A genome-wide association study was recently completed by the International OCD Foundation Genetic Collaborative (IOCDF-GC) 21 with a combined study sample from 22 sites, comprising 1 465 cases and 5 557 ancestry-matched controls, as well as 400 complete trios. In case-control analyses, the lowest P-values were found for two SNPs in perfect LD (rs11081062 and rs11663827; r2=1, D′=1 in reference samples from the 1000 genomes project 22; P=2.49×10−6 and P=3.44×10−6) Both were located on chromosome 18 within the discs, large (Drosophila) homolog-associated protein 1 gene (DLGAP1), a member of the neuronal postsynaptic density complex. In the trio analysis, a SNP near the BTB (POZ) domain containing 3 gene (BTBD3; rs6131295, chromosome 20), exceeded the genome-wide significance threshold with a P-value=3.84×10−8. However, when trios were meta-analyzed together with the case-control samples, the P-value for this variant was 3.62×10−5, losing genome-wide significance. Although no SNPs were found to be associated with OCD at a genome-wide significant level in the combined trio–case–control sample, a significant enrichment of methylation QTLs (P<0.001) and frontal lobe expression quantitative trait loci (eQTLs) (P=0.001) was observed within the
