Alzheimer's disease is an irreversible, progressive brain disease that slowly destroys memory and thinking skills, eventually leaving the person without the ability to carry out the simplest tasks of daily living. Estimates vary, but experts suggest that as many as 5 million Americans age 65 and older have Alzheimer's disease. Research works on ways to improve diagnosis and care for Alzheimer’s disease patients, as well as focusing on a way to cure and possibly prevent it.