The SCA12 mutation as a rare cause of spinocerebellar ataxia

Background: Spinocerebellar ataxias are a group of phenotypically and genetically heterogeneous disorders characterized by progressive degeneration of the cerebellum. The expansion of a CAG repeat upstream of the PP2APR55 beta gene has been recently reported as a novel cause of a dominantly inherited ataxia (SCA12) in a kindred with limb tremor as an early feature. Objective: To explore the relative frequency of SCA12 among familial and sporadic spinocerebellar ataxias in an ethnically diverse patient population. Methods: We used polymerase chain reaction to analyze CAG repeat size in a series of patients presenting to an ataxia clinic in California. Results: The SCA12 expansion was not detected in any of the cases investigated. The largest allele found had 22 repeats, a finding within the proposed nonpathogenic range. Distribution of repeat size and heterozygosity were similar to that described previously. Conclusions: These results, coupled with findings in other populations, indicate that the SCA12 mutation is a rare cause of spinocerebellar degeneration. Diagnostic testing for SCA12 should be considered in patients with cerebellum disorders and an atypical clinical phenotype, especially when tremor is initially present.