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| Early onset or syndromic epilepsy v2.518 | PABPC1 |
Konstantinos Varvagiannis gene: PABPC1 was added gene: PABPC1 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: PABPC1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: PABPC1 were set to 35511136 Phenotypes for gene: PABPC1 were set to Global developmental delay; Expressive language delay; Intellectual disability; Behavioral abnormality; Seizures Penetrance for gene: PABPC1 were set to unknown Review for gene: PABPC1 was set to AMBER Added comment: Wegler et al (2022 - PMID: 35511136) describe the phenotype of 4 individuals with de novo variants in the PABP domain of PABPC1. Overlapping features included DD (4/4) with weak expressive language (4/4), learning disability/borderline intellectual functioning (in 2) to more severe ID (in 2 others), treatable/self-limiting seizures (in 3 for whom this information was available) as well as variable behavioral issues (impaired social skills, concentration/sleeping problems, ADHD, anxiety or autism). Other features involved feeding difficulties (3/4), hearing impairment (in 2/3) or variable other phenotypes. Contribution of de novo variants found in other genes was thought possible. All 4 were investigated by trio exome sequencing following negative previous routine diagnostic work-up. WES revealed heterozygous de novo PABPC1 variants, 3 of which were missense SNVs (c.1687G>A/p.Gly563Ser, c.1691A>C/p.Glu564Gly, c.1709T>C/p.Ile570Thr using NM_002568.3) and a fourth an in-frame deletion (c.1664_1666del/p.Pro555del). Additional de novo variants were reported in 3 cases (IGF2R missense SNV, htz KDM5B stopgain, RBBP4 - the latter not associated with any phenotype to date). PABPC1 encodes Polyadenylate-binding protein, cytoplasmic, 1 which as the authors summarize has an important role overall in regulation of gene expression (poly(A) tail length, mRNA formation, export of processed mRNAs to cytoplasm, translation initiation promotion and termination, mRNA stability, NMD). Translation is regulated by Polyadenylate-binding protein–interacting proteins (PAIPs) which control PABP activity. PAIP2 in particular, which is highly expressed in CNS, is known to inhibit translation via binding to the PABP domain of PABPC1 and is thought to play an important role through transcriptional regulation for synaptic plasticity and memory. To evaluate plausibility as a DD gene the authors performed analyses using publicly available data, with PABPC1 ranking high in terms of protein-protein interaction (PPI) and co-expression with known DD genes. Variants were absent from gnomAD with in silico predictions in favour of a deleterious effect. While PABPC1 is intolerant to both missense and LoF variants (z-score 4.49, pLI of 1), occurrence of these 4 dn variants and their clustering in the PABP domain appeared to be of statistical significance (p=0.002 and p=2.8x10-8) rather than being explained by random occurrence. Structural modeling of variants suggested that all were in close spatial vicinity within the PABP domain, likely influencing PAIP2 binding. In HeLa cells the variants were shown not to affect subcellular localization (to the cytoplasm) compared to wt. In addition, there were no significant differences upon stress conditions under which the protein localizes to stress granules. In HeLa cells, co-immunoprecipitation assays using C-terminal HA tagged PABPC1, revealed that 3 variants (Gly563Ser, Glu564Gly, Ile570Thr) significantly reduced physical PABPC1-PAIP2 interaction compared with wt, which was also observed though to a not significant extent for Pro555del. (Other variants from literature also studied as discussed below). Pabpc1 is highly expressed in all regions of the developing mouse brain with remarkable decrease after birth, suggesting a critical role in prenatal brain development. Through electroporation with Pabpc1-directed shRNA the authors provided evidence that Pabpc1 LoF results in abnormal neural progenitor cell proliferation with rescue experiments using human WT or missense variants (Gly563Ser, Glu564Gly, Ile570Thr) showing that only the WT could rescue the proliferation phenotype. Overall a model whereby weakened PABPC1-PAIP2 interaction, leading to dysregulation to gene expression homeostasis and interference with proliferation of neural progenitors and the later to the NDD phenotype is proposed. Given previous reports in the literature for de novo PABPC1 variants, namely Lys138Glu, Asp204Val, Arg481His, Pro456Leu the authors noted that the phenotypes reported in the respective individuals were rather explained by other variants (16p11.2 dup, ARID1A dn, TBL1XR1 dn variants). These PABPC1 variants do not lie in the PABP domain, have lower in silico pathogenicity scores (MPC/CADD), with structural modelling suggestive of no significant effect. Importantly, upon co-immunoprecipitation studies with PAIP2 which were here performed, these variants had no effect. Pathogenicity of these variants - not located within the PABP domain - through another mechanism cannot be however ruled out. (PMIDs cited, though not reviewed based on this discussion: De Rubeis et al, 2014 - PMID: 25363760, Guo et al, 2019 - PMID: 30504930, Kaplanis et al, 2020 - PMID: 33057194). Currently there is no PABPC1-related phenotype in other databases (incl. OMIM, G2P, SysID, PanelApp Australia). Consider inclusion in the gene panels for ID and epilepsy with amber / green rating (DD with or without ID in >= 3 individuals/families/variants – also the case for seizures, role of the gene, statistical evidence for the gene/occurrence and clustering of variants, functional studies with strong evidence for at least 3 variants || learning difficulties/borderline intellectual functioning in 2 affected individuals, phenotype in few might be "blended" due to additional de novo variants). Sources: Literature |
