The U.S. Food and Drug Administration approved the first drug produced by genetically engineered livestock on February 6.

The drug, called Atryn® or recombinant antithrombin, will be used to treat patients suffering from hereditary antithrombin deficiency (also known as ATIII deficiency), a genetic disorder in which patients have either low levels of the antithrombin protein or produce dysfunctional variants of antithrombin. The end result is the same – excessive blood clotting.

Thrombin is a blood protein that promotes clotting; the antithrombin III protein, as its name suggests, inactivates thrombin and promotes the dissolution of blood clots.

People with hereditary antithrombin deficiency are at risk for a thromboembolism, when a clot forms in a blood vessel and then breaks loose and is carried by the blood stream to another part of the body. A migrating clot can lodge in blood vessels in the lungs (pulmonary embolism) or brain (stroke), with terrible and often fatal consequences. More than 200,000 people worldwide are estimated to suffer from the disease.

Atryn will be used to prevent thromboembolisms in hereditary antithrombin deficient patients during surgery or childbirth. Atryn will not be used to treat thromboembolisms.

What makes Atryn unique is the way in which it is produced. Scientists took the human antithrombin gene coding region DNA and placed it downstream of a promoter that drives gene expression in goat’s milk (milk protein promoter + protein coding DNA). This DNA is then inserted into the genome of a goat egg, the egg is implanted into a surrogate mother, allowed to develop, and then born – a transgenic goat. The transgenic goat is then mated with a nontransgenic goat to produce transgenic offspring. Scientists can purify Atryn from goat’s milk at lower cost and in greater quantities than extracting antithrombin from donated blood or producing it in cultured cells. Need more Atryn? Breed more goats.

Generating transgenic animals is standard practice in research labs – I generated a strain of transgenic zebrafish as part of my postdoctoral work, and I’m hardly a scientific pioneer. Recombinant insulin (such as Lilly’s Humulin), produced by transgenic E. coli bacteria, is used to treat diabetes, but Atryn is the first FDA-approved drug produced from transgenic livestock, whose sole function is to produce medicine.

The European Union approved Atryn in August 2006.

This new type of drug production raises some questions: Could the health of the animal affect protein production? Could a viral or bacterial infection modify the protein, altering its efficacy? Could transgenic goat meat enter the food supply? Could a transgenic goat escape and breed with normal goats? What do you think?