SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: In Dravet Syndrome (DRVT) (OMIM #607208), a severe form of drug-resistant epilepsy, the loss of function mutations of the SCN1A gene affect Nav1.1 and lead to a lack of neuronal inhibition in GABAergic interneurons resulting in neuronal hyperactivity.