Torsion Dystonia is a progressive disorder of involuntary muscle contractions that causes repetitive movements and unnatural twisting of the affected body part(s). Over time, the frequency and duration of the contractures increases, leading to progressive disability. Early development is usually normal, with symptoms often beginning in mid to late childhood. It is variable in its presentation, although the vast majority of cases begin in an arm or a leg. There is no cure for Torsion Dystonia, but there are treatments available that may alleviate some of the symptoms.

Torsion Dystonia is inherited as an autosomal dominant condition. With autosomal dominant inheritance, only one copy of the gene mutation is needed to cause the disease. The gene mutation can be inherited from either the mother or the father, or can occur as a new gene mutation in the affected person. New mutations are rare in Torsion Dystonia. The prevalence of the Torsion Dystonia gene mutation in the Ashkenazi Jewish population is between 1/1000 and 1/3000. However, only approximately 30% of individuals with the gene mutation ever develop the disease. This is called reduced penetrance. Therefore, the incidence of Torsion Dystonia in the Ashkenazi Jewish population is between 1/3000 and 1/9000.

The gene for Torsion Dystonia is located on chromosome 9. Greater than 99% of affected individuals have a deletion of a 3-base-pair GAG sequence in the Torsion Dystonia gene. Genetic testing for Torsion Dystonia can be offered to adult at-risk family members of affected individuals for the purpose of reproductive planning. However, if prenatal diagnosis identifies a gene deletion in the fetus, it does not predict whether or not the fetus will be affected, age of onset or the severity of symptoms. Genetic counseling is strongly recommended for anyone with a family history of Torsion Dystonia.