World Athletics’ mandatory genetic test for women athletes is misguided. I should know – I discovered the relevant gene in 1990

World Athletics president Sebastian Coe recently announced a new rule for women athletes, requiring mandatory genetic tests to verify their biological sex.

This test must be done if athletes wish to compete in September’s World Athletics Championships in Tokyo.

World Athletics has said all athletes competing as women must have an SRY gene test to identify whether a male Y chromosome is present.

Any athlete whose test shows the presence of the SRY gene will be banned from competing in the women’s category in elite events.

Coe said the decision was made to ensure “the integrity of women’s sport” with World Athletics asserting:

The SRY gene is a reliable proxy for determining biological sex.

I argue the science does not support this overly simplistic assertion.

I should know, because I discovered the SRY gene on the human Y chromosome in 1990. For 35 years I have been researching it and other genes required for testis development.

A brief primer on testes and ovary development

If a human embryo has XY chromosomes, then at six weeks of development the SRY gene on the Y chromosome triggers a cascade of events involving some 30 different genes that lead to the formation of testes.

In simplest terms, the testes then produce hormones including testosterone, leading to male development.

However, if an embryo has XX chromosomes, a whole different group of genes come into play, ovaries form and the hormones produced result in a female.

We know making testes or ovaries requires a complex network of many interacting genes and proteins.

Some genes promote testis development while others promote ovary development.

Other genes either suppress ovary formation or antagonise testis formation.

Even once ovaries or testes are fully formed, we require other genes to maintain them. These genes don’t always function as expected, affecting the development of these organs.

How does this relate to sex testing of elite women athletes?

Changes or variants in the many genes that regulate the development of a testis or ovary can result in sex reversal or a non-functioning testis or ovary.

What do I mean by this?

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.

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 Olympic Games in Atlanta, eight of 3,387 women athletes had positive test results for a Y chromosome. Of these, seven were resistant to testosterone.

The SRY test isn’t cut-and-dried

World Athletics asserts the SRY gene is a reliable proxy for determining biological sex. But biological sex is much more complex, with chromosomal, gonadal (testis/ovary), hormonal and secondary sex characteristics all playing a role.

Using SRY to establish biological sex is wrong because all it tells you is whether or not the gene is present.

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.

Other problems with the SRY testing process

World Athletics is recommending all women athletes take a cheek swab or blood sample to test for the presence of SRY.

Normally, the sample would be sent to a lab that would extract DNA and look for the presence of the SRY gene.

This may be easy enough in wealthy countries, but what is going to happen in poorer nations without these facilities?

It is worth noting these tests are sensitive. 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.

No guidance is given on how to conduct the test to reduce the risk of false 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.

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.

I, along with many other experts, persuaded the International Olympic Committee to drop the use of SRY for sex testing for the 2000 Sydney Olympics.

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

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