A convenient qualitative and quantitative method to investigate RHD-RHCE hybrid genes

D-- phenotype in a South Indian family: A multicentric approach to workup and management

BACKGROUND

The Rh system is an extremely important blood group system with over 50 antigens, 5 of which (D, C, E, c and e) are considered most clinically significant. Rare Rh deficient phenotypes include D--, which is a blood group characterised by the lack of expression of C, c, E and e and exalted expression of the D antigen on the red cells due to mutations in both alleles of the RHCE gene. This is a multicentre approach to a case of the rare D-- phenotype.

CASE REPORT

A 56-year-old lady with bad obstetric history presenting with severe anaemia had to be evaluated for a panreactive antibody affecting cross-matching. On identifying a D-- phenotype by serology, a thorough family study was performed on 18 of her first and second-degree relatives. Three family members were also found to be of the rare phenotype, one of whom was pregnant. This relative was counselled appropriately and provided with an overview of her phenotype for her obstetric care team. Molecular analysis by QMPSF confirmed the serological findings. This case eventually became the motivation behind an institutional "rare donor" registry programme.

RESULTS

Serology revealed a panreactive antibody affecting cross-matches. Her Rh phenotype was D+, C-, c-, E-, e-, K-, k+. Molecular analysis on her and three family members suggested homozygous CE-D hybrid alleles causing the D-- phenotype: RHCE-D(3-9)-CE.

CONCLUSION

D-- is an uncommon phenotype and was found to occur in a cluster in this family. Like most difficult immunohematological cases, it mandated a multicentric and a multi-technique approach to resolve.

Assessing reagents and techniques for identifying RhCE variants in routine serological testing

BACKGROUND AND OBJECTIVES

Identifying RhCE variants is essential to prevent alloimmunization and manage complex cases. Unfortunately, these variants are often only detected after antibody formation, as they may go unnoticed in serological tests. This study aimed to assess monoclonal antisera using various methodologies to define the reactivity patterns of some variants by variable expression of RhCE antigens.

MATERIALS AND METHODS

Samples were chosen based on atypical reactivity on routine RhCE typing of donors, screening of Afro-descendant donors using tube testing and patient samples with antibodies against their own antigens. All 53 samples were tested using tube, gel and microplate tests with five antisera. Antigen expression was assessed by flow cytometry, and RhCE variants were molecularly classified.

RESULTS

Tube test screening of African descent donors proved more effective in identifying a broad range of weak or partial antigens, particularly when using anti-e composed of MS-21, MS-16, MS63 clones and anti-c from the MS8011531019 clone. Automated instrument phenotyping successfully identified samples with RHCE*ceJAL allele, while most other variants were detected as positive (4+), similar to gel test, which intensified most reactions. When comparing methods and antisera for detecting variant e antigens, tube test identified a higher percentage of weak samples (63%-77%) compared with microplate (35%) and gel tests (14%).

CONCLUSION

The results highlight the critical role of tube test in serological routines and the need to select clones capable of identifying RhCE variants. Detecting reduced RhCE antigen expression during routine serological testing can guide further molecular investigations and help prevent Rh alloimmunization.

Blood group genotype matching for transfusion

The last decade has seen significant growth in the application of DNA-based methods for extended antigen typing, and the use of gene sequencing to consider variation in blood group genes to guide clinical care. The challenge for the field now lies in educating professionals, expanding accessibility and standardizing the use of genotyping for routine patient care. Here we discuss applications of genotyping when transfusion is not straightforward including when compatibility cannot be demonstrated by routine methods, when Rh type is unclear, when allo- and auto-antibodies are encountered in stem cell and organ transplantation, for prenatal testing to determine maternal and foetal risk for complications, and Group A subtyping for kidney and platelet donors. We summarize current commercial testing resources and new approaches to testing including high-density arrays and targeted next-generation sequencing (NGS).

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.

RHCE diversity among Brazilian patients with sickle cell disease (SCD) and selected groups of blood donors

BACKGROUND

Several centers have selected Black donors to prevent Rh alloimmunization of patients with sickle cell disease (SCD). As the Brazilian population is considered very admixed and race definition by self-declaration is questionable, this study aimed to compare RHCE diversity among patients with SCD and selected groups of Brazilian blood donors to define which group of donors would be the adequate red cell supply for patients with SCD.

METHOD

We compared RHCE allele frequencies between patients with SCD and four groups of Brazilian blood donors: self-declared Black donors (SDB), donors with predominant African genetic markers (AAM), donors with weak D expression (WDD), and random donors (RDs). Variant RHCE alleles were identified using molecular protocols.

RESULTS

Among patients with SCD, 47% had at least one variant RHCE, in SDB and WDD this frequency was higher, 53% and 58.6%, respectively. In AAM and in RD the frequencies were 32% and 27.6%, respectively. In patients with SCD and SDB, the most common alleles were RHCE*ce.01, RHCE*ceVS.01, and RHCE*ceVS.02. WDD had a high frequency of RHCE*ceAR and highest frequency of variant RHCE in both alleles, followed by patients with SCD and SDB.

CONCLUSION

This study showed that even in an admixed population the selection of SDB donors is the best choice of matching for transfusion support in patients with SCD. For specific RHCE alleles, selection of donors with weak D expression could be a good option.

