ATP1A2 and familial hemiplegic migraine: To date, three genes, when disrupted, have been identified as causing FHM: CACNA1A (FHM1) [11], encoding the α1 subunit of neuronal Cav2.1 Ca2+ channels; ATP1A2 (FHM2) [12], encoding the α2 subunit of Na+/K+ ATPase pumps; and SCNA1 (FHM3) [13], encoding the pore-forming α1 subunit of neuronal Nav1.1 Na+ channels.