterozygous for a missense as well as a splice variant.

All three presented with similar phenotype consisting of polyhydramnios (2 out of 3), IUGR and failure to thrive with short stature (3/3), severe developmental delay (3/3) with microcephaly (3/3) and seizures (3/3). Variable respiratory problems were also noted in all.

Western blot demonstrated loss of FUT8 protein expression in one individual homozygous for a stopgain mutation as well as the patient who was compound heterozygous for the missense and the splice variant. The splice variant was further shown to produce a shorter transcript due to lack of exon 9, leading to an in-frame deletion of 59 residues critical for the protein function.

Additional studies confirmed the fucosylation defect compared to controls.

The authors note that while Fut8 knockout mice are born normal, 70% die within the first 3 days due to severe growth retardation and respiratory deficiency (similarly to what is observed in humans, though to a lesser extent).

As a result this gene can be considered for inclusion in this panel probably as green (3 unrelated families, strong additional functional data, consistent phenotype) or amber.
Sources: Literature, Expert Review
Intellectual disability v2.535 ATP6V1A Konstantinos Varvagiannis gene: ATP6V1A was added
gene: ATP6V1A was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: ATP6V1A was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: ATP6V1A were set to 29668857; 28065471
Phenotypes for gene: ATP6V1A were set to # 618012 EPILEPTIC ENCEPHALOPATHY, INFANTILE OR EARLY CHILDHOOD, 3; IECEE3
Penetrance for gene: ATP6V1A were set to unknown
Review for gene: ATP6V1A was set to GREEN
Added comment: Heterozygous mutations in ATP6V1A cause Epileptic encephalopathy, infantile or early childhood, type 3 (MIM 618012).

PMID: 29668857 reports 4 individuals from 4 families with de novo pathogenic variants in ATP6V1A. The phenotype was consistent with a developmental encephalopathy with epilepsy.

All patients were found to harbor missense variants. The variants resulted in altered lysosomal homeostasis, abnormal neuritogenesis and synaptic density. However in one of the variants tested (p.Asp100Tyr) pathogenicity was mediated by loss-of-function mechanism while for another (p.Asp349Asn) by gain-of-function mechanism.

Differences in severity were noted, with two variants (incl. Asp100Tyr) being associated with a more severe phenotype and the two other (incl. Asp349Asn) with milder degrees of ID and epilepsy.

Biallelic ATP6V1A mutations cause Cutis laxa type IID (MIM 617403). PMID: 28065471 is the first report on 3 individuals from 3 different families (2 of which were consanguineous). All patients were homozygous for ATP6V1A pathogenic variants. All three presented with hypotonia, one (or possibly two) with developmental delay and two with seizures although the developmental phenotype is not further commented on. (Additional patients described in the article harbored mutations in other genes and were not considered).

As a result, this gene can be considered for inclusion in this panel as green (or amber).
Sources: Literature, Expert Review
Intellectual disability v2.535 ATP1A1 Konstantinos Varvagiannis gene: ATP1A1 was added
gene: ATP1A1 was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: ATP1A1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: ATP1A1 were set to 30388404
Phenotypes for gene: ATP1A1 were set to Hypomagnesemia; Seizures; Intellectual disability
Penetrance for gene: ATP1A1 were set to unknown
Review for gene: ATP1A1 was set to GREEN
Added comment: PMID: 30388404 reports on 3 subjects from 3 families with de novo pathogenic variants in ATP1A1. All 3 presented with similar phenotype consisting of hypomagnesemia, early onset refractory seizures as well as intellectual disability.

Alternative causes of hypomagnesemia with seizures (eg. due to TRPM6 mutations) were excluded while the phenotype of the 3 patients differed from similar disorder in that hypomagnesemia as well as seizures were not responsive to magnesium supplementation.

Three different missense variants are reported (L302R, G303R, M859R) all as de novo occurences and after confirmation of paternity.

Functional studies were suggestive of loss of the ATPase function, abnormal cation permeabilities as well as reduced level of expression (the latter was significant for at least for 2 of the 3 variants).

Mutations in ATP1A1 have also been reported in patients with Charcot-Marie-Tooth type 2 (CMT2DD - MIM: 618036) although the variants reported to date map seem to cluster within the helical linker region (residues 592 to 608). The young age of the patients with epilepsy and intellectual disability did not allow conclusions on eventual peripheral neuropathy in these individuals.

As a result this gene can be considered for inclusion in this panel as green (or amber).
Sources: Expert Review, Literature
Intellectual disability v2.531 NFIB Konstantinos Varvagiannis gene: NFIB was added
gene: NFIB was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: NFIB was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: NFIB were set to 30388402
Phenotypes for gene: NFIB were set to Global developmental delay; Intellectual disability; Macrocephaly
Penetrance for gene: NFIB were set to unknown
Review for gene: NFIB was set to GREEN
Added comment: Schanze et al. (PMID: 30388402) report on the phenotype related to NFIB haploinsufficiency.

