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Homozygous M


bldbnkr

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Hi Blood Bankers,

Question - if you find a patient who is demonstrating an Anti-M in the MM cells only, the MN cells are negative when testing in Gel, in otherwords the Anti-M is only showing up in homozygous M cells in Gel, and in tube testing with LISS, all cells both homozygous and heterozygous for M are completely negative in all phases, would you go ahead and call the patient Positive for Anti-M antibody?

I have always called these patients as having Anti-M even if it is showing with homozygous cells only but other people are telling me that they can rule out of 3 negative heterozygous cells.

 

Thank you.

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I certainly wouldn't use your nomenclature (only genes can be homozygous, heterozygous or hemizygous), but I know what you mean.

I would most certainly say that the patient's plasma contains an anti-M, but, despite the fact that many cases of "cold reacting" anti-M are IgG, if the anti-M does not react at strictly 37oC, it is not clinically significant.

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Thank you Malcom and David,

In doing some digging I did find another thread about Anti-M a few  years ago that both of you gave input on, and it was a similar situation but perhaps more tube testing rather than gel. 

Sorry about calling cells homozygous, Malcolm - what is the correct name for an M+, N- cell and an M+, N+ cell?  Just MM and MN  - no homos or heteros?

Maryann

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15 hours ago, bldbnkr said:

Sorry about calling cells homozygous, Malcolm - what is the correct name for an M+, N- cell and an M+, N+ cell?  Just MM and MN  - no homos or heteros?

Maryann

Hi Maryann,

The point is that the terms homozygous, heterozygous and hemizygous can only refer to genes, but, of course, red cells do not have a nucleus (it has been extruded during the maturation process), but, in any case, the terms should not be used for antigens.

In this case the closest to being correct is that M+N- red cells have "homozygous expression" and M+N+ red cells have "heterozygous expression".  However, particularly in the case of the MNS Blood Group System, this terminology is not completely correct.  There are many low prevalence antigens associated with both the glycophorin A and the glycophorin B molecules, and the many hybrids therein, that a red cell that groups as M+N- may not be as a result of MM homozygosity at a genetic level, but may have heterozygous expression, because there is one "M" antigen (for want of a better way of putting it), and one low prevalence antigen expressed on glycophorin A (or a hybrid), so that, in terms of expression, the M antigen has the strength of an M+N+ red cell, rather than an M+N- red cell.

I hope that helps.

Malcolm

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I totally agree with David. I would say most of our Anti-M's react only with the cells that have the homozygous expression and not with the heterozygous expression. I would say you have to call it an Anti-M especially if Gel is your primary method of testing with tube as your backup. I don't think you can call it negative just because the tube has no reactivity.  We sometimes (very rarely) would have a Warm autoantibody that showed pan-agglutination in Gel but was negative with tube method at one hour incubation, no enhancement excluding the auto control which is usually still reactive. We would just add a comment about the negative results in tube method just for proper documentation but still result as a Warm autoantibody.

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On 4/19/2019 at 7:07 AM, bldbnkr said:

Hi Blood Bankers,

Question - if you find a patient who is demonstrating an Anti-M in the MM cells only, the MN cells are negative when testing in Gel, in otherwords the Anti-M is only showing up in homozygous M cells in Gel, and in tube testing with LISS, all cells both homozygous and heterozygous for M are completely negative in all phases, would you go ahead and call the patient Positive for Anti-M antibody?

I have always called these patients as having Anti-M even if it is showing with homozygous cells only but other people are telling me that they can rule out of 3 negative heterozygous cells.

 

Thank you.

My question to your co-workers would be, if the same argument was applied to an antibody that reacted w/ Jk a+b- cells only, you would rule out anti-Jka? ... and have the potential for some transfusion reactions?

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