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What is Chimerism?

DNA analysis can determine the presence of chimerism.
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Chimerism is an rare disorder that mixes the chromosomal population in a single organism. In these cases, chimerism may manifest as the presence of two sets of DNA, or organs that do not match the DNA of the rest of the organism. In some cases, hermaphroditic characteristics, in other words, having both male and female sex organs, can be signs of chimerism. Alternately, small patches of DNA can be present throughout the body.

Chimerism tends to occur very early in the embryonic development. It is often the result of two non-identical twin embryos merging together instead of growing on their own. Although the condition is very rare, with only about 35 people in the US being identified as having chimerism, it tends to get attention from popular media.

Both the television shows, House and CSI have featured episodes dealing with chimerism. In the 2006 episode of House, a young child is found to have microchimerism, small patches of non-matching DNA that are causing the child to become ill as his body rejects the foreign DNA.

In CSI, a suspected criminal has two sets of DNA, one existing in the lower half of his body. Thus his DNA does not match samples found at a crime scene, though other evidence proves him the killer. When the suspect is identified as having chimerism, he is found guilty.

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Such cases may make for interesting television, but real cases are seldom identified. There was one legal case involving a woman with chimerism, who was proven not to be the mother of her own children. Later discovery of embryonic cells with different DNA disproved the earlier DNA results.

The number of people with chimerism may not be entirely accurate, since many with chimerism may never show any symptoms that they have other DNA present. Chimerism is most often noted in those considered as hermaphrodites, but not all hermaphrodites have chimerism.

In rare cases, the DNA that produces organs may cause organ rejection or failure if the rest of the DNA in the body attacks the organ as foreign. The odds of this happening are extremely minute.

In some cases, chimerism may be the deliberate result of scientists attempting to mix two species. In one case, scientists successfully produced a goat/sheep mix. They have also been able to produce a chimera quail/chicken. Most often these attempts fail, and if they do work, the animal produced is often sterile.

When scientists attempt to produce chimerism, they are actually merging embryos of two animals. They are not mixing the egg of one species with the sperm of another. That process is more common, more successful and is called hybridization.

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Discuss this Article

anon943483
Post 52

What happens when a person is the child of two chimera parents?

anon352816
Post 51

My son has dark curly hair on one side of his head and light straight hair on the other side. I have looked online to see how common it is and I have never seen another person with two different kinds of hair. He is only a year old but I wonder if this could be the reason.

anon335948
Post 50

I have two very distinct colors in my eyes. One is completely blue and the other is half blue and half brown. When I was young, 40 years ago, the doctors told my mom it was a sign of twins that didn't form. I have two children who, when together, are often told they look nothing alike, yet I am always told they look like me.

Are there any current studies that might benefit from testing us? I am more than willing to see if I am in fact a Chimera. It would be interesting to see if my children match me genetically in the same way or in opposite ways.

anon332678
Post 49

I have a line that goes from my sternum to below my belly bottom. The right side of said line is darker in skin tone (it also tans quickly like my father) than the left (which stays pale and even burns like my mother). My mother always joked to me growing up that I was half her half Dad and told me that it would go away with age but it hasn't. She's a pediatrician and has seen hundreds of babies over her career but never has she seen the two tone skin I have.

I am full grown now and still have no idea what's up with my belly. After searching for some time, I was led to this article by the comments of 5 and 18 matching my own. I read through everyone's comments, learning that there is chimerism and mosaicism. My question is, what is it I have? Or is a two skin toned belly the result of something completely different? I hope someone can be of some help because I have no idea what to make of it.

anon332658
Post 48

@comment 47: Love and lust are caused by chemicals in the brain. Part of this is from pheromones. They are the reason people are straight or gay. These classifications are based on their physical reaction to male or female pheromones. That means that there is a reason for heterosexuality, bisexuality, and homosexuality. However, there is nothing to change these reactions so they should be accepted. It is not a choice, as many believe. It is simply a chemical reaction which could, in fact, be altered by Chimerism. However, that is a slim chance.

@Post 45: Most likely, in the case of the gay uncle, he is simply gay and not at all changed by Chimerism. I do understand the confusion, however, as most research isn't explicit.

anon331510
Post 47

Comments 44 and 45 were first on my list. I really just have no words. @45: being homo or heterosexual has nothing to do with chimerism. Please stop trying to find reasons to justify why someone is gay. Just accept that they are gay and there is just no reason behind it, nor any reason to ponder it. They are a person just like you are. Imagine if people you met spent their free time wondering what kind of defect or abnormality in your genetic makeup made your nose look like that.

