GTC Biotherapeutics developed Atryn (antithrombin alfa) by altering the genes of goats so they would produce milk rich in antithrombin, a protein that in humans acts as a natural blood thinner. Atryn may be used by patients vulnerable to life-threatening blood clots. The preliminary FDA evaluations found the drug effective and safe and the FDA"s Blood Products Advisory Board will decide on the application Jan 8.