Progressive Ataxia with Hemiplegic Migraines: a Phenotype of CACNA1A Missense Mutations, Not CAG Repeat Expansions.

We report a 52-year-old woman presenting with autosomal dominant progressive cerebellar ataxia and familial hemiplegic migraine type 1 whose genetic evaluation, negative for spinocerebellar ataxia (SCA) types 1, 2, 3, and 6, revealed instead a heterozygous pathogenic missense mutation in CACNA1A (NM_001127221:c.1748G > A:p.Arg583Gln). A systematic literature review showed that Arg583Gln is associated predominantly with progressive ataxia combined with episodic disorders (overwhelmingly hemiplegic migraine) whereas Thr666Met, the other most common CACNA1A missense mutation, with a combination of progressive ataxia and episodic disorders in half the cases and episodic disorders only in the other half. While uncertainties remain in the genotype-phenotype correlation of all CACNA1A mutations, the accumulated evidence suggests that that the co-occurrence of hemiplegic migraine and autosomal dominant progressive cerebellar ataxia should guide the clinician to test for CACNA1A missense mutation rather than CAG expansions or truncating mutations.