Obsessive-compulsive disorder in schizophrenia: epidemiologic and biologic overlap.

To examine the co-existence of obsessive-compulsive disorder (OCD) with schizophrenia in terms of epidemiology and overlapping biologic substrates.Review of the relevant literature.There appears to be a significant prevalence of OCD in schizophrenia--higher than what would be expected on the basis of calculated comorbidity figures. There is significant overlap in the proposed functional circuits of OCD and schizophrenia, which may lead to co-expression of symptoms. Although there is overlap in neurotransmitter dysfunction, the interactions are complex, especially in regard to the serotonin and dopamine systems.The expression of OCD in schizophrenia is complex but very intriguing. Theoretical hypotheses of the pathology of the 2 disorders now need to be tested in larger controlled trials.