RHD*DOL1andRHD*DOL2encode a partial D antigen and are in cis with the rareRHCE*ceBIallele in people of African descent

Transfusion management of Africans with RHD variants in China

The presence of D variant among minorities could produce a higher rate of alloimmunization observed in patients from this group. This is partly due to the ethnic and racial specificity of RHD variants and the limited availability of Rh-matched blood donors. Approximately half a million African migrants in China carrying distinct Rh blood type composition have presented to the health care system with an imperative safety requirement of blood transfusion among 1.3 billion Chinese individuals. We depict the clinically significant RHD alleles among African migrants living in China and identify the genetic similarities and disparities to Chinese. We discussed practical strategies to manage the unique transfusion needs of African migrants in China.

Maternal red blood cell alloimmunisation Working Party, literature review. RH blood group system: Rare specificities

This report is part of a series reporting the GRADE review performed by the 2018-2020 French Working Party on maternal red blood cell alloimmunisation. This report focusses on the clinical significance in obstetrics, as published in the scientific literature, of the rare RH antibodies, variants and antigens (i.e. excluding conventional RH1 trough RH8 antigens, RH12, RH22 and RH27, which are discussed in other reports of this series). Extremely severe or severe haemolytic disease of the fetus and the newborn (HDFN), leading to death or requiring transfusions, have been reported for: anti-RH1 (-D) associated with DVI, DBT and DIVb phenotypes, RHD*12.04 (DOL4), RHD*03.03 (DIIIc), RHD*D-CE(2-5)-D, RHD*01EL.31 (RHD*148+1T), anti-RH9 (-C^X), anti-RH11 (-E^W), anti-RH17 (-Hr⁰), anti-RH18 (-Hr), anti-RH19 (-hr^S), anti-RH23 (-D^W), anti-RH29 ("total" Rh), anti-RH30 (-Go^a), anti-RH32, anti-RH34 (-Hr^B), anti-RH36 (-Be^a), anti-RH40 (-Tar), anti-RH46 (-Sec), anti-RH48 (-JAL), anti-RH54 (DAK), and antibodies to high prevalence antigens such as those associated with RHCE*02.08.02 (RHCE*C^W-RHD(6-10)), RHCE*03N.01 (RHCE*cEMI). HDFN of moderate, mild or undetailed severity have been reported for: anti-RH1 associated with DHar, DIIIa and DIVa phenotypes, RHD*01EL.08 (RHD*486+1A),RHD*01EL.44 (RHD*D-CE(4-9)-D),RHD*25 (DNB), anti-RH20 (-VS), anti-RH31 (-hr^B), anti-RH37 (-Evans), ani-RH42, anti-RH49 (-STEM), anti-RH51 (-MAR), anti-RH55 (-LOCR), anti-RH58 (-CELO). Positive direct antiglobulin test in the newborn but no clinically significant HDFN has been reported for anti-RH1 (-D) associated with RHD*10.05 (DAU5), RHD*12.02 (DOL2). Because so many specificities are associated with severe HDFN in the RH system, all RH antibodies should be considered as potentially able to cause HDFN, even if none has been reported yet.

Insights into anti-D formation in carriers of RhD variants through studies of 3D intraprotein interactions

BACKGROUND

Many RhD variants associated with anti-D formation (partial D) in carriers exposed to the conventional D antigen carry mutations affecting extracellular loop residues. Surprisingly, some carry mutations affecting transmembrane or intracellular domains, positions not thought likely to have a major impact on D epitopes.

STUDY DESIGN AND METHODS

A wild-type Rh trimer (RhD₁ RhAG₂ ) was modeled by comparative modeling with the human RhCG structure. Taking trimer conformation, residue accessibility, and position relative to the lipid bilayer into account, we redefine the domains of the RhD protein. We generated models for RhD variants carrying one or two amino acid substitutions associated with anti-D formation in published articles (25 variants) or abstracts (12 variants) and for RHD*weak D type 38. We determined the extracellular substitutions and compared the interactions of the variants with those of the standard RhD.

RESULTS

The findings of the three-dimensional (3D) analysis were correlated with anti-D formation for 76% of RhD variants: 15 substitutions associated with anti-D formation concerned extracellular residues, and structural differences in intraprotein interactions relative to standard RhD were observed in the others. We discuss the mechanisms by which D epitopes may be modified in variants in which the extracellular residues are identical to those of standard RhD and provide arguments for the benignity of p.T379M (RHD*DAU0) and p.G278D (RHD*weak D type 38) in transfusion medicine.

CONCLUSION

The study of RhD intraprotein interactions and the precise redefinition of residue accessibility provide insight into the mechanisms through which RhD point mutations may lead to anti-D formation in carriers.

