One of the problems in detecting prions is that the infectious agent is just a conformational isomer of a normal "self" protein. Typical diagnostic approaches, such as looking for tell-tale antibodies or nucleic acids, therefore won't work. The successful approach exploits conformational differences between the two protein variants, says Jiri Safar of the Institute for Neurodegenerative Diseases at the University of California, San Francisco. Safar and Stanley Prusiner, who won a Nobel Prize for his discovery of prions, recently received the latest in a series of patents for just such a system.

US patent 6,677,125 describes a battery of different detection methods, one of which forms the basis for the conformation-dependent immuno-assay (CDI). The European Commission approved Inpro's CDI test for mad cow disease testing in its member states last June. CDI employs two antibodies, one that binds both conformations and one that binds only the normal conformation. If...

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