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| Early onset or syndromic epilepsy v4.180 | SNF8 |
Achchuthan Shanmugasundram gene: SNF8 was added gene: SNF8 was added to Early onset or syndromic epilepsy. Sources: Literature Mode of inheritance for gene: SNF8 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: SNF8 were set to 38423010 Phenotypes for gene: SNF8 were set to neurodevelopmental disorder, MONDO:0700092; epilepsy, MONDO:0005027 Review for gene: SNF8 was set to AMBER Added comment: PMID:38423010 reported nine individuals from six families presenting with a spectrum of neurodevelopmental/ neurodegenerative features caused by biallelic variants in SNF8. The phenotypic spectrum included four individuals with severe developmental and epileptic encephalopathy with leukoencephalopathy and early death in three of those cases. Two individuals died too young to develop epilepsy. A second cohort shows a milder phenotype with intellectual disability, childhood-onset optic atrophy, or ataxia. All mildly affected individuals shared the same hypomorphic variant, c.304G>A (p.Val102Ile) as compound heterozygous. Functional studies using fibroblasts derived from patients and zebrafish model showed loss of function as the disease mechanism. This gene has not yet been associated with any phenotypes either in OMIM or in Gene2Phenotype. Sources: Literature |
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| Early onset or syndromic epilepsy v4.73 | PIP5K1C |
Achchuthan Shanmugasundram gene: PIP5K1C was added gene: PIP5K1C was added to Early onset or syndromic epilepsy. Sources: Literature Mode of inheritance for gene: PIP5K1C was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted Publications for gene: PIP5K1C were set to 37451268 Phenotypes for gene: PIP5K1C were set to neurodevelopmental disorder, MONDO:0700092; intellectual disability, MONDO:0001071 Review for gene: PIP5K1C was set to GREEN Added comment: Three de novo heterozygous missense variants in PIP5K1C (p.Glu146Lys, p.Tyr205Cys & p.Tyr221Cys) were identified in nine unrelated children exhibiting intellectual disability, developmental delay, acquired microcephaly, seizures, visual abnormalities, and dysmorphic features. Intellectual disability was reported in all nine children and seizures were present in seven children, of which three had developmental and epileptic encephalopathy. In addition, there is functional evidence available, which includes an in vivo zebrafish model that recapitulates the human phenotype (developmental defects affecting the forebrain, including the eyes, as well as craniofacial abnormalities) (PMID:37451268). This gene has been associated with another phenotype (Lethal congenital contractural syndrome 3, MIM #611369) in both OMIM and Gene2Phenotype, but not yet associated with this neurodevelopmental disorders in either databases. Sources: Literature |
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| Early onset or syndromic epilepsy v4.44 | CLDN5 |
Achchuthan Shanmugasundram changed review comment from: PMID:36477332 reported the identification of de novo heterozygous missense variants in CLDN5 in 15 unrelated patients who presented with a number of clinical features including developmental delay including intellectual disability, seizures (primarily infantile onset focal epilepsy), microcephaly and a recognisable pattern of pontine atrophy and brain calcifications. All 15 patients had seizures. In addition, functional studies from zebrafish model also provided parallel evidence that CLDN5 variants cause a neurodevelopmental disorder involving disruption of the blood brain barrier and impaired neuronal function. This gene has been associated with relevant phenotypes in Gene2Phenotype (CLDN5-related neurodevelopmental disorder with 'limited' rating in the DD panel), but not in OMIM. Sources: Literature; to: PMID:36477332 reported the identification of de novo heterozygous missense variants in CLDN5 in 15 unrelated patients who presented with a number of clinical features including developmental delay including intellectual disability, seizures (primarily infantile onset focal epilepsy), microcephaly and a recognisable pattern of pontine atrophy and brain calcifications. All 15 patients had seizures. In addition, functional studies from zebrafish model also provided parallel evidence that CLDN5 variants cause a neurodevelopmental disorder involving disruption of the blood brain barrier and impaired neuronal function. This gene has been associated with relevant phenotypes in Gene2Phenotype (CLDN5-related neurodevelopmental disorder with 'limited' rating in the DD panel), but not in OMIM. Sources: Literature |
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| Early onset or syndromic epilepsy v4.42 | CLDN5 |
Achchuthan Shanmugasundram changed review comment from: PMID: 36477332 identified de novo heterozygous missense variants in CLDN5 in fifteen unrelated patients who presented with a shared constellation of features including developmental delay, seizures (primarily infantile onset focal epilepsy), microcephaly and a recognizable pattern of pontine atrophy and brain calcifications. Sources: Literature; to: PMID:36477332 reported the identification of de novo heterozygous missense variants in CLDN5 in 15 unrelated patients who presented with a number of clinical features including developmental delay including intellectual disability, seizures (primarily infantile onset focal epilepsy), microcephaly and a recognisable pattern of pontine atrophy and brain calcifications. All 15 patients had seizures. In addition, functional studies from zebrafish model also provided parallel evidence that CLDN5 variants cause a neurodevelopmental disorder involving disruption of the blood brain barrier and impaired neuronal function. This gene has been associated with relevant phenotypes in Gene2Phenotype (CLDN5-related neurodevelopmental disorder with 'limited' rating in the DD panel), but not in OMIM. Sources: Literature |
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| Early onset or syndromic epilepsy v4.19 | PLXNA1 |
Achchuthan Shanmugasundram gene: PLXNA1 was added gene: PLXNA1 was added to Early onset or syndromic epilepsy. Sources: Literature Mode of inheritance for gene: PLXNA1 was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted Publications for gene: PLXNA1 were set to 28464511; 34054129 Phenotypes for gene: PLXNA1 were set to developmental and epileptic encephalopathy, MONDO:0100062 Review for gene: PLXNA1 was set to GREEN Added comment: Monoallelic cases: PMID:28464511 reported a male patient with a de novo variant in PLXNA1 and presenting with intractable infantile onset epilepsy, and intellectual disability with autism spectrum disorder. In addition, this patient also had features suggestive of Dubowitz syndrome, including growth failure, dermatologic symptoms, and characteristic dysmorphic facial features. It has also been reviewed in this publication that one of only two previously reported cases with missense PLXNA1 variants had epileptic encephalopathy. PMID:34054129 reported ten cases from seven families with PLXNA1 variants. Of these cases, three unrelated cases had monoallelic de novo variants and presented with global developmental delay, seizures and craniofacial, brain and eye anomalies. Biallelic cases: Out of ten cases reported in PMID:34054129, seven cases from four unrelated families exhibited biallelic variants in PLXNA1 gene. They presented with global developmental delay and craniofacial, brain and eye anomalies. However, seizures are not reported in biallelic cases except one family (15 episodes of febrile and nonfebrile seizures reported in family A). The biallelic variants in this gene has been associated with phenotypes in OMIM (MIM #619955). However, both monoalellic and biallelic variants in this gene has been associated with phenotypes in Gene2Phenotype (with 'limited' rating). Functional studies: Structural modeling of missense variants in PLXNA1 suggests distortion in the native protein. Knockdown of plxna1a leads to cerebral anomalies and eye anomalies in zebrafish larvae. Sources: Literature |
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| 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 |
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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 v2.403 | VPS50 |
Konstantinos Varvagiannis gene: VPS50 was added gene: VPS50 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: VPS50 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: VPS50 were set to 34037727 Phenotypes for gene: VPS50 were set to Neonatal cholestatic liver disease; Failure to thrive; Profound global developmental delay; Postnatal microcephaly; Seizures; Abnormality of the corpus callosum Penetrance for gene: VPS50 were set to Complete Review for gene: VPS50 was set to AMBER Added comment: Schneeberger et al (2021 - PMID: 34037727) describe the phenotype of 2 unrelated individuals with biallelic VPS50 variants. Common features included transient neonatal cholestasis, failure to thrive, severe DD with failure to achieve milestones (last examination at 2y and 2y2m respectively), postnatal microcephaly, seizures (onset at 6m and 25m) and irritability. There was corpus callosum hypoplasia on brain imaging. Both individuals were homozygous for variants private to each family (no/not known consanguinity applying to each case). The first individual was homozygous for a splicing variant (NM_017667.4:c.1978-1G>T) and had a similarly unaffected sister deceased with no available DNA for testing. The other individual was homozygous for an in-frame deletion (c.1823_1825delCAA / p.