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| Early onset or syndromic epilepsy v2.507 | DTYMK |
Konstantinos Varvagiannis gene: DTYMK was added gene: DTYMK was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: DTYMK was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: DTYMK were set to 31271740; 34918187; 35346037 Phenotypes for gene: DTYMK were set to Global developmental delay; Intellectual disability; Microcephaly; Seizures; Global brain atrophy; Cardiorespiratory arrest Penetrance for gene: DTYMK were set to Complete Review for gene: DTYMK was set to GREEN Added comment: 4 individuals (from 3 families) harboring biallelic DTYMK pathogenic variants have been reported. Consider inclusion in the current panel with green rating given consistent and relevant phenotype and evidence provided to date [effect of variants (LoF), pathogenesis, similar phenotypes in zebrafish model, etc]. Relevant studies are summarized below. ---- Lam et al (2019 - PMID: 31271740) described two siblings aged 25m and 7y, harboring biallelic DTYMK variants. The phenotype consisted of hypotonia, congenital microcephaly, DD, severe ID. Other shared features included raised serum lactate, pyruvate and alanine. The phenotype was more pronounced in the younger one (epilepticus during febrile illness, epilepsy on multiple anti-convulsants, evidence of regression, etc). Brain MRI revealed marked cerebral atrophy among the findings while a lactate peak was present in spectroscopy. The elder brother developed an episode of sudden onset coma with respiratory failure at the age of 7y. Quartet WES identified compound heterozygosity for a fs and a missense DTYMK variant (NM_012145.3:c.287_320del / p.Asp96Valfs*8 - c.295G>A / p.Ala99Thr). There were no additional findings. Previous genetic panel analysis for epilepsy was unremarkable for the 1st sib. There are two pathways for synthesis of dNTPs, the de novo pathway operating in the cytosol only and the salvage operating in both cytosol and mitochondria. DTYMK encodes (deoxy)thymidylate kinase which catalyzes conversion (phosphorylation) of dTMP to dTDP - a step right after convergence of both pathways - in the dTTP synthesis pathway. Mutations in TK2, an enzyme phosphorylating thymidine in mitochondria to dTMP have been associated with mitochondrial DNA depletion syndrome (MDDS). Given this and as the 2 sibs had raised serum lactate and pyruvate, the authors performed in silico analyses to calculate mtDNA/nDNA ratio dividing the respective read depths for mitochondrial and nuclear DNA obtained from WGS data of the two sibs (blood). This ratio was shown to be reduced in the more severely affected sib (65.5% of control) although this was not the case for the mildly affected brother (114.6%). As a control a non-MDDS mitochondrial cytopathy sample (corresponding to m.8993T>G) was used. The respective ratio which was calculated for a known POLG-related MDDS case was 15.6%. ---- Vanoevelen et al (2022 - PMID: 34918187) describe two unrelated children with hypotonia, absence of developmental progress, microcephaly, seizures (recurrent febrile seizures/myoclonic jerks). Severe cerebral atrophy (with unaffected cerebellum) was observed upon brain imaging. Other findings included puffy body/extremities. Both had complications following respiratory illness leading to demise. CNS pathology in the 1st individual revealed massive neuronal dropout, with sparing of dentate nucleus and brainstem. CMA in both cases was normal. This was also the case for extensive metabolic investigations (which provided no evidence of eventual mitochondrial dysfunction). WES revealed compound heterozygosity for 2 missense variants in the first individual (NM_012145.3:c.382G>A - p.Asp128Asn and c.242C>T - p.Pro81Leu). The second individual, born to consanguineous parents, was homozygous for c.242C>T / p.Pro81Leu. In silico predictions varied although each variant were (mostly) suggestive of a deleterious effect. Variants were both ultrarare without homozygotes in ExAC,. The authors generated a dtymk ko zebrafish model (hmz for a frameshift variant). Zebrafish exhibited markedly smaller eyes and pericardiac edema (3dpf-), twitching movements somewhat reminiscent of epilepsy (at 3dpf), prominent edema of brain and intestine. Head size was significantly smaller at a timepoint prior to brain edema (also after correction for length). Histology provided evidence of empty spaces in brain, suggestive of neurodegeneration, with high amounts of apoptotic cells. dTMPK activity was measured in zebrafish (at 5dpf) as well as in fibroblasts from one individual and in both cases, it was barely detectable and significantly lower compared to wt/htz zebrafish or to the activity in fibroblasts from the parents of the individual tested. In fibroblasts from the same individual with comparison to his parents, the authors demonstrated that DNA replication was impaired (using pulse-EdU staining to quantify cells in S-phase). Assessment of cell proliferation in the brain of dtymk ko zebrafish using phospo-Ser10-Histone H3 (pH3) staining was suggestive of severe proliferation defects in forebrain. Impaired biosynthesis of nucleotides for DNA synthesis/repair would be predicted to result in nucleotide pool imbalance, leading to incorporation of ribonucleotides in genomic DNA with - in turn - impairment of DNA replication and genomic instability (sensitivity to strand breakage). In line with this, genomic DNA of ko zebrafish following alkaline hydrolysis and alkaline gel electrophoresis was shown to migrate at lower position and to be