The Rhesus Site

Guide to Rho(D) Immune Globulin in Women With Molecularly Defined Asian-type DEL (c.1227G>A)

Rh hemolytic disease of the fetus and newborn is a potential risk for D-negative mothers who produce anti-D during pregnancy, which can lead to morbidity and mortality in subsequent pregnancies. To prevent this hemolytic disease, Rho(D) immune globulin (RhIG) is generally administered to D-negative mothers without anti-D at 28 weeks of gestation and shortly after delivery. However, current guidelines suggest that pregnant mothers with molecularly defined weak D types 1, 2, 3, 4.0, and 4.1 do not need RhIG as they are unlikely to produce alloanti-D when exposed to fetuses with D-positive red cells. This issue and the necessity of RHD genotyping have been extensively discussed in Western countries, where these variants are relatively common. Recent evidence indicates that women with Asian-type DEL (c.1227G>A) also do not form alloanti-D when exposed to D-positive red cells. We report that mothers with molecularly defined Asian-type DEL, similar to those with weak D types 1, 2, 3, 4.0, and 4.1, do not require RhIG before and after delivery. Collectively, this review could pave the way for the revision of international guidelines to include the selective use of RhIG based on specific genotypes, particularly in women with the Asian-type DEL.

When and why is red blood cell genotyping applicable in transfusion medicine: a systematic review of the literature

This review aims to provide a better understanding of when and why red blood cell (RBC) genotyping is applicable in transfusion medicine. Articles published within the last 8 years in peer-reviewed journals were reviewed in a systematic manner. RBC genotyping has many applications in transfusion medicine including predicting a patient's antigen profile when serologic methods cannot be used, such as in a recently transfused patient, in the presence of autoantibody, or when serologic reagents are not available. RBC genotyping is used in prenatal care to determine zygosity and guide the administration of Rh immune globulin in pregnant women to prevent hemolytic disease of the fetus and newborn. In donor testing, RBC genotyping is used for resolving ABO/D discrepancies for better donor retention or for identifying donors negative for high-prevalence antigens to increase blood availability and compatibility for patients requiring rare blood. RBC genotyping is helpful to immunohematology reference laboratory staff performing complex antibody workups and is recommended for determining the antigen profiles of patients and prospective donors for accurate matching for C, E, and K in multiply transfused patients. Such testing is also used to determine patients or donors with variant alleles in the Rh blood group system. Information from this testing aides in complex antibody identification as well as sourcing rare allele-matched RBC units. While RBC genotyping is useful in transfusion medicine, there are limitations to its implementation in transfusion services, including test availability, turn-around time, and cost.

DNA Reference Reagents for Genotyping RH Variants

Patients who carry Rhesus (RH) blood group variants may develop Rh alloantibodies requiring matched red blood cell transfusions. Serologic reagents for Rh variants often fail to specifically identify variant Rh antigens and are in limited supply. Therefore, red blood cell genotyping assays are essential for managing transfusions in patients with clinically relevant Rh variants. Well-characterized DNA reference reagents are needed to ensure quality and accuracy of the molecular tests. Eight lyophilized DNA reference reagents, representing 21 polymorphisms in RHD and RHCE, were produced from an existing repository of immortalized B-lymphoblastoid cell lines at the Center for Biologics Evaluation and Research/US Food and Drug Administration. The material was validated through an international collaborative study involving 17 laboratories that evaluated each DNA candidate using molecular assays to characterize RHD and RHCE alleles, including commercial platforms and laboratory-developed testing, such as Sanger sequencing, next-generation sequencing, and third-generation sequencing. The genotyping results showed 99.4% agreement with the expected results for the target RH polymorphisms and 87.9% for RH allele agreement. Most of the discordant RH alleles results were explained by a limited polymorphism coverage in some genotyping methods. Results of stability and accelerated degradation studies support the suitability of these reagents for use as reference standards. The collaborative study results demonstrate the qualification of these eight DNA reagents for use as reference standards for RH blood group genotyping assay development and analytical validation.

Serologic profiling of D variants in donor routine: unveiling the impact on false-negative results and alloimmunization

The high number of D variants can lead to the unnecessary use of Rh immune globulin, overuse of D- RBC units, and anti-D allommunization. D variant prevalence varies among ethnic groups, and knowledge of the main variants present in a specific population, their behavior in serologic tests, and their impact on clinical practice is crucial to define the best serologic tests for routine use. The present study aimed to explore the serologic profile of D variants and to determine which variants are most associated with false-negative D typing results and alloimmunization. Donor samples were selected in two study periods. During the first period, D typing was performed on a semi-automated instrument in microplates, and weak D tests were conducted in tube or gel tests. In the second period, D typing was carried out using an automated instrument with microplates, and weak D tests were performed in solid phase. Samples from patients typed as D+ with anti-D were also selected. All samples were characterized by molecular testing. A total of 37 RHD variants were identified. Discrepancies and atypical reactivity without anti-D formation were observed in 83.4 percent of the samples, discrepant D typing results between donations were seen in 12.3 percent, and D+ patients with anti-D comprised 4.3 percent. DAR1.2 was the most prevalent variant. Weak D type 38 was responsible for 75 percent of discrepant samples, followed by weak D type 11, predominantly detected by solid phase. Among the D variants related to alloimmunization, DIVa was the most prevalent, which was not recognized by serologic testing; the same was true for DIIIc. The results highlight the importance of selecting tests for donor screening capable of detecting weak D types 38 and 11, especially in populations where these variants are more prevalent. In pre-transfusion testing, it is crucial that D typing reagents demonstrate weak reactivity with DAR variants; having a serologic strategy to recognize DIVa and DIIIc is also valuable.

Transfusing children with sickle cell disease using blood group genotyping when the pool of Black donors is limited

BACKGROUND

Red blood cell transfusion is an effective treatment for patients with sickle cell disease (SCD). Alloimmunization can occur after a single transfusion, limiting further usage of blood transfusion. It is recommended to match for the ABO, D, C, E, and K antigens to reduce risks of alloimmunization. However, availability of compatible blood units can be challenging for blood providers with a limited number of Black donors.

