Alzheimer's disease can seem unrelentingly grim. There is no cure, no known way to prevent the illness, and the benefits of current treatments are modest at best. But in laboratories around the country, scientists are uncovering clues that may eventually — perhaps even in the next two decades — allow them to prevent, slow or even reverse the ruthless progression of the illness. "Things are more hopeful than perhaps people think," Dr. Karen Duff of the Nathan Kline Institute of New York University said. "We are on the cusp of having something really useful." That hope comes on the heels...