Rare coding variants in genes encoding GABAA receptors in genetic generalised epilepsies: an exome-based case-control study.

BACKGROUND: Genetic generalised epilepsy is the most common type of inherited epilepsy. Despite a high concordance rate of 80% in monozygotic twins, the genetic background is still poorly understood. We aimed to investigate the burden of rare genetic variants in genetic generalised epilepsy. METHODS: For this exome-based case-control study, we used three different genetic generalised epilepsy case cohorts and three independent control cohorts, all of European descent. Cases included in the study were clinically evaluated for genetic generalised epilepsy. Whole-exome sequencing was done for the discovery case cohort, a validation case cohort, and two independent control cohorts. The replication case cohort underwent targeted next-generation sequencing of the 19 known genes encoding subunits of GABAA receptors and was compared to the respective GABAA receptor variants of a third independent control cohort. Functional investigations were done with automated two-microelectrode voltage clamping in Xenopus laevis oocytes. FINDINGS: Statistical comparison of 152 familial index cases with genetic generalised epilepsy in the discovery cohort to 549 ethnically matched controls suggested an enrichment of rare missense (Nonsyn) variants in the ensemble of 19 genes encoding GABAA receptors in cases (odds ratio [OR] 2·40 [95% CI 1·41-4·10]; pNonsyn=0·0014, adjusted pNonsyn=0·019). Enrichment for these genes was validated in a whole-exome sequencing cohort of 357 sporadic and familial genetic generalised epilepsy cases and 1485 independent controls (OR 1·46 [95% CI 1·05-2·03]; pNonsyn=0·0081, adjusted pNonsyn=0·016). Comparison of genes encoding GABAA receptors in the independent replication cohort of 583 familial and sporadic genetic generalised epilepsy index cases, based on candidate-gene panel sequencing, with a third independent control cohort of 635 controls confirmed the overall enrichment of rare missense variants for 15 GABAA receptor genes in cases compared with controls (OR 1·46 [95% CI 1·02-2·08]; pNonsyn=0·013, adjusted pNonsyn=0·027). Functional studies for two selected genes (GABRB2 and GABRA5) showed significant loss-of-function effects with reduced current amplitudes in four of seven tested variants compared with wild-type receptors. INTERPRETATION: Functionally relevant variants in genes encoding GABAA receptor subunits constitute a significant risk factor for genetic generalised epilepsy. Examination of the role of specific gene groups and pathways can disentangle the complex genetic architecture of genetic generalised epilepsy. FUNDING: EuroEPINOMICS (European Science Foundation through national funding organisations), Epicure and EpiPGX (Sixth Framework Programme and Seventh Framework Programme of the European Commission), Research Unit FOR2715 (German Research Foundation and Luxembourg National Research Fund).

Ethnic variation of genetic (idiopathic) generalized epilepsy in Malaysia.

PURPOSE: Ethnic variation in epilepsy classification was reported in the Epilepsy Phenome/Genome Project. This study aimed to determine the ethnic variation in the prevalence of genetic (idiopathic) generalized epilepsy (GGE) and GGE with family history in a multi-ethnic Asian population in Malaysia. METHOD: In this cross-sectional study, 392 patients with a clinical diagnosis of GGE were recruited in the neurology outpatient clinic, University of Malaya Medical Centre (UMMC), from January 2011 till April 2016. RESULTS: In our epilepsy cohort (n=2100), 18.7% were diagnosed to have GGE. Of those, 28.6% >(N=112) had family history of epilepsy with a mean age of seizure onset of 16.5 years old, and 42.0% had myoclonic seizures (N=47). The lifetime prevalence of epilepsy among first-degree relative of those with GGE and positive family history was 15.0%. Analysis according to ethnicity showed that Malaysian Chinese had the lowest percentage of GGE among those with epilepsy (12.3%), as compared with Indian and Malay (25.3% and 21.3%, p<0.001). In addition, 32.1% of these Indian patients with GGE had positive family history, which is more than the Malay (26.4%) and Chinese (27.5%) ethnic groups. Consanguineous marriage was noted in 5 Indian families with positive family history (9.6%). CONCLUSION: There was ethnic variation in the prevalence of GGE, whereby the Malaysian Chinese had the lowest percentage of GGE as compared with Indian and Malay. A substantial proportion of GGE had positive family history among the three ethnics groups.

