Geneticists in the US have completed the first comprehensive genetic analysis of the world's oldest living people in an effort to figure out what gives them their longevity. And so far, the source of their super-powers remains unclear.

In the past, genetic studies have revealed that longevity runs in families. An analysis completed by the US National Institute on Ageing in 2002 of 444 relatives of centenarians - people who live to 100 years old - showed that they were much more likely to live to 100 themselves than the average person. In fact, these centenarian relatives were 17 times more likely than other people to reach 100, and sisters in particular were at least eight times more likely to make it to this age.

And, says Francie Diep at Popular Science, studies done on the lifestyle choices of supercentenarians - people who live past 110 - have shown that they don't have any different smoking, drinking, eating, or exercising habits than the general population. Together with the family studies, this suggests that a person's longevity is somewhere in their genetic make-up. All we have to do is find it.

So a team of researchers from Stanford University decided to investigate by looking for a single gene variant that might be present in 17 of the oldest living people and not in regular people. If they could find this point of difference, it could be the key to what's slowing down the ageing process in these people, and help scientists to develop new drugs that reproduce the effect in others.

The participants ranged in age from from 110 to 116, and all but one of them were female. Not only were these people surprisingly healthy for their age, but they were still practicing the skills that most of us will have given up long before we're 80 - if we make it that far. None of the participants had heart disease, stroke or diabetes, which become very common in old age, and only one participant had cancer. According to Rachel Rettner at LiveScience, one reportedly worked as a GP until the age of 103, and another one drove their car until they were 107.

As it turns out, the analysis found no rare genetic mutations that could have carried these 17 supercentarians through to their remarkable ages. 

Publishing the results in the open access journal PLOS One, the team is hoping that other researchers will use their data to continue the hunt for the supercentarians' secret. Perhaps rather than looking for a single gene variant, they should be looking for combinations of genes. Or maybe it's a case of tiny genetic differences working together across a person's entire genome that's the key to their longevity. "The best way forward is for people to pool their data so we can compare all the supercentenarians," lead researcher, Stuart Kim, told Rettner

Sources: Popular Science, LiveScience