Genetic testing in spinocerebellar ataxias: defining a clinical role.

Although genetic tests for known spinocerebellar ataxia (SCA) genes are increasingly available, their exact clinical role has received much less attention. Currently available DNA tests can define the genotypes of up to two thirds of patients with dominantly inherited SCAs. Certain characteristic clinical features and ethnic predilection of some of the SCA subtypes may help prioritize specific SCA gene testing. Available data on genotype-phenotype correlation suggest that currently available DNA tests cannot accurately predict age of onset or prognosis. Because of the mostly adult-onset symptoms and the absence of effective treatment, genetic counseling is essential for addressing ethical, social, legal, and psychological issues associated with SCA DNA testing.