Lack of evidence of an allelic association of a functional GABRB3 exon 1a promoter polymorphism with idiopathic generalized epilepsy

Purpose: Mutation screening and linkage disequilibrium mapping of the gene encoding the GABA(A) beta(3) subunit (GABRB3) identified a common genetic variant in the exon 1a promoter region (C-allele of rs4906902) which displayed a reduced transcriptional activity and showed a strong allelic association with childhood absence epilepsy (CAE). The present population-based association study tested whether the C-allele of rs4906902 confers susceptibility to CAE or other common syndromes of idiopathic generalized epilepsy (IGE) in a German sample. Methods: Seven hundred and eighty unrelated German IGE patients (250 CAE, 123 juvenile absence epilepsy, 303 juvenile myoclonic epilepsy (JME), 104 epilepsy with generalized tonic-clonic seizures on awakening) and 559 healthy population controls were genotyped for the single nucleotide polymorphism (SNP) rs4906902. Results: The frequency of the risk-conferring C-allele did not differ significantly between CAE patients (f(C)=0.190) and controls (f(C)=0.183; P=0.376, one-tailed). Similarly, no evidence for an allelic association was found for 373 patients with idiopathic absence epilepsy, 303 JME patients, and the entire IGE sample (P>0.77, two-tailed). Conclusion: Our study failed to replicate an association of the common GABRB3 exon 1a promoter SNP rs4906902 with CAE. Moreover, the present results do not provide evidence that the common functional C-variant confers a substantial epileptogenic effect to a broad spectrum of IGE syndromes in the German population