In this group of disorders, the length and nucleotide composition of the STR motif differs according to the causative gene: SCA1, SCA2, Machado-Joseph disease (MJD)/SCA3, SCA6-8, SCA10, SCA12, SCA17, SCA31, SCA36, SCA37, dentatorubral-pallidoluysian atrophy (DRPLA), and the recently identified SCA27B (Klockgether et al. 2019; Pellerin et al. 2023). This evidence concerns the gene ATXN2 and Machado-Joseph disease.