Molecular basis of weak D expression in the Indian population and report of a novel, predominant variantRHDallele

A Bioinformatically Initiated Approach to Evaluate GATA1 Regulatory Regions in Samples with Weak D, Del, or D- Phenotypes Despite Normal RHD Exons

Introduction

With over 360 blood group antigens in systems recognized, there are antigens, such as RhD, which demonstrate a quantitative reduction in antigen expression due to nucleotide variants in the non-coding region of the gene that result in aberrant splicing or a regulatory mechanism. This study aimed to evaluate bioinformatically predicted GATA1-binding regulatory motifs in the RHD gene for samples presenting with weak or apparently negative RhD antigen expression but showing normal RHD exons.

Methods

Publicly available open chromatin region data were overlayed with GATA1 motif candidates in RHD. Genomic DNA from weak D, Del or D- samples with normal RHD exons (n = 13) was used to confirm RHD zygosity by quantitative PCR. Then, RHD promoter, intron 1, and intron 2 regions were amplified for Sanger sequencing to detect potential disruptions in the GATA1 motif candidates. Electrophoretic mobility shift assay (EMSA) was performed to assess GATA1-binding. Luciferase assays were used to assess transcriptional activity.

Results

Bioinformatic analysis identified five of six GATA1 motif candidates in the promoter, intron 1 and intron 2 for investigation in the samples. Luciferase assays showed an enhancement in transcription for GATA1 motifs in intron 1 and for intron 2 only when the R 2 haplotype variant (rs675072G>A) was present. GATA1 motifs were intact in 12 of 13 samples. For one sample with a Del phenotype, a novel RHD c.1-110A>C variant disrupted the GATA1 motif in the promoter which was supported by a lack of a GATA1 supershift in the EMSA and 73% transcriptional activity in the luciferase assay. Two samples were D+/D- chimeras.

Conclusion

The bioinformatic predictions enabled the identification of a novel DEL allele, RHD c.1-110A>C, which disrupted the GATA1 motif in the proximal promoter. Although the majority of the samples investigated here remain unexplained, we provide GATA1 targets which may benefit future RHD regulatory investigations.

Autoimmune anti-D in an RhD-positive young infant: Learning from a rare case

BACKGROUND AND OBJECTIVES

Anti-D is usually immune in nature and is formed in individuals lacking D antigen or having variants/altered D phenotypes. In the Indian population, 93.8% are RhD positive, and R1 R1 is the commonest Rh phenotype. Here we report a rare and interesting case of autoimmune anti-D in an RhD-positive 3-month-old infant leading to warm autoimmune haemolytic anaemia.

STUDY DESIGN AND METHODS

Auto-anti-D was detected serologically by immunohaematological techniques such as direct antiglobulin test, antibody detection and identification, dithiothreitol, enzyme treatment, antibody titration and elution. Molecular studies were performed to rule out genetic variants of RhD.

RESULTS

Anti-D was confirmed in eluate and blood group post elution was B RhD positive. On genotyping using the Indian-specific RHD genotyping assay, the sample was found to be negative for the RHD*01W.150 (most common RhD variant in Indians) but positive for RHD exon 5 and RHD exon 10 along with glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The sample was further sequenced for RHD exons 1-10 by Sanger sequencing and found to be a wild type, thus, ruling out the presence of an RhD variant.

CONCLUSION

This case is of interest because of the rare occurrence of autoimmune anti-D in an RhD-positive patient of such a young age (3 months). To the best of our knowledge, only two case reports have been published on autoimmune anti-D in infancy (in 1961 and 1964).

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.

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.

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.

Variable reactivity of Rh D antigen and its serological characterization

Background: Variation in the reactivity on Rh D typing may pose challenges in interpretation and ambiguity in further patient management.Materials and Methods: A prospective study was conducted in the department of transfusion medicine for a period of 18 months. Blood grouping was performed by fully automated equipment employing column agglutination technique. All the samples with Rh D negative or discrepant reactions were subjected to weak D testing by the antihuman globulin testing method. Samples that tested positive were categorized as serological weak D type or Variant D and were further phenotyped with Partial D typing set with 6 monoclonal anti D antisera.Results: A total of 82,824 samples were tested for Rh D type during the study period. Of the study population, 65.7% were males. On Rh D type majority were Rh D positive (93%), 6.9% were negative, and the result was discrepant in 0.1% (70) samples. The overall prevalence of variant D was 1.28% (75) of the Rh D negative population and 0.09% of the total study population. The detection rate of variant D phenotype was significantly higher by the Column agglutination technique. Upon testing with Partial D kit, the partial D variant in the majority reacted wil all the 6 antisera and hence we could not rule out DIII(60%), in rest it was inconclusive. In 43% of subjects with Rh D discrepancy 'C' antigen was found in a homozygous state.Conclusion: The introduction of partial D typing kit alone may not help in the absolute characterization of variant D. Extended serological testing and selective integration of molecular testing is the need of the hour.

Molecular characterization of RhD variant phenotypes among blood donors: A study from the coastal region of India

BACKGROUND

RhD expression varies with population and ethnicity. Accurate typing of RhD antigen among blood donors is important to prevent development of anti-D among recipients of blood transfusion. We aimed to screen blood donors for variant D phenotypes and accurately characterize them by genotyping.

