The Alzheimer's Association estimated in 2009 that as many as 5.3 million Americans suffer from the mind-robbing illness. With that number expected to grow by double-digit percentages through 2025 as the population ages, scientists are working feverishly on strategies for prevention and treatment. But more than 100 years after the disease was discovered, it's still not clear what causes it. The only approved treatments barely dull the symptoms. Yet, numerous new approaches that have "cured" Alzheimer’s in mice are now being tested in people, with funding from the government and drug companies. Updated February 2010