Reduced penetrance in a Brazilian family with spinocerebellar ataxia type 10

Objective: To describe reduced penetrance associated with early onset in a Brazilian family with spinocerebellar ataxia type 10. Design: Clinical examination and molecular analysis for the ATTCT repeat responsible for spinocerebellar ataxia type 10 in a patient and family members through 3 generations. Setting: Ambulatory care. Patients: A 28-year-old female Brazilian patient who presented with early-onset cerebellar ataxia and epilepsy, and her 9 asymptomatic relatives. Main Outcome Measure: Genotype-phenotype correlation. Results: Molecular testing on this patient showed an expansion of approximately 850 ATTCT repeats at the SCA10 locus. Similar SCA10 expansions of approximately 850 repeats were identified in 6 of 8 asymptomatic paternal relatives examined. Conclusion: The stably transmitted pentanucleotide expansion of approximately 850 repeats may represent a mutant SCA10 allele with reduced penetrance that may express an early-onset, severe phenotype.