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| Early onset or syndromic epilepsy v2.500 | CACNA2D1 |
Helen Lord changed review comment from: Dahimne et al, 2022, 35293990 - two unrelated patients with biallelic CACNA2D1 variants - trio exome sequencing - identified by gene matcher. Patient 1: homozygous fs variant c.818_821dup p.(Ser275fs) - healthy parents het carriers. Patient 2: compound het for a fs c.13_23dup p.(Leu9fs) and a missense variant c.626G>A p.(Gly209Asp) - parents healthy carriers of each of the variants. Both individuals show a highly consistent phenotype, corresponding to DEE - microcephalic, severe hypotonia, absent speech, spasticity, choreiform movements, orofacial dyskinesia and cortical visual impairement. Brain imaging showed corpus callosum hypoplasia and progressive volume loss in both. Both patients also showed insensitivity to pain. Looking at mRNA level in patient fibroblasts in both patients showed it was reduced to 6-9% compared to control fibroblasts. Also data suggest the fs variants result in LOF. Gly209 - this Gly is important for maintaining a 3-strand-beta-sheet-stability and simultaneously provididn ga critial turn in the structure and is absoloutely invariant in both CACNA2D1 and CACNA2D2 orthologs in all vertebrates and paralogs and predecessors from low invertebrates. Functional work on the missense change shows it disrupts plasma membrane a2d-1 expression by 86.2% compared to wt. It abolishes the ability of a2d-1 to promote Cav2.2 currents, it does not promote Cav2.2 cell surface expression or trafficking in hippocampal neurons and it shows reduced complex formation with Cav2.2 and limited proteolytic cleavage. Suggests the HA-a2b-1 with the G209D variant remains largely as the uncleaved imaature form, indicating that it probably remains in the endoplasmic reticulum - suggests LOF effect. Sources: NHS GMS; to: Dahimne et al, 2022, 35293990 - two unrelated patients with biallelic CACNA2D1 variants - trio exome sequencing - identified by gene matcher. Patient 1: homozygous fs variant c.818_821dup p.(Ser275fs) - healthy parents het carriers. Patient 2: compound het for a fs c.13_23dup p.(Leu9fs) and a missense variant c.626G>A p.(Gly209Asp) - parents healthy carriers of each of the variants. Both individuals show a highly consistent phenotype, corresponding to DEE - microcephalic, severe hypotonia, absent speech, spasticity, choreiform movements, orofacial dyskinesia and cortical visual impairement. Brain imaging showed corpus callosum hypoplasia and progressive volume loss in both. Both patients also showed insensitivity to pain. Looking at mRNA level in patient fibroblasts in both patients showed it was reduced to 6-9% compared to control fibroblasts. Also data suggest the fs variants result in LOF. Gly209 - this Gly is important for maintaining a 3-strand-beta-sheet-stability and simultaneously providing a critial turn in the structure and is absoloutely invariant in both CACNA2D1 and CACNA2D2 orthologs in all vertebrates and paralogs and predecessors from low invertebrates. Functional work on the missense change shows it disrupts plasma membrane a2d-1 expression by 86.2% compared to wt. It abolishes the ability of a2d-1 to promote Cav2.2 currents, it does not promote Cav2.2 cell surface expression or trafficking in hippocampal neurons and it shows reduced complex formation with Cav2.2 and limited proteolytic cleavage. Suggests the HA-a2b-1 with the G209D variant remains largely as the uncleaved imaature form, indicating that it probably remains in the endoplasmic reticulum - suggests LOF effect. Sources: NHS GMS |
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| Early onset or syndromic epilepsy v2.500 | CACNA2D1 |
Helen Lord changed review comment from: Dahimne et al, 2022, 35293990 - two unrelated patients with biallelic CACNA2D1 variants - trio exome sequencing - identified by gene matcher. Patient 1: homozygous fs variant c.818_821dup p.(Ser275fs) - healthy parents het carriers. Patient 2: compound het for a fs c.13_23dup p.(Leu9fs) and a missense variant c.626G>A p.(Gly209Asp) - parents healthy carriers of each of the variants. Both individuals show a highly conssitent phenotype, corresponding to DEE - microcephalic, severe hypotonia, absent speech, spasticity, choreiform movements, orofacial dyskinesia and cortical visual impairement. Brain imaging showed corpus callosum hypoplasia and progressive volume loss in both. Both patients also showed insensitivty to apin Looking at mRNA level in patient fibroblasts in both pTIWNTS showed it was reduced to 6-9% compared to control fibroblasts. Also data suggest the fs variants result in LOF. Gly209 - this Gly is importnat for maintaining a 3-strand-beta-sheet-stability and simultaneously provididn ga critial turn in the structure and is absoloutely invariant in both CACNA2D1 and CACNA2D2 orthologs in all vertebrates and paralogs and predecessors from low invertebrates. Functional work on the missense change shows it disrupts plasma membrane a2d-1 expression by 86.2% compared to wt. It abolshes the ability of a2d-1 to promote Cav2.2 currents, it does not promote Cav2.2 cell surface exprtession or trafficking in hippocampal neurons and it shows reduced complex formation with Cav2.2 and limited proteolytic cleavage. Suggests the HA-a2b-1 with the G209D variant remians largely as the uncleaved imaature form, indicating that it probably remains in the endoplasmic reticulum - suggests LOF effect. Sources: NHS GMS; to: Dahimne et al, 2022, 35293990 - two unrelated patients with biallelic CACNA2D1 variants - trio exome sequencing - identified by gene matcher. Patient 1: homozygous fs variant c.818_821dup p.(Ser275fs) - healthy parents het carriers. Patient 2: compound het for a fs c.13_23dup p.(Leu9fs) and a missense variant c.626G>A p.(Gly209Asp) - parents healthy carriers of each of the variants. Both individuals show a highly consistent phenotype, corresponding to DEE - microcephalic, severe hypotonia, absent speech, spasticity, choreiform movements, orofacial dyskinesia and cortical visual impairement. Brain imaging showed corpus callosum hypoplasia and progressive volume loss in both. Both patients also showed insensitivity to pain. Looking at mRNA level in patient fibroblasts in both patients showed it was reduced to 6-9% compared to control fibroblasts. Also data suggest the fs variants result in LOF. Gly209 - this Gly is important for maintaining a 3-strand-beta-sheet-stability and simultaneously provididn ga critial turn in the structure and is absoloutely invariant in both CACNA2D1 and CACNA2D2 orthologs in all vertebrates and paralogs and predecessors from low invertebrates. Functional work on the missense change shows it disrupts plasma membrane a2d-1 expression by 86.2% compared to wt. It abolishes the ability of a2d-1 to promote Cav2.2 currents, it does not promote Cav2.2 cell surface expression or trafficking in hippocampal neurons and it shows reduced complex formation with Cav2.2 and limited proteolytic cleavage. Suggests the HA-a2b-1 with the G209D variant remains largely as the uncleaved imaature form, indicating that it probably remains in the endoplasmic reticulum - suggests LOF effect. Sources: NHS GMS |
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| Early onset or syndromic epilepsy v2.500 | CACNA2D1 |
Helen Lord gene: CACNA2D1 was added gene: CACNA2D1 was added to Genetic epilepsy syndromes. Sources: NHS GMS Mode of inheritance for gene: CACNA2D1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: CACNA2D1 were set to 35293990 Phenotypes for gene: CACNA2D1 were set to Early onset developmental epilepsy Review for gene: CACNA2D1 was set to AMBER Added comment: Dahimne et al, 2022, 35293990 - two unrelated patients with biallelic CACNA2D1 variants - trio exome sequencing - identified by gene matcher. Patient 1: homozygous fs variant c.818_821dup p.(Ser275fs) - healthy parents het carriers. Patient 2: compound het for a fs c.13_23dup p.(Leu9fs) and a missense variant c.626G>A p.(Gly209Asp) - parents healthy carriers of each of the variants. Both individuals show a highly conssitent phenotype, corresponding to DEE - microcephalic, severe hypotonia, absent speech, spasticity, choreiform movements, orofacial dyskinesia and cortical visual impairement. Brain imaging showed corpus callosum hypoplasia and progressive volume loss in both. Both patients also showed insensitivty to apin Looking at mRNA level in patient fibroblasts in both pTIWNTS showed it was reduced to 6-9% compared to control fibroblasts. Also data suggest the fs variants result in LOF. Gly209 - this Gly is importnat for maintaining a 3-strand-beta-sheet-stability and simultaneously provididn ga critial turn in the structure and is absoloutely invariant in both CACNA2D1 and CACNA2D2 orthologs in all vertebrates and paralogs and predecessors from low invertebrates. Functional work on the missense change shows it disrupts plasma membrane a2d-1 expression by 86.2% compared to wt. It abolshes the ability of a2d-1 to promote Cav2.2 currents, it does not promote Cav2.2 cell surface exprtession or trafficking in hippocampal neurons and it shows reduced complex formation with Cav2.2 and limited proteolytic cleavage. Suggests the HA-a2b-1 with the G209D variant remians largely as the uncleaved imaature form, indicating that it probably remains in the endoplasmic reticulum - suggests LOF effect. Sources: NHS GMS |
