Gilles de la Tourette's syndrome in monozygotic twins.

Concordance is reported of Gilles de la Tourette syndrome in a male twin pair in whom phenotyping revealed a >98·7% probability that they were monozygotic. The development and extent of the illness differed markedly in the two subjects. Our findings are compatible with the view that there is a genetic form of Gilles de la Tourette syndrome.