Defects in ataxin-1 are the cause of spinocerebellar ataxia type 1 (SCA1), also known as olivopontocerebellar atrophy I (OPCA I or OPCA1). Patients show progressive incoordination of gait and often poor coordination of hands, speech and eye movements, due to cerebellum degeneration with variable involvement of the brainstem and spinal cord. SCA1 is caused by expansion of a CAG repeat in the coding region of the ataxin-1 gene. Longer expansions result in earlier onset and more severe clinical manifestations of the disease. Ataxin-1 binds RNA in vitro and may be involved in RNA metabolism [taken from the Universal Protein Resource (UniProt) www.uniprot.org/uniprot/P54253].