SCN1A and Dravet syndrome: Dravet syndrome (DS) is a severe unremitting epileptic disorder with onset in infancy due to heterozygous expression of missense mutations and microdeletions (i.e., copy number variants) of SCN1A, the gene coding the voltage-gated sodium ion channel Nav1.1 that is expressed in the axon initial segment (AIS) of FSPV+ and somatostatin-expressing GABAergic inhibitory interneurons; these inhibitory interneurons are embryologically derived from the medial ganglion eminence [12].