Expansion of CAG repeat units coding for polyglutamine stretches has been identified in at least 9 hereditary neurodegenerative diseases, including spinal and bulbar muscular atrophy; Huntington disease; spinocerebellar ataxia (SCA) types 1, 2, 6, 7, and 17; Machado-Joseph disease (also called SCA3); and dentatorubral-pallidoluysian atrophy. Among these, SCA17, which is caused by expansion of a CAG/CAA repeat coding for a polyglutamine stretch of the TATA-binding protein (TBP) gene, is the latest polyglutamine disease.
Tsuji S. Spinocerebellar Ataxia Type 17Latest Member of Polyglutamine Disease Group Highlights Unanswered Questions. Arch Neurol. 2004;61(2):183-184. doi:10.1001/archneur.61.2.183