The results from studies of families ascertained through adults with OCD in which all available relatives were interviewed were not as consistent as those family studies of child and/or adolescent probands summarized above. As noted above, the study by McKeon and Murray52 did not observe an increased rate of OCD among relatives of adult OCD probands. In addition, Black et al54 reported results of a study examining 120 first-degree relatives of 32 adult OCD probands and 129 relatives of 33 psychiatrically age-matched normal controls. This was the first controlled study of OCD in which all relatives were assessed using structured interviews and all interviewers were blind to the diagnostic status of the proband. DSM-III criteria were used to assign all diagnoses from the direct interview data. While family history data had been obtained from all interviewed relatives about other first-degree relatives, none of those data were included in the diagnostic process. These investigators reported an age-corrected rate of DSM-III OCD of 2.5% among relatives of probands compared with 2.3% in controls. These data suggest that OCD is not familial. However,
