Topol and his collaborators will compare the gene sequences from the healthy volunteers with DNA samples collected from people who died from age-related diseases before they reached their eighties. The scientists have already found that the healthy people had only a slightly lower probability of carrying disease-linked variations. That supports the idea that protective genes are playing a major role in people's successful aging.

Scientists hope that identifying the molecular basis for this protective effect will enable them to mimic it with drugs. "We believe longevity genes are protecting against several age-related diseases rather than just one," says Nir Barzilai, head of the Longevity Genes Project at Albert Einstein College of Medicine, in New York, who is not involved in the Scripps study. "From a pharmaceutical perspective, it would be more cost effective to target these pathways, and it would really imitate exceptional longevity rather than just treating the diseases themselves."

Barzilai has already identified a couple of candidates for longevity genes. In an ongoing study of people of Ashkenazi Jewish descent age 95 or older, Barzilai and his colleagues showed that the elderly group was more likely to carry a gene variant that changes the way that people process cholesterol. More recently, the scientists sequenced the genes for IGF1 and its receptor and found mutations unique to female centenarians.

While Barzilai is taking a different approach to the gene hunt--using microarrays--he says that each group looks forward to learning what the other finds. Having two large studies of the genetics of healthy aging will allow each to confirm its findings in a second population--a crucial test of the validity of large-scale genomic studies.