Abstracts

Rationale: WERN, a co-operation of scientists and clinicians, facilitated a gene-discovery project which has provided a platform not only for novel gene-discovery, and candidate gene analysis in specialised cohorts but also has resulted in collections of dedicated epilepsy phenotypes and the formation of an epilepsy biobank. In 2005 clinical data collection initiated the study; The genetic basis of familial epilepsy in Wales, and thus far 67 families have been recruited. In families where conventional linkage analysis was not possible, further investigation of broad channelopathies was performed using known candidate genes, starting with GABRG2 in selected cohorts sourced from WERNs biological and clinical datasets. Interruption of gamma-aminobutyric acid(GABA), the major inhibitory neurotransmitter in the brain historically was thought to play a pivotal role in epilepsy mechanisms. Over the last decade pathogenic mutations have been discovered in two GABA receptor subunit genes. Six mutations in the gene encoding the gamma-2-subunit of the GABA A receptor(GABRG2) have been reported in childhood absence epilepsy, febrile seizures(FS) and generalised epilepsy with FS plus(GEFS+). Rare and unlikely to account for the majority of epilepsies diagnosed by clinicians these mutations have been shown to segregate in large rare families. Despite the emerging wave of negative GABA association studies, these mutations suggest GABRG2 as a gene of large effect in these monogenic families and also that it may play a mild to moderate role as a susceptibility gene in other multifactorial epilepsies with a more complex genetic architecture. Methods: Using polymerase chain reaction(PCR) to amplify GABRG2 coding regions, followed by DNA sequencing reactions we performed GABRG2 and SCN1A mutational analysis on a GEFS+ cohort and on phenotypic outliers. Cohort selection was confirmed following a blinded peer review by two neurology research fellows, a paediatric neurologist, a genetic counsellor and a molecular geneticist. Population studies were performed using high resolution DNA melt analysis on Idaho LightScanner Technology. Results: We describe a novel GABRG2 mutation(R97X), at position 97 in the polypeptide sequence(c.406C>T), in an index case. This heterozygous mutation introduces a premature stop codon in the N-terminal domain, which substitutes a highly conserved arginine and truncates GABRG2 with loss of all four transmembrane domains. The R97X mutation segregated with affected idiopathic generalised epilepsy family members and was not found in 190 healthy controls. Conclusions: The discovery of this GABRG2 R97X mutation has given way to ongoing functional platforms of PCR-directed mutagenesis, mutant and wild type GFP-tagging and fluorescent live cell imaging with confocal microscopy allowing the study of the potential pathogeneticity and epilepsy mechanisms in this family. This discovery represents the first molecular epilepsy outcome for WERN and is underpinned by WERNs bench-to-bedside translational research agenda which originates in clinician-centred case ascertainment and accurate phenotyping.