ATP1A2 and familial or sporadic hemiplegic migraine: Up to now, four causative genes have been described in hemiplegic migraine (HM): CACNA1A on chromosome 19p13 (FHM1, MIM #301011) (Ophoff et al. 1996), ATP1A2 at 1q23 (FHM2, MIM #182340) (De Fusco et al. 2003), SCN1A at 2q24 (FHM3, MIM #182389) (Dichgans et al. 2005) and, recently, PRRT2 at 16p11.2 (MIM #614386) (Riant et al. 2012).