more fragmented indicating increased sensitivity (due to incorporation of ribonucleotides). Visualization of DNA breakage by γH2AX staining, following UV-irradiation of zebrafish embryos revealed persistence of elevated γH2AX levels and DNA damage response signaling, interpreted as increase in unrepaired DNA breaks. mtDNA copy numbers in fibroblasts from the affected individual was somewhat but not significantly lower compared to his parents. Importantly, the copy numbers were similar to controls (N=5) which overall does not support mtDNA depletion as a consequence of DTYMK deficiency. Integrity of mtDNA did not appear to be compromised , with the mitochondrial genome migrating at the expected length of 16,5 kb with no indications of mtDNA deletions for both affected individual and his parents. Activity of the mitochondrial respiratory complexes I-V in fibroblasts from the affected individual was comparable to that of his parents. Overall, there was no evidence for mtDNA depletion (although not studied in muscle biopsy) while functional studies failed to demonstrate mitochondrial dysfunction. The authors discuss other disorders of impaired dTTP metabolism due to mutations in TYMP, RRM2B or CAD. ------ In a recent study using zebrafish model, Hu Frisk et al (2022 - PMID: 35346037) further demonstrate that Dtymk is essential for neurodevelopment providing evidence for expression of a compensatory thymidylate kinase-like enzyme at later stages of development (explaining survival of ko dtymk zebrafish despite the central role of this enzyme in dTTP generation). [Not further reviewed] Sources: Literature |
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| Early onset or syndromic epilepsy v2.498 | TIAM1 |
Konstantinos Varvagiannis gene: TIAM1 was added gene: TIAM1 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: TIAM1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: TIAM1 were set to 35240055; 33328293 Phenotypes for gene: TIAM1 were set to Delayed speech and language development; Global developmental delay; Intellectual disability; Seizures; Behavioral abnormality; Abnormality of the endocrine system; Hypothyroidism; Abnormality of nervous system morphology Penetrance for gene: TIAM1 were set to Complete Review for gene: TIAM1 was set to AMBER Added comment: Lu et al (2022 - PMID: 35240055) describe 5 individuals (from 4 families) with biallelic TIAM1 missense variants. The phenotype overall corresponded to a neurodevelopmental disorder with DD (5/5), ID (4/4 individuals of relevant age - 3 families), speech delay (5/5), seizures (5/5 - onset: 2m-13y) and behavioral abnormalities (2/2, sibs with autism and ADHD). Several subjects had endocrine symptoms, namely hypothyroidism (N=3 - 2 families), Addison's disease (1) or hypomagnesemia (1). Non-consistent abnormalities were reported in (3/3) subjects who had a brain MRI. Previous investigations were mentioned for 3 individuals (incl. 2 sibs) and included normal CMA and/or metabolic workup. Singleton or trio exome sequencing (in one family) revealed biallelic missense TIAM1 variants. 6 different missense variants were reported, all ultra-rare or not present in gnomAD (also o/e:0.2, pLI:0.96), with CADD scores in favor of deleterious effect (NM_001353694.2): c.67C>T/p.Arg23Cys*, c.2584C>T/p.Leu862Phe*, c.983G>T/p.Gly328Val*, c.4640C>A/p.Ala1547Glu, c.1144G>C/p.Gly382Arg, c.4016C>T/p.Ala1339Val. TIAM1 encodes a RAC1-specific guanine exchange factor (GEF), regulating RAC1 signaling pathways that in turn affect cell shape, migration, adhesion, growth, survival, and polarity, and influence actin cytoskeletal organization, endocytosis, and membrane trafficking. RAC1 signaling plays important role in control of neuronal morphogenesis and neurite outgrowth (based on the summary by Entrez and authors). TIAM1 is highly expressed in human brain (GTEx). The authors provide evidence that sif, the Drosophila ortholog, is expressed primarily in neurons of the fly CNS (but not in glia). Using different sif LoF mutant flies they demonstrate that loss of sif impairs viability. Surviving flies exhibited climbing defects and seizure-like behaviors, both significantly rescued upon UAS-sif expression. Neuronal specific sif knockdown resulted in similar phenotypes to ubiquitous knockdown, while glial knockdown did not result in climbing defects. The semi-lethal phenotype could be fully rescued by expression of the fly sif cDNA, but only partially by human TIAM1 cDNA reference. Upon expression, 3 patient-variants (R23C, L862F, G328V) had variable rescue abilities similar to or lower (R23C) than TIAM1 Ref. TIAM1 Ref and variants could not rescue the neurological phenotypes though. Higher/ectopic expression of sif or TIAM1 Ref was toxic, which was also observed to a lesser extent for variants. Overall, the evidence provided suggests that the 3 variants tested induce partial LoF. In a recent study cited (PMID: 33328293), Tiam1 KO mice had simplified dendritic arbors, reduced spine density and diminished excitatory transmission in dentate gyrus. The authors comment that this mouse model presented only subtle behavioral abnormalities which they speculate may be secondary to GEF redundancy (eg. Tiam2). There is no TIAM1-associated phenotype in OMIM/G2P/SysID. TIAM1 is included in PanelApp Australia in the ID and epilepsy panels with green rating. Consider inclusion in the current panel with amber rating [As authors discuss: some phenotypic features differed in their small cohort and the contribution of other recessive conditions in 2 consanguineous families cannot be excluded. Also: in fig S1 only status of parents but not of affected/unaffected sibs is specified with the exception of Fam1]. Sources: Literature |