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| Early onset or syndromic epilepsy v2.145 | TUBGCP2 |
Arina Puzriakova gene: TUBGCP2 was added gene: TUBGCP2 was added to Genetic epilepsy syndromes. Sources: Literature for-review tags were added to gene: TUBGCP2. Mode of inheritance for gene: TUBGCP2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: TUBGCP2 were set to 31630790 Phenotypes for gene: TUBGCP2 were set to Pachygyria, microcephaly, developmental delay, and dysmorphic facies, with or without seizures, 618737 Review for gene: TUBGCP2 was set to GREEN Added comment: Associated with phenotype in OMIM, and a probable gene for Microcephaly and Lissencephaly Spectrum Disorders in G2P. PMID: 31630790 (2019) - Five patients from four families with biallelic variants in the TUBGCP2 gene. Affected individuals shared phenotypic features that included progressive microcephaly (4/4), developmental delay (5/5, mild-severe), generalised seizures (4/5, onset at 6yrs-9m, 5m, and 7m). All patients exhibited lissencephaly-spectrum phenotypes with varying degrees of cortical malformations on brain imaging including pachygyria and subcortical band heterotopia. All variants segregated with disease in each family. Analysis of fibroblasts derived from one patient with a splice site variant revealed several abnormal transcripts, predicted to result in LoF. No further functional studies of other variants or patient cells were performed. Sources: Literature |
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| Early onset or syndromic epilepsy v2.143 | MADD |
Konstantinos Varvagiannis gene: MADD was added gene: MADD was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: MADD was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: MADD were set to 28940097; 29302074; 32761064 Phenotypes for gene: MADD were set to Global developmental delay / Intellectual disability / Seizures; Global developmental delay / Intellectual disability / Seizures / Abnormality of the endocrine system / Exocrine pancreatic insufficiency / Constipation / Diarrhea / Anemia / Thrombocytopenia / Abnormality of the autonomic nervous system Penetrance for gene: MADD were set to Complete Review for gene: MADD was set to GREEN Added comment: There are 3 reports on the phenotype of individuals with biallelic pathogenic MADD variants. Clinical presentation appears to be relevant for inclusion of this gene in both ID and epilepsy panels. A recent study provides extensive clinical details and suggests that the phenotype may range from DD/ID to a severe pleiotropic disorder characterized by severe DD (and ID), sensory and autonomic dysfunction, exocrine and endocrine insufficiency and haematological anomalies). Seizures have been reported in several individuals with either presentation. ----- Anazi et al (2017 - PMID: 28940097) identified MADD as a potential ID gene. The authors described a girl with profound DD and seizures among other features. The child, deceased at the age of 14m, was born to consanguineous Saoudi parents and was found to harbour a homozygous missense SNV [NM_003682.3:c.2930T>G:p.(Val977Gly)]. Through GeneMatcher, the authors identified a further 6 y.o. girl, compound heterozygous for a missense and a stopgain variant [NM_003682.3:c.593G>A:p.(Arg198His) and c.979C>T:p.(Arg327*)]. The child had normal development and milestones until the age of 15m, when she demonstrated delay in speech, social interactions, poor eye contact and was later diagnosed with ASD. ----- Hu et al (2019 - PMID: 29302074) provided details on a 22- and 30- y.o. female born to (reportedly) unrelated parents. Formal evaluation (WAIS-IV) suggested ID in the mild to moderate range(IQs of 50 and 60 respectively). Both were homozygous for an indel [NM_003682:c.3559del / p.(Met1187*)]. ----- Schneeberger et al (2020 - PMID: 32761064) report on 23 affected subjects. The authors categorized the phenotypes in 2 groups. 9 individuals belonging to group 1 presented with hypotonia, DD (9/9) with speech impaiment, ID (5/5) and seizures (6/9). 14 patients, belonging to group 2 had DD (9/9 - severe), ID (3/3), seizures (9/14), endo- and exocrine dysfunction, impairment of sensory and autonomic nervous system, haematological anomalies. The course was fatal in some cases, within the later group. Some facial features appeared to be more frequent (e.g. full cheeks, small mouth, tented upper lip - small palpebral fissures in some, etc). Genital anomalies were also common in males from both groups. All were found to harbor biallelic MADD variants (21 different - missense and pLoF SNVs as well as an intragenic deletion). Variants in all cases affected all 7 isoforms. Data did not allow genotype-phenotype correlations e.g. individuals with missense and a pLoF variant (in trans) were identified within either group. Studies using patient-derived fibroblasts supported the role of the variants, e.g. lower mRNA levels for those where NMD would apply, deficiency or drastic reduction of the protein upon immunobloting (also the case for missense variants) and mRNA analyses demonstrating aberrant transcripts for 2 relevant variants. MADD encodes the MAPK-activating protein containing a death domain implicated among others in neurotransmission (Rab3 GEF and effector playing a role in formation/trafficking of synaptic vessicles), cell survival (pro-apoptotic effects/protection against apoptosis upon TNF-a treatment), etc. The gene has relevant expression pattern in fetal and adult brain (discussed by Hu et al). Studies in patient fibroblasts provide evidence of reduced activation of MAP kinases ERK1/2 upon treatment with TNF-a, activation of the intrinsic (TNF-a-dependent-) apoptosis. MADD deficiency was shown to result to decreased EGF endocytosis (likely mediated by Rab3). Mouse model further supports the role of MADD (summary by MGI: "Mice homozygous for a knock-out allele die shortly after birth due to respiratory failure, are hyporesponsive to tactile stimuli, and exhibit defects in neurotransmitter release with impaired synaptic vesicle trafficking and depletion of synaptic vesicles at the neuromuscular junction."). You may consider inclusion in other gene panels e.g. for hematologic (low Hb and thrombocytopenia in several) or GI (e.g diarrhea) disorders. Sources: Literature |
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| 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 v1.497 | OXR1 |
Konstantinos Varvagiannis gene: OXR1 was added gene: OXR1 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: OXR1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: OXR1 were set to https://doi.org/10.1016/j.ajhg.2019.11.002 Phenotypes for gene: OXR1 were set to Central hypotonia; Global developmental delay; Delayed speech and language development; Intellectual disability; Seizures; Abnormality of the cerebellum Penetrance for gene: OXR1 were set to Complete Review for gene: OXR1 was set to GREEN Added comment: Wang et al (2019 - https://doi.org/10.1016/j.ajhg.2019.11.002 ) report on 5 individuals (from 3 families) with biallelic OXR1 LoF variants. Common features included hypotonia (4/5), severe global DD (5/5) and speech delay (5/5), ID (5/5), epilepsy (5/5) with cerebellar dysplasia/atrophy (5/5) and in some scoliosis. All were investigated by exome sequencing and were found to harbor biallelic loss-of-function variants (2 splice-site, a stopgain and a frameshift one) either in homozygosity (2 consanguineous families) or in compound heterozygosity. In all cases parental segregation studies were compatible and in one family, an unaffected sib shown to be carrier. Althouhgh OXR1 has been shown to affect several processes (among others DNA lesions induced by oxidative stress in E.coli, neuronal maintenance, mitochondrial morphology and DNA maintenance, etc), its mechanism of action is still not well defined. There