Tardive or atypical Tourette's disorder in a population with Down syndrome?

In a population of 425 individuals with Down syndrome, we observed 5 persons (1.2%) with Tourette's disorder. Because the prevalence of Tourette's disorder in the general population has been estimated to be between 0.03% and 1.6%, it is not likely that there is an increased prevalence of Tourette's disorder in Down syndrome, or that there is an interrelationship between Down syndrome and Tourette's disorder. This lack of relationship argues against an atypical Tourette's disorder. The absence of family histories of Tourette's disorder in our patients, the relatively late onset of the disorder in most of our patients, their previous treatment with neuroleptic and psychostimulant medication, and the lack of relationship between Down syndrome and Tourette's disorder in this Down syndrome population are factors that support the diagnosis of tardive Tourette's disorder.