Can Your Genes Predict When You Will Die?
New research suggests we can defy genetic destiny
- By Joseph Stromberg
- Smithsonian magazine, January 2013, Subscribe
In Greek myth, the amount of time a person spent on earth was determined at birth by the length of a thread spun and cut by the Fates. Modern genetics suggests the Greeks had the right idea—particular DNA threads called telomeres have been linked to life expectancy. But new experiments are unraveling old ideas about fate.
The DNA that makes up your genes is entwined in 46 chromosomes, each of which ends with a telomere, a stretch of DNA that protects the chromosome like the plastic tip on a shoelace. Telomeres are quite long at birth and shorten a bit every time a cell divides; ultimately, after scores of divisions, very little telomere remains and the cell becomes inactive or dies. And because elderly people generally have shorter telomeres than younger people, scientists believe that telomere length may be a marker for longevity as well as cellular health.
Now researchers are discovering that experiences can affect telomeres—intriguing new evidence for nurture’s impact on nature. In a Duke University study, researchers analyzed DNA samples from 5-year-old children, and again when they were 10. During that interval, some had been subjected to physical abuse or bullying, or had witnessed adults engage in domestic violence. “We found that children who experience multiple forms of violence had the fastest erosion of their telomeres, compared with children who experienced just one type of violence or did not experience violence at all,” says Idan Shalev, the study’s lead author.
Another study, conducted at Brigham and Women’s Hospital in Boston, hints at possible physical effects of chronic stress. Among a sample of 5,243 nurses nationwide, those who suffered from phobias had significantly shorter telomeres than those who didn’t. According to Olivia Okereke, the study’s lead author, “It was like looking at someone who is 60 years old versus someone who was 66 years old.”
“The telomeres are essential for protecting chromosome ends,” says Carol Greider, a molecular biologist at the Johns Hopkins University and a pioneer telomere researcher awarded a share of the 2009 Nobel Prize in Physiology or Medicine. “When the telomere gets to be very, very short, there are consequences,” she says, noting the increased risk of age-related ailments.
While researchers are adding to the list of things that can shorten telomeres (smoking, for instance, and infectious diseases), they’ve also zeroed in on activities that seem to slow down telomere degradation. In a German study, people in their 40s and 50s had telomeres about 40 percent shorter than people in their 20s if they were sedentary, but only 10 percent shorter if they were dedicated runners.
Scientists don’t understand exactly how negative life experiences accelerate telomere erosion—or how positive behaviors stave it off. Additionally, outside of a few age-related diseases in which telomeres have been directly implicated, they’re unable to say whether shorter telomeres cause aging or merely accompany it. But it’s clear the fates aren’t entirely in charge. According to the new science of telomeres, we can, to some extent, influence how much time we have.
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