There are a number of published twin studies for OCD. Results from the early studies should be interpreted with caution, given the limitations of those studies: most are case reports, others have small Volasertib mechanism sample sizes, still others used different criteria to diagnose individuals, and in most cases the investigator evaluating the cotwin was not blind to the diagnosis of the index twin. In the most comprehensive review to date, van Grootheest et al6 summarized all published

twin studies from 1929 through 2005 (Table I). Of note is that five of the six twin studies with Inhibitors,research,lifescience,medical adequate sample sizes32-36 (~100 twin pairs or more) attempted to estimate the heritability of obsessive-compulsive (OC) symptoms, not OCD. Only two studies29-30 were able to estimate the heritability of OCD as determined by DSM Inhibitors,research,lifescience,medical diagnostic criteria. 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 www.selleckchem.com/products/GDC-0449.html 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 Inhibitors,research,lifescience,medical sample sizes (Table I) in that the results support the hypothesis that Inhibitors,research,lifescience,medical genetic factors play a significant role in the etiology of OC behaviors as well as OCD. Table I Twin studies of OCD. In addition, these investigators also examined the relation between OCD and two commonly occurring comorbid disorders: tic disorder and anxiety disorders. Their findings support the hypothesis that there are shared etiologic factors for OCD and tics, as well Inhibitors,research,lifescience,medical as OCD and other anxiety disorders, and are consistent with the hypothesis that there may be different subtypes

of OCD that may have different underlying risk factors.37-41 This hypothesis will be discussed in more depth in the Family Studies section below. The second study, published in 2009 ,30 obtained data from 2801 young-adult Norwegian twins by means of the Composite International Diagnostic Interview (CIDI). This study examined the heritability of five anxiety disorders (Generalized Anxiety Disorder, Panic Disorder, Phobias, Obsessive-Compulsive Disorder, and PostTraumatic Stress Disorder.) Valid anxiety data were available for 1385 AV-951 twin pairs; however, there were only 57 pairs where one twin had a diagnosis of OCD. Because the prevalence of OCD was so low in this sample, the investigators included individuals who met criteria or subthreshold OCD (the number of pairs where at least one had a diagnosis of OCD or subthreshold OCD was 165). The estimate of heritability was 29%. However, these investigators reported that 55% of this heritability was due to a common factor shared by all five anxiety disorders.