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

Doping researchers said the study raised questions about what to do next.

“It’s disturbing,” said Dr. Don Catlin, the chief executive of Anti-Doping Research, a nonprofit group in Los Angeles. “Basically, you have a license to cheat.”

Should athletes give DNA samples for scientists to analyze as genes like the testosterone-metabolizing one are found to be important? Or would another approach, the so-called athlete’s passport, be sufficient? The passport, favored 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 antidoping agency reported that these drugs have been implicated in 43 percent of its positive doping tests.

Researchers 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 athletes have exploited this doping loophole, but Dr. Catlin says he suspects some athletes discovered their invulnerability by accident and took advantage of it.