STUDY DESIGN AND METHODS

A prospective cohort of 205 pediatric patients with SCD was genotyped for the RH and FY genes. Transfusion and alloimmunization history were collected. Our capacity to find RhCE-matched donors was evaluated using a database of genotyped donors.

RESULTS

Nearly 9.8% of patients carried a partial D variant and 5.9% were D-. Only 45.9% of RHCE alleles were normal, with the majority of variants affecting the RH5 (e) antigen. We found an alloimmunization prevalence of 20.7% and a Rh alloimmunization prevalence of 7.1%. Since Black donors represented only 1.40% of all blood donors in our province, D- Caucasian donors were mostly used to provide phenotype matched products. Compatible blood for patients with rare Rh variants was found only in Black donors. A donor with compatible RhCE could be identified for all patients.

CONCLUSION

Although Rh-compatible donors were identified, blood units might not be available when needed and/or the extended phenotype or ABO group might not match the patient. A greater effort has to be made for the recruitment of Black donors to accommodate patients with SCD.

Targeted next-generation sequencing and long-read HiFi sequencing provide novel insights into clinically significant KLF1 variants

BACKGROUND

Krüppel-like factor 1 (KLF1), a crucial erythroid transcription factor, plays a significant role in various erythroid changes and haemolytic diseases. The rare erythrocyte Lutheran inhibitor (In(Lu)) blood group phenotype serves as an effective model for identifying KLF1 hypomorphic and loss-of-function variants. In this study, we aimed to analyse the genetic background of the In(Lu) phenotype in a population-based sample group by high-throughput technologies to find potentially clinically significant KLF1 variants.

RESULTS

We included 62 samples with In(Lu) phenotype, screened from over 300,000 Chinese blood donors. Among them, 36 samples were sequenced using targeted Next Generation Sequencing (NGS), whereas 19 samples were sequenced using High Fidelity (HiFi) technology. In addition, seven samples were simply sequenced using Sanger sequencing. A total of 29 hypomorphic or loss-of-function variants of KLF1 were identified, 21 of which were newly discovered. All new variants discovered by targeted NGS or HiFi sequencing were validated through Sanger sequencing, and the obtained results were found to be consistent. The KLF1 haplotypes of all new variants were further confirmed using clone sequencing or HiFi sequencing. The lack of functional KLF1 variants detected in the four samples indicates the presence of additional regulatory mechanisms. In addition, some samples exhibited BCAM polymorphisms, which encodes antigens of the Lutheran (LU) blood group system. However, no BCAM mutations which leads to the absence of LU proteins were detected.

CONCLUSIONS

High-throughput sequencing methods, particularly HiFi sequencing, were introduced for the first time into genetic analysis of the In(Lu) phenotype. Targeted NGS and HiFi sequencing demonstrated the accuracy of the results, providing additional advantages such as simultaneous analysis of other blood group genes and clarification of haplotypes. Using the In(Lu) phenotype, a powerful model for identifying hypomorphic or loss-of-function KLF1 variants, numerous novel variants have been detected, which have contributed to the comprehensive understanding of KLF1. These clinically significant KLF1 mutations can serve as a valuable reference for the diagnosis of related blood cell diseases.

Characterization of Novel RHD Allele Variants and Their Implications for Routine Blood Group Diagnostics

The Rh system, including the highly immunogenic D antigen, is one of the clinically most important blood group systems in transfusion medicine. Numerous alleles of the RHD gene are associated with variant RhD phenotypes. In case of Rh incompatibility, some of them can induce hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. Thus, accurate blood group diagnostics are critical for safe transfusion therapy. We characterized phenotypes of four individuals revealing weakened D expression during routine pre-transfusion testing. Standard gel card matrix techniques with monoclonal and polyclonal anti-D antibodies were used for serological typing, complemented using D epitope and antigen density analysis. Genotyping employing PCR with sequence-specific primers, genomic and allele-specific Sanger sequencing and in silico protein analysis were performed. Four novel RHD alleles associated with weak D or partial D phenotypes were identified. One of the mutations is predicted to disrupt the terminal stop codon and result in an elongated translation of the mutant D protein that phenotypically exhibits a loss of D epitopes. Furthermore, a hybrid gene formed with the homologue RHCE gene is described. The presented data enhances the understanding of the Rh system and may contribute to continued advances in blood group diagnostics.

DEL phenotype in RhD-negative North Indian blood donors

BACKGROUND

Rh-DEL type is not detected on routine serology and requires specialized adsorption elution methods which are laborious. Identifying the DEL phenotype in blood donors is important to prevent alloimmunization in transfusion recipients. The present study aimed to determine the frequency of DEL phenotype in RhD-negative North Indian blood donors and correlate the results with Rh Cc/Ee phenotype.

MATERIALS AND METHODS

In this prospective descriptive cross-sectional study, a total of 205 blood donors with historic blood group RhD-negative were enrolled. All samples were subjected to blood grouping using a fully automated immunohematology analyzer and samples that typed as RhD negative by two different anti-D antisera were tested for Weak D. Weak D-negative samples were subjected to adsorption and elution for DEL phenotype. All samples were also tested for extended Rh phenotype for C/c and E/e antigens.

RESULTS

Of the total 11934 donors during the study, 6.2% (n = 743) donors were RhD negative. Of the 205 donors enrolled in the study, two donor samples were serologically weak D positive. None of the remaining 203 donors tested positive for the DEL phenotype. The extended Rh phenotype performed for these donors showed that 6.83% (n = 14) donors were positive for RhC antigen and 1.46% (n = 3) were positive for Rh E antigen. Both weak D-positive donors were also positive for the Rh C antigen.

CONCLUSION

The prevalence of DEL phenotype is low in the Indian population and studies with larger sample sizes are required to determine the effectiveness of routine C/E typing as a strategy to identify DEL-positive individuals.

Rh flow cytometry: An updated methodology for D antigen density applied to weak D types 164 and 165

BACKGROUND

An original methodology for determining the D antigen density on red cells was published in 2000 and has been applied in many publications since. This flow cytometry-based assay remained largely unrevised utilizing monoclonal anti-Ds that are not readily available anymore. We updated the methodology to quantify erythrocyte D antigen sites using microspheres and monoclonal anti-Ds that are commercially available today.

