CACNA1A and familial hemiplegic migraine: Specific genetic subforms of FHM have been identified: FHM type 1 (FHM1) is associated with mutations of the CACNA1A gene (coding for a calcium channel) on chromosome 19 p13; FHM type 2 (FHM2) with mutations of the ATP1A2 gene (coding for a K/Na-ATPase) on chromosome 1q23; and FHM type 3 (FHM3) with mutations of the SCN1A gene (coding for a sodium channel) on chromosome 2 [1].