@44: You are not talking about chimerism; you are talking about mosiacism. They are two very very different conditions. I suggest you let the Facebook group you run on the subject know you have no idea what you are talking about.

ja1194
Post 45

Someone mentioned that being gay or a lesbian was due to chimerism.

My uncle is a twin and he is gay, yet his twin sister is straight. Does this mean there were supposed to be triplets? And my uncle is a chimera and his third sister is "inside him" and that's why he's gay?

anon290419
Post 44

My name is Lorraine and I run the Facebook group on this subject. It is far from rare. In fact, it is proposed that at least two-thirds of the world's population is chimeric.

I suspect it is the normal state of man and we are only just discovering it. I see all autoimmune disease as a case of twin attack, not self attack as suggested. I also believe that parasitic twin cells are the basis of all cancers and that chimerism is also behind chromosome abnormalities. It's where the extra chromosome 21 comes from in Downs syndrome.

anon287247
Post 41

Chances are, all of these weird abnormalities are simply recessive gene apparition. It happens. I am also not willing to say that we should start testing everyone who is gay or has gender confusion. While chimerism may explain a very, very small handful of cases, evidence suggests that the majority of cases share different chemical levels in the brain than their heterosexual counterparts. Testing them to see who is and is not chimeric would be an enormous invasion of privacy, and would attach yet another stigma to an already struggling minority.

While chimerism may be a wee bit more common that we currently believe, the fact remains that, in a nation where DNA testing is becoming more and more prevalent, there have only ever been 35 legally verified and documented cases. Were it as common as people here are theorizing, it would have been proven by now.

I also get peoples' desire to identify a case of chimerism in their lives. Chimerism is rare, mysterious and it ignites our imaginations. How cool would it be, we think, to be not just one, but two people, in one body?

The chimera has been central to many mythologies for thousands of years, most prominently in Egyptian, Greek, and Roman mythologies, but making an appearance worldwide. It is a fascinating concept, and if one subscribes to the belief of an unconscious collective, we have millions of memories of living in a time where chimera legend was prominent, all locked in our unconscious, just out of reach.

So go ahead and imagine. We all deserve to have something that makes us wonder, "what if?" We all deserve to hold that childlike curiosity and wonder over something. Why not the chimera?

anon242712
Post 40

Consider that if the "absorbed twin," which happens in the first few days after conception, is of the opposite sex, determined by finding both DNA's, couldn't that explain homosexuality, gender identity disorders, and all of the confusion some people feel about being in the "wrong body"?

This may not be so rare. It is just not something that people have looked into yet, but how great it would be for gays and lesbians to be able to know it is medical and not a choice!

anon240611
Post 39

Such an unknown trait. I wonder how many of the sid's cases may be related.

anon178065
Post 38

There is a group on facebook called chimerism that may explain more.

anon166519
Post 36

i had always thought i had a twin and at 21 when i had twins, even though fraternal twins had not been recorded in the family, i thought that was the feeling i had.

I recently found out that even though both my parents are rh- that i am rh+. this is impossible, but it's true. this is when chimerism came into play. another fact: when i was in the womb they said there were signs of twins but in the end it was just me, and i, even though a normal girl who likes dresses, i also love video games, comics, and even fights, which somehow even against guys i would win.

my boy and girl twins are total split dna. They are half black and white and their dad is white but my daughter is brown like me with dark hair and eyes and my son is white with green eyes and sandy hair. and she is the leader and he cries a lot. Total opposites. She loves dresses and he loves guns, against my wishes, and it's just amazing how chimerism puts this all together.

anon161799
Post 35

What kind of crap are the comments? Almost every single dam comment claims to have seen some sort of chimerism in their lifetime. I'm a medical consultant and i know chimnerism is one of the rarest conventional syndromes to exist. I have no idea why these people are saying this stuff. Is it because you want to feel special?

anon150245
Post 34

This very interesting video has given me a lot to think about. I do not believe it as rare as some people think.

If everyone who is gay, or has a gender identity disorder were tested for obvious DNA, and internal, not so obvious DNA, they would probably find out that they indeed have

two sets.

When a chimeric are twins of the same sex, they are much less aware of the condition, but when the twins were two sexes, I believe the result is that the people are homosexual or have other gender issues.