METHODS

The absolute D antigen density of a frozen standard CcDEe cell, drawn in 2003, a fresh blood donation from the same individual, drawn in 2022, and an internal control CcDEe cell, was quantified by flow cytometry using fluorescence-labeled microspheres. The internal control CcDEe cell was used in conjunction with 9 commercial anti-Ds to determine D antigen densities of 7 normal D, 4 partial D, and 11 weak D type samples, including 2 novel alleles.

RESULTS

The reproducibility of the updated assay was evaluated with red cells of published D antigen densities. The current results matched the known ones closely. The new weak D types 164 and 165 carried 4500 and 1505 D antigens/red cell, respectively. The absolute D antigen density decreased from 27,231 to 26,037 in an individual over 19 years.

DISCUSSION

The updated assay gave highly reproducible results for the D antigen densities of Rh phenotypes. Readily available anti-Ds allowed for the determination of the D antigen densities of 7 weak D types. The assay is suitable to evaluate the effects of distinct amino acid substitutions on the RhD phenotype.

DEL variants: review of molecular mechanisms, clinical consequences and molecular testing strategy

Patients with DEL phenotype, a D variant with a low number of D antigens per red blood cell, are routinely typed as RhD-negative in serology testing and are detectable only by adsorption and elution techniques or molecular methods. DEL is of clinical importance worldwide, as indicated by its genotype-phenotype discrepancies among different populations and its potential to cause anti-D alloimmunization when DEL phenotype individuals are inadvertently managed as RhD-negative. This narrative review summarized the DEL alleles causing DEL phenotype and the underlying mechanisms. The clinical consequences and current molecular testing approach were discussed to manage the transfusion needs of patients and donors with DEL phenotype.

Molecular and serological analysis of the D variant in the Chinese population and identification of seven novel RHD alleles

BACKGROUND

The molecular basis of the D variant phenotype in the Chinese differs greatly from that of the Caucasian. Adapting a specific D typing strategy to the spectrum of prevalent RHD variant alleles is necessary.

STUDY DESIGN AND METHODS

Blood samples with ambiguous D phenotypes were collected in the Southern Chinese population. A special three-step typing strategy was applied. First, the common DVI type 3 was identified from epitope profiles of D antigen. Then, another common weak D type 15 (RHD*845A) was identified by epitope profiles of D antigen and Sanger sequencing of RHD exon 6. Finally, the remaining D variants were genotyped mainly by Sanger sequencing. For the novel RHD alleles in the coding region and exon-intron junction, in vitro transfection and minigene splicing assays were performed, respectively. The anti-D investigation was performed.

RESULTS

DVI type 3 (65/253, 25.7%) and weak D type 15 (62/253, 24.5%) were common Chinese D variants, and RHD*960A, DFR, RHD*weak D type 25, 72, and 136 were frequent variant RHD alleles. Besides, twenty-two sporadic and seven novel RHD alleles (RHD*188A; RHD*688C; RHD*782 T; RHD*1181C; RHD*165 T, 993A; RHD*148 + 3G > T and RHD*1227 + 5G > C) were identified. The deleterious effect of the novel RHD alleles on D antigen or mRNA expression was confirmed. Anti-D was detected in two DVI type 3 pregnant women.

DISCUSSION

The three-step typing strategy provides an effective approach for Chinese D variant typing. It can be anticipated that commercially available RHD genotyping kits have limitations for testing Chinese D variants, as some of the frequent variants are not interrogated.

Obstetric and Newborn Weak D-Phenotype RBC Testing and Rh Immune Globulin Management Recommendations: Lessons From a Blinded Specimen-Testing Survey of 81 Transfusion Services

CONTEXT.—

Modern RHD genotyping can be used to determine when patients with serologic weak D phenotypes have RHD gene variants at risk for anti-D alloimmunization. However, serologic testing, RhD interpretations, and laboratory management of these patients are quite variable.

OBJECTIVE.—

To obtain interlaboratory comparisons of serologic testing, RhD interpretations, Rh immune globulin (RhIG) management, fetomaternal hemorrhage testing, and RHD genotyping for weak D-reactive specimens.

DESIGN.—

We devised an educational exercise in which 81 transfusion services supporting obstetrics performed tube-method RhD typing on 2 unknown red blood cell challenge specimens identified as (1) maternal and (2) newborn. Both specimens were from the same weak D-reactive donor. The exercise revealed how participants responded to these different clinical situations.

RESULTS.—

Of reporting laboratories, 14% (11 of 80) obtained discrepant immediate-spin reactions on the 2 specimens. Nine different reporting terms were used to interpret weak D-reactive maternal RhD types to obstetricians. In laboratories obtaining negative maternal immediate-spin reactions, 28% (16 of 57) performed unwarranted antiglobulin testing, sometimes leading to recommendations against giving RhIG. To screen for excess fetomaternal hemorrhage after a weak D-reactive newborn, 47% (34 of 73) of reporting laboratories would have employed a contraindicated fetal rosette test, risking false-negative results and inadequate RhIG coverage. Sixty percent (44 of 73) of laboratories would obtain RHD genotyping in some or all cases.

CONCLUSIONS.—

For obstetric and neonatal patients with serologic weak D phenotypes, we found several critical problems in transfusion service laboratory practices. We provide recommendations for appropriate testing, consistent immunohematologic terminology, and RHD genotype-guided management of Rh immune globulin therapy and RBC transfusions.

RHD genotyping to resolve weak and discrepant RhD patient phenotypes

BACKGROUND

We instituted RHD genotyping in our transfusion service for obstetrical patients and transfusion candidates. We sought to examine how RHD genotyping resolved weak or discrepant automated microplate direct agglutination (MDA) RhD phenotypings and impacted needs for Rh Immune Globulin (RhIG) and D-negative RBCs.

STUDY DESIGN AND METHODS

We investigated RhD phenotypes with equivocal or reagent-discrepant automated MDA (Immucor, Norcross, GA), weak-2+ immediate-spin tube typings, historically discrepant RhD typings, or D+ typings with anti-D. We performed microarray RHD genotyping (RHD BeadChip, Immucor BioArray Solutions, Warren, NJ). Patients were managed as D+ with weak-D types 1, 2, and 3, and as D-negative with all other results.

