Gilles de la Tourette's syndrome and attention deficit disorder with hyperactivity. Evidence against a genetic relationship.

Results of a family study of Gilles de la Tourette's syndrome (TS) suggest that TS and attention deficit disorder (ADD) with hyperactivity are genetically separate disorders transmitted independently in families at risk. Although the rate of TS among the relatives of the two proband groups was virtually the same (10.3% vs 11.1%), the rate of ADD among the relatives of probands with TS and ADD with hyperactivity was approximately eight times higher than the rate of ADD among the relatives of the probands with TS only. In those families where the proband had both TS and ADD, the two traits segregated independently. Therefore, there is no evidence to suggest that the two disorders are genetically related.