A review of the evidence from family, twin and adoption studies for a genetic contribution to adult psychiatric disorders.
Obsessive compulsive disorder (OCD) often coexists with major depression (MD), with rates varying from 35 to 75%. The nature of the depressive symptomatology can be investigated by familial aggregation analysis, assuming that the disorder which occurs first is the one showing greater genetic liability and should have higher familial concentration. Therefore, the aim of our study was to assess the familial loading for OCD and mood disorders in the families of OCD patients with different chronology of onset for the mood disorder, to evaluate how the familial pattern of the diseases differs with different temporal sequences in which the two syndromes occur. A total of 172 OCD patients entered the study; 112 were pure OCD probands, 12 were unable to separate the onset of the two syndromes, 11 had prior mood disorder, and 37 of them had experienced their first depressive episodes after the onset of OCD. Information about the family history was collected by means of the Family History-Research Diagnostic Criteria (FH-RDC) and by directly interviewing at least 2 relatives per family. Morbidity risks for OCD indicate a familial concentration of the disorder in all groups, except the MD/OCD group. We found the highest rate of relatives affected by mood disorders in the families of patients with first onset of MD (28.8%), whereas in the other 3 groups MRs were much lower. These results suggest the affective nature of OCD patients who experienced first onset of MD. Thus, the chronology of onset seems to identify 2 different typologies of familial distribution.