You may have seen an episode of CSI where a man is exonerated from a crime he actually committed because he has two different genomes (sets of DNA). At the scene of the crime, he only leaves traces of the alternate genome behind. The lab tests the alternate genome, which doesn’t match the DNA in his blood. He is erroneously declared innocent. This might sound like science fiction, but this genetic condition is real and it silently impacts the lives of everyday people.
What is chimerism?
The term chimera is derived from a Greek mythological creature that was composed of a goat, a lion, and a snake. Although this monster never existed beyond our collective imagination, the health condition is quite real. Chimerism is a condition whereby a person has not one but two complete genomes (or sets of DNA) in their body. One genome is found in one region or organ(s), while the other genome can be predominant in other organs or tissues. So a DNA test result would be entirely different depending on where the sample was originally from (blood, saliva, fingernail clippings or hair, etc). As you can imagine, this condition can lead to confusing results when the person seeks medical care or relationship testing!
One young chimeric father I know reported being sent to a hospital after a car accident. When the hospital staff discovered he has two different, incompatible blood types flowing through his veins, they asked if he had received a bone marrow transplant. Hospitals are usually ill-equipped to identify and treat chimeric individuals.
One mother’s story
Perhaps the most famous example of a human chimera is Lydia Fairchild. Lydia applied for child support for her two children after separating from her husband in 2002. At the time, she was pregnant with their third child. She was required to prove a biological relationship to the kids, so she submitted DNA samples for routine DNA relationship testing. Her husband was confirmed as their biological father, but the test indicated she was not the mother.
How could this be possible? Lydia conceived both of her kids naturally, carried them to term, gave birth, and was being told she was not their mother. Without knowledge of her condition, Lydia was accused of fraud. She nearly lost her two children to child protective services.
Lydia was court ordered to have a witness present at the birth of her third child to take a DNA sample immediately following the birth. Again, the third child’s DNA test excluded her from being the mother. Thankfully, a geneticist thought to test her cervical cells’ DNA, and indeed that DNA matched her son’s genome. In essence, Lydia had delivered a child from her twin, thereby becoming both the child’s mother and biological aunt. Take a moment to let that sink in.
What causes chimerism?
There are many types of chimerism, and various root causes. For the type of chimerism mentioned in this blogpost (also known as ‘tetragametic’ chimerism), the most common cause is a twin pregnancy that naturally reduces to a single baby. This is referred to “vanishing twin syndrome” because one embryo doesn’t survive and the embryo’s cells are absorbed by its twin and the mother. The remaining embryo incorporates the disappearing (“ghost”) twin’s cells into various tissues and develops to a healthy baby.
Back to Lydia Fairchild, and her story. What most likely happened is Lydia absorbed cells from her fraternal (non-identical) twin while still in utero. Her twin did not survive to term and all that remained of the embryo were the cells that Lydia retained in her ovaries and other organs. Lydia’s blood had her dominant genome. So when social services took a blood sample for routine maternity DNA testing, it did not match her child’s genome.
Lydia unknowingly passed on her second genome to her baby. In doing so, Lydia became the child’s mother and simultaneously, the biological aunt.
An even more common form of chimerism is called microchimerism. Microchimerism is defined by a person harboring a small percentage of cells that originate from another individual. Frequently, this condition arises during pregnancy when a mother and the fetus exchange cells across the placenta. Microchimerism has been detected in women who have never had a full-term pregnancy, but may have been unknowingly pregnant and miscarried. A transient form of microchimerism can also occur after a blood transfusion or organ transplantation. The baby’s stem cells may be acting to help protect the mother from her own autoimmune condition. For reasons not fully understood, many mothers report relief from rheumatoid arthritis during pregnancy. There is reason to believe that microchimerism may be the underlying explanation.
How does a person learn that they have chimerism?
Most chimeras are believed to be asymptomatic and completely unaware of their condition. Medical literature has identified some common symptoms including having different colored eyes, patches of different skin tones, different colored sections of hair, and, sometimes, disorders of sexual differentiation (formerly called hermaphroditism). Some chimeras have autoimmune diseases because the body recognizes the twin’s genome as a foreign substance. This does not suggest that anyone who has different colored eyes or skin, or an autoimmune condition has chimerism.
