SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: Mutations in SCN1A resulting in Nav1.1 LoF are associated with a spectrum of phenotypic severity, from mild missense mutations causing febrile seizures plus (FS+) to more severe missense and protein truncating variants (PTVs) resulting in generalized epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome (DS) (Catterall, Kalume, & Oakley, 2010).