The mean serum cystatin C levels for the SCA and control groups were 0.872 ± 0.3 (95% confidence interval [CI], 0.811 to 0.933) and 0.922 ± 0.2 (95% CI, 0.88 to 0.962), respectively. This evidence concerns the gene CST3 and autosomal dominant cerebellar ataxia.