(Thr608del)). VPS50 encodes a critical component of the endosome-associated recycling protein (EARP) complex, which functions in recycling endocytic vesicles back to the plasma membrane [OMIM based on Schindler et al]. The complex contains VPS50, VPS51, VPS52, VPS53, the three latter also being components of GARP (Golgi-associated-retrograde protein) complex. GARP contains VPS54 instead of VPS50 and is required for trafficking of proteins to the trans-golgi network. Thus VPS50 (also named syndetin) and VPS54 function in the EARP and GARP complexes, to define directional movement of their endocytic vesicles [OMIM based on Schindler et al]. The VPS50 subunit is required for recycling of the transferrin receptor. As discussed by Schneeberger et al (refs provided in text): - VPS50 has a high expression in mouse and human brain as well as throughout mouse brain development. - Mice deficient for Vps50 have not been reported. vps50 knockdown in zebrafish results in severe developmental defects of the body axis. Knockout mice for other proteins of the EARP/GARP complex (e.g. Vps52, 53 and 54) display embryonic lethality. Studies performed by Schneeberger et al included: - Transcript analysis for the 1st variant demonstrated skipping of ex21 (in patient derived fabriblasts) leading to an in frame deletion of 81 bp (r.1978_2058del) with predicted loss of 27 residues (p.Leu660_Leu686del). - Similar VPS50 mRNA levels but significant reduction of protein levels (~5% and ~8% of controls) were observed in fibroblasts from patients 1 and 2. Additionally, significant reductions in the amounts of VPS52 and VPS53 protein levels were observed despite mRNA levels similar to controls. Overall, this suggested drastic reduction of functional EARP complex levels. - Lysosomes appeared to have similar morphology, cellular distribution and likely unaffected function in patient fibroblasts. - Transferrin receptor recycling was shown to be delayed in patient fibroblasts suggestive of compromise of endocytic-recycling function. As the authors comment, the phenotype of both individuals with biallelic VPS50 variants overlaps with the corresponding phenotype reported in 15 subjects with biallelic VPS53 or VPS51 mutations notably, severe DD/ID, microcephaly and early onset epilepsy, CC anomalies. Overall, for this group, they propose the term "GARP and/or EARP deficiency disorders". There is no VPS50-associated phenotype in OMIM or G2P. SysID includes VPS50 among the ID candidate genes. Consider inclusion in other relevant gene panels (e.g. for neonatal cholestasis, epilepsy, microcephaly, growth failure in early infancy, corpus callosum anomalies, etc) with amber rating pending further reports. Sources: Literature |
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| Early onset or syndromic epilepsy v2.149 | EXOC7 |
Arina Puzriakova gene: EXOC7 was added gene: EXOC7 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: EXOC7 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: EXOC7 were set to 32103185 Phenotypes for gene: EXOC7 were set to Brain atrophy; Seizures; Developmental delay; Microcephaly Added comment: PMID: 32103185 (2020) - 4 families with 8 affected individuals with brain atrophy, seizures, and developmental delay, and in more severe cases microcephaly and infantile death. Four novel homozygous or comp.heterozygous variants found in EXOC7, which segregated with disease in the families. They showed that EXOC7, a member of the mammalian exocyst complex, is highly expressed in developing human cortex. In addition, a zebrafish model of Exoc7 deficiency recapitulates the human disorder with increased apoptosis and decreased progenitor cells during telencephalon development, suggesting that the brain atrophy in human cases reflects neuronal degeneration. Sources: Literature |
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| Early onset or syndromic epilepsy v2.143 | FAM50A |
Konstantinos Varvagiannis gene: FAM50A was added gene: FAM50A was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: FAM50A was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) Publications for gene: FAM50A were set to 32703943 Phenotypes for gene: FAM50A were set to Mental retardation syndrome, X-linked, Armfield type (MIM #300261) Penetrance for gene: FAM50A were set to unknown Review for gene: FAM50A was set to AMBER Added comment: Lee et al (2020 - PMID: 32703943) provide evidence that Armfield X-Linked intellectual disability syndrome is caused by monoallelic FAM50A pathogenic variants. The current review is based only on this reference. The authors provide clinical details on 6 affected individuals from 5 families. Features included postnatal growth delay, DD and ID (6/6 - also evident for those without formal IQ assesment), seizures (3/6 from 2 families), prominent forehead with presence of other facial features and variable head circumference (5th to >97th %le), ocular anomalies (5/6 - strabismus/nystagmus/Axenfeld-Rieger), cardiac (3/6 - ASD/Fallot) and genitourinary anomalies (3/6). In the first of these families (Armfield et al 1999 - PMID: 10398235), linkage analysis followed by additional studies (Sanger, NGS of 718 genes on chrX, X-exome NGS - several refs provided) allowed the identification of a FAM50A variant. Variants in other families were identified by singleton (1 fam) or trio-ES (3 fam). In affected individuals from 3 families, the variant had occurred de novo. Carrier females in the other families were unaffected (based on pedigrees and/or the original publication). XCI was rather biased in most obligate carrier females from the 1st family (although this ranged from 95:5 to 60:40). Missense variants were reported in all affected subjects incl. Trp206Gly, Asp255Gly, Asp255Asn (dn), Glu254Gly (dn), Arg273Trp (dn) (NM_004699.3). Previous studies have demonstrated that FAM50A has ubiquitous expression in human fetal and adult tissues (incl. brain in fetal ones). Immunostaining suggests a nuclear localization for the protein (NIH/3T3 cells). Comparison of protein levels in LCLs from affected males and controls did not demonstrate significant differences. Protein localization for 3 variants (transfection of COS-7 cells) was shown to be similar to wt. Complementation studies in zebrafish provided evidence that the identified variants confer partial loss of function (rescue of the morpholino phenotype with co-injection of wt but not mt mRNA). The zebrafish ko model seemed to recapitulate the abnormal development of cephalic structures and was indicative of diminished/defective neurogenesis. Transcriptional dysregulation was demonstrated in zebrafish (altered levels and mis-splicing). Upregulation of spliceosome effectors was demonstrated in ko zebrafish. Similarly, mRNA expression and splicing defects were demonstrated in LCLs from affected individuals. FAM50A pulldown followed by mass spectrometry in transfected HEK293T cells demonstrated enrichment of binding proteins involved in RNA processing and co-immunoprecipitation assays (transfected U-87 cells) suggested that FAM50A interacts with spliceosome U5 and C-complex proteins. Overall aberrant spliceosome C-complex function is suggested as the underlying pathogenetic mechanism. Several other neurodevelopmental syndromes are caused by variants in genes encoding C-complex affiliated proteins (incl. EFTUD2, EIF4A3, THOC2, etc.). Please consider inclusion in the ID panel with green rating and epilepsy panel with amber (seizures in individuals from 2 families). Sources: Literature |
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| Early onset or syndromic epilepsy v2.131 | NARS |
Konstantinos Varvagiannis changed review comment from: [Please note that HGNC Approved Gene Symbol for this gene is NARS1] Manole et al (2020 - PMID: 32738225) provide evidence that both biallelic and monoallelic (de novo) pathogenic NARS1 variants cause a neurodevelopmental disorder. In total 32 individuals from 21 families are reported, with biallelic variants identified in individuals from 13 families and de novo in 8 families. Similar features were reported for AR/AD occurrences of the disorder and included of microcephaly (90% - most often primary), epilepsy (23/32 or 74% - variable semiology incl. partial/myoclonic/generalized tonic-clonic seizures), DD and ID (as a universal feature), abnormal tone in several (hypotonia/spasticity), ataxia, demyelinating peripheral neuropathy (in 3 or more for each inheritance mode - or a total of 25%). Some individuals had dysmorphic features. NARS1 encodes an aminoacyl-tRNA synthetase (ARS) [asparaginyl-tRNA synthetase 1]. Aminoacyl-tRNA synthetases constitute a family of enzymes catalyzing attachment of amino-acids to their cognate tRNAs. As the authors comment, mutations in genes encoding several other ARSs result in neurological disorders ranging from peripheral neuropathy to severe multi-systemic NDD. Dominant, recessive or both modes for inheritance for mutations in the same gene (e.g. AARS1, YARS1, MARS1, etc) have been reported. Some variants were recurrent, e.g. the c.1600C>T / p.Arg534* which occurred in 6 families as a de novo event or c.1633C>T p.Arg545Cys (homozygous in 6 families). 3 different variants were reported to have occured de novo (c.965G>T - p.Arg322Leu, c.1525G>A - p.Gly509Ser, p.Arg534*) with several other variants identified in hmz/compound htz individuals. A single SNV (c.1067A>C - p.Asp356Ala) was suggested to be acting as modifier and pathogenic only when in trans with a severe variant. [NM_004539.4 used as RefSeq for all]. The authors provide several lines of evidence for a partial loss-of-function effect (e.g. reduction in mRNA expression, enzyme levels and activity in fibroblasts or iNPCs) underlying pathogenicity of the variants identified in individuals with biallelic variants. A gain-of-function (dominant-negative) effect is proposed for de novo variants (such effect also demonstrated for the p.Arg534* in a zebrafish model). As also Manole et al suggest, NARS1 can be considered for inclusion in gene panels for DD/ID, epilepsy and/or demyelinating neuropathy. Sources: Literature; to: [Please note that HGNC Approved Gene Symbol for this gene is NARS1] Manole et al (2020 - PMID: 32738225) provide evidence that both biallelic and monoallelic (de novo) pathogenic NARS1 variants cause a neurodevelopmental disorder. In total 32 individuals from 21 families are reported, with biallelic variants identified in individuals from 13 families and de novo in 8 families. Similar features were reported for AR/AD occurrences of the disorder and included microcephaly (90% - most often primary), epilepsy (23/32 or 74% - variable semiology incl. partial/myoclonic/generalized tonic-clonic seizures), DD and ID (as a universal feature), abnormal tone in several (hypotonia/spasticity), ataxia, demyelinating peripheral neuropathy (in 3 or more for each inheritance mode - or a total of 25%). Some individuals had dysmorphic features. NARS1 encodes an aminoacyl-tRNA synthetase (ARS) [asparaginyl-tRNA synthetase 1]. Aminoacyl-tRNA synthetases constitute a family of enzymes catalyzing attachment of amino-acids to their cognate tRNAs. As the authors comment, mutations in genes encoding several other ARSs result in neurological disorders ranging from peripheral neuropathy to severe multi-systemic NDD. Dominant, recessive or both modes for inheritance for mutations in the same gene (e.g. AARS1, YARS1, MARS1, etc) have been reported. Some variants were recurrent, e.g. the c.1600C>T / p.Arg534* which occurred in 6 families as a de novo event or c.1633C>T p.Arg545Cys (homozygous in 6 families). 3 different variants were reported to have occured de novo (c.965G>T - p.Arg322Leu, c.1525G>A - p.Gly509Ser, p.Arg534*) with several other variants identified in hmz/compound htz individuals. A single SNV (c.1067A>C - p.Asp356Ala) was suggested to be acting as modifier and pathogenic only when in trans with a severe variant. [NM_004539.4 used as RefSeq for all]. The authors provide several lines of evidence for a partial loss-of-function effect (e.g. reduction in mRNA expression, enzyme levels and activity in fibroblasts or iNPCs) underlying pathogenicity of the variants identified in individuals with biallelic variants. A gain-of-function (dominant-negative) effect is proposed for de novo variants (such effect also demonstrated for the p.Arg534* in a zebrafish model). As also Manole et al suggest, NARS1 can be considered for inclusion in gene panels for DD/ID, epilepsy and/or demyelinating neuropathy. Sources: Literature |