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| Early onset or syndromic epilepsy v2.452 | GABRD |
Helen Lord changed review comment from: Screened the GABRD gene in a cohort of 933 individuals with various childhood-onse epilepsies sequentially referred for diagnostic gene panel testing. The genetic findings were obtained either through targeted epilpesy panels (n=4), WES (n=3) or sanger sequencing (n=3; family 1 patient 6 & 7, family 2 patient 10). Variants classified using the ACMG criteria and badsed on transcript NM_000815.4. From the original cohort of 933 individuals, presumed pathogenic variants were identified in 3 individuals from 2 unrelated families. Another 7 individuals from 6 families with epilepsy or neurodevelopmental disorders were identified through international collaberations and gene matcher. The V422I variant occured presumably de novo in two sibs thus one parent must be mosaic. The T291I variant was detected in an aff mother and her aff twin boys. The remaining variants M87L, P122A, P257L, L260V & I284T all occured de novo in sporadic patients. All 7 variants were predicted to be damaging by at least two different prediction tools and had CADD scores above 20. 6 of 7 were absent in gnomAD and our internal dataset. The M87L variant was seen once in gnomAD. The position of the different variants spans a large part of the delta subunit from the N-terminal end (M87L) to the final transmembrane M4 domain (V442I). Four of the variants (P257L, L260V, I284T & T291I) reside in the M1 and M2 transmembrane domains that are key to forming a functional ion channel. 5 of the 7 variants cause changes to AA residues fully (P122A, P257L & T291I) or highly (L260V & I284T) conserved across human GABAaR subunits. Functional analysis suggests: P122A variant results in a 5-fold decrease in the average maximal current amplitude and combined with its increaeed propensity to desensitise - LOF trait. The 4 variants in the transmembrane domains M1 & M2 (P257L, L260V, I284T, T291I) all resulted in a 3-18 fold increased in current amplitudes - GOF trait.The current amplitude increase in P257L was only 3 fold and this receptor also displayed increased sensitivty to GABA reinforcing the GOF trait. No functional changes noted for M87L and V422I. As these variants haven't shown any detectable functional changes the 3 individuals carrying these two changes are not included in the phenotypic analysis. The remaining 7 patients median age of 10 years (ranging from 3-37)/All 6 patients with a GOF variant suffered from generalised epilesy (nost common seizure types atypical absences, generalised myoclonic seizures, tonic seizures and generalised tonic-clonic seizures; occur daily in 4/6 patients and medically refractory in 5/6 patients)and various degrees of learning difficuties or intellectual disability (motor delay in 4/6 with regression or stagnation at seizure onset in at least 2, learning difficulties seen in 6/6 from mild to severe), EEG pattern suggests an underlying cortico-thalmic network tyocial for generalised epilepsys with diffuse spiked and slow waves shown in both humans and animal models~). The patient with the LOF variant has ASD, normal intelligence and no seizure history. In summary presumed pathogenic LOF variants were identified in 3 individuals (de novo) and one family (2 twin sibs and mother all aff) with an epilepsy and neurodev disorder. One GOF variant was identifed (de novo) in a patient with ASD but no seizures. Two other variants identified in this gene in patients with seizure phenotypes were excluded from phentoypic interpretation as the functional analysis undertaken showed no effect - unclear as to whether these are pathogenic or not.; to: Screened the GABRD gene in a cohort of 933 individuals with various childhood-onset epilepsies sequentially referred for diagnostic gene panel testing. The genetic findings were obtained either through targeted epilpesy panels (n=4), WES (n=3) or sanger sequencing (n=3; family 1 patient 6 & 7, family 2 patient 10). Variants classified using the ACMG criteria and badsed on transcript NM_000815.4. From the original cohort of 933 individuals, presumed pathogenic variants were identified in 3 individuals from 2 unrelated families. Another 7 individuals from 6 families with epilepsy or neurodevelopmental disorders were identified through international collaberations and gene matcher. The V422I variant occured presumably de novo in two sibs thus one parent must be mosaic. The T291I variant was detected in an aff mother and her aff twin boys. The remaining variants M87L, P122A, P257L, L260V & I284T all occured de novo in sporadic patients. All 7 variants were predicted to be damaging by at least two different prediction tools and had CADD scores above 20. 6 of 7 were absent in gnomAD and our internal dataset. The M87L variant was seen once in gnomAD. The position of the different variants spans a large part of the delta subunit from the N-terminal end (M87L) to the final transmembrane M4 domain (V442I). Four of the variants (P257L, L260V, I284T & T291I) reside in the M1 and M2 transmembrane domains that are key to forming a functional ion channel. 