Reader Tom Alves called my attention to the singer Taylor Muhl, a human chimera. Chimerism is the situation in which an individual results from the fusion of two early-stage fertilized eggs (zygotes), and thus has the genetic constitution of two separate individuals. This is a very rare condition: geneticists estimate that there are fewer than 100 people on Earth known to have it. That’s probably a big underestimate, though, as it’s often hard to diagnose. As Live Science explains:
Muhl has a type of chimerism called tetragametic chimerism. This can happen in cases of fraternal twins, where there are two separate eggs fertilized by two separate sperm, and the two zygotes “merge and form one human being with two different cell lines,” said Dr. Brocha Tarshish, a clinical geneticist at Nicklaus Children’s Hospital, in Miami, who is not involved in Muhl’s case. This happens very early in embryonic development, Tarshish said.
Most of the time, people with chimerism probably go undiagnosed, Tarshish said. Indeed, without specific biomedical tests (such as genetic testing), it’s impossible for doctors to tell that a patient is a chimera, according to a 2009 paper about the condition. But there may be subtle clues to this condition: Some people with chimerism have “patchy” skin coloration (like Muhl does) or different-colored eyes, the paper said. In some cases, chimerism is diagnosed when a person is found to have two different blood types.
Muhl discovered her condition when she noticed a difference in pigmentation on her torso that runs right down the middle, as shown in this picture from her Instagram site:
She also noticed, and you can see this on some pictures on the internet, that features on her left side are larger than those on the right. This suggests that the twins differed in genes affecting body size. (She also has a double tooth on the left side of her mouth.) I see that in her eyes and nose:
Finally, she’s been ill most of her life. That’s explained by the fact that she’s a fusion of two different people with genetically different tissues (since she’s fused with her sister’s embryo, the two sides share only half of their genes), so her immune system from one twin is constantly trying to reject the foreign tissue of the other—and there are also two immune systems. Apparently Muhl has an allergic reaction to some metals on one side of her body but not the other.
Further, Live Science, the Independent, and The Daily Mail (actually, the Mail‘s story is decent), report that Muhl has two different lymphatic systems and “two bloodstreams”. The circulatory system thing I don’t understand, for Muhl has only one heart, and that has to pump all the blood through her body. That means that the circulatory systems, if they are genetically different, still have to be fused into one functional system. She’s also reported to have two blood types.
Sometimes human chimeras are detected through paternity tests: a woman’s somatic cells, which are sampled to get her genotype, might be from one zygote, while her ovaries, which produce the eggs, could be from another. That means that her children would share only 1/4 of her genes instead of 1/2, something that could be detected genetically. The American woman Lydia Fairchild is one of these cases. She separated from her husband, and having had three children with him, had to take a paternity test when she and her ex-husband were dealing with child support. The tests showed that while her ex-husband was the father of all the kids, she didn’t seem to be. Although her kids were almost removed from her, they eventually found out that Ms. Fairchild was a chimera: her skin and hair cells didn’t match the genotype of her kids to the required degree, but her cervical cells did. Fairchild was a woman with two different genotypes.
One wonders if a male twin could fuse with a female, and produce a double-sex person. I know of no such cases, though male cells from a woman’s own fetus can be incorporated in parts of a woman’s body—a phenomenon called “microchimerism.” As Scientific American reported:
A 2015 study suggested that this happens in almost all pregnant women, at least temporarily. The researchers tested tissue samples from the kidneys, livers, spleens, lungs, hearts, and brains of 26 women who tragically died while pregnant or within one month of giving birth. The study found that the women had fetal cells in all of these tissues. The researchers knew that the cells were from the fetus, and not from the mother, because the cells contained a Y chromosome (found only in males) and the women had all been carrying sons.
Here’s a video of Muhl from a television show that tells a little bit more of her story.
So don’t absorb your twin, no matter how much you want to.
Glen Davidson
My wife is continually trying to do so – much to her sister’s annoyance.
sub
That is absolutely 100% bonkers bananas. I had no idea this condition exists.
