Snap

There she stood, in the street, smiling from her head to her feet
All right now - Free

Sometimes, 1 in 4 chances come up

My sister and I went for tissue-type testing to see if our stem cells are compatible. These tests are looking at specific antibody generator proteins (antigens) found on the surface of cells to see if we have the same ones. Big differences would mean our stem cells would be more likely to perceive each other as "other", and attempt to kill each other. The most important ones in this context are the human leukocyte antigens (HLA). Your HLA tissue type is different from, and more complicated than, your ABO-system blood type. Indeed, I know my sister's blood group is different from mine (though if I ever did have a transplant from her, my blood group would change to hers).

One's blood group depends largely on whether one produces blood antigens "A" or "B" (determined by genes in the ABO-system) and/or "D" (from a gene in the rhesus system). There are actually at least 30 blood group systems working in our bodies, but matching for those 2 is sufficient for transfusions. I have "A-" blood because I have "A" antigens but not "B", and no "D" antigens (the "-" representing "RHD-"). In contrast, my HLA type includes my specific combination of antigens from groups HLA-A, HLA-B, HLA-C, HLA-DRB, HLA-DQA, HLA-DQB and HLA-DPB (phew!). Ideally, you want to match them all. It's why finding a stem cell donor is more complicated and rare than finding a blood donor.

When people need unrelated donors, they talk about the percentage match. You want a pretty high percentage to minimize risks. With sibling donors it is less complex. We each inherit one "set" (haplotype) of HLA from each parent. If two siblings inherit the same sets, they will be a match. If not, they won't be. So you've got to toss a coin twice and get heads each time ("Heads we inherited the same haplotype from Mum, tails we didn't" / "Heads we inherited the same haplotype from Dad, tails we didn't") - so the chance is 25%, 1 in 4. Or looked at the other way, 3 in 4 against.

But 4 to 1 runners sometimes come in.
(Do you like the way I nonchalantly blend my chance metaphors, with playing cards morphing into coin-flips before casually turning into racehorses? What's the chance of that?)

And... drum roll... the winner is...



Not sure why my sister was notified, rather than me. But fortunately, we're on good speaking terms.

And now, in all its glory, the actual test result...



"No detectable HLA mismatches"
I hope I never need it, but it's nice to know.

This gave me an interesting puzzle in confidentiality. My usual rule of thumb here is to publish my own medical details and test results, because they are pertinent (but not my IDs and patient numbers). I generally try not to name other people (unless they are online already), and I specifically try to avoid identifying my doctors by name. (However, I use my immediate family's first names where appropriate, because otherwise I'd end off endlessly repeating "my wife" or calling her "DW" for "dear wife", like all those pseuds on Mumsnet do, which would irritate us all, I reckon.) I wouldn't want to reveal any personal details about anyone else, because it's not my right to do so, and not my information to share.
So should I publish my HLA profile? I decided, on the basis that I've already told you my sister's is the same, not. My genes are not all my own.