From OMIM
Dravet syndrome, first described by Dravet (1978), is a clinical term for a severe neurologic disorder characterized by the onset of seizures in the first year of life after normal early development. Affected individuals usually present with generalized tonic, clonic, and tonic-clonic seizures that may initially be induced by fever and are usually refractory to treatment. Later, patients tend to manifest other seizure types, including absence, myoclonic, and partial seizures. The EEG is often normal at first, but later characteristically shows generalized spike-wave activity and other abnormalities. Psychomotor development stagnates around the second year of life, and affected individuals show subsequent mental decline, behavioral problems, and learning disabilities (summary by Dravet et al., 1992; Sugawara et al., 2002; Harkin et al., 2007; Shbarou and Mikati, 2016). 'Severe myoclonic epilepsy of infancy' (SMEI) and 'migrating partial seizures of infancy' (MPSI) are other clinical manifestations of Dravet syndrome (summary by Ohmori et al., 2002; Carranza Rojo et al., 2011; Dravet et al., 2011). Although most cases of Dravet syndrome are caused by mutation in the SCN1A gene, there are other developmental and epileptic encephalopathies (DEEs) with clinical features similar to Dravet syndrome that are caused by mutations in other genes (summary by Steel et al., 2017). For a discussion of genetic heterogeneity of DEE, see 308350.  http://www.omim.org/entry/607208