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A medical mystery for Mother's Day...

Written by Dr Catherine Carver · Sunday 3rd March 2013

I'd like to tell you a curious story. Jane was a 52 year old woman in need of a kidney transplant. Thankfully she had three loving sons who were all very happy to give her one of theirs. So Jane's doctors performed tests to find out which of the three boys would be the best match, but the results surprised everyone. In the words of Jeremy Kyle, the DNA test showed that Jane was not the mother of two of the boys... Hang on, said Jane, child birth is not something you easily forget. They're definitely mine. And she was right. It turns out Jane was a chimera.

Chimerism is the existence of two genetically different cell lines in one organism. This can arise for a number of reasons- it can be iatrogenic, like when someone has an organ transplant, or it can be naturally occurring. In Jane's case, it began in her mum's womb, with two eggs that had been fertilised by different sperm creating two embryos. Ordinarily, they would develop into two non-identical twins. However in Jane's case the two balls of cells fused early in development creating one person with both cell lines.

Tetragametic chimerism

Thus when doctors did the first tissue typing tests on Jane, just by chance they had only sampled the 'yellow' cell line which was responsible for one of her sons. When they went back again they found the 'pink' cell line which had given rise to the other two boys.

Chimerism: Sons

This particular type of human chimerism is thought to be pretty rare- there are only 30 case reports in the literature. (Though remarkably both House and CSI's Gil Grissom have encountered cases.) What happens far more frequently is fetal microchimerism- which occurs in pregnant women when cells cross the placenta from baby to mum. This is awesome because we used to think the placenta was this barrier which prevented any cells crossing over. Now we've found both cells and free floating DNA cross the placenta, and that the cells can hang around for decades after the baby was born. Why? As is often the case in medicine we're not sure but one theory is that the fetal cells might have healing properties for mum. In pregnant mice who've had a heart attack, fetal cells can travel to the mum's heart where the develop into new heart muscle to repair the damage.

Whilst we're still in the early stages of understanding why this happens, we already have a practical application. In the United States today, a pregnant woman can have a blood test which isn't looking for abnormalities in her DNA but in that of her fetus. The DNA test isn't conclusive enough to be used to diagnose genetic conditions, but it is a good screening test for certain trisomies including Down's syndrome.

Now, we started with a curious tale, so lets close with a curious fact, and one that's appropriate for Mother's Day: This exchange of cells across the placenta is a two way process. So you may well have some of your mum's cells rushing through your veins right now. In my case they're probably the ones that tell me to put on sensible shoes and put that boy down...

(FYI: This is a story I originally posted on my own blog)

Responses

David Cooper
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Posted about 6 years ago
That's brilliant. Thank you. I was wondering how chimerism would affect the viability of kidney transplant from Jane's sons to Jane.
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(5)
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Raghad Sabbagh
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Medical Student - Sheffield
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Posted about 6 years ago
Very interesting!
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(3)
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Mhairi Hepburn
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Posted about 6 years ago
Thanks for posting this!
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(3)
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Dr Catherine Carver
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Posted about 6 years ago
Thanks everyone- glad you enjoyed it :) Interesting question David- Jane would be tolerant of both tissue types so she's actually in a better position than most organ recipients! For those of you wondering what would've happened if the two embryos
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(3)
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Laura Falvey
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Medical Student - Kings College London
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Posted about 6 years ago
How curious, very interesting, thank you.
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(3)
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Jaya Kolli
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Posted about 6 years ago
An excellent case history.
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(3)
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Kamal Eldirawi
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Posted about 6 years ago
quite brand new - model 2013 - god bless you
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(2)
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Hannah
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Medical Student - Dundee
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Posted about 6 years ago
wow incredible case! will maybe keep it in mind for further SSC/ research
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(2)
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Dr Alastair Buick
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Site Administrator
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Posted about 6 years ago
This is great. Really interesting and well written.
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(2)
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Jeremy Walker
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Site Administrator
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Posted about 6 years ago
Thanks for responding to the comments. Such an interesting article. I can't wait to read your next one!!
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(2)
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Helen Breen
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Medical Student - Queens Belfast
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Posted about 6 years ago
This happened in a Kathy Reichs novel: Mortal Remains. Embryology is fascinating! Thanks for an excellent article.
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(2)
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sampath kumar
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Posted almost 6 years ago
intersting mam
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(0)
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Liliana Amador
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Posted over 4 years ago
Siempre habia tenido duda de que este trastorno por asi decirlo tuviera un nombre, tengo un hijo que en la actualidad tiene 15 años cuando quede embarazada me senti muy feliz mas de saber que eran 2 embrioncitos pero cual fue mi sorpresa que uno de ellos
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Yasmin Booth
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Palliative Nurse
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Posted over 3 years ago
Great read!
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