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| Early onset or syndromic epilepsy v2.131 | NARS |
Konstantinos Varvagiannis gene: NARS was added gene: NARS was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: NARS was set to BOTH monoallelic and biallelic, autosomal or pseudoautosomal Publications for gene: NARS were set to 32738225 Phenotypes for gene: NARS were set to Abnormal muscle tone; Microcephaly; Global developmental delay; Intellectual disability; Seizures; Ataxia; Abnormality of the face; Demyelinating peripheral neuropathy Penetrance for gene: NARS were set to Complete Review for gene: NARS was set to GREEN Added comment: [Please note that HGNC Approved Gene Symbol for this gene is NARS1] Manole et al (2020 - PMID: 32738225) provide evidence that both biallelic and monoallelic (de novo) pathogenic NARS1 variants cause a neurodevelopmental disorder. In total 32 individuals from 21 families are reported, with biallelic variants identified in individuals from 13 families and de novo in 8 families. Similar features were reported for AR/AD occurrences of the disorder and included of microcephaly (90% - most often primary), epilepsy (23/32 or 74% - variable semiology incl. partial/myoclonic/generalized tonic-clonic seizures), DD and ID (as a universal feature), abnormal tone in several (hypotonia/spasticity), ataxia, demyelinating peripheral neuropathy (in 3 or more for each inheritance mode - or a total of 25%). Some individuals had dysmorphic features. NARS1 encodes an aminoacyl-tRNA synthetase (ARS) [asparaginyl-tRNA synthetase 1]. Aminoacyl-tRNA synthetases constitute a family of enzymes catalyzing attachment of amino-acids to their cognate tRNAs. As the authors comment, mutations in genes encoding several other ARSs result in neurological disorders ranging from peripheral neuropathy to severe multi-systemic NDD. Dominant, recessive or both modes for inheritance for mutations in the same gene (e.g. AARS1, YARS1, MARS1, etc) have been reported. Some variants were recurrent, e.g. the c.1600C>T / p.Arg534* which occurred in 6 families as a de novo event or c.1633C>T p.Arg545Cys (homozygous in 6 families). 3 different variants were reported to have occured de novo (c.965G>T - p.Arg322Leu, c.1525G>A - p.Gly509Ser, p.Arg534*) with several other variants identified in hmz/compound htz individuals. A single SNV (c.1067A>C - p.Asp356Ala) was suggested to be acting as modifier and pathogenic only when in trans with a severe variant. [NM_004539.4 used as RefSeq for all]. The authors provide several lines of evidence for a partial loss-of-function effect (e.g. reduction in mRNA expression, enzyme levels and activity in fibroblasts or iNPCs) underlying pathogenicity of the variants identified in individuals with biallelic variants. A gain-of-function (dominant-negative) effect is proposed for de novo variants (such effect also demonstrated for the p.Arg534* in a zebrafish model). As also Manole et al suggest, NARS1 can be considered for inclusion in gene panels for DD/ID, epilepsy and/or demyelinating neuropathy. Sources: Literature |
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| Early onset or syndromic epilepsy v2.78 | SEMA6B | Rebecca Foulger changed review comment from: PMID:32169168. In 4 unrelated patients (2 Japanese, ISraeli and Malaysian) with progressive myoclonic epilepsy, Hamanaka et al. (2020) identified de novo heterozygous frameshift mutations in the last exon of the SEMA6B gene. Variants were predicted to result in truncated proteins. Truncating variants in this region of the gene were not observed in the gnomAD database, although truncating variants in other regions of the gene were observed in gnomAD. The authors postulated a dominant-negative or gain-of-function effect rather than haploinsufficiency. In an animal model, the authors found that zebrafish with truncating sema6b variants were more susceptible to seizures.; to: PMID:32169168. In 4 unrelated patients (2 Japanese, 1 Israeli and 1 Malaysian) with progressive myoclonic epilepsy, Hamanaka et al. (2020) identified de novo heterozygous frameshift mutations in the last exon of the SEMA6B gene. Variants were predicted to result in truncated proteins. Truncating variants in this region of the gene were not observed in the gnomAD database, although truncating variants in other regions of the gene were observed in gnomAD. The authors postulated a dominant-negative or gain-of-function effect rather than haploinsufficiency. In an animal model, the authors found that zebrafish with truncating sema6b variants were more susceptible to seizures. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v2.47 | UGDH |
Konstantinos Varvagiannis gene: UGDH was added gene: UGDH was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: UGDH was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: UGDH were set to 32001716 Phenotypes for gene: UGDH were set to Epileptic encephalopathy, early infantile, 84 - MIM #618792 Penetrance for gene: UGDH were set to Complete Review for gene: UGDH was set to GREEN Added comment: Hengel et al (2020 - PMID: 32001716) report on 36 individuals with biallelic UGDH pathogenic variants. The phenotype corresponded overall to a developmental epileptic encephalopathy with hypotonia, feeding difficulties, severe global DD, moderate or commonly severe ID in all. Hypotonia and motor disorder (incl. spasticity, dystonia, ataxia, chorea, etc) often occurred prior to the onset of seizures. A single individual did not present seizures and 2 sibs had only seizures in the setting of fever. Affected subjects were tested by exome sequencing and UGDH variants were the only/best candidates for the phenotype following also segregation studies. Many were compound heterozygous or homozygous (~6 families were consanguineous) for missense variants and few were compound heterozygous for missense and pLoF variants. There were no individuals with biallelic pLoF variants identified. Parental/sib studies were all compatible with AR inheritance mode. UGDH encodes the enzyme UDP-glucose dehydrogenase which converts UDP-glucose to UDP-glucuronate, the latter being a critical component of the glycosaminoglycans, hyaluronan, chondroitin sulfate, and heparan sulfate [OMIM]. Patient fibroblast and biochemical assays suggested a LoF effect of variants leading to impairment of UGDH stability, oligomerization or enzymatic activity (decreased UGDH-catalyzed reduction of NAD+ to NADH / hyaluronic acid production which requires UDP-glucuronate). Attempts to model the disorder using an already developped zebrafish model (for a hypomorphic LoF allele) were unsuccessful as fish did not exhibit seizures spontaneously or upon induction with PTZ. Modelling of the disorder in vitro using patient-derived cerebral organoids demonstrated smaller organoids due to reduced number of proliferating neural progenitors. Sources: Literature |
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| Early onset or syndromic epilepsy v2.0 | RNF113A |
Konstantinos Varvagiannis gene: RNF113A was added gene: RNF113A was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: RNF113A 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: RNF113A were set to 25612912; 31880405; 31793730; 29133357; 30506991; 15256591; 24026126; 23555887 Phenotypes for gene: RNF113A were set to ?Trichothiodystrophy 5, nonphotosensitive, 300953 Penetrance for gene: RNF113A were set to Complete Review for gene: RNF113A was set to GREEN Added comment: The gene has been reviewed for the ID panel. Seizures have been reported in 4 affected males from 3 families. From the ID panel: Nonphotosensitive trichothiodystrophy-5 (TTD5 - #300953) is caused by mutation in the RNF113A gene on Xq24. DD, ID and seizures are part of the phenotype in males. (Several) heterozygous females have not been reported to exhibit these features (DD/ID/seizures) although a single female in the first report had speech/motor delay and learning difficulties. Corbett et al (2015 - PMID: 25612912) reported on 2 cousins with profound ID and epilepsy among other principal features of the disorder. Linkage analysis (probably low(?) LOD score) localized the gene to a 7.75 Mb region on Xq and subsequent Sanger and exome sequencing identified an RNF113A stopgain variant in both (NM_006978.2:c.901C>T / p.Q301*). Other X-chr variants did not segregate with the disorder. Previously sequencing of other trichothiodystrophy genes (in both) and CMA (X-chromosome BAC array / ISCA CMA) were non-diagnostic. The variant in this family was identified in a previous study (Tarpey et al 2009 - PMID: 19377476) but was 'incorrectly' discarded at the time due to a sequencing error in a control DNA sample (analysis repeated by Corbett et al). The same variant was also reported in 2 fetuses in a later report (PMID: 31793730). Mendelsohn et al (2019 - PMID: 31880405) reported on 2 unrelated affected males. The 1st presented with severe DD/ID (independent walking at 7y, single words/non-verbal with with special educational needs at 11y), seizures as well as typical features of the disorder. Metabolic work-up (incl. 7-DHCR) and genetic testing (Allagile, PFIC genes, CMA) were non-diagnostic. Duo WES revealed a frameshift variant [c.903_910delGCAGACCCA / p.