A total of 1 065 families were included in this study (comprising 1 406 patients with OCD and 2 895 individuals in total); 621 families were recruited and assessed specifically for this study at one of the five participating recruitment sites or the National Institute of Mental Health; 444 families had previously been evaluated in one of the earlier studies at Hopkins University or by one of the collaborating sites. The sample comprised of 460 complete trios (including an affected proband and both parents); 155 pedigrees with a proband and an unaffected sibling and 450 families with another structure (complex family structure). An additional 192 probands without an additional family member present in the study (singletons) were included. A breakdown of the families by site is found in Supplementary Table S1.
