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Genetics and Mental Health
It has long been known that some conditions tend to run in families. In fact, much of our understanding of mental health conditions comes from family, adoption, and twin studies. For example, if an identical twin has schizophrenia, the other twin has at least a 50% chance of also developing it. With the goal of adding to this body of knowledge, researchers are studying the possible links between certain genes and serious conditions like schizophrenia, depression, and bipolar disorder.
Schizophrenia is a chronic and severe brain condition that affects behavior and thoughts. People with schizophrenia may have hallucinations and delusions, such as seeing things that aren't really there or believing that they are being followed. If left untreated, schizophrenia can impact every aspect of a person's life, including their relationships with family and friends, as well as their careers.
While the family link to schizophrenia is well-established, paring down the risk to one specific gene is an extremely difficult challenge. A gene called catecho-O-methyltransferase (COMT) has been the focus of a lot of investigation. This gene makes an enzyme that breaks down dopamine, a neurotransmitter that is believed to play a role in the development of schizophrenia. Researchers found some evidence to support the idea that people who inherit a certain combination or a mutation of the COMT gene may be more susceptible to schizophrenia. Much more research is needed because of the complexity of how genes interact with each other and how different neurotransmitters affect the brain's functioning.
People suffering from depression experience a range of symptoms, such as sadness, emptiness, or hopelessness. These symptoms can greatly affect a person's quality of life and, in severe cases, lead to suicide.
One of the questions researchers have been trying to answer is why some people become depressed in reaction to stressful life events while others do not. A gene that has been studied is the serotonin receptor gene. In one study, researchers followed 847 New Zealanders over 5 years and charted their reaction to different life stressors. Stressors included things like loss of job, death of a loved one, broken relationships, or prolonged illness. What they found was that participants with a short version of a particular gene (the serotonin transporter gene) were more likely to become depressed than those who had the long version of the same gene. A more recent review, though, that included 14 studies did not find an association between this short serotonin transporter gene and an increased risk of depression. As with schizophrenia, many different genes may predispose someone to depression, so the odds of finding one gene that is responsible for this condition are very low.
Bipolar disorder is marked by episodes of mania and depression. During the manic phases, the person may have a lot of energy, feel extremely "high," be involved in a lot of different activities, and act very impulsively. The person can cycle from mania to depression, experiencing a loss of energy, feelings of sadness, decreased interest in things they once enjoyed, sleep problems, difficulty concentrating, and thoughts of suicide.
As with other mental health conditions, family and twin studies have shown that bipolar disorder can be inherited. An interesting study involving Swedish parents and their children found that that the genes that increase a person's risk of schizophrenia may also increase the risk of bipolar disorder. In addition, a review involving 550 cases of bipolar disorder found an association between a variation on a specific gene—called methylenetetrahydrofolate reductase (MTHFR) gene—and bipolar disorder. This gene variant may also be linked to schizophrenia and depression as well.
Can a Genetic Test Tell Me If I Will a Mental Health Condition?
The technology exists today for you to have your DNA analyzed by genetic testing companies. By identifying gene variants, these tests can provide information about your risk of getting certain conditions. While it is true that researchers have made strides in uncovering the complexities of genetics and mental illness, there are currently no genetic tests that can clearly tell you whether you will get schizophrenia, depression, bipolar disorder, or any other condition.
Whether you develop a mental health condition depends on a number of variables—with genetics being just one. Other variables can be exposures to toxins, bacteria, and viruses during fetal development, as well as nutritional status, stress, emotional trauma, childhood development, environment, and a history of other conditions. There is currently no precise way to predict whether a person will definitely develop a mental health condition.
National Human Genome Research Institute
National Institute of Mental Health
Canadian Mental Health Association
Mental Health Canada
Bipolar disorder. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated September 22, 2015. Accessed December 3, 2015.
Bipolar disorder in adults. National Institutes of Mental Health website. Available at: http://www.nimh.nih.gov/health/publications/bipolar-disorder/complete-index.shtml. Updated 2012. Accessed December 3, 2015.
Caspi A, Sugden K, Moffitt T, et al. Influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene. Science. 2003;301(5631):386-389.
Depression. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated November 9, 2015. Accessed December 3, 2015.
Egan MF, Goldberg TE, Kolachana BS, et al. Effect of COMT Val108/158 Met genotype on frontal lobe function and risk for schizophrenia. Proc Natl Acad Sci U S A. 2001;98(12):6917-6922.
Egan MF, Kojima M, Callicott JH, et al. The BDNF val66met polymorphism affects activity-dependent secretion of BDNF and human memory and hippocampal function. Cell. 2003;112(2):257-269.
Gilbody S, Lewis S, Lightfoot T. Methylenetetrahydrofolate reductase (MTHFR) genetic polymorphisms and psychiatric disorders: A HuGE review. Am J Epidemiol. 2007;165(1):1-13.
Hariri AR, Drabant EM, Munoz KE, et al. A susceptibility gene for affective disorders and the response of the human amygdala. Arch Gen Psychiatry. 2005;62(2):146-52.
Frequently asked questions about genome scans and genetic testing? National Institutes of Mental Health website. Available at: http://www.nimh.nih.gov/health/publications/looking-at-my-genes-what-can-they-tell-me/index.shtml. Accessed December 3, 2015.
Major depression and genetics. Stanford School of Medicine, Genetics of Brain Function website. Available at: http://depressiongenetics.stanford.edu/mddandgenes.html. Accessed December 3, 2015.
Risch N, Herrell R, Lehner T, et al. Interaction between the serotonin transporter gene (5-HTTLPR), stressful life events, and risk of depression: a meta-analysis. JAMA. 2009;301(23):2462-2471.
Rotondo A, Mazzanti C, Dell’Osso L, et al. Catechol o-methyltransferase, serotonin transporter, and tryptophan hydroxylase gene polymorphisms in bipolar disorder patients with and without comorbid panic disorder. Am J Psychiatry. 2002;159(1):23-29.
Schizophrenia. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated October 23, 2015. Accessed December 3, 2015.
Shifman S, Bronstein M, Sternfeld M, et al. A highly significant association between a COMT haplotype and schizophrenia. Am J Hum Genet. 2002;71(6):1296–1302.
What is schizophrenia? National Institute of Mental Health website. Available at: http://www.nimh.nih.gov/health/publications/schizophrenia/index.shtml. Updated 2009. Accessed December 3, 2015.
Williams H, Owen M, O'Donovan M. Is COMT a susceptibility gene for schizophrenia? Schizophr Bull. 2007;33(3):635-641.
- Reviewer: Michael Woods, MD
- Review Date: 11/2015
- Update Date: 12/03/2015