Our results provide new insights into the genomics architecture of OCD, impacting research design for genomic discovery and the ultimate clinical impact of such studies. While there is no doubt that rare and common genetic variation contributes to risk for OCD, the balance of their contributions has remained uncertain. Results from earlier studies (5, 16) implied an unexpectedly large role for very common variation in OCD risk and no evidence for heritability related to rarer variation (MAF < .05). This would be quite distinct from what is known about other psychiatric disorders, and consistent with some form of evolutionary selection, such as balancing selection. Our results differ substantially with those of the earlier studies, specifically we observe that the contribution to risk from common SNP variation follows expectations. Hence our results do not support a role for unusual evolutionary forces playing a role in OCD risk and do support a role for rare variation in risk.
