Since the introduction of the term dystonia by Oppenheim in 1911 to describe altering muscle tone and postural deformities seen in patients,1 there has been considerable controversy surrounding its aetiology, classification, and genetics. Dystonia can describe a symptom, a syndrome, or a clinical sign that is part of a more severe neurological disorder. Dystonia is now defined as a syndrome of sustained involuntary muscle contractions, often causing twisting and repetitive movements or abnormal posture.2

The dystonias are a relatively common group of neurological disorders with conservative estimates of 30 000 affected people in the United Kingdom.3 Dystonia has been divided into primary, in which there is no identifiable underlying cause, or secondary to other neurological conditions, which include structural lesions of the basal ganglia, exposure to drugs and toxins, and cerebral palsy. It was from the study of secondary dystonia that it became clear that disruption of basal ganglia motor circuits produces dystonia.2 4 5Primary dystonia is distinguished by the lack of other neurological involvement and absence of distinct neuropathology. Central dopaminergic pathways have been implicated in the production of dystonic movements from the study of tardive dystonia6(secondary to D2 receptor blockade) and dopa responsive dystonia (see later).

In recent years, advances in molecular genetic techniques have led to exciting discoveries which have expanded our knowledge of the pathogenesis of dystonia and led to a revision of its classification (table).7 This classification incorporates the advances in our understanding of the genetics and aetiology of dystonia, and also the increasing number of distinguishable clinical phenotypes. To date, eight genes causing dystonia have been mapped and three of these have been cloned. The following sections review these recent discoveries.