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Depression is an extremely common condition. In 2010, the US Centers for Disease Control (CDC) released a report finding that nearly 1 in 10 Americans suffered depression, and 1 in 30 suffered the more severe form of the illness, major depression. About 1 in 8 American women and 1 in 12 American men suffers at least one episode of major depression during life, and people in other countries are diagnosed with depression at about the same rate, with exceptions for some European countries such as Sweden and Hungary, where depression rates are unusually high.
Recent research has uncovered a genetic connection to depression, explaining how some people are more susceptible to depression. Knowing how the disease occurs suggests ways for preventing it, sparing tens of millions of people this debilitating, socially stigmatized condition.
Depression Is In DNA
A group of medical researchers at Stanford University took note of the finding that people who suffer major depressive disorders typically also have characteristic changes in their DNA. In people who deal with this relatively severe form of depression, the ends of the strands of DNA have shortened "buffer zones" known as telomeres. Formerly though of as junk DNA, telomeres exist to make sure the cell can line up the two strands of DNA to make a functioning double helix with the A, G, C, and T nucleotides in the right sequence.
If the strands of DNA don't line up, they aren't functional. As the telomeres get shorter and shorter, the cell is less and less able to reproduce itself without damaging its DNA. When the telomeres get too short, they cell cannot reproduce itself at all. If it dies, there is a tiny hole left in the tissue, and the inflammation required to get rid of the dead cell can damage healthy cells around it. People who have major depression tend to have lots of these DNA-damaged cells.
Stress Leads to Depression, Depression Leads to DNA Damage
What is it about depression that causes DNA damage? The Stanford research team decided to find out by recruiting 97 healthy girls aged 10 to 14, half of whom who had mothers who had had major depressive episodes, half whom did not. None of the girls had been diagnosed with depression, and the scientists expected that the girls' DNA would contain healthy, youthful, long telomeres, indicating no DNA damage yet.
However, when all of the girls were given a stress-inducing experimental task, the scientists found that levels of cortisol, a stress hormone, went up in the girls whose mothers had history of major depression. Cortisol levels did not go up in the girls whose mothers had not had bouts with major depression. Both groups of girls had normal stress hormone levels before doing the experimental task, which suggests that some of the girls made more stress hormones than others. Even though these girls did not show signs of stress or depression, their telomeres were already shorter than those of the other girls.
The scientists tracked the girls to age 18. By the time the girls reached adulthood, about 60% of them who (1) had mothers who had had depression and (2) had higher cortisol production developed depression and (3) telomeres in DNA shortened before the onset of depression. Stress was changing DNA in ways that predict depression before it occurs.