Researchers from the University of Melbourne found a genotype that affects a person's risk of developing long-term depression. According to the study, people with a particular genetic makeup have a more intense response to both good and bad environments.

The research team led by Dr. Chad Bousman from the University of Melbourne's psychiatry department looked into the genetic variation of 35 genes in the span of one decade. Bousman and his team zeroed in on one gene - the SLC6A4. Also called "SERT," SLC6A4 is a serotonin-transporting gene. Serotonin is responsible for mood regulation and contributes to a person's overall sense of well-being.

The three types of SERT genes are: short-short, short-long and long-long. The researchers hypothesized that a person with a short-short SERT gene is more susceptible to long-term depression following an abusive childhood compared to a person with a long-long SERT gene. This theory sheds light to how a formerly abused adult can find long-term happiness despite a traumatic experience during his or her formative years.

The research team observed the life of over 300 middle-aged patients in Northern Europe, all of whom suffer depression. They determined the type of SERT gene each of the participants possess through a DNA test. The team tracked down their life events in the past five years.

Twenty-three percent of the participants possess the short-short SERT gene. Among the short-short SERT patients, those with abusive childhoods also have severe depression in middle age. Patients who did not suffer abuse in their childhood years showed less symptoms of depression. While indications of depression can change over time, the researchers wrote that a fixed genotype joined by an unalterable experience during the formative years often lead to long-term depression. The researchers theorized that depressed people in a positive environment have higher chances of recovering from their depression compared to those in a negative environment.

"You cannot change your genotype or go back and change your childhood, but you can take steps to modify your current environment," said Bousman. "Our results suggest some people have a genetic makeup that makes them more susceptible to negative environments, but if put in a supportive environment these same people are likely to thrive."

Bousman and his team noted that people with the short-short genotype respond more dramatically to their environment. It is important to note that a person's genetic makeup and environment are the two main players that can amplify the effects of traumatic experiences.