How common is chimerism? The answer might surprise you…
To understand how frequent chimerism might be, we first need to understand some things about twin pregnancies. A surprising number of single babies were originally twin pregnancies, where the twin did not survive to term. An estimated one in eight (or 12%) babies born had a twin that disappeared, and left no evidence of their existence.
Unfortunately, we don’t have enough scientific evidence to make an accurate prediction for the rate of chimerism in humans. Currently, there is no public-wide screening program in the US, nor is there any real need for it since most chimeras are healthy folk. We do know that, through the popularity of assisted reproductive technologies (such as IVF), twinning is on the rise, and we can anticipate chimerism to become more common. Microchimerism is believed to be the most common form of chimerism, with an estimated 20-90% of women harboring cells from prior pregnancies. The rate of microchimerism in men is less well known but assumed to be the same as women.
What increases the likelihood of chimerism?
Anything that increases the likelihood of a twin pregnancy increases the chances of a person being an undiagnosed chimera. If your parents utilized assisted reproductive technologies, such as IVF or used fertility medications, your chances of having been a twin pregnancy are more likely. Left-handedness has been observed more frequently in twins, leading some experts to believe that a left-handed individual may be more likely to have had a twin in utero. There is also reason to believe that some individuals who identify as transgender may have dual-gender chimerism (XX and XY chromosomes).
What can I do if I suspect I have chimerism?
Chimeric individuals usually live healthy, normal lives–until something goes wrong involving DNA testing. If you have had a parental DNA test performed, and the result was (falsely) negative, chimerism may be an explanation.
Contact us at www.vibrantgene.com for additional information. We have a proven track record for successfully identifying chimeric individuals through cutting-edged DNA testing, and advocating for parental rights.
My husband has two different colored eyes. When younger he was always told he had blood type AB when giving blood and medical procedures. Recently previous to s surgery he was told that his blood type was A.
His mom was given blood transfusions while pregnant with him. Any connection?
Your husband seems to have two traits that are suggestive of chimerism. If that is the case, his condition would have arisen while he was developing in utero, much like Lydia Fairchild. His mother’s blood transfusion would not have impacted his blood type. Hope this helps! If you have children, be wary of any paternity or ancestry testing because both could give you misinformation!
I find this fascinating. It shows how imperfect we humans physically are.
Hello really interesting topic. Thanks
Glad you enjoyed reading our post! Cheers!
When my daughter gets a suntan she has a defined line down the middle of her stomach of different skin tones. The doctor was so baffled when he saw it he asked another person to come in and look at her belly. He said it was most likely just different pigments to her skin. I wonder if that’s true after reading this.
Look up chimerism
This is really an eye opening topic. This might explain why we can’t really jump into conclusion right away during maternal and paternity testing. This could be damaging if we just rely on single testing. Jeremy Kyle need to watch out!!
You are absolutely correct. If a parent has chimerism, and they’re unaware of their condition, they won’t know that the paternity test is failing them. This is a very tricky situation, and i recommend you contact a genetic specialist to get advice. At Vibrant Gene, we are regularly contacted by folks who are certain the DNA test is incorrect, and we provide private investigator services for them.
Every since I originally saw Ms. Fairchild’s story a while back I’ve always questioned DNA test on Paternity Court where the child looks exactly like the suspected father. This is a wild topic that many don’t consider or even know about. WOW!!!!
We have similar hesitations about paternity tests when they are negative, but the mother is certain that the father is the biological father. Chimerism is considered to be rare, but it has been proven to confound these results in surprising ways. It always pays to get a second opinion on these test results, and sometimes follow up with alternative (more robust) testing!
Thanks for your insightful comment!
Kayla and crew
I donated blood at 22, and found out I was A+. This ultimately led to me discovering I was born with the assistance of IVF. At 25, I had my blood tested before he birth of my 1st son, and it showed my blood type was O+. I have discovered who my sperm donor was through Ancestry, and a lot of sleuthing. I’m thankful the original test was able to enlighten me on the truth of my biological origins, but now I’m confused why the blood test during pregnancy showed something different…
So I am aware that my twin ‘died’ but my mom said that she was having difficulty with growing what chance would this be of me having 2 strands of DNA?
