ATXN2 and Huntington disease: The triplet CAG encodes for the amino acid glutamine (Q) and therefore, SCA2 belongs to the group of polyglutamine (polyQ) expansion diseases like Huntington’s disease (HD); SCA1, 3, 6, 7, 17; dentatorubral-pallidoluysian atrophy (DRPLA); and spinal and bulbar muscular atrophy (SBMA).