Analysis of the 549 123 autosomal markers revealed a nominally significant result at the level of α=0.05 for 27 283 markers. Among these, 456 markers reached a P-value of less than 0.001 and 54 markers were identified with a P<0.0001. As expected due to the stringent study design, no evidence for population stratification was observed (see also Supplementary Figure S1). Figure 1 shows the ‘Manhattan’ plot of the association results across the autosomal genome and Table 1 reports the association between single SNPs and OCD with P<1×10−5. No marker tested for association met the standard of genome-wide significance. The smallest P-value for our study was observed with a marker on chromosome 9 (rs4401971) at a P-value of 4.13×10−7. This SNP is 1.28 Mb from the 5′ end of the protein tyrosine phosphatase, receptor type, D gene (PTPRD, isoform 1; according to RefSeq). The second most significantly associated SNP (rs6876547, P=1.76×10−6) is located in a region of cadherin clusters and it is of note, that a second, independent SNP (rs6452234, P=1.13×10−5, r2<0.2, distance ~650kb) is located in the same region. The
