Spinocerebellar ataxia 8: variable phenotype and unique pathogenesis.

Spinocerebellar ataxia 8 (SCA8), a triplet repeat expansion disorder, is genetically distinct from the other inherited ataxias, but its unusually variable phenotype can make its diagnosis difficult. In this review we describe 3 new cases of genetically verified SCA8 to highlight the broad clinical spectrum of symptoms observed with this disorder and to draw attention to the features of myoclonus and migraine headaches, which in the context of cerebellar ataxia warrants the clinician to consider SCA8 as a potential diagnosis. We also address the controversy surrounding the genetic testing approach for diagnosing SCA8. Finally, we evaluate the evidence that SCA8 may affect calcium channel function and that the presentation of episodic ataxia and migraines suggests a clinical and pathogenic overlap of SCA8 with the channelopathies.