How a buildup of abnormal proteins in the brain may be the key to understanding Alzheimer disease.

Abstract

The term dementia describes a condition that causes trouble with thinking. The term does not tell us the cause of the problem. As scientists have studied dementia, they have identified many possible causes. For instance, if a person has had many brain injuries in life, he or she may develop problems with thinking. This type of dementia used to be called dementia pugilistica, which basically means dementia caused by fighting. This type of problem has been known to occur in boxers. However, this is not a common cause of dementia—after all, most people are not professional fighters. In the majority of people with dementia, the 2 most common causes are Alzheimer disease (AD) and multi-infarct dementia (MID).