A Tutsi family harbouring two new RHCE variant alleles and a new haplotype in the Rh blood group system

BACKGROUND

RHCE*ceEK is a rare RH allele mostly encountered in people of African descent. This allele is defined by four single nucleotide substitutions: c.48G>C, c.712A>G, c.787A>G and c.800T>A. Until now, it has only been reported to segregate with either RHD*01N.01 or RHD*DAR1.00.

MATERIALS AND METHODS

Blood samples were drawn from a 32-year-old Tutsi pregnant woman during an antenatal visit in order to perform her type and screen. To further investigate the results found in the patient, a family study was conducted. Standard haemagglutination methods were used to investigate the subjects' red blood cells and plasma. Molecular workup on RHD and RHCE genes was carried out by DNA microarray, real-time PCR and DNA sequencing techniques.

RESULTS

The patient was phenotyped as group B, D+C-E-c+e+, Hr-. A complex mixture of anti-E, anti-c, anti-Hr and anti-hr^S was detected in her plasma. She was found to carry a normal RHD gene, a conventional RHCE*ceEK allele and an alternative RHCE*ceEK allele (RHCE*ceEK without c.48G>C). The family study showed that the conventional RHCE*ceEK and the alternative RHCE*ceEK alleles were associated with a RHD*01 allele and a RHD*01N.01 allele, respectively. Molecular analysis performed in the proband's mother showed a novel RHCE*ce variant allele on a RHCE*ce^S -like background (RHCE*ce^S with c.609G>A).

CONCLUSIONS

This case study brought out new associations between RHD and RHCE alleles encoding the rare Hr- phenotype: the conventional RHCE*ceEK allele linked to the RHD*01 allele and an alternative RHCE*ceEK allele associated with the RHD*01N.01 allele. A novel RHCE*ce variant (RHCE*ce^S with c.609G>A) was also reported.

Molecular matching for patients with haematological diseases expressing altered RHD-RHCE genotypes

BACKGROUND AND OBJECTIVES

The high homology and the inverted orientation of RHD and RHCE may give rise to non-functional and aberrant RH alleles. RH genotyping is used to screen RH matched donors to African descent patients. This study aimed to define a strategy for testing RHD and RHCE variants in blood donors to provide compatible units for transfusion of patients with haematological diseases.

MATERIALS AND METHODS

Samples from 132 patients [101 Sickle cell disease (SCD), 14 myelodysplastic syndrome (MDS), 17 acute myelogenous leukaemia (AML)] and 198 Brazilian donors were studied. Major blood group alleles, RHD, RHCE alleles and RHD zygosity were determined by the blood-MLPA assay. Sequencing was performed to determine RHD and RHCE variant subtypes. A match was an RH genotype that did not encode Rh antigens absent in the patient, along with matching for ABO, MNS, KEL, FY, JK and DI antigens.

RESULTS

Overall, 7·6% of blood donors and 17.4% of patients presented RH genotypes that predict expression of partial Rh antigens or lack of high prevalence Rh antigens. From 23 patients with clinically relevant RH genotypes, 15 had available matched donors.

CONCLUSION

We report the presence of clinically relevant RH genotypes in SCD and in non-SCD patients. In our admixed population, many patients carry variant RHCE alleles in heterozygosity with normal RHCE alleles. Thus, our results suggest that donors could be selected based on the normal RH allele.

RHCE*ceAG (254C>G, Ala85Gly) is prevalent in blacks, encodes a partial ce-phenotype, and is associated with discordant RHD zygosity

BACKGROUND

RHCE*ceAG has the nucleotide change c.254C>G, which encodes p.Ala85Gly associated with altered expression of e antigen. We analyzed serologic and DNA-based testing data on samples with RHCE*ceAG to determine its effect on antigen expression, linkage with RHD, and its prevalence in African Americans.

STUDY DESIGN AND METHODS

Serologic testing was performed by standard methods. Genomic DNA was used for polymerase chain reaction-restriction fragment length polymorphism, RH-specific exon sequencing, and RHD zygosity, and Rh-cDNA was sequenced. Samples from 32 individuals referred for serologic problems, 57 patients with sickle cell disease, and 44 donors positive for c.254C>G were investigated. Allele prevalence was determined in random African Americans.

RESULTS

Red blood cells from samples homozygous RHCE*ceAG/ceAG or in trans to RHCE*cE reacted variably with anti-e reagents and 17 samples from the 32 referred patients had alloanti-e in their plasma. The majority of samples with RHCE*ceAG, when tested for RHD zygosity gave discordant results between PstI-RFLP and hybrid box assay. Rare samples with 254C>G had additional allelic changes: one with c.697G (p.233Glu), three with c.733G, 941C (p.245Val, 314Ala), and two with c.307T (p.103Ser) encoding robust C antigen expression in the absence of other C-specific nucleotides. A total of 101 samples with RHCE*ceAG were encountered in 1159 randomly selected African Americans.