Does anyone know if there is any further research being done on this?

anon113590
Post 33

ok so i have two different colored eyes, and no one else in my family does. one of my eyes is green, the other is blue. my mom has blue eyes and my dad has brown. I'm worried that i am intersex, or was born intersex and surgically made into a female, because i have a large clitoris. I'm freaking out so can someone tell me what they think? am i intersex and/or do i have chimerism? please let me know.

anon92564
Post 32

I have noticed growing up i kick always left legged. I am right handed, but also able to write well with my left.

also my dad has curly thick reddish brown hair. my mom has straight brown, but both when young had blondish hair. Now me, my hair is blond with some almost pink in the light. Some hair strands are straight brown, but the weirdest is that my hair is very fine but all through out my hair i find thick, coarse, curly black almost strands.

please, if possible, someone explain if this is chimerism.

anon80161
Post 31

I just found out recently that my nine year old is a chimera. He went through a lot of genetic testing.

He has the distinct brown patches that most of you talk about and he has one side of his body growing slower than the other, causing his hand and one finger to be very small. He also has a jaw deformity.

He has two sets of male chromosomes which was a big relief! It is a very interesting disease and I wish there was more out there for us to read or a support group to join!

anon76760
Post 30

I have one greenish eye and one hazel and sometimes they look different with certain clothes i wear. my dad and i have barely noticeable nipples under our normal ones. Is this Chimerism and is this hereditary? My two younger sisters are fine. anybody with info please let me know!

anon70172
Post 29

I recently had a trip to the dentist. he discovered a thicker bone structure. He discovered I had two extra premolars growing in the mandible area or "no-man's land" as he referred to it.

He went in to perform extractions and noticed that on the first one he did, it did not have a normal molar root system; instead it was a mushroom type root which caused me a lot of grief.

He gave a brief explanation on genetics and in womb chromosome changes and etc. when I asked if is this a genetic defect or mutation, he looked at me blankly, and then I said or is it like a chimera trait? he then looked at me and sighed a sigh of relief.

He told me I could seek out testing to get a proper diagnosis. This is all so new to me. I wish I could find more information. I read online some symptoms or "clues" to one being a chimera and I have some of them.

For example, different pigmentation patches on my torso area, different patches of hair color. I am balding now but in my youth I had long black hair with patches of brown and red and it was only in concentrated areas. I have a son but since he is of mixed ethnicity I have not noticed any of these traits in him.

I am simply trying to find out what is going on with me. I am a rather large man at over 6 foot 2 and over 300 pounds but I look like I weigh 220 or so. I ache a lot and that has only been as a adult.

Also my premolars (extras) grew in when I was in my 20s. Can anyone shed some light or point me in the right direction to get tested or etc.?

anon69714
Post 28

I have some abnormalities that lead me to believe that I have chimerism: supernumerary breasts (small extra set of nipples below my own), patches of brown in my face/neck, a "nodule" of skin at the anus, tipped uterus and I've been told my heart is tipped as well.

Not sure if the abnormalities would be contributed to chimerism but the extra nipples and patches of brown in my blue eyes suggests that I probably am.

anon49523
Post 27

I am Chimeric. My gynecologist was the first person to figure out what the heck was going on with me, and she was very excited. She published a paper on me. She died a year later, which was seven years ago, and I am still finding out strange things about myself, as time goes by. I had dental surgery, and the doctor had to take off 1/4 in of my jaw bone, and his saw blades kept going dull! He was incredulous, and kept saying things like "I've never seen crazy bones like yours!", and "I just can't believe how dense your bone is!" I finally told him I'm a chimeric, and he told me that *that* completely made sense to him as to why my bones were so dense. So, I've since had a bone density test, and they truly are extremely dense and healthy, especially considering I'll be 44 soon! Not to be too graphic, but one saving grace is that my twin would have been another girl, because if not, I would be an hermaphrodite. Yes, I have extra 'stuff' going on, and have never been able to have a baby. No one could ever tell me why though, until my obgyn finally figured it out! I have been looking for a support group of some kind, but to my knowledge, *none* exist. Maybe I'll have to start one up myself.

anon44572
Post 26

I would like to be a hermaphrodite. Does Chimerism help to become a hermaphrodite? Can a hermaphrodite get a female pregnant?

anon42771
Post 25

My 7-year-old grandson was diagnosed with testitoxicosis at around age 2 1/2 when his mother noticed pubic hair and other signs of puberty. After many examinations, it was determined to *not* be precocious puberty. He has been taking a steroid and an antifungal, both of which have slowed his hormonal race. He is tall for his age, exhibited fierce antagonism at an early age, and his bone growth was accelerated. He was one of a twin, but the other twin died early in the pregnancy. He has not been genetically tested, but could this be a form of chimerism?

