LONDON • Athletes at the Rio Olympic Games will be tested for the first time for "gene doping", a highly sophisticated cheating technique that improves performance by altering competitors' DNA.

Rather than injecting performance-enhancing drugs, gene doping seeks to tweak cells so that they produce the substances naturally. This makes it undetectable using standard tests.

However, scientists have said that a test has been developed to spot the gene cheats, and it will be applied for the first time at the Games which begin next week.

"We feel there is a great risk that these novel technologies will be used," Carl Sundberg, an exercise physiologist from the Karolinska Institute in Sweden, told the European Science Open Forum in Manchester.

Gene doping is based on the science of gene therapy, in which bad genes are removed and replaced with healthy ones.

Hundreds of trials are under way to develop the technique, which harnesses viruses to snip out specific genes and insert therapeutic versions instead. It has already shown promise in certain rare immune disorders and in treating particular kinds of blindness.

Sundberg said that doping officials were concerned it could also be used to supplement erythropoietin (EPO), a hormone naturally produced in the kidneys that can boost endurance.

At present, athletes who inject it can be caught, but gene therapy may provide a way for them to manipulate their own body to produce it in greater volume and in an undetectable fashion.

While it is unlikely that any athletes would be able to take advantage of this method without the backing of major laboratories, the science is advancing rapidly and it is anticipated that many more clinics will soon be able to carry out both gene therapy and gene doping.

"If gene therapy is approved for, say, diabetes, it will spread to many clinics. There are already more than 1,000 clinical trials under way. So quite a few research groups know what to do," Sundberg said.

The new test will look for the viral vectors used to snip out the DNA. It will also look at the DNA itself, to see if it matches the messy DNA you would expect, or has the signature of being engineered.

Sundberg said he hoped that its introduction will be a deterrent to future cheats but did not rule out the possibility that an athlete might be caught at the forthcoming Games.

Meanwhile, the International Olympic Committee (IOC) is facing issues after its decision not to impose a blanket ban on Russia, and giving individual federations the authority to rule on which Russian athletes would be permitted to compete in Rio.

A number of sports made announcements on Tuesday regarding the eligibility of Russian athletes, with glaring differences from how each international federation interpreted the IOC's criteria.

The world rowing federation, Fisa, was always expected to take a tough line and it has rejected 22 of the 28 rowers that Russia entered for the Games.

By contrast, the International Judo Federation, of which Russian President Vladimir Putin is an honorary president, has said all 11 of Russia's proposed team should be considered eligible.

Badminton and shooting also said that they would not be ruling out any Russians.

The International Canoe Federation, which last month banned Belarus and Romania over doping, ruled five sprint canoeists - including London 2012 champion Alexander Dyachenko - ineligible but stopped short of issuing a federation-wide ban.

Archery, equestrianism and tennis have confirmed the eligibility of Russian entries, while the Russian media reported that the seven-strong sailing team are in Rio and will be allowed to compete.

Russia initially selected 387 athletes for Rio but has already lost at least 105 of those, 67 from athletics which has been banned en masse by the International Association of Athletics Federations (IAAF), and the remainder via the individual vetting process that each sport is undertaking.

THE TIMES, LONDON