TBP and juvenile Huntington disease: Expanded trinucleotide repeat sequences in TBP have been shown to cause spinocerebellar ataxia-17 (SCA17) and to phenocopy Huntington's disease (Nakamura et al., 2001; Fujigasaki et al., 2001; Stevanin et al., 2003; Hsu et al., 2014).