Scientists have identified four genes that could increase the likelihood of a person living to a ripe old age. They were discovered by analysing the genomes of several elderly people who managed to live past 90 years old, and it's hoped that the findings could lead to better treatment for age-related diseases - and maybe even the secret to helping all of us live longer.

Researchers have been interested in the link between genetics and ageing for decades, and this is just the latest in a growing line of studies and reports looking at why certain people live well beyond their expected lifespan. Previous studies of identical twins suggested there was some kind of genetic link - twins often live to similar ages - and these results informed the latest study, led by geneticist Stuart Kim from Stanford University.

The newly identified longevity genes are ABO, which determines blood group; CDKN2B, which regulates cellular life cycle; SH2B3, which has been shown to extend lifespan in fruit flies; and one of the HLA genes, which are involved in how the immune system recognises our own cells. These four join a variant of APOE, which had previously been linked to Alzheimer's, as the five genes thought to be most closely associated with longevity.

Kim and his colleagues looked at the genetic make-up of 800 people over 100 and around 5,000 over the age of 90, then narrowed the focus by concentrating on the presence of genes already known to influence age-related diseases. Each of the genes they found had a variant that could increase a person's chances of reaching a century, they report.

"It seems intuitively obvious that avoiding disease is part of the strategy of becoming a centenarian," Kim explained to Alice Park at Time magazine. "But there is a really, really strong dogma in the field that there was no depletion of disease genes in centenarians, and that all of their survival benefit was coming from protection from anti-ageing genes. I think they were wrong."

As Park explains, previous studies have favoured the hypothesis that anti-ageing genes are doing more for our longevity than having fewer disease-causing genes. But these studies were generally smaller than Kim's, "and might not have isolated the signal from the noise".

By focusing on genes linked to age-related disease, Kim and his team were able to identify this new set of related genes, even despite having come up short in a similar search back in December 2014. Being able to predict someone's lifespan or even influencing how long they live is still a long way off, but Kim is confident that there's more to learn.

"The amount of data is going up extremely fast and the way we look at the data is improving all the time," he told Sam Wong at New Scientist. "I'm optimistic that in our lifetime or our children's lifetime, there are going to be amazing scientific advances that could change how we think about longevity."

The findings have been published in PLOS Genetics.