RESULTS

Our weak-D prevalence was 0.14%. Among 138 patients (73 obstetrics, 65 transfusion candidates), 38% had weak-D types 1, 2 or 3, 25% weak partial type 4.0, 21% other partial-D variant alleles, and 15% no variant detected. One novel allele with weak partial type 4.0 variants plus c.150T>C (Val50Val) was discovered. Weak D types 1, 2 or 3 were identified in 66% (48/73) of Whites versus 3% (2/62) of diverse ethnic patients (p < .0001). RHD genotyping changed RhD management in 60 patients (43%) (49 to D+, 11 to D-negative), resulting in net conservation of D-negative RBCs (98 avoided, 14 given) and RhIG (8 avoided, 3 given).

CONCLUSION

In our patient population, equivocal or reagent-discrepant MDA RhD phenotypes were highly specific for weak-D or partial-D RHD genotypes. Resolution of RHD genotype status reduced our use of D-negative RBCs and RhIG.

RHD alleles contributing to serologically weak D phenotypes in China: A single-centre study over 10 years

BACKGROUND AND OBJECTIVES

In cases of serologically weak D phenotypes, RHD genotyping may identify discrepant serotyping results and protect the patient against allogeneic immunization. This study aimed to conduct a comprehensive analysis of weak D alleles in China.

MATERIALS AND METHODS

We collected samples carrying weak D antigen during a 10-year period from 2005 to 2014. The intensity and epitopes of D were analysed serologically. Genomic DNA was extracted and used for RHD sequencing and heterozygote analysis. In particular, an in vitro expression method for functional verification of the rare and novel in-frame deletion mutation was developed and then combined with homologous modelling results for analysis.

RESULTS

We studied a total of 283 weak D samples from volunteer blood donors and identified 45 RHD alleles among them, 11 of which were reported for the first time. Ten (3.5%) samples surprisingly carried DEL allelic variants and as many as 40 (14.1%) carried the wild-type RHD genotype. Combination of the results of functional experiments and in silico analysis suggested that the rare in-frame deletion mutation may reduce the expression of D antigen by affecting the RhD protein structure.

CONCLUSIONS

This study provides an enhanced overview of the distribution characteristics of RHD alleles in Chinese subjects with serologically weak D. An in vitro method to predict the biological significance of variant RHD alleles was also provided. We found inconsistent genotyping and phenotypic results in some samples, indicating the existence of additional regulatory mechanisms.

Transfusion support for a woman with RHD*09.01.02 and the novel RHD*01W.161 allele in trans

According to recent work group recommendations, individuals with the serologic weak D phenotypes should be RHD genotyped and individuals with molecular weak D types 1, 2, 3, 4.0, or 4.1 should be treated as D+. We report an African American woman with a long-standing history of metrorrhagia, who presented for infertility evaluation. Blood grouping showed AB with a possible subgroup of A, based on mixed-field agglutination, and a serologic weak D phenotype. Results from routine red cell genotyping for the RHD gene was incongruent with the serologic RhCE phenotype. For the surgical procedure, the patient was hence scheduled to receive group AB, D- RBC transfusions. Subsequent molecular analysis identified the ABO*A2.01 and ABO*B.01 alleles for the ABO genotype and the novel RHD allele [NG_007494.1(RHD):c.611T>A] along with an RHD*09.01.02 allele for the RHD genotype. Using a panel of monoclonal anti-D reagents, we showed the novel RHD(I204K) allele to represent a serologic weak D phenotype, despite occurring as a compound heterozygote, designated RHD*weak D type 161 (RHD*01W.161). Individuals with a weak D type 4.2 allele are prone to anti-D immunization, while the immunization potential of novel RHD alleles is difficult to predict. For now, patients should be treated as D- in transfusion and pregnancy management, when they harbor a novel RHD allele along with any weak D allele other than weak D types 1, 2, 3, 4.0, or 4.1. This study exemplifies strategies for how and when a laboratory should proceed from routine genotyping to nucleotide sequencing before any decisions on transfusion practice is made.

RBCeq: A robust and scalable algorithm for accurate genetic blood typing

Background

While blood transfusion is an essential cornerstone of hematological care, patients requiring repetitive transfusion remain at persistent risk of alloimmunization due to the diversity of human blood group polymorphisms. Despite the promise, user friendly methods to accurately identify blood types from next-generation sequencing data are currently lacking. To address this unmet need, we have developed RBCeq, a novel genetic blood typing algorithm to accurately identify 36 blood group systems.

Methods

RBCeq can predict complex blood groups such as RH, and ABO that require identification of small indels and copy number variants. RBCeq also reports clinically significant, rare, and novel variants with potential clinical relevance that may lead to the identification of novel blood group alleles.

Findings

The RBCeq algorithm demonstrated 99·07% concordance when validated on 402 samples which included 29 antigens with serology and 9 antigens with SNP-array validation in 14 blood group systems and 59 antigens validation on manual predicted phenotype from variant call files. We have also developed a user-friendly web server that generates detailed blood typing reports with advanced visualization (https://www.rbceq.org/).

Interpretation

RBCeq will assist blood banks and immunohematology laboratories by overcoming existing methodological limitations like scalability, reproducibility, and accuracy when genotyping and phenotyping in multi-ethnic populations. This Amazon Web Services (AWS) cloud based platform has the potential to reduce pre-transfusion testing time and to increase sample processing throughput, ultimately improving quality of patient care.

Funding

This work was supported in part by Advance Queensland Research Fellowship, MRFF Genomics Health Futures Mission (76,757), and the Australian Red Cross LifeBlood. The Australian governments fund the Australian Red Cross Lifeblood for the provision of blood, blood products and services to the Australian community.

BGvar: A comprehensive resource for blood group immunogenetics

BACKGROUND

Blood groups form the basis of effective and safe blood transfusion. There are about 43 well-recognised human blood group systems presently known. Blood groups are molecularly determined by the presence of specific antigens on the red blood cells and are genetically determined and inherited following Mendelian principles. The lack of a comprehensive, relevant, manually compiled and genome-ready dataset of red cell antigens limited the widespread application of genomic technologies to characterise and interpret the blood group complement of an individual from genomic datasets.

