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Early onset or syndromic epilepsy v8.179 RNU6ATAC Ida Ertmanska gene: RNU6ATAC was added
gene: RNU6ATAC was added to Early onset or syndromic epilepsy. Sources: Literature
Mode of inheritance for gene: RNU6ATAC was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: RNU6ATAC were set to 40975062; 41864208; 41808409
Phenotypes for gene: RNU6ATAC were set to neurodevelopmental disorder, MONDO:0700092; Immune dysregulation, HP:0002958; neonatal diabetes mellitus, MONDO:0016391
Review for gene: RNU6ATAC was set to AMBER
Added comment: PMID: 41808409 Mendez et al., 2026
Individual A1 - 14-year-old female with intrauterine growth restriction, microcephaly (Z = -2.05 at 13 yrs), refractory epilepsy, cerebral structural anomalies, ataxia, autism, severe intellectual disability, and marked peripheral eosinophilia. Compound het RNU6ATAC variants: n.28C>T & n.36T>G.

Individual B1 - 30-year-old male with immune dysfunction, endocrinopathy, and ectodermal abnormalities (ichthyosis, dystrophic nails, dental anomalies, and alopecia universalis), primary hypothyroidism, failure to thrive, bronchiectasis, chronic inflammatory demyelinating polyneuropathy, and combined variable immunodeficiency (CVID), without neurodevelopmental involvement. Compound het RNU6ATAC variants: n.30C>T & n.64C>G.

Individual C1 - 17-year-old male who presents with microcephaly (no severity stated), growth failure, ID / global developmental delay, immunodeficiency, diabetes mellitus (diagnosed at 9 months), hypothyroidism, and severe skeletal dysplasia. Homozygous for n.43G>A. Parents are first cousins.

PMID: 41864208 Johnson et al., 2026
Identified 19 individuals with early-onset diabetes (diagnosed <5 years) and additional clinical features who had biallelic pathogenic variants in the novel disease gene RNU6ATAC (n=7) or in RNU4ATAC (n=12).

6/7 individuals had variable additional features of immune dysregulation: sepsis, atopic dermatitis, B cell lymphopenia, low IgA, low IgG, B cell lymphopenia, hypothyroidism (2 sibs), agammaglobulinemia, hypoagammaglobulinemia, immunodeficiency, thyroiditis (2 unrelated patients), alopecia (2 unrelated patients), vitiligo. No microcephaly or developmental delay reported. 3/7 individuals died in early infancy.

Among the 4 families with biallelic RNU6ATAC variants, the variants reported were: n.4T>C, n.6G>A, n.43G>A, n.68C>A, n.71C>T (homozygous or compound het).

PMID: 40975062 Arriaga et al., 2025
Individual D1 - comp het for RNU6ATAC variants: n.36T>G and n.28C>T. The individual presented with microcephaly, short stature, hypotonia, ID/DD, seizures, ataxia, ventriculomegaly, syndactyly, nystagmus, and oculomotor apraxia. Patient D1 did not have diabetes, hypothyroidism, or immunodeficiency. RNA analysis demonstrated excess minor intron retention.

RNU6ATAC has not yet been linked to any phenotypes in OMIM (accessed 31st Mar 2026).
Sources: Literature
Early onset or syndromic epilepsy v8.118 BORCS5 Ida Ertmanska gene: BORCS5 was added
gene: BORCS5 was added to Early onset or syndromic epilepsy. Sources: Literature
Mode of inheritance for gene: BORCS5 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: BORCS5 were set to 27435318; 40385417; 40621786
Phenotypes for gene: BORCS5 were set to arthrogryposis multiplex congenita, MONDO:0015168; neurodevelopmental disorder, MONDO:0700092
Review for gene: BORCS5 was set to GREEN
Added comment: PMID: 40621786 Fisher et al., 2025
Report of 2 fetal cases in a consanguineous Pakistani family. Exome seq revealed a homozygous nonsense variant c.283C>T, p.(Arg95Ter) in BORCS5 (NM_058169.4). Individuals showed neuroaxonal dystrophy with osteopetrosis.

PMID: 40385417 Mencacci et al., 2025 - pre-print
Report of 12 individuals from 7 unrelated families with biallelic BORCS5 variants (NM_058169.4): two missense variants (c.284G>A, p.R95Q; c.296A>C, p.H99P) and four LoF alleles (c.203–1G>T, p.?; c.316delG, p.A106Pfs*20; c.382_383delAG, p.L128Vfs*86; c.417C>G, p.Y139*).
Table 1 = phenotypic spectrum of 6 individuals from families 1-4: profound ID (6/6), severe spasticity (6/6), seizures (6/6), hyperreflexia (6/6), Parkinsonism/dystonia (3/6), limb contractures (5/6), optic atrophy (5/6), abnormal brain MRI including cerebral atrophy and/or corpus callosum agenesis (5/6), microcephaly (6/6 - severity not stated), muscle atrophy (5/6). Infantile onset.
Neuroimaging in 5 cases showed cerebral atrophy, white matter loss, hypomyelination, small T2-hypointense thalami, thin brainstem, and optic nerve atrophy.

PMID: 27435318 Charng et al., 2016
Patient BAB6775 homozygous for NM_058169.4 BORCS5: c.203-1G>T, with DD, microcephaly, seizures, cortical malformations, polymicrogyria, agenesis of corpus callosum. Also reported with more details in PMID:40385417 (do not count).

Additional functional evidence: Zebrafish borcs5 knockout leads to neurodevelopmental defects:microcephaly, ventriculomegaly, movement disorders and epilepsy.

BORCS5 is not yet associated with a disease in OMIM (accessed 20th Feb 2026).
Sources: Literature
Early onset or syndromic epilepsy v8.113 TCP1 Ida Ertmanska gene: TCP1 was added
gene: TCP1 was added to Early onset or syndromic epilepsy. Sources: Literature
Q1_26_promote_green tags were added to gene: TCP1.
Mode of inheritance for gene: TCP1 was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Publications for gene: TCP1 were set to 39480921
Phenotypes for gene: TCP1 were set to Intellectual developmental disorder with polymicrogyria and seizures, OMIM:621021
Review for gene: TCP1 was set to GREEN
Added comment: PMID: 39480921 Kraft et al., 2024
8 individuals reported with heterozygous TCP1 (CCT1) variants (frameshift, missense, stop gain - 5 confirmed de novo). Patients presented with ID, seizures, and brain malformations. Phenotype spectrum: DD/ID of variable severity (6/6 assessed), seizures (6/7), visual impairment (2/7), pyramidal signs (4 individuals), brain MRI abnormalities (7/8). MRI findings included polymicrogyria, heterotopia, ventriculomegaly and white matter hyperintensities, hypoplasia of corpus callosum.

TCP1 is associated with Intellectual developmental disorder with polymicrogyria and seizures, OMIM:621021 (OMIM accessed 20th Feb 2026).
Sources: Literature
Early onset or syndromic epilepsy v8.98 PAK2 Arina Puzriakova changed review comment from: Schnur et al. 2024 (PMID: 38894571) report a de novo heterozygous PAK2 variant c.1217C>T, p.(Thr406Met) in a newborn with clinical manifestations of Knobloch syndrome including congenital heart defects, atretic parietal meningocele, and rapidly progressive retinopathy. In vitro experiments indicated that this and another reported variant, p.(Asp425Asn), result in substantially impaired protein kinase activity.

