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 If you live to be 100, you’re in a special group, one that longevity scientists are eagerly studying for clues to battling aging. But are these centenarians long-lived because they don’t get the diseases that fell the rest of us—heart problems, diabetes, dementia, arthritis and more—or because they are protected somehow against the effects of aging? Based on the data so far, most experts have concluded that centenarians get to where they are because they have some anti-aging secret that shields them against the effects of aging. That’s because studies found that centenarians had just as many genes that contribute to disease as those with more average life spans. 
 
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 But in a paper published in PLOS Genetics, researchers led by Stuart Kim, professor of developmental biology and genetics at Stanford University, questions that dogma. He found that on the contrary, centenarians may have fewer of the genes that contribute to major chronic diseases. That doesn’t mean that people who live to their 100s also don’t possess some protective anti-aging genes as well, but Kim’s study shows that they don’t experience as much disease as people who are shorter-lived. 
 
 Kim’s team came to that conclusion after conducting a novel type of genetic analysis. Most attempts to look for genes related to aging compare the genomes of centenarians and people with average life spans and pick out the regions where the maps differ. Those are potential targets for aging, but, as Kim notes, they could also be red herrings. “Because you search through hundreds of thousands, and now millions of variants, there is a lot of noise. So it makes it difficult to see the signal amidst all the noise.” 
 
 MORE: How to Live Longer 
 
 To purify the signal, Kim layered another piece of information on this comparison. He made the assumption that disease genes can reduce the chances of someone reaching their 100s, and focused just on known disease-causing genes in his analysis. “With that, we can make better guesses about what is really bad for becoming a centenarian,” he says. 
 
 The filtered analysis pumped out five major regions of interest for longevity. Four are familiar; they involve the gene connected to Alzheimer’s, an area involved with heart disease, the genes responsible for the A-B-O blood type and the immune system’s HLA region that needs to be matched for organ transplants to avoid rejection. These four have known connections to longevity. The Alzheimer’s gene, ApoE, for example, is linked to shorter life span, while the heart disease variants are involved in directing a cell’s life span and the O blood type is known to be connected to better health outcomes and survival. 
 
 MORE: How to Live 100 Years 
 
 The fifth region was one that had never been linked to longevity before, and Kim admits that not much is known about how it might contribute to longer life, except that mutations in the gene region can contribute to neurological diseases such as ALS and that in fruit flies, other mutations help the insects to live longer. 
 
 “It seems intuitively obvious, that avoiding disease is part of the strategy of becoming a centenarian,” says Kim. “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-aging genes. I think they were wrong.” 
 
 Those previous studies that pointed to this anti-aging effect over the effect of fewer disease-causing genes were generally smaller, and might not have isolated the signal from the noise. 
 
 Kim’s team shows that the way centenarians reach their second century may involve more than just being blessed with anti-aging genes. “We found that, at least in part, they live longer because they don’t get sick,” he says. He also readily admits that they may also benefit from some anti-aging factor that researchers haven’t uncovered—yet. ||||| Several new genes linked to an exceptionally long life have been discovered, according to a new study that examined the genomes of people living into their 100s, known as centenarians. 
 
 Using a new method, the researchers found four genes linked with a very long life: A gene called ABO, which is involved in determining blood type; a gene called CDKN2B, which regulates cell division; a gene called APOE, which is linked with Alzheimer's disease; and a gene called SH2B3, which was previously found to extend life in fruit flies. 
 
 The researchers hope that future studies will uncover even more genes linked with longevity, and figure out how these genes may affect the aging process. 
 
 "There's a reasonably strong genetic component to becoming a centenarian, and we want to find out what that is," said study researcher Stuart Kim, a professor in the Department of Developmental Biology and Genetics at Sanford University. "We're beginning to unravel the mystery" of why some people age so successfully compared to the normal population, Kim said. [Extending Life: 7 Ways to Live Past 100] 
 
 Previous studies have attempted to find variations in genes that are more common in the very old compared with younger people, but haven't had much luck. These studies looked through millions of variations in the human genome, but they might have missed some important associations. 
 
 The new study aimed to narrow the search for genes linked with long life by focusing on ones that are known to strongly affect a person's risk of age-related disease, like heart disease and Alzheimer's. The thinking is that these diseases increase a person's risk of dying early, and so genetic variants that increase the risk of these diseases would also decrease the chances of a long life, the researchers said. 
 
 The researchers first searched for longevity-linked genes in a population of about 800 people over age 100 and 5,400 people over age 90. 
 
 They found eight genes that were linked with a long life span, and were able to confirm four of these genes in a follow-up analysis of about 1,000 people ages 100 or over. 
 
 The study found that certain variants in the ABO, CDKN2B, APOE and SH2B3 genes were more common in centenarians than in people with a typical life span. (Adults in the United States have an average life expectancy of about 79 years, according to the Centers for Disease Control and Prevention.) 
 
 For example, the study found that the a genetic variation associated with type O blood was more common in centenarians than in the study's control group, meaning that there were slightly more centenarians with type O blood, compared to people with a typical life span. Previous studies have found that people with type O blood have a lower risk of coronary heart disease and cancer, and have lower cholesterol levels than people with other blood types. 
 
 Another genetic variant in the CDKN2B gene seems to play a role in whether cells continue to divide, or stop dividing. Given that the stoppage of cell division, called senescence, is thought to contribute to aging, having a gene variation that reduces cell senescence could be a factor that contributes to successful aging, Kim said. 
 
 Kim suspects that there are still more genes linked with a longer life span. 
 
 "I hope our paper inspires other people to continue searching for" genes linked with longevity, Kim said. 
 
 The study was published yesterday (Dec. 17) in the journal PLOS Genetics. 
 
 Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.
– Science may be closer to figuring out why some people live so darn long. Researchers studying 1,800 people over the age of 100 and another 5,400 over the age of 90 discovered four genes linked to their longevity, Live Science reports. "There's a reasonably strong genetic component to becoming a centenarian, and we want to find out what that is," researcher Stuart Kim says. "We're beginning to unravel the mystery." Kim's study—published in PLOS Genetics—identified genes related to blood type, cell division, and Alzheimer's, as well as one known to make fruit flies live longer, that were either more or less common in the extremely old. In short, centenarians seem to have fewer genes connected to major diseases, according to Time. “It seems intuitively obvious that avoiding disease is part of the strategy of becoming a centenarian,” Time quotes Kim as saying. But he notes that conclusion goes against "really strong dogma in the field." Most researchers tend to believe undiscovered anti-aging genes are responsible, but Kim posits it could be much simpler: Centenarians may just get fewer diseases. According to Live Science, one of the four genes causes type O blood, which is known to be negatively associated with heart disease and cancer. Another of the genes is related to whether organ transplants are rejected or accepted, Time reports. According to Live Science, researchers hope further studies will turn up even more genetic similarities in centenarians. (This study says young blood can reverse the aging process.)