 Normal alleles usually have 22 or 23 repeats, but can contain up to 31 repeats.Longer expansions can cause spinocerebellar ataxia type 2 (SCA2), a fatal progressive genetic disorder in which neurons degenerate in the cerebellum, inferior olive, pons, and other areas.Symptoms of SCA2 include ataxia (a loss of coordinated movements), parkinsonism, and dementia in some cases.