ATP1A2 and familial hemiplegic migraine: The majority of FHM families carry missense mutations in either CACNA1A (FHM1) (9, 10), encoding a neuronal voltage-gated calcium channel (CaV2.1), or ATP1A2 (FHM2; refs. 11–13), encoding an ATP-dependent sodium-potassium pump expressed predominantly in astrocytes.