Obsessive-compulsive disorder (OCD) is a serious and often long-lasting psychiatric disorder characterized by intrusive and unwanted thoughts, images, or urges (obsessions) that are typically linked to ritualized behaviors (compulsions) (1–4). OCD affects 1–3% of the population and multiple studies provide reliable evidence for a significant genetic contribution to risk (1, 3–6), as well as a role for environmental factors impacting risk (7, 8). The heritability of OCD, historically estimated by analysis of twin and family studies and within the context of the ACE model (additive genetic, also known as narrow-sense heritability, A; shared environment, C; and nonshared environment, E), is reported to be 35–50% (1, 4, 8–14).
