Scientists Slam World Athletics’ Mandatory SRY Testing for Female Athletes

World Athletics has announced that starting this September, any athlete competing in the women’s category must undergo a mandatory genetic test, specifically, a once-in-a-career check for the presence of the SRY gene, found on the Y chromosome.

The policy, which comes into effect ahead of the World Championships in Tokyo, is being framed by president Sebastian Coe as a move to “protect the integrity of the female category.” If the SRY gene is detected, a signal, in their eyes, of male biological sex, the athlete is banned from elite female competition.

But to the man who actually discovered the gene, this policy doesn’t just oversimplify the science, it gets it flat-out wrong.

“I should know, because I discovered the SRY gene on the human Y chromosome in 1990,” writes Professor Andrew Sinclair, deputy director of the Murdoch Children’s Research Institute, in a widely shared op-ed. “For 35 years I have been researching it and other genes required for testis development.”

Why the science isn’t so simple

The presence of the SRY gene typically initiates the development of testes in an embryo, triggering a cascade of hormones, notably testosterone, that lead to male sexual development. But as Sinclair, who has spent decades studying sex determination, explains, it’s not a simple on/off switch.

“We know making testes or ovaries requires a complex network of many interacting genes and proteins,” he writes. “Some genes promote testis development while others promote ovary development. Other genes either suppress ovary formation or antagonise testis formation.”

In some individuals, the SRY gene is present but non-functional. In others, the body is resistant to testosterone, meaning even if internal testes are present, the testosterone can’t be used. These are people who may live their entire lives as women, with female genitalia and secondary sex characteristics, and no awareness that they carry a Y chromosome until flagged by a genetic test.

“If there is a change in the SRY gene so it does not function as usual, then a person can fail to develop testes and be biologically female. Yet they carry XY chromosomes and under the World Athletics tests they would be excluded from competition,” Sinclair writes.

Other XY individuals may have a functioning SRY gene but are female, with breasts and female genitalia, for example, but have internal testes.

“Importantly, the cells of these people are physically unable to respond to the testosterone produced by these testes. Yet, they would receive positive SRY tests and be excluded from competition.”

At the 1996 Atlanta Olympics, eight of 3,387 women athletes had positive test results for a Y chromosome. “Of these, seven were resistant to testosterone.”

Those tests were later scrapped by the International Olympic Committee, and Sinclair was one of many experts who helped persuade the IOC to abandon SRY-based testing ahead of the 2000 Sydney Olympics.

“It is therefore very surprising that, 25 years later, there is a misguided effort to bring this test back.”

High risk, low reward

World Athletics says the test will be administered through a cheek swab or dried blood spot, then analyzed in a lab to detect the presence of the SRY gene. But Sinclair says this oversimplifies both the logistical hurdles and scientific risks.

“If a male lab technician conducts the test he can inadvertently contaminate it with a single skin cell and produce a false positive SRY result.”

He also points out that no guidance has been given for preventing contamination, and no mention has been made of providing genetic counselling, even though that is considered essential when dealing with sensitive results.

“Nor does World Athletics recognise the impacts a positive test result would have on a person, which can be more profound than exclusion from sport alone,” he writes. “There was no mention from World Athletics that appropriate genetic counselling should be provided, which is considered necessary prior to genetic testing and challenging to access in many lower- and middle-income countries.”

A broader backdrop

This is only the latest in a string of increasingly exclusionary moves by World Athletics. In 2023, the organization banned transgender women who experienced male puberty from competing in the female category.

Intersex athletes with Differences of Sexual Development (DSD), such as Caster Semenya, have already been excluded unless they lower their testosterone to 2.5 nmol/L, a rule that has been challenged in multiple courts and human rights tribunals.

Now, the addition of a genetic test adds a new layer of scrutiny, one that risks excluding intersex women who live and identify as women, but may carry an SRY gene that says otherwise.

“Using SRY to establish biological sex is wrong because all it tells you is whether or not the gene is present,” Sinclair writes. “It does not tell you how SRY is functioning, whether a testis has formed, whether testosterone is produced and, if so, whether it can be used by the body.”

“Given all the problems outlined above, the SRY gene should not be used to exclude women athletes from competition.”