D--phenotype due to RHD-RHCE hybrid transcript in a case of severe haemolytic disease of newborn with anti-Rh 17(Hrₒ) antibodies

BACKGROUND

D antigen is one among the most immunogenic antigens and is the most common cause of Haemolytic Disease of Fetus and Newborn (HDFN). The D-phenotype is a rare Rh variant in which none of the RhCE antigens are expressed on the red cell surface. Individuals having D-phenotype are capable of producing a rare alloantibody named as anti-Rh17(Hrₒ) in response to pregnancy or transfusion and has the potential to react with C/c and E/e antigens causing severe haemolytic transfusion reaction (HTR) and haemolytic disease of fetus and newborn (HDFN).

CASE REPORT

We have encountered a case of severe HDFN with an accidental discovery of D- phenotype of the mother with anti-Rh-17 antibodies. D- phenotype has been confirmed with molecular typing along with genotyping of all family members.

CONCLUSION

Rare phenotypes like D- individuals especially if allo-immunised are of great concern at times of transfusion requirements. Hence, proper identification of these individuals are important to contribute them to the rare donor pool and to adopt adequate patient blood management strategies.

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.

Characterization of RHD alleles present in serologically RHD-negative donors determined by a sensitive microplate technique

BACKGROUND AND OBJECTIVES

Weak D phenotypes with very low antigen densities and DEL phenotype may not be detected in RhD typing routine and could be typed as D-negative, leading to D alloimmunization of D-negative recipients. The present study aimed to investigate the presence of RHD-positive genotypes in blood donors typed as D-negative by an automated system using the solid-phase methodology as a confirmatory test.

METHODS

Two screenings were performed in different selected donor populations. For the first screening, we selected 1403 blood donor samples typed as D-negative regardless of the CE status, and in the second screening, we selected 517 donor samples typed as D-negative C+ and/or E+. RhD typing was performed by microplate in an automated equipment (Neo-Immucor®), and the confirmatory test was performed by solid-phase technique using Capture R® technology. A multiplex PCR specific to RHD and RHDψ was performed in a pool of 6 DNA samples. Sequencing of RHD exons was performed in all RHD-positive samples, and a specific PCR was used to identify the D-CE(4-7)-D hybrid gene.

RESULTS AND CONCLUSION

No weak D type was found in either screening populations. Additionally, 353 (18·4%) D-negative samples presented previously reported non-functional RHD genes, 2 samples had a DEL allele, and 6 samples demonstrated new alleles, including one novel DEL allele. Our study identified six new RHD alleles and showed that the inclusion of a confirmatory test using serological methodology with high sensitivity can reduce the frequency of weak D samples typed as D-negative.

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.

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.

RHD-Positive Alleles among D- C/E+ Individuals from India

Background

Molecular bases of blood group systems, including Rh blood group, have been poorly studied in the Indian population so far, while specificities of Europeans, East Asians and Africans have been well known for years. In order to gain insights into the molecular bases of this population, we sought to characterize the RHD allele in D- Indian donors expressing C and/or E antigen(s).

Methods

RHD gene was analyzed in 171 serologically D-, C/E+ samples by standard molecular methods such as quantitative, multiplex PCR of short fluorescent fragments (QMPSF) and direct sequencing when necessary.

Results

RHD whole gene deletion at the homozygous state was found to be the most common genotype associated with D- phenotype (118/171, 69.0%). Nonfunctional, negative hybrid genes with reported molecular backgrounds were observed in approximately one-third of the samples, while only four samples carry single-nucleotide variations, including one novel nonsense (RHD(Y243X)), one novel frameshift (RHD(c.701delG)), and two missense (RHD(T148R) and RHD(T148R, T195M)) alleles.

Conclusion

Overall we report for the first time the molecular bases of D antigen negativity in the D-, C/E+ Indian population, which appears to be qualitatively similar to other populations, but with a population-specific, quantitative distribution of D-- alleles.

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.

Distribution of Rhesus blood group antigens and weak D alleles in the population of Albania

BACKGROUND

Determination of Rhesus (Rh) status is of critical importance in the field of both transfusion and obstetric medicine. As the distribution of Rh phenotypes was unknown in the Albanian population, we investigated the donor population in Albania to estimate the prevalence of each phenotype, as well as to identify and characterise the variants at the molecular level.

MATERIALS AND METHODS

A total of 38,836 blood donors were phenotyped for Rh D, C, c, E and e antigens by routine serological methods, and samples with reduced D antigen expression underwent molecular characterisation by a Tm-shift genotyping method and direct sequencing.

RESULTS

Among all donors 89.00% and 10.86% were D-positive and D-negative, respectively, while 0.14% (n=55) of the donors were found to be weak D-positive. Overall 45/55 samples (81.8%) were resolved by Tm-shift screening, showing that approximately 67% of the variant D alleles were weak D type 1, while weak D type 3 (9.1%) and weak D type 2 (3.6%) were less common. A novel c.932A>G (p.Y311C) variant was also found in the heterozygous state by direct sequencing.

DISCUSSION

This extensive study reveals the distribution of Rh phenotypes in the Albanian population, the low prevalence of individuals with a weak D phenotype, and the specific pattern of distribution of the three most common variant alleles in this Caucasian population.