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Matthew Kim

DAR/Cdes question

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Hello. I've tried to come up with an answer over and over, but I've failed so far.

Can I ask a question here?

Our patient was identified to harbor DAR/Cdes (compound heterozygote) in our commercial kit.

His Rh phenotype is Dwce. (c,e antigens are strongly positive) 

If his Cdes (RHD-CE(3-7)-D) allele is true, the patient's phenotype should Cces. But why ce?

I am looking at blood group antigen factsbook and other papers, but I cannot find an answer.

Any help would be appreciated.

Edited by Matthew Kim

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I am a little confused by your question, in as much as, in one place you say that the patient has the Partial D Type DAR, but in another you say that the patient has the Dw antigen, sometimes known by its trivial name Weil, or more properly as Rh23, which is a low prevalence antigen associated with Partial DV Type 4.  I think you mean that your patient has the DAR D Type, and that the D antigen is typing weakly.  Am I correct in thinking this?  I hope so, otherwise it doesn't make sense (at least, to me).

Turning to the CdeS type, there are several (at least 8) of these in terms of genetic background.  All have one thing in common, and that is a Leucine to Valine substitution at position 245 of the mature position, due to a point mutation in exon 5 of the RHCcEe gene.  Five of these also have the Tryptophan to Cysteine substitution at position 16, resulting in the expression of (normally) the C antigen, due to a point mutation in exon 1.  However, 74% of C-, c+ Black Americans with normal expression of c have Cysteine at position 16.

The thing is though, that any C antigen that is expressed is weakened, and some anti-C reagents do not react with it.  On the other hand, because there are at least 4 amino acid residues that are involved in the expression of the C and/or c antigen (at positions 16, 60, 68 and 120), it is more than possible (in fact, probable) where mutations are present, that the c antigen is expressed at a normal strength, whilst the C antigen is also expressed in the weakened form.  Indeed, the C antigen itself is a Partial C antigen, and such an individual can produce a form of anti-C, rather in the same way that an individual with a Partial D can produce a form of anti-D.

So, to cut a long story short, this is why the individual will express the c and e antigens in the cis position, even though they also express the C and e antigens (in a manner of speaking) in the cis position, and why the ce (compound) antigen can also be expressed.

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Wow. Now I understand the cause of C-negative phenotype.

Malcolm, I am sorry for my mistake about Dw. I meant that the patient has the weak D phenotype. 

However, there is one thing I cannot fully understand.

CdeS type has (RHD-CE(3-7)-D) on his RHD gene capable of causing altered C antigen.

You previously mentioned that Trp16Cys is a source of weakened C antigen expression. 

Do you think that both mutated RHD and RHCE genes affect altered C antigen expression?

Thank you for such a great answer.

 

 

 

Edited by Matthew Kim

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I should warn you that I am no molecular biologist - all I know is what I have adsorbed from reading and from some of my friends and colleagues who are accomplished molecular biologists - but I am absolutely certain that both the mutated RHD and RHCE genes contribute to the weak expression of the C antigen, as you seem to suggest.

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