MATERIALS AND METHODS

A range of public datasets was used to systematically annotate the variation compendium for its functionality and allele frequencies across global populations. Details on phenotype or relevant clinical importance were collated from reported literature evidence.

RESULTS

We have compiled the Blood Group Associated Genomic Variant Resource (BGvar), a manually curated online resource comprising all known human blood group related allelic variants including a total of 1700 International Society of Blood Transfusion approved alleles and 1706 alleles predicted and curated from literature reports. This repository includes 1682 single nucleotide variations (SNVs), 310 Insertions, Deletions (InDels) and Duplications (Copy Number Variations) and about 1360 combination mutations corresponding to 43 human blood group systems and 2 transcription factors. This compendium also encompasses gene fusion and rearrangement events occurring in human blood group genes.

CONCLUSION

To the best of our knowledge, BGvar is a comprehensive and a user-friendly resource with most relevant collation of blood group alleles in humans. BGvar is accessible online at URL: http://clingen.igib.res.in/bgvar/.

To Give or Not to Give: RhD Immunoglobulin for an RHD *39 Pregnant Woman with Sickle Cell Disease

Introduction

Patients with sickle cell disease (SCD) have repeated episodes of red blood cell (RBC) sickling and microvascular occlusion that manifest as pain crises, acute chest syndrome, and chronic hemolysis. These clinical sequelae usually increase during pregnancy. Given the racial distribution of SCD, patients with SCD are also more likely to have rarer RBC antigen genotypes than RBC donor populations. We present the management and clinical outcome of a 21-year-old pregnant woman with SCD and an RHD*39 (RhD[S103P], G-negative) variant.

Case Presentation

Ms. S is B positive with a reported history of anti-D, anti-C, and anti-E alloantibodies (anti-G testing unknown). Genetic testing revealed both an RHD*39 and homozygous partial RHCE*ceVS.02 genotype. Absorption/elution testing confirmed the presence of anti-G, anti-C, and anti-E alloantibodies but could not definitively determine the presence/absence of an anti-D alloantibody. Ms. S desired to undergo elective pregnancy termination and the need for postprocedural RhD immunoglobulin (RhIG) was posed. Given that only the G antigen site is changed in an RHD*39 genotype and the potential risk of RhIG triggering a hyperhemolytic episode in an SCD patient, RhIG was not administered. There were no procedural complications. Follow-up testing at 10 weeks showed no increase in RBC alloantibody strength.

Discussion/Conclusion

Ms. S represents a rare RHD*39 and partial RHCE*ceVS.02 genotype which did not further alloimmunize in the absence of RhIG administration. Her case also highlights the importance of routine anti-G alloantibody testing in women of childbearing age with apparent anti-D and anti-C alloantibodies.

Blood groups of Neandertals and Denisova decrypted

Blood group systems were the first phenotypic markers used in anthropology to decipher the origin of populations, their migratory movements, and their admixture. The recent emergence of new technologies based on the decoding of nucleic acids from an individual’s entire genome has relegated them to their primary application, blood transfusion. Thus, despite the finer mapping of the modern human genome in relation to Neanderthal and Denisova populations, little is known about red cell blood groups in these archaic populations. Here we analyze the available high-quality sequences of three Neanderthals and one Denisovan individuals for 7 blood group systems that are used today in transfusion (ABO including H/Se, Rh (Rhesus), Kell, Duffy, Kidd, MNS, Diego). We show that Neanderthal and Denisova were polymorphic for ABO and shared blood group alleles recurrent in modern Sub-Saharan populations. Furthermore, we found ABO-related alleles currently preventing from viral gut infection and Neanderthal RHD and RHCE alleles nowadays associated with a high risk of hemolytic disease of the fetus and newborn. Such a common blood group pattern across time and space is coherent with a Neanderthal population of low genetic diversity exposed to low reproductive success and with their inevitable demise. Lastly, we connect a Neanderthal RHD allele to two present-day Aboriginal Australian and Papuan, suggesting that a segment of archaic genome was introgressed in this gene in non-Eurasian populations. While contributing to both the origin and late evolutionary history of Neanderthal and Denisova, our results further illustrate that blood group systems are a relevant piece of the puzzle helping to decipher it.

High prevalence of weak D type 42 in a large-scale RHD genotyping program in the province of Quebec (Canada)

BACKGROUND

The determination of the RhD phenotype is crucial to avoid alloimmunization, especially in childbearing women. Following the 2015 recommendation from the Work Group on RHD Genotyping, a large-scale RHD genotyping program was implemented in the province of Quebec (Canada) and offered to women ≤45 years old with a serological weak D or discordant results. Since weak D type 42 was previously shown to be prevalent among French Canadians, genotyping for that variant was also performed. Our aim was to report the prevalence of the weak D alleles in the province of Quebec.

STUDY DESIGN AND METHODS

A retrospective study of 2105 women with serological weak D referred to Hema-Quebec's immunohematology reference laboratory (IRL) between June 2016 and May 2020 was conducted. Results from the serological tests performed by the referring hospital were compiled and RHD were genotyped.

RESULTS

Most patients presented at least one serological result ≤2+ before being referred to Hema-Quebec. Weak D type 42 was the most prevalent variant, representing 17.5% (368/2105) of all individuals tested. Only 15.3% (323/2105) of patients were weak D type 1, 3.3% (69/2105) were type 2, and 8.6% (180/2105) were type 3. Weak D type 42 is highly expressed in regions with low immigration rate and known for their founder effect.

CONCLUSION

Our RHD genotyping program allowed for a better management of weak D. The province of Quebec presents a unique RHD genotype distribution. We confirmed that weak D type 42 is associated with a founder effect found in Caucasian French Canadians.

Missense RHD single nucleotide variants induce weakened D antigen expression by altering splicing and/or protein expression

BACKGROUND

Although D variant phenotype is known to be due to genetic defects, including rare missense single nucleotide variants (SNVs), within the RHD gene, few studies have addressed the molecular and cellular mechanisms driving this altered expression. We and others showed previously that splicing is commonly disrupted by SNVs in constitutive splice sites and their vicinity. We thus sought to investigate whether rare missense SNVs located in "deep" exonic regions could also impair this mechanism.

