People who die from Alzheimer's disease typically have
accumulations of two types of proteins in their brains: amyloid
beta, which forms plaques, and abnormal tau, which forms tangles.
However, because most Alzheimer's studies have been conducted
using the brains of people who had severe memory problems, no one
was sure if the accumulations of amyloid beta and tau began to form
early in the disease when symptoms were still mild.
Now a study in the March 22/29 issue of the Journal of the
American Medical Association (www.jama.com) shows that even in
people with very mild forms of Alzheimer's dementia, plaques have
already begun to form. In the study, the amount of amyloid beta
also correlated with the severity of a person's memory problems.
Although this report does not prove that plaques cause the disease,
it suggests that preventing early development of plaques may delay
the onset of Alzheimer's disease.
Between 1986 and 1997, researchers led by Jan Naslund, of the
Rockefeller University, New York, studied 79 residents of nursing
homes. They tested the study participants on the Clinical Dementia
Rating scale, which measures the severity of memory problems
associated with diseases like Alzheimer's. The investigators then
divided the patients, according to their scores, into five groups:
no dementia, questionable, mild, moderate and severe dementia.
When the participants eventually died, pathologists examined
their brains for evidence of Alzheimer's disease. They found that
amyloid beta was present even in people with questionable dementia.
The amount of amyloid beta increased along with the severity of
dementia.
Also, the researchers found that, in frontal parts of the brain,
increases in amyloid beta accumulations developed before
significant increases in tau.
``From a possible treatment perspective, attempts to prevent or
slow the course of Alzheimer's disease should focus on inhibiting
the cellular production of amyloid beta and/or slowing the
pathogenic assembly of amyloid beta into aggregates,'' the authors
wrote in the study.
According to Dr. Dennis Selkoe, of the center for neurologic
diseases at Harvard Medical School and Brigham and Women's Hospital
in Boston, by finding that plaques start forming before tangles,
this research begins to settle an old debate. It suggests that to
prevent Alzheimer's, researchers could develop drugs that block the
formation of plaques.
``In the future, it is likely individuals entering their fifth
or sixth decade of life will undergo a formal Alzheimer's disease
risk assessment as part of routine health maintenance,'' Selkoe
wrote in an accompanying editorial. This could potentially include
measurements of amyloid beta levels in blood plasma and
cerebrospinal fluid. Then, people could receive early interventions
to prevent the disease from progressing past its initial stages.
