Reconciling the roles of genetics and the environment in risk for major depression - The research issue
Genetic and environmental models make very different assumptions about the causes of depression. Kendler et al. (1995) conducted a study in an effort to determine the extent to which genetic and environmental factors contribute to depression. In their study, Kendler and his colleagues examined two important questions: (1) do genetic factors and stressful life events make unique contributions to risk for depression in women? and (2) do genetic factors and stressful life events interact to create risk for depression? In particular, the researchers wondered whether the association between stressful life events and risk for depression would be greater among people at high genetic risk compared to people at low genetic risk.
Design and procedure
To examine these questions, Kender and colleagues studied four groups of women: (1) women with a depressed monozygotic (MZ) twin, (2) women with a depressed dizygotic (DZ) twin, (3) women with a non-depressed MZ twin, and (4) women with a non-depressed DZ twin. Women with a depressed MZ twin are at the highest genetic risk for depression, and women with a non-depressed MZ twin are at the lowest genetic risk for depression. For each woman, they assessed whether the person in question had experienced a depressive episode in any given month over the course of approximately one year, and they recorded whether any severe life events occurred during each month over this one year time period.
Results and implications
Both stressful life events and genetic factors made unique contributions to depression. Regardless of genetic risk, stressful life events were associated with depression, and regardless of life stress, genetic risk was associated with depression. However, the impact of stressful life events on risk for depression was greater among women at high genetic risk than it was for women at low genetic risk Interestingly, the stressful life events that were found to be most strongly associated with depression were mainly interpersonal in nature (death of a close relative, serious marital problems, divorce/break-up, and assault), highlighting the importance of relationship factors in risk for depression.The findings suggest that both genetic risk and stressful life events are important factors in understanding women’s risk for depression. Moreover, consistent with a diathesis-stress model, women at high genetic risk who experience a stressful life event in the interpersonal domain of their lives are at greatest risk of all. Therefore, to understand risk for depression among women best, we must consider both genetic factors and environmental factors.
Genetic and environmental models make very different assumptions about the causes of depression. Kendler et al. (1995) conducted a study in an effort to determine the extent to which genetic and environmental factors contribute to depression. In their study, Kendler and his colleagues examined two important questions: (1) do genetic factors and stressful life events make unique contributions to risk for depression in women? and (2) do genetic factors and stressful life events interact to create risk for depression? In particular, the researchers wondered whether the association between stressful life events and risk for depression would be greater among people at high genetic risk compared to people at low genetic risk.
Design and procedure
To examine these questions, Kender and colleagues studied four groups of women: (1) women with a depressed monozygotic (MZ) twin, (2) women with a depressed dizygotic (DZ) twin, (3) women with a non-depressed MZ twin, and (4) women with a non-depressed DZ twin. Women with a depressed MZ twin are at the highest genetic risk for depression, and women with a non-depressed MZ twin are at the lowest genetic risk for depression. For each woman, they assessed whether the person in question had experienced a depressive episode in any given month over the course of approximately one year, and they recorded whether any severe life events occurred during each month over this one year time period.
Results and implications
Both stressful life events and genetic factors made unique contributions to depression. Regardless of genetic risk, stressful life events were associated with depression, and regardless of life stress, genetic risk was associated with depression. However, the impact of stressful life events on risk for depression was greater among women at high genetic risk than it was for women at low genetic risk Interestingly, the stressful life events that were found to be most strongly associated with depression were mainly interpersonal in nature (death of a close relative, serious marital problems, divorce/break-up, and assault), highlighting the importance of relationship factors in risk for depression.The findings suggest that both genetic risk and stressful life events are important factors in understanding women’s risk for depression. Moreover, consistent with a diathesis-stress model, women at high genetic risk who experience a stressful life event in the interpersonal domain of their lives are at greatest risk of all. Therefore, to understand risk for depression among women best, we must consider both genetic factors and environmental factors.
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