The core Dravet syndrome phenotype.

Dravet syndrome was described in 1978 by Dravet (1978) under the name of severe myoclonic epilepsy in infancy (SMEI). The characteristics of the syndrome were confirmed and further delineated by other authors over the years. According to the semiologic features, two forms have been individualized: (1) the typical, core, SMEI; and (2) the borderline form, SMEIB, in which the myoclonic component is absent or subtle. Clinical manifestations at the onset, at the steady state, and during the course of the disease are analyzed in detail for the typical Dravet syndrome, and the differential diagnosis is discussed. Onset in the first year of life by febrile or afebrile clonic and tonic-clonic, generalized, and unilateral seizures, often prolonged, in an apparently normal infant is the first symptom, suggesting the diagnosis. Later on, multiple seizure types, mainly myoclonic, atypical absences, and focal seizures appear, as well as a slowing of developmental and cognitive skills, and the appearance of behavioral disorders. Mutation screening for the SCN1A gene confirms the diagnosis in 70-80% of patients. All seizure types are pharmacoresistent, but a trend toward less severe epilepsy and cognitive impairment is usually observed after the age of 5 years.