Redefining the Pathogenic CAG Repeat Units Threshold in <i>CACNA1A</i> for Spinocerebellar Ataxia Type 6

Our findings suggest that clinical manifestation within a typical lifespan likely requires at least 19 RUs. The 19-20 RU range represents an intermediate zone where OA may influence disease likelihood. For 21-22 RUs, OA significantly affects AAO, indicating a complex interplay between EA and OA. ≥23 RUs seem sufficient to cause disease onset within a typical lifespan, regardless of OA. These results provide a new paradigm for SCA6 diagnosis and genetic counseling, emphasizing the need for cautious interpretation of the intermediate RU range and consideration of OA.