To investigate the possible correlation between genotype and phenotype of epilepsy, we analyzed the voltage-gated sodium channel alpha1-subunit (SCNIA) gene, beta1-subunit (SCN1B) gene, and gamma-aminobutyric acidA receptor gamma2-subunit (GABRG2) gene in DNAs from peripheral blood cells of 29 patients with severe myoclonic epilepsy in infancy (SME) and 11 patients with other types of epilepsy. Mutations of the SCNIA gene were detected in 24 of the 29 patients (82.7%) with SME, although none with other types of epilepsy. The mutations included deletion, insertion, missense, and nonsense mutations. We could not find any mutations of the SCN1B and GABRG2 genes in all patients. Our data suggested that the SCNIA mutations were significantly correlated with SME (p < .0001). As we could not find SCNIA mutations in their parents, one of critical causes of SME may be de novo mutation of the SCNIA gene occurred in the course of meiosis in the parents. (C) 2002 Elsevier Science (USA). All rights reserved.