Table 1. Mutations in CACNA1A underlie three allelic disorders: EA2, FHM and SCA6.

Disease	Core clinical features	Additional features	Inheritance	Mutations	Functional consequences
Episodic ataxia type 2 (EA2)	Attacks of ataxia, vomiting, vertigo, oscillopsia lasting hours to days, and interictal nystagmus	Epilepsy, migraine, and progressive cerebellar syndrome	Autosomal dominant	Nonsense and missense mutations, small deletions and insertions, and large deletions	Loss of function
Familial hemiplegic migraine type 1 (FHM1)	Rare subtype of MA: attacks of hemiparesis and hemisensory disturbance lasting hours to days	Confusion, encephalopathy, ataxia, coma, and seizures	Autosomal dominant	Missense mutations	Gain of function
Spinocerebellar ataxia type 6 (SCA6)	Late-onset progressive cerebellar ataxia		Autosomal dominant	CAG expansion in C-terminus	Alteration of CaV2.1 channel kinetics; polyglutamine cytotoxicity?

The clinical and genetic features of each disorder are described. The effect of mutations on Ca_V2.1 channel function is stated. MA, migraine with aura.