Dravet syndrome: a genetic epileptic disorder.
Dravet syndrome (DS), or severe myoclonic epilepsy in infancy, is one of the most severe types of genetic epilepsy. It is characterized by the initial occurrence of febrile or afebrile seizures that often evolve into status epilepticus in infants with normal development, and by the subsequent appearance of myoclonic and/or atypical absence seizures as well as complex partial seizures. The key feature that characterizes DS is fever sensitivity, although photosensitivity and pattern-sensitivity are also often seen. The prognosis is unfavorable in most cases. Seizures become drug-resistant and persist, with many patients suffering from motor and cognitive impairment. Mutations of SCN1A, which encodes the voltage-gated sodium channel NaV1.1, are the most frequent genetic cause of this syndrome. SCN1A mutations and/or microchromosomal rearrangements involving SCN1A are detected in about 85ｵ of patients. Mutations of PCDH19 have also been reported in female patients with clinical findings compatible with DS. PCDH19 mutations might account for 5ｵ of overall DS cases. Thirty years after its first description, DS is considered as a model of channelopathy. This survey reviews recent developments in the research literature on DS, focusing on the clinical course, as well as its genetic causes.