The causes of Alzheimer’s disease are not fully known and scientists continue to investigate this area.
So far, research into the causes of this brain disease has found two main forms of neural damage or abnormalities that can be linked to the disease and its progression.
Genetic studies have shed new light on possible causes of Alzheimer’s disease, but these must be researched further. Aluminium and zinc as causes were the topics of controversial studies and are discussed in less detail.
Tangled nerve cell fibres
A microscopic study of the brain of a person who has died from Alzheimer’s disease reveals tangled nerve cell fibres in certain areas of the brain. (Nerve cell fibres are typically found inside nerve cells). As the nerve fibres become tangled, protein deposits called “plaques” build up in the affected tissue. A protein called “tau” is found in the tangles.
Scientists are not sure how these neurofibrillary tangles are formed, but they’re characteristic of the condition.
Senile or neuritic plaques
These patches are situated outside the nerve cells and are surrounded by dying neurons, or nerve cells. The plaques contain a sticky protein called beta amyloid, which causes malfunctioning of nerve cells. This eventually results in the death of these cells.
The plaques are made of amyloid precursor protein (APP) molecules, which are usually essential components of the brain. Plaques are formed when an enzyme takes APP apart at a specific location and leaves the fragments (beta amyloid) in brain tissue, where they deposit abnormally.
The presence of neuritic plaques may be linked to a reduction in acetylcholine, an important chemical that’s instrumental in relaying messages in the brain.
The association between Down syndrome and Alzheimer’s disease has led scientists to look for genetic factors on chromosome 21, the chromosome involved in Down syndrome. Chromosomes are found in each cell in the body and carry the hereditary information (genes).
Other chromosomes that scientists have studied in relation to Alzheimer’s disease include chromosomes 14 and 19. The study of chromosome 19 is the most significant. It was in this chromosome that scientists discovered the ApoE-e4 gene, a well-known marker for heart disease that’s commonly found in people who developed Alzheimer’s disease at age 65 or older.
The gene was less likely to be found in people who didn’t have Alzheimer’s disease. These findings led scientists to believe that people with this gene might be more susceptible to Alzheimer’s disease, although it’s not a definite indicator.
Some researchers found increased levels of aluminium, mercury and other metals in the brains of victims of Alzheimer’s disease. This led to a controversial theory suggesting that the ingestion of small particles of one of these metals, especially aluminium, may lead to the development of Alzheimer’s disease.
However, much more research is necessary to determine whether aluminium build-up is a cause or a result of Alzheimer’s disease, and to better understand the exact role of this and other metals in the development of the disorder.
Zinc is the focus of another controversial theory about the possible causes of Alzheimer’s disease.
Studies suggesting a link between zinc and improved mental alertness in the elderly led scientists to give Alzheimer’s disease patients zinc supplements in a 1991 study. However, after only two days the patients’ mental abilities deteriorated rapidly. A few years later, laboratory tests revealed that zinc could make proteins form clumps similar to the plaques found in the brains of Alzheimer’s disease sufferers.
This needs to be further investigated, as scientists are not sure yet whether the plaques actually cause the disease or whether they’re a result of it.
The risk factors
Increasing age is the main risk factor for Alzheimer’s disease. Other risk factors include a family history of dementia and previous head trauma.