It sounds like you were originally a fraternal twin pregnancy, and with a demise, it is not impossible that you have tetragametic chimerism. If you are interested in learning about DNA testing, feel free to contact us.
My son may have this. My son was born with multiple double anomalies. At 5 months gestation, he was thought to be a hermaphrodite bc he had what looked to be a urethra track of a male and the labia of a female. An amniocentesis was performed and showed he had the xy chromosome of a male. When he was born, he had hydrocephalus, white brain matter damage, ambiguous genitalia, duplicate right kidney, hypospadious (2 urethra), a 13th lumbar vertebrae (you are only born with 12 typically), and an imperforated rectum. The geneticists also noted that he had a 3rd and 4th nipple. It wasn’t discovered until he was almost a year old that he had 2 different eye colors. The geneticists stated that he was supposed to be a twin in early utero and that the twin’s embryo didn’t survive for whatever reason and Christian absorbed the embryo, causing multiple double anomalies. Could this be a form of chimera?
Based on your description of your son’s condition (in particular, his genitalia, and two different eye colors) chimerism is quite possible. Does he have patches of two-toned skin or hair of different colors/textures? It can be extremely challenging to isolate the alternate genome, and part of that challenge is just getting enough tissue samples. Feel free to message us privately if you’d like more information. Best wishes to you and to your son.
This is really interesting. I came across the story of Lydia and wanted to learn a little more. I’m currently pregnant and NIPT has shown abnormal sex chromosomes. While this may be nothing or a variety of things, I’m wondering if chimerism is a possibility. My husband and I had IUI done while I was on fertility meds. While there wasn’t another egg to cause fraternal twins, it’s still something that now has me curious. I have another appointment for more testing although I really don’t care to have more testing done. This is my baby regardless of any abnormalities.
You’re very welcome, Ruth. Thanks for taking time to read it!
Very interesting. My son has a defined line down his abdomen and one side is darker than the other. He also has brown hair but has a patch of white hair. I wonder if he is a chimera. I need to get some test done.
Feel free to message us if you would like to find out more information about a private consultation. The easiest way is to email us at: email@example.com or to click the green “contact us” button on the website.
I have A+ blood my husband had O my son has AB+ his sister has A+ same dad.. how is this possible?? Both my son and I have allergies to drugs and metals.. regular MMR boosters and flu shots ,peroxide, bleach,Alfa blockers, beta blockers all antibiotics out side of tetracycline we are allergic to..his sister did not have the same allergies but both her kid’s have them with an auto immune disorder..
Interesting scenario you are describing. I had a client with undiagnosed chimerism who fathered a son with his alternate genome, thus the son had a discrepant blood type from his parents’. If you would like to get more information, feel free to contact us (click the green “contact us” button) or email (firstname.lastname@example.org)
Best wishes to you and to your family!
The left side of my face has always been different than the ride side… my left eyebrow, eye, and ear are 1/4 inch lower than the right, the left side of my upper lip is fuller than the right. Recently all of my teeth had to be removed due to presistent and chronic periodontal disease and we discovered that the gums on the right side are smooth but the gums on the left have tons of bony bumps and ridges. Also I have a line that starts at the libial frenum and goes all the way to the back of my mouth. I’m able to write with both hands and my hands are different sizes (ring finger on left is 6.5 and on right is 7.5). I’ve always felt that I have a twin that my parents gave away. Is it possible that these are caused from chimerism?
Very interesting story you have shared with us. If you would like to find out more about DNA testing, feel free to contact us privately via email: email@example.com Best wishes, Kayla
How about mine? I have different skin tone in my forehead and my forehead isn’t flat, the darker skin tone is the lower ground. The lighter skin tone is healthier based on the thickness of my eyebrows. Is that chimerism?
You also have interesting findings, thank you for sharing this. If you would like to fill out our clinical questionnaire to help us better assess if it is chimerism, please email us at:
In the subject line simply put, “Chimerism questionnaire”.
Best wishes to you!
