SCN1A and familial hemiplegic migraine: Mutations in four genes have been identified in familial hemiplegic migraine (FHM), from which CACNA1A (FHM type 1) and SCN1A (FHM type 3) code for neuronal voltage-gated calcium or sodium channels, respectively, while ATP1A2 (FHM type 2) encodes the α2 isoform of the Na+,K+-ATPase's catalytic subunit, thus classifying FHM primarily as an ion channel/ion transporter pathology.