Werren et al. 2025 (PMID: 39876536) report a male infant with a de novo heterozygous PAK2 variant c.1273G>A, p.(Asp425Asn) identified by WGS. Clinical features include GDD, congenital retinal detachment, mild cerebral ventriculomegaly, hypotonia, failure to thrive, pyloric stenosis, feeding intolerance, patent ductus arteriosus, and mild facial dysmorphism. The p.(Asp425Asn) variant resides within the protein kinase domain and was predicted functionally damaging by in silico tools. Further functional studies were not performed.

Lodha et al. 2025 (PMID: 40262506) revealed a PAK2 c.1115A>T, p.(Asp372Val) variant in a neonate with bilateral pleural effusion, suggestive of chylothorax on prenatal imaging, and respiratory distress, purpura fulminans and retinal detachment after birth.


Other PAK2 cases not reporting ocular abnormalities:

Domenach et al. 2025 (PMID: 39994693) identified a novel de novo PAK2 missense variant in the kinase domain, c.836A>C, p.(Gln279Pro), by prenatal trio exome sequencing in a 24 weeks of gestation fetus whose only identifiable sign was severe bilateral pleural effusion.

Shen et al. 2025 (PMID: 40247748) reported a Chinese family with a proband who primarily presented with epilepsy and developmental delay without the characteristic ocular and structural malformations that define Knobloch syndrome. WES and Sanger validation identified a de novo heterozygous PAK2 variant c.1049G>A, p.(Arg350Lys) located in the kinase domain. In vitro studies demonstrated the variant may lead to reduced protein levels and decreased PAK2 phosphorylation.; to: Antonarakis et al., 2021 (PMID: 33693784) reported two affected siblings from a non-consanguineous New Zealand family. Both had retinal detachment and interstitial parenchymal pulmonary changes on chest X-rays, but only one child had additional significant features such as cataract, posterior encephalocele, severe DD/ID with ASD, and epilepsy. WES revealed a heterozygous PAK2 variant (c.1303 G>A, p.Glu435Lys) in both individuals that apparently occurred de novo indicating parental germ-line mosaicism; however, mosaicism could not be detected by deep sequencing of blood parental DNA. Functional studies showed that the variant, located in the kinase domain, results in a partial loss of the kinase activity.

Shen et al. 2025 (PMID: 40247748) reported a Chinese family with a proband who primarily presented with epilepsy and developmental delay without the characteristic ocular and structural malformations that define Knobloch syndrome. WES and Sanger validation identified a de novo heterozygous PAK2 variant c.1049G>A, p.(Arg350Lys) located in the kinase domain. In vitro studies demonstrated the variant may lead to reduced protein levels and decreased PAK2 phosphorylation.


Other PAK2 cases not reporting epilepsy:

Schnur et al. 2024 (PMID: 38894571) report a de novo heterozygous PAK2 variant c.1217C>T, p.(Thr406Met) in a newborn with clinical manifestations of Knobloch syndrome including congenital heart defects, atretic parietal meningocele, and rapidly progressive retinopathy. In vitro experiments indicated that this and another reported variant, p.(Asp425Asn), result in substantially impaired protein kinase activity.

Werren et al. 2025 (PMID: 39876536) report a male infant with a de novo heterozygous PAK2 variant c.1273G>A, p.(Asp425Asn) identified by WGS. Clinical features include GDD, congenital retinal detachment, mild cerebral ventriculomegaly, hypotonia, failure to thrive, pyloric stenosis, feeding intolerance, patent ductus arteriosus, and mild facial dysmorphism. The p.(Asp425Asn) variant resides within the protein kinase domain and was predicted functionally damaging by in silico tools. Further functional studies were not performed.

Lodha et al. 2025 (PMID: 40262506) revealed a PAK2 c.1115A>T, p.(Asp372Val) variant in a neonate with bilateral pleural effusion, suggestive of chylothorax on prenatal imaging, and respiratory distress, purpura fulminans and retinal detachment after birth.

Domenach et al. 2025 (PMID: 39994693) identified a novel de novo PAK2 missense variant in the kinase domain, c.836A>C, p.(Gln279Pro), by prenatal trio exome sequencing in a 24 weeks of gestation fetus whose only identifiable sign was severe bilateral pleural effusion.
Early onset or syndromic epilepsy v7.80 FUT2 Arina Puzriakova gene: FUT2 was added
gene: FUT2 was added to Early onset or syndromic epilepsy. Sources: Literature
Mode of inheritance for gene: FUT2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: FUT2 were set to 39350204
Phenotypes for gene: FUT2 were set to Developmental and epileptic encephalopathy
Added comment: PMID: 39350204 (2024) - homozygous missense variant (NC_000019.10:g.48703291C>T) in the FUT2 gene was identified in an infant with vitamin B12-responsive developmental and epileptic encephalopathy and megaloblastic anemia. Although the mechanism of how the FUT2 gene variant affects vitamin B12 absorption is unclear.

