杏吧原创

SCIENTISTS in Germany have developed a test that can detect a single clump of
prions, the deformed proteins thought to cause the fatal brain condition
Creutzfeldt-Jakob disease (CJD). Currently, a diagnosis of CJD can only be
confirmed after death. The new technique might permit earlier diagnosis of
CJD鈥攁nd maybe Alzheimer鈥檚 disease.

Prions form clumps in the body, one way in which they are believed to damage
the brain. Hans Kretzschmar and colleagues at the University of G枚ttingen
attached antibodies that seek out the deformed prion to molecules that fluoresce
red or green when illuminated with lasers. Clumps from hamsters with scrapie, a
prion disease that normally affects sheep, became coated with labelled
antibodies and fluoresced so strongly under lasers beamed through a microscope
that a single clump could be detected.

At present, the most sensitive test for prions is to inject suspect tissue
into the brain of a susceptible animal and then see if it gets sick, says
Kretzschmar. But this needs around a million prion molecules, whereas a single
clump contains only a thousand. That makes the new technique more sensitive: the
team detected prions in 21 per cent of spinal fluid samples from people who had
CJD, while it was found in only 15 per cent with the animal test. Ketzschmar
expects to increase the sensitivity tenfold, allowing more reliable detection.
The test should also distinguish the new variant CJD caused by BSE prions from
the more common form. Ketzschmar wants to adapt the test to find protein
clumps left by Alzheimer鈥檚 disease.

Markus Moser of Swiss company Prionics, which makes a BSE prion test, says
several different tests are under development. Together, he says, these should
enable scientists to work out where different prions accumulate in different
species.