are 6 RefSeq transcripts, the longest (NM_018002.3) encoding 3 protein domains (LysM, GRAM, TLDc). The TLDc domain is encoded by all transcripts. Identified variants affected (probably all - fig1D) transcripts expressed in the CNS, namely NM_018002.3, NM_001198532.1, NM_181354.4. The 3 transcripts not expressed in the CNS are NM_001198533.1, NM_001198534.1 and NM_001198535.1. Western blot with 2 different antibodies which would bind upstream of the truncation site failed to detect presence of truncated proteins in 2 affected individuals from 2 families. The Drosophila homolog of OXR is mustard (mtd). The authors provide evidence that loss of mtd is lethal. This was however rescued by expression of an 80kb fly BAC clone covering mtd, or the fly mtd-RH isoform cDNA, or a short human OXR1 cDNA containing only the TLDc domain or a human NCOA7 cDNA. The latter is another human mtd homolog which also contains the TLDc domain. As a result the TLDc domain compensated sufficiently for loss of mtd. Flies that survived displayed bang sensitivity and climbing defects the former assay being suggestive of susceptibility to seizures and the latter of impaired neurological/muscular function. The authors provided evidence that mtd is broadly expressed in the fly CNS. RNAi mediated mtd knockdown specific to neurons (elav/nSyb-GAL4 expression of mtd RNAi) led to lethal eclosion defects for RNAis targeting most (18)/all(23) mtd isoforms. Lifespan was increased upon expression of human OXR1 cDNA. Neuronal loss and vacuolization was demonstrated and additional experiments in R7 photoreceptors showed presence of aberrant lysosomal structures (autolysosomes, autophagosomes and/or endolysosomes). Aberrant lysosomal structures were also observed in fibroblasts from affected individuals (accumulation of lysosomes and/or presence of highly aberrant compartments with content typical of lysosomal dysfunction). Overall the data presented suggest a critical role for OXR1 in lysosomal biology. Although previous reports suggested that OXR1 is involved in oxidative stress resistance, studies performed by the authors suggested that oxidative stress is probably not the driver of the mutant fly defects. Sources: Literature |
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| Early onset or syndromic epilepsy v1.475 | TMX2 |
Konstantinos Varvagiannis gene: TMX2 was added gene: TMX2 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: TMX2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: TMX2 were set to 31586943; 31735293; 31270415 Phenotypes for gene: TMX2 were set to Global developmental delay; Intellectual disability; Seizures; Microcephaly; Abnormal cortical gyration Penetrance for gene: TMX2 were set to Complete Review for gene: TMX2 was set to GREEN Added comment: This gene was reviewed for the intellectual disability panel. Epilepsy is part of the phenotype. Therefore green rating should be considered. From the ID panel : A recent report by Vandervore, Schot et al. following the previous review (Am J Hum Genet. 2019 Nov 12 - PMID: 31735293), provides further evidence that biallelic TMX2 mutations cause malformations of cortical development, microcephaly, DD and ID and epilepsy. As a result this gene should probably be considered for inclusion in the ID/epilepsy panels with green rating. Overall, 14 affected subjects from 10 unrelated families are reported in the aforementioned study. The majority had severe DD/ID (failure to achieve milestones, absent speech/ambulation and signs of cerebral palsy) with few having a somewhat milder impairment. 12 (of the 14) presented with epilepsy (spasms, myoclonic seizures, focal seizures with/without generalization or generalized tonic-clonic seizures) with onset most often in early infancy. Upon brain MRI (in 12 individuals), 5 presented polymicrogyria, 2 others pachygyria, 4 with brain atrophy, etc. All individuals were found to harbor biallelic TMX2 mutations by exome sequencing while previous investigations in several had ruled out alternative causes (infections, metabolic or chromosomal anomalies). Missense variants, an in-frame deletion as well as pLoF (stopgain/frameshift) variants were reported. [NM_015959.3 used as ref below]. The effect of variants was supported by mRNA studies, eg. RT-qPCR/allele specific RT-qPCR. The latter proved reduced expression for a frameshift variant (c.391dup / p.Leu131Profs*6) most likely due to NMD. Total mRNA levels were also 23% lower in an individual compound htz for a missense variant and a stopgain one localized in the last exon (c.757C>T / p.Arg253*). As for the previously reported c.614G>A (p.Arg205Gln), affecting the last nucleotide of exon 6, total mRNA in skin fibroblasts from a homozygous individual was not significantly decreased. RNA-Seq however demonstrated the presence of 4 different transcripts (roughly 25% each), one representing the regular mRNA, one with intron 6 retention (also present at low levels in healthy individuals), one with loss of 11 nucleotides within exon 6 and a fourth one due to in-frame skipping of exon 6. *To the best of my understanding : Thioredoxin (TRX)-related transmembrane proteins (TMX) belong to the broader family of oxidoreductases of protein disulfide isomerase (PDI) having an important role in protein folding. Study of the data from the Allen Human Brain Atlas suggest relevant fetal expression also increasing during postnatal life. As RNA-seq was carried out for 2 individuals, GO analysis suggested that the most deregulated clusters of genes are implicated in post-translational protein modifications (as would be expected for PDIs), membranes and synapse while pathway analysis suggested that relevant categories were inhibited eg. nervous system development/function and cell growth/proliferation/survival. Upon transfection of HEK293T cells, exogenous TMX2 was shown to co-localize with calnexin (CNX) to the (ER) mitochondria-associated-membrane. Mass-spectrometry based analysis of co-immunoprecipitated proteins confirmed interaction with CNX but also other regulators of calcium homeostasis, mitochondrial membrane components and respiratory chain NADH dehydrogenase. Study of the mitochondrial activity of TMX2-deficient fibroblasts suggested reduced respiratory reserve capacity, compensated by increased glycolytic activity. TMX2 occurs in both reduced and oxidized monomeric form. It also forms (homo)dimers with the ratio of dimers/monomers increasing under conditions of oxidative stress. Variant TMX2 increased propensity to form dimers, thus mimicking increased oxidative state. This was observed under stress but also under native conditions. --------- Created: 26 Nov 2019, 11:21 p.m. | Last Modified: 26 Nov 2019, 11:21 p.m. Panel Version: 2.1122 [Previous review] PMID: 31586943 - Ghosh et al. 2019 - reported on 8 individuals from 4 consanguineous families from the Middle East and Central Asia, all with a phenotype of DD/ID, seizures and microcephaly with lissencephaly (microlissencephaly is the term applying to the combination of two) upon brain MRI. All patients were investigated by exome sequencing and the variant localized within a region of ROH which was common to all 4 families. All were homozygous for a TMX2 missense variant (NM_001144012.2:c.500G>A or p.Arg167Gln / NM_015959.4:c.614G>A p.Arg205Gln or hg38 - Chr11:g.57739039G>A). The variant was considered to be the best candidate, upon review of all other homozygous ones. Sanger sequencing confirmed homozygosity for the variant in affected subjects, with additional compatible segregation studies including parents in all families as well as unaffected sibs (in two families). Despite presence of the same mutation in all, several proximal to this variant SNPs did not appear to be shared among the families studied, thus suggesting that the variant had arisen within different haplotype blocks. The authors comment that the variant was not previously identified in public databases. (The variant seems to correspond to rs370455806, present in 10 htz individuals in gnomAD, as well as in the GME database [GME Genotype Count 992:0:1 (hmz?) | Allele Count: 2,1984] . GME includes primarily - although not necessarily - healthy individuals). This SNV affecting the last nucleotide of an exon of several transcripts (correct ref. is NM_001144012.2 as appears in the supplement / using NM_001347898.1 as in the fig./text the variant would lie within an intron), an eventual splicing effect was studied. mRNA transcript levels were assessed following RT-PCR using different sets of primers. There was no evidence of novel splice isoforms but mRNA levels were reduced compared to controls (15-50% in affected individuals, to a lesser level in carriers). This led to the hypothesis that NMD of an aberrantly spliced mRNA might apply, although this was not proven. TMX2 encodes a protein disulfide isomerase (PDI). PDIs are transmembrane ER proteins which have a critical role in protein folding (PMID cited: 12670024). There were no relevant studies carried out in the article. As for animal models, the authors comment that mice homozygous for null mutations display preweaning lethality with complete penetrance.