STRs database » TBP locus
Overview of repeats
Individuals with at least 43 total glutamine-encoding CAG/CAA repeats in the coding region of TBP have been reported with spinocerebellar ataxia type 17 (SCA17) (Silveira et al. (2002)). Repeats of 25-42 were reported in the healthy population studied (Koide et al. (1999)).
In six families, De Winter et al. (2025) investigated intermediate TBP expansions together with heterozygous STUB1 variants. The family carrying both findings had ataxia with cognitive and extrapyramidal involvement; intermediate TBP expansion was also reported in an individual with mild late-onset ataxia without a STUB1 variant. Conventional allele categories distinguish 41-48 repeats with reduced or variable penetrance from 49 or more, although published full-penetrance boundaries differ. Marelli et al. (2026) reported enrichment of 39 and 40-or-more-repeat alleles among patients with pathogenic STUB1 variants and proposed a lower threshold for TBP modifier effects in that genetic context.