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Chimera Twins Story
skelley writes "Below is an audio link on this morning's story on NPR about Chimera twins, or people with two sets of DNA.
It turns out that every once in a while a set of fraternal twin eggs merge into one embryo. The resulting person has two sets of DNA.
The story says it is possible for a Chimera to have different sets of DNA in different body parts. This can cause complication for body identification, DNA typing for organ transplants, crime investigation, etc.
Researchers have no idea how common this is, but suppose that it is a reasonable percentage of all fraternal twin pregnancies, which would mean millions worldwide.
No text version. NPR often doesn't publish one.
"
The interesting thing is that since invitro fertilization has a much higher probability of twins (or more), chimeras will become more common.
we should study this so we can give different parts of ourselves different DNA. If it is to be appropriated as a universal identification and control technology, we have to give it up if we want to remain sovereign. It is not that far away to have DNA identified radio tagging of people and, thus, near-absolute control.
Doesn't DNA to some extent at least determine blood type? Would it be possible to have two blood types? Surely not, but as I do not have any way to listen to the link I will never know until some kind soul gives us the gist of it.
Any known birth defects/oddities arrise from this which manifest themselves in the physical sence? IE if your trying to test someone's DNA and realise they have blond hair on one half of there skull and black on the other you would know something was up.
The story says it is possible for a Chimera to have different sets of DNA in different body parts. This can cause complication for body identification, DNA typing for organ transplants, crime investigation, etc.
Wouldn't this cause complications a little more important to the individual than those listed? Like say, stuff not fitting together right? I mean, I wouldn't want to try and build a working car from half Ford Explorer parts and half Ford Focus parts.
I wonder how many people with this condition die before birth or at a very young age.
Nature published a short article on this a couple of years ago that we covered in our Journal Club meeting at my lab. The only one people detect right now are chimeric male/female twin pairs because its so easy but they had lots of cool shots under UV light where you can actally see like tiger striping of the two chimeric skin types. That was my favorite part.
DNA typing for... crime investigation
Interesting phenomena in itself, but I wonder if there are people who would (or already) exploit this sort of pseudo-anonymitity. Does anyone know how far this dual-DNA goes? can individual hairs have differing DNA? or will the blood have different DNA than the hair or skin? (I am not a biologist, so please be kind regarding these questions)
-John
"The definition of insanity is continuing to do the same thing and hoping for different results"
You can reconstitute the absorbed brother/sister through cloning the right cell?
Could he/she then sue their sibling for attempted murder?
In Greek mythology the Chimera was part lion, goat and serpent. This is why people with organ or limb transplants are sometimes referred to as a Chimera. So my question... do these people also present the same identification complications?
This isn't directly related to what you said. but what happens if the fraternal twins that merge to become a single chimera twin are male and female? is this a possible explaination for hermaphrodites?
:)
Again, as I said elsewhere in another reply to this article. I am not a biologist, please be kind if this question has an obvious, or easily googlable, answer.
-John
"The definition of insanity is continuing to do the same thing and hoping for different results"
There's an organizitaion called the The Innocence Project headed by Barry Scheck which prides itself on freeing prisoners who didn't have the technology of DNA testing avaible to them during their trials.
In light of this article, I wonder how many guilty people have been set free. I'm sure there are guilty parties that proclaim their innocence and see no harm or foul in having the DNA testing done by said non profit organization, in hopes of some fluke in their favor.
The human genome isn't like the automarket...That is you're still building 1 car, but all the parts can be slightly different, but come from 1 supplier. After all, in a normal diploid animal (ie. humans) half of the chromosome content is from the mother, the other half from the father. As far as liver, heart, skin, etc. all working together, there is no problem with this.
There is a problem though with the immune system. Since each organism's cells contain a unique combination of cell surface receptors that let's their body know the difference between "self" and a bug or virus, then depending which copy of DNA founded the cells of the thymus (where "self" is first determined), a chimera's immune system could see cells with the other DNA set as foreign - causing a massive systemic allergic reaction. The good news is that chimeras with this problem would spontaneously abort within the first few months of the pregnancy, so if a chimeric human is born, they probably don't have to worry to much about such genetic mismatches.
"Nokia is not a country, it's the capital of Finland!" -Moderated "Informative". Yeesh.
Dr. Jeckle(sp?) and Mr. Hyde isn't too far fetched after all. The "formula" Jeckle drinks to become Hyde simple turns on the alternate DNA sequence.
--Im an oven mitt, not an engineer! (SLArbys Radio Commercial)
Actually, I know of one case where this was so. I used to work with a guy who was a chimeric twin. He volunteered for some genetic research at Stanford and they came back and said he had two sets of DNA. He had one of the oddest shaped bodies I've ever seen. Looked kind of like something from Star Wars - like a ball perched on top of really long legs.
I had always heard that a person that has eyes of different colors is really a chimeral twin.
