Influence of Genetics on Depression

If a parent has been diagnosed with depression, what are the risks of the children inheriting it?

Many different studies have been conducted to examine the influence of genetics on the development of depression. First-degree relatives of persons with major depression are two to three times more likely to have major depression than are the first-degree relatives of non-depressed persons. In adoption studies, the biological children of affected (depressed) parents remain at an increased risk for a mood disorder even when adopted by non-affected (non-depressed) parents. Identical twins (who share 100% of genetic material) have concordance rates for depression of approximately 50%, and non-identical twins have concordance rates of 10% to 25%. In a strictly genetic illness, identical twins would both be affected because they share 100% of the genes. Twin studies have shown that a twin of a depressed person has only a 50% likelihood of also having depression. This number, however, is significantly greater than the rate in non-identical twins, thereby demonstrating that there is at least some genetic contribution to development of this disorder. The fact that there is not 100% concordance between identical twins demonstrates that environmental influences also have a role in precipitating a depressive episode.

Genetic and environment factors
Life circumstances are often expected to precipitate a depressive episode in affected individuals. Trauma, financial distress, death of a loved one, and relationship problems are some types of stressors that may be associated with development of depression. No matter how extreme, however, no specific environmental situation will cause a depressive episode in all persons. Therefore, environmental conditions alone are not usually sufficient to explain a depression. The specific event more typically will precipitate a depression in one who is vulnerable to its development at that time.

Family history of depression
Putting together genetic and environmental factors as contributors to the onset of depression means that with a family history of depression, an individual has a higher relative risk than the general population for developing depression. In fact, the greater number of mood disorders that are present in a person’s family, the higher the risk becomes for development of depression. Stressful life events, specific environmental circumstances, or certain psychological processes may serve as a trigger of a depressive episode in someone with a genetic predisposition for the disorder.