Additional evidence is required before conclusively implicating FUT2 in human disease and therefore rating Red for now.
Sources: Literature
Early onset or syndromic epilepsy v4.182 PIK3R2 Arina Puzriakova Phenotypes for gene: PIK3R2 were changed from Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 1 603387 to Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 1, OMIM:603387
Early onset or syndromic epilepsy v4.138 ASL Eleanor Williams Phenotypes for gene: ASL were changed from Seizure; Neurodevelopmental delay; Intellectual disability; Autism; Abnormality of movement; Ataxia; Hepatomegaly; Elevated hepatic transaminase; Renal tubular dysfunction; Abnormal hair morphology to Argininosuccinic aciduria, OMIM:207900; argininosuccinic aciduria, MONDO:0008815
Early onset or syndromic epilepsy v4.133 ASL Nour Elkhateeb gene: ASL was added
gene: ASL was added to Early onset or syndromic epilepsy. Sources: Literature,ClinGen
Mode of inheritance for gene: ASL was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: ASL were set to 36994644; 21744316; 28251416
Phenotypes for gene: ASL were set to Seizure; Neurodevelopmental delay; Intellectual disability; Autism; Abnormality of movement; Ataxia; Hepatomegaly; Elevated hepatic transaminase; Renal tubular dysfunction; Abnormal hair morphology
Penetrance for gene: ASL were set to Complete
Review for gene: ASL was set to GREEN
Added comment: Epilepsy is reported as a common phenotype in individuals with argininosuccinic aciduria (ASA) with incidence between 42%-60%. The epilepsy phenotype occurs early in the natural history of ASA. The epilepsy phenotype is severe, with a significant cohort of patients presenting with pharmacoresistant seizures, and with status epilepticus. Epilepsy onset preceded ASA diagnosis in several reported patients.
Sources: Literature, ClinGen
Early onset or syndromic epilepsy v4.114 ST3GAL3 Arina Puzriakova Tag Q1_23_promote_green was removed from gene: ST3GAL3.
Early onset or syndromic epilepsy v4.110 ST3GAL3 Arina Puzriakova reviewed gene: ST3GAL3: Rating: GREEN; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v4.109 ST3GAL3 Arina Puzriakova Source Expert Review Green was added to ST3GAL3.
Rating Changed from Amber List (moderate evidence) to Green List (high evidence)
Early onset or syndromic epilepsy v4.83 AKT3 Arina Puzriakova Phenotypes for gene: AKT3 were changed from Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 2 615937 to Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 2, OMIM:615937
Early onset or syndromic epilepsy v3.62 ST3GAL3 Sarah Leigh Tag Q1_23_promote_green tag was added to gene: ST3GAL3.
Early onset or syndromic epilepsy v3.62 ST3GAL3 Sarah Leigh edited their review of gene: ST3GAL3: Added comment: Associated with Developmental and epileptic encephalopathy 15, OMIM:615006, but not associated with the same phenotype in Gen2Phen. At least two variants have been reported in two unrelated families (PMIDs: 23252400 & 31584066). Supportive functional studies are presented in PMID: 30089820.; Changed rating: GREEN; Changed publications to: 23252400, 30089820, 31584066
Early onset or syndromic epilepsy v3.62 ST3GAL3 Sarah Leigh Classified gene: ST3GAL3 as Amber List (moderate evidence)
Early onset or syndromic epilepsy v3.62 ST3GAL3 Sarah Leigh Gene: st3gal3 has been classified as Amber List (Moderate Evidence).
Early onset or syndromic epilepsy v3.61 ST3GAL3 Sarah Leigh Publications for gene: ST3GAL3 were set to 27604308; 21907012; 23252400; 31584066; 17120046; 25529582
Early onset or syndromic epilepsy v3.60 ST3GAL3 Sarah Leigh Mode of inheritance for gene: ST3GAL3 was changed from to BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v3.59 ST3GAL3 Sarah Leigh Added comment: Comment on phenotypes: ST3GAL3 are also associated with: Intellectual developmental disorder, autosomal recessive 12, OMIM:611090; intellectual disability, autosomal recessive 12, MONDO:0012612, however, this phenotype does not include seizures.
Early onset or syndromic epilepsy v3.59 ST3GAL3 Sarah Leigh Phenotypes for gene: ST3GAL3 were changed from Developmental and epileptic encephalopathy 15, OMIM:615006; developmental and epileptic encephalopathy, 15, MONDO:0014003; Intellectual developmental disorder, autosomal recessive 12, OMIM:611090; intellectual disability, autosomal recessive 12, MONDO:0012612 to Developmental and epileptic encephalopathy 15, OMIM:615006; developmental and epileptic encephalopathy, 15, MONDO:0014003
Early onset or syndromic epilepsy v2.593 ST3GAL3 Sarah Leigh Publications for gene: ST3GAL3 were set to 21907012; 23252400; 31584066
Early onset or syndromic epilepsy v2.592 ST3GAL3 Sarah Leigh Phenotypes for gene: ST3GAL3 were changed from Epileptic encephalopathy, early infantile, 15 to Developmental and epileptic encephalopathy 15, OMIM:615006; developmental and epileptic encephalopathy, 15, MONDO:0014003; Intellectual developmental disorder, autosomal recessive 12, OMIM:611090; intellectual disability, autosomal recessive 12, MONDO:0012612
Early onset or syndromic epilepsy v2.591 ST3GAL3 Sarah Leigh Publications for gene: ST3GAL3 were set to
Early onset or syndromic epilepsy v2.524 DROSHA Konstantinos Varvagiannis gene: DROSHA was added
gene: DROSHA was added to Genetic epilepsy syndromes. 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
Early onset or syndromic epilepsy v2.519 ADD1 Konstantinos Varvagiannis gene: ADD1 was added
gene: ADD1 was added to Genetic epilepsy syndromes. Sources: Literature
Mode of inheritance for gene: ADD1 was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Publications for gene: ADD1 were set to 34906466
Phenotypes for gene: ADD1 were set to Global developmental delay; Intellectual disability; Seizures; Ventriculomegaly; Abnormality of the corpus callosum
Penetrance for gene: ADD1 were set to unknown
Review for gene: ADD1 was set to AMBER
Added comment: A recent study suggests an ADD1-related phenotype (3 subjects with monoallelic de novo variants/1 with biallelic variants) with DD/ID and ventriculomegaly or corpus callosum dysgenesis and possibly seizures among the features.

There is currently no associated phenotype in other databases (OMIM, G2P, SysID, PanelApp Australia).

Consider inclusion in the current panel with amber / green rating (3 subjects/variants/families, role of the gene and mouse models recapitulating ventriculomegaly/CC abnormalities, relevant expression, variant studies demonstrating abn. protein levels and/or disruption of adducin heterodimer formation || monoallelic vs bi-allelic variants).

Please consider inclusion in other possibly relevant gene panels (e.g. for corpus callosum / ventriculomegaly) [ Not added ].

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Qi et al (2022 - PMID: 34906466) describe the phenotype of 3 unrelated individuals with monoallelic de novo ADD1 pathogenic variants as well as of a fourth homozygous for a missense SNV.

Overall, the authors propose a common phenotype consisting of morphological brain abnormalities (incl. ventriculomegaly and corpus callosum dysgenesis) and neurological symptoms such as DD and/or ID and attention deficit.

All individuals were investigated with singleton/trio ES.

De novo variants - phenotype:
One individual investigated for hypotonia, DD & ID, partial ACC, well controlled seizures (on ketogenic diet) and proportional short stature harbored a de novo stopgain variant (NM_014189.3:c.1418G>A / p.Trp473*) absent from gnomAD.
Another affected subject with hypotonia, FTT/feeding difficulties, mild motor delays complete ACC, a seizure (2y11m), staring spells without EEG correlate, and fatigue (with low coenz. Q10, and complex I & IV deficiency in muscle biopsy) had a de novo fs variant (NM_001119:c.2029_2039del / p.Glu680Argfs*7 - gnomAD:0) and a VUS in a gene not associated with phenotype to date.
A 3rd subject investigated for seizures (onset:1y), speech delay, mild ID, ADHD, without MRI abnormalities harbored a de novo missense SNV (NM_001119:c.670C>T / p.His224Tyr - gnomAD:0) and with cmp htz for 2 missense SPTBN2 SNV not fitting the phenotype (no ataxia).

Biallelic variants - phenotype:
One individual with ID, and ACC, abnormal sulcation, enlarged lateral and 3rd ventricles, abnormal of white matter and hypoplastic vermis upon MRI was reported to harbor in homozygosity a missense SNV (NM_001119:c.169A>T / p.Arg57Trp). There was an additional variant in a gene without associated phenotype to date and not expressed in brain.

Role of the encoded protein:
ADD1 encodes adducin 1/alpha (similar to ADD2, ADD3 encoding other adducins). As the authors note, adducins are cytoskeleton proteins critical for osmotic rigidity and cell shape. In neurons they have been reported to form membrane associated periodic ring-like structures with actin and β-spectrin. Deletion of Add1 in mice results in increased MPS ring diameter and axonal degeneration (several refs provided).

ADD1/2/3 form heterodimers which in turn form heterotetramers. ADD1 is expressed in most tissues.

Mouse model:
Previous mouse models have demonstrated that Add1 null mice have also undetectable ADD2/3 (suggesting a role for stabilization of the latter) and exhibit growth delay, anemia and develop lethal hydrocephalus and ventriculomegaly with 50% penetrance (cited PMIDs: 27068466, 18723693). Here the authors demonstrated that surviving mice had ventriculomegaly and thinning of corpus callosum thus recapitulating the respective human phenotypes. Htz mice also presented thinner CC, though not to a statistically significant extent.

