Inherited movement disorders.

A high proportion of neurological diseases characterized by movement disorders are caused by single genes; in others, such as Parkinson's disease, there appears to be a genetic component. Gene mapping studies have made substantial progress in unravelling the aetiology of dystonias and Huntington's disease, and are underway in other disorders such as essential tremor and Gilles de la Tourette syndrome. These advances are already applicable to clinical practice, particularly in Huntington's disease where identification of the disease mutation has led to the possibility of improved diagnosis and more widespread availability of predictive testing for asymptomatic family members.