Alzheimer's disease (AD), named after the German physician Alois Alzheimer, is the most common form of dementia (the loss of mental function) among people age 65 and older. Alzheimer's disease is an irreversible, progressive brain disorder that occurs gradually and results in memory loss, erratic behavior, mood and personality changes, and a decline in thinking and reasoning abilities. These changes are related to the death of brain cells and the breakdown of the connections between them. The course of AD varies from person to person, as does the rate of decline. On average, people with AD live for eight to ten years after they are diagnosed; however, they can live with the disease for up to 20 years.

Alzheimer's disease is the fourth leading cause of death in adults after heart disease, cancer, and stroke. Between two and four million Americans have AD; that number is expected to...