It has long been known that certain diseases tend to run in families. In fact, most of our understanding of mental illness comes from family, adoption, and twin studies. Researchers have discovered a gene that can double the risk of
, another that can increase the risk of
schizophrenia, and others that may play a role in the risk of
The Genetics of Depression
People suffering from depression experience symptoms of sadness, emptiness, or hopelessness that interfere with their lives. One of the questions scientists have been trying to answer is why some people become depressed in reaction to life stresses while others do not.
One study sheds some light on this question. Researchers followed 847 New Zealanders over five 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 were more likely to become depressed than those who had the long version of the same gene.
The Genetics of Schizophrenia
The family link to schizophrenia is well-established, but paring down the risk to one specific gene has proven difficult. For example, we each inherit two copies of the COMT (catecho-O-methyltransferase) gene, one from each parent.
There are two COMT types possible: the
type (short for the amino acid valine) and the
type (short for the amino acid methionine). Research suggests that the
type may increase the susceptibility to schizophrenia by reducing dopamine activity.
The Genetics of Bipolar Disorder
Bipolar disorder is a disease that causes extreme shifts of mood from depression to mania to a mixed state. While family and twin studies have shown that bipolar disease can be inherited, they have not yet pinpointed the exact gene. Evidence suggests that this condition is affected by the presence and interaction of many genes. Researchers have also discovered that the genes that cause schizophrenia may also cause bipolar disorder.
Despite the growing number of genetic tests available, there are no genetic tests for depression, schizophrenia, or bipolar disorder. Genetic testing also causes concerns among many people, particularly in regards to privacy. Therefore, as new tests are developed, people who choose to be tested must weigh the benefits against the risks of finding out what their genes contain.
As exciting as these discoveries may be, researchers are quick to note that mental illness, like other diseases, is an equation of sorts, with genetics being only one of the variables. For example, while your genes may increase your risk for a disease, other factors also play a role. These factors 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 medical conditions.
Egan MF, Goldberg TE, Kolachana BS, et al. Effect of COMT Val108/158 Met genotype on frontal lobe function and risk for schizophrenia.
Proceedings of the National Academy of Sciences of the United States of America
Egan MF, Kojima M, Callicott JH, et al. The BDNF val66met polymorphism affects activity-dependent secretion of BDNF and human memory and hippocampal function.
Hariri AR, Drabant EM, Munoz KE, et al. A susceptibility gene for affective disorders and the response of the human amygdala.
Arch Gen Psychiatry
Merikangans KR, Risch N. Will the genomics revolution revolutionize psychiatry? Am J Psychiatry
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
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