A genetic test for how quickly a person will age over the course of a lifetime may soon be possible following a study that has for the first time definitively identified DNA variations in the population that can be linked with biological ageing.
Scientists found that people who inherit two copies of a particular DNA variant – about 7 per cent of the population – show the biological signs of being about eight years “older” than people of the same age who carry neither genetic variant.
Individuals who have inherited just one copy of the genetic variation – about a third of the population – are on average about four years “older” than their exact contemporaries, as revealed by analysing the individual’s chromosomes for a recognised sign of biological ageing.
The findings are important because they could lead to more sophisticated ways of determining the likely chances of a young person ageing significantly more quickly than the average, and therefore being more prone to age-related illnesses such as coronary heart disease and senile dementia.
The study supports the idea that ageing is based not just on straight forward chronology but on biology as well – some people are born with a genetic predisposition to age more quickly.
It could explain why some people look older for their years than their contemporaries of the same age, even though they may not engage in activities that are known to accelerate the ageing process such as smoking.
“The motivation behind this study was the evidence from coronary research showing that some people who are in their 80s have completely normal arteries but others in their 40s, with no obvious risk factors, have diseased arteries. The difference seems to be biological,” said Nilesh Samani, professor of cardiology at Leicester University.
“There is accumulating evidence that the risk of age-associated diseases including heart disease and some types of cancers are more closely related to biological rather than chronological age,” Professor Samani said.
The researchers focussed on the structure at the tips of chromosomes called a telomere which gets progressively shorter as someone grows older. The telomere plays a critical role in cell division and ageing and has been likened to the plastic caps at the end of shoelaces which keep them from fraying.
Nearly 3,000 people of varying ages took part in the study. Their telomeres were measured from blood samples and their entire genomes were analysed for DNA variations that could be linked with shorter-than-average telomeres.
“Individuals are born with telomeres of certain length and in many cells telomeres shorten as the cells divide and age. Telomere length is therefore considered a marker of biological ageing,” Professor Samani said.
“We found that those individuals carrying a particular genetic variant had shorter telomeres, that is [they] looked biologically older. Given the association of shorter telomeres with age-associated diseases, the finding raises the question of whether individuals carrying the variant are at greater risk of developing such diseases,” he said.
The genetic variant identified by the scientists is located close to a gene called TERC that is known to be involved in maintaining the length of the telomere using an enzyme called telomerase. The study, published in Nature Genetics, suggests that the DNA variants may reflect difference in the way telomerase works between people.
“What our study suggests is that some people are genetically programmed to age at a faster rate. The effect was quite considerable in those with the variant, equivalent to between three and four years of ‘biological ageing’ as measured by telomere length loss,” said Professor Tim Spector of King’s College London.
“Alternatively, genetically-susceptible people may age even faster when exposed to proven ‘bad’ environments for telomeres such as smoking, obesity or lack of exercise, and end up several years biologically older or succumbing to more age-related diseases,” Professor Spector said.