The study included 236 probands seeking treatment at university-based OCD clinics in Paris and in Germany (Table 1). Patients had to meet DSM-IV criteria for full OCD [24], had to have OCD as their main disorder, and had to be of European descent to be included in the study. Patients with clear dysmorphic features or severe mental retardation were excluded from the study. However, no neuropsychological tests were performed to determine the intellectual quotient of patients enrolled in the study. Lifetime psychiatric evaluation was carried out during a direct interview by trained psychiatrists using either the French or German version of the Diagnostic Interview for Genetic Studies (DIGS) [25] for patients over 17 years of age, or the Kiddie Schedule for Affective Disorders and Schizophrenia - Epidemiologic version (K-SADS-E) [26] for probands under 17 years of age. Among the French probands, 31% (22/71) had a history of chronic tic disorders (including chronic motor or vocal tics and Tourette syndrome), 23% (16/71) had a family history of OCD and 11% (8/71) had a family history of chronic tic disorders. No equivalent
