Analysis of previously identified GWAS hit regions for the IOCDF-GC study 21 revealed that 12 out of the 15 strongest signals in that study showed associations with the same direction of effects (based on the same effect alleles) in both the IOCDF-GC and OCGAS analyses (sign test P=0.0176). This observation supports the hypothesis that future collaborative studies (meta- and mega-analyses) will be able to identify OCD genes at the level of genome-wide significance. Support for association with OCD was particularly found in two previously identified genetic regions (see above). The most interesting region harbors the DLGAP1 gene. In the IOCDF-GC study signals in this gene were the top signals from the case-control analysis. Although the specific SNP from the former study was not found significant in this study, there was a prominent signal for an independent nearby marker (P=2.67×10−4). This observation potentially serves as independent evidence for association of markers in this region. DLGAP1 is a member of the neuronal postsynaptic density complex and is in the same family as the DLGAP3 gene, which has been shown in a convincing