Here is a pretty freaky story of a boy who seems to have assumed his twin in the womb. No one knew until when,at age seven, he had a stomach ache and surgeons removed his brother.
While I don't know for sure if I am a chimera, I was born with XX/XY sex chromosomes, something I only found out in my early 20s.
For many of us born this way we don't appear to be completely male or female and like most I was surgically "repaired" very soon after birth. This means I had what appeared to be testicles removed, testicles which MAY have permitted me to have children one day. Part of my body was stolen because I looked different. I was raised female, always felt that didn't quite fit, and it took me a lot of messing through courts to obtain my birth records. As I am now I have to settle with knowing where I fit originally, why I am like I am, and can accept living as a mostly normal female. By nature however, I was born part male part female. That's me. The chance to live and develop naturally was stolen from me.
It's fucked. Science continues to find so many variations on human development but society so often manages to force decisions on people. How odd that I was considered unnatural enough when I was born that doctors decided surgery was the only acceptable option, when my birth and very existence is just one more facet of nature.
For more info on how intersexed kids (chimeric or any other variation) are treated, see isna.org
Regarding organ rejection: rejection is a "trained" response. Fetuses/embryos can recieve organs without fear of rejection, because the immune response is not trained against the offending organ. That's why some people can have two different blood types: they recieved some blood of a different blood type before they were born, and their immune system adapted to this other type of blood and accepted it as part of the body. That's why chimeras can exist.
Not a problem in this case; the immune system hasn't 'initialized' at that point, and so would imprint both types as self when it comes online.
This is why people are interested in freezing fetal blood samples; the theory is that you keep a backup of the immune system install media to reinstall if it goes bad. Um, except that we have no idea how to do that yet... works in theory, though.
is this a possible explaination for hermaphrodites?
Take this question one step further? Has it ever been recorded where one set of DNA contains a genetic disorder and the other does not?
IANAB, I just find the idea insteresting and maybe a possiblity for treatment (Find the problem early enough, then introduce an extra set of DNA to reduce the impact of the disease; though this idea definitely has some ethics baggage attached.)
-B
Any court appointed expert worth his salt will give the jury a detailed, precise p-value for the probability that the DNA came from some other person. A simple t-test is all that is needed for this.
Given the known variability of the population of DNA, it is not uncommon to have a p-value of 1E-8. That means there's a 1 in 100,000,000 chance that someone else committed the crime. In other words, there's about 3 people in the U.S. who match that DNA. Reasonable doubt? Your call.
Now admittedly, if you have p-values of anything less that 1E-3 or 4 being admitted into court, you should laugh the "expert" out of the courtroom.
IIRC (from speaking to my mcirobiologist ex), DNA profiling can only guarantee negatives, never positives, and thus in the UK cannot be used to convict someone, only to acquit them.
"The invisible and the non-existent look very much alike." -- Delos B. McKown
In a sense a non-chimeras already have different sets of DNA in different body parts. The DNA expresses differently in a liver cell vs. skin or some other cell type. These differences appear to be controlled epigenetically: not in the DNA sequence itself, but in the run-time environment particular to any given cell type. Just because these differences are epigenetic, doesn't mean they are not structural and important.
DNA Methylation and chromatin structure appear to control the epigenetic regulation of the DNA. These issues appear the be the reason behind cloning problems, where taking DNA expressing run-time environment appropriate for an adult cell doesn't always work in a embryo.
IANAL, but IUTWIBB ... I used to work in blood banks doing crossmatches. A small number of people have two different ABO blood types. They are not "AB", they have some red blood cells that are pure "A" and some that are pure "B" and that is violating Mendelian genetics. The same mechanism that creates this could easily create other "blood chimeras" with the other several hundred lesser-known blood types. And a third mechanism (sex chromosome abnormalities) can create a kind of blood chimera that has nothing to do with twins.
Apparently, most of these blood chimera individuals shared a blood supply with a non-identical twin before birth (the cells that make blood and populate your bone marrow float around the fetal blood supply while waiting for bones to develop to give them a place to settle, and the placentas and their blood vessels can merge without producing conjoined twins). In some cases, people are unaware that they had a twin because he or she died early in gestation and was spontaneously aborted (or disintegrated by the mother's defense mechanisms, or walled off in the mother or living twin). They show up in the National Enquirer when someone is operated on for a cyst and it has bits of the encysted twin in it.
As many as 8% of non-identical twins may have chimeric blood. Some people are microchimeric--they have a small amount of blood of a different type in their system that has persisted from a blood transfusion or passed across the placental barrier from their mother before birth.
"Blood chimerism" does NOT cause a problem for the person with the chimerism as far as receiving blood in a transfusion ... they will tolerate any phenotype they possess if you transfuse it - they have had it since they were fetuses and it is "self" in the immunological sense of the word.
It can, however, be hell on blood banks trying to figure out what the heck is wrong with the blood during the initial typing and screening in a transfusion where the blood chimera is the donor. The potential recipient is not at risk because the tech says &^$^$#%@!!!, sets the donor unit back in the frig with a "do not use" note and sends it off to a research lab to find out what's going on. That's how you usually find blood chimeras and new blood types ... anomalous results in what should be a routine crossmatch.