On Chimeriam, this is very interesting. I’m in no way a Chimera. My question is could Chimerism be associated with same-sex attraction. Charles an me have a dear friend who insist that she was suppose to be a man. Ricky has always said that something happened when her Mom was pregnant. Her or her Mom got things mixed up and she has all the looks of a woman but has the brain of a man. In no article can I find this question. If a person has different eye colors, why not the body of one twin and the brain from a deceased twin of the opposite sex. One article had a teenager boy that had internal female organs. Dorothy
I think what you are describing is your friend Ricky may have a trans-gendered identity. Your question is very timely, because this is a question I am asked often lately. It makes logical sense that if a person is born with both XX (female) and XY (male) sets of DNA, that it is possible that one is more predominant in their brain cells and the other parts of their body. However this theory needs to be confirmed by studying a large group of trans-gendered folks, and that simply has not happened yet.
If your friend has any questions, please feel free to have Ricky contact me directly. Our email for general questions is: firstname.lastname@example.org
My face skin has two different tones. One is fair and other is little bit darker. My left side of the face is little darker and fair skin tones and right side is totally fair. And also on my arms there are white little patches
Thanks for sharing this with us! These skin findings sound very much like a couple of clients we have worked with, and were found to have chimerism. If you are interested in exploring if you have additional findings, you might consider completing our secure online chimerism questionnaire. If so, email us at: email@example.com It is at no cost, and something we provide for our private clients. Best wishes! Kayla
My daughter (Twin A) has slightly darker skin that is perfectly symmetrical on half of her trunk – literally a perfect line down the middle of her stomach where one half is darker than the other. Twin A has a fraternal twin, Twin B, and I’m wondering if it is possible that Twin B split into an identical twin that did not survive and Twin A absorbed her cells. Twin A is also left handed. Both were conceived via ivf and ICSI and were day 3 transfers. I have tried to have Twin A tested with 23 and me and they cannot extract her dna (tried twice). Wondering what your thoughts would be. Doctors have just said it’s different pigments or a birthmark. I just feel like it isn’t either of those.
My mum told me that she that we was bleeding very heavy and was taking to to hospital were she passed something, but I was still there she has always said that must have been a twin, I have a blue and green eye.. and I have always thought that there was some kind of connection, I also get sick a lot, Sometimes it feels like my body is fight against it self..
Thank you for sharing a bit of your story. Having two different colored eyes (heterochromia) can be associated with chimerism, but not always. However, your mother’s medical history is also an interesting piece of the puzzle. If you would like to complete a chimerism questionnaire to learn about other physical findings that you may have that are also associated with the condition, feel free to drop us a line: firstname.lastname@example.org The information would not likely change your course of care, but it certainly can help resolve questions!
Hi! With the skin tone differences, do they have to be clearly separate on different sides of the body? I’ve got patches of lighter skin “marbled” across my torso, which has baffled doctors and they’ve just told me it’s a loss of pigmentation. The fingers on my left hand are also longer than on my right, my right eye is a different shape to my left, and I’m left-handed and have several auto-immune disorders, so this was a very interesting read.
Thank you for asking about skin pigmentation patterns in chimerism. We have noticed that the patterns vary quite a bit from person to person. Sometimes it is segmental (or a very large checkerboard); other times we see more of a swirly pattern, especially on the torso. The other traits you mentioned are also very interesting. If you would like to complete our chimerism questionnaire to learn about traits that are associated with the condition, feel free to drop us a line at email@example.com
I’m pleased that you found the blog article useful!
A really interesting topic! I wonder how it is spread world wide since many people would never believe such thing. In addition, this rises many questions about who we are !!!
Fascinating, isn’t it? We are a ways away from understanding the prevalence of the condition, but we anticipate that the more that people undergo genome sequencing (like the NIH project that will enroll 1 million people) that we will see an increase in the number of cases diagnosed. Stay tuned!
It certainly does challenge our notion of what it means to be human. If you’ve not yet read about microchimerism, you might also be interested in this. Most (MOST!) women are believed to be microchimeras!!
