Significance of genetic factors in Gilles de la Tourette syndrome: a review.

Observations suggesting a genetic basis for Gilles de la Tourette syndrome are reviewed with particular emphasis on the finding of familial aggregation. Studies of both Tourette syndrome and simple tic have found that approximately 30% of patients have a positive family history of tic. The significance of this figure depends on a number of factors, in particular the prevalence of positive tic histories in the population. If the latter figure is 10%, which the best available evidence suggests is a reasonable estimate, approximately 30% of families in the general population would be expected to contain at least one present or former tiquer. It is argued, therefore, that the family aggregation findings in Tourette syndrome do not support the hypothesis that the condition has a significant genetic component. Methodological considerations for future research are discussed.