More than 300 mutations in SCN1A (Nav1.1) are responsible for genetic epilepsy syndromes ranging in severity from simple febrile seizures to Generalized Epilepsy with Febrile Seizures (GEFS+), an autosomal dominant epilepsy disorder associated to missense mutations, to Severe Myoclonic Epilepsy of Infancy (SMEI or Dravet syndrome; prevalence: <1/40,000), the most severe form of often intractable epilepsy mainly caused by truncation or deletion mutations in Nav1.1 channels (Catterall, 2014). Here, SCN1A is linked to encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.