10 individuals with intragenic NFIB or larger deletions encompassing also other genes as well as 8 individuals with nucleotide variants (5 loss-of-function and 3 missense ones) are described.

Intellectual disability was a universal feature while macrocephaly was noted in the majority of the patients. The phenotype of individuals deletions was similar to the phenotype of intragenic mutations as also seems to be the case with the degree of ID.

Functional studies support loss of function for the pathogenic missense variants reported. Cortical-specific knockout of Nfib in mice results in enlargement of the cortex.

While most of the variants occurred as de novo events, a few individuals had inherited a variant (deletion or nucleotide variant) from a similarly affected parent.

As a result, this gene can be considered for inclusion in the ID panel as green.
Sources: Expert Review, Literature
Intellectual disability v2.530 CHD3 Konstantinos Varvagiannis gene: CHD3 was added
gene: CHD3 was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: CHD3 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CHD3 were set to 30397230
Phenotypes for gene: CHD3 were set to Global developmental delay; Intellectual disability; Macrocephaly
Penetrance for gene: CHD3 were set to unknown
Review for gene: CHD3 was set to GREEN
Added comment: PMID 30397230 is a collaborative study reporting on the phenotype of 35 individuals including 4 subjects from the DDD study, (most) with de novo mutations in CHD3.

Common features include developmental delay, variable degrees of intellectual disability, impaired speech and language (all 3 were universal features) as well as macrocephaly (in approximately 60%) or vision problems. Widely spaced eyes and high/broad/prominent forehead were among the most constant facial features (noted in around 80% each).

The majority of the variants reported are missense and cluster within the helicase domain although exceptions of missense variants in other domains or loss-of-function variants are provided. A few variants were recurrent and/or concerned the same residue.

Two pairs of affected siblings are reported, in one case this was explained by maternal mosaicism for the mutation.

Perturbed ATPase and/or chromatin remodeling activity relative to wild-type were demonstrated although both gain and loss of these activities were noted depending on the variant tested.

CHD3 is intolerant to both loss-of-function and missense variants (pLI of 1.0 and Z-score of +7.15).

As a result this gene can be considered for inclusion in the ID panel as green.
Sources: Expert Review, Literature
Intellectual disability v2.530 RHOBTB2 Konstantinos Varvagiannis gene: RHOBTB2 was added
gene: RHOBTB2 was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: RHOBTB2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: RHOBTB2 were set to 29276004; 29768694; 26740508
Phenotypes for gene: RHOBTB2 were set to Global developmental delay; Intellectual disability; Seizures; Postnatal microcephaly
Penetrance for gene: RHOBTB2 were set to unknown
Mode of pathogenicity for gene: RHOBTB2 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: RHOBTB2 was set to GREEN
gene: RHOBTB2 was marked as current diagnostic
Added comment: PMID: 29276004 reports on 10 unrelated patients with de novo pathogenic missense variants in RHOBTB2. The phenotype in all individuals was compatible with a developmental and epileptic encephalopathy including early-onset seizures, severe intellectual disability, postnatal onset microcephaly (6/10) and movement disorders (8/10).

The variants occured as de novo events and clustered within the BTB-domain encoding region (within and between the 2 BTB domains). Three missense variants were recurrent and/or concerned the same residue (p.Arg483His in 4 individuals, Arg511Gln was reported in 2, and Arg511Trp was was found in another 2 individuals).

Functional studies in HEK293 cells suggested increased abundance of the mutant protein secondary to decreased proteasome degradation. Using Drosophila as a model organism, altered expression of RhoBTB (the single ortholog of the 3 vertebrate paralogs, closest to RHOBTB2) was shown to result in neurological phenotypes. RhoBTB overexpression in particular was associated with increased bang sensitivity (which was not the case or milder in the case if knockdown of this gene) and impaired performance upon the negative geotaxis assay, similar to the human neurological phenotypes. Altered RhoBTB dosage was shown to be associated with impaired dendrite development.

As commented by the authors, these results as well as the clustering of missense variants and the pLI score of 0.51 reported for RHOBTB2 are consistent with altered protein function (due to the missense variants) rather than haploinsufficiency or loss-of-function.

PMID: 29768694 describes 3 additional individuals, all found to harbor de novo missense variants again within the BTB-domain encoding region. Two of the variants had been reported in the previous study (Arg511Gln and Arg483His) while the third was a private one (Arg507Cys). The phenotype was similar to the previous descriptions. Functional studies were suggestive of impaired degradation of the mutant protein by the CUL3 complex although this was not secondary to decreased binding with CUL3.

PMID: 26740508 (cited by the two aforementioned publications) reports briefly on an individual with de novo missense variant in the same region of RHOBTB2 (Asn510Asp) and Rett-like phenotype.

RHOBTB2 is included in gene panels for intellectual disability offered by different diagnostic laboratories.

