Suspect Causes of Alzheimer's Disease Symptoms

The physical changes that cause brain damage in Alzheimer's disease are known, but the exact causes of Alzheimer's disease remain a mystery. Although certain conditions and genetic markers appear to accompany Alzheimer's, none of these conditions can account for brain damage in all cases. Many theories abound about the causes of Alzheimer's disease—theories that often cause intense debate among Alzheimer's researchers.

 

The most commonly accepted theory suggests that brain damage occurs due to a combination of events. Genetic factors may combine with external or environmental factors to cause Alzheimer's symptoms.

Although not causes of Alzheimer's disease, age and gender are both considered risk factors. Alzheimer's symptoms generally do not appear before age sixty, and the risk of symptoms increases with age. Women appear to be twice as likely to develop Alzheimer's symptoms as men. However, women also live longer than men, so while being female may increase the risk of Alzheimer's, this may simply reflect the fact that Alzheimer's disease rates increase with age.

Researchers have also considered genetic causes of Alzheimer's disease and have found that some genetic mutations do seem to increase the chance of developing Alzheimer's symptoms. Mutations in the genetic codes of beta-amyloid proteins and presenilin 1 and 2 have been considered as causes of early-onset Alzheimer's. While the mutations often appear with early-onset Alzheimer's, the majority of patients with Alzheimer's-related brain damage do not show any evidence of these mutations.

 

APOE provides the genetic code for the protein apolipoprotin E. The presence of a variant of APOE (APOE 4) appears to increase the risk of Alzheimer's disease. People who inherit APOE 4 from one parent are four times more at risk that those without the variant, while people who inherit APOE 4 from both parents are ten times more likely to develop Alzheimer's disease.

 

However, fifty percent of people with Alzheimer's symptoms do not carry the APOE 4 variant. Therefore, while APOE 4 may increase the risk of Alzheimer's, the presence of this gene alone cannot account for the development of Alzheimer's.

Hypertension (high blood pressure) and high cholesterol levels increase the risk of Alzheimer's disease, but this risk is most likely an indirect link. Both hypertension and high cholesterol increase the chances of atherosclerosis, which impairs blood flow to the brain. Impaired blood flow can cause strokes and other forms of brain damage.

 

A direct link between Alzheimer's and hypertension or high cholesterol has not been proven. However, it is interesting to note that APOE is involved in the transport of cholesterol through the blood.

A recent study connected the herpes simplex virus with amyloid precursor protein (APP). APP breaks down to form beta-amyloid, which is associated with brain plaques in Alzheimer's patients. The discovery was an accidental one: The researchers were really trying to determine how the herpes virus travels around the body and why it causes a breakout after a period of inactivity. What they found is that the herpes virus uses APP as a means of transportation and causes the APP to break down into beta-amyloid at a very rapid rate. Further research is needed to determine what exactly is the connection between the herpes virus and the development of Alzheimer's disease.

 

Herpes simplex is the virus that causes genital herpes and oral herpes (a.k.a., cold sores).

Many different causes of Alzheimer's disease have been suggested. Aluminum build-up in the body has been considered as a cause of Alzheimer's. However, measuring aluminum build-up is difficult, and most researchers have discounted this theory.

 

Head injuries can lead to brain damage that may increase the chance of developing Alzheimer's disease. However, relatively few people with Alzheimer's symptoms have a history of head trauma, so while injuries may increase the risk, they do not cause the disease.

 

National Institutes of Health. (updated 2005). Alzheimer's disease: Causes and risk factors.