(http://www.informatics.jax.org/diseasePortal/popup?isPhenotype=true&markerID=MGI:1914208&header=mortality/aging). ------- Previously, Schot el al. (ESHG Conference 2018 Oral Presentation - Mutations in the thioredoxin related gene TMX2 cause primary microcephaly, polymicrogyria and severe neurodegeneration with impaired mitochondrial energy metabolism - available in PMID: 31270415 / https://www.nature.com/articles/s41431-019-0407-4 ) reported on 7 individuals from 5 unrelated families with biallelic TMX2 mutations. A newborn with microcephaly, polymicrogyria who died of refractory epilepsy, was compound heterozygous for 2 TMX2 variants. 6 additional individuals (from 4 unrelated families) with similar phenotype were found to harbor biallelic TMX2 mutations. It was commented that TMX2 is enriched in mitochondria-associated membrane of the ER with a role in ER stress protection and regulation of neuronal apoptosis. In line with this, fibroblasts from 2 unrelated patients showed secondary OXPHOS deficiency and increased glycolytic activity (the latter possibly as a compensatory mechanism). ------- There is no associated phenotype in OMIM/G2P/SysID. ------- Overall this gene could be considered for inclusion in the ID/epilepsy panel probably with amber (/red) rating pending further evidence. Sources: Literature Sources: Literature |
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| Early onset or syndromic epilepsy v1.437 | PTS | Rebecca Foulger changed review comment from: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call 22nd November 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed that there is enough evidence to rate this gene Green. Seizures may present before 9 months, and could be the primary presentation in these cases. Promoted from Amber to Green.; to: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call 22nd November 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed that there is enough evidence to rate this gene Green. Seizures may present before 9 months, and could be the primary presentation in these cases. Since the last group review, PTS has also been promoted to Green on the 'Inborn errors of metabolism' panel (v 1.407). Promoted PTS from Amber to Green on the epilepsy panel. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.437 | PTS | Rebecca Foulger Classified gene: PTS as Green List (high evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.437 | PTS | Rebecca Foulger Gene: pts has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.436 | PTS | Rebecca Foulger commented on gene: PTS: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call 22nd November 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed that there is enough evidence to rate this gene Green. Seizures may present before 9 months, and could be the primary presentation in these cases. Promoted from Amber to Green. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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 v1.274 | PIGP |
Konstantinos Varvagiannis changed review comment from: Johnstone et al. (2017 - PMID: 28334793) report on 2 sibs born to non-consanguineous parents of French-Irish ancestry. Both presented with seizures (onset at the age of 2 and 7 weeks respectively), hypotonia and profound DD. Other features included CVI and feeding difficulties. Extensive metabolic testing as well as prior genetic testing (ARX, STXBP1, MECP2, aCGH) in the family were non-diagnostic. WES suggested the presence of 2 PIGP variants with Sanger sequencing used for confirmation and segregation studies. PIGP encodes a subunit of the enzyme that catalyzes the first step of glycophosphatidylinositol (GPI) anchor biosynthesis. Mutations in other genes whose proteins are in complex with PIGP (PIGA, PIGC, PIGQ, PIGY, DPM2) lead to similar phenotypes. The phenotype overall was also overlapping with the inherited GPI deficiencies (belonging to the broader group of CDGs). PIGP has 2 isoforms, which differ by 24 amino acids due to utilization of alternative start codons [corresponding to NM_153681.2 (158 aa) and NM_153682.2 (134 aa)]. The variants identified affected both transcripts with the first SNV leading either to loss of the start codon (NM_153682.2:c.2T>C - p.Met1Thr) or to substitution of a methionine at position 25(NM_153681.2:c.74T>C;p.Met25Thr). The second variant led to frameshift in the last exon of both transcripts predicting a longer protein product (NM_153681.2:c.456delA / p.Glu153AsnfsTer34 or NM_153682.2:c.384delA / p.Glu129AsnfsTer34). Overall extensive studies demonstrated decreased levels of PIGP mRNA in patient fibroblast, decreased amounts of mutant protein in tranfected HEK293 cells. The decreased levels of GPI-APs further supported the effect of variants : - mRNA levels in patient fibroblasts were reduced compared to controls. Conclusions could not be drawn from Western blot, since no antibodies could specifically detect PIGP. HEK293 cells transfected of mt or wt HA-tagged PIGP cDNA led to undetectable amounts for the first variant (both M1T/M25T) and a protein product of increased molecular weight for the frameshift one. - Flow cytometry of patient granulocytes indicated reduced signal of CD16 (a GPI-anchored protein) and FLAER (binding directly to the GPI anchor). - Reduced levels of GPI-APs were also observed in PIGP deficient HAP1 cells transfected with either wt, or mutant PIGP cDNA (of both isoforms for the M1T/M25T or isoform 2 for the frameshift mutation). -------- Krenn et al. (2019 - PMID: 31139695) described a patient born to non-consanguineous Polish parents. Features were highly similar to those reported by Johnstone et al. and incl. intractable infantile seizures (onset at 7m), hypotonia, severe DD and feeding difficulties. Metabolic work-up failed to identify an alternative diagnosis. WES revealed homozygosity for the frameshift variant reported by Johnstone et al. Sanger sequencing confirmed the variant and carrier state in both parents. Identified ROH of less than 7 Mb in the WES data, suggested a founder mutation rather than unreported consanguinity. The variant is present 9 times in gnomAD (AF of 3.2e-5 / no homozygotes). Flow cytometry of patient granulocytes, revealed markedly reduced expression of GPI-APs (CD157, CD59, FLAER) compared to parents/controls. ALP was normal in all aforementioned individuals (probably in line with PIGP being involved in the 1st step of the GPI anchor biosynthesis). -------- A further individual with phenotype of EIEE-55;GPIBD-14 is reported in LOVD [Individual #00246132]. This individual, born to conanguineous parents, was tested by WES and found to be homozygous for a frameshift variant, also affecting the last exon in both transcripts (NM_153681.2:c.384delA (p.Glu129ArgfsTer7) / NM_153682.2:c.312delA (p.Glu105ArgfsTer7). This was probably in agreement with segregation studies according to the respective entry. The specific variant is reported as pathogenic [variant ID #0000500090]. -------- ?Epileptic encephalopathy, early infantile, 55 (MIM 617599) is the corresponding phenotype in OMIM. There is no relevant G2P entry. PIGP is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx). -------- As a result, PIGP can be considered for inclusion in the ID/epilepsy panels probably as green (3 individuals, role of the gene and similarity to other inherited GPI deficiencies, extensive supporting studies) or amber. (Please consider inclusion in other possibly relevant panels eg. CDGs, etc). Sources: Literature; to: Johnstone et al. (2017 - PMID: 28334793) report on 2 sibs born to non-consanguineous parents of French-Irish ancestry. Both presented with seizures (onset at the age of 2 and 7 weeks respectively), hypotonia and profound DD. Other features included CVI and feeding difficulties. Extensive metabolic testing as well as prior genetic testing (ARX, STXBP1, MECP2, aCGH) in the family were non-diagnostic. WES suggested the presence of 2 PIGP variants with Sanger sequencing used for confirmation and segregation studies. PIGP encodes a subunit of the enzyme that catalyzes the first step of glycophosphatidylinositol (GPI) anchor