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| Early onset or syndromic epilepsy v1.405 | NSF |
Konstantinos Varvagiannis gene: NSF was added gene: NSF was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: NSF was set to MONOALLELIC, autosomal or pseudoautosomal, imprinted status unknown Publications for gene: NSF were set to 31675180 Phenotypes for gene: NSF were set to Seizures; EEG with burst suppression; Global developmental delay; Intellectual disability Penetrance for gene: NSF were set to unknown Review for gene: NSF was set to AMBER Added comment: Suzuki et al. (2019 - PMID: 31675180) report on 2 unrelated individuals with de novo missense NSF variants. Overall the phenotype corresponded to an early infantile epileptic encephalopathy. The first patient developed vomiting and tonic seizures immediately after birth, with burst-suppression pattern upon EEG. Trio exome sequencing, followed by Sanger sequencing of proband and parents, revealed a de novo missense variant (NM_006178.3:c.1375G>A / p.Ala459Thr), absent from public databases and predicted in silico to be deleterious (CADD score of 30). The girl died 36 days after birth due to respiratory failure. Another subject, having necessitated mechanical ventilation due to absence of spontaneous respiration after birth, developed myoclonic seizures. EEG showed a burst-suppression pattern. At the age of 3, she was noted to have persistence of seizures and profound ID. Trio exome sequencing identified a missense NSF variant (c.1688C>T / p.Pro563Leu) also confirmed and shown to be de novo by Sanger sequencing. Again the variant was absent from public datasets and had a CADD score of 34. While expression of wt NSF allele in the developing eye of Drosophila had no effect, expression of mutants severely affected eye development - suggesting a dominant negative effect. NSF encodes a homo-hexameric AAA ATPase, which is recruited by SNAPs (Soluble NSF Attachment Proteins) - and the latter by SNAREs (SNAP REceptors) - thus having a role in vesicular transport and membrane fusion. There is currently no associated phenotype in OMIM/G2P. Overall, this gene could be considered for inclusion probably with amber/red rating pending further evidence (eg. additional work-up or alternative causes/explanations not discussed). Sources: Literature |
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| Early onset or syndromic epilepsy v1.405 | FDFT1 |
Konstantinos Varvagiannis gene: FDFT1 was added gene: FDFT1 was added to Genetic epilepsy syndromes. Sources: Literature Mode of inheritance for gene: FDFT1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: FDFT1 were set to 29909962 Phenotypes for gene: FDFT1 were set to Profound global developmental delay; Intellectual disability; Seizures; Abnormality of nervous system morphology; Cortical visual impairment; Abnormality of the skin; Abnormality of the face Penetrance for gene: FDFT1 were set to Complete Review for gene: FDFT1 was set to AMBER Added comment: Biallelic pathogenic FDFT1 variants cause Squalene synthase deficiency (MIM 618156). 3 individuals from 2 families (and 3 variants) have been reported. DD, ID and seizures are part of the phenotype (3/3). The metabolic profile observed is specific and highly suggestive of disruption of the cholesterol biosynthesis pathway (at the specific level) while the clinical presentation is similar to other disorders of the pathway (SLO). The effect of 2 variants has been studied in detail (in one case mis-splicing demonstrated and in the other regulatory effect). Overall, this gene could be considered for inclusion in the ID/epilepsy panel with amber rating. As the gene is currently present only in the DDG2P panel, please consider adding it to relevant ones (eg. IEMs, undiagnosed metabolic disorders, etc). [Details provided below]. ---- Coman et al. (2018 - PMID: 29909962) reported on 3 relevant individuals from 2 unrelated families. The phenotype consisted of seizures (3/3 - neonatal onset - generalized), profound DD (ID can be inferred from the description in the supplement), variable brain MRI abnormalities (white matter loss, hypoplastic CC), cortical visual impairment, dry skin with photosensitivity as well facial dysmorphic features. Male subjects presented genital anomalies (cryptorchidism/hypospadias). FDFT1 encodes squalene synthase, the enzyme which catalyzes conversion of farnesyl-pyrophosphate to squalene - the first specific step in cholesterol biosynthesis. A specific pattern of metabolites was observed in all, similar to a pattern previously observed in animal models/humans treated with squalene synthase inhibitor or upon loading with farnesol (in animals). Overall the pattern was suggestive of a cholesterol biosynthesis defect at the level of squalene synthase as suggested by increased total farnesol levels (farnesyl-pyrophosphate + free farnesol), reduced/normal squalene, low plasma cholesterol as well as other metabolites. Clinical features also resembled those observed in Smith-Lemli-Opitz syndrome (another disorder of cholesterol biosynthesis). WES was carried out in affected individuals and their parents and revealed for sibs of