Background. Overall findings of our first direct interview family study of obsessive–compulsive disorder (OCD) indicated that OCD is familial. In this replication study, we carefully examined the role of informant data in ascertaining OCD in relatives.

Method. We interviewed 112 relatives of 57 OCD patients and 115 relatives of 41 not ill controls predominantly by telephone. Additional analyses included a combined sample of relatives about whom any diagnostic information was available (228 OCD and 239 controls). To examine the contribution of proband information about relatives, we considered two sets of best-estimate diagnoses. First, we ascertained best-estimate diagnoses for relatives using information from direct interviews and from all informants except the proband. Then, we re-diagnosed relatives based on all available information, including reports from the proband about their relatives.

Results. When relative diagnoses were derived without the benefit of proband informant reports, no evidence of familial OCD transmission was found. When diagnoses were made including information from the proband about the relative, evidence of familial OCD was found, but only when the diagnostic threshold was lowered to include cases with probable OCD or OCD symptoms. Other diagnoses (generalized anxiety disorder, social phobia, drug use disorder) were also higher among OCD relatives.

Conclusions. This second study provides less robust support for familial transmission of OCD. Evidence for familial transmission of OCD was found only when diagnoses were made using information from the affected proband about their relatives. Taken in context of past findings, our own inconsistent results suggest that OCD may be heterogeneous with regard to familial transmission. Also, more careful attention should be paid to the contribution of informant reports, especially from relatives affected by the same disorder.