There are over 40 SCAs, including common SCAs (SCA1, SCA2, and SCA3/Machado-Joseph, SCA6, SCA7, and SCA17) and dentatorubral-pallidoluysian atrophy (DRPLA), all of which are caused by an expansion of a CAG trinucleotide repeat in the distinct disease genes (Soong and Morrison, 2018). The gene discussed is ATXN3; the disease is dentatorubral-pallidoluysian atrophy.