As a result the gene can be considered for inclusion in the intellectual disability and epilepsy panels as green.
Sources: Expert Review, Literature
Intellectual disability v2.510 MUT Louise Daugherty Tag new-gene-name tag was added to gene: MUT.
Intellectual disability v2.510 MUT Louise Daugherty commented on gene: MUT
Intellectual disability v2.510 EMC1 Konstantinos Varvagiannis gene: EMC1 was added
gene: EMC1 was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: EMC1 was set to BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal
Publications for gene: EMC1 were set to 26942288; 29271071
Phenotypes for gene: EMC1 were set to Cerebellar atrophy, visual impairment, and psychomotor retardation, MIM 616875
Penetrance for gene: EMC1 were set to Complete
Review for gene: EMC1 was set to GREEN
gene: EMC1 was marked as current diagnostic
Added comment: Harel et al. (PMID: 26942288) describe 7 individuals from 3 families with biallelic pathogenic variants in EMC1.

In the first family, a single individual (born to non-consanguineous parents) was found to harbor a homozygous frameshift variant in a small (approx. 100 kb) stretch of absence of heterozygosity. The patients in the other two families were homozygous for missense variants (private to each family) in the context of parental consanguinity.

The common phenotype was suggestive of a progressive neurodegenerative disorder and consisted of hypotonia, severe developmental delay with marked speech delay, diminished deep tendon reflexes, cerebellar atrophy, vision as well as skeletal problems. Seizures were a feature in one subject.

One further patient from an additional (fourth) family was found to have a similar but milder phenotype and was only found to harbor a de novo missense variant in EMC1 following trio exome sequencing. Sanger sequencing of the promoter region as well as CNV calling from the exome data failed to reveal other variants in this specific individual.

Similarly to what has been observed in other genes the authors propose that both monoallelic and biallelic pathogenic variants may be causative of the specific phenotype, though the presentation may be more severe in case of biallelic variants.

Altogether this study reports 1 homozygous frameshift and 3 missense variants (2 of the latter found in homozygous state and one as a de novo heterozygous mutation). //

Geetha et al. (PMID: 29271071) describe an individual born to consanguineous parents presenting with hypotonia, developmental delay, and cerebellar atrophy as well as early onset epilepsy. Exome sequencing demonstrated a homozygous splice variant in EMC1. This variant was demonstrated to result to retention of intron 11 upon RNA sequencing. This was predicted to lead to premature truncation of the protein. //

EMC1 is associated in OMIM with Cerebellar atrophy, visual impairment, and psychomotor retardation (MIM 616875) for which an autosomal recessive inheritance mode is retained. //

Apart from the variants reported in the previous studies [p.Pro874Argfs*21, p.Thr82Met, p.Gly868Arg, p.Gly471Arg, c.1212+1G>A - NM_015047.2] further variants have been submitted in ClinVar as likely pathogenic (Variation IDs : 521479, 445564). //

The gene has been included in intellectual disability gene panels offered by a few other diagnostic labs. //

As a result this gene can be considered for inclusion in the panel as green (or amber).
Sources: Expert Review, Literature
Intellectual disability v2.510 CACNA1E Konstantinos Varvagiannis gene: CACNA1E was added
gene: CACNA1E was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: CACNA1E was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: CACNA1E were set to 29942082
Phenotypes for gene: CACNA1E were set to Global developmental delay; Intellectual disability; Seizures; Dystonia; Congenital contracture; Macrocephaly
Penetrance for gene: CACNA1E were set to Incomplete
Mode of pathogenicity for gene: CACNA1E was set to Other
Review for gene: CACNA1E was set to GREEN
Added comment: Helbig et al. (https://doi.org/10.1016/j.ajhg.2018.09.006) report on 30 individuals with pathogenic variants in CACNA1E.

The phenotype was consistent with a developmental and epileptic encephalopathy, with hypotonia, early-onset and refractory seizures, severe to profound developmental delay and intellectual disability. Additional relatively common features included hyperkinetic movement disorder (severe dystonia which was observed in 40%, other dyskinesias in another 20%), congenital joint contractures of variable degree and joint involvement (approx. 40% of individuals) and macrocephaly (approx. 40%). There were no common facial dysmorphic features observed.

Of note, epilepsy was not a feature in 4 cases (age 1 to 4 years) so few of these individuals may be investigated for their developmental delay/intellectual disability or other features.

Missense variants:
All the 30 subjects described harbored a missense variant in CACNA1E which in all cases where parental studies were possible (29/30) occurred as a de novo event. There were 4 recurrent variants, explaining the phenotype in 20 patients in total while the rest of the individuals had private mutations. Functional studies were performed and suggested a gain-of-function effect for these variants (increased calcium inward currents).

