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Tag: fraternal twin

A Case Fit for House MD Part 2

A little over two years ago, I blogged on a very interesting New England Journal of Medicine paper about a bizarre medical case where a young female patient actually took on the blood type of a little boy who’s liver she had taken in a transplant. I had noted then that such an amazing (and not fully-understood) event definitely qualified for being a House MD moment, after one of my favorite TV shows about everyone’s favorite misanthropic genius doctor.

Two years later, a friend of mine from college shows me another case with a similar “signature”, making me dub this “A Case Fit for House MD Part 2”!

The setup (more details in Wikipedia): a 52-year-old woman named Karen Keegan was in need of a kidney transplant and, of course, tested her children for donor compatibility. What she discovered, completely rocked her world. To quote the Damn Interesting page I just linked to:

Imagine if you discovered one day that two of your three children were genetically not yours. Recriminations, marital troubles, perhaps a divorce, right? Now add a twist. What if you were these children’s mother? Suddenly the question becomes not “Who?” but rather “Huh?”

“Huh?” is right.

So, what’s the explanation for how a mother could possibly give birth to children who are genetically not matched to her? The current theory is chimerism.

imageThe type of  biological chimerism, named after the mythical chimera which had the parts of a lion, snake, and goat all in one (see image on the right), we usually see involves an organism having DNA from multiple species. This is usually something more mundane and research/medicine-oriented like creating mice that have genes which give them a human being’s immune system. These “humanized” mice are then used to produce human antibodies which can then be used for medicinal purposes.

A more dramatic example in nature would be the parasitic chimerism that the Ceratioid Anglerfish practices – where the males of the species actually fuse with females to become some sort of chimeric (and immediately fertile) hermaphrodite.

In humans, a common form of chimerism that is observed is in a small proportion of fraternal twins where, because of linkages between their blood supply and blood-producing organs,end up having “shared blood”. They each have and will continue to produce blood cells from their other twin, despite the rest of their body being genetically distinct.

But what about the curious case of our mother who’s kids don’t appear to be hers? What sort of chimerism explains this? A New England Journal of Medicine paper dives into the science, but basically, the theory is that Karen Keegan had a fraternal twin. But, rather than simply share blood cells/blood-producing cells, Keegan and her twin had actually fused in the womb. This theory was supported when they found two sets of DNA in her tissues (one set of which matched her un-matching children).

Interestingly, this paper was cited in the 2002 trial of a British woman named Lydia Fairchild who was denied custody of her children and welfare support because she could not prove with a genetic test that she was the mother of her children. The story was later put into a documentary called “I Am My Own Twin”.

So, anyone want to pitch using this to House MD?

(Edit: It’s been brought to my attention by… pretty much all of my friends who watch House that genetic chimerism was actually the diagnosis for the second episode of season 3 — I suppose I won’t be able to sell this screenplay to the writers after all…)

(Image credit)