Gene-engineered cattle resist mad cow disease: study(ZT)

U.S. and Japanese scientistsreported on Sunday that they had used genetic engineering toproduce cattle that resist mad cow disease.

They hope the cattle can be the source of herds that canprovide dairy products, gelatin and other products free of thebrain-destroying disease, also known as bovine spongiformencephalopathy or BSE.

Writing in the journal Nature Biotechnology, theresearchers said their cattle were healthy at the age of 20months, and sperm from the males made normal embryos that wereused to impregnate cows, although it is not certain yet thatthey could breed normally.

The cattle lack the nervous system prions, a type ofprotein, that cause BSE and other related diseases such asscrapie in sheep and Creutzfeldt-Jakob disease, known as CJD,in humans, the researchers said.

"(Prion-protein-negative) cattle could be a preferredsource of a wide variety of bovine-derived products that havebeen extensively used in biotechnology, such as milk, gelatin,collagen, serum and plasma," they wrote in their report.

Yoshimi Kuroiwa of Kirin Brewery Co. in Tokyo, Japan andcolleagues made the cattle, known as knockouts because aspecific gene has been "knocked" out of them, using a methodthey call gene targeting.

"By knocking out the prion protein gene and producinghealthy calves, our team has successfully demonstrated thatnormal cellular prion protein is not necessary for the normaldevelopment and survival of cattle. The cows are now nearly 2years old and are completely healthy," said James Robl ofHematech, a South Dakota subsidiary of Kirin.

"We anticipate that prion protein-free cows will be usefulmodels to study prion disease processes in both animals andhumans," Robl, an expert in cloning technology, said in astatement.

Misfolded prion proteins are blamed for BSE and other,similar brain diseases. It is known that certain geneticvariations make animals more susceptible to the diseases.

BSE swept through British herds in the 1980s and peoplebegan developing an odd, early-onset form of CJD called variantCJD or vCJD a few years later. CJD normally affects one in amillion people globally, usually the elderly, as it has a longincubation period.

There is no cure and it is always fatal.

As of November 2006, 200 vCJD patients were reportedworldwide, including 164 patients in Britain, 21 in France, 4in the Republic of Ireland, 3 in the United States, 2 in theNetherlands and 1 each in Canada, Italy, Japan, Portugal, SaudiArabia and Spain.

The disease may have first started to infect cattle whenthey were fed improperly processed remains of sheep, possiblysheep infected with scrapie. Although people are not known tohave ever caught scrapie from eating sheep, BSE can betransmitted to humans.

BSE occasionally occurs in cattle outside Britain althoughit is now rare.