9/1/2023 0 Comments A negative blood type originIn 1946 Fisher and Race ( 9) proposed a model for the evolution of the RH polymorphism in which the less common haplotypes (CDE, Cde, cdE and CdE) are generated and maintained by recombination from those found at higher frequency. In the presence and absence, respectively, of RHD, the four alleles of RHCE make up all possible haplotypes, although there are marked differences in their relative frequencies, both within and between populations (see Table 1). There are, in addition, rare variants of C, c, E and e, whose molecular basis is, for the most part, unknown. Only four of these result in amino acid substitutions, and that at nucleotide 307 (serine to proline, residue 103) is most consistently associated with C or c antigenicity, respectively. ![]() Alleles of RHCE that express the C antigen differ from those expressing c at six nucleotide positions, one in exon 1 and five in exon 2. A single C to G transition in exon 5 of RHCE results in a polypeptide that reacts with anti-e, rather than anti-E, antisera. Lack of D antigen expression is usually due to the absence of the entire RHD gene from the genome of RhD− individuals ( 7), whereas variant forms of the C and E antigens are generated by base substitutions in RHCE ( 5, 8). Alternative mRNA splicing is probably responsible for the production of two distinct polypeptides from the single RHCE gene ( 6). The Rh antigens are carried on three non-glycosylated transmembrane proteins that are encoded in only two genes, RHD and RHCE ( 1– 5). Incompatibility for the other products of the RH locus, the C-series and E-series antigens, can also occasionally give rise to hemolytic reactions. In addition to the problems caused by incompatibility for RhD type between transfusion donor and recipient, incompatibility between a multiparous RhD− mother and her unborn child can result in a severe immune reaction leading to neonatal hemolytic disease (HDN) or even intrauterine death. Although the Rh system is highly polymorphic, and comprises at least 44 distinct antigens, clinically the most significant polymorphism is due to the presence or absence of the RhD antigen on red cells. ![]() The Rh blood group, popularly referred to as Rhesus, is second only to the ABO system in its importance in transfusion medicine.
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