5 of the 7 variants cause changes to AA residues fully (P122A, P257L & T291I) or highly (L260V & I284T) conserved across human GABAaR subunits. Functional analysis suggests: P122A variant results in a 5-fold decrease in the average maximal current amplitude and combined with its increaesed propensity to desensitise - LOF trait. The 4 variants in the transmembrane domains M1 & M2 (P257L, L260V, I284T, T291I) all resulted in a 3-18 fold increased in current amplitudes - GOF trait.The current amplitude increase in P257L was only 3 fold and this receptor also displayed increased sensitivty to GABA reinforcing the GOF trait. No functional changes noted for M87L and V422I. As these variants haven't shown any detectable functional changes the 3 individuals carrying these two changes are not included in the phenotypic analysis. The remaining 7 patients median age of 10 years (ranging from 3-37)/All 6 patients with a GOF variant suffered from generalised epilesy (nost common seizure types atypical absences, generalised myoclonic seizures, tonic seizures and generalised tonic-clonic seizures; occur daily in 4/6 patients and medically refractory in 5/6 patients)and various degrees of learning difficuties or intellectual disability (motor delay in 4/6 with regression or stagnation at seizure onset in at least 2, learning difficulties seen in 6/6 from mild to severe), EEG pattern suggests an underlying cortico-thalmic network tyocial for generalised epilepsys with diffuse spiked and slow waves shown in both humans and animal models~). The patient with the LOF variant has ASD, normal intelligence and no seizure history. In summary presumed pathogenic LOF variants were identified in 3 individuals (de novo) and one family (2 twin sibs and mother all aff) with an epilepsy and neurodev disorder. One GOF variant was identifed (de novo) in a patient with ASD but no seizures. Two other variants identified in this gene in patients with seizure phenotypes were excluded from phentoypic interpretation as the functional analysis undertaken showed no effect - unclear as to whether these are pathogenic or not. |
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| Early onset or syndromic epilepsy v2.343 | CAD | Arina Puzriakova Phenotypes for gene: CAD were changed from Epileptic encephalopathy, early infantile, 50 - MIM 616457 to Developmental and epileptic encephalopathy 50, OMIM:616457 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v2.47 | CDC42BPB |
Konstantinos Varvagiannis gene: CDC42BPB was added gene: CDC42BPB was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: CDC42BPB was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: CDC42BPB were set to 32031333 Phenotypes for gene: CDC42BPB were set to Central hypotonia; Global developmental delay; Intellectual disability; Seizures; Autistic behavior; Behavioral abnormality Penetrance for gene: CDC42BPB were set to unknown Review for gene: CDC42BPB was set to AMBER Added comment: Chilton et al (2020 - PMID: 32031333) report on 14 individuals with missense and loss-of-function CDC42BPB variants. Features included hypotonia (8/11), DD (12/13 - the 14th was a fetus), ID (7/13), ASD (8/12), clinical seizures (in 3 - a 4th had abnormal EEG without seizures), behavioral abnormalities. Variable non-specific dysmorphic features were reported in some (sparse hair being the most frequent - 4/8). Additional features were observed in few (=<4) incl. cryptorchidism, ophthalmological issues, constipation, kidney abnormalities, micropenis, etc. All individuals had non-diagnostic prior genetic testing (incl. CMA, FMR1, MECP2, Angelman/Prader-Willi methylation studies, autism gene panel - suggesting relevance to the current panel) or metabolic testing. Variants were identified following clinical exome sequencing with Sanger confirmation. Most occurred as de novo events (11/14) while inheritance was not available for few (3/14). Missense variants did not display (particular) clustering. Almost all variants were absent from gnomAD and were predicted to be deleterious in silico (among others almost all had CADD scores >25). As the authors comment, CDC42BPB encodes myotonic dystrophy-related Cdc42-binding kinase β (MRCKβ) a serine/threonine protein kinase playing a role in regulation of cytoskeletal reorganization and cell migration in nonmuscle cells (through phosporylation of MLC2). Previous studies have demonstrated that it is ubiquitously expressed with prenatal brain expression. The gene appears to be intolerant to pLoF (pLI of 1) as well as to missense variants (Z-score of 3.66). CDC42BPB is a downstream effector of CDC42. Mutations of the latter cause Takenouchi-Kosaki syndrome with DD/ID and some further overlapping features (with CDC42BPB-associated phenotypes). Homozygous Cdc42bpb KO in mouse appears to be nonviable (MGI:2136459). Loss of gek in the eyes of Drosophila results in disrupted growth cone targeting to the lamina (gek is the fly CDC42BPB ortholog). Sources: Literature |
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| Early onset or syndromic epilepsy v1.497 | SNX27 |
Konstantinos Varvagiannis gene: SNX27 was added gene: SNX27 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: SNX27 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: SNX27 were set to 25894286; 31721175; 21300787; 23524343 Phenotypes for gene: SNX27 were set to Generalized hypotonia; Global developmental delay; Intellectual disability; Seizures Penetrance for gene: SNX27 were set to Complete Review for gene: SNX27 was set to AMBER Added comment: (From the ID panel) Evidence from 2 publications suggests that DD, ID and seizures are part of the phenotype of individuals with biallelic SNX27 pathogenic variants : --------- Damseh, Danson et al (2015 - PMID: 25894286) first reported on a consanguineous family with 4 affected sibs, homozygous for an SNX27 pathogenic variant. Features incl. hypotonia soon after birth, failure to thrive, severely delayed psychomotor development with no milestone acquisition, occurrence of myoclonic seizures with 3 individuals deceased early. Exome sequencing in one revealed a few candidate variants, with an SNX27 frameshift one [NM_030918.6:c.515_516del - p.