Prevalence of SCN1A mutations in children with suspected Dravet syndrome and intractable childhood epilepsy

Mutations of the gene encoding the α1 subunit of neuronal sodium channel, SCN1A, are reported to cause Dravet syndrome (DS). The prevalence of mutations reported in such studies (mainly in clinically confirmed DS) seems high enough to make genetic diagnosis feasible. In fact, commercially operating genetic diagnostic laboratories offering genetic analyses of SCN1A are available. Still, the exact prevalence of mutations of SCN1A remains elusive. Fukuoka University has been serving as a genetic diagnostic laboratory for DS for the last 10 years. In this study, we determined the prevalence of SCN1A mutations (SCN1A, SCN2A, SCN1B and SCN2B) in 448 patients with suspected DS and intractable childhood epilepsy. A total of 192 SCN1A mutations were identified in 188 of 448 patients (42.0%). The frequencies of SCN1A mutations in suspected severe myoclonic epilepsy of infancy (SMEI), its borderline phenotype (SMEB) and intractable epilepsy were 56.2%, 41.9% and 28.9% respectively. In addition, four SCN2A mutations were identified in 4 of 325 patients. No mutations of SCN1B and SCN2B were identified. These results are potentially helpful for the diagnosis of DS at early stage.