A hereditary disease resembling LOCOMOTOR ATAXIA, and due to degenerative changes in nerve tracts and nerve cells of the spinal cord and the brain. It usually occurs in young people and often affects brothers and sisters. Its chief symptoms are unsteadiness of gait, with loss of the knee jerks, followed later by difficulties of speech, tremors of the hands, head and eyes, deformity of the feet, and curvature of the spine. There is often associated heart disease. The sufferer gradually gets worse, but may live, with increasing disability, for 20–30 years.