Alzheimer’s (AHLZ-high-merz) disease is a progressive, degenerative disease that attacks the brain and results in impaired memory, cognitive ability and behavior. Alzheimer’s is the most common form of dementia, a group of conditions that all gradually destroy brain cells and lead to decline in mental function. Over 4 million Americans have Alzheimer’s type dementia. Although Alzheimer’s disease can occur in persons in their 40s and 50s, most of those diagnosed with Alzheimer’s disease are 65 or older.