SCN1A and familial hemiplegic migraine: Familial hemiplegic migraine (FHM) is a rare monogenic subtype of migraine with aura caused by mutations in genes encoding either neuronal voltage-gated ion channels (CaV2.1 in FHM1; NaV1.1 in FHM3) or the predominantly astrocytic α2 Na+, K+ ATPase (in FHM2; Pietrobon, 2007).