According to Stanford psychiatry professors, Douglas F. Levinson, M.D. and Walter E. Nichols, M.D., at least 10 percent of people in the United States experience a major depressive disorder at some point in their lives. Scientists believe that genetic factors play a role in some depressive disorders, but it is unlikely that there is a specific depression gene. Parents do not pass depression directly to their offspring, but combinations of genes inherited from one's mother and father may predispose an individual to ending up with a particular illness.
Families
A U.S. Public Health Service report of the Surgeon General on the Etiology of Mood Disorders explains that depression tends to run in families and "evidence strongly suggests that vulnerability to mood disorders may be associated with several genes distributed among various chromosomes."
If a person's parent or sibling suffers from major depression, she has a 20 to 30 percent chance of developing depression compared with the average person, whose chance of developing depression is about 10 percent. If a person's parent or sibling has recurrent depression, especially early onset depression that started in childhood or adolescence, the likelihood of developing depression is four to five times greater than average.
Twins
Twin studies about genetic conditions have yielded valuable information when it comes to distinguishing environmental from genetic factors. Simple genetic theory proposes that if scientists compare rates of occurrence of a condition, such as depression, among same-sex twins, a hereditary trait that appears in one identical twin should almost always appear in the other twin, whereas the trait should appear only around 50 percent of the time in same-sex fraternal twins.
Some variation exists when it comes to results of studies comparing the presence of depression among twins, but the reported concordance for mood disorders is greater among identical than among fraternal twins. Often, the proportion is two to one, according to a Surgeon General report discussing research presented by Drs. Ming T. Tsuang and S. V. Faraone.
Adopted Children
Depressive disorders among adoptive family members do not significantly affect an adopted child's risk of depression. The disorder is, however, three times more common among adopted children whose biological relatives suffered depression, according to HealthyPlace.com.
Women
Almost twice as many women as men experience major depression and genes are more likely to contribute to the risk of depression in women than in men. The American Journal of Psychiatry reported that "heritability of depression is higher in women - approximately 42 percent -- than in men, where it is approximately 29 percent."
(reference 4
http://www.news-medical.net/news/2006/01/05/15183.aspx)
In a study by Virginia Commonwealth University researchers, professor of psychiatry Kenneth S. Kendler, M.D. and his team found that genes may influence a woman's risk for major depression and change her risk for depression in response to cyclic sex hormones. The interaction between stress, experiences and genetic factors also influences depression in women. Research suggests that genetic factors may alter women's sensitivity to life events.
References
- Stanford School of Medicine: Major Depression and Genetics
- U.S. Public Health Service: Mental Health: A Report of the Surgeon General
- HealthyPlace.com: Causes of Depression
- News-Medical.Net: Genetic Risk Factors for Depression Greater in Women
- Virginia Commonwealth University: VCU Study Suggests that Heritability of Major Depression is Higher in Women Than in Men