Loss-of-function (LoF) variants:
Apart from the main cohort of patients, the authors note the presence of 3 individuals with such variants incl.:
- one individual with a nonsense variant present in the mosaic state (6/22 reads) in peripheral blood.
- one individual with a frameshift variant inherited from his unaffected parent.
- one individual with a nonsense variant for whom parental studies were not possible.

The authors comment that these indivdiduals presented with milder phenotype compared to those with missense variants. More information on these subjects is provided in the supplement as the article focuses on missense SNVs.

As the authors also note, several LoF variants exist in gnomAD, although the gene appears to be LoF intolerant (pLI=1).

Penetrance:
Seems to be complete for missense SNVs and possibly incomplete for LoF ones.

---

A previous study by Heyne et al. (PMID: 29942082) implicated de novo variants (DNVs) in CACNA1E with neurodevelopmental disorders for the first time. This study however does not provide clinical details on the phenotype of the affected individuals, while it seems to present overlap as to the individuals reported (eg. includes subjects from the DDD study and others).

---

Details as to a few - possibly further - de novo coding variants reported to date can be found at the denovo-db:
http://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=CACNA1E

---

As a result this gene can be considered for inclusion in this panel as green.
Sources: Expert Review, Literature
Intellectual disability v2.510 VARS Konstantinos Varvagiannis gene: VARS was added
gene: VARS was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: VARS was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: VARS were set to 26539891; 29691655; 30275004
Phenotypes for gene: VARS were set to # 617802. NEURODEVELOPMENTAL DISORDER WITH MICROCEPHALY, SEIZURES, AND CORTICAL ATROPHY; NDMSCA
Penetrance for gene: VARS were set to Complete
Review for gene: VARS was set to GREEN
gene: VARS was marked as current diagnostic
Added comment: PMID: 26539891 is the first report on individuals with biallelic pathogenic variants in VARS. 3 individuals from 2 consanguineous families are briefly reported. The phenotype was similar in all 3, consisting of severe developmental delay, microcephaly, seizures and cortical atrophy. Subjects from the first family were homozygous for a missense variant in the tRNA synthetase catalytic domain [p.(L885F)]. The patient from the second family was homozygous for a missense SNV affecting the anticodon-binding domain [p.(R1058Q)].

PMID: 29691655 reports on a further patient born to non-consanguineous parents, with 2 in-trans pathogenic variants in VARS. The phenotype consisted of progressive microcephaly (OFC at birth -2SD, at the age of 2 months -4SD), global developmental delay, seizures and progressive cerebral and cerebellar atrophy. An affected brother presented with more severe phenotype (OFC -6SD at birth and -8SD at 2 months of age), seizures, hearing loss but was deceased and unavailable for genetic testing. cDNA studies demonstrated absence of the reference allele for the missense mutation downstream the splice variant (in line with a reduced or absent mRNA allele harboring the splice variant). Similarly, mRNA expression studies demonstrated 50-60% reduction in the transcripts (due to NMD of the allele with the splice SNV). Western blot showed severe reduction in protein levels (more pronounced compared to what would be expected by mRNA expression) presumably secondary to decreased protein stability due to the missense variant. Severe defects in aminoacylation were further confirmatory of a pathogenic role of these variants. The missense variant was affecting the anticodon-binding domain, important for aminoacylation.

PMID: 30275004 reports on 2 siblings with developmental delay, intellectual disability, severe speech impairment and microcephaly, similar to what has been described for the disorder. Clinical findings were somewhat different from previous studies in that microcephaly was acquired, while seizures and cortical atrophy were not part of the phenotype. Both sibs were compound heterozygous for 2 missense variants, though only one of these mutations affected the anticodon binding domain and the other was in the N-terminal region of the protein. Previous metabolic studies and extensive genetic testing (karyotype, CMA, MECP2, FMR1) was normal.

Epilepsy was a feature in 4 of the 6 individuals for whom genetic testing was possible (or 5/7 in total).

VARS belongs to the family of amino acyl-tRNA synthetases (ARSs). Mutations in several cytoplasmic ARSs are associated with severe neurological manifestations including seizures, intellectual disability associated with microcephaly.

VARS is included in gene panels for intellectual disability (but not for epilepsy) offered by different diagnostic labs.

As a result this gene can be considered for inclusion in the ID and epilepsy panel as green (or amber).
Sources: Expert Review, Literature
Intellectual disability v2.510 ADAT3 Konstantinos Varvagiannis gene: ADAT3 was added
gene: ADAT3 was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: ADAT3 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: ADAT3 were set to 23620220; 26842963; 30296593; 29796286
Phenotypes for gene: ADAT3 were set to # 615286. MENTAL RETARDATION, AUTOSOMAL RECESSIVE 36; MRT36
Penetrance for gene: ADAT3 were set to Complete
Review for gene: ADAT3 was set to GREEN
gene: ADAT3 was marked as current diagnostic
Added comment: Initially reported in PMID 23620220, the findings in several individuals with biallelic ADAT3 pathogenic variants (including also those from the first report) are summarized in PMID 26842963.

