Alzheimer's disease - a progressive, degenerative brain disease - causes more than simple forgetfulness. It may start with slight memory loss and confusion, but it eventually leads to irreversible mental impairment that destroys a person's ability to remember, reason, learn and imagine. Alzheimer's disease is the most common cause of dementia, which is the loss of intellectual and social abilities severe enough to interfere with daily functioning. Dementia occurs in people with Alzheimer's disease because healthy brain tissue degenerates, causing a steady decline in memory and mental abilities. Alzheimers develops usually in people age 65 or older. Although there's no cure for Alzheimer's disease, researchers have made progress. Treatments are available that improve the quality of life for some people with Alzheimer's. Also, more drugs are being studied, and scientists have discovered several genes associated with Alzheimer's, which may lead to new treatments to block progression of this complex disease.