I hope David Cronenberg just read about this. I assume he didn’t know because, if he did, there would already be a movie about it. Dead Ringers 2?
So, what happens if a human chimera needs a blood transfusion? Is it impossible? Can they accept one of the two blood types? Combining the two blood types?
Never go full Scanners, man. Never.
O negative blood should be ok.
Should be, but there are other blood cell surface antigens that can have an effect on transfusion acceptance apart from the well-known ABO typing system.
Yes. But I don’t think those are even checked in most blood transfusions because they are less of a problem. Not sure why that is, but perhaps those are other antigen markers that are less abundant so they do not cause much a a reaction.
For pretransfusion testing, a “type (that’s the ABO/Rh) and screen (testing for atypical antibodies)” is performed. If antibodies to red cell antigens are detected, then the donor unit is tested for the corresponding antigens. Most people don’t have atypical antibodies. These antibodies can be formed in response to blood exposure, via transfusion or pregnancy.
In fraternal twins, about 8 percent have two different red cell lines, due to engraftment of stem cells in the embryonic stage.
Typically, this extremely early exposure to different cells leads to immune tolerance so it is no problem.
I was going to comment the same – that her immune system must be fully tolerant to antigens of both cell lines, like in the fraternal calf twins in the pioneer work of Owen.
Very interesting and she does state in the video that she has two bloodstreams.
How indeed can this work with one heart?
I would be fascinated to know or is there a simple explanation.
Beyond my expertise that is for certain.
It could mean two different types of blood cell going through the same plumbing.
Yeah but that’s not two different “circulatory systems.”
Perhaps it means the circulatory system is slightly different on each side of her body, which could be described as “two” circulatory systems, combined to be one whole.
How can that be? two circulatory systems with one Heart.?
I think it more likely means that she has one circulatory system, and two genetically different populations of blood cells in circulation, from different regions of bone marrow that produce blood cells.
My thought too. The lymph nodes (very important components of the immune system) might also be differentiated between one side and the other.
Way back in 1977, an Oxford biologist studying and cloning frog embryos (as I recall) told me about the lady who became sunburnt in patches, `two-tone’, over her body: a chimera. He suggested that there were probably two fathers in this case… long before DNA testing.
This might also be a consequence of Lyonization, where different X chromosomes were inactivated at the early embryo stage. The calico cat phenomenon!
Scratching my head, thinking back to 1977, the differential sunburn was the result of two skin pigmentations suggesting fathers of very different skin colouration..
I was thinking along those lines. Also, since only one X chromosome is active in any female cell aren’t all female mammals in some sense chimeric? Isn’t mosaicism chimerism from a single zygote?
[/notageneticist]
I’d previously ever heard “chimera” used only in a figurative sense, as in John Barth’s novel of that name.
Damned if you don’t learn something new around here every day. Thanks!
Great book, Barth’s.
this is a CSI nightmare, and has already happened in a few legal cases. I have been covering chimerism in my Forensic Biology course for many years at Ohio University. Sometimes students think that I am making it up, LOL.
Do you have a more accurate estimate for the prevalence?
“100 people known to have it” would imply at first glance one person in 70 million. But if it’s 100 people in “western world”, it’s more like one person in 10 million, and if it’s 100 people in the US, it’s one person in about 4 million. Quite a difference.
Chimerism is not rare, but rarely discovered, because it seldom generates any observable anomalies. I quote a part of a 2007 EMBO REPORT but it is worth reading the whole thing excluding the silly first two paragraphs:
Very interesting, thanks.
Prevalence versus detection is always a point to remember. Absence of evidence is not evidence of absence – but checking a dozen or a thousand samples does permit one to put limits in the likely prevalence.
“About one-eighth of all conceptions and about one-eighth of live births are twins…”
This surprises me! Double ovulations or identical twins, one wonders?