biosynthesis. Mutations in other genes whose proteins are in complex with PIGP (PIGA, PIGC, PIGQ, PIGY, DPM2) lead to similar phenotypes. The phenotype overall was also overlapping with the inherited GPI deficiencies (belonging to the broader group of CDGs). PIGP has 2 isoforms, which differ by 24 amino acids due to utilization of alternative start codons [corresponding to NM_153681.2 (158 aa) and NM_153682.2 (134 aa)]. The variants identified affected both transcripts with the first SNV leading either to loss of the start codon (NM_153682.2:c.2T>C - p.Met1Thr) or to substitution of a methionine at position 25(NM_153681.2:c.74T>C;p.Met25Thr). The second variant led to frameshift in the last exon of both transcripts predicting a longer protein product (NM_153681.2:c.456delA / p.Glu153AsnfsTer34 or NM_153682.2:c.384delA / p.Glu129AsnfsTer34). Overall extensive studies demonstrated decreased levels of PIGP mRNA in patient fibroblast, decreased amounts of mutant protein in tranfected HEK293 cells. The decreased levels of GPI-APs further supported the effect of variants : - mRNA levels in patient fibroblasts were reduced compared to controls. Conclusions could not be drawn from Western blot, since no antibodies could specifically detect PIGP. HEK293 cells transfected of mt or wt HA-tagged PIGP cDNA led to undetectable amounts for the first variant (both M1T/M25T) and a protein product of increased molecular weight for the frameshift one. - Flow cytometry of patient granulocytes indicated reduced signal of CD16 (a GPI-anchored protein) and FLAER (binding directly to the GPI anchor). - Reduced levels of GPI-APs were also observed in PIGP deficient HAP1 cells transfected with either wt, or mutant PIGP cDNA (of both isoforms for the M1T/M25T or isoform 2 for the frameshift mutation). -------- Krenn et al. (2019 - PMID: 31139695) described a patient born to non-consanguineous Polish parents. Features were highly similar to those reported by Johnstone et al. and incl. intractable infantile seizures (onset at 7m), hypotonia, severe DD and feeding difficulties. Metabolic work-up failed to identify an alternative diagnosis. WES revealed homozygosity for the frameshift variant reported by Johnstone et al. Sanger sequencing confirmed the variant and carrier state in both parents. Identified ROH of less than 7 Mb in the WES data, suggested a founder mutation rather than unreported consanguinity. The variant is present 9 times in gnomAD (AF of 3.2e-5 / no homozygotes). Flow cytometry of patient granulocytes, revealed markedly reduced expression of GPI-APs (CD157, CD59, FLAER) compared to parents/controls. ALP was normal in all aforementioned individuals (probably in line with PIGP being involved in the 1st step of the GPI anchor biosynthesis). -------- A further individual with phenotype of EIEE-55;GPIBD-14 is reported in LOVD [Individual #00246132]. This individual, born to consanguineous parents, was tested by WES and found to be homozygous for a frameshift variant, also affecting the last exon in both transcripts [NM_153681.2:c.384delA (p.Glu129ArgfsTer7) / NM_153682.2:c.312delA (p.Glu105ArgfsTer7)]. This was probably in agreement with segregation studies according to the respective entry. The specific variant is reported as pathogenic [variant ID #0000500090]. -------- ?Epileptic encephalopathy, early infantile, 55 (MIM 617599) is the corresponding phenotype in OMIM. There is no relevant G2P entry. PIGP is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx). -------- As a result, PIGP can be considered for inclusion in the ID/epilepsy panels probably as green (3 individuals, role of the gene and similarity to other inherited GPI deficiencies, extensive supporting studies) or amber. (Please consider inclusion in other possibly relevant panels eg. CDGs, etc). Sources: Literature |
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| Early onset or syndromic epilepsy v1.272 | PIGP |
Konstantinos Varvagiannis gene: PIGP was added gene: PIGP was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: PIGP was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PIGP were set to 28334793; 31139695 Phenotypes for gene: PIGP were set to Generalized hypotonia; Global developmental delay; Seizures; Intellectual disability; Feeding difficulties; Cortical visual impairment Penetrance for gene: PIGP were set to Complete Review for gene: PIGP was set to GREEN Added comment: Johnstone et al. (2017 - PMID: 28334793) report on 2 sibs born to non-consanguineous parents of French-Irish ancestry. Both presented with seizures (onset at the age of 2 and 7 weeks respectively), hypotonia and profound DD. Other features included CVI and feeding difficulties. Extensive metabolic testing as well as prior genetic testing (ARX, STXBP1, MECP2, aCGH) in the family were non-diagnostic. WES suggested the presence of 2 PIGP variants with Sanger sequencing used for confirmation and segregation studies. PIGP encodes a subunit of the enzyme that catalyzes the first step of glycophosphatidylinositol (GPI) anchor biosynthesis. Mutations in other genes whose proteins are in complex with PIGP (PIGA, PIGC, PIGQ, PIGY, DPM2) lead to similar phenotypes. The phenotype overall was also overlapping with the inherited GPI deficiencies (belonging to the broader group of CDGs). PIGP has 2 isoforms, which differ by 24 amino acids due to utilization of alternative start codons [corresponding to NM_153681.2 (158 aa) and NM_153682.2 (134 aa)]. The variants identified affected both transcripts with the first SNV leading either to loss of the start codon (NM_153682.2:c.2T>C - p.Met1Thr) or to substitution of a methionine at position 25(NM_153681.2:c.74T>C;p.Met25Thr). The second variant led to frameshift in the last exon of both transcripts predicting a longer protein product (NM_153681.2:c.456delA / p.Glu153AsnfsTer34 or NM_153682.2:c.384delA / p.Glu129AsnfsTer34). Overall extensive studies demonstrated decreased levels of PIGP mRNA in patient fibroblast, decreased amounts of mutant protein in tranfected HEK293 cells. The decreased levels of GPI-APs further supported the effect of variants : - mRNA levels in patient fibroblasts were reduced compared to controls. Conclusions could not be drawn from Western blot, since no antibodies could specifically detect PIGP. HEK293 cells transfected of mt or wt HA-tagged PIGP cDNA led to undetectable amounts for the first variant (both M1T/M25T) and a protein product of increased molecular weight for the frameshift one. - Flow cytometry of patient granulocytes indicated reduced signal of CD16 (a GPI-anchored protein) and FLAER (binding directly to the GPI anchor). - Reduced levels of GPI-APs were also observed in PIGP deficient HAP1 cells transfected with either wt, or mutant PIGP cDNA (of both isoforms for the M1T/M25T or isoform 2 for the frameshift mutation). -------- Krenn et al. (2019 - PMID: 31139695) described a patient born to non-consanguineous Polish parents. Features were highly similar to those reported by Johnstone et al. and incl. intractable infantile seizures (onset at 7m), hypotonia, severe DD and feeding difficulties. Metabolic work-up failed to identify an alternative diagnosis. WES revealed homozygosity for the frameshift variant reported by Johnstone et al. Sanger sequencing confirmed the variant and carrier state in both parents. Identified ROH of less than 7 Mb in the WES data, suggested a founder mutation rather than unreported consanguinity. The variant is present 9 times in gnomAD (AF of 3.2e-5 / no homozygotes). Flow cytometry of patient granulocytes, revealed markedly reduced expression of GPI-APs (CD157, CD59, FLAER) compared to parents/controls. ALP was normal in all aforementioned individuals (probably in line with PIGP being involved in the 1st step of the GPI anchor biosynthesis). -------- A further individual with phenotype of EIEE-55;GPIBD-14 is reported in LOVD [Individual #00246132]. This individual, born to conanguineous parents, was tested by WES and found to be homozygous for a frameshift variant, also affecting the last exon in both transcripts (NM_153681.2:c.384delA (p.Glu129ArgfsTer7) / NM_153682.2:c.312delA (p.Glu105ArgfsTer7). This was probably in agreement with segregation studies according to the respective entry. The specific variant is reported as pathogenic [variant ID #0000500090]. -------- ?Epileptic encephalopathy, early infantile, 55 (MIM 617599) is the corresponding phenotype in OMIM. There is no relevant G2P entry. PIGP is included in gene panels for ID offered by some diagnostic laboratories (eg. GeneDx). -------- As a result, PIGP can be considered for inclusion in the ID/epilepsy panels probably as green (3 individuals, role of the gene and similarity to other inherited GPI deficiencies, extensive supporting studies) or amber. (Please consider inclusion in other possibly relevant panels eg. CDGs, etc). Sources: Literature |
