Since the identification of a CAG repeat expansion in the TATA-box binding protein (TBP) gene in a patient with ataxia in 1999 and then verification of this expansion in patients with SCA17 in 2001, several SCA17 rodent models, including both knock-in and transgenic models in mice and rats, have been established to explore the phenotypic features and pathogenesis of SCA17.
To investigate whether the expansion of CAG repeats of the TATA-binding protein (TBP) gene is involved in the pathogenesis of neurodegenerative diseases, we have screened 118 patients with various forms of neurological disease and identified a sporadic-onset patient with unique neurologic symptoms consisting of ataxia and intellectual deterioration associated with de novo expansion of the CAG repeat of the TBP gene.
Our results show that (1) a significant number of isolated cases of ataxia are due to TNR expansions; (2) expanded DRPLA alleles in Portuguese families may have evolved from an ancestral haplotype; and (3) small (CAG)(n) expansions at the TBP gene may cause SCA17.
We conclude that, however rare, SCA17 must be considered as a cause of Huntington's disease-like phenotypes and ataxia syndromes, also in isolated cases.
The SCA17 clinical phenotype includes characteristics associated with cerebellar and cortical atrophy such as ataxia, dementia, epilepsy, chorea and parkinsonian features.