A case of a zebra with spots, rather than stripes?

[Dr. Pepper]

You're right, they had their drawbacks and advantages, just as the monoclonals do. (Those are long lists: T activation, B(A) and A(, Ax etc. etc.)

[Brenda K Hutson]

That was going to be "my" guess but I didn't read the e-mail in time! Ha Ha Ha

Brenda Hutson

Here is the answer.

When we initially saw the results we were getting serologically with the baby's red cells (K+k-), we first thought that the mum could have been "playing away", and that the male partner was not the father. There was absolutely no doubt, however, that this was not so.

The next thing we did was to get another sample from the baby, just in case there had been a swap of cord samples - but, again, this was doubtful, as the cord was DAT+, with anti-D eluted and, although the host hospital has a Specialist Foetal Medicine Unit, no other lady under their care had given birth that day.

The new sample from the baby gave identical results (K+k-).

As a result, I sent samples to the International Blood Group Reference Laboratory (IBGRL), and their results came back as K+k+ (serologically), and KEL1/KEL2 (molecular). This foxed me a bit.

It just so happened that I was at the Centre where they are based on a training course a couple of days later, and so I went to have a word with my old friend Joyce Poole.

As you may know, Joyce published a paper in 2006 describing a Serine amino acid residue substitution at 193 on the Kell glycopreotein that meant that some anti-K reagents did not detect the "new" K antigen (Poole J, Warke N, Hustinx H, Taleghani BM, Martin P, Finning K, Crew VK, Green C, Bromilow I, Daniels G. A KEL gene encoding serine at position 193 of the Kell glycoprotein results in expression of KEL1 antigen. Transfusion 2006; 46 (11): 187901885.).

I suggested to her that their may be the possibility of a similar mutation on the KEL2 gene that meant that our monoclonal anti-k reagent was not detecting the resultant k antigen. Surprisingly, considering the small amount of evidence that I could produce, she agreed to get Vanja Karamatic Crew to perform a full gene sequence of all 19 exons of the KEL gene.

The sample was found to be heterozygous for 578C>T mutation in exon 6, resulting in a Thr193Met change in the Kell glycoprotein, which is the common (wild-type) characteristic of the K+k+ (KEL1/KEL2 genotype).

In addition, however, there was a novel heterozygous mutation in the KEL gene; 1720G>A in exon 16, encoding an Ala574Thr change in the Kell glycoprotein.

No other mutations were found in the KEL gene.

Now, although position 574 is "geographically remote" from position 193, the Kell glycoprotein is highly folded, and so these positions may not be quite so "remote" from each other as may be thought. We think, therefore, that this substitution of a non-polar amino acid for a polar amino acid may have altered the quarternery structure of the glycoprotein just enough for our monoclonal anti-k not to detect the presence of the k antigen, whilst other monoclonal anti-k reagents do.

There is, of course, a lot more work to be done to absolutely prove all this, but a lot of you got very close to the correct answer.

:clap::clap: