Isolated Generalized Chorea in a Patient with Small-Expanded Allele Spinocerebellar Ataxia 17

Spinocerebellar ataxia type 17 (SCA17) is an autosomal dominant disease caused by a polyglutamine-encoding CAG/CAA repeat expansion within the TATA box-binding protein (TBP) gene. It is characterized by a markedly heterogeneous phenomenology and complex genotype-phenotype relationships.

We describe the clinical, neuropsychological, and neuroimaging findings of a 73-year-old patient who presented a 10-year history of generalized hyperkinetic movements and depressive symptoms. The patient's family history was unremarkable. Neurological examination revealed choreic movements affecting the upper and lower limbs, the face and the trunk with no additional neurological signs. Blood sample analysis, brain imaging, and neuropsychological evaluation revealed normal results. Genetic analysis identified, in the TBP gene, the 41-CAG pathological allele with reduced penetrance.

The present case report provides further insight into the small-expanded allele SCA17-associated phenotype, supporting the recently updated genotype-phenotype assessment for SCA17.