How Genetics Can Factor Into Depression

The causes of depression are confounding to researchers, the doctors and mental health professionals who treat it, and perhaps most of all, the millions of people in the world who have it.

The relationship between genetics and other factors that are known to contribute to depression is complex. While the topic can be challenging to understand in theory, most people with depression just want to know what it means for them individually.

If you were told that you have a “depression gene,” you might worry that you will become depressed. However, having a genetic predisposition to a condition does not mean that you will get it.  

If you are genetically predisposed to depression, it simply means that you may be more susceptible to it than someone who doesn’t have the same genetic makeup. 

As far as researchers know, it's the interplay of genes and other factors (such as environment and trauma) that determines whether someone develops depression.

Research has demonstrated that genes play a role in someone’s risk for many health conditions, including depression. Research has indicated that someone with a first-degree relative diagnosed with depression (a parent, sibling, or child) may be more likely to be diagnosed with depression in their lifetime compared to the general population.

However, it’s important to note that while studies have suggested a clear link within families, these findings don’t account for the many people who develop depression without a family history.  

Twin studies completed in the last few decades have suggested there is a heritable component to depression. Several of the studies also indicated that women may be more susceptible to the genetic influences associated with depression than men. 

Genetic Variants

These studies make it sound simple, but heredity is a complex interplay of many factors, not just individual genes. When studying depression or other health conditions, researchers often look for changes in genes called variants. These changes are classified according to the effect (if any) they have on the gene.

Eye color is an example of how variants affect genes. Changes in certain genes that affect melanin production, as well as several other genes, determine what color your eyes are. You inherit a combination of genes, each with their own unique variants, from your parents.

Families can often predict what color a child's eyes will be by looking to parents and other close relatives, but variants can behave unexpectedly. For example, parents with blue eyes may have a child with brown eyes.

Genetics and heritability is a complex process even for a seemingly simple trait like eye color. For conditions like depression, researchers know even less and suspect the process is much more involved.

Variants and Depression

In general terms, benign genetic variants are less likely to alter a gene in a way that would contribute to a person’s chance of developing a condition associated with that gene than pathogenic variants.  

If a gene associated with a specific condition is altered, it may be more (or less) likely to contribute to the development of that condition. Essentially, that means having a genetic variant can make it more likely—but not definite—that you will develop a condition associated with that variant. 

In some cases, researchers identify a genetic variant but don’t know what (if any) effect it has. These variants are referred to as having "unknown significance."

Several large genome-wide studies have proposed potential genetic connections to major depressive disorder. In 2017, researchers identified two new genetic variants associated with depression. 

A 2018 study published in the journal Nature Genetics identified several genetic variants that appeared to be associated with symptoms of depression and, in some cases, physical differences in the brain.  

While the research has provided valuable insight into the potential heritability of mental illness, no studies have definitively identified a single gene as the cause of depression. Scientists believe it's more likely that all the different genes and genetic variants each make a small contribution to a person's overall risk.

Research has indicated that genes may be passed down in different ways (modes of inheritance); another factor that could affect someone's genetic predisposition to depression.

Depression can be treated with medication, psychotherapy, and other interventions, like cognitive-behavioral therapy. Some people use a combination of treatments.

Your genes may influence how well a specific treatment works for you. For example, research has indicated that certain genes might affect how well your body absorbs, uses, and excretes drugs, including antidepressant medications.

Several genes are known to influence drug metabolism, but the results from these studies are primarily of interest to doctors and researchers. While some consumer genomic test kits provide information about topics like drug metabolism, genomic testing is not the same as genetic testing.

Furthermore, doctors and scientists don't know how useful this information is for consumers. Talk to your doctor before using your genomic health information to make decisions about your health care, including your depression treatment.

Genetics aside, if you've been diagnosed with depression and are trying to decide on a treatment, keep in mind that the process can take time. You may need to try more than one type of therapy before finding the right fit. You might even need to adjust or change your treatment plan over time.  

Before starting a medication for depression, tell your health care provider about any medications, vitamins, or herbal remedies you already take. These products can interact with antidepressants and affect how well they work.  

As you try different approaches, stay in touch with your doctor and your mental health care team. Be sure to let them know if you experience any side effects.  

People with depression might be concerned they will pass on the condition to their children. While there could be a heritable component to depression, genetics is not the only determinant. Other factors contribute to risk, while some can be protective.  

A child who has a parent with depression may have a genetic predisposition but will not necessarily become depressed. Other factors, including environmental factors or “triggers,” are also involved.  

On the other hand, a child who does not have a family member with depression and is not genetically predisposed to the condition may become depressed if they are exposed to a triggering event — such as experiencing a trauma. 

Genetics is not the only potential cause of depression. Other factors are known to contribute to the development of all forms of depression and other mental health conditions.  

Understanding the possible causes can help you better understand depression, but remember that depression can also develop in the absence of a clear cause. 

• Brain chemistry. People with depression sometimes have lower levels of neurotransmitters (brain chemicals that affect mood and well-being). The neurotransmitters they have might be inefficient or function poorly.  
• Changes in brain structure. The brains of people with depression may be physically and structurally different from the brains of people who are not depressed.  
• Hormones. Conditions like pregnancy, thyroid disorders, and menopause can affect hormone levels. Low or high levels of hormones may trigger symptoms of depression, particularly in someone who is genetically susceptible.  
• Extreme stress. Situational depression, or adjustment disorder with depressed mood, may develop in someone who is in a highly stressful situation or experiences trauma.  

Having a genetic predisposition to depression can exacerbate these factors and may influence when someone becomes depressed as well as how long symptoms last. However, it’s important to remember that depression can develop in anyone—even someone who isn’t genetically predisposed and doesn’t have obvious risk factors.  

Knowing the signs of depression and being able to recognize them in yourself and others is crucial to ensuring the condition doesn’t go untreated.