STUDY DESIGN AND METHODS

Forty-six missense SNVs reported within exons 6 and 7 were first selected from the Human RhesusBase. Their respective effect on splicing was assessed by using an in vitro assay. An RhD-negative cell model was further generated by using the CRISPR-Cas9 approach. RhD-mutated proteins were overexpressed in the newly created model, and cell membrane expression of the D antigen was measured by flow cytometry.

RESULTS

Minigene splicing assay showed that 14 of 46 (30.4%) missense SNVs alter splicing. Very interestingly, further investigation of two missense SNVs, which both affect codon 338 and confer a weak D phenotype, showed various mechanisms: c.1012C>G (p.Leu338Val) disrupts splicing only, while c.1013T>C (p.Leu338Pro) alters only the protein structure, in agreement with in silico prediction tools and 3D protein structure visualization.

CONCLUSION

Our functional data set suggests that missense SNVs damage quantitatively D antigen expression by, at least, two different mechanisms (splicing alteration and protein destabilization) that may act independently. These data thereby contribute to extend the current knowledge of the molecular mechanisms governing weakened D expression.

Next-generation sequencing of 35 RHD variants in 16 253 serologically D- pregnant women in the Finnish population

Fetal RHD screening for targeted routine antenatal anti-D prophylaxis has been implemented in many countries, including Finland, since the 2010s. Comprehensive knowledge of the RHD polymorphism in the population is essential for the performance and safety of the anti-D prophylaxis program. During the first 3 years of the national screening program in Finland, over 16 000 samples from RhD- women were screened for fetal RHD; among them, 79 samples (0.5%) containing a maternal variant allele were detected. Of the detected maternal variants, 35 cases remained inconclusive using the traditional genotyping methods and required further analysis by next-generation sequencing (NGS) of the whole RHD gene to uncover the variant allele. In addition to the 13 RHD variants that have been previously reported in different populations, 8 novel variants were also detected, indicating that there is more variation of RHD in the RhD- Finnish population than has been previously known. Three of the novel alleles were identified in multiple samples; thus, they are likely specific to the original Finnish population. National screening has thus provided new information about the diversity of RHD variants in the Finnish population. The results show that NGS is a powerful method for genotyping the highly polymorphic RHD gene compared with traditional methods that rely on the detection of specific nucleotides by polymerase chain reaction amplification.

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.

A Review of the Literature Organized Into a New Database: RHeference

Hundreds of articles containing heterogeneous data describe D variants or add to the knowledge of known alleles. Data can be difficult to find despite existing online blood group resources and genetic and literature databases. We have developed a modern, elaborate database for D variants, thanks to an extensive literature search with meticulous curation of 387 peer-reviewed articles and 80 abstracts from major conferences and other sources. RHeference contains entries for 710 RHD alleles, 11 RHCE alleles, 30 phenotype descriptions (preventing data loss from historical sources), 35 partly characterized alleles, 3 haplotypes, and 16 miscellaneous entries. The entries include molecular, phenotypic, serological, alloimmunization, haplotype, geographical, and other data, detailed for each source. The main characteristics are summarized for each entry. The sources for all information are included and easily accessible through doi and PMID links. Overall, the database contains more than 10,000 individual pieces of data. We have set up the database architecture based on our previous expertise on database setup and biocuration for other topics, using modern technologies such as the Django framework, BioPython, Bootstrap, and Jquery. This architecture allows an easy access to data and enables simple and complex queries: combining multiple mutations, keywords, or any of the characteristics included in the database. RHeference provides a complement to existing resources and will continue to grow as our knowledge expands and new articles are published. The database url is http://www.rheference.org/.

Optimization of diagnostic strategy for non-invasive cell-free foetal RHD determination from maternal plasma

BACKGROUND AND OBJECTIVES

The aim of the study was to optimize routine non-invasive prenatal detection of fetal RHD gene from plasma of RhD-negative pregnant women (the median of gestational age was 25 weeks, range 10-38) to detect RhD materno-fetal incompatibility and to avoid the redundant immunoprophylaxis.

MATERIALS AND METHODS

Initially only one exon of RHD gene (exon 10) was investigated in 281 plasma samples (144 verified after delivery), in the second phase three RHD exons (5, 7, 10) were analyzed in 246 samples of plasma and maternal genomic DNA (204 verified) by real-time PCR method. Detection of Y-chromosomal sequence DYS-14 and five X-chromosomal insertion/deletion polymorphisms was used to confirm the fetal cfDNA detectability in plasma. Specific polymorphisms in RHD gene were detected by sequence-specific primer PCR in nine samples.

RESULTS

When only the RHD exon 10 was tested, 2·8% of verified samples were false positive and 3·5% false negative. With three RHD exons (5, 7, 10) and maternal genomic DNA testing, only one case was false negative (0·5%). Nine samples were inconclusive due to RHD-positive results in maternal genomic DNA. These samples were analyzed for specific mutations in RHD gene. Combination of both methods for fetal cfDNA verification succeeded in 75% of tested group.

CONCLUSION

Implementation of analysis of three RHD exons and maternal genomic DNA to routine practice lowers dramatically the ratio of false positive and negative results. This method enables more accurate determination of fetal RHD status with the reduction of unnecessary medical care and RhD immunoprophylaxis.

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.

Nation-wide investigation of RHD variants in Thai blood donors: Impact for molecular diagnostics

BACKGROUND

Knowledge of the molecular determinants driving antigen expression is critical to design, optimize, and implement a genotyping approach on a population-specific basis. Although RHD gene variability has been extensively reported in Caucasians, Africans, and East-Asians, it remains to be explored in Southeast Asia. Thus the molecular basis of non-D+ blood donors was investigated in Thailand.

STUDY DESIGN AND METHODS

First, 1176 blood samples exhibiting an inconclusive or negative result by automated serological testing were collected in the 12 Regional Blood Centres of the Thai Red Cross located throughout Thailand. Second, the RHD gene was analyzed in all samples by 1) quantitative multiplex PCR of short fluorescent fragments, and 2) direct sequencing, when necessary, for identifying structural variants and single nucleotide variants, respectively.

