Adult OCD probands (325 white subjects) were recruited through an ongoing outpatient OCD program at the National Institute of Mental Health, Bethesda, Maryland. All probands were aged at least 18 years at the time of inclusion (mean age at time of interview, 38 years; standard deviation [SD], 16 years) and gave written informed consent. The diagnosis was made on the basis of the Structured Clinical Interview for DSM-IV. Exclusion criteria were active psychosis or schizophrenia, severe mental retardation that would prohibit an evaluation of OCD, and OCD symptoms that occurred exclusively in the context of major depression.
