The Genetics of Depression

Depression is a very common, serious, and misunderstood illness. In fact, many do not realize that it is classified as a disease: Major Depressive Disorder (MDD). It is estimated that approximately 10% of the population will experience clinical depression at some point in their lifetime, and depression can exist in many forms — making it even harder to recognize.

Like many diseases, doctors and researchers spend millions of dollars and countless hours studying its causes, symptoms, and treatments. Typically, one question remains throughout the research — is depression caused by genetics, or is it purely environmental?

What is Depression? 

Depression is a disease that negatively affects how you feel, how you think, and how you act. Depression causes feelings of sadness and can cause a loss of interest in activities once enjoyed. It can lead to a variety of problems at work and at home — both physically and emotionally. Some characteristic signs include:

  • An overall feeling of being sad, or being in an upset mood
  • Trouble sleeping, or sleeping too much
  • Loss of appetite
  • Difficulty concentrating
  • Slowed movements
  • Thoughts of suicide or death

It might seem obvious that experience and external circumstances might be a major factor in whether someone becomes depressed. But is it linked to one’s genetic background as well?

What are the Genetics Behind Depression? 

To start, the most common way researchers test the genetic influence on illness is with family, twin, and adoption studies. Comparing the increased probability for depression among these certain groups allows researchers to see the impact of genes on the likelihood of the illness manifesting. This is common in determining if heredity, or the passing of genes and traits among family, is impacting a disease.

In the case of depression, researchers have found that family history, or heredity, can in fact play a part. For example, if one identical twin has depression, the other has a 70 percent chance of also having the illness sometime in their life.

However, this isn’t always the case – which makes it tricky. People who have a first-degree relative (like a parent or sibling) with depression appear to have a two to three times greater risk of developing the condition than average. However, many people who develop depression do not have a family history of the disorder, and many people with an affected relative never develop the disorder. This means that there are causes other than simply genetics that impact the disease.

Neural Networks and Depression  

The genes thought to be associated with depression are believed to have diverse functions within the nervous system and brain. Some of these genes may control the synthesis (creation),  transport, and activity of neurotransmitters. Neurotransmitters are chemicals that relay signals throughout the nervous system. These signals allow brain cells, also known as neurons, to be able to communicate with one another.

Other genes that may influence depression are involved in the growth, maturity, and maintenance of neurons, as well as the connections that bring neurons together (known as a neuronal synapse). Additionally, some research indicates that genes involved in depression may also impact synaptic plasticity, or a brain cell’s ability to adapt and grow over time.

Environmental factors are also believed to play a significant role. Some environmental factors cause changes in an individual’s genetic makeup based on events that occur — like substance abuse and certain medication usage. Some physical ailments, such as cancer or chronic disease, are also thought to have potential links to genetics.

Unfortunately, despite determining that genetics likely impacts depression, being able to identify which specific genes or indicators might be causing the disease has proven more difficult. Gene localization, or identifying which part of a gene, or which gene, in particular, causes disease is a tedious, difficult process that requires a great deal of research.

Currently, we are studying depression at several Meridien Research locations. If you are interested in more information on a study, please visit our website here: