Genetic predisposition explains the etiology of depression

Genetic researchers argue that genetic predisposition can explain the development of Major Depressive Disorder (MDD). A genetic predisposition to depression means an increased likelihood of developing depression based on a person’s genetic makeup. This genetic presentation results from specific genetic variations that are often inherited from a parent. These genetic variations contribute to the development of depression but do not directly cause it. Some people with a predisposing genetic variation will never get the disease while others will, even within the same family.^[1] Therefore, many psychologists lean towards gene-environment interaction. Environmental factors determine which genes are turned on and off. Genes that mediate stress response and synaptic plasticity can impact the vulnerability risk for MDD.^[2] Many family, twin, and adoption studies point to a genetic basis for depression. For example, Caspi et al. (2003) investigated the relationship between stressful life events and depression in individuals with different alleles of the 5-HTT gene. They concluded that the 5-HTT gene influences an individual’s reaction to stressful life events. Genetic predisposition can moderate a person’s reactivity to stressful life events –an instance of gene-environment interaction. Specific alleles of 5-HTT increase the vulnerability to depression.^[3] Similarly, Kendler et al. (2006) determined the level of heritability of depression through a longitudinal twin study. The estimated heritability of major depression for the entire sample was 38%. Researchers demonstrated that genes play a role in depression. They also found a sex difference in the heritability of depression; it is higher in females than in males.^[4] Overall, genetic predisposition can explain the etiology of depression. Empirical evidence shows that depression is a heritable mental disease.