Chimerism, Intersex Conditions, and Sports Eligibility

[Query]

The IOC is likely to rule that transgender and intersex athletes cannot compete as female. If I understand correctly, it is already true in some countries under some sport rules - including to some extent, in the USA, for some sports.

Some forms of intersex involve an individual (a chimera) having more than one set of chromosomes. For example, you might have some cells that are female, and some that are male.

I've been reading about chimerism
https://en.wikipedia.org/wiki/Chimera_(genetics)
(Though I admit Wikipedia is not a well respected scholarly source.)

Apparently human chimerism induced by transplants or large transfusions is more common than previously thought - though I'm not sure how common.

It appears that if a female receives a transplant of an organ from a male, or even a large transfusion of blood from a male, she may retain cells in her body that have male chromosomes. She could then be disqualified for competition as a female.

So - if you are a female who wishes to compete in sports as a female, perhaps you should be careful of the gender you receive any transplants or transfusions from.

This is probably something that very few athletes have considered. I wonder if there are any competitive athletes who have done this without intending to - and if so, how common it is.

If so, it shows what an incredible mess such rules could create.

 

[FethryDuck]

You seem to have a talent for funny topics


Imho it makes sense that xy-chromosome persons (commonly regarded as "biological men") are not allowed to compete in the same "league" as xx-chromosome persons (commenly regarded as "biological women").

Otherwise there would soon be no more biological women left as medal winners.
Because xy-athlethes mostly have more physical strength.
And would thus be better at doing all those multi-rotational jumps, compared to biological women.

(There is a reason why most sports were divided into male and female in the first place ...).

In terms of "chimera" persons (not sure if they would call themselves like that ...) who wrt their chromosome setting cannot be placed in the xx or xy category:
The statistical chance that such a person is among the top 100 figure skaters is close to zero I would think.
Thus no issue wrt the Olympics or other high level competitions.

 

[Query]

In terms of "chimera" persons (not sure if they would call themselves like that ...) who wrt their chromosome setting cannot be placed in the xx or xy category:
The statistical chance that such a person is among the top 100 figure skaters is close to zero I would think.
Thus no issue wrt the Olympics or other high level competitions.

Olympic athletes are self evidently not statistically normal. Thus it wouldn't be surprising if an Olympic athlete had an unusual genetic makeup. Especially if that genetic makeup imparts an advantage.

E.g., claims have sometimes been made that some Olympic female athletes might be considered male by some criteria. E.g., Olympic gold medalist boxer Imane Khelif, though AFAIK, that remains unproven, and the detailed tests are unlikely to be published. And females with naturally high testosterone levels have been disqualified. But these are completely separate issues.

In any event, I wasn't talking about people born as chimera or with other genetically atypical conditions. And I'm ignoring the issue of women who have sons, or who are born to women who previously had sons, and retain some of their Y chromosomes, which is apparently fairly common. I'm only wondering whether female athletes should worry about the gender of blood and tissue donors.

For various related studies from reputable sources, see
https://pmc.ncbi.nlm.nih.gov/articles/PMC5293315/
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0045592
https://pmc.ncbi.nlm.nih.gov/articles/PMC3169192/
https://pubmed.ncbi.nlm.nih.gov/16084184
https://pmc.ncbi.nlm.nih.gov/articles/PMC6714269/

BTW, that's a very incomplete list, and some are only peripherally relevant, though some of their references might be.

Also, it isn't just Olympic athletes who might be tested.

Also - I don't know how sensitive the proposed tests might be. E.g., if only a small proportion of blood cells have Y chromosomes, such as might be caused by a bone marrow transplant or old blood transfusion (or having had a son) maybe that would be ignored?

 

[lariko]

Blood transfusions are already tightly controlled by WADA since they are considered a form of doping, so the amount allowed for a medical treatment in and out of competition is minimal. No Olympic athlete is going to leave a medical center without a full record of what happened, what blood producst they recieved etc or they risk disqualification. I think that chimerism introduced by blood transfusion is not going to be an issue that can't be addressed on a case by case basis. Chimerism can also be proven if necessary by DNA testing, which is reliable.

