GENTECH archive 8.96-97
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Test for Mad Cow Disease May Be Near

Tuesday, December 23, 1997 · Page A4 
Tuesday, December 23, 1997 · Page A4 

   ©1997 San Francisco Chronicle 
Test for Mad Cow Disease May Be Near
UCSF team bred mice to screen disorder in cattle 

    David Perlman, Chronicle Science Editor

        Laboratory mice engineered to carry genes that make them sensitive
to mad cow disease could provide
        the first rapid test for the infection in cattle and help protect
humans against a closely related brain
        disorder, researchers are reporting today. 

        At least a million cows in Britain and France have contracted the
highly infectious disease, which turns
        their brains to spongy tissue, and infection from tainted beef is
believed to have caused in more than 25
        people a form of an extremely rare disorder known as
Creutzfeldt-Jakob disease. 

        At the root of both diseases are prions, the protein particles
discovered 15 years ago by Dr. Stanley B.
        Prusiner, a neurologist at the University of California at San
Francisco who won the Nobel Prize in
        medicine this year for his work in the field. 

        The shape of the proteins can change suddenly for reasons that are
still unclear, but in their distorted
        forms, they become the cause of severe neurological diseases in
many animals, including cattle, sheep
        and even humans, according to the revolutionary theory first
proposed by Prusiner. 

        Today, Prusiner and his UCSF colleagues, including Dr. Steven J.
DeArmond and Dr. Fred E. Cohen,
        report two major new findings from their work in the Proceedings of
the National Academy of Sciences: 

        -- After six years of trial and error, they have produced
``transgenic'' strains of laboratory mice that carry
        within their cells mixtures of genes for the creation of normal
prions that occur naturally in humans, cows
        and mice. 

        -- As a result, they say, they have identified a unique portion of
the prion protein that allows the
        disease-causing form to cross the species barrier between animals
and humans. 

        When cattle are infected with the distorted prion proteins that
cause mad cow disease, Prusiner said in
        an interview, the symptoms do not show up for at least three to
five years. 

        But the genetically engineered mice Prusiner and his colleagues
have developed can display the
        staggered gait and other warning symptoms of the fatal brain
disorder within 120 days, he said. By
        further manipulating the mice in the lab, the group expects to cut
that time down to 40 days or less,
        Prusiner said. 

        Like the warnings offered by canaries in a coal mine, the mice
could be inoculated with cells from
        symptom-free cattle and thus serve to determine whether the animals
are unfit for human consumption. 

        Some human foods, cosmetics and drugs are made from cattle bones,
and the ``transgenic'' mice could be
        used, the scientists say, to screen for the presence of the
infectious prion proteins and to ensure that
        tainted material not be used in the manufacture of such products. 

        Mad cow disease, first detected in Britain in 1986, is known
technically as bovine spongiform
        encephalitis. It is apparently caused by feed supplements
contaminated with prion-infected animal
        protein products from diseased cattle and sheep. 

        Cattle in the United States are known to be free of the spongiform
diseases, and the use of potentially
        contaminated animal- based feed is banned. No cases of
Creutzfeldt-Jakob disease attributable to
        infection from diseased animals have occurred in this country,
according to public health experts at the
        U.S. Centers for Disease Control. 

        Prusiner and his group are now trying to determine how normal
prions -- which are found in all human
        and animal tissues -- can become transformed into highly infectious
disease-causing agents. 

        The answer, Prusiner believes, is a mysterious ``Factor X,'' a
protein molecule that binds with a normal
        prion and distorts its shape. But he expects extensive research
will be needed to identify the molecule
        and how it works. ``It's not an easy secret to extract from
nature,'' he said. 
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