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| Early onset or syndromic epilepsy v1.256 | HNRNPR |
Konstantinos Varvagiannis gene: HNRNPR was added gene: HNRNPR was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: HNRNPR was set to MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted Publications for gene: HNRNPR were set to 31079900; 26795593 Phenotypes for gene: HNRNPR were set to Global developmental delay; Intellectual disability; Seizures; Postnatal microcephaly; Short digit Penetrance for gene: HNRNPR were set to unknown Review for gene: HNRNPR was set to AMBER Added comment: Duijkers et al. (2019 - PMID: 31079900) report on the phenotype of 4 individuals with de novo HNRNPR variants and provide additional information on a previously published case (Helbig et al, 2016 - PMID: 26795593). All 5 were unrelated. The phenotype consisted of DD (5/5 - moderate to severe in 4 for which this has been commented on), postnatal microcephaly, seizures (4/5), brachydactyly, with additional (cardiac, urogenital, etc) anomalies observed in few. Some partially overlapping facial features were also noted. 3 truncating variants as well as a missense one, all localizing within the last exon of the gene (NM_001102398.2 used as ref. although this exon is shared by all transcripts). HNRNPR encodes heterogeneous nuclear ribonucleoprotein R, which is part of the spliceosome C. The latter functions in the nucleus to process and transport mRNA. Apart from splicing hnRNPs are also involved in other levels of gene regulation (PMID: 27215579). Some hnRNPs have been found in the cytoplasm in stress granules, aggregations of protein, RNAs and stalled initiation complexes that are formed as stress response upon oxidative insult and dissipate upon cessation of this insult. Western blot in LCLs from affected individuals demonstrated the presence of the truncated protein as well as the full-length and short isoform (as expected by the variant localization). As the C-terminal part has features of a "prion-like domain" (PrLD), critical for the formation of stress granules in the case of hnRNP-related disorders, comparison of fibroblasts from affected and healthy individuals revealed abnormal persistence of these granules in affected individuals following a recovery period, despite similar formation either at basal levels or under conditions of stress. In line with a role of hnRNPs in splicing and gene regulation, RNA-Sequencing in fibroblasts from 2 affected individuals revealed abnormal splicing of some genes (eg. HOXA5, HOXB3, LHX9) and significant dysregulation of genes important for the development (upregulation of FOXG1, TBX1, several members of the HOX family and downregulation of LHX9, IRX3, etc) possibly contributing to the patient features. Helbig et al. provide details on animal studies incl.expression in neural tissues (cerebrum and cerebellum), higher levels of expression early in the development (of both R1/R2 isoforms), etc (extensive discussion in the supplement with several articles cited). HNRNPR is not associated with any phenotype in OMIM/G2P. As a result this gene can be considered for inclusion as amber (seizures in 4/5) or green. Sources: Literature |
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| Early onset or syndromic epilepsy v1.233 | PTS | Rebecca Foulger Marked gene: PTS as ready | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.233 | PTS | Rebecca Foulger Gene: pts has been classified as Amber List (Moderate Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.233 | PTS | Rebecca Foulger Classified gene: PTS as Amber List (moderate evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.233 | PTS | Rebecca Foulger Gene: pts has been classified as Amber List (Moderate Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.232 | PTS | Rebecca Foulger commented on gene: PTS: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call Thursday 8th August 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed that this gene should be rated Amber to match the rating on the 'Inborn errors of metabolism' panel. The prevailing phenotype is a movement disorder. Demoted from Green to Amber. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.232 | PTS | Rebecca Foulger commented on gene: PTS: Re-reviewed this gene when curating panel for GMS Clinical Indication R59 Early onset or syndromic epilepsy. In summary: Severe Hyperphenylalaninemia, BH4-deficient, is accepted to include seizures (PMID:8801112). Because this condition is diagnosed and treated from an early age, seizures may not be reported frequently. PMID:31000854 (Ahmed et al., 2019)assessed hyperphenylalaninemia patients and found 14/18 (78%) had seizures and ID however genetic analysis to see which of these had PTPS/PTS variants was not performed. PMID:9222757 report 1 case of seizures. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.191 | PTS | Rebecca Foulger Source Wessex and West Midlands GLH was added to PTS. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.190 | PTS | Rebecca Foulger Source NHS GMS was added to PTS. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.189 | PTS | Rebecca Foulger reviewed gene: PTS: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.188 | PTS | Tracy Lester reviewed gene: PTS: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: Hyperphenylalaninemia BH4-deficient A, 261640; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.35 | SNAP25 |
Konstantinos Varvagiannis gene: SNAP25 was added gene: SNAP25 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: SNAP25 was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: SNAP25 were set to 29491473; 28135719; 29100083; 25381298; 25003006 Phenotypes for gene: SNAP25 were set to ?Myasthenic syndrome, congenital 18, 616330 Penetrance for gene: SNAP25 were set to Complete Review for gene: SNAP25 was set to GREEN Added comment: Probably 9 individuals with heterozygous SNAP25 pathogenic variants have been reported to date, most summarized in the first reference (NM_130811.2 used as reference for all variants below): - Fukuda et al. (2018 - PMID: 29491473) 2 sibs (~11 and 2.5 y.o) with seizures and cerebellar ataxia but not ID. harboring c.176G>C (p.Arg59Pro) variant which was inherited from a mosaic unaffected parent. - DDD study (2017 - PMID: 28135719) [also in Heyne et al. 2018 - PMID: 29942082] 3 inividuals (11 m - 7 y of age) with DD and seizures due to c.118A>G (p.Lys40Glu), c.127G>C (p.Gly43Arg) and c.520C>T (p.Gln174*) de novo variants. - Hamdan et al. (2017 - PMID: 29100083) a 23 y.o. male with epilepsy and ID and c.496G>T (p.Asp166Tyr) de novo variant - Shen et al. (2014 - PMID: 25381298) a 11 y.o. female with epilepsy and ID and c.200T>A (p.Ile67Asn) de novo variant - Rohena et al. (2013 - PMID: 25003006) a 15 y.o. female with epilepsy and ID and c.142G>T (p.Val48Phe) de novo variant - Decipher patient 292139, a male with c.212T>C (p.Met71Thr) with hypotonia, DD, poor coordination and additional features (epilepsy not reported). Seizures of variable type [absence seizures, generalized tonic-clonic (most), focal clonic, myoclonic, etc] have been reported for most (8/9) of these individuals. DD was a feature in several subjects and intellectual outcome has been specifically commented on for 5 (2 without and 3 with ID - moderate/severe/not further specified). SNAP25 encodes a (t-)SNARE protein essential for synaptic vesicle exocytosis. Mutations in genes for other components of the SNARE complex (eg. STXBP1) have been associated with epilepsy and/or ID. SNAP25a and SNAP25b are the 2 major protein isoforms [corresponding transcripts: ENST00000304886 (NM_003081) and ENST00000254976 (NM_130811) respectively]. These isoforms are produced by utilization of alternative exons 5 (5a or 5b) though the amino-acid sequence encoded by these exons appears to be identical except for 9 residues. Most variants reported to date affect both transcripts (and protein isoforms) although 2 were specific for ENST00000254976 (or SNAP25b isoform - Fukuda et al. and Shen et al.). Mouse Snap25 has also 2 isoforms. Both are predominantly localized in embryonic and adult mouse brains. Snap25a is produced before Snap25b though the latter becomes the major isoform early postnatally (by the second week) [PMIDs cited: 7878010, 21526988]. Based on the phenotype of some individuals with chromosome 20 deletions in Decipher (note: only 3 deletions