Health Conditions

What causes it?

Researchers have defined two significant changes in the brain that occur in patients with Alzheimer's disease (AD): twisted nerve cell fibers, known as neurofibrillary tangles, and development of protein deposits or clumps, called neuritic plaques. While the exact cause of this disease is still unknown, researchers have found several factors that may contribute to the development of the disease, including an inflammatory response, genetic factors, and environmental influences. Damage to the brain resulting from AD primarily affects the nervous system. The nervous system can be thought of as the body's wiring system for electricity.

In Alzheimer's disease, placques and tangles impair the transmission of neurotransmitters.

Impulses travel through the wires - the axons and dendrites - of the nervous system in a way similar to the way electricity travels through wiring. In patients with AD, these wires become damaged as a result of the development of neuritic amyloid plaques and neurofibrillary tangles. The protein responsible for the development of these deposits or plaques is called beta-amyloid. The deposits are clustered in and around the nerve cells, or neurons, just outside of brain cells. Neurofibrillary tangles are twisted fibers that build up inside neurons. Just as electricity cannot flow through damaged wires, nerve impulses cannot travel smoothly through these obstructions.

Communication between nerve cells in the brain eventually deteriorates. This causes the nerve cells to stop functioning and they inevitably die. The damage generally affects key areas of the brain that are involved in the control of memory, such as the hippocampus (located deep within the brain). Portions of the cerebral cortex, the outer area of the brain that is responsible for functions such as language and reasoning, are also affected.

Possible causes. As previously mentioned, it is believed that the changes in the brain that result from AD could be caused by several different factors described below.

• Inflammatory response: Some researchers think that beta-amyloid may release oxygen free radicals. These are unstable chemicals that are believed to bind to other molecules through a process called oxidation, causing damage to DNA and triggering other harmful processes. The end result is the production of an inflammatory response, in which the immune system overproduces substances used to fight harmful agents in the body. The overproduction results in damage to the body's own cells.

• Genetic factors: An increased risk for Alzheimer's disease has been linked to a gene called ApoE/e4. The presence of this gene is considered a risk factor but not a direct cause of the disease. An increased incidence has also been found for people who have a first-degree relative (parent, brother, or sister) who has had the disease. Three other genes are being researched to see if they have a connection to the development of AD.

• Environmental and other influences: Genetics appears to play a major role, yet it does not offer a complete answer to the occurrence of Alzheimer's disease. A severe head injury may accelerate the development of AD in people who are already susceptible. Additionally, childhood malnutrition may render people more susceptible to mental impairments late in life, including Alzheimer's disease.