Expansion in Atx1 above 35–42 glutamines is associated with spinocerebellar ataxia type 1 (SCA1), an autosomal dominant neurodegenerative disorder characterized by motor coordination deficits caused by progressive loss of Purkinje cells in the cerebellar cortex and neurons in the brain stem and spinocerebellar tracts. The gene discussed is ATXN1; the disease is spinocerebellar ataxia type 1.