We report results from the first genome-wide association study (GWAS) to search for common DNA sequence variation predisposing individuals to OCD. After removing low performing SNP assays and DNA samples, we analyzed 400 trios, 1,465 cases and 5,557 controls for 469,410 autosomal and 9,657 X-chromosome SNPs. The trio and case-control subsamples were analyzed individually, and then these results were combined in both case-control and trio-case-control meta-analyses. One SNP, rs6131295, located on chromosome 20p12.1-p12.2, approximately ∼90 kb from the BTBD3 gene, achieved genome-wide significance in the trio analysis (p=3.84×10-8), but not in the combined trio case-control meta-analysis, suggesting that further examination will be required using independent samples. BTBD3 is a member of a large family of transcription factors, which includes BTBD9, a gene that has been associated with Tourette Syndrome, a disorder frequently co-morbid with OCD.62 BTBD3 participates in multiple cellular functions including transcriptional regulation, cytoskeleton dynamics, ion channel assembly and gating, protein ubiquitination and degradation63 and has also been associated with primary open-angle glaucoma.64 BTBD3 is expressed in the brain, with the highest observed levels in childhood and adolescence (www.BrainSpan.org,
