Project Summary Spinocerebellar ataxia type 1 (SCA1) is one of nine fatal inherited neurodegenerative diseases caused by expansion of an inframe CAG trinucleotide repeat. Each repeat tract encodes a stretch of glutamine residues in the affected protein, in the case of SCA1 the protein is ataxin-1 (ATXN1). Symptoms of SCA1 include loss of motor coordination and balance, slurred speech, swallowing difficulty, spasticity, and some cognitive impairment. A characteristic feature of SCA1 pathology is atrophy and eventual loss of Purkinje cells from the cerebellar cortex. Like many neurodegenerative disorders, SCA1 is typically a late onset disease suggesting that physiological changes due to aging contribute to the onset of the disease. There is currently no effective treatment. Identifying signaling pathways and cellular mediators of SCA1 pathogenesis in the cerebellum leading to ataxia and in the brainstem that underlie lethality are critical in the search for therapeutics and are the focus of the research outlined in this application for continued support.