MATERIAL AND METHODS

We have done prospective study on blood donors by performing RhD typing using three different commercial monoclonal anti-D reagents by both column agglutination and conventional tube techniques. Samples that showed ambiguous results were further screened with the Bio-Rad Partial RhD typing kit. Minor phenotyping for C, c, E, e antigens was performed. Multiplex PCR and Sequencing of all RHD exons with Sanger's sequencing was performed for molecular characterization of variant D.

RESULTS

A total of 16,974 blood donors were screened during the study period. Among them, 31 (0.18 %) donors were found to have a RhD variant phenotype. The male to female ratio was 10:1. The presence of 'C' antigen was noted among all RhD variant samples. Serological typing identified two samples as DV phenotype and the rest could not be characterized. Molecular genotyping characterized 90.3 % of the samples as Indian specific weak D type 150 variants. Three samples were subjected to Sangers sequencing and showed wild type pattern.

CONCLUSION

The present study showed that the most common variant in this population was Weak D type 150. This study highlights that serological methods may serve as a screening tool, however, molecular techniques are essential for characterization of RhD variants.

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/.

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.

Molecular characterisation of RhD variants in North Indian blood donor population

OBJECTIVES

A molecular analysis of serologically RhD variant samples was conducted to find the incidence of various D variants in our blood donor population.

BACKGROUND

Determining a blood donor's RhD phenotype and genotype is important as transfusion of units with a weak D or partial D phenotype can result in immunisation of the recipients.

METHODS

Samples with discrepant D and weak D phenotypes identified on testing with at least five different monoclonal anti-D antisera were considered serological RhD variant and subjected to molecular testing (Massarray kit, Agena Bioscience, San Diego) for variant RHD gene.

RESULTS

A total of 39 samples, including 19 RhD discrepant samples and 20 weak D samples, were identified as serological RhD variant from a total of 4386 samples. Thirteen (13/39) samples carried variants leading to weak D phenotype, and eight samples had variants leading to partial D categories. Seven samples (7) could not be characterised, whereas 11 samples were identified as Rh negative (RHD*01N.01) after molecular testing. Overall incidence of D variants in the study population was 0.48%. RHD*weak D type 1(5, 0.1%) and RHD*DFR1 (5, 1%) were the most common variants identified.

CONCLUSIONS

Few samples with weak reaction on serological testing were found to be partial D variant and vice versa. Donor centres should develop a protocol for genotyping of samples with aberrant results on serological testing for assessing the actual RhD status of an individual as results of serological testing may be misleading.

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.

Comparison of serology and molecular detection of common red cell antigens in multitransfused thalassemia major and sickle cell disease patients

BACKGROUND

Serological testing for extended RHCcEe, Kell, Kidd and Duffy blood grouping from multitransfused patients may not give correct blood grouping of the recipient. Hence molecular testing for these blood groups was compared with serological groups in a cohort of multitransfused thalassemia mjor and sickle cell anaemia patients.

OBJECTIVE

Molecular genotyping of antigens of Rh (D, C, c, E, e), Kell (K, k), Duffy (Fy^a, Fy^b) and Kidd (Jk^a, Jk^b) blood group antigens by PCR and PCR-RFLP methods and comparison of predicted genotypes with their serological phenotypes.

MATERIALS AND METHODS

A cohort of multitransfused thalassemia and sickle cell anemia patient were serologically and molecularly tested for RHCc, RHEe, K, k Fy^a, Fy^b, Jk^a and Jk^b antigens and compared. Serological testing was done by tube agglutination and molecular testing was done either by allele specific PCR or by RFLP technique just before next transfusion.

RESULTS

In more than 80% of the cases recipient's molecular testing blood groups were at variance with serologically tested blood groups (p < 0.0001). Mixed field reactions in serological typing were common. In sickle cell anemia patients no discrepancy was found. Molecular technique results were checked by Sanger's sequencing.

DISCUSSION

Extended phenotyping in multitransfused thalassemia patients by serological technique often donot detect the exact red cell phenotype of the recipient and molecular techniques for such grouping is preferable, especially in multitransfused thalassemia patients where red cells from previous transfusions continues to be present in significant numbers whenever the testing is done.

Comprehensive Molecular Analysis of Serologically D-Negative and Weak/Partial D Phenotype in Thai Blood Donors

Background

Molecular genetics of the Rh system has been extensively studied in Caucasians, Black Africans, East Asians, and Indians more recently. In this work, we sought to investigate the molecular basis of variant D expression in the Thai population, which remains unknown.

Materials and Methods

Blood samples from 450 Thai donors showing the variant D phenotype were collected. The RHD gene was analyzed by quantitative multiplex polymerase chain reaction of short fluorescent fragments and/or Sanger sequencing.

Results

The most frequent alleles in 200 D-negative and 121 DEL samples were the whole RHD gene deletion and the Asian DEL alleles, respectively. In 129 weak/partial D samples, 36 variant alleles were identified, including eight novel alleles. RHD*06.03, which is common in variant D samples from South China, is the most prevalent variant allele, followed by the recently reported Indian RHD*01W.150 allele.

Discussion

For the first time, a comprehensive overview of the nature and distribution of variant RHD alleles in Thailand is reported. It is a milestone to pave the way towards improvement of the current screening strategy to identify DEL donors accurately. The next step will be the design and implementation of a simple molecular test for screening the most frequent alleles, specifically in this population.