Good question. Alejandro Lucia, a reputed scientist with lots of studies on genes, sport performance, health and longevity, said me recently that he has no idea how gene doping could be done... I get surprised at first but it makes sense as sport performance is the result of the interaction of lots of genes with ambient influences (including epigenetics), while no single gene can do directly influence any physiological function. In fact, the current literature on the influence of some polymorphisms on performance does not support this possibility.

There is a paper by Pokrywka et al. from 2013 about this topic.

http://biolsport.com/fulltxt.php?ICID=1059606

I think that in near future is possible (genetic doping in humans).

Wang et al. (2004) demonstrated that mouse genetically modified overexpressing specific gene (PPAR-delta) alters skeletal muscle phenotype, increase endurance performance and resistance to obesity.

https://www.researchgate.net/publication/8382735_Regulation_of_muscle_fiber_type_and_running_endurance_by_PPARdelta?ev=srch_pub

I agree with Professor Daniel that polymorphism studies is limited. However, i belive that overexpression of key genes can alter significantly sport performance (e.g marathon).

I don´t know about side effects of gene therapy (overexpression) in human body.

Article Regulation of Muscle Fiber Type and Running Endurance by PPARδ

Good point Alex. Let me comment however that overexpression would be an advantage to one or few factors (not a complete physiological function) while top-level performance is the result of the non-linear interaction (complexity) of lots of factors. For example, one sprinter could improve his maximum strength with genetic doping but what about the risk of tendon rupture?

Very good question. As a historian of sport I cannot say much about the possible future developments in gene doping. But comparing the debate today with past debates on doping, high-altitude training etc. shows that the initial worst-case scenarios doesn't always come true, thankfully. It partly depends on how well international organizations of sport manage the situation. As for sport's biggest battle, I'd say it is to balance commercialization. Economy is the most severe threat to the uncertainty of sport. Things are done in this area, like in football with the Financial Fair Play regulations. How well it works remains to be seen, though.

What wont be possible in the future? It depends how far in the future you want to look. There was a recent article in The Lancet 2013 about drugs in sport that covered slightly on gene doping by Prof Chris Cooper (Uni Essex). Might be worth a read.

Thanks for the replies to date. I have no doubt that there are athletes who are interested in this, and monitoring scientific progress in this field. IOC medical commission chairman Arne Ljungqvist said that "there seems to be mental readiness to take it [gene doping] on once it is available in some sort of safe way," As pointed out by Alex, one of the key issues is safety. People have died from gene therapy when it first emerged, but new adenoviruses seem to be safer and provoking smaller immunological reactions. The other key issue, as pointed out by Daniel, is which gene to target? Many of the current diseases being targeted by gene therapy can be linked more closely to one 'faulty' gene (e.g., Glybera - can't break down triglycerides,). However, sporting performance is obviously more complicated/multi-faceted. Until there are some genes that can be more strongly linked with performance, it is difficult to see gene therapy taking off.