Alzheimer's Disease Alzheimer's Disease is a progressive and irreversible brain disease that destroys mental and physical functioning in human beings, and invariably leads to death. It is the fourth leading cause of adult death in the United States. Alzheimer's creates emotional and financial catastrophe for many American families every year. Fortunately, a large amount of progress is being made to combat Alzheimer's disease every year. To fully be able to comprehend and combat Alzheimer's disease, one must know what it does to the brain, the part of the human body it most greatly affects. Many Alzheimer's dise