In common with AHC, episodic hemiplegia or hemiparesis is a clinical feature of familial hemiplegic migraine type 1 (FHM1), an autosomal dominant disorder caused by missense mutations in the CACNA1A gene encoding the pore-forming α1A-subunit of neuronal, voltage-gated CaV2.1 calcium channels [42]. This evidence concerns the gene CACNA1A and familial or sporadic hemiplegic migraine.