New York: Some athletes might have genes that outwit doping test, researchers say.

According to a new study, 17 out of 55 normal and healthy individuals injected with testosterone tested negative and their urine seemed fine with no excess of the hormone.

It was, researchers were quoted as saying by the New York Times, a striking demonstration of a genetic discovery. Those 17 men can build muscles with testosterone, they respond normally to the hormone, but they are missing both copies of a gene used to convert the testosterone into a form that dissolves in urine.

The result is that they may be able to take testosterone with impunity.

The gene deletion is especially common in Asian men, the paper quoted Jenny Jakobsson Schulze, a molecular geneticist at the Karolinska University Hospital in Stockholm as saying.

Schulze is the first author of the testosterone study, published recently in The Journal of Clinical Endocrinology and Metabolism.

Schulze, the paper said, learned from an earlier study that about two-thirds of Asian men are missing both copies of the gene, as are nearly 10 per cent of Caucasians. The prevalence in other groups is not known.

Doping researchers, however, said the study raised many questions.

"It s disturbing," said Don Catlin, the chief executive of Anti-Doping Research, a non-profit group in Los Angeles.

"Basically, you have a licence to cheat," he was quoted as saying by the newspaper.

The passport, favoured by the World Anti-Doping Agency, is a record of all of an athlete's screening tests and would detect results that vary from the athlete's baseline values  but it would not include gene testing and therefore may not detect those athletes lacking this gene.

But nothing will happen soon, and certainly not in time for the Beijing Olympics in August.

Testosterone and substances that act like it are the most frequently detected drugs in screening tests of athletes. The anti-doping agency reported that these drugs have been implicated in 43 per cent of its positive doping tests.

Researchers, the study says, have long known that some men, Asians in particular, seemed to be able to take the drugs without getting caught, although no one had identified the cause of the phenomenon.

Without gene testing, there is no way to know whether any athlete has exploited this doping loophole, but Dr Catlin says he suspects some athletes discovered their invulnerability by accident and took advantage of it.

Men with the gene deletion still metabolize testosterone, Schulze says. But, she adds, she does not know where the hormone goes. "We have no idea," she says. "That's what we're trying to find out."

The gene in question adds a chemical, glucuronide, to testosterone. That converts it from a substance that dissolves in oil into one that dissolves in water and urine.

The testosterone screening test looks for testosterone and another substance, epitestosterone, that is produced in parallel to testosterone but does not have its effects.

Source : PTI