A genetic peculiarity could help devious athletes beat drug tests and could unfairly ruin players who are honest. The genetic variation affects an enzyme that processes testosterone. Although testosterone is primarily known as a male sex hormone, it is made in the body by both men and women.
To differentiate 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 by-product of testosterone. Testosterone abuse is usually assessed by the urinary testosterone/epitestosterone (T/E) ratio. Levels above 4.0 are considered suspicious.
The large variation in TG excretion and its strong association with a deletion polymorphism in the uridine diphospho-glucuronosyl transferase (UGT) 2B17 gene challenge the accuracy of the T/E ratio test. The enzyme UGT2B17 adds a chemical to testosterone to prepare it for secretion in the urine. Scientists in Sweden found that some people completely lack the gene that produces UGT2B17, and this difference can affect results of doping tests.
About 15 percent of 145 healthy male volunteers lacked the enzyme entirely; 52 percent of the men 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 injection of testosterone. The researchers monitored production of TG in the men's urine for 15 days after the injection. About 40 percent of the subjects who lacked the enzyme never secreted enough TG to raise suspicions in the standard test even after their hormone injection. …