- LOS ANGELES (AP) -- A bacterium found unexpectedly in the brains of Alzheimer's
patients could mean that the dementia-producing disorder has an infectious
basis.
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- Scientists who examined brain tissue
of Alzheimer's patients after autopsy found that a bacterium called Chlamydia
pneumoniae had invaded brain cells in regions where Alzheimer's damage
can be detected.
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- Researchers were surprised to find the
presence of the bacterium because it had penetrated the protective blood-brain
barrier, traveling far beyond its common entry point into the body, the
sinuses and lungs.
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- The finding is important to "our
potential understanding of how an infectious agent could lead to the neurodegeneration
observed in Alzheimer's disease," according to Brian J. Balin, a researcher
at Allegheny University of the Health Sciences in Philadelphia.
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- Balin and a team of colleagues found
DNA segments from the bacterium in post-mortem brain samples of 17 of the
19 Alzheimer's patients he analyzed. Conversely, 18 of 19 brain samples
from people without Alzheimer's showed no signs of the organism.
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- "At this time, we do not know if
the presence of this organism is causative or if it is a risk factor for
the disease," Balin wrote. "However, we believe that our findings
support those of others suggesting that inflammation, which can be stimulated
by this bacterial infection, is a very important aspect of late-onset Alzheimer's
disease."
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- When cells become infected with the bacterium,
they make chemicals to fend off the infection. Those inflammatory chemicals,
called cytokines, can damage surrounding nerve cells.
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- "The damage may cause changes in
an individual's ability to recall information such as people and places
and the ability to think coherently -- common clinical features which are
seen in Alzheimer's disease," Balin wrote.
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- A top Alzheimer's expert said Balin's
report -- which was presented Wednesday at the annual meeting of the Society
for Neuroscience -- was a "provocative, exciting finding."
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- "I think that it's something that's
really worth taking seriously because of the issue of what's triggering
the degeneration process," said Zaven Khachaturian, a consultant to
the Alzheimer's Association.
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- Khachaturian said the critical question
is to identify the trigger, which he suggested might be some sort of trauma
or other incident that creates damage to the blood-brain barrier and lets
the bacteria in.
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- "Now you have a break in the pipe
all of a sudden setting the stage for other events to occur," Khachaturian
said. "I think this is a likely scenario."
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- Khachaturian said it's also important
to find out whether the bacteria has set the stage for Alzheimer's in the
patients who died, or whether the Alzheimer's damaged the brain, letting
in the bacteria.
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- Cells infected by the bacterium make
chemicals to fend off the infection. Those inflammatory chemicals, called
cytokines, can in turn damage surrounding nerve cells.
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- The same bacterium has been detected
in the fatty plaques that clog heart arteries, though researchers do not
yet know if it is responsible for the clogging.
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- Researchers have also found a correlation
between late-onset Alzheimer's and infection with herpes simplex virus
type 1.
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