Furthermore, many of these antiepileptic drugs are not effective or can worsen clinical presentation in disorders such as Dravet syndrome, a severe early childhood encephalopathy that is commonly caused by mutations in the VGSC SCN1A (encoding Nav1.1)16–18. This evidence concerns the gene SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.