It has taken scientists almost 50 years to cure rare diseases through gene therapy. The risks are still great but the field is developing fast, bringing hope to those with untreatable conditions. Now there are growing concerns that athletes will abuse this pioneering technology. Tim Franks speaks to David Epstein, an American journalist and sports enthusiast, who has been investigating the issue of gene doping. David reveals how athletes have 'inundated' researchers with requests to improve their abilities through genetic manipulation.

Tim also speaks to French geneticist Philippe Moullier, who was left in shock after a group of former Tour de France cyclists visited his lab. They wanted to learn whether the technology he developed to cure children with a rare muscle disease could be used to enhance sporting performance. Although the World Anti-Doping Agency banned the practice in 2003 there is still no test which can detect gene doping. Athletes do not have to look hard if they want to experiment. Moullier tells Tim how it’s possible to buy genes on the internet and grow them at home. Tim Franks finds out just how easy it is.

(Photo: A genetic researcher carries blood samples to have their DNA tested at his Laboratory in the Lebanese-American University. Credit: Joseph Eid/AFP/Getty Images)