SCA17, also known as Huntington disease-like 4, is a neurodegenerative disorder characterized by ataxia, involuntary movements, dementia and cerebellar atrophy. Affected individuals may exhibit gait and limb ataxia, pyramidal signs, dysarthria, apraxia, dystonia, bradykinesia, myoclonus and ocular movement anomalies. Psychiatric manifestations of the condition include paranoia, hallucinations, aggression, disorientation and depression. Brain imaging studies of patients reveal cerebellar and diffuse cerebral atrophy as well as neuronal loss and gliosis in the striatum, medial thalamic nuclei and inferior olives. SCA17 is a rare type of spinocerebellar ataxia that has affected less than 100 families worldwide. The condition has a median onset at around 23 years of age. However, SCA17 is a highly variable disorder and the severity, presentation and progression can differ even between family members. The prognosis is currently poor, with many patients succumbing to the condition by the sixth decade of life. 

Mutations in the TBP gene have been associated with Spinocerebellar Ataxia 17 (SCA17), which follows an autosomal dominant pattern of inheritance. SCA17 is caused by the heterozygous expansion of the CAG/CAA trinucleotide repeat in the TBP gene increasing it from 25-42 repeats in the wild-type to 43-66 repeats in the mutant protein. The resulting protein which is abnormally long, accumulates in neurons, leading to their dysfunction and eventual death. Recent studies have also found homozygous and compound heterozygous mutations in the TBP gene of SCA17 affected individuals.