Alzheimer's disease is the most common form of dementia, a general term used to describe the loss of memory and other intellectual abilities severe enough to interfere with day-to-day life. Alzheimer's is not a normal part of aging. It is progressive and incurable, a debilitating condition that slowly destroys memory, intellect, and personality. Eventually, it renders its sufferers helpless. Scientists aren't sure what causes Alzheimer's, but they do know its symptoms, how they develop, and the ways they affect the body and brain.