By analyzing the DNA of the world's oldest people, Boston University scientists said Thursday they have discovered a genetic signature of longevity. They expect soon to offer a test that could let people learn whether they have the constitution to live to a very old age.

The researchers, who studied more than 1,000 people over the age of 100, identified a set of 150 unique genetic markers that, taken together, are linked to extreme longevity. They acknowledged they didn't know all the genes involved, nor their exact function...