(His172Argfs*6) / absent from ExAC] being the only retained following Sanger segregation studies. Using fibroblasts from an affected individual, Western blot with an antibody which would also bind prior to the truncation site, was consistent with dramatically reduced/absent SNX27 truncated mutant protein. Protein levels of VPS35, a component of the retromer responsible for direct cargo binding (not mediated by a cargo adaptor as SNX27), were normal. --------- Parente et al (2019 - PMID: 31721175) reported on a 13-year-old male with motor and language delay, ADHD, ID (kindergarten academic level at the age of 13) and seizures with onset at the age of 9 years (GTC, with abnormal EEG and postical SV tachycardia). Variable physical findings were reported. White matter hyperintesities were noted upon initial brain MRI (but were less marked in subsequent ones). Initial genetic testing (Alexander's disease, CMA, FMR1) was normal. Exome revealed compound heterozygosity for 2 SNX27 variants (NM_030918.5/NM_001330723.1 both apply c.510C>G - p.Tyr170* and c.1295G>A - p.Cys432Tyr) each inherited from healthy carrier parents. There were no other potentially causative variants. A parental history of - isolated - late onset seizures was reported (so this individual may not be considered for the seizure phenotype here). The authors also reported on a further 31-year old affected male. This individual had infantile hypotonia, poor eye contact with subsequent significant DD, seizures (febrile/afebrile T-C with onset at the age of 14m) and ID estimated in the severe range. Variable - though somewhat different - physical findings were reported. Initial work-up included basic metabolic testing, standard karyotype, FISH for 15q11 and subtelomeric regions and PHF6 genetic testing - all normal. Exome (and subsequent Sanger confirmation/parental studies) revealed compound heterozygosity for a missense and a frameshift variant (c.989G>A / p.Arg330His and c.782dupT / p.Leu262Profs*6 same in NM_001330723.1, NM_030918.6). --------- SNX27 encodes sorting nexin 27, a cargo adaptor for the retromer. The latter is a multi-protein complex essential for regulating the retrieval and recycling of transmembrane cargos from endosomes to the trans-Golgi network or the plasma membrane [Lucas et al 2016 - PMID: 27889239 / McNally et al 2018 - PMID: 30072228]. As summarized by Parente et al, the encoded protein by regulating composition of the cell surface influences several processes eg. neuronal excitability, synaptic plasticity, Wnt signaling etc. It has been shown to interact with surface receptors and their ligands including GIRK channels, 5-HT4, ionotropic glutamate receptors (incl. NMDA- and AMPA-type receptors) and mGluR5 [several refs. provided]. Knockout of Snx27 in mice resulted in embryonic lethality (16% hmz of the 25% expected), severe postnatal growth retardation and death within the first 3 weeks. Snx27(+/-) mice have normal neuroanatomy but exhibit cognitive deficits (in learning and memory) and defects in synaptic function/plasticity with reduced amounts of NMDA and AMPA receptors (Cai et al - PMID: 21300787, Wang et al - PMID: 23524343). --------- There is no associated phenotype in OMIM/G2P. Sources: Literature |
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| Early onset or syndromic epilepsy v1.405 | NSF |
Konstantinos Varvagiannis gene: NSF was added gene: NSF was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: NSF was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: NSF were set to 31675180 Phenotypes for gene: NSF were set to Seizures; EEG with burst suppression; Global developmental delay; Intellectual disability Penetrance for gene: NSF were set to unknown Review for gene: NSF was set to AMBER Added comment: Suzuki et al. (2019 - PMID: 31675180) report on 2 unrelated individuals with de novo missense NSF variants. Overall the phenotype corresponded to an early infantile epileptic encephalopathy. The first patient developed vomiting and tonic seizures immediately after birth, with burst-suppression pattern upon EEG. Trio exome sequencing, followed by Sanger sequencing of proband and parents, revealed a de novo missense variant (NM_006178.3:c.1375G>A / p.Ala459Thr), absent from public databases and predicted in silico to be deleterious (CADD score of 30). The girl died 36 days after birth due to respiratory failure. Another subject, having necessitated mechanical ventilation due to absence of spontaneous respiration after birth, developed myoclonic seizures. EEG showed a burst-suppression pattern. At the age of 3, she was noted to have persistence of seizures and profound ID. Trio exome sequencing identified a missense NSF variant (c.1688C>T / p.Pro563Leu) also confirmed and shown to be de novo by Sanger sequencing. Again the variant was absent from public datasets and had a CADD score of 34. While expression of wt NSF allele in the developing eye of Drosophila had no effect, expression of mutants severely affected eye development - suggesting a dominant negative effect. NSF encodes a homo-hexameric AAA ATPase, which is recruited by SNAPs (Soluble NSF Attachment Proteins) - and the latter by SNAREs (SNAP REceptors) - thus having a role in vesicular transport and membrane fusion. There is currently no associated phenotype in OMIM/G2P. Overall, this gene could be considered for inclusion probably with amber/red rating pending further evidence (eg. additional work-up or alternative causes/explanations not discussed). Sources: Literature |
