Alzheimer's disease (AD) is an irreversible, progressive brain disease that slowly destroys memory and thinking skills and, eventually, the ability to carry out the simplest tasks of daily living. In most people with AD, symptoms first appear after age 60. AD is the most common cause of dementia among older people, but it is not a normal part of aging. Dementia refers to a decline in cognitive function that interferes with daily life and activities. AD starts in a region of the brain that affects recent memory, then gradually spreads to other parts of the brain. Although treatment can slow the progression of AD and help manage its symptoms in some people, currently there is no cure for this devastating disease.