The anti-doping laboratory at the 2012 Olympics will work around the clock to test over half the competitors for drugs. Its task in future years, however, may become more challenging, with a new threat to the integrity of competitive sport on the horizon: gene doping.
Gene doping has been banned by the World Anti-Doping Agency since 2003, though there is currently no evidence that it has been attempted. An article in the June issue of the Society of Biology's magazine, The Biologist, discusses the potential threat of gene doping and the challenges of detecting it.
The article comes from Dr Cristiana Velloso, a research associate at the Centre for Human and Aerospace Physiological Sciences, King's College London. She says: "Gene doping is enhancing athlete performance using cells, genes, or genetic material, or altering the expression of genes. There are huge technical challenges to gene doping, but current research suggests it has great potential to enhance athlete performance.
"Gene doping in animals has already produced fascinating results. Perhaps the most remarkable transgenic animal so far is the marathon mouse which is genetically modified so a specific enzyme in skeletal muscles is present in higher quantities. These animals can run virtually non-stop for distances of 5km, compared to an average of 0.2km observed in wild type mice."
In most transgenic animals, however, the altered gene is introduced in the fertilised egg, whereas gene doping is likely to involve the manipulation of genes by adult athletes, which is more difficult to achieve.
Another challenge for gene therapy in large animals such as humans is producing vectors in sufficient purity and quantity to provide adequate dosage. However, the body may have to express the genes at a far lower level to produce small gains in performance, relative to achieving therapeutic dosages for people with genetic diseases. Even if only a small amount of muscle expressed the gene this could deliver enough improvement to overcome the very small differences often seen among competitors.
The question of major concern to the anti-doping authorities is whether gene doping would be detectable. Unlike most drugs, which are chemical compounds that do not occur naturally in the body, gene doping would result in the production of biological molecules. If the new gene was only expressed in a small area, such as specific leg muscles, then detection will be extremely difficult. A tissue biopsy may be the only way to detect it, but this would be an extremely invasive technique for a routine test.
What we don't yet know is how gene doping would affect expression of other genes in the body. It could switch on other genes which cause particular compounds to be secreted into the blood stream. Potentially, this could be a way to detect gene doping with blood samples.
Dr Velloso says: "Ultimately, the health of the athlete, in addition to fairness in competition, is the goal of anti-doping authorities. The potential for gene doping is real, but so far the results, or indeed the safety, are in no way guaranteed.
"The lack of efficient gene delivery and expression, and the unpredictability of gene expression compared to drugs - which can be started, stopped and dosed precisely - suggest that genetically engineered athletes are still a distant reality.
"However, the time may not be far off when someone's genes could be used as an additional tool to identify performance potential, or shape training, nutrition and drugging regimens. The counterpoint is that this advancing knowledge will also provide new weapons in the fight against doping, whether genetic or not."
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