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| Early onset or syndromic epilepsy v1.399 | DNAJC5 | Rebecca Foulger commented on gene: DNAJC5: PMID:22978711: Cadieux-Dion et al., 2013. report a p.L116del variant in DNAJC5 in two distinct American families, and a p.L115R variant in an additional family. All individuals showed generalized tonic-clonic seizures. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.191 | CAD | Rebecca Foulger Source Wessex and West Midlands GLH was added to CAD. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.190 | CAD | Rebecca Foulger Source NHS GMS was added to CAD. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.189 | CAD | Rebecca Foulger edited their review of gene: CAD: Added comment: Review and rating collated by Tracy Lester (Oxford Medical Genetics Laboratories Oxford University Hospitals NHS Foundation Trust, 2019_02_06) on behalf of Wessex and West Midlands GLH for GMS Neurology specialist test group, for Clinical Indication R59 'Early onset or syndromic epilepsy'. Review contributors: John Taylor and Helen Lord. Suggested gene rating: Green. ; Changed rating: AMBER | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.188 | CAD | Tracy Lester reviewed gene: CAD: Rating: GREEN; Mode of pathogenicity: ; Publications: 28007989; Phenotypes: Epileptic encephalopathy early infantile, 616457; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.174 | FLNA | Rebecca Foulger commented on gene: FLNA: PMID:25755106. In a woman and her 3 daughters with a complex phenotype comprising both periventricular nodular heterotopia and Melnick-Needles syndrome, Parrini et al. (2015) identified a c.622G-C transversion in exon 3 of the FLNA gene (G208R). The 3 daughters had onset of seizures in the first decade. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.30 | TRRAP |
Konstantinos Varvagiannis gene: TRRAP was added gene: TRRAP was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: TRRAP was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: TRRAP were set to 30827496 Phenotypes for gene: TRRAP were set to Global developmental delay; Intellectual disability; Autism; Microcephaly; Abnormal heart morphology; Abnormality of the urinary system; Seizures Penetrance for gene: TRRAP were set to unknown Mode of pathogenicity for gene: TRRAP was set to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments Review for gene: TRRAP was set to AMBER Added comment: Cogné et al. (DDD study among the co-authors - PMID: 30827496) report on 24 individuals with pathogenic TRRAP variants. 17 different variants were reported. All variants were missense SNVs and on most occasions had occurred as de novo or apparently de novo events (paternity and maternity not checked). On one occasion, a parent was not unavailable although the respective grand-parents were not found to harbor the variant. Parental germline mosaicism explained the occurence of a variant in 2 sibs. The authors suggest a strong genotype-phenotype correlation. Individuals whose variant localized within the residues 1031-1159 (NM_001244580.1) presented with a syndromic form of ID with additional malformations. ID was a universal feature in this group (for those subjects evaluated). For variants outside this cluster of residues the phenotype was rather that of ASD without ID or isolated ID with or without ASD, albeit with some exceptions (eg. F860L also associated with a syndromic presentation). ID was a feature in the majority of individuals belonging to the latter group (67% - all with DD) or overall irrespective of the variant localization (85% for those evaluated - all with DD). ** Epilepsy was a feature in 4 individuals (4/24) belonging to either group. ** All 17 variants were absent from gnomAD with CADD scores supporting a deleterious effect (SIFT/PolyPhen2 (both) predicted a tolerated/benign effect for some eg. Ala1043Thr). A few variants were recurrent, namely Ala1043Thr (5 individuals), Glu1106Lys (2), Gly1883Arg (2), Pro1932Leu (in 2 sibs). 6 further subjects (individuals 25-30, reported separately in the supplement) harbored 6 additional variants with lesser evidence for pathogenicity. TRRAP is among the 5 most intolerant genes to missense mutations (z-score of 10.1 in ExAC) while it is also intolerant to LoF variants (pLI of 1). No deletions have been reported in DECIPHER and no LoF were identified in the study. Given type of variants and their clustering rather a gain-of-function effect or dominant-negative effect is suggested. As the authors note a LoF effect of non-clustering variants, associated with a milder phenotype cannot excluded. [Mode of pathogenicity to change if thought to be useful]. TRRAP encodes a protein involved in the recruitment to chromatin of histone acetyltransferases. The latter control the process of acetylation of lysine residues in histones and other DNA-binding proteins thus playing a major role in regulation of gene expression. In line with this, RNA sequencing analysis in skin fibroblasts from affected subjects demonstrated dysregulation of expression for several genes implicated in neuronal function and ion transport. As summarized by the authors: In mice, Trapp knockout is embryonically lethal. Brain-specific knockout leads to premature differentiation of neural progenitors and abnormal brain development. Brain atrophy and microcephaly are observed (microcephaly was a feature in some affected individuals as well, primarily those with variants affecting residues 1031-1159). [PMIDs cited: 11544477, 24792116]. De novo TRRAP variants have been reported also in individuals with neuropsychiatric disorders (PMIDs: 21822266, 23042115, 28392909, 30424743) while TRRAP has been classified among the prenatally-biased genes relevant to its brain expression (PMID:23042115). A de novo missense variant (c.11270G>A or p.R3757Q) was also previously reported in a study of 264 individuals with epileptic encephalopathy (Epi4K Consortium - PMID: 23934111 - indiv. ND29352). ----------- TRRAP is not associated with any phenotype in OMIM, nor in G2P. ----------- As a result, this gene can be considered for inclusion in the epilepsy panel as amber or green. Sources: Literature |