RESULTS

Additional serological typing yielded 51 and 1125 samples with weak/partial D and D-negative (D-) phenotype, respectively. In the first subset, partial RHD*06.03 was the most common variant allele (allele frequency: 18.6%). In the second subset, the whole deletion of the gene is largely the most frequent (allele frequency: 84.9%), followed by the Asian DEL allele found in 15.6% of the samples. Eight novel alleles with various mutational mechanisms were identified.

CONCLUSION

We report, for the first time at the national level, the molecular basis of weak/partial D and serologically D- phenotypes in Thai blood donors. The design and implementation of a dedicated diagnostic strategy in blood donors and patients are the very next steps for optimizing the management and supply of RBC units in Thailand.

Transfusion and Cellular Therapy in Pediatric Sickle Cell Disease

Red blood cell (RBC) transfusion is critical in managing acute and chronic complications of sickle cell disease. Alloimmunization and iron overload remain significant complications of transfusion therapy and are minimized with prophylactic Rh and K antigen RBC matching and iron chelation. Matched sibling donor hematopoietic stem cell transplant (HSCT) is a curative therapeutic option. Autologous hematopoietic stem cell (HSC)-based gene therapy has recently shown great promise, for which obtaining sufficient HSCs is essential for success. This article discusses RBC transfusion indications and complications, transfusion support during HSCT, and HSC mobilization and collection for autologous HSCT with gene therapy.

Frequency of RHD variants in serologically weak D Turkish blood donors

BACKGROUND

RhD typing has remained of primary importance, as being the leading cause of hemolytic disease of the newborn. Among Rh system's 55 blood group antigens, RhD is the most immunogenic. We aimed with this study to determine weak D/partial D variant frequency in blood donors who were admitted to our blood center and have serologically designated blood group weak D.

MATERIALS AND METHODS

We screened blood donors who admitted between 2011 and 2017 to our blood center. Sixty-seven serologically weak D phenotyped donors have participated in the study. These donors' samples were studied further by Polymerase Chain Reaction Sequence- Specific Primers (PCR-SSP) for determining D variants.

RESULTS

Weak D phenotype was detected in 228(0.12 %) out of 177,554 donors. Sixty-seven of them agreed to take part in the study. The frequency of weak D and partial D was 68.7 % (n = 46), and 22.4 % (n = 15), in order. The most encountered weak D and partial D variant was type 15 and DFR type, respectively.

CONCLUSIONS

The prevalence of serologically weak D phenotypes varies by race and ethnicity. Turkey is a country covering a mixture of European and Asian DNA with different ethnic groups. Thus, our research as giving the overall distribution of RHD variants from the largest city of Turkey, which may reflect the general ethnic background of the country, would help to the establishment of a databank for blood banking. This paper is the first molecular study on RHD variants in Turkey. New molecular research would be more reliable and precise.

Molecular and computational analysis of 45 samples with a serologic weak D phenotype detected among 132,479 blood donors in northeast China

Background

RH1 is one of the most clinically important blood group antigens in the field of transfusion and in the prevention of fetal incompatibility. The molecular analysis and characterization of serologic weak D phenotypes is essential to ensuring transfusion safety.

Methods

Blood samples from a northeastern Chinese population were randomly screened for a serologic weak D phenotype. The nucleotide sequences of all 10 exons, adjacent flanking intronic regions, and partial 5′ and 3′ untranslated regions (UTRs) were detected for RHD genes. Predicted deleterious structural changes in missense mutations of serologicl weak D phenotypes were analyzed using SIFT, PROVEAN and PolyPhen2 software. The protein structure of serologic weak D phenotypes was predicted using Swiss-PdbViewer 4.0.1.

Results

A serologic weak D phenotype was found in 45 individuals (0.03%) among 132,479 blood donors. Seventeen distinct RHD mutation alleles were detected, with 11 weak D, four partial D and two DEL alleles. Further analyses resulted in the identification of two novel alleles (RHD weak D 1102A and 399C). The prediction of a three-dimensional structure showed that the protein conformation was disrupted in 16 serologic weak D phenotypes.

Conclusions

Two novel and 15 rare RHD alleles were identified. Weak D type 15, DVI Type 3, and RHD1227A were the most prevalent D variant alleles in a northeastern Chinese population. Although the frequencies of the D variant alleles presented herein were low, their phenotypic and genotypic descriptions add to the repertoire of reported RHD alleles. Bioinformatics analysis on RhD protein can give us more interpretation of missense variants of RHD gene.

Comprehensive phenotypic and molecular investigation of RhD and RhCE variants in Moroccan blood donors

BACKGROUND

To date, more than 650 (weak and partial) Rh variants have been reported. Nature and frequency of these variants are known to be ethnodependent. In transfusion medicine, their identification is important to ensure blood safety. The aim of this study is to investigate and describe the nature and estimate the frequency of Rh variants in blood donors in Morocco by serological tests and molecular analysis.

MATERIALS AND METHODS

Blood samples from 4,458 blood donors were collected and typed for Rh antigens (D, C, c, E and e) by an automated system with monoclonal antibodies. RhD-negative samples were tested for weak D expression by indirect antiglobulin test (IAT), as well as weak C, c, E, and e expression with monoclonal antibodies, by column agglutination technique. All samples exhibiting a weak D agglutination by the automated system and IAT were tested for partial D. RHD and RHCE genes were analysed by quantitative multiplex PCR of short fluorescent fragments (QMPSF) and/or Sanger sequencing.

RESULTS

4,038 (90.58%) and 420 (9.42%) samples were respectively typed serologically as D-positive and D-negative, including 23 (0.52%) presenting with a weak D phenotype. In 21 weak D samples investigated by molecular analysis, RHD*weak D type 4.0 was found to be the most prevalent variant allele (n=11), and a novel RHD(V270A) missense allele was found once. Variant Rh CcEe antigen expression was observed in 17 samples carrying 20 variant RHCE alleles, including a novel RHCE*ce(499G) missense allele (p.M167V).

