How would you catch a gene-doping athlete? Currently, there are no reliable gene-doping tests, but they're being designed. Besides, fancy tests may not be needed. At the 1998 Tour de France, a car inspection was enough [source: Rosenthal]. Police busted the Festina team's masseur with drugs, including erythropoietin, in his car [source: Abt]. The team's entourage was investigated, and the team was expelled before the race's end [source: Abt].
For inconclusive evidence, you could examine the athlete's body. The effects of gene doping in healthy humans aren't known. But healthy animals have suffered drastic side effects, from fatal anemia, caused by an immune reaction, to blood vessels clogged with overproduced blood cells [source: Reynolds]. With no other medical explanation, an athlete's sudden sickness could signal a side effect of gene doping, but it's a stretch.
In addition, any gene an athlete injects will make a protein. You could test for the protein. But the transgenic protein, or the protein made from the transferred gene, would need to show up in fluids like blood, urine or saliva, and it would need to be distinguishable from the natural protein. That's easier with some transgenic proteins than others.
You could look for an immune reaction. When athletes inject genes, they put foreign material -- a virus carrying the gene or pieces of nonhuman DNA attached to the gene -- into their bodies. In gene therapy trials, humans have made rafts of antibodies against some viruses, which have stayed in blood for up to six months [source: Manno 2003]. But suppressing the immune system or using a specially engineered virus would foil this test. And you'd need to periodically test athletes' immune reactions to many viruses [source: Baoutina].
Could you find the injected DNA? Maybe. The best place to look would be in muscle, where the DNA probably would be injected, but so far, that test is impossible. The athlete would need to tell you the muscle she or he injected and let you biopsy, which is unlikely [source: Baoutina]. If an athlete delivers his or her genes by virus, your chances are better. You could look in bodily fluids for viral DNA. Of course, how long the viral DNA stays depends on the virus, the person, the injection site and where you look.
Researchers are trying to image injected genes and transgenic proteins inside an athlete's body. This test, unlike a urine test, could find a gene or protein inside muscle. So far, the imaging requires radioactive tracers. While the tracers are safe, athletes may not want the tests routinely [source: Baoutina].
Finally, you could catch a gene-doper with body "signatures." Adding a gene isn't like flipping a switch; it's like pushing a domino in a line. It will touch off other changes: genes turned on or off, proteins booming and busting, cells building and dismantling things. The changes may leave clues in blood, urine or saliva. Scientists are injecting genes into mice and looking for testable changes. The hope is to build a chip to detect them [source: Baoutina]. "This seems to be a very promising approach," says Friedmann. Of course, testers would need ongoing samples to know athletes' normal ranges [source: Baoutina].
If you don't have the technology to catch a gene-doping athlete, policies are on your side. At the Beijing Olympics in 2008, the top five finishers in each event, plus two more athletes, gave blood and urine samples [source: Macur]. The International Olympic Committee keeps the samples for eight years for retesting [source: The New York Times].
Keep reading for more stories on gene therapy and performance-enhancing drugs.