Also, I suppose there are identical twin chimeras, but how would you tell? 😉
I’m in that slightly fuzzy state that occurs halfway through the 2nd bottle of a beautiful British wheat beer & you hit me with the concept of “identical twin chimeras.” You are a cruel woman! I tried to ignore you because I’m halfway through 3rd season, Episode 1 of Homeland on Netflix UK [Homeland is new to me believe it or not]…
QUORA SEZ…
Well, thanks for the research!
If I’m reading the Quora responses correctly, it sounds as if they’re referring to sets of identical twins being born with both babies being chimeras. I was thinking of a single baby, the result of one identical twin zygote fusing with its womb-mate. I’m easily confused, however.
If they do mean twin babies who are both chimeras–would that mean that the, er, litter started out as identical quadruplets?
🙂
Aaaaagh! *head explosion*
Several of you brought up her comment as to having separate bloodstreams; of course, that is impossible, she is not a biologist, what she was making reference too was two blood types
Yes, now that is the simple explanation.
Thank you.
The part of blood that defines blood type:
What part is it?
Where – what organ[s] I mean, make that part? I can imagine the marrow being different in the two halves of the body for example.
Cheers Zeus
ABO blood type refers to particular cell surface antigens, which are molecules that the immune system can recognize and respond to using antibodies. The marrow makes blood cells and might well produce different blood types, as you surmise, if the marrows are genetically distinct, as can be the case in bilateral chimerism.
Sub
If a male egg fused with a female egg then I would expect the result to be male, since the sex is determined by hormones circulating in the blood. Since there is a Y chromosome the resulting hormones would produce a male.
Ummm, I bet it’s not that simple. It’s biology, things rarely are that simple.
Ah – does the occurrence of at least one problem in a recent Olympics from a “female” athlete being found to have an XXY genome illuminate the question? I’m not going to claim knowledge to interpret the genetics/ biology of such cases, and I may have mis-heard the sport news as I scrabbled for the tuner to move to an interesting channel.
There are a few women who have a Y chromosome, but this is very unusual. I think it is something to do with not having a certain receptor (for testosterone?) on the cell membrane. Usually a Y chromosomes does result in a male.
It sounded cool at first, like she could be a super hero, “The Chimera” but then I read this part, “she’s been ill most of her life.”
She seems like a great coupla gals.
Ba dum da! Tisssssh!
If I end up dating her, will I finally be able to say I’ve had a threesome?
That’s what I was thinking !
No, because two halfs make one.
I don’t quite get why she has health problems from one immune system trying to reject the ‘foreign’ tissue.
It has been a very long time since I had immunology, but from I had been told the immune system is “educated” to accept ones’ cells as part of you during development. Based on experiments in animals, doing grafts between two different embryos results in the graft being accepted since the immune system, when it develops, learns to accept both of them.
But if her claim is true, then obviously the view I describe is a bit wrong.
Isn’t it possible that having two immune systems, as well as fighting each other, might also protect her more from infections?
That was what I understood as well. And I have not heard of any other chimeras having similar problems. (That does not mean none of them do, of course)
Just think of it as Kirk and Spock fighting when Spock went into Pon Farr. This music should help.
Gotta say, for all its cheesiness the original ST had music bits that were damn good.
Would make a good addition to a workout mix tape.
The Star Trek episode that comes to my mind is about the alien society where one race is black on the left side and white on the right side and the other race is coloured the opposite way round.
Many complications. My daughter is a chimera twin. She has x & y chromosomes..2 sets of dna…has the red ‘birthmark’…immunology issues, mast cell activation sydrome…etc etc. Learned of chimerism voa Rare disease dept at Vanderbilt…yesterday! This answers YEARS of questions for us
Disgraced American cyclist Tyler Hamilton once tried to escape blood doping charges by claiming he was a chimera.
His absorbed twin was the one doing the doping?
His evil twin, of course.
Glen Davidson
I am surprised so few people seem to have heard of chimerism since there was a House episode that dealt with it. (Very inaccurately, IIRC)
I have read about a XX/XY chimera that had both male and female organs. A baby that was conceived by IVF. It was a very long time ago though and I cannot give a link, I’m afraid.
