Childhood-Onset Huntington's Disease-Like Presentation of SCA17 with Intermediate Repeats, A Case Report.

Objectives: In Spinocerebellar Ataxia type 17 (SCA17), penetrance is determined by repeat number of the CAG/CAA trinucleotide in the TATA-binding protein (TBP) gene. The intermediate range (41–48) exhibits only partial penetrance but may manifest a Huntington’s disease-like (HDL-4) syndrome with onset at age 50–60 years. We report a unique case of HDL-4 with childhood onset despite intermediate range repeats. Methods: This patient was evaluated at the University of Minnesota Movement Disorders Clinic. Standard Protocol Approvals, Registrations, and Patient Consents: Informed consent to disclose was obtained from the legal guardian of the subject of this report. Results: A 14-year-old male of Chinese descent presented with generalized dystonic and choreoathetoid movements since age 11 alongside motor delays, epilepsy, and speech, balance, and coordination dysfunction since infancy. Family history was limited given his adoptive status. Subsequent workup confirmed SCA17 with repeat numbers of 43 and 37 in the intermediate range. Discussion: This is the first case of intermediate range SCA17 of childhood-onset, emphasizing the evolving classification of intermediate vs. full penetrance while suggesting that the TBP repeat length may not be the sole determinant of disease onset and severity. It also highlights the importance of repeat expansion panels when investigating complex movement disorders.