Linkage analysis between idiopathic generalized epilepsies and the GABAA receptor α5, β3 and γ3 subunit gene cluster on chromosome 15

Introduction - We tested the hypothesis that genetic variants within the GABA_Aα₅, β₃ and γ₃ subunit gene cluster on chromosome 15q11-q13 confer genetic susceptibility to common subtypes of idiopathic generalized epilepsy (IGE). Material and methods - Ninety-four families were selected from IGE patients with either juvenile myoclonic epilepsy (JME), juvenile (JAE) or childhood absence epilepsy (CAE). Cosegregation was tested between dinucleotide polymorphisms associated with the human GABA_Aα₅, β₃ and γ₃ subunit gene cluster and three different IGE trait models. Results - Evidence against linkage to the GABA_Aα₅, β₃ and γ₃ subunit gene cluster was found in the entire family set and subsets selected from either CAE or JAE. In 61 families of JME patients, a maximum lod score (Z_max=1.40 at θ_max=0.00) was obtained for a broad IGE spectrum ("idiopathic" generalized seizure or generalized spike and wave discharges in the electroencephalogram) assuming genetic heterogeneity (α=0.37; P =0.06) and an autosomal recessive mode of inheritance. Conclusion - The possible hint of linkage in families of JME patients emphasizes the need for further studies to determine whether a recessively inherited gene variant within the GABA_Aα₅, β₃ and γ₃ subunit gene cluster contributes to the pathogenesis of "idiopathic" generalized seizures and associated EEG abnormalities in a proportion of families.