A total of 39 individuals from 19 consanguineous families are described in the two studies. These individuals were homozygous for a specific missense variant (probably a Saudi Arabian founder mutation).

The common phenotype consists of intellectual disability (39/39 patients) and strabismus (32/39). Additional features included failure to thrive (33/39), microcephaly (22/39), short stature (11 of 15 individuals for whom this was information was available).

Epilepsy was observed in some of these individuals (6/39).

A few facial features were more common, although there was no distinct facial gestalt. //

PMID 30296593 reports on 2 additional subjects born to consanguineous parents and found to be homozygous for the same missense variant. These individuals presented with features similar to the previous reports (although none of them was reported to have seizures). //

Of note, the variant is either referred to as V144M (using NM_138422.2 or NM_138422.3) or as V128M (using NM_138422.1 as a reference / c.382G>A) as in the initial report. [ClinVar : https://www.ncbi.nlm.nih.gov/clinvar/variation/183301/#summary-evidence]

PMID 29796286 describes a 6-year-old female, born to consanguineous Iranian parents, investigated for developmental delay,intellectual disability, behavioral difficulties as well as microcephaly. A homozygous 8-basepair duplication in ADAT3 was identified by exome and was further confirmed by Sanger sequencing. This individual did not have seizures. //

This gene is included in DD/ID (but not epilepsy) panels offered by different diagnostic labs. //

As a result this gene can be considered for inclusion in the intellectual disability panel as green.
Sources: Expert Review, Literature
Intellectual disability v2.510 NBEA Konstantinos Varvagiannis gene: NBEA was added
gene: NBEA was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: NBEA was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Phenotypes for gene: NBEA were set to Global developmental delay; Intellectual disability; Seizures
Penetrance for gene: NBEA were set to unknown
Review for gene: NBEA was set to GREEN
gene: NBEA was marked as current diagnostic
Added comment: PMID: 30269351 is a collaborative study reporting in 24 individuals with pathogenic de novo variants affecting NBEA.

All subjects presented with neurodevelopmental disorder including developmental delay or intellectual disability. Half of the patients (12/24) had autistic features or autism.

Epilepsy was a feature in 15/24 (62.5%) of patients with onset before the age of 4 years in the majority (approx. 85%). Of the 15 patients with seizures, 80% presented with generalized seizures of variable type (myoclonic, atonic and/or myoclonic-atonic, absence, tonic, clonic or tonic-clonic), 6.67% with focal seizures only and 13.33% with unclassified seizure type.

Other features included developmental microcephaly (or borderilne microcephaly) in 3/24 individuals or developmental regression in 2/24.

Among the variants identified:
8/24 were stopgain SNVs
5/24 were frameshift
4/24 were missense SNVs
1/24 was a splice site SNV
5/24 concerned an intragenic NBEA deletion
1/24 concerned a 2.87 Mb deletion spanning NBEA as well as additional genes (none of latter associated with disease in OMIM).

Two of these individuals were reported in a previously published study of children with DD/ID (PMID: 28554332).

Individuals with developmental disorders and de novo coding mutations in NBEA have been reported in further publications including the DDD study (PMID: 28135719 - subject DDD4K.01714), most summarized in the denovo-db (http://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=NBEA).

As also commented in the article, a patient with autism and a de novo balanced translocation disrupting NBEA has been reported (PMID: 12746398) as has also been the case with other deletions spanning NBEA (PMIDs: 12826745, 11450821, 3377648).

Previous studies have suggested a role for NBEA in regulation of synaptic structure and function (PMID: 23277425,22109531) as well as a role of neurobeachin in autism-like behaviors in mice (PMID: 23153818).

NBEA is intolerant to loss-of-function mutations (pLI=1 in ExAC). Most variants in the study predict loss-of-function. As a result happloinsufficiency seems to be the underlying mechanism.

As the authors propose, loss-of-function variants might be associated with more specific (eg. microcephaly or myoclonic-atonic seizures) or severe phenotypic presentations, although the size of the cohort did not not allow safe conclusions. //

NBEA is included in DD/ID (but not epilepsy) gene panels offered by different diagnostic labs. //

As a result this gene can be considered for inclusion as green in the intellectual disability and epilepsy panels.
Sources: Literature, Expert Review
Intellectual disability v2.510 TRAF7 Konstantinos Varvagiannis gene: TRAF7 was added
gene: TRAF7 was added to Intellectual disability. Sources: Expert Review,Literature
Mode of inheritance for gene: TRAF7 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: TRAF7 were set to 29961569; 27479843; 28135719; 25363760; 25961944
Phenotypes for gene: TRAF7 were set to Global developmental delay; Abnormal heart morphology; Abnormality of digit; Abnormality of limbs
Penetrance for gene: TRAF7 were set to unknown
Review for gene: TRAF7 was set to GREEN
Added comment: PMID: 29961569 reports on 7 unrelated individuals with pathogenic variants in TRAF7. Common features included developmental delay, congenital heart defects, limb and digital anomalies as well as shared facial features (including epicanthal folds, ptosis, abnormal ears, excess nuchal skin). Two (or possibly three) of these patients had seizures. Some of these individuals had been investigated in the past for disorders of the Ras-MAPK pathway (CFC, Noonan and Costello syndrome).

