Many researchers speculate that rather than having a single cause, Alzheimer’s disease may be the outcome of several types of insults to the brain. While we do not know exactly what causes this mysterious illness, theories have centered on these agents of destruction.
A virus. Because a virus is known to produce a very rare type of dementia, some researchers think — even though none has been found — that a slow-acting virus, one taking years to incubate in the body, might be implicated in Alzheimer’s disease. But there is no evidence of anyone’s ever catching Alzheimer’s disease from someone else.
A disorder of the immune system. Another hypothesis is that an immune system «error» may be partly to blame. In 1987 researchers at Rockefeller University reported finding abnormal antibodies in patients with Alzheimer’s disease; they speculate that these antibodies, instead of functioning normally to destroy outside invaders such as viruses, may attack the blood/brain barrier, the vital chemical sheath that keeps injurious substances from gaining access to the brain. Once the integrity of the blood/brain barrier is breached, a virus or other harmful substance might gain access to the brain and set off the disease.
Aluminum. Besides a virus, a strong candidate for instigating Alzheimer’s disease is aluminum, because a striking feature of the brains of Alzheimer’s victims is an abnormal concentration of this particular element. Does absorbing too much aluminum over a lifetime play any part in producing the disease? So far, laboratory studies of this hypothesis have been negative; but because high aluminum levels are such an important feature of the illness, many scientists think this substance is likely to play some role in the puzzle of Alzheimer’s disease.
A genetic defect. Without doubt, the most exciting new research lead involves genetics. In 1987 scientists at Massachusetts General Hospital reported identifying a genetic defect in people with a strong family history of Alzheimer’s disease.
The Alzheimer’s-related genetic marker is found on chromosome number 21, the very chromosome that is duplicated in people suffering from the birth defect Down’s syndrome. For several years researchers had been tantalized by what they knew was an important connection between these two illnesses, because victims of Down’s syndrome (mongolism) universally develop Alzheimer’s disease if they live to age forty. Now the mystery is solved. Having an extra chromosome 21 may be giving people victimized by Down’s syndrome the Alzheimer’s-related genetic program in spades.
Other research reported in the February 1987 issue of Science suggests that the illness may be set off by abnormal deposits of a protein called amyloid accumulating in the brain. Amyloid is a major component of senile plaques and neurofibrillary tangles — the abnormal structures that replace the normal neurons. Do the genetic instructions «produce amyloid» trigger Alzheimer’s disease directly by causing this toxic protein to build up? Does an Alzheimer’s gene (or set of genes) act in concert with a chemical such as aluminum or with a virus to produce these harmful deposits? Whatever the answer, some scientists now believe amyloid is central to the mystery of this devastating disease.
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