Depression is often a family affair. Scientists, for example, have identified a gene that may be linked to bipolar disorder. In addition, they have found a common genetic mutation associated with a person developing clinical depression when faced with traumatic events in his or her life.
Research also shows that when one identical twin has a mood disorder, there is about a 50 percent chance that the other twin, who shares the same genes, will develop the illness at some point in life. One study found that if one twin developed depression, the other twin also suffered from depression in 46 percent of identical twins, compared with 20 percent of fraternal twins (who share half of their genes, like any full siblings).
Studies have also found that adopted children whose biological parents had a mood disorder had a three times greater incidence of depressive illness than the biological children of the same adoptive parents. Finally, children whose parents and grandparents experienced moderate to severe depression are at much greater risk for developing psychiatric problems than those whose relatives were not affected, according to a three-generation study.
Genetics also plays a role in treatment, influencing an individual's response to a particular drug, for example. There is evidence that people may do better if prescribed the same antidepressant medication that has been effective for a depressed first-degree relative (a parent, sibling, or child).
Because researchers are not sure exactly which genes are linked to depression or bipolar disorder, specific genetic tests will not be available for years to come. But as with heart disease and cancer, it is important to know if you have a family history of depression or bipolar disorder.
Although genetic factors may make a person more susceptible to mood disorders, a trigger—such as a serious medical condition or psychological stress—is often what causes a mood disorder to emerge at a specific time.