Go-ahead for drug from GM goats

A new drug based on a human protein extracted from the milk of genetically altered goats has been approved for use by European regulators. Atryn, given the go-ahead by the European Medicines Agency (EMEA) last week, is the first treatment of its kind to be approved for clinical use. The drug was developed by US firm GTC Biotherapeutics, for treating patients affected by a rare  inherited blood clotting disorder. The EMEA has now reversed its earlier decision not to licence the treatment after taking further expert advice.

Atryn contains the human version of antithrombin (AT), a blood protein that blocks the formation of clots. People born with congenital antithrombin deficiency have low levels of the protein, which can lead to an increased risk of abnormal blood clots forming - particularly in 'high-risk' situations, such as when patients are undergoing surgery. Infusions of Atryn would temporarily control the disorder, say its manufacturers.

The protein is made by inserting the human AT gene into goat embryos, creating genetically altered animals that act as living drug factories. To ensure the drug is produced in the correct place, the AT gene is hooked up with the 'control switch' for casein, a protein exclusively present in milk. Therapeutic AT protein is currently obtained by purifying it from human blood. GTC says its method is much more efficient - just one goat can produce the equivalent amount of protein to 90,000 blood collections, the company claims. Another advantage of the approach is that it bypasses contamination concerns with products derived from human blood plasma products. 'This is a technology which has the potential to dramatically change the way in which expensive biological drugs are developed for the commercial marketplace', Tom Newberry of GTC told the BBC News website.

The EMEA had originally turned down a licence application for Atryn in February 2006, saying that GTC had not presented enough scientific evidence to show that the drug's benefits outweighed its risks. But after meeting with experts and re-examining the application data, the EMEA has now approved Atryn's use in Europe, subject to final approval later this year. Commenting on the decision, Professor Isobel Walker, consultant haematologist at Glasgow Royal Infirmary, said: 'It is a good day for European patients with congenital anti-thrombin deficiency and for their physicians'.