(Gln302fs*12)] inherited from the mother. Maternal XCI was completely skewed (100:0). The 2nd individual (briefly reported as REQ18-0616 by Monies et al - PMID: 31130284) presented global DD and seizures along with all other core features of the disorder at the age of 16m. Karyotype was normal. Exome revealed a frameshift variant [NM_006978.3:c.897_898delTG / p.(Cys299*)]. Further evidence is based on the role of the RNA113A, being involved in mRNA splicing (/spiceosome function) [Gatti da Silva et al 2018 - PMID: 30506991 & many other Refs] as well in DNA repair (E3 ubiquitin-protein ligase in a mechanism for sensing DNA damage induced by alkylation) [Brickner et al 2017 - PMID: 29133357]. In the latter study, LCLs from individuals harboring Q301* were shown to be hypersensitive to an alkylating agent (MMS) which was also the case for an RNF113A knockdown cell line. The cells had reduced ASCC alkylation repair complex foci formation, which was rescued upon reconstitution of patient cells with wt RNF113A. Animal models : Disruption of rnf113a in zebrafish resulted among others in small head and underdeveloped gut (PMID cited : 15256591 - Amsterdam et al) similar to the microcephaly observed in several individuals and/or abnormal gut development/diarrhoea reported in few. Knockdown of the Drosophila ortholog (mdlc) led to reduced proliferation of neuroblasts. Neuronal differentiation was initiated but not completed. Expression of the full-length human gene rescued the CNS defects (discussed by Mendelsohn et al citing PMID: 24026126 - Carney et al). RNA-seq data from the same study were analyzed by Corbett et al, and differentialy expressed genes were enriched for genes involved in DNA damage response and repair. Knockdown of RNF-113 in C.elegans sensitises cells to UVA-induced DNA damage. RNF-113 was shown to be involved in interstrand DNA crosslink repair and interact with a RAD51C homolog (PMID cited: 23555887 - Lee et al). [Please consider upgrade/inclusion in other relevant panels eg. the 'Xeroderma pigmentosum, Trichothiodystrophy or Cockayne syndrome panel' where the gene has red rating]. Sources: Literature |
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| Early onset or syndromic epilepsy v2.0 | DLL1 |
Konstantinos Varvagiannis gene: DLL1 was added gene: DLL1 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: DLL1 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: DLL1 were set to 31353024 Phenotypes for gene: DLL1 were set to Global developmental delay; Intellectual disability; Morphological abnormality of the central nervous system; Seizures; Behavioral abnormality; Autism; Scoliosis Penetrance for gene: DLL1 were set to unknown Review for gene: DLL1 was set to AMBER Added comment: Gene added to the ID panel. Epilepsy has been reported in 6 unrelated individuals. Please consider inclusion with amber/green rating. ---- Heterozygous DLL1 pathogenic variants cause Neurodevelopmental disorder with nonspecific brain abnormalities and with or without seizures (# 618709). Fischer-Zirnsak et al (2019 - PMID: 31353024) reported on 15 affected individuals from 12 unrelated families. Most common features included DD/ID (12/14), ASD (6/14 - belonging to 6 families) or other behavioral abnormalities, seizures (6/14 - from 6 unrelated families) and various brain MRI abnromalities. As commented by OMIM (based on the same ref) "Cognitive function ranges from severely impaired to the ability to attend schools with special assistance". Among other features, scoliosis was observed in 4. The authors could not identify a distinctive facial gestalt. Variable initial investigations (where discussed/performed - also suggesting relevance to the current panel) included CMA, FMR1, FLNA, mitochondrial DNA analysis and metabolic work-up but had not revealed an alternative cause. The DLL1 variants were identified by WES (with the exception of a 122-kb microdeletion spanning DLL1 and FAM120B detected by CMA). Nonsense, frame-shift, splice-site variants in positions predicted to result to NMD were identified in most. One individual was found to harbor a missense variant (NM_005618.3:c.536G>T / p.Cys179Phe) and another the aforementioned microdeletion. The variant in several individuals had occurred as a de novo event. In 2 families, it was inherited from an also affected parent (an unaffected sib was non-carrier) while in 3 families parental studies were not possible/complete. In frame insertion of 4 residues was demonstrated for a splice site variant, from LCLs of the corresponding individual. For another individual, material was unavailable for mRNA studies. The missense variant affected a cysteine (of the DSL domain) conserved in all Notch ligands while AA changes affecting the same position of JAG1 (another Notch ligand) have been described in patients with Alagille s. Based on the variants identified and reports of deletions spanning DLL1 in the literature, haploinsufficiency is the proposed underlying mechanism. The gene has also a pLI of 1 and %HI of 4.65. DLL1 encodes the Delta-like canonical Notch ligand 1. Notch signaling is an established pathway for brain morphogenesis. Previous in vivo and in vitro studies have demonstrated the role of DLL1 in CNS. The gene is highly expressed in neuronal precursor cells during embryogenesis. Expression of Dll1 (and other molecules of the Notch signalling pathway) in an oscillatory/sustained pattern and cell-cell interactions important for this pathway have been demonstrated to play a role in neuronal differentiation. [Most discussed by Fischer-Zirnsak et al with several refs provided / also Gray et al., 1999 - PMID: 10079256 & OMIM]. Animal models as summarized by the authors: [Mouse] Loss of Dll1 in mice has been shown to increase neuronal differentiation, cause CNS hyperplasia and increased number of neurons (PMIDs cited: 9109488, 12397111, 20081190). Reduced Dll1 expression was associated with scoliosis and mild vertebral defects (cited PMIDs: 19562077, 14960495, 22484060 / among others Dll1 haploinsufficiency and dominant negative models studied). Scoliosis and vertebral segmentation defects were features in 4 and 1 individual, respectively in the cohort of 15. [Zebrafish] Homozygous mutations in dlA, the zebrafish ortholog, disrupted the Delta-Notch signaling and led to patterning defects in the hindbrain and overproduction of neurons (cited: 15366005). Sources: Literature |
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| Early onset or syndromic epilepsy v2.0 | UGP2 |
Konstantinos Varvagiannis gene: UGP2 was added gene: UGP2 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: UGP2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: UGP2 were set to 31820119 Phenotypes for gene: UGP2 were set to Seizures; Global developmental delay; Intellectual disability; Feeding difficulties; Abnormality of vision; Abnormality of the face Penetrance for gene: UGP2 were set to Complete Review for gene: UGP2 was set to GREEN Added comment: Perenthaler et al. (2019 - PMID: 31820119) provide evidence that homozygosity for a variant abolishing the start codon of the UGP2 transcript (NM_001001521.1) encoding the predominant (short) protein isoform in brain, leads to a severe epileptic encephalopathy. This variant (chr2:64083454A>G / NM_001001521.1:c.1A>G - p.?) is also predicted to result in a substitution of a methionine at position 12 by a valine of the longer UGP2 transcript (NM_006759.3:c.34A>G - p.Met12Val). The 2 isoforms differ only by 11 amino acids at the N-terminal and are otherwise expected to be functionally equivalent. The authors provide details on 22 individuals from 15 families (some of which consanguineous). Features included intractable seizures (in all), absence of developmental milestones (in all), progressive microcephaly, visual impairment. The authors reported also presence of somewhat similar facial features. Some of these individuals passed away early. Previous work-up in several of them (incl. SNP-array, gene panel testing and metabolic investigations) had not revealed any abnormality, apart from ROH in some individuals. In all cases, the homozygous UGP2 SNV was the only P/LP variant for the neurodevelopmental phenotype following exome/genome sequencing. Segregation studies in affected/unaffected family members were compatible. Families came from the Netherlands (but mostly from) India, Pakistan and Iran. Presence of a region of homozygosity shared between individuals from different families suggested that the variant might represent a mutation that originated several generations ago (in the area of Balochistan). The variant is present 15x in gnomAD, only in heterozygous state (in Asian mostly, reported once in Ashkenazi Jewish or Europeans) [ https://gnomad.broadinstitute.org/variant/2-64083454-A-G ]. UGP2 encodes UDP-glucose pyrophosphorylase which is an essential enzyme in sugar metabolism, catalyzing conversion of glucose-1-phosphate to UDP-glucose. UDP-glucose, in turn, serves as precursor for production of glycogen by glycogen synthase. The authors provide several lines of evidence for a the role of the gene in the CNS as well as for the deleterious effect of the specific variant : - In patient fibroblasts total UGP2 levels were not signifficantly different compared to parent / control fibroblasts, the longer isoform being upregulated (and stable) when the shorter is missing. Immunocytochemistry demonstrated similar localization of UGP2 in the case of mutant or wt cells. Enzymatic activity (/capacity to produce UDP-glucose) was similar between homozygous mut, heterozygous and wt fibroblasts. - In H9-derived neural stem cells, Western Blot, RT-PCR and qRT-PCR suggested that the short isoform is the predominant one. (In embryonic stem cells, or fibroblasts the ratio between short and long isoform was lower). - Analysis of RNA-seq data from human fetal tissues suggested that the short isoform is the predominant in brain. - UGP2 was detected upon immunohistochemistry in fetal brain tissues from first to third trimester of pregnancy while Western Blot confirmed preferential expression of the shorter