spanning SNAP25 however appear currently, the phenotype is not specified and 2 of them are >4.5Mb) or the pLI of 0.96 in gnomAD, haploinsufficiency has been proposed as a likely mechanism. A dominant-negative effect was however suggested for the Ile67Asn studied by Shen et al. Functional studies have not been performed for other variants. Animal models discussed: - Snap25 null drosophila show complete loss of synaptic transmission upon electroretinogram recordings (PMID cited: 12242238). - In mice, elimination of Snap25b expression resulted in developmental defects, seizures and impaired short-term synaptic plasticity (PMID cited: 19043548). - Mice with a 4.6 Mb deletion encompassing 12 genes (incl. Snap25) display seizure predisposition (PMID cited: 23064108). - Heterozygosity for Ile67Thr in (blind-drunk mutant) mice results in impaired vesicle trafficking, impaired sensorimotor gating and ataxia (PMID cited:17283335). In OMIM, heterozygous SNAP25 mutations are associated with ?Myasthenic syndrome, congenital, 18 (with intellectual disability and ataxia). SNAP25 is part of the DD panel, associated with "Epilepsy and intellectual disability" (disease confidence: probable). This gene is included in gene panels for ID offered by some diagnostic laboratories (incl. Radboudumc). As a result SNAP25 can be considered for inclusion in the epilepsy and ID panels as green (or amber). Sources: Literature |
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| Early onset or syndromic epilepsy v1.35 | P4HTM |
Konstantinos Varvagiannis gene: P4HTM was added gene: P4HTM was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: P4HTM was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: P4HTM were set to 30940925 Phenotypes for gene: P4HTM were set to Central hypotonia; Muscular hypotonia; Global developmental delay; Intellectual disability; Seizures; Abnormality of the eye; Hypoventilation; Sleep apnea; Dysautonomia Penetrance for gene: P4HTM were set to Complete Review for gene: P4HTM was set to GREEN Added comment: Gene added in the ID panel. Epilepsy is a feature of the disorder. ----- Rahikkala et al. (2019 - PMID: 30940925) report on 13 individuals from 5 families with biallelic pathogenic P4HTM variants. 6 of these individuals from a large consanguineous family from Finland were previously reported by the same group, although studies at the time had revealed a 11.5 Mb region of homozygosity with 3 genes within this interval considered to be candidate for the patients' phenotype (P4HTM, TKT, USP4) [Kaasinen et al. - PMID: 25078763]. Common features included Hypotonia (13/13), DD and ID (the latter present in 12/13 individuals with appropriate age for evaluation) and Eye Abnormalities, reason why the acronym HIDEA is suggested for the disorder. Epilepsy was observed in 10 individuals (10/13). Hypoventilation, sleep apnea and dysautonomia were additional features reported. Muscle biopsies from 4 individuals had variable findings suggestive of disruption of normal mitochondrial function. Finnish patients were homozygous for a SNV - possibly a founder variant in this population - predicted to lead to a missense change in the canonical transcript (NM_177938.2:c.1073G>A) but causing an in-frame loss of the complete exon 6 of another transcript (NM_177939.2). The latter transcript (encoding a 502 aa protein) is the prevalent one in fibroblasts/myoblasts instead of the canonical one (563 aa). It is not known whether the canonical transcript is the prevalent in brain tissue although northern blot analysis in a previous study suggested presence of a 2.3 kb mRNA in brain instead of a 1.8 kb observed in other tissues, a finding which may be suggestive of expression of the canonical transcript. [Reviewer's note: In gnomAD based on the pext values from the GTEx, the noncanonical transcript appears to be prevalent in brain regions - https://gnomad.broadinstitute.org/gene/ENSG00000178467] All variants reported affected both transcripts. All 5 variants have been submitted to LOVD ( https://databases.lovd.nl/shared/variants/P4HTM?search_var_status=%3D%22Marked%22%7C%3D%22Public%22 - first author appearing as the submitter). Overexpression of wt and 3 mutants (His161Pro, Gln352*and Exon6del) in insect cells followed by analysis with SDS-PAGE and western blot revealed severly reduced/abolished fraction of soluble protein for the 3 studied variants suggesting improper protein folding. Knockout of the gene in mice leads to retinal defects and/or visual impairment in line with eye abnormalites (nystagmus, strabismus, achromic retinal fundi or cortical blindness) being a prominent feature in affected individuals. Mouse studies suggest that this gene is also important for renal function, although kidney problems were not reported in any affected individual. Overall loss-of-function is suggested to be the underlying mechanism. P4HTM is not associated with any phenotype in OMIM, nor in G2P. This gene is not (at least commonly) included in gene panels for ID offered by diagnostic laboratories. As a result P4HTM can be considered for inclusion in the ID and epilepsy panels probably as green (several affected individuals) or amber. Sources: Literature |
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| Early onset or syndromic epilepsy v1.31 | KMT2E |
Konstantinos Varvagiannis gene: KMT2E was added gene: KMT2E was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: KMT2E was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: KMT2E were set to https://doi.org/10.1101/566091 Phenotypes for gene: KMT2E were set to Global developmental delay; Intellectual disability; Autism; Seizures; Abnormality of skull size Penetrance for gene: KMT2E were set to unknown Review for gene: KMT2E was set to GREEN Added comment: Gene added in the ID panel (comments below). Epilepsy was a feature in - at least - 11 individuals (with all categories of variants : 4 with truncating, 3 with CNVs, 4 with missense SNVs). As a result this gene can be considered for inclusion in the current panel as green (or amber). From the ID panel : In a collaborative study, O'Donnell-Luria et al. (2019 - https://doi.org/10.1101/566091 - DDD study among the co-authors) report on 38 individuals from 36 families with heterozygous KMT2E variants. Some of these individuals were previously included in previous publications. Developmental delay, intellectual disability, epilepsy and ASD were among the features reported, albeit of variable degree and not universal. 34 of 38 individuals had SNVs or indel variants in KMT2E and 4 individuals had CNVs spanning KMT2E (in one case intragenic, in 3 further as a contiguous gene deletion). For 26 (of 38 individuals) the variant had arisen as a de novo event while in some cases parental sample(s) was/were unavailable to confirm the de novo occurrence or origin (from a reportedly affected parent). The variant in one family was inherited from a parent for whom information on affected/unaffected status was unavailable. As for the variants reported: 30 were protein-truncating (of which 23 predicted to produce transcripts subject to NMD). 4 were missense. 4 were CNVs (de novo deletions, of which 1 intragenic). Truncating variants and deletions of KMT2E suggest haploinsufficiency as the underlying mechanism for this category of variants (KMT2E has a pLI of 1 in gnomAD). However, the somewhat different phenotype related to missense variants (degree of ID, epilepsy in all, microcephaly in some versus macrocephaly in subjects with truncating variants) may suggest a different mechanism for these variants eg. gain of function or dominant negative effect. There was no clustering observed for the missense variants reported. Expressivity of certain features may be variable between males and females. As the authors note : KMT2E encodes a member of the lysine N-methyltransferase 2 family, a family of enzymes with critical role in H3K4 methylation. It is highly expressed in brain, particularly during fetal development. Several monogenic neurodevelopmental disorders due to impaired regulation of H3K4 methylation are known (eg. due to KMT2D/C/B/A mutations, etc). Studies suggest that KMT2E may lack intrinsic methyltransferase activity although it may have an indirect effect on H3K4 methylation. In contrast to other members of the KMT2 family functioning as global activators of open chromatin, KMT2E is believed to be a repressor (although it's function in gene transcription regulation needs to be clarified). A neurological phenotype of Kmt2e (Mll5) deficiency mouse models has not been reported (features included growth restriction, impaired hematopoiesis, etc). KMT2E is not associated with any phenotype in OMIM. The gene is included in the DD panel of G2P, associated with Intellectual disability (disease confidence: confirmed / mutation consequence registered in the db : LoF). KMT2E is included in gene panels for ID offered by some diagnostic laboratories (eg. among those participating in the study). As a result, this gene can be considered for upgrade to green (or amber). Sources: Literature |
