Not all <i>SCN1A</i> epileptic encephalopathies are Dravet syndrome

Here, we present a phenotype-genotype correlation for <i>SCN1A</i>. We describe a distinct <i>SCN1A</i> phenotype, early infantile <i>SCN1A</i> encephalopathy, which is readily distinguishable from the well-recognized entities of Dravet syndrome and genetic epilepsy with febrile seizures plus. This disorder has an earlier age at onset, profound developmental impairment, and a distinctive hyperkinetic movement disorder, setting it apart from Dravet syndrome. Remarkably, 8 of 9 children had the recurrent missense mutation p.Thr226Met.