Natural History Study of Infants and Children With Developmental and Epileptic Encephalopathies

Inclusion Criteria: * Aged between 6 months and 60 months. * Confirmed SCN1A mutation. * Normal development prior to onset of first seizure as defined by the Centers for Disease -Control and Prevention (CDC 2019). * Onset of seizures between age 3 and 15 months, inclusive. Exclusion Criteria: * Copy number variant of SCN1A, including SCN1A microdeletion, if affecting other genes. * SCN1A mutation present on both alleles. * Known pathogenic or clinically suspected mutation in a seizure-associated gene besides SCN1A. * Confirmed mutation in a gene besides SCN1A that is known to increase the severity of the seizure phenotype. * Known gain-of-function genetic mutation, as defined by functional studies, including p.Thr226Met. * History of notable developmental deficit that was evident prior to seizure onset. * Known central nervous system structural abnormality as found on magnetic resonance imaging or computed tomography scan of brain. * Currently taking or has taken for 6 or more consecutive weeks anti-seizure medications (ASMs) at a therapeutic dose that are contraindicated in SCN1A-positive Dravet Syndrome, including sodium channel blockers. * Known concomitant genetic mutation or clinical comorbidity that potentially confounds typical Dravet phenotype.