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| Early onset or syndromic epilepsy v0.1135 | PTS | Sarah Leigh Marked gene: PTS as ready | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1135 | PTS | Sarah Leigh Gene: pts has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1135 | PTS | Sarah Leigh Classified gene: PTS as Green List (high evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1135 | PTS | Sarah Leigh Gene: pts has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1134 | PTS | Sarah Leigh Publications for gene: PTS were set to 11916314; 16364672 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1050 | PTS | Sarah Leigh Classified gene: PTS as Red List (low evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1050 | PTS | Sarah Leigh Added comment: Comment on list classification: Although the phenotype in OMIM and Gen2Phen gene. However, unable to find reports of seizures in variant carriers. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1050 | PTS | Sarah Leigh Gene: pts has been classified as Red List (Low Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.990 | PTS | Sarah Leigh Classified gene: PTS as Green List (high evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.990 | PTS | Sarah Leigh Gene: pts has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.989 | PTS | Sarah Leigh Phenotypes for gene: PTS were changed from to Hyperphenylalaninemia, BH4-deficient, A, 261640 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.988 | PTS | Sarah Leigh Publications for gene: PTS were set to | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.987 | PTS | Sarah Leigh Mode of inheritance for gene: PTS was changed from to BIALLELIC, autosomal or pseudoautosomal | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.505 | VARS |
Konstantinos Varvagiannis gene: VARS was added gene: VARS was added to Genetic Epilepsy Syndromes. Sources: Expert Review,Literature Mode of inheritance for gene: VARS was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: VARS were set to 26539891; 29691655; 30275004 Phenotypes for gene: VARS were set to # 617802. NEURODEVELOPMENTAL DISORDER WITH MICROCEPHALY, SEIZURES, AND CORTICAL ATROPHY; NDMSCA Penetrance for gene: VARS were set to Complete Review for gene: VARS was set to GREEN Added comment: PMID: 26539891 is the first report on individuals with biallelic pathogenic variants in VARS. 3 individuals from 2 consanguineous families are briefly reported. The phenotype was similar in all 3, consisting of severe developmental delay, microcephaly, seizures and cortical atrophy. Subjects from the first family were homozygous for a missense variant in the tRNA synthetase catalytic domain [p.(L885F)]. The patient from the second family was homozygous for a missense SNV affecting the anticodon-binding domain [p.(R1058Q)]. PMID: 29691655 reports on a further patient born to non-consanguineous parents, with 2 in-trans pathogenic variants in VARS. The phenotype consisted of progressive microcephaly (OFC at birth -2SD, at the age of 2 months -4SD), global developmental delay, seizures and progressive cerebral and cerebellar atrophy. An affected brother presented with more severe phenotype (OFC -6SD at birth and -8SD at 2 months of age), seizures, hearing loss but was deceased and unavailable for genetic testing. cDNA studies demonstrated absence of the reference allele for the missense mutation downstream the splice variant (in line with a reduced or absent mRNA allele harboring the splice variant). Similarly, mRNA expression studies demonstrated 50-60% reduction in the transcripts (due to NMD of the allele with the splice SNV). Western blot showed severe reduction in protein levels (more pronounced compared to what would be expected by mRNA expression) presumably secondary to decreased protein stability due to the missense variant. Severe defects in aminoacylation were further confirmatory of a pathogenic role of these variants. The missense variant was affecting the anticodon-binding domain, important for aminoacylation. PMID: 30275004 reports on 2 siblings with developmental delay, intellectual disability, severe speech impairment and microcephaly, similar to what has been described for the disorder. Clinical findings were somewhat different from previous studies in that microcephaly was acquired, while seizures and cortical atrophy were not part of the phenotype. Both sibs were compound heterozygous for 2 missense variants, though only one of these mutations affected the anticodon binding domain and the other was in the N-terminal region of the protein. Previous metabolic studies and extensive genetic testing (karyotype, CMA, MECP2, FMR1) was normal. Epilepsy was a feature in 4 of the 6 individuals for whom genetic testing was possible (or 5/7 in total). VARS belongs to the family of amino acyl-tRNA synthetases (ARSs). Mutations in several cytoplasmic ARSs are associated with severe neurological manifestations including seizures, intellectual disability associated with microcephaly. VARS is included in gene panels for intellectual disability (but not for epilepsy) offered by different diagnostic labs. As a result this gene can be considered for inclusion in the ID and epilepsy panel as green (or amber). Sources: Expert Review, Literature |
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| Early onset or syndromic epilepsy v0.503 | PIGG |
Konstantinos Varvagiannis gene: PIGG was added gene: PIGG was added to Genetic Epilepsy Syndromes. Sources: Literature,Expert Review Mode of inheritance for gene: PIGG was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PIGG were set to 26996948; 28581210 Phenotypes for gene: PIGG were set to # 616917. MENTAL RETARDATION, AUTOSOMAL RECESSIVE 53; MRT53 Penetrance for gene: PIGG were set to Complete Review for gene: PIGG was set to GREEN Added comment: PMID: 26996948 reports on 5 individuals from 3 families, with biallelic pathogenic variants in PIGG. Individuals from first family, were born to consanguineous parents from Egypt and were homozygous for a stopgain variant [p.(Gln310*)]. The patient from the second family had a rare missense SNV [p.(Arg669Cys)] and a de novo microdeletion affecting PIGG on her other allele. In the third family (consanguineous parents from Pakistan), two affected sibs were found to be homozygous for a splice variant. The phenotype consisted of hypotonia, early-onset seizures and intellectual disability. Ataxia was an additional feature in one of the families. Seizures, were observed in most of patients but do not appear to be a universal feature as they were absent in one of the sibs from the third family (10 years of age), while the other had a single episode by the age of 12 years. In vitro testing of lymphoblastoid cell lines (generated from individuals from the 1st and 3rd family) indicated that the variants abolished completely the function of PIGG, whereas the surface level of GPI anchored proteins was normal. // PMID: 28581210 describes the phenotype of 2 sibs from Palestine, homozygous for a stopgain variant [p.(Trp547*)]. Hypotonia, feeding difficulties, severe non-progressive ataxia (with cerebellar hypoplasia), intellectual disability and seizures were common features. Differences in severity and/or additional features might be explained by other homozygous variants (the girl had a concurrent diagnosis of MCAD deficiency). The authors demonstrated that the PIGG transcript levels were significantly lower (approximately half) in the two siblings compared to their parents, while the transcripts with the mutation in the heterozygous parents were very low due to nonsense-mediated decay. Patient fibroblasts showed decreased surface level of GPI-anchored proteins, in contrast with what was noted in lymphoblastoid cells in the previous study. // As a result this gene can be considered for inclusion in this panel as green (or amber). Sources: Literature, Expert Review |
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| Early onset or syndromic epilepsy | PTS | Zornitza Stark reviewed gene: PTS | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy | PTS | Sarah Leigh Added gene to panel | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||