ATXN1 and spinocerebellar ataxia type 1: The causative gene for SCA1 is ATXN1, with the major transcript (ENST00000436367.6) containing 8 exons, although only the last 2 exons encode the 815 amino acid (aa), 87 KDa protein, ataxin-1 (ATXN1) (Figure 3).