Depressive illnesses may run in families, and people may inherit a vulnerability or tendency toward developing depression, but despite decades of scientific investigation, researchers still do not have absolute proof that people are born with a genetic predisposition to depression. Some people believe genes are the major cause of depression and others believe events occurring in a person's life or environment causes depression. Many researchers, mental health practitioners and scientists agree a combination of genetics and the environment in which a person lives are what create depression in an individual.
Heredity And Depression
Research focusing on inherited illnesses in families shows that some people have a greater chance of developing certain conditions than others. People with a parent or sibling diagnosed with major depression may be two to three times more likely to develop the condition than those who do not have a family member with depression, according to The Medical Disability Advisor. This strongly suggests that depression may be an inherited illness.
Twins And Clinical Depression
Scientists often use identical twins as research subjects because both individuals have identical genetic codes. Results of identical twin studies examining the influence of genetics on clinical depression suggest if one identical twin suffers from clinical depression, the other will also develop this condition around 76 percent of the time, and separately raised twins will both develop clinical depression about 67 percent of the time, according to the 2007 MentalHelp.net article titled "Biology of Depression: Genetics and Imaging" by Mental Help Net contributors Rashmi Nemade, Ph.D. and Natalie Staats Reiss, Ph.D., and website director, Mark Dombeck, Ph.D. Because both twins did not develop depression closer to 100 percent of the time, researchers surmised that genetics plays a part but is not wholly responsible for determining who will develop depression. Whether someone will become clinically depressed is also influenced by environmental factors such as family history, experiences in childhood and adulthood, trauma, substance exposure and illness.
Depression Gene
In 2003, researchers believed they had found a single gene -- called the serotonin gene -- they concluded was helpful in determining whether or not someone would develop depression as a result of a difficult life event. Since then, researchers have attempted to replicate this exciting finding, with some scientists finding similar results and others not being able to replicate what was thought to be a genetic breakthrough. Neil Risch, Ph.D., director of the Institute for Human Genetics at UCSF and Kathleen Merikangas, Ph.D., of the Genetic Epidemiology Research Branch of the National Institute of Mental Health, reanalyzed data from 14 studies and found "no evidence of an association between the serotonin gene and the risk of depression." In an article published in 2009 in the "Journal of the American Medical Association," they presented their conclusion that the original studied has not been replicated and that widespread acceptance of the serotonin gene discovery was premature.
Genetic Connection: Bipolar And Unipolar Depression
About 20 percent of people suffer from mood disorders and these conditions are considered a serious cause of disability throughout the world. Bipolar disorder and unipolar depression are known to occur in the same families and scientists have long suspected the two mental illnesses may be connected genetically. A scientific study led by Francis McMahon, MD, of the National Institute of Mental Health Mood and Anxiety Disorders Program, found that the same genes may be involved in depression and bipolar illness, and that increased risks for these disorders may evolve from variations in specific genes' on/off switches. People who carry the risk variants of these genes may differ in a dimension of brain development that could increase the risk for mood disorders later in life, according to McMahon who, along with an international team of researchers, analyzed data from five genome-wide association studies representing more than 13,600 people. Their results support the view that there are not common genes with large effects that lead to increased risk for mood disorders, because if there were, a study with such a large sample size would probably have located them. The researchers believe that mood disorders involve many genes with small effects, and that different genes in different families further complicate the research.
References
- Rhode Island Department of Labor and Training: The Medical Disability Advisor: Workplace Guidelines for Disability Duration
- University of California, San Francisco: Depression Gene Risk Doubted
- MentalHelp.net: Biology of Depression - Genetics and Imaging
- National Institute of Mental Health: Same Genes Suspected in Both Depression and Bipolar Illness
