CACNA1A and migraine, familial hemiplegic, 2: Gain of function mutations in CACNA1A encoding the alpha 1a subunit of the Cav2.1 (P/Q type) neuronal calcium channel are responsible for FHM-1 (Ophoff et al., 1996), loss of function mutations in ATP1A2, encoding the alpha 2 subunit of the Na+/K+ ATPase are responsible for FHM-2 (De Fusco et al., 2003).