ATXN2 and Machado-Joseph disease: This allows the presumption that the differences between SCA2 and SCA3/MJD transmissions to the offspring should not be attributed to distinct psychological or social pictures, but to the biological context of the expansions in ATXN2 and ATXN3. Due to that, SCA2 and SCA3/MJD are probably good prototypes to test the dynamics of the CAGexp in general and to answer the question: “for how many generations will the descendants of a de novo expansion last?” This was the aim of the present study.