Sweeney focuses on muscle growth, but other scientists have recently developed drugs that boost endurance. Last month, scientists at the Salk Institute for Biological Studies in La Jolla, Calif., identified two new endurance-building compounds. One, which increases the activity of a muscle lipoprotein called PPARdelta, allowed mice to run 68 percent longer and 70 percent farther after a four-week training stint. The other activates a muscle enzyme called AMPK, which is typically produced after exercise. Mice given that drug did not even have to train to increase their endurance. Compared with sedentary mice that were not given the drug, AMPK-doped mice ran 23 percent longer and 44 percent farther.
Erythropoietin (EPO), a hormone that boosts red blood cell counts and therefore increases blood oxygen levels, also boosts endurance. It is currently available as an injectable hormone, and although WADA has a test that detects EPO administered in this form, EPO delivered via gene therapy could go unnoticed. England-based pharmaceutical company Oxford BioMedica is currently developing such a therapy: Called Repoxygen, it delivers the EPO gene into DNA, where it becomes activated whenever the body detects low blood oxygen levels. In 2006 German track coach Thomas Springstein, on trial for trying to supply underage female athletes steroids, was also found to have attempted to buy Repoxygen for his athletes even though it was still in development.
The U.S. Food and Drug Administration has yet to approve any gene therapies, but athletes do not seem to care. "No matter what I say to them about [gene therapy] being dangerous and experimental," Sweeney explains, "it doesn't slow them down—they just keep pushing, saying, 'I want to be the guinea pig, I want to the first person you try this on.' I kindly just say, 'look, it's not possible, I can't do it.'"
The question remains as to how, exactly, WADA will be able to detect gene doping in athletes who get their hands on such therapies. The agency is funding a project to develop ways of detecting molecules that interact with myostatin, based on the fear that myostatin inhibitors could soon become a popular doping choice. In addition, the agency is looking into developing a kit that could detect traces of gene transfer vehicles called plasmids in blood, which would help them catch gene dopers who use plasmid-based approaches.
But because some therapies would not make it into the bloodstream at all—they could be injected directly into the muscles, for example—these tests would, in some cases, be fruitless. "I personally think I can prove to [WADA], if they really want the challenge, that I can dope dogs and they will never figure out which dogs were doped unless they take tissue biopsies," Sweeney says.
It may, however, be possible to detect gene doping in other ways. Theodore Friedmann, a gene therapy specialist at the University of California, San Diego, and chairman of WADA's gene-doping panel, believes it will one day be possible to detect gene doping by looking for its more overarching impacts on the body and particular tissues. WADA is currently developing what it calls a "passport" program to build long-term blood and urine profiles of elite athletes based on the idea that if athletes are totally clean, their blood will look pretty much the same over time. If they are not, various parameters in their blood will be affected by the doping, thereby fluctuating—and thus be detectable—over time.