SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: The most severe of the SCN1A related epilepsies is Dravet Syndrome (DS), an early onset, pharmacoresistant epilepsy associated with complete loss-of-function mutations leading to Nav1.1 haploinsufficiency and characterized by multiple seizure types, including lifelong sensitivity to thermally evoked seizures, persistent cognitive impairment, and other behavioral comorbidities (Dravet, 2011).