anon37137
Post 24

Looking forward to that WiseGeek article about heterochromia, since I too have it: two distinctly different colors of hair (dark brown mainly, with a blond streak down the middle that's so light, people assume I bleach it -- but I was born that way!) and heterochromial eyes as well. Before the Internet, I was the only person I knew like this (and I'm very well-traveled).

anon34708
Post 23

I believe that i may be a chimera. I have heterochromia. There is no sign of it in my family. My bone structure in my face and clavicles are subtly different. When i was younger around 12 i noticed that there was a straight line of discoloration on my face. It went straight down my face. It wasn't very prominent and you had to look closely. I also have 2 different colors of hair. And what intrigues me about this is that my eyes, the left one brown the right one green, go along with my hair. On the left side my hair is dark brown as is my eye and on the right side my hair is blonde, that eye is green. My hair is a straight split of the colors right down the middle. My eyebrows are slightly different colors and the hair that grows on my arms are lighter on the right side. I am very freaked out. Does it cost a lot to get your dna tested??

DDWyatt
Post 22

Among some of the unusual pieces of evidence I refer to are:

One ear from each of my parents. My father has a point behind his ears, my mother does not.

I am both left and right handed.

I am both left and right brained. Very logical, very artistic. I learn faster with better understanding than 99.9% of the population.

I have had many surgeries and found that the right side of my body will require a tube or other form of method to remove a build up of liquid around the incision site. This does not occur on the left side of my body.

On occasion, during a visit to the dentist, injecting Novocaine on one side of my mouth will numb the other side with no effect on the injection site. It always takes trial and error to numb me for dental work. 12 injections minimum.

I have an inflection on the right side that will not transfer to the left side, yet spreads on the right side.

There have been many other things that have occurred that support the idea.

Is there anyone studying Chimera that would be interested in helping me find out for sure?

anon30193
Post 20

My chimera body is not proportional, infused with a short person and a tall person.

My torso is too short for my height. When sitting down in a row tall people (who are the same height as me) are taller and people who are shorter than me are the same height.

My legs and arms are the too long for my height.

When standing up in a row of tall people who are the same height as I am, they have shorter legs and arms than I do.

My feet are too small for my height. My shoe size is only 8 & 1/2 and my height is 5 feet 8 inches.

I have never met anyone or seen anyone else like me in my lifetime.

anon29532
Post 19

So today in my high school biotechnology course we watched a video on chimerism called "I Am My Own Twin". They showed some pictures of human chimeras with a line running down their chest separating two different skin tones. I then realized that all my life I have had the same thing! Except in my case it is not as noticeable because my relatives were all Caucasian. I suppose the next time that I talk to my doctor I'll mention it lol.

Vonnie
Post 18

My 3 year old granddaughter has 2 distinct skin tones running in a straight line from her sternum to below her belly button. Is this a symptom of Chimerism?

anon27139
Post 16

My eyes change color almost all the time but they are never the same or one of them is split. It freaks people our around me. One day it even freaked me out when both of my eyes were split. My left was gray and blue the right was reddish-brown and yellowish-green. Any explanation?

anon26001
Post 15

i am a scientist that is studying genetic grafting,or in other words, the alternate chimera. what is your take on this situation?

kcoburn222
Post 14

I have one blue eye and the other is blue with 1/4 brown (exactly 1/4). I was always under the assumption that it was suppose to be fully brown but just didn't develop that way. Years ago I came across a "Surgeons certificate" in some papers of my mother's when we moved. It was an insurance paper that was written out for "baby boy" and relationship to father - "son". I thought it was for one of my brothers until I saw the birthday. Mine. I am the only girl. My mother's explanation was that the doctor made a mistake. I'm 53 now and a few years ago came into possession of a family tree. It seems my mother's side of the family is loaded with twins. They stopped with her mother. Reading your article and now looking back, could my 1/4 brown be an indication of chimerism? Thanks.

ajtlawyer
Post 13

The article mentioned one legal case in the US that involved a woman with chimerism and the paternity case she was involved in when initial DNA tests excluded her as her kids' mother. I was her attorney in that case and, as far as I know, it was the first such case in American and possibly world legal history and it may be the only such case; I haven't heard of any other cases like it since. You can see the entire documentary about the case on Youtube under the title "I Am My Own Twin" and the documentary is often shown on Discovery Health Channel.

