At least 10 percent of people in the United States suffer from clinical depression at some point in their lives, says the Stanford School of Medicine. One way to study the genetic elements involved in depression is to study depressed individuals who have a twin to find out whether the twin also suffers from depression. Some scientists have also focused on studying whether certain genes can be linked to depression.
Depressed Family Members
There is a strong risk of developing depression if a person has a depressed family member, says the Stanford School of Medicine. An average person without a family history for depression has approximately 10 percent risk of getting depression. This risk is two to three times higher if a person has a parent or sibling that has been diagnosed with clinical depression. If a person's relative is suffering from recurrent depression, the likelihood of getting diagnosed with depression is even higher. Also, if the depression of the relative has started during childhood or as a teenager, person's risk of getting depression is approximately four to five times higher than that of an average person.
Adoption Studies
A person with depressed parents or relatives also shares their environment. Thus, the increased risk found in the studies may not only be related to the genetics but could partly be explained by an environment that is making it more likely for a person to get ill. To rule out the effects of an environment, some scientists study adopted people whose biological parent has been diagnosed with depression. Erin C. Tully, Ph.D. and colleagues studied of 692 adopted and 416 non-adopted adolescents. Their study, published in "American Journal of Psychiatry" in June 2008, showed that if an adolescent's mother had a major depression, both an adopted and non-adopted teenager was at a significantly higher risk for depression. Interestingly, paternal depression did not have a notable effect on the depression of the adolescents in the study.
Depression Gene?
Dr. A. Caspi and colleagues linked the 5-HTT gene to the risk of getting depression in a study that was published in the journal "Science" in 2003. The study stated that people who experienced a significant amount of stressful events in their lives during a period of at least five years were much more likely to develop depression if they had two copies of the short allele for the 5-HTT gene than if they had two copies of the long allele. However, some subsequent studies have had difficulties replicating these findings. For example, Kathleen Merikangas, Ph.D. and colleagues did a meta-analysis of 14,250 subjects in 14 studies published from 2003 to 2009. The study did not find any relationship between the 5-HTT gene and depression. There might be several reasons for this: most mental illnesses are considered partially genetic; thus, they are sometimes inherited and sometimes not; depression is likely to be caused by a combination of genetic risks and several environmental triggers; and numerous genes are likely to be linked to depression, as shown by ModernPsychiatry.com, and it is highly unlikely that any one gene alone could causes depression, says the Stanford School of Medicine, so genetics is likely to explain 40 to 50 percent of depression cases, but approximately half of the causes are unrelated to the genetics.
References
- Stanford School of Medicine: Major Depression and Genetics
- All About Depression: Genetic Causes of Depression
- "American Journal of Psychiatry": An Adoption Study of Parental Depression
- "Science"; Influence of Life Stress on Depression: Moderation in the 5-HTT Gene; Caspi A., et al.; July 2003
- Science Daily: Much Touted 'Depression Risk Gene' May Not Add To Risk After All
