Dystonia is a movement disorder in which a person's muscles contract uncontrollably. The contraction causes the affected body part to twist involuntarily, resulting in repetitive movements or abnormal postures. Dystonia can affect one muscle, a muscle group, or the entire body. Dystonia affects about 1% of the population, and women are more prone to it than men. When Dystonia appears in early adulthood, it typically begins in the upper body. Then there is a slow progression of symptoms. Dystonia that start in early adulthood remain focal or segmental: They affect either one part of the body or two or more adjacent body parts. Most cases of Dystonia do not have a specific cause. Dystonia seems to be related to a problem in the basal ganglia. That's the area of the brain that is responsible for initiating muscle contractions. The problem involves the way the nerve cells communicate.