isoform. - Homozygous embryonic (ESC) or neural stem cells (NSC) for the variant (knock-in/KI) or for a frameshift variant (knock-out/KO) were generated. Study of NSCs demonstrated reduced total UGP2 protein expression upon Western Blot in the case of KI cells and depleted in KO ones. Transcriptome analysis did not show major transcriptome alterations in KI/KO ESCs compared to wt. In NSC KI/KO cells transcriptome alterations were observed compared to wt with upregulation among others of genes for synaptic processes and genes implicated in epilepsy. - The absence of UGP2 was shown to result in reduced ability of KO/KI NSCs to produce UDP-glucose, reduced capacity to synthesize glycogen under hypoxia (rescued in the case of KO cells by overexpression of wt or long isoform), defects of protein glycosylation as well as in increased unfolded protein response (/susceptibility to ER stress). These alterations are commented to be possibly implicated in pathogenesis of epilepsy, progressive microcephaly, etc. - A CRISPR-Cas9 zebrafish model leading with loss of ugp2a and hypomorphic ugp2b (the zebrafish homologs of UGP2) demonstrated abnormal behavior, reduced eye movements and increased frequency/duration of movements upon stimulation with a potent convulsant (suggestive of increased seizure susceptibility). - UGP knockout in drosophila is lethal while flies compound heterozygous for hypomorphic alleles are viable but show a movement defects due to altered synaptogenesis secondary to glycosylation defects (cited PMID: 27466186). - The authors make speculations as for the occurrence of a single variant (and not others) eg. absence of UGP2 (in the case of LoF variants affecting both isoforms) would possibly be incompatible with life, Met12Val being tolerable for the long transcript not affecting stability/enzymatic activity (which may not be the case for other substitutions affecting Met12), etc. Sources: Literature |
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| Early onset or syndromic epilepsy v2.0 | AFF3 |
Konstantinos Varvagiannis changed review comment from: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb affecting only AFF3 (LAF4) and removing also this sequence. The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy]. 9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13. AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development. Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot. Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study]. Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects. Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant. Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3. ---- In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM. ---- As a result this gene can be considered for inclusion in the epilepsy panel as green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article). Sources: Literature --------------- Shimizu et al. (8/2019 - PMID: 31388108) describe an additional individual with de novo AFF3 missense variant. The phenotype overlaps with that summarized by Voisin et al. incl. mesomelic dysplasia with additional skeletal anomalies, bilateral kidney hypoplasia and severe DD at the age of 2.5 years. Seizures and pulmonary problems were not observed. Although a different RefSeq is used the variant is among those also reported by Voisin et al. [NM_002285.2:c.697G>A (p.Ala233Thr) corresponding to NM_001025108.1:c.772G>A (p.Ala258Thr)].; to: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb deletion affecting only AFF3 (LAF4) and removing also this sequence. The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy]. 9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13. AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development. Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot. Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study]. Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects. Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant. Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3. ---- In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM. ---- As a result this gene can be considered for inclusion in the epilepsy panel as green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article). Sources: Literature --------------- Shimizu et al. (8/2019 - PMID: 31388108) describe an additional individual with de novo AFF3 missense variant. The phenotype overlaps with that summarized by Voisin et al. incl. mesomelic dysplasia with additional skeletal anomalies, bilateral kidney hypoplasia and severe DD at the age of 2.5 years. Seizures and pulmonary problems were not observed. Although a different RefSeq is used the variant is among those also reported by Voisin et al. [NM_002285.2:c.697G>A (p.Ala233Thr) corresponding to NM_001025108.1:c.772G>A (p.Ala258Thr)]. |
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| Early onset or syndromic epilepsy v1.405 | PCYT2 |
Konstantinos Varvagiannis gene: PCYT2 was added gene: PCYT2 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: PCYT2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PCYT2 were set to 31637422 Phenotypes for gene: PCYT2 were set to Global developmental delay; Developmental regression; Intellectual disability; Spastic paraparesis; Seizures; Cerebral atrophy; Cerebellar atrophy Penetrance for gene: PCYT2 were set to Complete Review for gene: PCYT2 was set to GREEN Added comment: Vaz et al. (2019 - PMID: 31637422 - DDD study among the co-authors) report on 5 individuals - from 4 families - with biallelic PCYT2 mutations. The phenotype corresponded to a complex hererditary paraplegia with global DD, regression (4/5), ID (mild in 3/5, severe in 2/5), spastic para-/tetraparesis, epilepsy (5/5 - variable onset 2-16 yrs - focal or tonic-clonic seizures) and progressive cerebral and cerebellar atrophy. Exome sequencing in all revealed biallelic PCYT2 variants, confirmed with Sanger s. in probands and their parents (NM_001184917.2 - corresponding to the canonical transcript used as Ref below): - P1 (Fam1) : 2 missense SNVs in trans configuration, c.730C>T or p.His244Tyr and c.920C>T or p.Pro307Leu - P2 (Fam2 - consanguineous of White British origin), P3 (Fam3 - Consanguineous of Turkish origin), P4,5 (Fam4 - consanguineous, unspecified origin) : homozygosity for c.1129C>T or p.Arg377Ter) affecting the last exon of 8/12 transcripts, including the canonical one. Individuals with the same genotype displayed variable degrees of ID (eg P3 - severe / P2, P4,5 - mild ID). For sibs in Fam4, homozygosity for a missense SACS variant led to consideration of the respective disorder (AR spastic ataxia of Charlevoix-Saguenay) though the variant was predicted to be tolerated in silico and notably the MRI images not suggestive. All variants were absent from / had extremely low AF in public databases, with no homozygotes. Posphatidylethanolamine (PE) is a membrane lipid, particularly enriched in human brain (45% of phospholypid fraction). PE is synthesized either via the CDP-ethanolamine pathway or by decarboxylation of phosphatidylserine in mitochondria. PCYT2 encodes CTP:phosophoethanolamine cytidyltransferase (ET) which is an ubiquitously expressed rate-limiting enzyme for PE biosynthesis in the former pathway. In silico, the 2 missense variants - localizing in the CTP catalytic domain 2 - were predicted to be damaging, as well as to affect protein stability. Fibroblasts of 3 patients (P1, P2, P3) representing all variants were studied: - Enzymatic activity was shown to be significantly reduced (though not absent) compared to controls. Abnormalities were noted upon Western Blot incl. absence in all 3 patients studied of one of the 2 bands normally found in controls (probably representing the longer isoform), reduced intensity in all 3 of another band probably corresponding to a shorter isoform, and presence of an additional band of intermediate molec. mass in patients with the truncating variant. - RT-PCR on mRNA from patient fibroblasts did not reveal (significant) reduction compared to controls. - Lipidomic profile of patient fibroblasts was compatible with the location of the block in the phospholipid biosynthesis pathway and different from controls. The lipidomic profile had similarities with what has been reported for EPT1 deficiency, the enzyme directly downstream of ET. The SELENO1-related phenotype (/EPT1 deficiency) is also highly overlapping. CRISPR-Cas9 was used to generate pcyt2 partial or complete knockout (ko) zebrafish, targeting either the final (ex13) or another exon (ex3) respectively. mRNA expression was shown to be moderately reduced in the first case and severely reduced/absent in the second, compared to wt. Similarly, complete-ko (ex3) led to significantly lower survival, with impaired though somewhat better survival of partial-ko (ex13) zebrafish. Complete knockout of Pcyt2 in mice is embryonically lethal (PMID cited: 17325045) while heterozygous mice develop features of metabolic syndrome (PMID cited: 22764088). Given lethality in knockout zebrafish / mice and the residual activity (15-20%) in patient fibroblasts, the variants reported were thought to be hypomorphic and complete loss of function possibly incompatible with life. PCYT2 is not associated with any phenotype in OMIM/G2P/SysID and not commonly included in gene panels for ID. As a result this gene could included in the ID / epilepsy panels with green (~/>3 indiv/fam/variants with the nonsense found in different populations, consistent phenotype, lipidomics, in silico/in vitro/in vivo evidence) or amber rating. [Please consider inclusion in other possibly relevant panels eg. for metabolic disorders, etc]. Sources: Literature |
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| Early onset or syndromic epilepsy v1.351 | TDP2 |
