Tics and heredity. A study of the relatives of child tiqueurs.

The limited literature on the pedigrees of tiqueurs, including those with Gilles de la Tourette's syndrome, is reviewed. Most statistical analyses have been restricted to affected family members without specifying the unaffected ones. The present statistical analysis of a series of child tiqueurs, including 91 probands and 1293 first- and second-degree relatives, 46 of whom were tiqueurs, predicts the odds on being a tiqueur for individuals, and establishes how those odds are affected by certain explanatory variables using log-linear models. The data do not confirm a familial pattern beyond reasonable doubt, but if the suggested prevalence of tics in the population is 10% then the figure for parents is large enough to support a familial hypothesis. The pedigrees do not indicate a simple mode of genetic transmission. Further research is needed to confirm that there is a connection between childhood tics and Gilles de la Tourette's syndrome, to establish that the predisposition to tics is familial, and, if so, whether there is a complex genetic mechanism involved, or some other environmental aetiology so far undisclosed.