New Study Sheds Light on Progression of Alzheimer's Disease
March 21, 2000 (Atlanta) -- Protein deposits typically found in the brains
of Alzheimer's patients may begin forming before symptoms of the disease are
present and increase as the disease progresses, according to a recent study
published this week in TheJournal of the American Medical
The study paints a more complete picture of the progression of Alzheimer's
disease, linking the severity of dementia with the amount of plaque found in
the brain. Plaque is made up of deposits of protein called beta-amyloid.
The study also established that, at least in one part of the brain, the
beta-amyloid proteins found in the plaque occur before another Alzheimer's
trademark, called neurofibrillary tangles, forms. These are tangles made of
another protein called tau, and they are found inside the brain's cells.
"I think it is a particularly well done study that correlates the
density and presence of amyloid with the level of dementia in a fairly good
size patient population," says Bill Thies, PhD, vice president of medical
and scientific affairs at the Alzheimer's Association in Chicago. "So in
terms of showing a sequential relationship -- that is, if you have more
amyloid, you have more dementia -- this paper is quite good."
From the very first description of Alzheimer's, researchers recognized that
beta-amyloid plaque and tau protein tangles were present in the brains of
patients with the disease, according to Thies.
"There has been fairly steady debate as to which is the cause of
Alzheimer's, does one cause the other, and which comes first," he says.
"And if you are going to try to treat it, where would you like to attack
[it]: either at the formation of the plaque or at the formation of the
A better understanding of the sequence of events leading up to Alzheimer's
could help researchers target therapies for the disease.
Researchers led by Jan NÃ¤slund, PhD, from the Laboratory of Molecular and
Cellular Neuroscience at Rockefeller University in New York, conducted analyses
on the brain tissue of 79 nursing home residents who died between 1986 and
1997. Patients were excluded if they had abnormal brain changes caused by
something other than Alzheimer's.
Researchers measured the amount of two different kinds of beta-amyloid
proteins in five regions of the brain and found that patients who hadn't had
Alzheimer's had lower levels than those who did have Alzheimer's. The average
levels of both proteins were generally higher in patients who had in life had
more severe Alzheimer's.
When the researchers looked at the tau protein tangles in the front part of
the brain, a part of the brain involved only late in the disease's progression,
they found increases in both beta-amyloid proteins came before the formation of
the tangles, and that these increases occur before many symptoms of Alzheimer's