The SNVs reported are missense and occured de novo in all patients for whom parental studies were possible (6 out of 7). A recurrent mutation [p.(Arg655Gln)] was found in 4 of the 7 individuals. One patient was found to harbor a mutation in the mosaic state, as a de novo occurrence.

The variants resulted in reduced activation of ERK1/2 (also known as MAPK3/MAPK1). //

7 individuals with de novo coding variants have previously been reported in large cohorts of patients with intellectual disability (PMIDs : 27479843, 28135719 - DDD study) and/or ASD (25363760, 25961944). One of the individuals from the DDD study had a stopgain variant.

The individuals from these studies are summarized in the denovo-db (http://denovo-db.gs.washington.edu/denovo-db/QueryVariantServlet?searchBy=Gene&target=TRAF7). //

As a result this gene can be considered for inclusion in the ID panel as green (or amber).
Sources: Expert Review, Literature
Intellectual disability v2.510 PIGG Konstantinos Varvagiannis gene: PIGG was added
gene: PIGG was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: PIGG was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PIGG were set to 26996948; 28581210
Phenotypes for gene: PIGG were set to # 616917 MENTAL RETARDATION, AUTOSOMAL RECESSIVE 53; MRT53
Penetrance for gene: PIGG were set to Complete
Review for gene: PIGG was set to GREEN
gene: PIGG was marked as current diagnostic
Added comment: PMID: 26996948 reports on 5 individuals from 3 families, with biallelic pathogenic variants in PIGG.

Individuals from first family, were born to consanguineous parents from Egypt and were homozygous for a stopgain variant [p.(Gln310*)]. The patient from the second family had a rare missense SNV [p.(Arg669Cys)] and a de novo microdeletion affecting PIGG on her other allele. In the third family (consanguineous parents from Pakistan), two affected sibs were found to be homozygous for a splice variant.

The phenotype consisted of hypotonia, early-onset seizures and intellectual disability. Ataxia was an additional feature in one of the families.

Seizures, were observed in most of patients but do not appear to be a universal feature as they were absent in one of the sibs from the third family (10 years of age), while the other had a single episode by the age of 12 years.

In vitro testing of lymphoblastoid cell lines (generated from individuals from the 1st and 3rd family) indicated that the variants abolished completely the function of PIGG, whereas the surface level of GPI anchored proteins was normal. //

PMID: 28581210 describes the phenotype of 2 sibs from Palestine, homozygous for a stopgain variant [p.(Trp547*)]. Hypotonia, feeding difficulties, severe non-progressive ataxia (with cerebellar hypoplasia), intellectual disability and seizures were common features. Differences in severity and/or additional features might be explained by other homozygous variants (the girl had a concurrent diagnosis of MCAD deficiency).

The authors demonstrated that the PIGG transcript levels were significantly lower (approximately half) in the two siblings compared to their parents, while the transcripts with the mutation in the heterozygous parents were very low due to nonsense-mediated decay.

Patient fibroblasts showed decreased surface level of GPI-anchored proteins, in contrast with what was noted in lymphoblastoid cells in the previous study. //

PIGG has been included in gene panels for intellectual disability offered by different diagnostic labs. //

As a result this gene can be considered for inclusion in this panel as green (or amber).
Sources: Literature, Expert Review
Intellectual disability v2.510 MAP1B Konstantinos Varvagiannis gene: MAP1B was added
gene: MAP1B was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: MAP1B was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: MAP1B were set to 30150678; 29738522
Phenotypes for gene: MAP1B were set to Intellectual disability
Penetrance for gene: MAP1B were set to unknown
Review for gene: MAP1B was set to AMBER
Added comment: In PMID 30150678 the authors report on a family with 5 individuals diagnosed with intellectual disability (ID, IQ <= 70 and associated impairments in adaptive function) and 3 further relatives with IQ below 70, not fulfilling the criteria for a clinical diagnosis of ID. A frameshift variant in MAP1B segregated with the ID/low IQ phenotype. This variant was not found in 31463 Icelanders for whom whole genome sequencing data were available.

The authors confirmed association of MAP1B loss-of-function (LoF) variants by demonstrating the presence of 2 other stopgain mutations in 2 further families. Among the 6 mutation carriers in these families, the average IQ was 81 with 2 of these subjects fulfilling the criteria for intellectual disability. 3 of the 6 mutation carriers had a diagnosis of autism spectrum disorder. Carriers demonstrated 24% less white matter volume (-2.1 SD) and 47% less corpus callosum volume (-2.4 SD) compared to controls.

