There have been only two additional twin study OCD published since 2005.29-30 The first study29 included 854 6year-old twins who had been identified in a community sample and subsequently diagnosed using DSM-IV criteria with information obtained in a maternal-informant interview. This was the first study with sufficient sample size to adequately evaluate the influence of genetic factors on OCD, not just OC symptoms in the general population of twins. The Bolton et al29 findings are consistent with the majority of studies with sufficient sample sizes (Table I) in that the results support the hypothesis that genetic factors play a significant role in the etiology of OC behaviors as well as OCD.
