Genetic predisposition explains the etiology of depression
Genetic researchers argue that there is an increased chance of developing depression based on one’s genetic makeup. This genetic predisposition results from specific genetic variations that are inherited from parents. Many twin, family, and adoption studies support this view.
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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. 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. 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. 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. Overall, genetic predisposition can explain the etiology of depression. Empirical evidence shows that depression is a heritable mental disease.
The field of psychiatric genetics has failed to find common gene variants of large effect in the development of depression. Many of the family, twin, and adoption studies supporting this argument have too small patient cohorts. No findings have been consistently replicated as well. Additionally, the effects of genetic variants identified such as 5-HTT, are very weak, with odds ratios of 1.0 to 1.2. The impact of lifestyle and environmental factors seem to be larger than genetic predisposition. Risch et al. (2009) found in their meta-analysis that there is no correlation between 5-HTT variation and depression. Therefore, the reliability of Caspi et al. (2003) is very low. Establishing such a concrete relationship between genes and depression as in the argument is very problematic. It may lead to genetic determinism –the attribution of the formation of traits to genes where genes are ascribed more causal power than what scientific consensus suggests. Researchers should emphasize that the relationship is only correlational and not causal.
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