Wednesday, April 9, 2008

Genes to Blame for Positive Steroid Testing?

It’s always disappointing when an inspiring, encouraging and not to mention rippling athlete is tested positive for ‘stimulants’. But at this year’s controversial Beijing Olympics, athletes may just have a viable excuse for that embarrassing urine test.
A study just published in the JOURNAL OF CLINICAL ENDOCRINOLOGY & amp by Jenny Jakobsson Schulze suggests that the genetic makeup of an athlete could allow the guilty to escape detection or even convict the innocent. The standard doping test for testosterone abuse relies on measuring the ratio of two chemicals found in the urine: testosterone glucuronide (TG) and epitestosterone glucuronide (EG). Any ratio above 4TG:1EG is considered suspicious.
However, the production of TG is controlled by an enzyme that is encoded by a gene called UGT2B17 which can come in two varieties: working or not-working. An individual can therefore either have none, one or two working copies of this gene (inherits one copy from each parent). Dr Schulze hypothesized that these genetic variations would affect the results when testing a group of healthy male volunteers that had their DNA investigated and then injected with a single 360mg shot of testosterone.
The results were as she had expected. Nearly half of the men who carried no functional copies of UGT2B17 would have gone undetected in the standard doping test. By contrast, 14% of those with two functional copies of the gene were over the detection threshold before they had even received the injection.
From these results it is estimated that this would give a false-positive testing rate of 9% in a random population of young men. So, maybe at this year’s Olympics when the suspiciously hairy track runner flatly denies testosterone abuse after a positive doping test they may just be telling the truth.

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