Very interesting, twins run on my mother’s side. I have an autoimmune disorder. When I was pregnant with first child was told a boy up until delivery it’s a girl. Second child I was a lot bigger than should be for only one baby and she was only 6 lb 15oz at birth. She is left handed to write but does everything else with right hand. She says it just feels natrual. She also has a distinct line down her arm with a lighter tone on one side and darker tone on the other. I find this very interesting it could explain alot of things that go on with humans. We are so complex yet one tiny little thing can mess up. Make me wonder if that where autoimmune disorder originated from.
Could chimerism result in a wrongful exoneration of a criminal when DNA testing is used to identify a perpetrator?
Very astute observation of yours! I co-authored a chapter on a reference book about Chimerism (for clinicians) and in it, we describe a couple of cases that prove this is a possibility. Interestingly, no cases of mistaken identity, and wrongful exonerations due to chimerism have been documented yet. Let us know if you come across a documented case.
I understand how and why the odds of having a case of mistaken identity would be negligible, but how would we *know* about a case of wrongful exoneration? The list of things that would have to occur in order for that to happen would definitely make such an event unusual, but the only way to know about a wrongful exoneration would be for genomic testing to be done on the crime scene evidence and the accused’s samples after the verdict, correct? Given the scarcity of funding for even basic DNA testing, that scenario seems slightly less probable than a wrongful conviction. I’d be fascinated to learn more.
I’m interested in who we really are? If it is possible that our brain has one dna and the blood of another dnk? How does our brain work with blood that has a different DNA? Are we a person or just blood and flesh?
Great philosophical questions you are asking, Lazar. It appears as though we are much more complex beings that we once believed. Chimerism and other genetic/genomic differences were once thought to be rarities, but now that DNA testing is widely used, we are discovering these differences can be quite common. Fetal-maternal microchimerism is now believed to be more common in women than not. Our bodies have managed with these complexities (presumably) since the beginning of time, but HOW is the question. And a great question at that. Thank you for sharing your insightful comment.
I had my hormones checked right before I got pregnant at 42 yrs. old. The doctors told me I have normal estrogen but surprisingly high levels of male hormones. They said it was quite odd and warned me that this could put me at higher risk for breast cancer and heart disease. Later, when I went for a chest X-ray, the tech was taken aback by how wide-set my lungs are. Said he had read of women with this, but it’s normally only found in men. Now my hair line is fading along the temples to make the classic “M” seen on some older men, plus I have heavy facial hair. I’m definitely female but have always been exceptionally strong and react to physical threats very aggressively (shocking a few unmannerly men). Although definitely female, I’ve always felt there is a very masculine side to me. Does any of this sound like chimerism? I wouldn’t be the least bit surprised.
Feel free to drop me a line via email: firstname.lastname@example.org This sounds like a fairly personal matter, and I’d like to maintain your privacy.
Great article. I have one blue eye and one blue and brown eye. Always loved it. Could it be Chimerism? Or do I hear galloping and am thinking Zebras?
Thanks for sharing your story with us. There are many different causes of heterochromia – some causes are more rare than others. Because we do not know the incidence of chimerism, it’s hard to guess about the likelihood. If you would like to fill out our questionnaire about chimerism, drop us a line at: email@example.com and we can send it to you via email. If it sounds like you could have chimerism, you could consider DNA testing. Just know that there are several different paths to uncovering the genetics underlying your condition. Fascinating time to be human isn’t it?
I believe my son may be chimera. His hair color at birth was black with platinum tips, then turned red, then brown with platinum sprinkled throughout. At 3 years old, he developed a dark discoloration on the lower left torso from next to his navel to the middle of his back. And he’s a lefty. Twins run in my family.
Hi, how would i go about genetic testing? I don’t have any physical features but have auto immune stuff, allergies and have always felt that i am somehow two people. Like that my right side is somehow partially another unclear person. I never really talked about it cos it sounds mental. My right side is partially numb for no apparent reason. I am genderqueer, trans masculine. I’d really like to find answers, if i could. When i heard about chimerism i wondered
Thank you for your time
Hi, when my first son was born in 1990, the DNA testing agency back then I think in Georgia? Sent me paperwork showing my son had 99.98% DNA of his father. None of mine. Tho my son and i share same blood type. The agency said they never send any documentation to anyone but never seen an outcome that high. I still have the paperwork. I was recently made aware of this condition? I was told I was chimeric. My mother also had a chromosomal defect found much later in her life. Pls feel free to e mail me.
