A patient with SCA17 featuring 41 CAG repeats presents with spastic paraplegia and involuntary movement

Spinocerebellar ataxia 17 (SCA17) is among the most heterogeneous forms of autosomal dominant cerebellar ataxia; it is caused by triplet repeat expansions within the TATA box-binding protein (TBP) gene. Its features include ataxia, dementia, involuntary movement and psychiatric symptoms, with parkinsonism and dystonia being common manifestations. However, SCA17 is a complex disease with extensive phenotypic variability. Alleles with 50 or greater CAG/CAA repeats are pathologic with full penetrance, while alleles with 43 to 49 CAG/CAA repeats have a reported penetrance between 50% and 80%.
Source: Parkinsonism and Related Disorders - Category: Neurology Authors: Tags: Correspondence Source Type: research