Because the genes are foreign material, people's immune system may reject the gene and destroy it, causing the operation to fail. If the operation is done poorly enough, the immune system's response may be severe enough to kill the patient (i.e., shutting down organs, including the brain). Also, gene therapy does not last for a long period of time, so multiple operations are required until the therapy actually works and cures the patient.

In 2006, a German track and field coach tried to allow genetic juicing to his athletes for the 2008 Olympics in China, but was caught before anyone could be treated. In an attempt to stop genetic manipulation in athletics, the World Anti-Doping Agenc

http://www.scientificamerican.com/blog/post.cfm?id=athlete-alert-is-genetic-juicing-se-2010-02-04http://en.wikipedia.org/wiki/Gene_therapyhttp://en.wikipedia.org/wiki/Jesse_Gelsinger