Hi, I can say humans are complex in nature. Thanks for this insightful piece. I have a question though. Does this condition “chimerism” also have effect on genotype? For example, could it be the reason why a person’s genotype reads or gives different results after testing a particular individual. A case where an individual genotype test result shows AS and a confirmation shows SS and vice-versa. I am thinking if it’s possible with blood group test result then genotype test result should be looked into also to know if it is “chimerism”. What can you say about this genotype test result issues as regards chimerism?
This is so interesting! I took a DNA test for a child about 5 years ago. The results came back in the 80 percentile range but i was determined not to be the father. I’ve often wondered how this could be without the women being involved with someone in my immediate family. Needless to say, but the child is now 19 years of age and he favors my looks and has taken my mannerisms without knowing me. Very very interesting!
Thank you for sharing your personal story! If you would like to discuss this further, feel free to email me directly at firstname.lastname@example.org I’m sorry for all you’ve had to go through.
This is very interesting. One side of my face looks different to the other, if you photograph them and turn opposite side together so you have the left and left side together and the two right sides together they look like a completely different person, totally different eye, eyebrow, lips are fuller on one side and lip turns up on that side, my cheek bones are very different and the shape of my jaw, ears are different heights. As a child i use to joke that I looked different because it was my twin & use to pretend I had a twin often. I also have many autoimmune conditions and my feet and hands are quite different in size, along with arm & leg length. I have a ridge line in the roof of my mouth like a join. One side of my face looks like my mother, the other my father. As a child, even though I was really girlie, I use to feel like half of me was Male, I really don’t know why. Would it be worth me looking into do you think? Thanks
It sounds like you have several unusual traits that are leading you to wonder about chimerism. Feel free to drop me a line directly at Kayla@vibrantgene.com – I’d be happy to send you our online chimerism questionnaire to investigate this further. Best wishes, Kayla
Hello, I was always told my blood type was A+, but after having my second child the doctor was doing old me I was B+. I also have a couple of white spots on my body, auto immune disease, and dark patches on my face. I just feel like there are so many similarities. Is it possible?
You are describing traits that can be associated with chimerism. Feel free to reach out via email, I can share our chimerism questionnaire to find out more. Email: email@example.com Best wishes! KMS
With the possibility that a person may have two differing DNA profiles, should the police be alerted to test a persons DNA from the same type of sample? e.g. if they have a crime-scene sample of blood, should this be compared with the blood of a suspect; semen with semen or saliva with saliva etc?
Maybe they already do, but in television programs the police are mostly shown taking samples from a suspect’s mouth.
Just found out about this.
I was born with half my belly a different color from the other. There’s a perfect straight line separating both color tones. A few years ago I also found that my reproductive sistem was split in half, with a membrane separating left and right side.
Putting these two pieces together, I started imagining that my left and right side were somehow two different humans. Now that I know about chimerism, I wonder if that’s a possibility for me.
Hello. Thanks for the eye opener. What can we say about a child with genotype SS given birth to by an AA mother and AS father. Can this also be traced to chimerism?
Thank you for sharing! If you are describing a single variant, that could be caused by mosaicism. Do you have any more data on this couple and the baby? Feel free to send it my way, or any other questions that you might have. Email: firstname.lastname@example.org Best wishes, KMS
Thank you for sharing this with us. Did you read about the case recently in Australia? Amazing story, and science, isn’t it?
Yes, that case in Australia of sisquizygous, or semi-identical twins, is very interesting. More and more, we’re finding old ideas falling before new discoveries in science. The absolute certainty of DNA tests (nope), the differences between male and female (on a continuum), and cases where genes are switched on and off . . . it al makes the world a fascinating place!
Agreed! The more that DNA technology comes available, the more common these “rare” cases will come to light. Very exciting time to be on this planet.
I am only aware of 15 published cases of tetragametic chimerism, so I’m not sure the 100 figure is quite correct yet. But in the near future, it might be, with the huge uptick of DNA testing we are seeing more of these cases come to light than ever before.