Maggie Koerth-Baker is a guest blogger on Boing Boing. A freelance science and health journalist, Maggie lives in Minneapolis, brain dumps on Twitter, and writes quite often for mental_floss magazine.
One person outside: But two people "inside": That's the gist of the chimera, a human being who carries the DNA (and sometimes the body parts) for two. It sounds crazy, but it happens. In fact, doctors think it probably happens more often than we realize. Unless there were some reason to test the DNA from cells in different parts of your body, you could easily be a chimera and never know it. Happy Freaky Friday, everybody.
So how's it happen? In this excerpt from my book, Be Amazing, I explained how chimeras happen, and how confusing it can be to be one.
First: Get That Meddling Sibling Out of Your Way
Imagine you're a fertilized egg, just a few days old. There you are, floating around the womb and minding your own business, when, BAM! You run smack into another just like you. Well, not just like you. But certainly close enough to be a threat. Now, you have a choice. You can roll over and let yourself be born as just another fraternal twin, or you can stand up for your individuality and absorb the interloper. Naturally, you do the smart thing, and nine months later your parents take home one healthy baby.
Then: Discover That They Aren't As Dead As You Thought
Like a horror-movie villain locked into a three-picture contract, your twin never really died. Instead, she'll end up hiding in plain sight--within your very cells--rendering you a chimera, a single human who carries the genetic makeup of two different people. Most of the time, there aren't any outward signs that your body is harboring a stowaway. But when you do notice, things get a little crazy. Take Karen Keegan, who discovered her chimera-ness at age 52. When Keegan needed a kidney transplant, she and her two adult children underwent DNA testing to figure out which kid's kidney would be the best match for mom. Surprisingly, the tests showed neither. In fact, according to DNA, Keegan's children weren't her children at all. The case confounded doctors for more than two years until, in 2000, the docs finally realized that Keegan's blood cells carried different genes from the cells in her ovaries---the long-absorbed twin was found.
Perhaps you're wondering whether chimeras can incorporate twins of two different sexes. The answer is yes, and the results are often much stranger. In 1998, Scottish doctors reported treating a teenage boy for an undescended testicle. But when they put the kid under the knife, no second testicle could be found to pull down. Instead, where the ball should have been, doctors discovered an ovary and fallopian tube. Chimera strikes again.
For some fun further reading, check out the story of Lydia Fairchild. Like Karen Keegan, Fairchild's chimeric nature was discovered after DNA tests said she wasn't the mother of the children she was pretty sure she remembered giving birth to. Unlike Keegan, however, Fairchild's kids were still young and the initial DNA test almost cost her custody.
Much like Professor Xavier of the X-Men, illustrator Michael Rogalski is locked in deadly, psychic battle with his evil, chimeric twin.
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A more common form of chimerism is mom's picking up cells from the fetus.
http://www.npr.org/templates/story/story.php?storyId=5195551
That's right! It's a natural embryonic stem cell transplant!
I've read about women who were found to have some random cells with male DNA in them because they had given birth to boys and some of their son's cells had stayed behind and survived.
the most common form of a chimera is part goat, part snake, part goat and part fox... news.
The Lydia Fairchild story is chilling and a good example of how courts and the legal system can be fallible. Saying that DNA is "100% foolproof" is stupid. Nothing is 100% foolproof.
I have a chimera friend.
The top half of his eyes are blue, and the bottom half brown.
He has to take immune-system suppressants to stop his body rejecting various organs, so he always has a cold.
My son is a liver transplant recipient. He was had his new liver for 24 yrs. he has been enrolled in a study to see if he can stop using the anti rejection medication and see if his body adapts to the new cells in the liver....chimerism at it best
I've always been partial to the legendary Esquilax, the horse with the head of a rabbit, and the body of a rabbit.
A friend of mine underwent a complete bone marrow transplant to treat a dangerous blood disorder.
Her new marrow came from stem cells harvested from her brother and infused into her own blood stream.
She now has her brother's blood flowing through her body.
I guess that makes her a chimera.
A fairly common example of this is a calico cat. The orange spots have a diferent DNA makeup than the white parts.
Another example is probably Corky, the guy with Downs syndrome, from the TV show Life Goes On. His trisomy 21 probably didn't occur until later on and thus only a part of him has Downs. Thus he appears, and is, much more high functioning (can act, memorize scripts) than the vast majority of people with Downs syndrome.
It may be exceedingly rare, but Dr. House totally figured it out.
@8
Dr. House knew what it was all along and just didn't bother to tell anyone until the end of the episode, because of how he is such a smug, yet (supposedly) lovable, jerk.
I think that's really cool - and so do I.
This explains The Great Roe: "The great roe is a mythological beast with the head of a lion and the body of a lion, though not the same lion." (Woody Allen, from Without Feathers)
One of the US cable channels aired a program about chimerae about 2 years ago, but I can't find a link to it. Anybody else remember?
Was probably Discovery or TLC, but I don't remember.
Fascinating stuff...and makes your head spin thinking of the possiblities and problems that it raises.
#6 - From your description of the esquillax, either you've got a normal rabbit or a rabbit with the neck of a horse.
I need pictures, please.
@12: Used as a logo:
http://ourworld.compuserve.com/homepages/r_harvey/rabbit.htm
#8: Gil Grissom sussed it too...
Discovery Health Channel just reaired a documentary about chimerism the other day. It's called "I Am My Own Twin." This is why I minored in biology - the human body is so fascinating!
is this where the voice in your head comes from???
"Half Life" by Shelley Jackson. Nuff said.
