Comorbid Down's syndrome, Tourette syndrome and intellectual disability: registry prevalence and developmental course.

The co-occurrence of Tourette syndrome (TS) and Down's syndrome (DS) has been previously reported in the literature. In the present study, a retrospective record review was conducted using the North Dakota TS registry in order to ascertain the number of cases of TS and DS, and to develop case descriptions. We identified five cases from North Dakota. Two of these patients were simply comorbid for TS and DS. One was additionally comorbid for bipolar disorder, another for childhood disintegrative disorder and a third had a D/G group translocation. The association between DS and TS occured in 2% of TS patients. Contrary to the situation in patients with pervasive developmental disorders, the presence of TS in DS may be a negative prognostic indicator.