CACNA1A and sporadic hemiplegic migraine: Genetic variants in the gene encoding the pore-forming CaV2.1 (P/Q-type) channel α1A subunit (CACNA1A) result in heterogeneous human neurological disorders of autosomal dominant inheritance, including familial and sporadic hemiplegic migraine (FHM/SHM), episodic ataxia type 2 (EA2), and spinocerebellar ataxia type 6 (SCA6).