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 PP2APR55β 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.
To explore the relative frequency of SCA12 among familial and sporadic spinocerebellar ataxias in an ethnically diverse patient population.
We used polymerase chain reaction to analyze CAG repeat size in a series of patients presenting to an ataxia clinic in California.
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.
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.