Alzheimer's Disease - Causes

The causes of AD are currently not known. Research has produced some strong leads, however, and made possible the development of some promising experimental treatments. This research has been based largely on autopsies of people who have died from AD. These autopsies show that brain cells responsible for learning, reasoning, and memory have been damaged. They have become clogged with two kinds of abnormal structures known as neurofibrillary (pronounced noor-o-FIB-ruhl-ary) tangles and senile plaques.

No one knows how these structures cause AD, but researchers have some theories. They think the structures keep brain cells from functioning normally, which prevents the transmission of brain signals from one cell to another.

This discovery has led to the development of one class of drugs for the treatment of AD. These drugs increase the amount of neurotransmitters produced in the brain. Neurotransmitters are chemicals that carry signals between brain cells. The first two drugs of this kind were approved for use by the U.S. Food and Drug Administration (FDA) in January 1998.

What triggers the formation of tangles and plaques is not known. But researchers are pursuing some possible leads. First, inflammation in the brain may be a factor. A class of drugs known as nonsteroidal anti-inflammatory drugs (NSAIDs) may prevent inflammation and reduce the risk of AD.

Free radicals are another factor in the formation of tangles and plaques. Free radicals are very active chemicals that form in the brain and damage brain cells. Chemicals known as antioxidants react with and destroy free radicals. Vitamin E is a naturally occurring antioxidant.

Genetic factors seem to be important in the development of AD. Scientists have discovered certain gene defects that appear to be related to the disease. They have found that mutations (changes) in certain genes are connected with some forms of AD. However, research in this area is at a very early stage. Little information that can be used for treatment of the disease has been uncovered.

In spite of how little is known about the causes of AD, a number of risk factors have been identified. The most obvious of these factors is age. The older a person is, the more likely he or she will be to develop AD. Another risk factor is heredity. People whose family members have had AD, Down's syndrome (see down's syndrome entry), or Parkinson's disease (see Parkinson's disease entry) are more likely to develop Alzheimer's disease than those whose families do not have this history. People who have hypothyroidism (reduced levels of thyroid in the blood) or have experienced head injuries are also at relatively high risk for AD.

Environmental factors have sometimes been proposed as possible causes for AD. For example, the ingestion of aluminum was once thought to be a possible factor in the disease. So far, scientific studies have not been able to confirm the role of any environmental factor in causing AD.