What role does genetics play in depression?

Major depressive disorder (MDD) has serious consequences for patients: isolation, inability to work, sleep disorders, etc. Optimising treatments and preventing relapses are major public health issues. A better understanding of the causes and mechanisms of depression is essential to both improving treatment and helping patients in the long-term. 

What role do genetics play in depression? 

According to INSERM, a French research institute, the risk of developing depression is multiplied by 2 or even 4 when just one of the two parents has experienced a depressive episode. Similarly, the identical twin of a person affected by depression is more likely to have depression than a fraternal twin.  

It is therefore likely that genetic inheritance could increase the risk of being affected by depression.  

In 2000, research from the Department of Psychiatry at Columbia University showed that depression in young children and adolescents was more common when their parents had experienced depression themselves. 

Then, in 2001, a study published in The American Journal of Psychiatry examined how depression is transmitted. The results showed that major depression in parents leads to a high risk of social phobias, major behavioural and social problems, but also a risk of developing depression in their children. 

More recently, in 2016, an American study published in the journal Nature Genetics confirmed the influence of genes on the risk of developing depression. This large study looked at the genetic variants associated with major depression. The study population was 97% Caucasian, and their genome was analysed to identify possible genes involved in depression.

The scientists found 17 independent genetic variations in 15 regions of the genome. Most of these variations are located in genes expressed in the central nervous system and involved in brain development.   

One of the genes associated with depression is already known to be involved in epilepsy and intellectual disability. Thus, these results indicate that, depending on genetic variability, the same gene can cause different diseases.  

Another gene was found to be related to social isolation in a mouse model of depression.  

The role of other genes has yet to be identified. 

Could these discoveries lead to new therapeutic avenues? 

The discovery of genes' influence on the risk of developing depression could make it possible to change treatments for this pathology. 

Indeed, the majority of treatments for depression target the consequences of the illness, forgetting the original cause. While these treatments are effective for some patients, they are sometimes less effective for patients suffering from severe depression. 

Advances in gene therapy could, in the future, allow the development of new therapeutic approaches.  

Could genetics explain everything behind depression? 

A better understanding of the causes and mechanisms of depression is opening up new avenues of research for more appropriate treatments and better prevention of relapses. 

However, genetics does not seem to be the direct cause of depression. If a person is 2 to 4 times more likely to develop depression if one of their parents is affected by depression, there is still the possibility that they will never develop it. 

It is important to remember that environmental factors also play an important role in depression. The occurrence of a serious event such as trauma, death or divorce can be a trigger for depression, especially in genetically predisposed individuals.