Late onset cerebellar ataxia can be caused by several genetic mutations but a large percentage of patients remain undiagnosed. Thirty-eight patients with onset of slowly progressive, pure cerebellar ataxia ≥40 years-of-age were identi fied from a large ataxia database. Their clinical findings and quantitative ocul omotor tests were reviewed; all were screened for SCA1, SCA2, SCA3, SCA6, SCA8, SCA14, and the Fragile X premutation (FMR1). All 47 exons of CACNA1A were screen ed for mutations. Genetic analysis uncovered a mutation in 11 patients. The SCA6 mutation was present in 8 patients (repeats 22-23). Three additional genetic m utations were found: SCA1 (42 repeats), SCA3 (66 repeats), and SCA8 (121 repeats ). Patients without identified genetic mutations were characterized by 1) a late r age of onset, 2) truncal without extremity ataxia, 3) and down beat nystagmus. Although only a third of these idiopathic late onset ataxia patients had a posi tive family history, this homogeneous syndrome probably represents a yet to be i dentified genetic disorder.
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