RThe gene most commonly associated with depression is the serotonin transporter gene SLC6A4 (Bleys et al., 2018). Serotonin is a neurotransmitter affecting multiple physiological processes and cognitivebrain functions, among them mood and emotions, which is why it has been linked to mood disorders such as depression. Indeed, low serotonin levels have been associated with depressed mood (Jenkins et al., 2016), and selective serotonin reuptake inhibitors (SSRIs) are the most commonly prescribed antidepressants. SSRIs block the reuptake of serotonin during cellular communication in the brain, making more serotonin available, and thus in theory helping to reduce depression.
Along these lines, the idea that the serotonin transporter gene could affect depression risk or severity intuitively made sense. Specifically, many scientists focused on the so-called 5-HTTLPR polymorphism in the promoter region of the serotonin transporter gene to research the effects of this gene on depression…
A new study recently published by Richard Border and colleagues in The American Journal of Psychiatry(Border et al., 2019) aimed to resolve the controversy about whether or not the 5-HTTLPR genotype affects depression and whether there is a gene-by-environment interaction between this genotype and stressful life events once and for all. To avoid the statistical problems of previous studies, they obtained data from several large genetic datasets available to researchers, leading to a sample size of several hundred thousand individuals. The results of the analysis were clear as well: There was no statistical evidence for a relation between the 5-HTTLPR polymorphism and depression, and there was also no evidence that traumatic life events or adverse socioeconomic conditions might show a gene-by-environment interaction with this genotype.
This, of course, does not mean that there is no relationship between serotonin and depression (there clearly is, as shown by the treatment success of SSRIs), but it lends further support to an emerging insight in psychiatry genetics: Mental illness is a highly complex process that is likely influenced by a large number of genetic and non-genetic effects. As such, it is unlikely that single genetic variations such as the 5-HTTLPR polymorphism have a huge impact on whether or not an individual develops depression or any other form of mental illness.
