Most Dravet syndrome (DS) and Generalized Epilepsy with Febrile Seizures Plus (GEFS+) cases have mutations in SCN1A. Both inherited and de novo mutations in SCN1A genes cause epilepsy and epileptic encephalopathies. The gene discussed is SCN1A; the disease is encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.