ATP1A3 and migraine, familial hemiplegic, 2: The neurological disorders familial hemiplegic migraine type 2 (FHM2), alternating hemiplegia of childhood (AHC), and rapid-onset dystonia parkinsonism (RDP) are autosomal dominant disorders caused by mutations of the Na+/K+-ATPase α2 (FHM2 and AHC1) and α3 (AHC2 and RDP) isoforms.