Rare coding variants in genes encoding GABA(A) 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 GABA(A) receptors and was compared to the respective GABA(A) 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 GABA(A) receptors in cases (odds ratio [OR] 2.40 [95% CI 1.41-4.10]; p(Nonsyn)=0.0014, adjusted p(Nonsyn)=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]; p(Nonsyn)=0.0081, adjusted p(Nonsyn)=0.016). Comparison of genes encoding GABA(A) 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 GABA(A) receptor genes in cases compared with controls (OR 1.46 [95% CI 1.02-2.08]; p(Nonsyn)=0.013, adjusted p(Nonsyn)=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 GABA(A) 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. Copyright (C) 2018 The Author(s). Published by Elsevier Ltd.Peer reviewe

De novo INF2 mutations expand the genetic spectrum of hereditary neuropathy with glomerulopathy

Objective: Identification of mutations in the inverted formin-2 (INF2) gene in patients with Charcot-Marie-Tooth (CMT) disease combined with focal segmental glomerulosclerosis (FSGS) in order to expand the genetic and phenotypic spectrum. Methods: We sequenced INF2 in 5 patients with CMT disease and FSGS. Mutations were subsequently screened in family members of the index patient and 264 control individuals. Results: In 3 patients, we detected 2 novel de novo INF2mutations (p.Leu77Arg and p.Leu69-Ser72-del) and a third, most likely de novo mutation (p.Gly114Asp). One of our patients displayed intellectual disability, a phenotypic characteristic not previously associated with INF2. The same patient also showed a more pronounced sensorineural hearing loss than described before. Conclusions: In exon 2 of INF2, we identified 3 novel mutations that likely affect the protein structure and function. Our findings expand the genetic spectrum of INF2-associated disorders and broaden the associated phenotype with the co-occurrence of intellectual disability and more severe hearing loss than previously reported. De novo INF2 mutations may be more common in patients with CMT disease and FSGS in comparison to FSGS alone. Furthermore, renal dysfunction is more severe and starts earlier in life when associated with CMT disease. Our study confirms that INF2 mutations are a major cause of disease in patients with CMT disease and early signs of nephropathy. Diagnostic screening of INF2 is strongly recommended in isolated patients presenting with CMT disease and FSGS. © 2013 American Academy of Neurology