By Steve Connor
A genetic test has been developed that can predict whether someone is likely to live an extremely long life, but scientists have warned that society is still not ready for such predictions.
The test is based on a scan of a person's entire genome; so far it can predict whether someone is likely to live to 100 with an accuracy of 77 per cent. However, refinements to the test will improve its precision, raising the prospect that it could one day be used to predict whether someone is genetically predisposed to extreme longevity.
Commercial organisations are likely to market the test within a few years. But the scientists behind the research warn that there should be a public debate on the ethical implications behind such testing.
Researchers developed the test by analysing the genomes of 1,055 centenarians from different parts of the world and comparing slight variations in their DNA with the genetic makeup of a set of people younger than 100. The scientists found that by concentrating on just 150 individual mutations in the human genome, they could predict with 77 per cent accuracy whether someone belonged to the group of centenarians. Although the test is still at a rudimentary stage, scientists said that they could foresee it being developed commercially within a few years to identify people with an inherited predisposition to live a long life that is likely, until the final years, to be largely free of age-related disorders such as cancer and heart disease.
Thomas Perls of the Boston University School of Medicine, who led the study published in the journal Science, said the aim of the research was to understand the genetic reasons why some people live longer than others despite having similar lifestyles.
"We embarked on the study to understand the genetics of exceptional longevity," Professor Perls said. "Clearly we realise that this is a very complex genetic puzzle. Exceptional longevity is not the vacuous entity that some people make it out to be. This really opens the door to understanding the genetic and lifestyle determinants of longevity."
Professor Perls said that a predictive accuracy of 77 per cent is "fairly unprecedented" and there is nothing to stop biotechnology companies from using this information, which is now freely available in the public domain, to develop commercial tests for extreme longevity. But he warned: "I for one don't think we're ready from a social point of view, but I think that won't stop companies from trying to market this."
The scientists found that 90 per cent of the centenarians in the study possessed a definite "genetic signature" of extreme longevity, denoted by the particular combination of genetic mutations they carried. The researchers also found that 45 per cent of the oldest centenarians – those over the age of 110 – had a genetic signature with the highest proportion of longevity-associated mutations.
Professor Perls said: "These genetic signatures are a new advance towards personalised genomics and predictive medicine, where this analytic method may prove to be generally useful in prevention and screening of numerous diseases, as well as in the tailored uses of medications."
Extreme longevity is known to have a strong genetic component as it tends to run in families, though a healthy lifestyle is also important. The team concluded: "This prediction is not perfect, and although it may improve with better knowledge of the variations in the human genome, its limitations confirm that environmental factors, for example lifestyle, also contribute in important ways to the ability of humans to survive to very old ages."
Scientists have tried for decades to find the genetic basis of human longevity by investigating the genes that influence ageing in a range of lifeforms, from simple yeast cells to laboratory strains of mice.
In 2008, scientists managed to extend the life of yeast cells tenfold by altering their genetic make-up and putting them on a calorie-restricted diet, which is widely observed to increase longevity across the animal kingdom. The search of similar "ageing genes" in humans, however, has had limited success.
But following the completion of the mapping of the human genome, it is now possible for scientists to scan the entire DNA of a person to identify the many different inherited traits that may be linked with a particular condition, whether it is an age-related illness such as coronary heart disease or cancer, or extreme longevity.
Paola Sebastiani, who worked with Professor Perls on the study, said: "The methodology we developed can be applied to other complex genetic traits, including Alzheimer's disease, Parkinson's, cardiovascular disease and diabetes."