Genetic Factors

Evidence: Twin Studies
Much of what we know about the genetic influence of clinical depression is based upon research that has been done with identical twins. It has been found that when one identical twin becomes depressed the other will also develop clinical depression approximately 76% of the time. When identical twins are raised apart from each other, they will both become depressed about 67% of the time. Because both twins become depressed at such a high rate, the implication is that there is a strong genetic influence.

Twin studies provide a strong argument that depression is largely biological based, however because the rate at which the twins develop depression is not 100%, then there must be other factors contributing or causing the depression, for example environment could play a role.

A Gene for Depression?
Research on the genetic causes of clinical depression has attempted to identify one or more specific genes that may lead to the development of a depressive illness. Although there have been a number of studies that appear to name a particular gene as the culprit there has been little consistency among their results. However, the outcome of some research has suggested that there may be specific genes that cause clinical depression to develop within certain families and not in others.