ADD1 expression and isoforms:
- Performing mRNA studies and W.Blot in (developing - GW15-17) human or mouse brain (E12.5-P40) the authors demonstrated dynamic expression of ADD1 with differentially expressed isoforms, notably alternative splicing of ex10 and ex15 with NM_176801 (extended ex10, inclusion of ex15) corresponding to a neuronal isoform and NM_001119 (shorter ex10, exclusion of ex15) corresponding to a neural progenitor cell (NPC) isoform.
- Variants here reported appear to affect both isoforms with the exception of NM_001119:c.2029_2039del / p.Glu680Argfs*7 affecting only the longer NPC one.
- PTBP1 is an RNA binding protein expressed in NPCs known to suppress neuronal exon insertion. The authors demonstrated in mouse Neuro2A cells, through shRNA targeting of Ptbp1, that the latter suppresses the neuronal Add1 isoform.

Variant studies demonstrated that effect of variants was mediated by decreased protein levels and/or disruption of adducin complex formation (ADD1-ADD2 dimer formation known to be mediated by N- and C- terminal ADD1 domains):
- Expression of Arg57Trp (found in hmz in one individual) NPC and neuronal isoforms in Neuro2a cells showed that while protein levels were not significantly affected, there were (also) truncated protein products for both isoforms suggesting that aberrant splicing or protein translation/cleavage may apply.
- The authors generated HEK293FT cells for the truncating variants demonstrating decreased protein levels (using N-/C- terminal antibodies).
- Reduced (HA-tagged)-ADD1-(V5-tagged)-ADD2 protein interaction was shown to apply for the Arg57Trp and Arg473* in HEK293FT cells. Similarly in Neuro2a cells, reduced ADD1-ADD2 interaction was shown for His224Tyr.
Sources: Literature
Early onset or syndromic epilepsy v2.518 GLRA2 Konstantinos Varvagiannis gene: GLRA2 was added
gene: GLRA2 was added to Genetic epilepsy syndromes. Sources: Literature
Mode of inheritance for gene: GLRA2 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: GLRA2 were set to 20531469; 20479760; 26370147; 28588452; 35294868
Phenotypes for gene: GLRA2 were set to Global developmental delay; Intellectual disability; Autism; Behavioral abnormality; Seizures; Microcephaly; Abnormality of eye movement
Penetrance for gene: GLRA2 were set to unknown
Mode of pathogenicity for gene: GLRA2 was set to Other
Review for gene: GLRA2 was set to AMBER
Added comment: Heterozygous or hemizygous pathogenic GLRA2 variants cause Intellectual developmental disorder, X-linked, syndromic, Pilorge type (# 301076) as summarized in a recent OMIM entry.

The phenotype is characterized by DD with variably impaired intellectual development, behavioral abnormalities (autistic features in some), variable ocular findings (nystagmus, strabismus, oculomotor apraxia) and seizures in some [ 6/13 in Ref4 ].

GLRA2 encodes the α2 subunit that is expressed in embryonic and perinatal CNS with expression decreasing after birth.

Animal models support the role of the gene in CNS.

Studies have been performed for several of the variants reported to date (in all cases missense and a htz deletion of the last 2 exons).

As summarized by OMIM, most affected females carry de novo htz missense GoF variants, and most affected males inherited hemizygous LoF ones.

XCI has not been studied in most htz (affected/unaffected) females (with the exception of the del in Ref2, see also Ref3).

Details provided below.

(Note: Most articles refer to variants using HGVS nomenclature while few without incl. the signal peptide eg. p.Arg350Leu corresponding to Arg323Leu).

Consider inclusion in the current panel with amber/green rating.


[1]----
Piton et al (2011 - PMID: 20479760) sequenced 111 X-linked synaptic genes in a cohort of 142 individuals with ASD and identified a female (S00125) harboring Arg350Leu (NM_002063 chrX:14618871 G/T), inherited from her mother (no clinical information provided). Functional evaluation of the variant was performed in a later publication (Ref3), providing additional clinical details on the proband.

[2]----
Pilorge et al (2016 - PMID: 26370147) review the role of glycine receptors (GlyRs). These typically consist of pentameric combinations of alpha (α1-α4) and beta (β) subunits and form a pore that controls transmembrane flux of chloride. GlyRs can be formed either as homomers comprising five α subunits or as heteromers of α and β subunits (in 2:3 or 3:2 stoichiometry). Each subunit has an N-terminal extracellular domain with the ligand-binding site and 4 transmembrane domains. GLRA2 encodes the α2 subunit that is expressed in embryonic and perinatal CNS with expression decreasing after birth. The authors discuss the role of glycine as inhibitory neurotransmitter in adult CNS and depolarizing/excitatory action in immature neurons, as well as the role of GlyR α2 in proliferation and neuronal migration during cortical development.

The authors previously (2010 - PMID: 20531469) identified a boy with ASD, language delay and low average IQ (verbal 93, performance 75, full-scale IQ 82) harboring a 142 kb microdeletion spanning the last 2 exons of GRLA2 (hg19 - chrX:14693216-14836199). This CNV was confirmed with qPCR and the breakpoints localized to intron 7 after sequencing. Reverse transcription of mRNA from blood revealed presence of a truncated transcript in the child suggestive of little or no NMD. In the mother, the non-truncated transcript was amplified. Further it was shown that the product leaded to incorporation of intron 7, with inclusion of 5 residues followed by a stop codon. The mother had a normal, non-skewed XCI. Previous testing had excluded an FMR1 expansion.

Screening of 400 males with ASD identified a further male with de novo missense SNV (NM_002063.3:c.458G>A / p.Arg153Gln). This child had non-syndromic autism, severe language delay, mild ID (fs IQ 63) and GTC seizures with onset at 18y. Previous testing incl. a normal karyotype, FMR1 analysis, and CMA. The boy had an older sister with ASD, not harboring the same GLRA2 variant (interpreted in the context of intrafamilial genetic heterogeneity for ASD).

The authors also studied a dn missense variant (NM_001118886.1:c.407A>G / p.Asn136Ser) previously reported in a proband with autism (11842.p2 - Iossifov et al, 2014 - PMID: 25363768).

In vitro studies demonstrated that the 3 aforementioned variants impaired GlyR2 α2 function:
- The authors generated constructs for wt, the deletion (of last 2 exons) and Arg153Gln and performed co-transfection with EGFP cDNA in Chinese hamster ovary (CHO) cells. While wt and Arg153Gln were observed at the plasma membrane of transfected cells, the del was undetectable at the cell surface and was mislocalized in the cytoplasm (as also expected by loss of the transmembrane domains).
- Upon isolation of biotinylated surface receptors and western blot, Arg153Gln was shown to result to 56% decreased surface expression compared to wt, while the intracellular fragment was also reduced by 32% suggesting impaired synthesis or degradation. Asn136Ser had 67% lower surface (and 15% lower intracellular) expression.
- Whole-cell patch clamp recordings of transfected CHO cells suggested that the minimum concentration of glycine to evoke whole-cell current was ~100 higher for Arg153Gln compared to wt. High concentrations of glycine were unable to evoke any current in the case of the deletion (due to loss of surface expression). Asn136Ser also reduced glycine sensitivity (14x increase in EC50).

Zebrafish studies for glra2 and the del or Arg153Gln variants:
Morpholino mediated knockdown of glra2 led to hyperbranching of spinal motor axons compared to ctrls. Co-injection of human wt mRNA with glra2 morpholino, rescued the aberrant branching phenotype which was not the case for the 2 variants.

