inability to coordinate voluntary muscular movements. In common usage, the term describes an unsteady gait.

Most hereditary ataxias of neurological origin are caused by degeneration of the spinal cord and cerebellum; other parts of the nervous system are also frequently involved. The most common of these is Friedreich ataxia, named after the German neurologist Nicholaus Friedreich. During the first three to five years of life, only a few physical deformities (e.g., hammertoe) may be present. During adolescence, the gait becomes progressively unsteady—frequently interpreted as clumsiness. The unsteadiness further progresses to a broad-based, lurching gait; sudden turns are extremely difficult without falling. Tremors develop in the upper extremities and in the head. Speech is slow, slurred, and monotonous. Skeletal deformities and muscle weakness are common.

Although the course of the disease is slow, it is progressive. Spontaneous remissions occur rarely, and there is usually almost complete incapacity by age 20. There is no specific therapy, and death is usually the result of another complicating disease or heart failure.