Milder phenotype with SCN1A truncation mutation other than SMEI

Till now truncation mutations of voltage-gated sodium channel alpha subunit type I (SCN1A) gene were mostly found in severe myoclonic epilepsy of infancy (SMEI) patients. In this research we first identified two novel de novo truncation mutations (S662X and M145fx148) in two patients whose phenotypes were quite milder compared with SMEI patients. One patient was diagnosed as generalized epilepsy with febrile seizures plus (GEFS+); the other had focal seizures. Both patients had good response to anti-epileptic therapy (valproate or the combination of valproate and topiramate). Our findings extended the utility of the SCN1A gene testing and further confirmed the complex relationship between genotype and phenotype of SCN1A mutations. Further work is needed to optimize the protocol for specific genetic testing in children with epilepsy.