There is an extensive and growing body of literature on risk and protective factors in depression. Presentation of the details of this literature is beyond the scope of this review. Interested readers are referred to a number of reviews that are available (see for example, Birmaher et al., 1996; Fleming & Offord, 1990; Gotlib & Hammen, 1992; Harrington, 1993; Kashani & McNaul, 1997;
Lewinsohn, Rhode, & Seeley, 1996). Rather, I would like to note several themes that have emerged from this body of research.
First, there appears to be a strong genetic and family aggregation component to depression, particularly early-onset depression. For example, twin and adoption studies have provided evidence that genetic factors account for up to 50% of the variance in transmission of mood disorders. Children of depressed parents are about three times more likely to have a lifetime episode of major depression. Finally, lifetime prevalence of depression in first-degree relatives of depressed children and adolescents are estimated to be 20-46% (for a review, see Birmaher et al., 1996).
Second, psychosocial factors also clearly play a role. Depressed adolescents, drawn from community and clinical samples, have lower self-esteem, higher self-criticism, increased cognitive dysfunction, negative attributions, hopelessness, a tendency to attribute outcomes to external causes, and social skills deficits compared with nonaffective psychiatric and normal controls (see, for example, Birmaher et al., 1996; Lewinsohn et al., 1996).
Research also has demonstrated that depression is a recurrent condition, with almost three-fourths of adolescents having a recurrence within 5 years of the initial episode, and with almost an equal probability of the risk of depression episodes persisting into adulthood (Birmaher et al., 1996).
Comorbidity of other psychiatric disorders is one of the hallmarks of depression, including depression in adolescence. Half or more of depressed youths have comorbid psychiatric disorders, and 20% to 50% have two or more co-morbid disorders, The most frequent comorbid diagnoses are dysthymia, anxiety disorders, disruptive disorders, and substance abuse. Except for substance abuse, major depression is more likely to occur after the onset of other psychiatric disorders (see Birmaher et al., 1996; Lewinsohn et al., 1996).
A number of studies have documented a range of psychosocial deficits among formerly depressed adolescents, which no doubt account in large part for future vulnerability for episodes of depression. One of the critical sequelae of depressive episodes among adolescents is the increased risk of suicidal behaviors (see Birmaher et al., 1996; Kashani & McNaul, 1997; Lewinsohn et al., 1996). I revisit this point in more depth below in my discussion of suicidal behaviors.
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