© 2006 by Taylor & Francis Group, LLC. Dystonia is a class of disorders in which the role of genetics has become increasingly apparent. Dystonia is not a diagnosis, rather it is a descriptive term which identifies a class of symptoms. Dystonia is characterized by sustained muscle contractions, frequently causing twisting and repetitive movements, or abnormal postures (1). Dystonia may be seen in isolation or as the predominant symptom of disease. Isolated dystonias may be constant or task-specific, e.g., occurring only when writing or even exclusively when playing a particular musical instrument. Dystonia may also occur in association with a variety of other abnormalities of the nervous system, including neurodegenerative disorders, structural lesions of the basal ganglia, and after pharmacological blockade of dopaminergic receptors.