When Russell Snell and his colleagues at the University of Auckland, New Zealand, were recently designing a study to test a candidate Alzheimer's gene, they ran up against a roadblock: How to put together a control group? "It's a problem," says Snell. "How do you identify a person who is not going to develop Alzheimer's?"
The obvious answer was to find a group of healthy people who had passed the usual age of onset of the disease. "If you reach 95 or 100, or more, and you don't have Alzheimer's then you probably won't be getting it," he says. But gathering a sizeable cohort of centenarians and near-centenarians is no easy matter, certainly not in New Zealand, with a population of just 4.16 million. So Snell took to the literature, searching for other groups who had a cohort he might borrow.
He found the perfect sample in May 2005, when ...