Mean full-scale IQ, performance IQ and verbal IQ were 68.3 (with a SD of 10.5), 66.4 (SD of 9.3) and 74.5 (SD of 14.8) in MAP1B LoF carriers.

All 3 LoF variants reported result in a truncated but stable MAP1B protein as demonstrated by western blot analysis.

MAP1B undergoes post-translational modification and is cleaved (at position 2206) into a heavy chain and a light chain. The authors note that all LoF variants lead to truncation prior to the cleavage site.

As commented by the authors, LoF variants are found in publicly available databases at a frequency of approx. 1 in 10000.

One individual with de novo frameshift variant in Decipher ( https://decipher.sanger.ac.uk/search?q=gene%3AMAP1B#research-variants/results ).

De novo and inherited MAP1B variants have previously been described in individuals with periventricular nodular heterotopia (PMID: 29738522). This was also a feature in 9 individuals in the previous ID study.

Although PMID 30150678 is entitled "MAP1B mutations cause intellectual disability and extensive white matter deficit", intellectual disability was not a feature in all individuals or was rather mild when present.
Sources: Literature, Expert Review
Intellectual disability v2.510 NSD2 Konstantinos Varvagiannis gene: NSD2 was added
gene: NSD2 was added to Intellectual disability. Sources: Literature,Expert Review
Mode of inheritance for gene: NSD2 was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: NSD2 were set to 29892088; 29760529; 29884796; 30244530
Phenotypes for gene: NSD2 were set to Intrauterine growth retardation; Growth delay; Microcephaly; Muscular hypotonia; Neurodevelopmental delay; Intellectual disability
Penetrance for gene: NSD2 were set to unknown
Review for gene: NSD2 was set to GREEN
gene: NSD2 was marked as current diagnostic
Added comment: PMID: 29892088 reports on 2 individuals with de novo SNVs affecting NSD2 (WHSC1). Both individuals presented with pre- and postnatal growth retardation, hypotonia, developmental delay / intellectual disability, as well as microcephaly. The authors suggest partial overlap with the phenotype of Wolf-Hirschhorn syndrome (WHS). Seizures are not part of the phenotype.The first subject had a splice site mutation while the second individual had a stopgain variant (affecting the PWWP domain).

PMID: 29760529 describes a further patient with de novo nonsense mutation in NSD2. The boy was evaluated for probable growth delay ("low physical development"), hypotonia, psychomotor delay and microcephaly. The variant affected the SET domain.

Three individuals with de novo likely loss-of-function (two frameshift and one stop gained) variants in Decipher [ https://decipher.sanger.ac.uk/search?q=NSD2#research-variants/results ].

A further patient with de novo frameshift mutation in NSD2 and a phenotype overlapping WHS reported in ClinVar [ https://www.ncbi.nlm.nih.gov/clinvar/variation/547999/ ]

PMID: 29884796 (Zollino M and Doronzio PN) comments that NSD2 (WHSC1) is a neurodevelopmental gene with a role in growth delay, intellectual disability and dysmorphic facial features.

PMID: 30244530 describes patients with 4p16.3 microdeletions spanning (exclusively) NSD2 and reviews the literature on patients with small microdeletions reported to date. All relevant individuals present with developmental delay and (rather mild) intellectual disability apart from other characteristics such as microcephaly, growth retardation and some facial features also observed in WHS.

In Decipher one individual (286913) with a single CNV spanning exclusively NSD2 presenting with IUGR, failure to thrive, feeding difficulties, postnatal microcephaly, hypotonia, developmental delay as well as possibly relevant facial features.

The gene is included in ID gene panels offered by various labs (either as NSD2 or WHSC1).

As a result it can be considered for inclusion in the panel as green.
Sources: Literature, Expert Review
Intellectual disability v2.510 PORCN Ellen McDonagh Mode of inheritance for gene: PORCN was changed from X-LINKED: hemizygous mutation in males, biallelic mutations in females to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.509 RAC3 Konstantinos Varvagiannis gene: RAC3 was added
gene: RAC3 was added to Intellectual disability. Sources: Literature
Mode of inheritance for gene: RAC3 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: RAC3 were set to 30293988; 29276006
Phenotypes for gene: RAC3 were set to Abnormality of brain morphology; Abnormal muscle tone; Neurodevelopmental delay; Intellectual disability
Penetrance for gene: RAC3 were set to unknown
Mode of pathogenicity for gene: RAC3 was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments
Review for gene: RAC3 was set to GREEN
Added comment: PMID: 30293988 reports on 5 individuals (from 4 different families) with de novo missense variants in RAC3. All individuals demonstrated structural anomalies on brain MRI (notably agenesis/dysgenesis of the corpus callosum, variable degrees of polymicrogyria and ventricular anomalies) as well as shared non-specific neurological features including abnormal muscular tone, global developmental delay and severe to profound intellectual disability. Feeding difficulties were observed in 4/5 patients.

