FHM3 is caused by mutations in the SCN1A gene (sodium voltage-gated channel alpha subunit 1) coding for a sodium channel and has been related to epilepsy syndromes such as Dravet syndrome and generalized epilepsy with febrile seizures plus [21]. Here, SCN1A is linked to encephalopathy, progressive, early-onset, with brain edema and/or leukoencephalopathy.