Co‐occurrence of ATXN3 and ATXN2 repeat expansions in Chinese ataxia patients with slow saccades

BACKGROUND: The presence of more than one polyQ‐related gene within a single individual is a rare incidence, which may provide the potential opportunity to study the combined effects of these spinocerebellar ataxia (SCA) genes. METHODS: We retrospectively analyzed genetic data from 112 SCA3 probands and found Patient 1 harbored expanded ATXN2 allele (33 repeats) and intermediate TBP allele (41 repeats), and Patient 2 with intermediate ATXN2 allele (32 repeats). Detailed clinical and oculomotor performances were investigated. The age at onset and oculomotor parameters of both patients were compared with matched pure SCA3 groups controlling either disease severity or CAG repeats. RESULTS: Most of the clinical phenotypes and oculomotor characteristics of these two patients were common to typical SCA3 patients. Compared to pure SCA3 groups controlling disease severity, mild reduced horizontal saccade velocity could be detected in both patients. However, mild expansions of the ATXN2 allele seemed to have no influence on the age at onset of Patient 1 but might have a mild impact on Patient 2. CONCLUSION: Our study provides supporting evidence that mild expansions of ATXN2 may have modifying effects on SCA3 phenotype. Larger control series and longitudinal data are warranted to confirm our results.