Familial studies on obsessive-compulsive disorders (OCD) have suggested that OCD is a heterogeneous condition, with some cases being familial and others being isolated cases in their families. Nevertheless, no studies evaluated whether there are clinical differences between OCD cases with and without a familial component. The current report presents data on the prevalence of OCD in first-degree relatives of OCD probands and compares phenomenological characteristics of familial and non-familial OCD types. The family study and the family history methods were used to estimate the prevalence of OCD in first-degree relatives of 74 OCD probands. A statistical comparison between OCD probands with and without familial loading was performed using Pearson's chi(2) test, Fisher's exact test, or Student's t test when appropriate. The rate of OCD was 3.5% in directly interviewed first-degree relatives. Eleven percent of the probands had at least one family member with OCD. There were no differences between the two types of OCD (familial vs. non-familial) except for life events prior to the onset of OCD, which were more common and more severe in non-familial OCD subtypes. In conclusion, our results (1) confirm that there is a familial component in the expression of some forms of OCD and (2) indicate that familial OCD patients are not characterized by peculiar clinical features, but appear to have a lower threshold for precipitating events.