No relation between EFHC2 gene polymorphism and Idiopathic generalized epilepsy.

BACKGROUND: Idiopathic generalized epilepsy (IGE) is an epilepsy form without an underlying brain lesion or neurological indication or symptom. Recent investigations on the genetic origins of IGE and its subtypes report that certain mutations of various ion and non-ion channels genes in the central nervous system may be associated with IGE. PURPOSE: In this study we evaluated the relation between IGE and S430Y polymorphism in EFHC2 gene in a Turkish population. MATERIAL/METHODS: The study enrolled 96 healthy volunteers (47 male, 49 female), served as controls, and 96 IGE patients (41 male, 55 female), IGE diagnosis was confirmed in the neurology department. DNA extractions were performed. The presence of S430Y polymorphism in the exon 9 of EFHC2 gene were analyzed by Real-Time PCR. The findings obtained from the control and patient groups were compared. RESULTS: In the patient group there was one heterozygous male with 685 T>C mutation. In the control group, there were two objects with 685 T>C mutation; one heterozygous male, one heterozygous female. 662 G>A mutation was determined in neither controls nor patients. CONCLUSION: In our series of 96 IGE patients and 96 healthy controls, there was no relation between S430Y polymorphism in EFHC2 gene and IGE presence.

Failure to detect association between polymorphisms of the sodium channel gene SCN1A and febrile seizures in Chinese patients with epilepsy.

Arecent study in Caucasians found an association between the single nucleotide polymorphism (SNP) of SCN1A, IVS5N +5 G>A (rs3812718), and febrile seizures (FS). We examined whether this and other tagging SNPs of SCN1A were associated with an increased risk of FS in Han Chinese. A total of 728 Han Chinese patients with focal epilepsy were recruited: 97 had a history of FS (58% male, mean age 35 ± 12 years) and 631 did not (50% male, mean age 40 ± 15 years). Genotyping was performed for IVS5N +5 G>A and seven other tagging SNPs selected from the HapMap database. Genotyping was also performed in 848 ethnically matched population controls (50% male, mean age 37 ± 17 years). There was no statistically significant difference in either allele or genotype frequency of any of the SNPs studied between epilepsy patients with and without FS, and between epilepsy patients with FS and controls. The results do not suggest that SCN1A SNPs are susceptibility factors for FS in Han Chinese.

A novel HAX1 gene mutation in severe congenital neutropenia (SCN) associated with neurological manifestations.

Autosomal recessive severe congenital neutropenia (SCN) results from a maturation arrest of granulopoiesis at the level of promyelocytes and apoptosis of myeloid cells. In SCN patients, mutations have been described in the HAX1 gene. Most of the SCN patients who carry nonsense mutations that are common to both transcript variants of the HAX1 gene also exhibit neurological deficits. This study describes an SCN patient with neurological manifestations including daily episodes of atonic seizures, learning disabilities, and developmental delay. Sequencing of the HAX1 gene of this SCN patient identified a novel nonsense c.463_464insC homozygous mutation in exon 3, which is common to both transcript variants of the gene. This mutation encodes for a p.Gln155ProfsX14 change and causes premature truncation of the HAX1 protein. Neutrophils isolated from the patient exhibited spontaneous apoptosis and loss of inner mitochondrial membrane potential, which were further enhanced upon treatment with hydrogen peroxide. This study adds to the spectrum of novel HAX1 gene mutations and disease manifestations in ethnically distinct SCN patients. Our report describes the only nonsense mutation in the HAX1 gene present in SCN patients of Arab origin.

Genetic screening of two Tunisian families with generalized epilepsy with febrile seizures plus.