Glra2 ko mouse model (also on chrX):
- Mutant mice (Glra2-/Y) had normal adult body, brain weight, were fertile and had a normal lifespan. They displayed no differences in locomotor activity, or social behavior compared to wt. They however exhibited impaired learning and memory in the novel object recognition task (spatial learning and memory in the novel location recognition task and Morris water maze were N).
- Long-term potentiation in prefrontal cortex after high frequency stimulation was significantly impaired in mutant mice compared to wt, overall supporting that impaired glycinergic signaling results in abnormal synaptic plasticity in this relevant for ASD region.

[3]----
Zhang et al (2017 - PMID: 28588452) determined the functional effects of Arg350Leu which was reported by Piton et al (Arg323Leu without the signal peptide).

The authors provide further clinical details on this female with autism, macrocephaly, loss of acquired words, seizures, mild motor delay and hypothyroidism. The mother of the, also carrier of the SNV, was reportedly unaffected.

The potency of glycine in activating recombinant homomeric α2 and heteromeric α2β receptors was examined by whole-cell patch-clamp recording (HEK293 cells).

In homo-/ and heteromeric receptors this variant resulted in small decrease in glycine sensitivity with peak currents not significantly different compared to wt (the latter suggestive of normal surface expression).

This variant resulted in prolonged inhibitory postsynaptic currents (IPSCs) with ~2-fold slower rise and decay times, while IPSC amplitude did not differ significantly. Overall, the slowed decay times, prolongation of active periods and small but significantly increased conductance of mutant channels suggested that this variant exerts a gain-of-function effect.

The authors briefly cite a study by Cotton et al (2015, PMID: 25381334) providing evidence that GLRA2 escapes XCI in the vast majority of tissues and brain.

[4]----
Marcogliese et al (2022 - PMID: 35294868) functionally tested the effects of missense DNM observed in individuals with ASD diagnosis in Drosophila. The authors generated TG4 (MiMIC cassette) fly mutants for candidate ASD genes (creating LoF alleles for the respective genes). Using a GAL4/UAS system with human cDNA constructs for reference/variants they performed the rescue/overexpression assays to study the functional consequences.

Flies expressing human ref GLRA2 cDNA failed to copulate but exhibited normal movement. Flies for Asn136Ser (a variant reported by Iossifov et al, 2014 - PMID: 25363768) copulated similar to the TG4 mutant providing evidence for a LoF effect of this variant.

Upon GAL4/UAS expression and co-staining with neuronal (Elav) and glial (Repo) nuclear markers, GLRA2 was shown to be expressed in CNS with expression in a subset of neurons and in some glia.

Upon ubiquitous overexpression of human reference or variant cDNA, Asn136Ser also behaved as a LoF allele.

Based on the evidence on this gene, and following re-analyses of exome data, GeneMatcher collaborations etc, the authors identified 13 additional unrelated subjects harboring GLRA2 variants (8 females/5 males). These had DD/ID of variable severity (13/13) w/wo autistic features (in 4 or 5), microcephaly (4-5/13 all females), epilepsy (6/13 - both sexes) and ocular manifestations (10/13 - incl. nystagmus, strabismus, etc). Hypotonia/incoordination was observed in 7/13.

All females had dn missense variants (8/8, NM_001118886.1:c.887C>T/p.Thr296Met in 6/8, others: c.140T>C/p.Phe47Ser, c.777C>G/p.Ile259Met), while all males had inherited missense SNVs from their unaffected mothers (p.Arg252Cys, p.Ala288Thr, p.Pro396Thr, p.Pro400Leu, p.Arg445Gln).

The authors studied an variant which was recurrent in females (Thr296Met) and another found in a male (Arg252Cys). Upon overexpression, the latter behaved - similarly to Asn136Ser - as LoF allele, while Thr296Met did not differ significantly from reference.

Structural modeling suggested that Thr296 is adjacent to a residue important for keeping the ion pore in closed conformation.

Upon pnr-GAL4 (over)expression in the dorsolateral stripe in the notum, Thr296Met caused lethality, which was not the case for the reference. When expressed at lower levels, Thr296Met formation of melanized nodules in thorax, a phenotype not previously observed upon overexpression of ref/other variants.

The authors performed ERGs in fly eyes. They first used a pan-neuronal driver (nSyb-GAL) leading to GLRA2 ref / variant expression in pre-synaptic photoreceptors and post-synaptic neurons. A significant increase of "OFF" transients was observed for Thr296Met, suggesting increase in synaptic transmission and a GoF effect. Expression limited to pre-synaptic photoreceptors (Rh1-GAL4 driver) did not lead to significant differences compared to ref allele, while Arg252Cys was associated with decreased amplitudes of "OFF" transients, suggestive of decreased synaptic transmission and confirming a LoF effect.

Marcogliese et al conclude that reduced GLRA2 activity can lead to disease in males but can be tolerated in htz females (as was the case for asymptomatic mothers), while GoF variants leading to overactivation of the channel could be overrepresented in affected females.
Sources: Literature
Early onset or syndromic epilepsy v2.507 HEPACAM Arina Puzriakova Phenotypes for gene: HEPACAM were changed from Megalencephalic leukoencephalopathy with subcortical cysts 2A, 613925 to Megalencephalic leukoencephalopathy with subcortical cysts 2A, OMIM:613925
Early onset or syndromic epilepsy v2.491 GALNT2 Sarah Leigh Tag for-review was removed from gene: GALNT2.
Early onset or syndromic epilepsy v2.491 GALNT2 Sarah Leigh commented on gene: GALNT2: The rating of this gene has been updated following NHS Genomic Medicine Service approval.
Early onset or syndromic epilepsy v2.490 GALNT2 Sarah Leigh Source Expert Review Green was added to GALNT2.
Rating Changed from Amber List (moderate evidence) to Green List (high evidence)
Early onset or syndromic epilepsy v2.463 COLGALT1 Ivone Leong Tag Q4_21_rating was removed from gene: COLGALT1.
Tag watchlist tag was added to gene: COLGALT1.
Early onset or syndromic epilepsy v2.463 COLGALT1 Ivone Leong gene: COLGALT1 was added
gene: COLGALT1 was added to Genetic epilepsy syndromes. Sources: Expert Review Amber,Literature
Q4_21_rating tags were added to gene: COLGALT1.
Mode of inheritance for gene: COLGALT1 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: COLGALT1 were set to 30412317; 33709034; 31759980
Phenotypes for gene: COLGALT1 were set to Brain small vessel disease 3, OMIM:618360
Early onset or syndromic epilepsy v2.409 GALC Arina Puzriakova Phenotypes for gene: GALC were changed from Krabbe disease, 245200; seizures; CALC deficiency; Galactosylceramide beta-galactosidase deficiency to Krabbe disease, OMIM:245200
Early onset or syndromic epilepsy v2.287 GALNT2 Sarah Leigh commented on gene: GALNT2: For-review tag has been added to highlight whether this gene should be green on this panel due to the uncoupling of metabolic genes from Genetic epilepsy syndromes panel.
Early onset or syndromic epilepsy v2.283 GALNT2 Sarah Leigh Phenotypes for gene: GALNT2 were changed from Congenital disorder of glycosylation, type IIt 618885 to Congenital disorder of glycosylation, type IIt OMIM:618885
Early onset or syndromic epilepsy v2.281 GALNT2 Helen Lord reviewed gene: GALNT2: Rating: GREEN; Mode of pathogenicity: None; Publications: 32293671, 27508872; Phenotypes: ; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v2.163 USP18 Arina Puzriakova gene: USP18 was added
gene: USP18 was added to Genetic epilepsy syndromes. Sources: Literature
treatable, for-review tags were added to gene: USP18.
Mode of inheritance for gene: USP18 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: USP18 were set to 12833411; 27325888; 31940699
Phenotypes for gene: USP18 were set to Pseudo-TORCH syndrome 2, 617397
Review for gene: USP18 was set to GREEN
Added comment: - PMID: 27325888 (2016) - Three sibs from a consanguineous Turkish family with a homozygous variant (c.652C>T, p.Q218X) in USP18. Antenatal presentation in one sib led to termination of pregnancy at 22 wk of gestation, and in the remaining two children presentation was neonatal and resulted in death within 2 weeks of life. In the latter two individuals manifestations included severe intracerebral haemorrhages, liver dysfunction, ascites, and lactic acidosis. One sib additionally had severe thrombocytopenia with petechiae, while the other developed seizures.