There was also an episode of CSI (the original series) where chimerism explained the inability to DNA match the suspect.
I’ve never seen an episode of CSI (but the genus of programme is common enough…), but I’m going to guess that the alleged perpetrator committed the offence with his penis/ right hand/ head of one genotype, while the DNA samples and/ or blood were take from the left hand/ arm hair or a chimerically different part of the body. Or something similar.
Blood samples shouldn’t be different – they’d be a mixture of the two gnomes. If the chimerism involved any of the active blood-forming bones. Which change through life, so there’s a potential plot twist.
I can’t abide any of the CSI TV thingies, but a quick Google reveals that in one episode a rapist almost walks free until crime scene investigators realize he is a chimera: the semen found at the crime scene came from his unborn twin. [see link in my other comment]
I could see that working as a plot.
yes, I saw the episode.
“they’d be a mixture of the two gnomes.”
What, are we bringing dwarfism into now? 😉
cr
I really need to replace the keyboard on this laptop. But since the casing of the screen is also cracked … I’ll probably just use it until it dies totally.
Somewhere there must be website discussing how many souls she has.
One for each foot.
Good comment! Identical twins by evangelical doctrine should have one soul between them, endowed at conception and then segregated during embryo division. The second twin is just faking it. In a chimera, one soul probably eats the other. I find it curious that Taylor Muhe’s linked video essentially claims that her isolated created soul destroyed that her sister. An alternative view is that the “soul”, unitary self-awareness, is a epiphenomenon of neurological integration and comes about at the end of embryological development.
When I read the subject line, I had no idea what to expect as I’ve only heard of the mythical chimera. Thanks for the education of this strange biological phenomenon.
Creationists: please explain.
I too thought, “she doesn’t look part lion, goat, and snake.
Ummm, is the phrase [crickets] appropriate?
More crickets.
I don’t intend to hold my breath waiting for an answer.
She says in the video you have to work with “what God gave you.” So she believes this is His doing. Hrmm…
Perhaps surprisingly, the Daily Mail’s science coverage is pretty good. I know from what appears in my own research field that they will often carry pure science stories that the “quality” papers (Times, Guardian, Indie, Telegraph) just don’t.
Agreed; the Daily Mail is a bit of a chimera.
Automatic threesomes!
I was thinking – “I know what President Trump would think, if he understood this.”
Glad to see I’m not the only one who can scrape that barrel.
Sub
At least she doesn’t seem to be her own grandma.
That was very interesting.
With regard to male and female twins fusing, that actually does exist. Here are two links:
https://www.quora.com/Is-it-possible-for-a-chimera-to-be-genetically-male-and-female
https://en.wikipedia.org/wiki/Intersex#.22True_hermaphroditism.22
Another interesting link:
http://genetics.thetech.org/ask/ask335
Doesn’t everyone have one hand, one foot, one leg, one arm, one eye a little bit larger or longer than the other, usually the right side? Place your palms together and see if one of your hands is a wee bit longer than the other. 🙂
I don’t. I have only one of each.
My left hand is larger, surprisingly.
What if a woman were inseminated by two different men producing two zygotes, one from each man, that then fused?
And what if these two men were Donald Trump and Jason Alexander?
Is her brain also split with the same symmetry? If so does that mean the left side of her body is controlled by the right side of her brain and the two are not from the same person?
No.
When I was a little kid, my dad had a two-tone ’56 Ford Fairlane with the same color scheme.
Anybody know if Ms. Muhl comes with the chrome and white sidewalls?
I wonder how this affects her reproductive system. Would she be fertile, and id so what affect would it have on any offspring?
*If
“The tests showed that while her ex-husband was the father of all the kids, she didn’t seem to be.”
Say what???
(You probably meant to write “parent” rather than “father.”)
Reblogged this on The Logical Place.
Is this another way to “create” a human tetrachromat?
Human XX/XY chimeras are known:
https://www.ncbi.nlm.nih.gov/pubmed/6575956