Mutation screen of GABRA1, GABRB2 and GABRG2 genes in Japanese patients with absence seizures.

Absence seizures are classified into typical and atypical absences according to clinical and EEG characteristics. Although missense mutations in the GABA(A) receptor gamma2 subunits (GABRG2) gene have recently been detected in two families with typical absence seizures, no study has been carried out to clarify the relationship between atypical absence and GABA(A) receptors. We performed mutation analysis of all the coding exons of GABA(A) receptor alpha1, beta2 and gamma2 subunit (GABRA1, GABRB2 and GABRG2) genes by direct sequencing to clarify whether there was common molecular biological mechanism underlying both typical and atypical absences. We recruited 52 unrelated Japanese patients, thirty-eight with typical absences and 14 with atypical absences. They consisted of 38 with childhood absence epilepsy, three with Lennox-Gastaut syndrome, two with epilepsy with myoclonic-astatic seizures and nine with epilepsy with continuous spike-waves during slow wave sleep. All of the subjects were idiopathic or cryptogenic cases without any organic brain lesions or underlying diseases. We detected five polymorphisms (T156C in GABRA1, C1194T in GABRB2, and C315T, T588C and C1230T in GABRG2), and they are silent mutations. In conclusion, mutations in GABRA1, GABRB2 and GABRG2 do not seem to be a major genetic cause of epilepsy with typical and atypical absences in Japanese subjects.