Two German sibs, previously reported in PMID: 12833411 (2013), were found to be compound het for the same p.Q218X variant and a cryptic 3-prime deletion of the USP18 gene. They presented thrombocytopenia, petechiae, ascites, hepatomegaly, and systemic calcifications. Within the first days of life, they developed seizures and died from severe cerebral haemorrhage.

Haplotype analysis of the region containing the Q218X mutation suggested a common ancestor between the 2 families and a founder effect.

- PMID: 31940699 (2020) - One Saudi Arabian boy with a homozygous splice-site variant (c.1073+1G>A) in USP18, presented hydrocephalus with seizures, intraventricular haemorrhage, brain calcifications, necrotizing cellulitis, systemic inflammation, multiple organ failure, and respiratory failure. This was the only patient to survive beyond the perinatal period owing to supportive care and prompt treatment with ruxolitinib. At the time of publication, the child was 3-years-old and was in full remission of clinical manifestations while continuing to receive oral ruxolitinib. He continues to grow normally, however authors note delay in developmental milestones.
Sources: Literature
Early onset or syndromic epilepsy v2.118 GALNT2 Sarah Leigh Classified gene: GALNT2 as Amber List (moderate evidence)
Early onset or syndromic epilepsy v2.118 GALNT2 Sarah Leigh Gene: galnt2 has been classified as Amber List (Moderate Evidence).
Early onset or syndromic epilepsy v2.117 GALNT2 Sarah Leigh gene: GALNT2 was added
gene: GALNT2 was added to Genetic epilepsy syndromes. Sources: Literature
for-review tags were added to gene: GALNT2.
Mode of inheritance for gene: GALNT2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: GALNT2 were set to 27508872; 32293671
Phenotypes for gene: GALNT2 were set to Congenital disorder of glycosylation, type IIt 618885
Review for gene: GALNT2 was set to GREEN
Added comment: Associated with relevant phenotype in OMIM, but not associated with phenotype in Gen2Phen. At least 5 variants reported in at least 5 unrelated cases, together with mouse and rat models (PMID 27508872;32293671).
Sources: Literature
Early onset or syndromic epilepsy v2.62 TUBA8 Rebecca Foulger commented on gene: TUBA8: Reviewing 2020 review comment by Zornitza noting additional publication: PMID:31481326. PMID:31481326. Lee et al., 2020 used targeted gene sequencing to identify malformations of cortical development in 81 patients. A homozygous TUBA8 p.Asn356ProfsTer63 variant was identified in one patient with 'Polymicrogyria, agenesis of CC, ventriculomegaly'. All patients had a confirmed diagnosis of epilepsy or DD.
Early onset or syndromic epilepsy v2.25 PTEN Rebecca Foulger changed review comment from: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call Thursday 8th August 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed to demote AKT1 from Green to Red. This panel is not the appropriate test for somatic variant detection due to the coverage. R110 Segmental overgrowth disorders (panel #98) should be used where megalencephaly is present to allow detection of somatic mosaic mutations.; to: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call Thursday 8th August 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed to demote PTEN from Green to Red. This panel is not the appropriate test for somatic variant detection due to the coverage. R110 Segmental overgrowth disorders (panel #98) should be used where megalencephaly is present to allow detection of somatic mosaic mutations.
Early onset or syndromic epilepsy v2.0 ST3GAL3 Zornitza Stark edited their review of gene: ST3GAL3: Added comment: Additional family reported recently with seizure phenotype.; Changed rating: AMBER; Changed publications: 23252400, 31584066
Early onset or syndromic epilepsy v1.497 OXR1 Konstantinos Varvagiannis gene: OXR1 was added
gene: OXR1 was added to Genetic epilepsy syndromes. 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
Early onset or syndromic epilepsy v1.425 DMXL2 Konstantinos Varvagiannis changed review comment from: This gene can be considered for inclusion in both ID and epilepsy panels probably with green (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) or amber rating.

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 constant 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.
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[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).
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[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) .
Sources: Literature; to: This gene can be considered for inclusion in both ID and epilepsy panels probably with green (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) or amber rating.

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 constant 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.
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[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).
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[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) .
Sources: Literature
Early onset or syndromic epilepsy v1.425 DMXL2 Konstantinos Varvagiannis gene: DMXL2 was added
gene: DMXL2 was added to Genetic epilepsy syndromes. Sources: Literature
Mode of inheritance for gene: DMXL2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown
Publications for gene: DMXL2 were set to 25248098; 30237576; 31688942; 30732576
Phenotypes for gene: DMXL2 were set to Epileptic encephalopathy, early infantile, 81, MIM 618663; ?Polyendocrine-polyneuropathy syndrome, MIM 616113
Penetrance for gene: DMXL2 were set to unknown
Review for gene: DMXL2 was set to GREEN
Added comment: This gene can be considered for inclusion in both ID and epilepsy panels probably with green (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) or amber rating.

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 constant 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) .
Sources: Literature
Early onset or syndromic epilepsy v1.411 GFM1 Rebecca Foulger commented on gene: GFM1: PMID:21986555. Galmiche et al., 2012 report two unrelated patients with homozygous GFM1 variants (R671C). The parents were both heterozygous for this variant For the first patient (an Algerian boy from consanguineous parents), no clinical seizures were noted but EEG showed burst of multifocal spikes.
Early onset or syndromic epilepsy v1.357 CCND2 Rebecca Foulger Phenotypes for gene: CCND2 were changed from to Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 3, 615938
Early onset or syndromic epilepsy v1.351 APC2 Konstantinos Varvagiannis gene: APC2 was added
gene: APC2 was added to Genetic epilepsy syndromes. 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; 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: APC2 were set to Complete
Review for gene: APC2 was set to AMBER
Added comment: This gene was reviewed for the ID panel (details below).

It could be also be considered for inclusion in the epilepsy panel as amber/green.

[Seizures in 8/14 individuals (generalized tonic-clonic/myoclonic, onset 3m - 6yrs) although some individuals were too young when last examined (eg. 8m) and sibs in one family (F7) were discordant for this feature at the ages of 4y7m (+) and 6y (-). Lissencephaly is often associated with seizures which have occasionally been observed in Apc2-deficient mice (PMID cited: 22573669)].

-----

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.

In OMIM, the APC2-related phenotype is ?Sotos syndrome 3 (MIM 617169 - AR). G2P does not have any associated phenotype for this gene.

