With as many as 5 million Americans suffering from this mind-robbing illness, and their numbers soaring as the population ages, scientists are working feverishly on strategies for prevention and treatment. But more than 100 years after the disease was discovered, scientists still aren't sure what causes it. The only approved treatments barely dull the symptoms, and there is no cure. 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.