A
phenotype… what’s going on here. The patient has not been recently transfused.
A patient’s phenotype is cut-and-dry. It is clearly positive for an antigen or
it is not… Like the C, c, E and E wells (or the control come to that).
But look at the K well. What’s going on there?
I was wondering
about McLeod syndrome or Kx, and I asked on the Facebook Immunohematology
Reference Laboratory group.
There were
uite a few comments. Some helpful, others not so. But a world-leading expert on
the matter (and an old drinking friend of forty years ago) commented:
“The K
antigen is not always straightforward. K is usually characterised by a
methionine residue at position 193, however, a weak expression of K is seen
when either an arginine (1) or a serine (2) residue replace the methionine
residue at position 193. See also reference (3) for amino acid substitutions
remote from position 193 that affect the expression of either the K or the k
antigen. In addition, similar reactions can be seen when the individual is a
chimera, although, of course, this is extremely rare.
(1)
Uchikawa M, Onodera T, Tsuneyama H, Enomoto T, Ishijima A, Yuasa S, Murata S,
Tadokoro K, Nakajima K, Juji T. Molecular basis of unusual Kmod phenotype with
K+wk-. Vox Sang 2000; 78 Suppl. 1: Abstract O011.
(2) 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:
1879-1885. DOI: 10.1111/j.1537-2995.2006.00993.x.
(3)
Yazdanbakhsh K, Lee S, Yu Q, Reid ME. Identification of a defect in the
intracellular trafficking of a Kell blood group variant. Blood 1999; 94 (1):
310-318. DOI: 10.1182/blood.V94.1.310.413k12_310_318.”
We’ve sent
the sample off to the reference lab… and in the meantime I’ve learned
something.
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