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]
Sources: Literature
Early onset or syndromic epilepsy v1.235 PIK3CA Rebecca Foulger commented on gene: PIK3CA: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call Thursday 8th August 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed to demote PIK3CA from Green to Red. This panel is not the appropriate test for somatic variant detection due to the coverage. R110 Segmental overgrowth disorders (panel #98) should be used where megalencephaly is present to allow detection of somatic mosaic mutations.
Early onset or syndromic epilepsy v1.234 PTEN Rebecca Foulger commented on gene: PTEN: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call Thursday 8th August 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed to demote AKT1 from Green to Red. This panel is not the appropriate test for somatic variant detection due to the coverage. R110 Segmental overgrowth disorders (panel #98) should be used where megalencephaly is present to allow detection of somatic mosaic mutations.
Early onset or syndromic epilepsy v1.233 AKT1 Rebecca Foulger commented on gene: AKT1: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call Thursday 8th August 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed to demote AKT1 from Green to Red. This panel is not the appropriate test for somatic variant detection due to the coverage. R110 Segmental overgrowth disorders (panel #98) should be used where megalencephaly is present to allow detection of somatic mosaic mutations.
Early onset or syndromic epilepsy v1.191 GAL Rebecca Foulger Source Wessex and West Midlands GLH was added to GAL.
Early onset or syndromic epilepsy v1.191 ST3GAL3 Rebecca Foulger Source Wessex and West Midlands GLH was added to ST3GAL3.
Early onset or syndromic epilepsy v1.191 ST3GAL5 Rebecca Foulger Source Wessex and West Midlands GLH was added to ST3GAL5.
Early onset or syndromic epilepsy v1.191 GALC Rebecca Foulger Source Wessex and West Midlands GLH was added to GALC.
Early onset or syndromic epilepsy v1.190 GAL Rebecca Foulger Source NHS GMS was added to GAL.
Early onset or syndromic epilepsy v1.190 ST3GAL3 Rebecca Foulger Source NHS GMS was added to ST3GAL3.
Early onset or syndromic epilepsy v1.190 ST3GAL5 Rebecca Foulger Source NHS GMS was added to ST3GAL5.
Early onset or syndromic epilepsy v1.190 GALC Rebecca Foulger Source NHS GMS was added to GALC.
Early onset or syndromic epilepsy v1.189 GAL Rebecca Foulger reviewed gene: GAL: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance:
Early onset or syndromic epilepsy v1.189 ST3GAL3 Rebecca Foulger reviewed gene: ST3GAL3: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance:
Early onset or syndromic epilepsy v1.189 ST3GAL5 Rebecca Foulger reviewed gene: ST3GAL5: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance:
Early onset or syndromic epilepsy v1.189 GALC Rebecca Foulger reviewed gene: GALC: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance:
Early onset or syndromic epilepsy v1.188 GAL Tracy Lester reviewed gene: GAL: Rating: AMBER; Mode of pathogenicity: ; Publications: 21716262, 25691535 ; Phenotypes: ?Epilepsy, familial temporal lobe, 8, 616461 ; Mode of inheritance: MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Early onset or syndromic epilepsy v1.188 ST3GAL3 Tracy Lester reviewed gene: ST3GAL3: Rating: AMBER; Mode of pathogenicity: ; Publications: 21907012; Phenotypes: ?Epileptic encephalopathy, early infantile, 15, 615006 , Mental retardation 12, 611090 ; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 CCND2 Tracy Lester reviewed gene: CCND2: Rating: RED; Mode of pathogenicity: ; Publications: 24705253; Phenotypes: Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 3, 615938; Mode of inheritance: MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Early onset or syndromic epilepsy v1.188 WDR73 Tracy Lester reviewed gene: WDR73: Rating: GREEN; Mode of pathogenicity: ; Publications: 30315938, 20083416 ; Phenotypes: Galloway-Mowat syndrome 1, 251300; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 ST3GAL5 Tracy Lester reviewed gene: ST3GAL5: Rating: GREEN; Mode of pathogenicity: ; Publications: 15502825, 22990144, 24026681 ; Phenotypes: Salt and pepper developmental regression syndrome, 609056; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 RNASET2 Tracy Lester reviewed gene: RNASET2: Rating: GREEN; Mode of pathogenicity: ; Publications: 19525954; Phenotypes: Leukoencephalopathy cystic without megalencephaly, 612951; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 PTEN Tracy Lester reviewed gene: PTEN: Rating: GREEN; Mode of pathogenicity: ; Publications: 11726927, 12085208, 11726926 ; Phenotypes: Cowden syndrome, 158350, Lhermitte-Duclos syndrome, 158350, Macrocephaly/autism syndrome, 605309, VATER association with macrocephaly and ventriculomegaly, 276950, {Glioma susceptibility 2}, 613028, {Meningioma}, 607174, ; Mode of inheritance: BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 PIK3R2 Tracy Lester reviewed gene: PIK3R2: Rating: GREEN; Mode of pathogenicity: ; Publications: 26860062; Phenotypes: Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome, 603387; Mode of inheritance: MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Early onset or syndromic epilepsy v1.188 MTR Tracy Lester reviewed gene: MTR: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: Homocystinuria-megaloblastic anemia, cblG complementation type, 250940; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 MLC1 Tracy Lester reviewed gene: MLC1: Rating: GREEN; Mode of pathogenicity: ; Publications: 29466841; Phenotypes: Megalencephalic leukoencephalopathy with subcortical cysts, 604004; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 HEPACAM Tracy Lester reviewed gene: HEPACAM: Rating: GREEN; Mode of pathogenicity: ; Publications: 21419380; Phenotypes: Megalencephalic leukoencephalopathy with subcortical cysts 2A, 613925, Megalencephalic leukoencephalopathy with subcortical cysts 2B, remitting, with or without mental retardation, 613926; Mode of inheritance: BOTH monoallelic and biallelic, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 GALC Tracy Lester reviewed gene: GALC: Rating: GREEN; Mode of pathogenicity: ; Publications: 25260228; Phenotypes: Krabbe disease, 245200; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.188 AKT3 Tracy Lester reviewed gene: AKT3: Rating: GREEN; Mode of pathogenicity: ; Publications: 21159799, 22729224 ; Phenotypes: Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome, 615937; Mode of inheritance: MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted
Early onset or syndromic epilepsy v1.188 STRADA Tracy Lester reviewed gene: STRADA: Rating: GREEN; Mode of pathogenicity: ; Publications: 17522105, 23616120, 27170158 ; Phenotypes: Polyhydramnios, megalencephaly, and symptomatic epilepsy, 611087; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v1.125 HEXB Rebecca Foulger commented on gene: HEXB: PMID:28553389: Gowda et al., 2017 report a 1 year old boy with Sanhoff disease without hepatosplenomegaly, and a homozygous missense variant in HEXB (p.Cys534Tyr). The boy suffered from focal seizures from 11 months. A sibling died age 18 months with 'similar complaints'. Further controls or segregation analysis was not performed. The authors say the same variant was reported previously in a Japanese case which showed myoclonic epilepsy and hepatosplenomegaly (PMID:7626071).
