A genetic quirk could help cheating athletes beat drug tests and could unfairly taint fair players.
The genetic variation affects an enzyme that processes testosterone. Testosterone is naturally made in the body by both men and women, although it is primarily known as a male sex hormone. In order to distinguish between naturally present hormone and synthetic testosterone from steroid use, drug tests measure a ratio of two chemicals found in urine.
One chemical, epitestosterone glucuronide (EG), is made at a constant level in the body, regardless of testosterone levels. The other chemical, testosterone glucuronide (TG), is a testosterone by-product.
Testers measure the ratio of TG to EG. Any amount of TG greater than four times the level of EG is considered a red flag for doping.
An enzyme called UGT2B17 adds a chemical to testosterone to prepare it for secretion in the urine. A group of scientists in Sweden found that some people completely lack the gene that produces UGT2B17, and this difference could affect results of doping tests.
About 15 percent of 145 healthy male volunteers lacked the enzyme entirely. Just over half the volunteers (52 percent) had one copy of the gene, and one-third of the men had two copies.
Some of the men were selected to get a single shot of testosterone. The researchers monitored production of TG in the men’s urine for 15 days after the injection.
About 40 percent of the people who lacked the enzyme never secreted enough TG to raise warning flags in the standard test, even after getting a hormone shot, the team reports online in the Journal of Clinical Endocrinology & Metabolism.
“There is a risk that many such individuals have escaped detection,” says Anders Rane of the Karolinska Institute in Stockholm, Sweden, and one of the authors of the study.
On the other hand, 14 percent of people with two copies of the gene made so much TG that the current test would flag them as cheaters even before they got testosterone shots.
“Have there been any false positives or false negatives among the winners of various games? We don’t know, but in all probability it could have happened,” Rane says.
About two-thirds of the East Asians in the study lacked the enzyme compared with fewer than 10 percent of the Swedish people tested. Different ethnic groups may use different enzymes to process testosterone, says Glenn Cunningham, a clinical endocrinologist at Baylor College of Medicine in Houston.
There is no apparent athletic advantage or disadvantage associated with lacking the enzyme, Rane says. He suggests combining genetic testing with periodic urine testing that tracks individual athletes over time.
“I think that they’ve made a strong case for doing the genetic testing in addition to” current testing methods, Cunningham says.
Because of the expense of genetic testing, “this is not something that is feasible to do for large numbers of people,” he says. Such tests will likely be used in elite amateur and professional sports, but “I just don’t know if it will be available for college and high school athletes.”