No one knows how many people are chimeras. It might be far more common than anyone knows. But it is hard to test for and most people have no symptoms of it or any consequence of it that might cause them to look into it. Some doctors believe it could involve problems with immune system disorders, autism, transgenderism, mental health problems, cancer, etc. But proving someone is a chimera takes highly specialized testing. And if you are a chimera I would expect that there's no cure for it, if that's what you're looking for.

anon22191
Post 12

Could Chimerism be associated with mixed dominance?

I am completely dominant on the left side of my body (kick with left foot, prefer the left ear to listen with, left-eye dominant, etc.) with the exception of my handedness- I have always written with my right hand. I also have sectoral heterochromia, as does my brother.

anon13741
Post 11

I recently watched a show where a woman was trying to get welfare and the DNA test said that she wasnt her 2 kids mother, they kept asking her whose kids were they (at this time she is also pregnant with her 3rd kid)and they were actually gonna take them away from her until they actually had someone from the court be there when she had her 3rd kid and took a DNA sample from her and the baby and sure enough a couple months later it proved she wasnt the mother. But the women herself actually heard about another women that it happened to and they found the second DNA (which was the same as her kids) in her thyroid. So i guess if you want to know if u could be a chimera then get 2 different blood test!!

WGwriter
Post 10

Hi Gojerae,

You might want to investigate the National Organization of Rare Diseases, also called NORD, for more information. They often have links to other resource sites and support groups too.

gojerae
Post 9

Several years ago, I had a doctor tell me that I was "duo-chromatic" and recently, the same doctor told me that I am a chimera. I have spent a crazy amount of time trying (unsuccessfully, I might add,) to find out information about this "condition". I would really like to know more about chimerism and how to be tested/diagnosed with more accuracy. Can anyone help?

anon9106
Post 8

I am a student doing a paper on chimerism. I found your website and I am very interested in finding out more information.

Kitty
Post 7

The bone structure on the left and right side of my face is different. It's like taking two almost identical bodies and putting one half of each together to make one. Can it be a sign of chimerism or what else could it be?

meansuga
Post 6

When I was in my 20`s, my eye doctor said I had signs of a degenerative eye disease, but could not conclude it then. Now I am 41 years old and recovering from breast cancer and lymphoma and the cancer treatments. In the summer of 06, during my radiation for my cancer, I went to an eye doctor to have my eyes checked and update my eyeglass scrip.

The doctor there told me he saw an antrophophy (?) in my right eye, and to come back to see their retinal specialist at another time and to clear my exam with my cancer specialists.

When I saw the retinal specialist - he told me that I did not have a disease, but rather signs of chimerism in my eye - a strand or piece of DNA that was probably different then my own lodged in my eye.

They wanted to set an appointment to run more tests, and bring in more doctors. Although it was very interesting, I really couldn't take the time from work for the treatment and rest I needed to recover for these tests at that time. They never ran the standard exam, because they were too busy being fascinated by my eye! I was a bit perturbed- I just wanted new glasses so I could see!

I went to another doctor - so I could get my new glasses quickly and stop the 'run around'.

The new doctor told me - yes- it did seem to look like chimerism, possibly DNA from a weaker twin that my body absorbed in utero. And that he knew many doctors that would by interested in this find when and if I ever had the time.

It brings up questions... is this worth checking out? Would I have to pay for any testing?

And does this chimerism contribute to health issues I have had - the cancer, poly cystic ovary syndrome,

and my personality quirks (i.e. oxy moronic)?

Any advice, input or ideas would be appreciated.

Jenny720
Post 5

My child has a line down her stomach on one side is darker skin than the other. Can this be a sign of chimerism, what else can cause this?

Dayton
Post 2

Heterochromia (two different colored eyes) can be caused by chimerism, although there are other genetic and acquired causes as well.

I have requested a new wiseGEEK article entitled What is Heterochromia?, so look for that in the future if you have more questions.

kayleywade
Post 1

I understand what the article is saying about how a chimera is from two fertlized eggs that fuse together, therefore creating one individual with two genetic profiles. My daughter has a friend who has one very blue eye and one very dark brown eye. She also has one deformed finger. It is a possibility that she is a chimera, and the two different colored eyes are a result of one set of the DNA having the blue eyed trait, and the other set of DNA having the brown eyed trait? I find this extremely fascinating and wish there was more information to be known.

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