Alzheimer's Disease?

References in this post are taken entirely from Fundamentals of Abnormal Psychology, sixth edition, by Ronald J. Comer.

What are the structural and biochemical causes of Alzheimer's disease? 

1. Abnormal formation of proteins

Background: Proteins are produced in key brain cells as new memories are formed. In the brain of an Alzheimer's patient, the amount of neurofibrillary tangles (twisted protein fibres found within the hippocampal cells and certain other brain areas) found are much higher than the average aged person. Senile plaques (sphere-shaped deposits of a small molecule known as the beta-amyloid protein that form in spaces between cells in the hippocampus, cerebral cortex, and certain other brain regions, as well as in some nearby blood vessels) are also found in excessive amounts as compared to other aged persons.

Research suggests that some of the above proteins may take an abnormal form and run amok in people with Alzheimer's disease. Studies suggest, for example, that two important proteins - beta-amyloid protein and tau protein - operate abnormally in such individuals, which seem to be involved in the formation of senile plaques in the hippocampus and other brain regions, and formation of neurofibrillary tangles in those brain regions respectively.

I hope my paraphrasing isn't too confusing :/

2. Abnormal activity by neurotransmitters and other chemicals involved in production of memory proteins. 

Many studies have found, for example, that acetylcholine and glutamate are low in supply, or at least function differently, in the brains of Alzheimer's victims.

Still other studies suggest that victims may display an imbalance in the metabolism of calcium, one of the chemicals responsible for protein production in cells.

3. Natural substances acting as toxins

Such substances may cause brain damage. For example, high levels of zinc in the brains of some Alzheimer's victims have been detected. This has drawn particular attention because in some animal studies, zinc has been observed to trigger a clumping of the beta-amyloid protein, similar to the plaques found in the brains of Alzheimer's patients.

Yet another explanation suggests that the environmental toxin lead may contribute to the development of Alzheimer's disease. Many of today's elderly population were exposed to high levels of lead in the 1960s and 1970s, regularly inhaling air pollution from vehicle exhausts. Such an exposure might have damaged or destroyed many of their neurons. Several studies suggest that this previous absorption of lead and other pollutants may indeed be having a negative effect on the current cognitive functioning of such individuals.

4. Autoimmune theory

An autoimmune response happens when a mistaken attack by the immune system happens against itself.

On the basis of certain irregularities found in the immune systems of people with Alzheimer's disease, several researchers have speculated that changes in aging brain cells may trigger an autoimmune response that leads to this disease.

5. Viral theory 

A virus similar to the slow-acting virus that is known to have caused the Creutzfeldt-Jacob disease (which Alzheimer's resembles) has been proposed by some researchers to have caused the Alzheimer's disease. However, no such virus has been detected in the brains of Alzheimer's victims.