Dravet syndrome with favourable cognitive and behavioral development due to a novel SCN1A frameshift mutation.

Children with Dravet syndrome (DS) often have severe cognitive, behaviour and motor impairments. Patients with truncating mutations would logically have the more severe phenotype. Here we present a case of DS with an unusually favourable cognitive and behavioral development with a novel SCN1A frameshift mutation (c.4233-4234insAT). Under regular following up for ten years, the patient had normal expressive language and mild motor clumsiness. It is suggested that besides the type of SCN1A mutation, other mechanisms may be existed to influence the SCN1A phenotype, such as modifier genes, developmental variability, accumulation of somatic mutation in lifetime and environmental insults can all contribute to the cognitive and behavioral outcome.