Psychiatric disorders in the relatives of depressed probands. II. Familial loading for comorbid non-depressive disorders based upon proband age of onset.

This study examined familial loading for non-depressive disorders in first-degree relatives (FDRs) of early-(< 20 years of age) and adult-onset (> or = 20 years of age) depressed probands. Our previous work, which demonstrated that FDRs of early-onset probands have higher rates of major depression as compared to FDRs of adult-onset probands, has not yet examined risk for non-depressive disorders in FDRs. In this paper, we focus on best-estimate diagnoses of anxiety disorders, alcoholism, and antisocial personality conducted on 639 first-degree relatives. The FDRs of early-onset probands had significantly higher rates of comorbid transmission of alcoholism and depression, and antisocial personality and depression, respectively. Significant co-transmission of anxiety disorders and depression was found in the FDRs of both early- and adult-onset probands. Future genetic studies of depression, especially early-onset depression, should hence broaden their definitions of phenotypes to include comorbid disorders when searching for the etiology of this complex disorder.