WASHINGTON -- Look for a fundamental shift in how scientists hunt for ways to ward off the devastation of Alzheimer's disease, by testing possible therapies in people who don't yet show many symptoms, before too much of the brain is destroyed.

The most ambitious attempt: An international study announced yesterday will track whether an experimental drug can stall the disease in people who appear healthy but are genetically destined to get a type of Alzheimer's that runs in the family. If so, it would be exciting evidence that maybe regular Alzheimer's is preventable too.

A second study will test whether a nasal spray that sends insulin to the brain helps those with early memory problems, based on separate research linking diabetes to an increased risk of Alzheimer's.

The new focus emerges as the Obama administration adopts the first national strategy to fight the epidemic -- a plan that sets the clock ticking toward finally having effective treatments by 2025.

"We are at an exceptional moment," with more important discoveries about Alzheimer's than in recent years, Dr. Francis Collins, director of the National Institutes of Health, declared.

But a meeting of the world's top Alzheimer's scientists this week made clear that meeting the 2025 deadline will require developing a mix of treatments to attack the different ways that Alzheimer's damages the brain -- much like it can take a cocktail of drugs to treat high blood pressure or the AIDS virus.

It will require testing possible drugs before full-blown Alzheimer's sets in, when it may be too late to do much good. Alzheimer's starts ravaging the brain at least a decade before memory problems appear. Doctors don't wait until the worst symptoms appear before treating heart disease, cancer or diabetes, noted Dr. Reisa Sperling of Harvard Medical School.

"Once the train leaves the station of degeneration, it might be too late to stop it," she said.

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