#12 posted by skabob, May 1, 2009 8:50 AM
#6 - From your description of the esquillax, either you've got a normal rabbit or a rabbit with the neck of a horse.
I need pictures, please.
Isn't that used in the Comcast commercial? A genetically modified jackrabbit, ridden by an overly caffinated fighter pilot, blah-blah-blah...
How awkward it must be to learn that you not only have a phantom twin, but that she's been sleeping with your husband.
can't believe you did a whole post about chimeras without discussing Barr bodies. Every human female with two normal X chromosomes is a chimera- each and every one of her cells has only one active X chromosome in it.
http://en.wikipedia.org/wiki/Barr_body
I am just beside myself now.
I too am beside myself.
When originally nabbed for doping in 2005, former pro-cyclist Tyler Hamilton claimed the strange blood in his system came from his chimeric twin: http://www.nytimes.com/2005/05/10/health/10bloo.html?ex=1273377600&en=7455147a21b4f286&ei=5088&partner=rssnyt&emc=rss.
His case was rejected and he was suspended from cycling for two years.
Surprising no one, he recently left cycling for good after testing positive again and finally admitting to doping the whole time.
I have to agree w/ dculberson - the description of the Fairchild's ordeal - from the callous/abusive social workers on through the legal system and the way she was treated by state officials (irrespective of hospital records, character witnesses, and even direct observation)... is quite sobering.
Chimeras are crazy and mind blowing and all, but I'm still just chuckling at the people trying to dissect a Simpson's quote.
I WANT to be a chimera!. My liver is failing and I need a transplant. I often wonder what it will be like to have 2 pounds-ish of someone else's DNA.
If you're not an organ donor. Please consider it. There's a lot of people waiting for organs... but not enough to go around.
Normal females (including tortoiseshell and calico cats) are mosaics, not chimeras. Very similar, in the variable expression of X-linked traits, but from a single DNA profile.
I think I'm a chimera... My hair on my head, eyelashes, etc. is blond on one half and brown on the other. And it isn't a pigmentation thing because my skin is fine, my eyes are the same color. It's just my hair.
#9 and #30 - I believe Corky is also probably a mosaic, not a chimera. Trisomy mosaics are not uncommon, and in fact mosaics are able to survive with trisomies (e.g. trisomy of chromosome 16) that are otherwise completely lethal.
I heard about this on WNYC's RadioLab a while back. That show does for me the same thing Boing Boing does, makes my mind do double takes.
Fun example in the Venture Bros where Dr. Venture's Chimera twin leaves the body to exact revenge and take his place as the true son of Dr Jonas Venture
Chimeric humans have been made as a way to eliminate the use of anti-rejection drugs. You take bone marrow from the organ donor and implant it into the transplantee, then subject them to radiation. The chimeric immune system doesn't reject either the original body nor the replacement organ, so no drugs are required.
I recently started writing a sci-fi story about a girl who had two sets of DNA and had to time travel backwards to find out why. I had never heard about chimeras as double DNA, only as 'animal' creatures. Endless possibilities here ...
@ 9, 23, 30: X chromosome inactivation in "normal" females is not the same thing as mosaicism. X-inactivation results in the formation of Barr bodies (condensed chromosomes) and accounts for tortoiseshell coat color in cats (along with the expression of many other X-linked traits in humans and other animals), but all of the cells in that individual have the same genotype.
True mosaicism results when chromosomes fail to segregate properly during embryonic cell division. The individual has some cells with a typical chromosome number, and some cells with an atypical chromosome number (i.e. an aneuploidy).
Chris Burke is not a chimera. Knowing him, but without ever personally asking him (because it ws a neither here nor there question...it did not matter, in other words), I do believe he has Mosaic Down Syndrome. MDS is different than Trisomy 21 Down Syndrome in many ways. Chris is very smart about politics and movies and he is in a band with twins. He is a nice man and a bit different than his acted role of Corky.
Chimerism, like twins, can be inherited.
I have a son, diagnosed with mosaicism 50%, but I believe it is chimerism; Dad ppears to be one also. At first, I thought I was going crazy (and frankly others did also) because kept thinking my husband was a twin and playing tricks on me. Long story short, when my son was born, he started what they call "shape shifting" also. Others saw it as well;he is like a chameleon. Anyways, I really startedto wonder about myself UNTIL I caught it on film with someone else taking the photos. We did a remake of a portrait for my son and compared the two which were taken in the same month. WOW!!! He looks like TWO DIFFERENT PEOPLE!!! One looks like Trisomy 21 and the other looks just like a normal kid. Weird, but the full moon has an effect on him (and my husband) as does mood and environment (kinda like a chameleon). I asked the geneticist to test for chimerism, but he (at that time) said it was not and was just Mosaic Down Syndrome 50%. Husband has not been tested due to lack of insurance and adequate $$$$ because those testsare too expensive for our budget.I am pretty darn sure they are both chimerics, especially after all this and then I found out twins are common in his family. I wish there was a way I could post the pictures of my son, but no upload button here.
Susan
would i be a chimera if one half of my eye is greenish yellow and the rest is blue, i have a extra wisdom tooth and index wrinkle on my pinky finger???? just wondering
hi everyone,i was pregnant with fraternal twins and at about 15weeks they said one had vanished,months later my son was born and i think hes a chimera,he has 2 totally different faces,one side is smaller than the other,his ears dnt match at all,head on both sides is a different shape and so are his eyes...anybody else have a baby or themselves have this going on? hes only 4 months old now...im wondering if he grows out of this or its permenant...thanks