The European Medicines Agency’s Committee for Medicinal Products for Human Use has turned down an application by US firm GTC Biotherapeutics that could have made it the first to market a drug produced in a genetically-modified animal.

The CHMP rejected GTC’s application for ATryn (antithrombin alfa), a protein derived from the milk of genetically-engineered goats that has been developed to treat patients with antithrombin deficiency, an inherited inability to produce the protein that is characterised by the formation of potentially life-threatening clots in the blood vessels of the legs.

GTC had applied to use ATryn to treat sufferers of the condition who undergo major surgery and other high-risk situations as an alternative to anticoagulants and human blood plasma. But the CHMP said it had not tested the treatment in enough patients to demonstrate safety and efficacy.

GTC said it would appeal the decision, and press ahead with plans to file for approval of ATryn in the USA next year.

Antithrombin alfa is currently extracted from donated blood, and GTC's transgenic version would not only reduce the cost of manufacture but also increase the supplies available to patients.

The company’s shares fell 40% to close at $1.35 yesterday.