You’ve likely heard of diseases and disorders being genetic, meaning they are passed to you through your parent’s genes. But have you ever considered that mental illnesses like depression could also be genetic?
First, it’s important to understand what it means for a disease to be genetic. In order to determine that genes play a role in causing depression, scientists looked at family medical histories and made note of illnesses that seemed to pop up frequently. By doing this they were able to estimate the illness’s “heritability,” or roughly what percentage of its cause is genetic (Levinson, M.D., 2021).
In order to find out if depression is hereditary, scientists and doctors normally begin by studying twins, since they share so much of the same genetic material. Identical twins share 100% of their genes while fraternal twins share 50% of their genes. One twin being studied will already be diagnosed with clinical depression, while scientists try to determine the other twin’s genetic chance of developing the same disorder.
Scientists at Stanford Medicine did just that and concluded that heritability for depression to be around 40-50%. This could mean that in most cases of depression, around 50% of the cause is solely genetic and the other 50% is a result of personal stressor or trauma (Levinson, M.D., 2021). In order to further prove that depression can be genetic, the same scientists looked at adopted individuals and found that if either of the biological parents had suffered from depression, the chances their child would also be affected increased.
Now you may be thinking, I don’t have a twin with depression but other people in my family do. Am I at a higher risk for developing depression? If someone has a parent or sibling with depression, that person has a two or three times greater risk of developing depression compared with the average person. With a family history of depression present, the chances of developing the disorder are around 20-30%, while if there were no family history the chance would be only around 10% (Levinson, M.D., 2021). However, there are other factors that may increase the chances of a child developing depression. A British research team found that a child who watches a depressed parent or sibling may learn to mimic that person’s behavior under certain conditions. For example, a child who sees a parent spend days in bed may not think it unusual (Faris, 2017).
Diseases like Huntington’s, cystic fibrosis, and forms of muscular dystrophy are all passed on through one specific gene. Things like depression and high blood pressure are still considered genetic but are not passed through one gene, rather a group of genes. There is no single depression gene, and depression cannot be inherited from a specific parent. All individuals inherit unique combinations of genes, some of which predispose them to depression (Levinson, M.D., 2021).
Interestingly enough, the British research team recently isolated a chromosome, 3p25-26, that was found in more than 800 families with histories of depression (Faris, 2017). Although scientists were able to isolate that chromosome, much more research needs to be done before it can actually be concluded that it is the “depression gene”, considering there is currently no single gene responsible for causing depression. Another study was conducted and found that women are at higher risk for inheriting depression, with a 42% chance, while men have only a 29% chance. (Faris, 2017).
Understanding that depression has genetic links may bring comfort to those suffering in silence, wondering where all their pain came from. Perhaps they cannot recall any traumatic event that caused their depression, or any major event. Knowing that they could just be predisposed to the disease may ease the anxiety of wondering why they feel depressed. Sometimes genetics really are a factor. If you or anyone you know is struggling with depression, never hesitate to reach out to family or friends for help. You are never alone.
References
Faris, S. (2017, July 25). Is Depression Genetic? Retrieved March 2021, from https://www.healthline.com/health/depression/genetic#genetics
Levinson, D. (n.d.). Major depression and genetics. Retrieved March 07, 2021, from https://med.stanford.edu/depressiongenetics/mddandgenes.html