the first family, compound heterozygosity for a maternally inherited 120-kb deletion spanning exons 6-10 of FDFT1 and CTSB and a paternally inherited FDFT1 variant in intron 8 (TC deletion/AG insertion). Variant studies for the latter included: - Minigene splice assay demonstrating retention of 22 bp in intron 8. - Partial splicing defect with both nl and mis-spliced cDNA (patient fibroblasts) - Reduced protein levels in lymphoblasts/fibroblasts from both sibs upon Western blot. Contribution of the CTSB deletion was considered unlikely (carrier mother was unaffected). As for the 2nd family, WES data allowed identification of a homozygous deep-intronic (although this is transcript-specific) 16-bp deletion in the proband. Parents were carriers. For the specific variant : - cDNA studies failed to detect 3 (of 10) isoforms which are normally present in control fibroblasts. Eventual NMD (which would be predicted if the deletion resulted in splicing defect) was eliminated given the absent effect of cyclohexamide addition, thus suggesting a regulatory effect. - Given a predicted promoter/enhancer effect of the deleted region, a luciferase assay performed, suggested that the sequence had promoter capacity, with the construct containing the 16-bp deletion showing reduced promoter activity. Fdft1 knockout mice demonstrate embryonic lethality around mid-gestation while they exhibit severe growth retardation and defective neural tube closure. In G2P FDFT1 is associated with 'Defect in Cholesterol Biosynthesis' (confidence:possible/biallelic/LoF). The gene belongs to the Current primary ID gene group of SysID. It is not commonly included in gene panels for ID offered by diagnostic laboratories. 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 v1.191 | HEXA | Rebecca Foulger Source Wessex and West Midlands GLH was added to HEXA. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.190 | HEXA | Rebecca Foulger Source NHS GMS was added to HEXA. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.189 | HEXA | Rebecca Foulger reviewed gene: HEXA: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.188 | HEXA | Tracy Lester reviewed gene: HEXA: Rating: GREEN; Mode of pathogenicity: ; Publications: 21937992, 9222766 ; Phenotypes: GM2-gangliosidosis, several forms, 272800, Tay-Sachs disease, 272800, [Hex A pseudodeficiency], 272800; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v1.10 | HEXA | Louise Daugherty Phenotypes for gene: HEXA were changed from Tay-Sachs disease, 272800 to GM2-gangliosidosis, several forms, 272800; Tay-Sachs disease, 272800 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.1062 | HEXA |
Ivone Leong commented on gene: HEXA: Tay-Sachs disease is rare in the general population but has increased frequency in Ashkenazi Jews. Many of the papers do not specify whether patients have seizures/epilpsy and many report on the patient's phenotype as classic infantile (seizures can be a symptom), juvenile or adult late-onset (seizures can be a symptom), which may or may not necessarily mean patients have seizures. I have only included studies that mention seizures/epilepsy specifically. Three studies have reported 3 patients with different variants in HEXA gene who have seizures (PMID: 30006889, 21937992, 7551830). PMID: 14972682 describe a mouse model of HEXA which also exhibited seizure/epilpsy phenotype. |
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| Early onset or syndromic epilepsy v0.1061 | HEXA | Ivone Leong Publications for gene: HEXA were set to | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.879 | HEXA | Ivone Leong Marked gene: HEXA as ready | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.879 | HEXA | Ivone Leong Gene: hexa has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.879 | HEXA | Ivone Leong Classified gene: HEXA as Green List (high evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.879 | HEXA |
Ivone Leong Added comment: Comment on list classification: Promoted from Amber to Green as seizures is a phenotype of Tay-Sachs disease in accordance with the review by Zornitza Stark (Australian Genomics). Tay-Sachs disease is confirmed to be associated with this gene by both OMIM and Gene2Phenotype. |
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| Early onset or syndromic epilepsy v0.879 | HEXA | Ivone Leong Gene: hexa has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.878 | HEXA | Ivone Leong Mode of inheritance for gene: HEXA was changed from BIALLELIC, autosomal or pseudoautosomal to BIALLELIC, autosomal or pseudoautosomal | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.877 | HEXA | Ivone Leong Mode of inheritance for gene: HEXA was changed from to BIALLELIC, autosomal or pseudoautosomal | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy v0.876 | HEXA | Ivone Leong Phenotypes for gene: HEXA were changed from to Tay-Sachs disease, 272800 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy | HEXA | Zornitza Stark reviewed gene: HEXA | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Early onset or syndromic epilepsy | HEXA | Sarah Leigh Added gene to panel | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||