Definitively diagnosing Alzheimer's disease is an extremely difficult
task. Up until now, the only way to diagnose it was by studying
brain tissue during an autopsy -- far too late to do anything about
it.
However, hope may be on the horizon: A team of researchers developed
a highly effective new test to locate the disease in its early stages,
when the patient is still alive and can be treated. The test is
called a bio-barcode assay; it detects small amounts of proteins
in spinal fluid and is up to 1 million times more sensitive than
other available tests.
The connection between the test and Alzheimer's began after a member
of the research team had done previous research associating the
disease with a small soluble protein in the brain known as amyloid-beta-derived
diffusible ligand (ADDL). With this data, the team set out to detect
ADDL in spinal fluid: They took samples of spinal fluid from 30
people (15 who had Alzheimer's and 15 who did not) and found at
least some ADDL was found in every participant. It was also discovered
that as the Alzheimer's in patients got worse, the concentration
of ADDL increased, making it possible to follow the progression
of the disease.
The Bio-Barcode Assay at Work
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To detect the ADDLs, researchers used nanoscale particles --
some particles were magnetic and some of gold with strings of
DNA attached -- that contained antibodies specific to ADDL.
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The antibodies bind to the ADDL, sandwiching the protein between
the two particles.
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They are then magnetically removed from the solution and hundreds
of thousands of DNA strands attached to the gold particles serve
as a barcode because they can be used to label the specific
target with standard detection methods.
Though the bio-barcode assay needs to be repeated and tested on
more patients, researchers are confident the test provides a reliable
detection method for diagnosing Alzheimer's. The research team also
aspires to use the test to search for proteins and other chemicals
that can offer early diagnosis of other diseases.
Proceedings
of the National Academy of Sciences of the United States of America
February 4, 2005
USA Today February 1, 2005
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