Depression: Biological Predisposition, Environmental Triggers
The exact cause of depression has long been debated and questioned. While it is true that depressive episodes can be triggered by events and circumstances, our biology, heredity and makeup of the brain are often at the root of major depressive disorder. Evidence is clear that depression can be passed down from family member to family member, which much like conditions such as cancer, diabetes, and heart disease, make one more prone to depressive episodes that may be triggered by environment and situational elements.
Detailed studies involving first-level family members and both identical and fraternal twins have shown a familial connection regardless of environmental factors. Also, studies of brain fluids have shown differences in the levels of various chemicals, proteins, and peptides between samples from depressed patients and non-depressed control samples. In addition, differences in Amygdala activity between depressed and non-depressed brain scans are evidence of a biological root to depression.
Studies have shown that depression has a familial connection. In two relevant studies, depression in more first-degree (direct descendants) of probands (persons with a diagnosed disorder who are the first to be studied-Merriam Webster Dictionary) with major depression showed signs of depression themselves. In another five studies done, a clear connection of familial aggregation was shown, though in the Gershon study, probands were not matched to comparison subjects by age, gender, etc. In the study by Weissman and the study by Khoury, the control subjects (who did not show signs of depression) showed significantly less aggregation of depression to their first-degree relatives. For example, in the 1993 Weissman study, probands’ first-degree relatives showed a morbidity risk of 21.0, whereas the comparison subjects showed a 5.5 morbidity risk (morbidity risk is defined as the...