DISCUSSION

For the first time, molecular genetics of the Rh system was investigated in the Moroccan population. On the basis of our data and in order to optimise donor/recipient matching to prevent from a potential risk of alloimmunisation in recipients, we suggest that 1) quality control of serological reagents and screening strategies must be reviewed in Morocco, and 2) molecular analysis should be implemented and performed in blood donor centers.

Repository of Enriched Structures of Proteins Involved in the Red Blood Cell Environment (RESPIRE)

The Red Blood Cell (RBC) is a metabolically-driven cell vital for processes such a gas transport and homeostasis. RBC possesses at its surface exposing antigens proteins that are critical in blood transfusion. Due to their importance, numerous studies address the cell function as a whole but more and more details of RBC structure and protein content are now studied using massive state-of-the art characterisation techniques. Yet, the resulting information is frequently scattered in many scientific articles, in many databases and specialized web servers. To provide a more compendious view of erythrocytes and of their protein content, we developed a dedicated database called RESPIRE that aims at gathering a comprehensive and coherent ensemble of information and data about proteins in RBC. This cell-driven database lists proteins found in erythrocytes. For a given protein entry, initial data are processed from external portals and enriched by using state-of-the-art bioinformatics methods. As structural information is extremely useful to understand protein function and predict the impact of mutations, a strong effort has been put on the prediction of protein structures with a special treatment for membrane proteins. Browsing the database is available through text search for reference gene names or protein identifiers, through pre-defined queries or via hyperlinks. The RESPIRE database provides valuable information and unique annotations that should be useful to a wide audience of biologists, clinicians and structural biologists.

Database URL:http://www.dsimb.inserm.fr/respire

Implementation of Molecular RHD Typing at Two Blood Transfusion Institutes from Southeastern Europe

Introduction

Determination of RhD variants in blood donors, pregnant women, and newborns is important for transfusion strategies, in order to prevent RhD alloimmunisation and hemolytic disease of fetuses and newborns. Implementation of molecular RHD typing in two transfusion institutes is presented in this article, from Banja Luka (Bosnia and Herzegovina) and Belgrade (Serbia).

Study Design and Methods

Blood donors' RhD was checked by direct agglutination assays (tube) and indirect antiglobulin test (gel). Molecular RHD typing was performed by PCR-SSP with fluorometric signal detection in both centres. Donors were selected by weak RhD serological reactivity (Banja Luka, 85 samples; Belgrade, 62 samples) or serologically RhD-negative C/E-positive results (Banja Luka, 92 samples; Belgrade, 61 samples).

Results

Among serologically determined weak D donors from the institute from Banja Luka, weak D type 3 was the most frequent (58.8%), followed by type 1 (35.3%) and DNB (1.2%), whereas results obtained at the Belgrade institute were distributed between weak D type 1 (41.9%), type 3 (30.7%), type 14 (6.5%), type 15 (1.6%), and DNB with anti-D (1.6%). In 17.7% of serologically typed weak D samples from the Belgrade institute, the molecular typing result was standard D. Additionally, RHD presence was detected in 9.8% of serologically RhD-negative, C/E-positive samples from both institutes.

Conclusion

Rh molecular testing was successfully implemented in both blood transfusion institutes in Banja Luka and Belgrade. This study proved the efficiency of serological algorithms for weak D, as well as the presence of the RHD gene among serologically tested RhD-negative, C/E-positive samples.

Two large deletions extending beyond either end of the RHD gene and their red cell phenotypes

Only two partial deletions longer than 655 nucleotides had been reported for the RHD gene, constrained within the gene and causing DEL phenotypes. Using a combination of quantitative PCR and long-range PCR, we examined three distinct deletions affecting parts of the RHD gene in three blood donors. Their RHD nucleotide sequences and exact boundaries of the breakpoint regions were determined. DEL phenotypes were caused by a novel 18.4 kb deletion and a previously published 5.4 kb deletion of the RHD gene; a D-negative phenotype was caused by a novel 7.6 kb deletion. Examination of the deletion-flanking regions suggested microhomology-mediated end-joining, replication slippage, and non-homologous end-joining, respectively, as the most likely mechanisms for the three distinct deletions. We described two new deletions affecting parts of the RHD gene, much longer than any previously reported partial deletion: one was the first deletion observed at the 5' end of the RHD gene extending into the intergenic region, and the other the second deletion observed at its 3' end. Large deletions present at either end are a mechanism for a much reduced RhD protein expression or its complete loss. Exact molecular characterization of such deletions is instrumental for accurate RHD genotyping.

Transfusion strategy for weak D Type 4.0 based on RHD alleles and RH haplotypes in Tunisia

BACKGROUND

With more than 460 RHD alleles, this gene is the most complex and polymorphic among all blood group systems. The Tunisian population has the largest known prevalence of weak D Type 4.0 alleles, occurring in one of 105 RH haplotypes. We aimed to establish a rationale for the transfusion strategy of weak D Type 4.0 in Tunisia.

STUDY DESIGN AND METHODS

Donors were randomly screened for the serologic weak D phenotype. The RHD coding sequence and parts of the introns were sequenced. To establish the RH haplotype, the RHCE gene was tested for characteristic single-nucleotide positions.

RESULTS

We determined all RHD alleles and the RH haplotypes coding for the serologic weak D phenotype among 13,431 Tunisian donations. A serologic weak D phenotype was found in 67 individuals (0.50%). Among them, 60 carried a weak D Type 4 allele: 53 weak D Type 4.0, six weak D Type 4.2.2 (DAR), and one weak D Type 4.1. An additional four donors had one variant allele each: DVII, weak D Type 1, weak D Type 3, and weak D type 100, while three donors showed a normal RHD sequence. The weak D Type 4.0 was most often linked to RHCE*ceVS.04.01, weak D Type 4.2.2 to RHCE*ceAR, and weak D Type 4.1 to RHCE*ceVS.02, while the other RHD alleles were linked to one of the common RHCE alleles.

CONCLUSIONS

Among the weak D phenotypes in Tunisia, no novel RHD allele was found and almost 90% were caused by alleles of the weak D Type 4 cluster, of which 88% represented the weak D Type 4.0 allele. Based on established RH haplotypes for variant RHD and RHCE alleles and the lack of adverse clinical reports, we recommend D+ transfusions for patients with weak D Type 4.0 in Tunisia.