D category IV: a group of clinically relevant and phylogenetically diverse partial D.

BACKGROUND: The D typing strategies in several European countries protect carriers of D category VI (DVI) from anti-D immunization but not carriers of other partial D. Besides DVI, one of the clinically most important partial D is D category IV (DIV). A detailed description and direct comparison of the different DIV types was missing. STUDY DESIGN AND METHODS: RHD nucleotide sequences were determined from genomic DNA. D epitope patterns were established with commercial monoclonal anti-D panels. RESULTS: DIV comprises several variants of the D antigen with distinct serology, molecular structures, evolutionary origins, and ethnic prevalences. The DIV phenotype is determined by 350H shared by all, but not limited to, DIV variants which are further divided into DIVa and DIVb. The DIVa phenotype is expressed by DIV Type 1.0 harboring 350H and the dispersed amino acids 62F, 137V, and 152T. The DIVb phenotype is expressed by DIV Type 3 to Type 5 representing RHD-CE-D hybrids. Four of the six postulated DIV variants were encountered among 23 DIV samples analyzed. Of 12 DIV carriers with anti-D, 10 were female and seven likely immunized by pregnancy. Two DIV-related alleles are newly described: DWN, which differs from DIV Type 4 by 350D and epitope pattern. DNT carries 152T, known to cause a large D antigen density. CONCLUSION: DIV alleles arose from at least two independent evolutionary events. DIV Type 1.0 with DIVa phenotype belongs to the oldest extant human RHD alleles. DIV Type 2 to Type 5 with DIVb phenotype arose from more recent gene conversions. Anti-D immunization, especially dreaded in pregnancies, will be avoided not only in carriers of DVI but also in carriers of other D variants like DIV, if our proposed D typing strategy is adopted.

RHD genotyping from maternal plasma: guidelines and technical challenges.

Rhesus D (RhD) blood group incompatibility between mother and fetus can occasionally result in maternal alloimmunization where the resultant anti-D can cross the placenta and attack the fetal red cells, which in worse case scenarios can cause fetal anemia and ultimately death. Fetal RHD genotyping was introduced in the mid-1990s after the molecular characterization of the RH genes as an aid to the clinical management of these cases. Initially, these tests used fetal DNA extracted invasively from chorionic villus and amniocyte samples. RHD genotyping of fetuses carried by RhD-negative women has become the first large-scale application of noninvasive prenatal diagnosis (NIPD). Initially the real-time polymerase chain reaction (PCR)-based tests were devised to characterize free fetal DNA in maternal plasma and serum, and RHD genotyping was a convenient assay to develop this exciting new technology, because the accuracy of tests could easily be confirmed after the simple RhD phenotyping of fetal cord blood cells after birth. "First generation" RHD genotyping tests were based on the incorrect concept that all D-negative phenotypes were caused by a complete RHD gene deletion. Thus, it was a relatively simple task to develop diagnostic PCR strategies based on the detection of RHD where D-negative genomes will completely lack RHD. Subsequent research into the molecular basis of D-negative phenotypes revealed that a significant number of D-negative genomes possess fragments of, or mutated RHD genes, the most notable of which is the RHD pseudogene found in Africans. Thus, more comprehensive RHD genotyping tests have evolved to differentiate these alleles, and are more appropriate in the diagnosis of multi-ethnic population groups such as those found in Europe and North America. Many European Union countries have suggested the mass application of RHD NIPD for all fetuses carried by D-negative women. This is of clear benefit, because most RhD prophylaxis programs have switched to antenatal administration. This will help conserve anti-D stocks and it will prevent unnecessary administration of a human-derived blood product to a vulnerable patient group. Although anti-D stocks are inherently safe, there is a moral obligation to eliminate unnecessary administration of it because there have been instances of hepatitis C infection due to contamination. Furthermore, as yet undescribed viruses may be contaminants of blood products. Mass-scale RHD NIPD will shortly be implemented in several countries in the European Community as a consequence.

[The erythrocyte phenotype Rh: 32,-46: transfusional and obstetric importance]. / Le phénotype érythrocytaire Rh: 32,-46: importance transfusionnelle et obstétricale.

The red blood cells and sera from 21 RN/RN individuals were studied. The study confirmed the Rh type D+C+E-c-e+, CW-, characterized by an increased expression of the D antigen, a markedly decreased expression of the C and e antigens, the presence of a low incidence antigen (Rh32) and the absence of a high incidence antigen (Rh46) associated with an epitope recognized by a murine monoclonal antibody (MR 432). Four individuals exposed to Rh46 cells by pregnancy and/or transfusion had an anti-Rh46 antibody. This antibody gave positive reactions with all red blood cells of common and rare Rh phenotype except Rh null, D--, D.., DC(W-) and RN/RN cells. This antibody is considered to be of clinical significance in case of transfusion or pregnancy.