Scientists from U.S. and Japan have reported in the journal Nature Biotechnology yesterday about the genetic engineering techniques to produce the first //cattle that may be biologically incapable of getting mad cow disease.

They hope the cattle can be the source of herds that can provide dairy products, gelatin and other products free of the brain-destroying disease, also known as bovine spongiform encephalopathy or BSE. The animals, which lack a gene that is crucial to the disease's progression, were not designed for use as food. They were created so that human pharmaceuticals can be made in their blood without the danger that those products might get contaminated with the infectious agent that causes mad cow.

Writing in the journal, the scientists said their cattle were healthy at the age of 20 months, and sperm from the males made normal embryos that were used to impregnate cows, although it is not certain yet that they could breed normally. They added that the cattle lack the nervous system prions, a type of protein, that cause BSE and other related diseases such as scrapie in sheep and Creutzfeldt-Jakob disease, known as CJD, in humans.

Yoshimi Kuroiwa of Kirin Brewery Company in Tokyo, Japan and colleagues made the cattle, known as knockouts because a specific gene has been "knocked" out of them, using a method they call gene targeting. "By knocking out the prion protein gene and producing healthy calves, our team has successfully demonstrated that normal cellular prion protein is not necessary for the normal development and survival of cattle. The cows are now nearly 2 years old and are completely healthy," said James Robl of Hematech, a South Dakota subsidiary of Kirin.

Mr Robl, an expert in cloning technology, said: "We anticipate that prion protein-free cows will be useful models to study prion disease processes in both animals and humans."
SRI
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