Early onset or syndromic epilepsy v0.1350 MTR Louise Daugherty Phenotypes for gene: MTR were changed from Homocystinuria-megaloblastic anemia, cblG complementation type, 250940; seizures to Homocystinuria-megaloblastic anemia, cblG complementation type, 250940; methionine synthase deficiency type cblG; seizures
Early onset or syndromic epilepsy v0.1349 MTR Louise Daugherty Phenotypes for gene: MTR were changed from to Homocystinuria-megaloblastic anemia, cblG complementation type, 250940; seizures
Early onset or syndromic epilepsy v0.1290 MLC1 Rebecca Foulger commented on gene: MLC1: In a woman with megalencephalic leukoencephalopathy with subcortical cysts-1 (MLC1; 604004), Lopez-Hernandez et al. (2011, PMID:21624973) identified a homozygous misssense 206C-T variant in the MLC1 gene (p.S69L). The patient had epilepsy amongst her symptoms.
Early onset or syndromic epilepsy v0.1287 MLC1 Rebecca Foulger Phenotypes for gene: MLC1 were changed from Megalencephalic leukoencephalopathy with subcortical cysts, 604004 to Megalencephalic leukoencephalopathy with subcortical cysts, 604004; generalized tonic-clonic seizures; focal seizures
Early onset or syndromic epilepsy v0.1285 MLC1 Rebecca Foulger Phenotypes for gene: MLC1 were changed from to Megalencephalic leukoencephalopathy with subcortical cysts, 604004
Early onset or syndromic epilepsy v0.1245 RNASET2 Sarah Leigh Phenotypes for gene: RNASET2 were changed from to Leukoencephalopathy, cystic, without megalencephaly 612951
Early onset or syndromic epilepsy v0.1058 PIK3CA Eleanor Williams Phenotypes for gene: PIK3CA were changed from to Megalencephaly-capillary malformation-polymicrogyria syndrome, somatic 602501
Early onset or syndromic epilepsy v0.1051 GALC Louise Daugherty Marked gene: GALC as ready
Early onset or syndromic epilepsy v0.1051 GALC Louise Daugherty Gene: galc has been classified as Green List (High Evidence).
Early onset or syndromic epilepsy v0.1051 GALC Louise Daugherty Classified gene: GALC as Green List (high evidence)
Early onset or syndromic epilepsy v0.1051 GALC Louise Daugherty Gene: galc has been classified as Green List (High Evidence).
Early onset or syndromic epilepsy v0.1049 GALC Louise Daugherty Publications for gene: GALC were set to
Early onset or syndromic epilepsy v0.1048 GALC Louise Daugherty Mode of inheritance for gene: GALC was changed from to BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v0.1047 GALC Louise Daugherty Phenotypes for gene: GALC were changed from to Krabbe disease, 245200; seizures; CALC deficiency; Galactosylceramide beta-galactosidase deficiency
Early onset or syndromic epilepsy v0.1037 GAMT Louise Daugherty Added comment: Comment on phenotypes: Not added the expert review phenotype Krabbe disease as it related to the previously reviewed gene GALC. Cerebral creatine deficiency syndrome 2, 612736 is the disorder associated to variants of this gene, and is relevant for inclusion on the Genetic Epilepsy Syndromes panel
Early onset or syndromic epilepsy v0.875 HEPACAM Ivone Leong Added comment: Comment on list classification: Promoted from amber to green based on evidence in the literature. One study (PMID: 21419380) reported 8 families with 10 patients with either homozygous or compound heterozygous variants in this gene having epilepsy. Another study (PMID: 27389245) reported on a patient with a homozygous variant in this gene having generalized tonic-clonic seizure.
Megalencephalic leukoencephalopathy with subcortical cysts 2A confirmed to be associated with this gene on OMIM but not Gene2Phenotype.
Early onset or syndromic epilepsy v0.863 HEPACAM Ivone Leong Phenotypes for gene: HEPACAM were changed from to Megalencephalic leukoencephalopathy with subcortical cysts 2A, 613925
Early onset or syndromic epilepsy v0.833 FGFR3 Louise Daugherty Added comment: Comment on phenotypes: added additional relevant phenotype Muenke syndrome Millichap, J.G., 2012. Epilepsy in Muenke Syndrome. Pediatric Neurology Briefs, 26(12), pp.93–93. DOI: http://doi.org/10.15844/pedneurbriefs-26-12-6 : A review of 789 published cases of Muenke syndrome with neurological complications identified epilepsy in 6 cases, with intracranial anomalies in 5. The intracranial anomalies were agenesis of the corpus callosum, hemimegalencephaly, and porencephaly. In the review of 58 patients with Muenke syndrome in the Washington, DC cohort, 7 (12%) had epilepsy and 4 survived neonatal apnea. Patients with Muenke syndrome should be monitored for apnea and seizures.
Early onset or syndromic epilepsy v0.588 PIK3R2 Sarah Leigh Phenotypes for gene: PIK3R2 were changed from to Megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 1 603387
Early onset or syndromic epilepsy v0.573 ST3GAL5 Sarah Leigh Publications for gene: ST3GAL5 were set to
Early onset or syndromic epilepsy v0.572 ST3GAL5 Sarah Leigh Mode of inheritance for gene: ST3GAL5 was changed from to BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy v0.571 ST3GAL5 Sarah Leigh Phenotypes for gene: ST3GAL5 were changed from to Salt and pepper developmental regression syndrome 609056
Early onset or syndromic epilepsy v0.570 ST3GAL5 Sarah Leigh Classified gene: ST3GAL5 as Green List (high evidence)
Early onset or syndromic epilepsy v0.570 ST3GAL5 Sarah Leigh Gene: st3gal5 has been classified as Green List (High Evidence).
Early onset or syndromic epilepsy v0.514 PEX10 Sarah Leigh gene: PEX10 was added
gene: PEX10 was added to Genetic Epilepsy Syndromes. Sources: Literature
Mode of inheritance for gene: PEX10 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: PEX10 were set to 20695019
Phenotypes for gene: PEX10 were set to Peroxisome biogenesis disorder 6A (Zellweger) 614870
Review for gene: PEX10 was set to GREEN
Added comment: Associated with phenotypes in OMIM and confirmed in Gen2Phen. At least 4 variants in Peroxisome biogenesis disorder 6A (Zellweger) 614870 in at least 2 cases which includes hepatomegaly (according to Gen2Phen). Seizures are a major feature of this phenotype (clinical fellow Arianna Tucci).
Sources: Literature
Early onset or syndromic epilepsy v0.505 ST3GAL5 Sarah Leigh Marked gene: ST3GAL5 as ready
Early onset or syndromic epilepsy v0.505 ST3GAL5 Sarah Leigh Gene: st3gal5 has been classified as Amber List (Moderate Evidence).
Early onset or syndromic epilepsy v0.485 GAL Sarah Leigh Marked gene: GAL as ready
Early onset or syndromic epilepsy v0.485 GAL Sarah Leigh Gene: gal has been classified as Red List (Low Evidence).
Early onset or syndromic epilepsy v0.470 ST3GAL3 Sarah Leigh Marked gene: ST3GAL3 as ready
Early onset or syndromic epilepsy v0.470 ST3GAL3 Sarah Leigh Gene: st3gal3 has been classified as Amber List (Moderate Evidence).
Early onset or syndromic epilepsy ST3GAL5 Zornitza Stark reviewed gene: ST3GAL5
Early onset or syndromic epilepsy ST3GAL3 Zornitza Stark reviewed gene: ST3GAL3
Early onset or syndromic epilepsy GALC Zornitza Stark reviewed gene: GALC
Early onset or syndromic epilepsy GAL Sarah Leigh classified GAL as Red List (low evidence)
Early onset or syndromic epilepsy GAL Sarah Leigh Added gene to panel