Konstantinos Varvagiannis gene: TDP2 was added gene: TDP2 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: TDP2 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: TDP2 were set to 24658003; 30109272; 31410782 Phenotypes for gene: TDP2 were set to Spinocerebellar ataxia, autosomal recessive 23, 616949 Penetrance for gene: TDP2 were set to unknown Review for gene: TDP2 was set to GREEN Added comment: Biallelic pathogenic TGP2 variants cause Spinocerebellar ataxia, autosomal recessive 23 (MIM 616949). At least 6 affected individuals from 4 families have been reported, in all cases homozygous for LoF variants (3 different). ID, epilepsy and ataxia are consistent features of the disorder. TDP2 encodes a phosphodiesterase that is required for efficient repair of double strand breaks (DSBs) produced by abortive topoisomerase II (TOP2) activity. The gene is expressed in fetal and adult human brain. Evidence at the variant level (mRNA, protein levels) and additional studies for impairment of TOP2-induced DSB repair support a role. Animal models (primarily mice) reproduce the DSB repair defect, provide some histopathological evidence, show transcriptional dysregulation of genes (in line with the role of TOP2 in transcription). They have however failed to reproduce relevant neurological phenotypes. Published studies are summarized below. TDP2 is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc and GeneDx). There is no associated phenotype in G2P. TDP2 is listed among the current primary ID genes in SysID. Overall, this gene could be considered for inclusion in the ID and epilepsy panels probably as green (>=3 patients/families/variants, relevant ID and seizures in all, expression in brain, mRNA/protein levels tested, impaired activity) or amber (absence of neurological phenotypes in mouse model). ------------ [1] - PMID: 24658003 (Gómez-Herreros et al. 2014): Reports 3 individuals from a consanguineous Irish family. Features included seizures (onset by 2m, 6m and 12y), ID (3/3) and ataxia (3/3). A splicing variant (NM_016614.3:c.425+1G>A) was found in a 9.08-Mb region of homozygosity shared by all. A further ZNF193 missense variant localizing in the same region was thought unlikely to contribute to the phenotype (evidence also provided in subsequent study). The effect of the specific variant was proven by abnormal mRNA size, lower mRNA levels due to NMD (corrected upon cyclohexamide treatment), loss of TDP2 protein upon WB, loss of protein activity in lymphoblastoid cells from affected individuals, decreased repair of DSBs and increased cell death upon addition of etoposide (which promotes TOP2 abortive activity). The authors report very briefly on a further patient (from Egypt), with ID, 'reports of fits' and ataxia. This individual, with also affected sibs, was homozygous LoF (c.413_414delinsAA / p.Ser138*). Again, the authors were not able to detect TDP2 activity in blood from this subject. As also commented: - TDP2 has relevant expression in human (particularly adult) brain. - Mouse model : Tdp2 is expressed in relevant tissues, absence of Tdp2 activity was observed in neural tissue of mice homoyzgous for an ex1-3 del, with impairment of DSB repair. The authors were unable to detect a neurological phenotype with behavioral analyses, preliminary assesment of seizure propensity. Mice did not show developmental defects. Histopathology however, revealed ~25% reduction in the density of interneurons in cerebellum (a 'hallmark of DSB repair' and associated with seizures and ataxia). Transcription of several genes was shown to be disregulated. - Knockdown in zebrafish appears to affect left-right axis detremination (cited PMID: 18039968). [2] - PMID: 30109272 (Zagnoli-Vieira et al. 2018): A 6 y.o. male with seizures (onset by 5m), hypotonia, DD and ID, microcephaly and some additional clinical features and testing (ETC studies on muscle biopsy, +lactate, +(lactate/pyruvate) ratio) which could be suggestive of mitochondrial disorder. This individual from the US was homozygous for the c.425+1G>A variant but lacked the ZNF193 one (despite a shared haplotype with the Irish patients). Again absence of the protein was shown upon WB in patient fibroblasts, also supported by its activity. Complementation studies restored the DSB repair defect. The defect was specific to TOP2-induced DSBs as suggested by hypersensitivity to etoposide but not to ionizing radiation. CRISPR/Cas9 generated mutant human A549 cells demonstrated abnormal DSB repair. Fibroblasts / edited A549 cells failed to show mitochondrial defects (which were noted in muscle). [3] - PMID: 31410782 (Ciaccio et al. 2019): A girl born to consanguineous Italian parents, presented with moderate/severe ID, seizures (onset at 12y) and - among others - gait ataxia, tremor and dysmetria. MRI at the age of 12, demonstrated cerebellar atrophy (although previous exams were N). WES revealed a homozygous nonsense variant (c.400C>T / p.Arg134Ter) for which each parent was found to be carrier. Previous investigations included aCGH, NGS testing for epilepsy and metabolic testing. Sources: Literature |
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| Early onset or syndromic epilepsy v1.260 | KATNB1 |
Konstantinos Varvagiannis gene: KATNB1 was added gene: KATNB1 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: KATNB1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: KATNB1 were set to 25521378; 25521379; 26640080 Phenotypes for gene: KATNB1 were set to Lissencephaly 6, with microcephaly (MIM 616212) Review for gene: KATNB1 was set to GREEN Added comment: Biallelic pathogenic KATNB1 variants cause Lissencephaly 6, with microcephaly (MIM 616212). At least 13 affected individuals from 9 (mostly consanguineous) families have probably been reported in the following articles: - Mishra-Gorur et al. (2014 - PMID: 25521378) [7 individuals from 5 unrelated families] - Hu et al. (2014 - PMID: 25521379) [5 individuals from 3 families] - Yigit el al. (2016 - PMID: 26640080) [1 subject born to consanguineous parents] Seizures can be part of the phenotype (although not universal / reported in all 3 studies in several families). Several different variants have been reported to date. Extensive studies as for the impact of mutations at the cellular level as well as animal models (zebrafish, mouse, drosophila) support involvement of KATNB1. These arguments, provided mainly by the first two studies, are summarized in the respective OMIM entry for the disorder : https://omim.org/entry/616212 (variants and their effect are discussed in the entry for KATNB1 - https://omim.org/entry/602703). The individual reported by Yigit el al. was a 5 year-old girl with - among others - severely delayed psychomotor development and seizures. The child was found to harbor a homozygous splice site variant (removing the acceptor AG signature). Confirmation of the variant and segregation studies were performed with Sanger sequencing. cDNA studies were carried out and demonstrated aberrant splicing. KATNB1 is not associated with any disorder in G2P. The gene is included in panels for ID offered by several diagnostic laboratories (incl. Radboudumc). As a result, this gene can be considered for inclusion in the current panel probably as green (or amber). Sources: Literature |
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| Early onset or syndromic epilepsy v1.256 | GOT2 |
Konstantinos Varvagiannis gene: GOT2 was added gene: GOT2 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: GOT2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: GOT2 were set to 31422819 Phenotypes for gene: GOT2 were set to Global developmental delay; Intellectual disability; Seizures; Increased serum lactate; Hyperammonemia; Microcephaly; Failure to thrive; Feeding difficulties; Abnormality of nervous system morphology Penetrance for gene: GOT2 were set to Complete Review for gene: GOT2 was set to GREEN Added comment: van Karnebeek et al. (2019 - PMID: 31422819) report on 4 individuals from 3 families, with biallelic GOT2 pathogenic variants (3 missense SNVs and 1 in-frame deletion). The phenotype corresponded to a metabolic encephalopathy with onset of epilepsy in the first year of life (4/4) with DD and ID (4/4). Additional features included postnatal microcephaly, failure to thrive/feeding difficulties and cerebral anomalies (atrophy and white matter). All subjects had high blood lactate and hyperammonemia. Plasma serine was low in one case (alternative causes were ruled out). Administration of serine and pyridoxine led to clinical improvement (cessation / better control of seizures) in 2 subjects suggesting that GOT2 deficiency may be amenable to therapeutic intervention. [Treatment could not be started in the 2 further affected individuals]. GOT2 encodes the mitochondrial glutamate oxaloacetate transaminase, a component of the malate-aspartate shuttle (MAS). The latter is important for intracellular NAD(H) redox homeostasis. The authors provide several lines of evidence that GOT2 deficiency explains the patients' phenotype and metabolic defects incl. : - Reduced GOT2 protein levels (due to lower expression/impaired stability) and diminished activity in patient fibroblasts (lower activity was also shown for carriers). Rescue of the GOT enzymatic activity was observed upon transduction of patient fibroblasts using lentiviral particles with wt GOT2. - Impairment of de novo serine biosynthesis in patient (and to a lesser extent in carrier) fibroblasts compared to controls. This was similar in GOT2-knockout HEK293 cells. Serine biosynthesis in these cells was restored by pyruvate supplementation. - CRISPR/Cas9 Got2-knockout mice resulted in early lethality (during pregnancy). Heterozygous mice were viable and healthy. - Morpholino knockdown of got2a in zebrafish was shown to perturb embryonic development (smaller head, slow circulation, bend body, brain developmental defects, etc). Pyridoxine and serine in embryo water resulted in milder phenotypes/improved morphant survival. Zebrafish got2a morphants had seizure-like spikes upon EEG that were rescued by treatment with pyridoxine. GOT2 is not associated with any phenotype in OMIM/G2P. As a result, this gene can be considered for inclusion in both epilepsy and ID gene panels probably as green (3 families, relevant phenotypes and severity, evidence from cell and animal studies) or amber. [Please consider inclusion in other relevant panels eg. mitochondrial disorders, metabolic disorders and/or addition of the 'treatable' tag]. Sources: Literature |
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| Early onset or syndromic epilepsy v1.196 | AFF3 |