 

[Query]

What if the athlete isn't yet at a sufficiently high level of competition that they are monitored by WADA?

And do you really expect WADA's decision to never be controversial?

Regardless, one would hope that the tests for "microchimerism" won't be too sensitive.

E.g., apparently it is quite common for women who have male children to retain some Y chromosomes in their body for many years. Perhaps most women who compete at elite levels haven't had children - figure skating is a sport which favors relatively young participants, especially for ladies - but some have. Likewise, it is fairly common for girls who are twins, in which the other (obviously non-identical) twin is male, to retain some Y chromosomes too. One would hope that any testing won't label these women and girls as male.

What we have right now is an indeterminate state, in which the current president of IOC was elected in part on a platform which indicated that trans and intersexual (of which this is one of several examples) females could not compete as females. But, AFAIK, we don't yet know how that would be implemented. She has said she wants to take a scientific approach - but not all scientists - or doctors - agree on what constitutes "female".

And where such distinctions have been made, different sports have used different criteria.

I am also making the perhaps unjustified assumption that Y chromosomes would be considered sufficient evidence of being male. That is not currently true in IOC sports. There are a number of genetic conditions in which the effect of Y chromosomes is somewhat suppressed (e.g., 46,XY). Children who have those conditions and appear to have female anatomy are typically labelled "female" at birth, and in the past, have typically competed as females. Including in the Olympics.

Note: 46,XY is not one specific condition. I'm not sure if all 46,XY females have Y chromosomes.

There have been studies which appeared to show that 46,XY females are more prevalent among elite female athletes than among the general female population. Will the current president of IOC, and those who support her efforts to "protect" the female category, claim that 46,XY females are not female? I'm not sure. "World Athletics" has already implement such a rule for some sports:
https://thednaexchange.com/2025/09/03/why-sry-world-athletics-decides-who-is-female
which would have excluded several athletes who competed in the Olympics as female in the past, or in some cases required them to lower their testosterone levels.

If standards are changing, how are currently competitive athletes supposed to guess what criteria will apply in the near future? E.g., what target testosterone levels should the seek to achieve? I think the only fair criteria in sports are determined by the rules of the sport. But if those rules are changing in a TBD manner, how can that be fair?

I also find it interesting that she is concentrating on "female" athletes in this regard. But there is evidence that XXY and XYY males are taller on average than XY males. (And incidentally that XXX females are taller on average than XX females). So, in those sports where tall height is an advantage, should XXY and XYY males be excluded? (E.g., studies have claimed that the NBA has a much higher than normal proportion of XYY than the general population. Which, if valid, shows that there might be a significant genetic advantage to XYY in basketball, a sport where being tall is an advantage. Is that "fair"? I don't know.

There are "46,XY males" in elite level sports, including the Olympics. E.g., among male figure skaters nominated to be on the 2026 US Figure Skating team (for Olympic competition), if a quick Google search is correct (which it might not be!), 8 of them are said to be 46,XY (male).

(I didn't find a similar list of 46,XY female figure skaters - only of 46,XY athletes in other sports. And it is hard to know whether such lists are accurate.)

Human gender biochemistry is a lot more complicated and varied than I was taught in grade school. Any criteria that is used will be considered unfair by some people. I want sports to be fair. But I'm not sure exactly what that means.

 

[lariko]

I believe WADA covers international and national levels of competitive sports, sometimes lower. As more research becomes available on actual impact on performance, rules will be adjusted. No adjustment to rules ever pleases everyone, but the whole point of sport is playing by the rules.

 

[Query]

The whole point of sport is playing by the rules.

Maybe you've never watched hockey?

 

[lariko]

Maybe you've never watched hockey?

You are correct.