DNA death predictors: What do they really tell you?

Posted on 16 Dec 2011


https://i1.wp.com/www.navigenics.com/static/images/visitor/scientist-microscope.jpg… gene-sequencing companies such as 23andme, deCodeMe and Navigenics can do a quick scan of your risk of developing everything from lung cancer to multiple sclerosis. Now two new firms are offering to tell us how well we are ageing, based on an analysis of structures at the ends of our chromosomes called telomeres.

If these developments continue, a person’s lifespan could become as quantifiable as the shelf life of a carton of milk. So instead of parading around blissfully unaware of how long we have left, we could find out our own use-by dates. For some, this knowledge would be a burden, while others may be glad of the chance to plan their future. But whether you find the prospect of being able to foretell your own death terrifying or enticing, how realistic is it? Are these new tests really a game changer? After all, we have long been able to test for life-threatening factors such as high cholesterol and blood pressure. … According to Timothy Caulfield, a bioethicist and lawyer at the University of Alberta in Edmonton, Canada, who has been looking into how people react to tests like these … “People don’t seem to do much with this risk information,” he says. “They don’t freak out. And they don’t start exercising more, eating better or getting more screening.” This should not surprise us, he adds, since we have never responded much to other more traditional predictive information, such as weight, blood pressure and cholesterol levels. …

At 23andme, I was tested for a “longevity trait” identified by the company. Apparently I don’t possess it and have merely typical odds of living to age 95 or 100. … At best, the particular genes you carry will only ever explain about 25 per cent of your propensity to live a long life, says Slagboom. So can the new telomere-based tests do any better?

Like the plastic tips at the ends of shoelaces, telomeres keep your chromosomes from fraying and getting tangled up with one another. Every time chromosomes replicate during cell division the telomeres get a bit shorter. This process starts even before you are born and about a third of their length is lost in the first 20 years of life, says Calvin Harley, president and chief scientific officer of Telome Health, based in Menlo Park, California. As we age, the shortening continues – by about 9 per cent each decade, on average. It is not clear whether some people have a higher natural rate of loss but we do know that telomeres respond to lifestyle, and that smoking, heavy drinking, obesity and stress can all shorten them a little more quickly. That is bad news because short telomeres are associated with earlier death. One study by Richard Cawthon at the University of Utah, for instance, looked at their lengths in adults over 60. People whose telomeres were shorter than average for their age cohort were 3.18 times more likely to die of heart problems and 8.54 times more likely to die from infectious disease, than those who had longer than average telomeres for their age (The Lancet, vol 361, p 393).

It is easy to see why people trying to divine their own personal expiration date would be interested in knowing how long their telomeres are, and how they compare with other people of the same age. This is exactly the information offered by a Spanish company called Life Length, based in Madrid, which began selling its €500 test a year ago. Telome Health had also planned to offer a telomere test. Back in May, co-founder Elizabeth Blackburn – a Nobel laureate for her discovery of telomerase, the enzyme that stimulates telomere elongation – told New Scientist its test would be available for under $200 by the end of the year. However, Harley now says it will only be used for research purposes for the foreseeable future. …

Carol Greider at Johns Hopkins University in Baltimore, Maryland, who shared the Nobel prize with Blackburn, points out that there is no consensus yet on the best technique for measuring telomeres. In fact, her work on mice found no correlation between telomere length and lifespan (Nucleic Acids Research, vol 28, p 4474) and she argues that little is known about how telomere length affects health and longevity in humans. “There’s a very wide distribution of telomere lengths,” she says, and they can vary a lot for any given age. If you fall below the first percentile, you are clearly at risk for age-related diseases, she adds, but the science hasn’t really established much beyond that. Greider concludes that telomere testing for the general public is premature. …

via DNA death predictors: What do they really tell you? – health – 15 December 2011 – New Scientist.

Posted in: Biology, Health, Survival