brain, spinal cord, and nerve disorders
Alzheimer Disease
Causes of Alzheimer Disease
What causes Alzheimer disease is unknown, but genetic factors play a role: About 5 to 15% of cases run in families. Several specific gene abnormalities may be involved. Some of these abnormalities can be inherited when only one parent has the abnormal gene. That is, the abnormal gene is dominant. An affected parent has a 50% chance of passing on the abnormal gene to each child. About half of these children develop Alzheimer disease before age 65. In most other cases, a single gene is not dominant. Instead, other genes affect the risk of getting Alzheimer disease. One gene abnormality affects apolipoprotein E (apo E)—the protein part of certain lipoproteins, which transport cholesterol through the bloodstream. There are three types of apo E: Epsilon-4: People with the epsilon-4 type develop Alzheimer disease more commonly and at an earlier age than other people. Epsilon-2: In contrast, people with the epsilon-2 type seem to be protected against Alzheimer disease. Epsilon-3: People with the epsilon-3 type are neither protected nor more likely to develop the disease. However, genetic testing for apo E type cannot determine whether a specific person will develop Alzheimer disease. Therefore, this testing is not routinely recommended. Risk factors, such as High Blood Pressure , In Alzheimer disease, parts of the brain degenerate, destroying nerve cells and reducing the responsiveness of the remaining ones to many of the chemical messengers that transmit signals between nerve cells in the brain (neurotransmitters). The level of acetylcholine, a neurotransmitter that helps with memory, learning, and concentration, is low. Alzheimer disease causes the following abnormalities to develop in brain tissue: Beta-amyloid deposits: Accumulation of beta-amyloid (an abnormal, insoluble protein), which accumulates because cells cannot process and remove it Neuritic (senile) plaques: Clumps of dead nerve cells around a core of beta-amyloid Neurofibrillary tangles: Twisted strands of insoluble proteins in the nerve cell Increased levels of tau: An abnormal protein that is a component of neurofibrillary tangles and beta-amyloid Such abnormalities develop to some degree in all people as they age but are much more numerous in people with Alzheimer disease. Doctors are not sure whether the abnormalities in brain tissue cause Alzheimer disease or result from some other problem that causes both the dementia and the abnormalities in brain tissue. Researchers have also discovered that the abnormal proteins in Alzheimer disease (beta-amyloid and tau) resemble the abnormal proteins in Overview of Prion Diseases . That is, they are misfolded and cause other proteins to misfold, causing the disease to progress. Inflammation may also contribute to the development of Alzheimer disease. Inflammation has been observed in the brains of people with Alzheimer disease. With aging, some brain abnormalities characteristic of Alzheimer disease develop in everyone. 