Konstantinos Varvagiannis changed review comment from: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb affecting only AFF3 (LAF4) and removing also this sequence. The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy]. 9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13. AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development. Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot. Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study]. Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects. Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant. Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3. ---- In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM. ---- As a result this gene can be considered for inclusion in the epilepsy panel as green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article). Sources: Literature; to: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb affecting only AFF3 (LAF4) and removing also this sequence. The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy]. 9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13. AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development. Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot. Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study]. Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects. Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant. Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3. ---- In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM. ---- As a result this gene can be considered for inclusion in the epilepsy panel as green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article). Sources: Literature --------------- Shimizu et al. (8/2019 - PMID: 31388108) describe an additional individual with de novo AFF3 missense variant. The phenotype overlaps with that summarized by Voisin et al. incl. mesomelic dysplasia with additional skeletal anomalies, bilateral kidney hypoplasia and severe DD at the age of 2.5 years. Seizures and pulmonary problems were not observed. Although a different RefSeq is used the variant is among those also reported by Voisin et al. [NM_002285.2:c.697G>A (p.Ala233Thr) corresponding to NM_001025108.1:c.772G>A (p.Ala258Thr)]. |
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| Early onset or syndromic epilepsy v1.193 | AFF3 |
Konstantinos Varvagiannis gene: AFF3 was added gene: AFF3 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: AFF3 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: AFF3 were set to https://doi.org/10.1101/693937; 18616733 Phenotypes for gene: AFF3 were set to Intellectual disability; Seizures; Abnormality of skeletal morphology; Abnormality of the urinary system; Hypertrichosis; Abnormality of the respiratory system Penetrance for gene: AFF3 were set to unknown Mode of pathogenicity for gene: AFF3 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: AFF3 was set to GREEN Added comment: Voisin et al. (2019 - https://doi.org/10.1101/693937) report on 10 individuals with de novo missense AFF3 variants affecting a 9-amino-acid sequence (degron) important for the protein's degradation and summarize the phenotype of an additional individual previously described by Steichen-Gersdorf et al. (2008 - PMID: 18616733) with a 500 kb affecting only AFF3 (LAF4) and removing also this sequence. The phenotype of missense variants consisted of kidney anomalies, mesomelic dysplasia, seizures, hypertrichosis, intellectual disability and pulmonary problems and was overlapping with that of the deletion. [10 of 11 subjects exhibited severe developmental epileptic encephalopathy]. 9 probands harbored missense variants affecting the codon 258 while one individual had a variant affecting codon 260 [c.772G>T or p.Ala258Ser (x2), c.772G>A or p.Ala258Thr (x6), c.773C>T or p.Ala258Val (x1) and c.779T>G or p.(Val260Gly) (x1) - NM_001025108.1 / NP_001020279.1]. The deletion removed exons 4-13. AFF1-4 are ALF transcription factor paralogs, components of the transcriptional super elongation complex regulating expression of genes involved in neurogenesis and development. Using HEK293T cells expressing FLAG-tagged AFF3 (and AFF4) wt or mutants, accumulation of mutated forms was shown upon immunoblot. Aff3+/- and/or -/- mice exhibit skeletal defects. These were more pronounced in homozygous mice which demonstrated also some elements in favor of kidney dysfunction and/or metabolic deregulation and possible neurological dysfunction (signs of impaired hearing and diminished grip strength). Homozygous mice had CNS anomalies (enlarged lateral ventricles and decreased corpus callosum size) similar to some affected individuals, although these were not observed in another Aff3-/- model. Knock-in mice modeling the microdeletion and the Ala258Thr variant displayed lower mesomelic limb deformities and early lethality respectively [cited PMIDs : 21677750, 25660031, knock-in model was part of the present study]. Accumulation of the protein in zebrafish (by overexpression of the human wt AFF3 mRNA), led to morphological defects. Reanalysis of transcriptome data from previously generated HEK293T cell lines knocked down for AFF2, AFF3 and AFF4 by shRNAs (study) suggested that these transcription factors are not redundant. Finally, CHOPS syndrome (#616368) due to mutations of AFF4 also leading to increased protein stability presents a partially overlapping phenotype (incl. cognitive impairment) to that of AFF3. ---- In G2P, AFF3 is associated with Skeletal dysplasia with severe neurological disease (disease confidence : probable / ID and seizures among the assigned phenotypes). There is no associated phenotype in OMIM. ---- As a result this gene can be considered for inclusion in the epilepsy panel as green (relevant phenotype and severity, sufficient cases, evidence for accumulation similar to AFF4, animal models, etc) or amber (pending publication of the article). Sources: Literature |
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| Early onset or syndromic epilepsy v1.193 | WDR37 |
Konstantinos Varvagiannis gene: WDR37 was added gene: WDR37 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: WDR37 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: WDR37 were set to 31327510; 31327508 Phenotypes for gene: WDR37 were set to Global developmental delay; Intellectual disability; Seizures; Abnormality of the eye; Abnormality of nervous system morphology; Hearing abnormality; Abnormality of the cardiovascular system; Abnormality of the skeletal system; Abnormality of the genitourinary system Penetrance for gene: WDR37 were set to unknown Mode of pathogenicity for gene: WDR37 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: WDR37 was set to GREEN Added comment: Two concurrent publications by Reis et al. and Kanca et al. (2019 - PMIDs: 31327510, 31327508) report on the phenotype of individuals with de novo WDR37 mutations. The study by Reis et al. provides clinical details on 4 affected individuals, while 5 further are described by Kanca et al. 4 different de novo variants were reported in these individuals who appear to be unrelated in (and between) the 2 studies [NM_014023.3]: - c.356C>T (p.Ser119Phe) [Reis indiv. 1 - 3y, Kanca proband 3 - 5m2w] - c.389C>T (p.Thr130Ile) [Reis indiv. 2 - 22m , Kanca proband 5 - 6 w] - c.374C>T (p.Thr125Ile) [Reis indiv. 3 - 8y , Kanca proband 1 - 7y] - c.386C>G (p.Ser129Cys) [Reis indiv. 4 - unkn age, Kanca probands 2 and 4, 6.5y and 19y] Common features included DD/ID (severity relevant for the current panel), seizures (9/9), ocular anomalies (corneal opacity/Peters anomaly, coloboma, microphthalmia etc.) and variable brain, hearing, cardiovascular, skeletal and genitourinary anomalies. Some facial and/or other dysmorphic features (incl. excess nuchal skin / webbed neck) were also frequent among affected individuals. Feeding difficulties and growth deficiency were also among the features observed. The function of WDR37 is not known. Variants demonstrated comparable protein levels and cellular localization compared to wt. Reis et al. provide evidence using CRISPR-Cas9 mediated genome editing in zebrafish, to introduce the Ser129Cys variant observed in affected individuals as well as novel missense and frameshift variants. Poor growth (similar to the human phenotype) and larval lethality were noted for missense variants. Head size was proportionately small. Ocular (coloboma/corneal) or craniofacial anomalies were not observed. Zebrafish heterozygous for LoF variants survived to adulthood. Based on these a dominant-negative mechanism was postulated for missense alleles. RNA-seq analysis in zebrafish showed upregulation of cholesterol biosynthesis pathways (among the most dysregulated ones). Previous data in mice, suggest a broad expression pattern for Wdr37 with enrichment in ocular and brain tissues, significant associations in homozygous mutant mice for decreased body weight, grip strength, skeletal anomalies and possible increase (p =< 0.05) in ocular (lens/corneal) and other anomalies [BioGPS and International Mouse Phenotyping Consortium cited]. CG12333 loss (the Drosophila WDR37 ortholog) causes increased bang sensitivity in flies (analogous to the human epilepsy phenotype), defects in copulation and grip strength, phenotypes that were rescued by human reference but not variant cDNAs. As discussed by Kanca et al. based on data from Drosophila and mice, limited phenotypic similarity of CNVs spanning WDR37 and adjacent genes with the reported individuals and the presence of LoF variants in control populations haploinsufficiency appears unlikely. Gain-of-function is also unlikely, as expression of human variants in flies did not exacerbate the observed phenotypes. A dominant-negative effect is again proposed. WDR37 is not associated with any phenotype in OMIM/G2P. As a result WDR37 can be considered for inclusion in the ID and epilepsy panels with green (relevant phenotype, sufficient cases, animal models) or amber rating. Sources: Literature |
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| Early onset or syndromic epilepsy v1.191 | BRAF | Rebecca Foulger Source Wessex and West Midlands GLH was added to BRAF. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.190 | BRAF | Rebecca Foulger Source NHS GMS was added to BRAF. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.189 | BRAF | Rebecca Foulger reviewed gene: BRAF: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.188 | BRAF | Tracy Lester reviewed gene: BRAF: Rating: GREEN; Mode of pathogenicity: ; Publications: 19206169, 18042262; Phenotypes: Adenocarcinoma of lung, somatic 211980, Cardiofaciocutaneous syndrome, 115150, Colorectal cancer, somatic, LEOPARD syndrome, 613707, Melanoma, malignant, somatic, Nonsmall cell lung cancer, somatic, Noonan syndrome, 613706; Mode of inheritance: MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.167 | DEGS1 |