BACKGROUND AND PURPOSE: Febrile Seizure can be associated with heterogeneous epilepsy phenotypes regrouped in a syndrome called generalized epilepsy with febrile seizures plus (GEFS+). The aim of this report is to search for the gene responsible for GEFS+ in two affected Tunisian families. METHODS: Microsatellite marker analysis was performed on the known FS and GEFS+ loci. According to the results obtained by statistical analyses, GABRG2 on GEFS+3 locus and SCN1A on GEFS+2 locus were considered as two of the potential candidate genes and were tested for mutations by direct sequencing. RESULTS AND CONCLUSIONS: The mutation analysis and statistical test of the GABRG2 gene revealed a disease association with rs211014 in intron 8 (chi(2) = 5.25, P = 0.021). A sequencing analysis of the SCN1A gene was performed for the two tested families and showed a known mutation (c.1811G>A) and a putative disease-associated haplotype in only one family. Our results support that SCN1A is the responsible gene for GEFS+ in one of the two studied Tunisian families and suggest a positive association of an intronic SNP in the GABRG2 gene in both families.

A novel SCN1A mutation associated with severe GEFS+ in a large South American pedigree.

Generalized epilepsy with febrile seizures plus (GEFS+) is an inherited epileptic syndrome with a marked clinical and genetic heterogeneity. Here we report the molecular characterization of a large pedigree with a severe clinical form of GEFS+. Genetic linkage analysis implied the involvement of the FEB3 in the disease phenotype of this family (parametric two-point lod-score of 2.2). Sequencing of the SCN1A gene revealed a novel aspartic acid for glycine substitution at position 1742 of this sodium channel subunit. The amino-acid replacement lies in the pore-forming region of domain IV of SCN1A. Our observations are consistent with the genotype-phenotype correlation studies suggesting that mutations in the pore-forming loop of SCN1A can lead to a clinically more severe epileptic syndrome.

Mah-Jong-induced epilepsy: a special reflex epilepsy in Chinese society.

We present five patients of epilepsy in which seizures were triggered by playing or watching the traditional Chinese gambling game "Mah-Jong." One patient also experienced seizures while playing a computer version of the Mah-Jong game. This condition appeared to have a predominance of males (80%) and middle-aged onset (39.4 years). Four patients had generalized tonic-clonic seizures and one patient had partial seizures with secondary generalization. No spontaneous seizure occurred in these patients. Three patients had been receiving antiepileptic drug therapy, but without effective control over their seizures. Mah-Jong-induced epilepsy is a very peculiar form of complex reflex epilepsy that involves the higher mental activities. This phenomenon may consist of distinct pathophysiologic mechanisms from other reflex epilepsy induced by thinking and spatial tasks in idiopathic generalized epilepsies. This unusual reflex epilepsy is relatively benign in nature and antiepileptic drug therapy has uncertain benefits. It may be necessary to avoid playing the Mah-Jong game in order to prevent seizures.

Evidence for linkage between juvenile myoclonic epilepsy-related idiopathic generalized epilepsy and 6p11-12 in Dutch families.

PURPOSE: Previous linkage studies provided evidence for juvenile myoclonic epilepsy (JME) susceptibility loci at 6p11-12, HLA-6p21.3 region, 15q14, and 5q34. These results indicate locus heterogeneity or interpopulation differences, thus underlining the importance of replication studies. METHODS: We describe a replication linkage study of the 6p-q13 region in 18 families ascertained from JME probands of Dutch descent. In the presence of heterogeneity, the definition of the disease status may be crucial, and we therefore used two disease phenotypes: narrow [JME/idiopathic generalized epilepsy (IGE)-"only"] and broad (JME/IGE-plus-fast EEG background activity). RESULTS: We found evidence of linkage at 6p11-12 in multipoint analyses (p < 0.01 in a replication study) for both these disease definitions. Analysis of this region, assuming heterogeneity and autosomal dominant inheritance with a conservative 60% of penetrance, gave a maximum multipoint parametric lod score of 2.07 at D6S1573 for the narrow phenotype and peaked at 2.53 between D6S1623 and D6S1573 for the broad phenotype. The p value for nonparametric linkage reached 0.0013 for the narrow phenotype and 0.0010 for the broad. Significant exclusion (lod score