CONCLUSIONS

RHCE*ceAG (c.254G, p.85Gly) encodes a partial phenotype and the absence of the high-prevalence antigen RH59 (CEAG). The allele was present in one in 11 African Americans and is most often in cis to a RHD deletion associated with discordant RHD zygosity. To further determine clinical significance, detection of this allele should be part of routine RHCE genotyping in this population.

Insights into RHCE Molecular Analysis in Samples with Partial D Variants: the Experience of Western France

BACKGROUND

Although systematic blood group genotyping of patients/donors is virtually possible, serological studies remain the gold standard to identify samples of clinical interest that may be further genotyped. In this context, we sought to identify variant D alleles that are likely to be clinically relevant in terms of other Rh antigens in a subset of population genotyped in Western France.

METHODS

Samples presenting with the RHD*weak D type 4.2.2 allele (n = 47) were selected for the study. RHCE exons 1-7 were directly sequenced, and expression of Rh antigens was predicted on the basis of the molecular data.

RESULTS

Of the 47 samples tested, 19 (40.4%) were predicted to be of potential clinical interest. Moreover, we could show that selecting the samples to be genotyped by the nature of their variant D allele (i.e., RHD*weak D type 4.2.2 allele) rather than by their Duffy-null status appears to increase significantly the likelihood of identifying clinically relevant individuals for Rh status.

CONCLUSION

On the basis of our findings we suggest that all individuals genotyped as weak D type 4.2.2 should be systematically screened for RHCE variants by molecular analysis on a routine basis.

RH diversity in Mali: characterization of a new haplotype RHD*DIVa/RHCE*ceTI(D2)

BACKGROUND

Knowledge of RH variants in African populations is critical to improving transfusion safety in countries with populations of African ancestry and to providing valuable information and direction for future development of transfusion in Africa. The purpose of this report is to describe RH diversity in individuals from Mali.

STUDY DESIGN AND METHODS

Blood samples collected from 147 individuals self-identified as Dogon and Fulani were analyzed for Rh antigens and alleles.

RESULTS

The most common RHD allele variant was RHD*DAU0. Five predicted partial-D phenotypes were attributed to RHD*DAU3 or RHD*DIVa. Neither RHD*DAR nor RHD*DIIIa was found. Investigation of RHCE revealed three predicted partial-e antigens encoded by RHCE*ce(254G) in trans to RHCE*cE. Regarding C antigen, 28 Fulani typed as C+ and 16 of 28 harbored at least one RHCE*Ce-D(4)-ce, two being homozygous and predicted to show a rare RH:32,-46 phenotype. A new RHCE*ceTI with replacement of Exon 2 by RHD (RHCE*ceTI(D2)) was identified in Dogon and was identified by inheritance study to be in cis to RHD*DIVa. These samples typed C- with anti-C polyclonal antibody and monoclonal antibodies (MoAbs) MS24, P3X2551368+MS24, and MS273, but positive with anti-RhCe MoAb-BS58. The same pattern was observed in sample with RHD*DIVa/RHCE*ceTI.

CONCLUSION

Our survey indicated an uneven distribution of RH variant alleles between Dogon and Fulani, suggesting that study in well-documented cohorts is warranted. A high incidence of predicted partial-C phenotype encoded by RHCE*Ce-D(4)-ce was found in Fulani. Further study will also be needed to clarify the clinical significance of the new DIVa/ceTI(D2) haplotype encoding partial D and variant ce antigens.

[Contribution of red blood group genotyping for recipients in immune-hematology through three years of activity at the EFS Alpes-Méditerranée]

AIM OF THE STUDY

Current knowledge of the molecular basis of most blood groups enables genetic testing for blood groups to overcome the limitations of agglutination. A retrospective review was carried out on genotyping assays performed between 2011 and 2013.

METHODS AND PATIENTS

The Molecular Hematology Laboratory of the EFS Alpes-Méditerranée implements commercially available tools (BioArray, Gen-Probe) and other techniques (TaqMan, tetra-primer ARMS-PCR, sequencing). It provides a high-level of expertise in molecular biology, complying with regulatory requirements and standards.

RESULTS

A total of 2382 genotyping assays was performed including 764 extended typings and 115 large extended typings essentially in cases involving multiple transfusion and suspected rare blood type. Phenotype discrepancies linked to the RH system accounted for 1501 genotypings. Discrepancies linked to the D and E were mainly related to an allele coding for weak antigen (weak D type 1, 2, 3 and EIV) while those linked to C, c and e antigens were related to an allele coding for a partial antigen (RN, ces(340), ceMo). A high prevalence of (C)ces haplotype in trans of a DAR allele was observed in Afro-Caribbean (54/62).

CONCLUSION

In transfusion medicine, red-cell genotyping can overcome the limitations of hemagglutination. It must be used only in situations where it provides a benefit either for the patient or resource management. For implementation of appropriate transfusional practices, this technique requires a sound knowledge of the genetic characteristics of blood groups and clinically relevant variants. It also requires competency with molecular biology tools and continuously updated scientific data.