London - Scientists have developed a blood test to estimate how quickly someone is ageing, which they believe could predict a person's risk of developing Alzheimer's disease.
It also offers the prospect of evaluating the “youthfulness” of organs donated for transplant operations.
The test measures the vitality of certain genes, which the researchers believe is an accurate indication of a person's “biological age”. This may be younger or older than their actual chronological age.
A study has shown that the test can distinguish between healthy individuals and patients with Alzheimer's and so might also be used it to identify people in the early stages of the brain disease who have not yet developed symptoms, scientists said.
The “ageing test” could also be used on organs to assess their risk of them failing once they have been transferred from a donor into a recipient, said James Timmons, professor of precision medicine at King's College London.
“We use birth year, or chronological age, to judge everything from insurance premiums to whether you get a medical procedure or not. Most people accept that all 60-year-olds are not the same, but there has been no reliable test for underlying biological age,” said Professor Timmons.
“Our discovery provides the first robust molecular 'signature' of biological age in humans and should be able to transform the way that age is used to make medical decisions. This includes identifying those more likely to be at risk of Alzheimer's, as catching those at early risk is key to evaluating potential treatments.”
He added: “For kidney transplantation, older organs are being used more and more, and the older the donor the more likely the transplantation will fail and it would be valuable to know the biological age of the organ before using it.”
It may also be possible to screen elderly people who have a young biological age so that they could be considered for organ donation if they die of other causes, such as traffic accidents, he said.
The research, published in the online journal Genome Biology, analysed the activity levels of a panel of key genes of healthy 65-year-old subjects by measuring the levels of RNA (a close cousin of DNA) in their blood.
The scientists used this information on gene activity as a marker of biological ageing. They then studied the RNA of healthy 70-year-olds and analysed their health records over two decades, finding found that a high gene-activity score was associated with better cognitive health and kidney function across a 12-year period - both predict the risk of an early death.
An important finding from the research was that this gene activity was the same in the brain and the blood for people with Alzheimer's disease, giving scientists a way of quickly and easily diagnosing what is happening in the brain just by looking at a blood sample.
Professor Timmons said the blood test, the first of its kind, could also act as a “screen for looking at drugs in human cells - an early step in drug discovery”.
The Independent