Exploring genetic roots of depression
Q. Episodes of depression seem to be common over several generations in my family. Is depression genetic?
There is substantial evidence that depression is a hereditary disease. A depression gene known as 5-HTTLPR has been found. The World Health Organization reports that about 121 million people worldwide suffer from depression. WHO estimates that depression will become the first cause of disease burden worldwide by the year 2020. Disease burden is defined as years patients must live with a disability.
At least 10 percent of people in the U.S. will experience major depressive disorder at some point in their lives. Two times as many women as men experience major depression.
In 2011, Dr. Srijan Sen, a professor of psychiatry at University of Michigan, and his team of researchers reported that people with a short variation of the serotonin transporter (5-HTTLPR) gene are more likely to become depressed under stress than those with the longer variation of the gene.
Serotonin is a neurotransmitter, a chemical substance that transmits impulses across the spaces (synapses) between nerve cells (neurons). Alterations in serotonin levels in the brain can influence mood. The 5-HTTLPR gene interferes with the serotonin process in the brain. Some antidepressant medications work by affecting the action of serotonin.
The Michigan research confirmed the findings of a 2003 study in which scientists for the first time established the link between genes and environment in depression.
In 2009, however, an analysis in which scientists pooled 14 studies, found no heightened risk of depression among those with different versions of the gene. Dr. Sen’s team wanted to settle the controversy that arose after the 2009 report. The group gathered all of the 54 studies on the subject. This included data from about 41,000 volunteers. Based on this much broader analysis, the team concluded that 5-HTTLPR does confer a greater risk of depression when combined with stress.
“This is the final word,” Dr. Sen said. “This meta-analysis includes three or four times as many studies, and clearly there is an effect.”
One of Dr. Sen's findings is especially interesting to me. He said it seems that people who have 5-HTTLPR are more reactive to all events, both positive and negative. Any study of artists reveals a high incidence of depression.
Could it be that writers, musicians, painters and other artists with higher sensitivity have the shorter gene? I hope science will explore art someday and produce data on this subject.
Later in 2011, a British-led international team found a DNA region linked to depression. This finding was replicated by another team from the United States. The researchers said they believed many genes were involved in depression.
"These findings will help us track down specific genes that are altered in people with this disease," said Gerome Breen of King's College London's Institute of Psychiatry, who led one of the research groups.
Recently, a study in Florida reported that there is a happy gene that affects females, but not males. The gene that can make women happy is known as MAOA, which affects brain chemistry.