Konstantinos Varvagiannis gene: DEGS1 was added gene: DEGS1 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: DEGS1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: DEGS1 were set to 30620337; 30620338; 31186544 Phenotypes for gene: DEGS1 were set to Leukodystrophy hypomyelinating 18, 618404 Penetrance for gene: DEGS1 were set to Complete Review for gene: DEGS1 was set to GREEN Added comment: Several individuals with biallelic pathogenic DEGS1 variants have been reported to date, in the following studies : [1] Pant et al. 2019 (PMID: 30620337) : 19 patients from 13 unrelated families [2] Karsai et al. 2019 (PMID: 30620338) : 1 individual [3] Dolgin et al. 2019 (PMID: 31186544) : 4 individuals belonging to a large consanguineous kindred As summarized in the first article and OMIM, affected individuals may have very poor psychomotor development, dystonia, spasticity, seizures with hypomyelinating leukodystrophy upon brain imaging and/or progressive atrophy of corpus callosum, thalami and cerebellum. Although a severe form overall was reported for many individuals in the first study, variable severity (eg. mild to severe ID) was reported among individuals belonging to the same kindred in the report by Dolgin et al. DEGS1 encodes Δ4-dehydroceramide desaturase which catalyzes conversion of dihydroceramide (DhCer) to ceramide (Cer) in the de novo ceramide biosynthetic pathway. Ceramide is the central unit of all sphingolipids, which are components of cellular membranes and play key roles in several processes incl. cell differentiation, neuronal signaling and myelin sheath formation. Sphingolipid balance is important for the CNS as demonstrated in the case of lysosomal disorders (eg. Gaucher, Niemann Pick, Farber) one enzymatic step away from DEGS1. Variants of all types (missense, stopgain, frameshift) have been reported with the majority/almost all located in the fatty acid desaturase (FAD) domain. Extensive studies have been carried out and demonstrated: - impaired DEGS1 activity in patients' fibroblasts and muscle suggested by increased DhCer/Cer ratio and compatible broader biochemical effects (higher levels of dihydrosphingosine, dihydrosphingomyelins, etc. and lower levels of sphingosine, monohexosylceramides, etc). - increased ROS production in patient fibroblasts (similar to a Drosophila model of excess DhCer), - high expression of the gene in child and adult CNS tissues from control individuals (evaluated by RT-qPCR in Ref. 1). A previous study has suggested that DEGS1 expression is upregulated during the 4-9th week of human embryogenesis (PMID cited: 20430792) which may suggest an important role for neural system development. - decreased expression for some variants either evaluated at the mRNA (RT-qPCR) / protein level (by Western Blot) - In zebrafish loss of Degs1 resulted in increased DhCer/Cer ratio, locomotor disability and impaired myelination similar to the patients' phenotype. Fingolimod, a sphingosine analog inhibiting Cer synthase (one step prior to DEGS1 in the de novo ceramide biosynthesis pathway, and converting sphingosine to ceramide in the salvage pathway) reduced the DhCer/Cer imbalance, ameliorated the locomotor phenotype and increased the number of myelinating oligodendrocytes in zebrafish, while it reduced the ROS levels in patient fibroblasts. Previous animal models: Apart from the zebrafish model (Pant et al.), higher DhCer/Cer ratios have been shown in homozygous Degs1 -/- mice similar to what is also observed in D. melanogaster. As summarized in MGI (and the previous studies as well) "mice homozygous for a knock-out allele exhibit premature death, decreased to absent ceramide levels, decreased body weight, scaly skin, sparse hair, tremors, hematological and blood chemistry abnormalities, decreased bone mineral content and density and decreased liver function." (PMIDs cited: 17339025, 28507162). ---- The respective OMIM entry is Leukodystrophy, hypomyelinating, 18 (#618404). DEGS1 is not associated with any phenotype in G2P. ---- As a result, DEGS1 can be considered for inclusion in the ID and epilepsy panels probably as green (relevant phenotype, sufficient number of individuals, supportive expression and biochemical studies, animal models, etc). Sources: Literature |
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| Early onset or syndromic epilepsy v0.927 | GNB5 |
Konstantinos Varvagiannis gene: GNB5 was added gene: GNB5 was added to Genetic epilepsy syndromes. Sources: Literature,Expert Review Mode of inheritance for gene: GNB5 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: GNB5 were set to 27523599; 27677260; 28697420; 29368331 Phenotypes for gene: GNB5 were set to Intellectual developmental disorder with cardiac arrhythmia, 617173; Language delay and ADHD/cognitive impairment with or without cardiac arrhythmia, 617182 Penetrance for gene: GNB5 were set to Complete Review for gene: GNB5 was set to GREEN Added comment: Biallelic GNB5 pathogenic variants cause Intellectual developmental disorder with cardiac arrhythmia (MIM 617173) or language delay and ADHD/cognitive impairment with or without cardiac arrhythmia (MIM 617182). PMID: 27523599 is the first report on the associated phenotype. A total of 9 individuals from 6 different families (from various ethnic backgrounds) are described. The common features included hypotonia (noted in 6 out of 9 patients), intellectual disability (9/9 - in 3 cases mild, in 6 severe), heart rate disturbance (9/9 - in most cases sick sinus syndrome), seizures (4/9), ophthalmological problems (nystagmus in 6 out of 7 for whom this information was available) as well as gastric problems (5/8 with G-E reflux). The 6 variants (summarized in table S1) included : 2 nonsense mutations, 1 synonymous (demonstrated to affect splicing and leading to retention of 25 intronic bp), 2 further splice variants (positions +1 and +3) and a missense one (S81L). Nonsense mediated decay was the case for the product of the synonymous/splice variant as well as for a stopgain one. As noted by the authors, individuals homozygous for the S81L variant had a less severe phenotype - among others - with mild degree of intellectual disability. Functional studies included knockout of gnb5 in zebrafish, which was able to reproduce the human neurological, cardiac and ophthalmological phenotypes. Alternative causes for these phenotypes (incl. chromosomal or metabolic disorders) were ruled out. Affected individuals might benefit interventions for their heart rate disturbance as appears to be the case in the article as well as subsequent studies. PMID: 27677260 describes an extended consanguineous Saudi family with 5 individuals homozygous for the S81L variant. Common features included severe language delay, ADHD, but normal cognition in those available for evaluation. Seizures were not reported. Pathogenicity of the S81L variant is further supported by functional studies. PMID: 28697420 describes in detail 2 individuals from a large consanguineous pedigree confirmed to be homozygous for a single nucleotide deletion in GNB5. The phenotype included severe DD/ID, seizures, sinus bradycardia with frequent sinus pauses and ophthalmological problems. Sinus arrhythmia and or seizures were documented in several other relatives deceased and unavailable for testing. PMID: 28327206 reports on 2 subjects previously included in PMID: 27523599. PMID: 29368331 describes a child with severe developmental delay, nystagmus and sinus arrhythmia necessitating a pacemaker. EEG was abnormal although no frank seizures were observed. The child was compound heterozygous for a novel missense variant (R246Q) as well a 5 basepair deletion. Epilepsy was a feature in at least 6 individuals reported. 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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| Early onset or syndromic epilepsy v0.744 | BRAF | Sarah Leigh Marked gene: BRAF as ready | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.744 | BRAF | Sarah Leigh Added comment: Comment when marking as ready: Associated with relevant phenotypes in OMIM and as confirmed Gen2Phen gene for Cardiofaciocutaneous syndrome 115150 & LEOPARD syndrome 3 613707. PMID 18039946 reported seizures in around half of their genetically confirmed Cardiofaciocutaneous syndrome 115150 cases (n=38) and PMID 19206169 reports 11 variants in 9 cases of Cardiofaciocutaneous syndrome 115150, 2 cases of Noonan syndrome 7 613706 and one case of LEOPARD syndrome 3 613707. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.744 | BRAF | Sarah Leigh Gene: braf has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.744 | BRAF | Sarah Leigh Classified gene: BRAF as Green List (high evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.744 | BRAF | Sarah Leigh Gene: braf has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.743 | BRAF | Sarah Leigh Phenotypes for gene: BRAF were changed from Cardiofaciocutaneous syndrome 115150; LEOPARD syndrome 3 613707 to Cardiofaciocutaneous syndrome 115150; Noonan syndrome 7 613706; LEOPARD syndrome 3 613707 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.739 | BRAF | Sarah Leigh Added comment: Comment on mode of pathogenicity: Activating variants responsible for phenotype | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.739 | BRAF | Sarah Leigh Mode of pathogenicity for gene: BRAF was changed from None to Loss-of-function variants (as defined in pop up message) DO NOT cause this phenotype - please provide details in the comments | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.736 | BRAF | Sarah Leigh Publications for gene: BRAF were set to | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.735 | BRAF | Sarah Leigh Phenotypes for gene: BRAF were changed from to Cardiofaciocutaneous syndrome 115150; LEOPARD syndrome 3 613707 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.734 | BRAF | Sarah Leigh Mode of inheritance for gene: BRAF was changed from to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy | BRAF | Zornitza Stark reviewed gene: BRAF | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy | BRAF | Sarah Leigh Added gene to panel | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||