All variants reported are missense and are presumed to result in constitutive protein activation, as suggested by previous observations either in RAC3 [eg. the p.(Gln61Leu) mutation] or the highly homologous RAC1 and RAC2. According to the authors this is further supported by the fact that Rac3 -/- mice do not show a severe phenotype while missense variants are underrepresented in the ExAC database (z=1.97) as opposed to loss-of-function variants (pLI=0.04 / probability of loss-of-function intolerance).

Of the 3 SNVs reported, 2 variants were in adjacent amino-acid positions [p.(Gln61Leu) and p.(Glu62Lys)]. The latter variant was found in 2 half-sibs born to different fathers, due to suspected maternal gonadal mosaicism (variant absent in all sequencing reads in the maternal DNA sample). The specific variant was also found in a further affected individual from an unrelated family.

Finally, as the authors point out a further individual with de novo RAC3 missense variant [p.(Ala59Gly)] was reported previously in an individual with thin corpus callosum and global developmental delay, although the phenotype was felt to be more reminiscent of Robinow syndrome (PMID: 29276006).

As a result, this gene can be considered for inclusion in the ID panel as green (or amber).
Sources: Literature
Intellectual disability v2.509 MSL3 Konstantinos Varvagiannis reviewed gene: MSL3: Rating: GREEN; Mode of pathogenicity: None; Publications: 30224647; Phenotypes: Muscular hypotonia, Feeding difficulties, Neurodevelopmental delay, Intellectual disability; Mode of inheritance: X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Intellectual disability v2.458 KDM1A Louise Daugherty edited their review of gene: KDM1A: Added comment: Recommendation that this gene should be Green. Three patients https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4902791/, there is functional characterisation of the three described mutations https://www.ncbi.nlm.nih.gov/pubmed/27094131?dopt=Abstract and the patients seem to share a similar phenotype, which recapitulates features of other deleterious mutations in better-characterised lysine demethylase and chromatin remodelling genes. There is also a recurrent de novo variant p.Tyr831Cys which has been reported in two separate "autism spectrum" patients in large cohort studies. The gene is also extensively constrained against both missense and LOF variation in humans http://exac.broadinstitute.org/gene/ENSG00000004487. I think what's been reported so far is probably robust enough to use the gene clinically.Pers comm. Ian Berry (NHS Leeds Genetics Laboratory); Changed rating: GREEN
Intellectual disability v2.443 ISCA-46290-Gain Louise Daugherty Region: ISCA-46290-Gain was added
Region: ISCA-46290-Gain was added to Intellectual disability. Sources: ClinGen,Expert Review Green
Mode of inheritance for Region: ISCA-46290-Gain was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females
Publications for Region: ISCA-46290-Gain were set to 25425167; 19716111; 21418194
Phenotypes for Region: ISCA-46290-Gain were set to Idiopathic mental retardation, speech delay, and a peculiar electroencephalographic (EEG) pattern in childhood. Autism and epilepsy, severe intellectual disability and dysmorphic facial features. Moderate to severe intellectual disability, early onset of puberty, language impairment, and age related epileptic syndromes such as West syndrome and focal epilepsy with activation during sleep evolving in some patients to continuous spikes-and-waves during slow sleep; 300801
Intellectual disability v2.420 AP1S1 Louise Daugherty edited their review of gene: AP1S1: Added comment: New gene added by external expert review, who notes French Canadian (founder effect); however, Sephardic Jewish family also reported with a different variant. ID is part of the phenotype, added publication to support gene-disease association.
The patients cases described in the literature to date are likely to be linked to a founder effect. 5 children from 3 families all from Quebec, Canada (with the same mutation) and 1 patient from a consanguineous Sephardic-Jewish background has been described (a different mutation in AP1S1).
However, this gene was rated Green on the Vici Syndrome and other autophagy disorders panel for MEDNIK syndrome after discussion with Emma Baple (South West GMC and Genomics England); as there is a second, independent case with a different variant, plus functional data, so this gene can be green on the ID panel, since intellectual disability is part of the phenotype; Changed rating: GREEN
Intellectual disability v2.398 ISCA-37439-Gain Louise Daugherty Region: ISCA-37439-Gain was added
Region: ISCA-37439-Gain was added to Intellectual disability. Sources: ClinGen,Expert Review Green
Mode of inheritance for Region: ISCA-37439-Gain was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Publications for Region: ISCA-37439-Gain were set to 17546640; 20004760; 18047645
Phenotypes for Region: ISCA-37439-Gain were set to 28300815; Chromosome Xq duplication syndrome
Intellectual disability MUT BRIDGE consortium edited their review of MUT
Intellectual disability MUT BRIDGE consortium edited their review of MUT
Intellectual disability MUT BRIDGE consortium reviewed MUT