Alzheimer's is the most common form of dementia, a general term for loss of memory and other cognitive abilities that interfere with everyday life.
Alzheimer's disease is responsible for 60 to 80 percent of dementia cases. Alzheimer's is not a normal feature of aging. The most important known risk factor is age, and most people with Alzheimer's are older than 65 years. But Alzheimer's is not just a disease of old age. Approximately 200,000 Americans under the age of 65 have early-onset Alzheimer's disease (also known as early-onset Alzheimer's).