Genetic Explanation of Depression
Research on the heredity of depression within families shows that some individuals are more likely than others to develop the disorder. If you have a parent or sibling with depression, you may be 1.5 to 3 times more likely to develop the condition than those who do not. This suggests there may be some kind of genetic influence.
Gershon 1990 studied 10 families, and found rates of MDD in first degree relative ranged between 7-20%, which i considerably higher than the rest of the population. Weisman 1984 also found that relatives of people diagnosed with depression before the age of 20 had 8x greater chance of being diagnosed with it. Behaviourists would suggest environmental influences playing a part. Living and being in the same environment means learning will definitely take place.
The Maudsley Twin Register found concordance rates for monozygotic twins was 46% and for dizygotic twin 20%. Both of these rates are higher than the general public, giving support to the genetics.
Diathesis - stress model suggests that certain individuals have a genetic predisposition which makes them vulnerable to developing depression, when exposed to an environmental stressor. Kendler 1995 studied twins in Virginia. He found women are predisposed to depression, meaning their twin already has been diagnosed, are far more likely to develop symptoms when faced with negative life events than women who are less at risk. Adoption studies provide the best way of disentangling genetic factors from environmental as they are brought up away from biological families.
Caron and Zhang 2005 found that the neurotransmitter serotonin is important in mood regulation and low levels of serotonin in the brain have long been associated with depression. This mutant gene has been found to be 10 times more likely to occur in depressed patients.
Although MDD has been consistently shown to run in families, it is not easy to disentangle the effect of genetics from...