The temporal relation between depression and comorbid psychopathology in adolescents at varied risk for depression

Depression in youth rarely occurs in “pure” forms (Angold, Costello, & Erkanli, 1999; Sorensen, Nissen, Mors, & Thomsen, 2005). Comorbidity is the rule rather than the exception. The presence of major depressive disorder (MDD) or dysthymic disorder (DD) in children and adolescents is estimated to increase the likelihood of another disorder at least twenty-fold (Angold & Costello, 1993). Comorbidity is associated with a greater likelihood of recurrence, longer episodes, suicide attempts, increased utilization of mental health services, and functional impairment (Birmaher et al., 1996; Ezpeleta, Domenech, & Angold, 2006). Diagnoses frequently comorbid with MDD in youth include anxiety disorders, conduct disorders, and substance abuse and dependence (Wagner, 2003). Depression and anxiety are among the most commonly co-occurring conditions, with estimates ranging from 16% to 50% (Angold et al., 1999; Seligman & Ollendick, 1998) and as high as 70% in clinical samples of depressed youth (Birmaher et al., 1996). A meta-analysis of studies of comorbidity in children revealed a median odds ratio of 8.2 between anxiety and depression, 6.6 between conduct disorder and depression, and 3.3 between substance use disorders and depression (Angold et al., 1999; Armstrong & Costello, 2002). Less is known about the temporal course of disorders co-occurring with depression in youth. That is, to what extent does the occurrence of one disorder increase the likelihood of others? Results of studies of the developmental sequence of depression and other forms of psychopathology have varied. In a longitudinal study of a community sample, Costello, Mustillo, Erkanli, Keeler, and Angold (2003) found that, controlling for other comorbidities, anxiety significantly predicted depression, depression significantly predicted anxiety, ADHD significantly predicted oppositional defiant disorder, and anxiety significantly predicted substance use disorders. In a follow-up of a clinical sample, Kovacs, Gatsonis, Paulauskas, and Richards (1989) reported that two thirds of children with comorbid depression and anxiety disorders experienced the anxiety disorder prior to the depression. Similarly, the Oregon Adolescent Depression Project (Rohde, Lewinsohn, & Seeley, 1991) showed that anxiety, externalizing, and substance use disorders all preceded depression. Additionally, Weissman, Fendrich, Warner, and Wickramaratne (1992) found that among offspring of depressed parents, 28.6% of those with an initial diagnosis of conduct disorder developed depression over the next two years, which is consistent with the finding by Lahey, Loeber, Burke, Rathouz, and McBurnett (2002) that CD preceded depression in clinic-referred boys. Few studies, however, have examined within the same individuals the prospective relation between prior psychopathology and subsequent depression as well as the reverse (i.e., prior depression predicting subsequent psychopathology). The purpose of the present longitudinal study was to investigate the temporal relations of depression with anxiety, externalizing, and substance use disorders (SUDS) through adolescence. Given the episodic nature of depressive disorders, examining these diagnoses prospectively within the same individuals decreased the chances of inadvertently missing disorders when they occurred and strengthened our ability to test temporal precedence. The present study explored these relations in a sample of offspring of mothers who either had histories of mood disorders (`high risk') or were lifetime-free of psychiatric disorders (`low risk'). Given the higher rates of depression, anxiety, conduct, and substance use disorders among high-risk youth compared to their low-risk counterparts (Beardslee et al., 1996; Weissman, Wickramaratne, Moreau, & Olfson, 1997; Weissman, Warner, Wickramaratne, Moreau, & Olfson, 2000), the current sample was particularly appropriate for studying comorbidity (Avenevoli & Merikangas, 2006). In addition, we explored whether the relations between depression and comorbid psychopathology varied as a function of sex. The developmental trajectories of comorbid disorders have been found to differ for initially depressed male and female adolescents (Kovacs, Obrosky, & Sherrill, 2003). In contrast, Sorensen and colleagues (2005) found no sex differences in disorders comorbid with depression symptoms. Clarifying the complex temporal link between depression and other disorders in males and females could help to inform future investigations about the processes underlying these conditions and guide the formulation of gender-specific interventions. Finally, studies have highlighted the importance of investigating subsyndromal symptoms, that is, symptoms that do not meet all the criteria for a threshold diagnosis (Georgiades, Lewinsohn, Monroe, & Seeley, 2006; Lewinsohn, Shankman, Gau, & Klein, 2004). Adolescents with subthreshold depression are at elevated risk of developing MDD, SUDs, and anxiety disorders (e.g., Lewinsohn, Solomon, Seeley, & Zeiss, 2000; Pickles et al., 2001), and subthreshold depressive disorders are associated with impaired psychosocial functioning (Rapaport & Judd, 1998). Therefore, we examined the temporal relations between depression and other psychopathology at both the threshold and subthreshold levels of the disorders.