Hereditary ataxia.

The hereditary ataxias, also referred to as the spinocerebellar degenerations, comprise a series of clinical manifestations that include ataxia and dysmetria, resulting from the predominant involvement of the cerebellum and its afferent and efferent pathways. These disorders are system degenerations; many of them are specific entities clearly inherited as autosomal dominant or autosomal recessive traits. Although the clinical manifestations and neuropathologic findings of cerebellar disease dominate the spinocerebellar degenerations, there may also be characteristic changes in the basal ganglia, optic atrophy, retinitis pigmentosa, or peripheral nerve disease. There are many gradations from pure cerebellar manifestations to mixed cerebellar and brain-stem disorders, cerebellar and basal ganglia syndromes, and spinal syndromes or peripheral nerve disease. The clinical picture may be consistent in one family, but sometimes there is a characteristic syndrome in the majority of family members and an entirely different disorder in one or several members.