While one person going through a divorce may feel a variety of painful emotions that linger for many months or longer, another person may sink into clinical major depression. And genetics may explain why: The person experiencing depression was at much greater risk when the triggering event occurred due to hereditary factors.
Researchers have been looking for the specific genes responsible for major depression for years, fueled by the prospect of improving understanding, early detection and treatment. Studies, such as a recent one that surveyed 22,000 subjects, have found that children are at higher risk of depression if one parent has a history of depression, and that risk is even higher if major depression affects both parents [source: Dotinga].
Genetics seem to play a role in how we react to and process negative events. A multigenerational study of family members who survived a devastating 1988 earthquake in Armenia showed that genetics was a significant factor determining whether survivors developed major depression, anxiety or post-traumatic stress disorder [source: Cassels]. The study found that genetics was responsible for more than 60 percent of the variation in depressive symptoms among survivors.
The hippocampus -- a part of the brain tasked with processing memory and emotions -- tends to be smaller on average for people with major depression [source: Nazario]. Researchers aren't sure if this area of the brain is smaller due to genetics or if it shrinks from overexposure to the stress hormone cortisol that exists in higher levels in depressed people.
German researchers believe they've identified the gene responsible for major depression: SLC6A15 [source: Cell Press]. This particular gene is responsible for coding an amino acid transporter protein. Certain genetic variants, however, present themselves in people susceptible to major depression. These individuals have less expression of that gene in the hippocampus, and mice were shown to have less expression of the gene in question when faced with unrelenting social stress.
So while there are many different situational triggers for the onset of depression, some people may be predisposed to it from the beginning of their lives. While that thought in itself could be, well, depressing, knowing of one's risk of depression has many advantages. A person with this knowledge could be more aware of symptoms in early stages of depression. One could develop a pattern of obtaining annual or semi-annual screenings for depression by a trained professional. Finally, it could offer some sense of understanding when asking the question, "Why do I feel this way?"
Keep reading for lots more information about depression and heredity.