We all experience stressful events in life. Yet some of us seem to bounce back from life’s adversities faster and better than others. What makes some emotionally resilient and others prone to depression? According to a group of psychologists and geneticists, the answer may be written in our genes.

Depression , as defined by the researchers conducting the study, is a period of at least two weeks in the past year in which a person falls into a permanently sad, depressed mood. People who suffer from depression often lose interest in activities they previously enjoyed and seem to derive little to no pleasure from life. And, their ability to function in both their work and home environments is significantly impaired.

Like other chronic conditions, researchers have long suspected that an increased risk for depression under stressful circumstances was, at least in part, due to genetics. Because they were aware of a genetic variation in the serotonin transporter (5-HTT) gene (short versus long), the researchers selected this gene as a good candidate for the genetic link for depression. This is because serotonin, a chemical messenger in the brain, is known to have an effect on depression and is the target of the serotonin reuptake inhibitors that are often used in its treatment.

The researchers assumed that in a group of people who underwent the same number of stressful life events, those with two copies of the least resistant (shorter) version of the serotonin transporter gene would be more likely to become depressed than those with two copies of the longer (more protective) version of the gene. The results of this study were published in the July 18, 2003 issue of the journal Science. The researchers found that variations in the length of the serotonin transporter (5-HTT) gene helped determine the potential depressive effect of a stressful life event.

About the study

The researchers tracked the number of stressful events that occurred between the 21st and 26th birthdays of 847 people. Among these 847 participants, 17% had two short copies of the serotonin transporter gene, 31% had two long copies of the gene, and 51% had one short and one long copy of the gene.

Using a life calendar, the participants recorded all the stressful life events that occurred between their 21st and 26th birthdays. The 14 categories of events they recorded included: employment, financial, housing, health, and relationship stressors. In total, 30% of the participants experienced no stressful life events, 25% experienced one event, 20% experienced two events, 11% experienced three events, and 15% experienced four or more stressful life events.

The participants also recorded any major depressive episodes or suicide attempts within the year preceding the study.

The findings

The researchers found that the relationship between the serotonin transporter (5-HTT) gene and depression following stressful life events was significantly higher in participants who had at least one short version of the gene. Indeed, among participants who had two short (less protective) copies of the gene and underwent multiple stressful life events, 43% became depressed. Among those experiencing multiple life events with more moderate protection (one long and one short version of the gene), 33% became depressed. And only 17% of those having multiple stressful life experiences and two long (more protective) versions of the gene became depressed.

How does this affect you?

This study is part of a growing body of research that suggests that genes confer susceptibility to depression. This supports the emerging view that the majority of mental illnesses and other complex diseases cannot be explained by either genetic or environmental factors alone. Rather, they arise from an interaction between genetic and environmental factors.

While the results of this study attest to the role of the serotonin transporter (5-HTT) gene in depression and stress, evidence of a direct relation between the serotonin transporter (5-HTT) gene and depression has been inconsistent. It is quite likely that other genes yet to be studied will have the same, if not a greater, impact on emotional resiliency. Some researchers are predicting that it may one day be possible to screen individuals for a genetic susceptibility to depression so they can prepare in advance for life’s inevitable stressors. Even without such a test, the results of this study give strong support for a biological explanation for why some people bounce back and others do not.