She doesn't look it, but Alice Treister is about to turn 100 years old. How have Treister and other centenarians managed to live such long lives? That's a question that researchers feel they're a little closer to answering.

While environment and lifestyle choices are certainly factors in healthy aging, some Boston researchers say they are closer to pinpointing the precise genetics that allow some people to live long lives.

In a study released online by the journal Science, a team from the Boston University Schools of Public Health and Medicine and the Boston Medical Center say they have identified a group of genetic variants that can predict long life with 77 per cent accuracy – a breakthrough in understanding the role of genes in human lifespan.

Alice Treister may be one of those blessed with the right genetic signature. At 99, she has no major health problems, beyond a bit of hearing loss. She used to bowl most days but the friends who drove her to the bowling alley became too old themselves to drive.

Looking over her long life, the resident of Baycrest Terrace seniors' home in Toronto says she's never had a special diet, vitamins or fitness routine that might explain her exceptional longevity.

"I have no idea, I can't begin to tell you," she tells CTV. "I don't know what to put my finger on to say. ‘This is why'."

Margaret Kamin Zysman, too, seems to have the genetic gift. Decked out in pearls and stylish clothing, with her long hair pinned up on her head, few would be able to guess she's 101.

"I don't accept my age at 101 because I don't feel 101," she says.

Though she battled breast cancer in the early 1990s, Zysman is still limber and healthy. Her only real regret in getting old is lack of male companionship.

"I am sorry that I have reached the age where there is no more romance in my life, no more men in my life," she says. "I try to make myself adjustable to the circumstances, which are not too bad."

Only 1 in about 6,000 people live past 100. So how have women like Treister and Zysman done it? The Boston research team thinks it may come down to 150 genetic variants.

Geriatrician Dr. Thomas Perls and Paola Sebastiani, a professor of biostatistics, analyzed DNA from over 1,000 centenarians born between 1890 and 1910 and compared them with 1,267 people born later. They identified 150 genetic markers in the older group that they didn't find in ordinary people.

The centenarians were divided into 19 groups with different genetic signatures. Some genes correlate with longer survival, others seem to delay the onset of various age-related diseases, such as dementia.

"This is probably the first time that anyone has actually found a large number of genes that interact with one another to cause this wonderful trait," says Perls.

After they narrowed down the genetic variants – or single nucleotide polymorphisms – that were associated with longevity, the scientists then looked into whether the absence of certain gene variants that have been linked to disease also played a role in longevity.

They did this by analyzing how many disease-associated variants each centenarian had, compared to group of other people who acted as controls. Their analysis found little difference between the two groups -- suggesting that the presence of the genetic variants linked to longevity is of more importance than the absence of disease-associated variants.

For example, some of the healthy centenarians had genes predisposing them to dementia and heart disease, but they seemed to be protected from these diseases by their longevity genes.

The study, begun in 1995, focused only on Caucasians, but the researchers said they plan to extend it to other ethnic groups, including Japanese, which has a large population of elderly.

The researchers say that by using the data they've gathered, they can predict with 77 per cent accuracy whether someone will live to a ripe old age.

"So if you give me your genetic code I can tell you what the genetic probability you can live up to 100," says Sebastiani.

"It is true that it is really quite amazing to us and perhaps part of the reason is how strongly genetics this is. The test is quite accurate compared to what people have seen with other traits or diseases," says Perls.

Scientists acknowledge that lifestyle plays a role in longevity – the fact that the test is not perfectly predictive is itself indication that environmental factors affect one's life span. But they say their discovery offers the possibility of genetic tests and perhaps, one day, drugs that could mimic the effects of these longevity genes.

As for the test, Perls says he is curious to find out if he has the potential to live a long life long live, but so far he has not tested his own genetic code.

"I might want to down the road. I am a little curious, but for now I am holding off," he says.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip