SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: De novo loss-of-function mutations in the VGSC SCN1A (encoding Nav1.1) are the main cause of Dravet syndrome (DS), a catastrophic early-life encephalopathy associated with prolonged and recurrent early-life febrile seizures, refractory afebrile epilepsy, and behavioral deficits (Claes et al., 2001; Claes et al., 2009; Lossin 2009; Escayg and Goldin 2010).