SCN1A and encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy: As an example, monozygotic twins discordant for an SCN1A mutation have been described (a Dravet syndrome patient, carrier of the variant c.664C>T; p.(Arg222*) vs. her twin, without detected mutation of DNA from lymphocytes, hair, buccal cells, skin fibroblasts, and cell lines derived from the olfactory neuroepithelium, was only affected by two simple febrile seizures before four years of age) [29].