FHM is caused by either gain-of-function mutations in neuronal voltage-gated ion channels (the Ca2+ channel CaV2.1 in FHM1 [16, 17] and the Na+ channel NaV1.1 in FHM3 [18, 19]) or by loss-of-function mutations in the predominantly astrocytic α2 Na+, K+ ATPase (α2NKA, in FHM2 [20, 21]). Here, SCN1A is linked to familial hemiplegic migraine.