ATP1A2 and familial hemiplegic migraine: Three genes contribute to family hemiplegic migraine (FHM): calcium voltage-gated channel subunit alpha1 A—CACNA1A (FHM1); ATPase Na+/K + transporting subunit alpha 2—ATP1A2 (FHM2) and sodium voltage-gated channel alpha subunit 1—SCN1A (FHM3).