Possible association of a silent polymorphism in the neuronal nicotinic acetylcholine receptor subunit alpha4 with common idiopathic generalized epilepsies.
The alpha4 subunit gene of the neuronal nicotinic acetylcholine receptor (CHRNA4) has recently been identified as the first gene underlying an idiopathic partial epilepsy syndrome in human, autosomal-dominant nocturnal frontal lobe epilepsy (ADNFLE). CHRNA4 is located in the candidate region for benign familial neonatal convulsions and low-voltage EEG on chromosome 20q. In the present study, we examined the possible role of CHRNA4 in common subtypes of idiopathic generalized epilepsy (IGE), comprising childhood and juvenile absence epilepsy and juvenile myoclonic epilepsy (JME), by systematically screening the coding region of the gene for sequence variants. We present here a population-based association study testing the hypothesis that variants of the CHRNA4 gene confer genetic susceptibility to common subtypes of IGE. The missense mutation (Ser248Phe), associated with ADNFLE, and four silent polymorphisms in the CHRNA4 gene were genotyped in 103 IGE patients and 92 controls by polymerase chain reaction and subsequent restriction analysis. Without correction for multiple testing, the frequency of the T-allele of the silent CfoI bp595 polymorphism was increased in the entire group of IGE patients (f(T) = 0.085) compared to that in the controls (f(T) = 0.027). The allelic association was not restricted to any subgroup of IGE with either JME or idiopathic absence epilepsies. This result suggests that variation of the CHRNA4 gene, or so-far-undetected sequence variants near the CHRNA4 locus, confer susceptibility to the common IGE syndromes.