A group of rare hereditary disorders characterized by neurodegenerative changes of certain brain regions, including the cerebellum and specialized groups of nerve cells (nuclei) in the brainstem (e.g., olivary and pontine nuclei). With most forms of the disorder, initial symptoms become apparent from adolescence to mid-adulthood; however, a rare form has been identified that may be evident at birth. Depending upon the type of OPCA, symptoms may include progressively impaired coordination, postural instability, slurred speech (dysarthria), and other associated findings (i.e., cerebellar ataxia); parkinsonism; rapid, involuntary, rhythmic eye movements (nystagmus); and/or retinal degeneration. Some affected individuals may also have additional symptoms and findings, such as involuntary, rapid, jerky movements (chorea); relatively slow, writhing motions that appear to “flow” into one another (athetosis); increased muscle stiffness (rigidity) with associated twisting or distorted posturing of affected muscles (dystonia); and/or other abnormalities. Most forms of OPCA are inherited as autosomal dominant traits; however, autosomal recessive forms have also been identified.