The ARCA Registry has (i) enabled the harmonization of clinical outcomes across ataxia centers around the world; (ii) has demonstrated its capacity to act as a centralized database for genotype–phenotype and natural history studies in the >100 ARCAs, already exemplified for COQ8A-, RFC1-, and POLG-related ataxias; and (iii) aggregates the necessary large-scale longitudinal progression datasets for calculating sample sizes, modeling trial designs and randomization procedures, and running pharmacometric models simulating treatment effect sizes for anticipated clinical trials. This evidence concerns the gene COQ8A and cerebellar ataxia.