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| Early onset or syndromic epilepsy v0.1514 | CAD | Rebecca Foulger Marked gene: CAD as ready | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1514 | CAD | Rebecca Foulger Gene: cad has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1514 | CAD | Rebecca Foulger commented on gene: CAD: Confirmed DD-G2P gene for Uridine-responsive epileptic encephalopathy. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1514 | CAD | Rebecca Foulger Classified gene: CAD as Green List (high evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1514 | CAD | Rebecca Foulger Added comment: Comment on list classification: Updated rating from Grey to Green: 5 patients from 4 families in total (1 patient from PMID:25678555 and 4 more patients from 28007989) all with epileptic seizures (generalized tonic clonic seizures, severe epilepsy, generalised/focal seizures). Note that 2 of the families in PMID:28007989 were Serbian Roma descent with the same homozygous c.98T>G (Met33Arg) transversion, although listed as unrelated. Overall sufficient (>3) unrelated cases of epileptic seizures in patients with CAD variants, for inclusion on diagnostic panel. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1514 | CAD | Rebecca Foulger Gene: cad has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1362 | CAD |
Konstantinos Varvagiannis gene: CAD was added gene: CAD was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: CAD was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: CAD were set to 25678555; 28007989 Phenotypes for gene: CAD were set to Epileptic encephalopathy, early infantile, 50 - MIM 616457 Penetrance for gene: CAD were set to Complete Review for gene: CAD was set to GREEN Added comment: Biallelic pathogenic variants in CAD cause Epileptic encephalopathy, early infantile, 50 - MIM 616457. Overall 5 individuals from 4 unrelated families have been reported in detail in PMIDs 25678555 and 28007989 (table 1 in this article provides a summary). The phenotype consisted of developmental delay which preceded the onset of seizures (6 months to 2 years) and hematologic anomalies (anemia and anisopoikilocytosis). The patients presented developmental stagnation/regression, which in most cases occurred several months following the seizure onset. CAD is a tri-functional protein catalyzing the first 3 steps of the de novo pyrimidine biosynthesis. In total, 5 variants have been reported (2 missense, 1 nonsense and 2 splice-site SNVs) with functional studies (cDNA, metabolites) supporting pathogenicity and disruption of this pathway. CAD mutations have previously been studied in other model organisms. Mutations in enzymes catalyzing downstream steps of the same pathway are associated with other syndromes. The disorder appears to be amenable to dietary intervention (uridine supplementation). As a result, this gene can be considered for inclusion in the epilepsy panel as green (or amber). Sources: Literature |
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| Early onset or syndromic epilepsy v0.503 | PIGG |
Konstantinos Varvagiannis gene: PIGG was added gene: PIGG was added to Genetic Epilepsy Syndromes. Sources: Literature,Expert Review Mode of inheritance for gene: PIGG was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PIGG were set to 26996948; 28581210 Phenotypes for gene: PIGG were set to # 616917. MENTAL RETARDATION, AUTOSOMAL RECESSIVE 53; MRT53 Penetrance for gene: PIGG were set to Complete Review for gene: PIGG was set to GREEN Added comment: PMID: 26996948 reports on 5 individuals from 3 families, with biallelic pathogenic variants in PIGG. Individuals from first family, were born to consanguineous parents from Egypt and were homozygous for a stopgain variant [p.(Gln310*)]. The patient from the second family had a rare missense SNV [p.(Arg669Cys)] and a de novo microdeletion affecting PIGG on her other allele. In the third family (consanguineous parents from Pakistan), two affected sibs were found to be homozygous for a splice variant. The phenotype consisted of hypotonia, early-onset seizures and intellectual disability. Ataxia was an additional feature in one of the families. Seizures, were observed in most of patients but do not appear to be a universal feature as they were absent in one of the sibs from the third family (10 years of age), while the other had a single episode by the age of 12 years. In vitro testing of lymphoblastoid cell lines (generated from individuals from the 1st and 3rd family) indicated that the variants abolished completely the function of PIGG, whereas the surface level of GPI anchored proteins was normal. // PMID: 28581210 describes the phenotype of 2 sibs from Palestine, homozygous for a stopgain variant [p.(Trp547*)]. Hypotonia, feeding difficulties, severe non-progressive ataxia (with cerebellar hypoplasia), intellectual disability and seizures were common features. Differences in severity and/or additional features might be explained by other homozygous variants (the girl had a concurrent diagnosis of MCAD deficiency). The authors demonstrated that the PIGG transcript levels were significantly lower (approximately half) in the two siblings compared to their parents, while the transcripts with the mutation in the heterozygous parents were very low due to nonsense-mediated decay. Patient fibroblasts showed decreased surface level of GPI-anchored proteins, in contrast with what was noted in lymphoblastoid cells in the previous study. // As a result this gene can be considered for inclusion in this panel as green (or amber). Sources: Literature, Expert Review |
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