However, you will probably find NPR stations run by public colleges, that obtain some portion of their revenue from the college's budget - which in turn may come partially from taxes.
In this case, I don't begrudge NPR my tax dollars. They have some truly interesting programming that probably wouldn't survive if it depended on commercials (not to mention that we'd have to listen to the commercials - bleh.) Whine as much as you like about government subsidy of media or a particular point of view. But as for me, I refuse to depend on Fox News et al for intelligent, balanced news coverage and information.
Mosaics aren't Chimeras.
To quote the nature article that's been mentioned several times here:
Mosaicism is more common than chimaerism and is also better studied. Human mosaics arise when a mistake during cell division in the early embryo stops the correct number of chromosomes segregating to each cell, or creates a mutation in a single gene.
Chimaerism, on the other hand is "people carrying tissues that originated in two separate embryos."
Mod me down and I will become more powerful than you can possibly imagine!
Well if you are a guy, it would still be easy to get a DNA match, as the Y Cromisome comes only from the father with no recombination, so that will be uniform. Even if other stuff won't be. And since both sets of DNA come from the same parents they are going to look rather similar. More so now that labs know to look for this stuff.
Erlang Developer and podcaster
Not to be totally pedantic, but being fraternal twins could mean that two fathers impregnated two eggs at nearly the same time. If it were possible for these two zygotes to merge, which I _highly_ doubt, then the resulting Chimera twin could have seperate Y-chromosomes from two fathers.
--If you code for the exceptions, the rules fall into place
More often than not, things don't go right.
Everyone has heard of Downs syndrome, when a child has an "extra" chromosome. Well, think of having twenty three extra pairs.
I am a fraternal twin, and I don't know if I am a chimera or not, but my wife and I have had trouble with a similar situation of too much DNA. Last year, we had a molar pregnancy.
"What is that?" you may ask. A molar pregnancy happens when an egg is fertilized, but no baby is formed. It happens when the egg "looses" the genetic information from the mother (complete molar), or has three sets of chromosomes (69 total, partial molar). Molar pregnancies are about 1 in 1500 births, with 98% of those being the complete type.
Either way, it is a horrific experience, and should be considered cancerous. The mother's hormone levels will climb to dangerous levels as the mass of cells that should have been an embryo rapidly grow and divide inside the womb. She will become extremely pregnant, without a child, and morning sickness becomes a 24 hour a day nightmare. Relief only comes with complete removal of all molar tissue. After this, the mother has to be monitored and be "pregnancy free" for a year, to tell if any of the molar tissue has become cancerous.
Our case was a partial molar. If things would have gone right, we would now have a set of identical twins, but it didn't. DNA is a funny and powerful thing and too much is never good.
-- Len
haha that's only half true. I ate the most shrooms in my life in may and proved God's existence to myself. I didn't talk to anyone, I just had a moment of clear thought. I'm not sure how I did it but it made perfect sense at the time :)
Either way, a quarter of purple shrooms and two blunts is not the way to effectively prepare for a final the next day!
PS people bitching about atheism: there's no such thing as atheism, it's just as extreme as believing in an intangible (G)(g)od. Both require a substantial amount of illogic, but that's what makes us all interesting. But seriously, he was joking.
You aren't a mix of your parent's genes, you are a mix of your grandparent's genes. Sex cells go through a process called meiosis whereby 1 cell splits into 4 cells, each with half the genetic content.
The mother's ovum are formed shortly after conception. A woman is born with every ovum she will ever produce, they just leave the final assembly steps for ovulation. Men form sperm throughout their lives, but these cells are all decendents from the cells that were set aside during the developmental process.
Now how is it that you are actually a combination of your grandparent's genes? Well every human actually has 2 complete sets of DNA. Even the Y chromosome. Only half are expressed at a time. During sex-cell production, all genes come into play. During Metaphase I the chromosomes pair up and swap genes.
If you think of Mendel's experiments, hybrids of a dominant and recessive gene don't express the recessive trait until the second generation. This is why.
"Learning is not compulsory... neither is survival."
--Dr.W.Edwards Deming
This brings up some interesting questions. First off, what are the implications for the present organ donation system? The radio story talks about a women who discovered her condition when she needed a kidney, and her own children were tested as incompatable. It turns out that they inherited genes from one of her sets and that was not the genome responsible for her blood supply. But what about the other possibility. I need a kidney, my sister tests as a viable donor, but it turns out her kidney has a different genome then the one that tested positive for a match. The kidney gets transplanted and my body rejects it. How often does this happen in real life?
Also, is anyone studying the way the body's immune system handles having two omnipresent genomes? What implications, if any, does this have for the study of drugs that could help lower the threat of organ rejection?
Does anyone know the answers to these questions, and if not, is anyone looking into them?