Genomic typing of human red cell miltenberger glycophorins in a Taiwanese population

Prevalence of GP. Mur variant phenotype among Malaysian blood donors

BACKGROUND AND OBJECTIVE

A number of glycophorin variant phenotypes or hybrid glycophorin variants of the MNS blood group system bear multiple immunogenic antigens such as Mia, Mur, and MUT. In the East and Southeast Asian populations, glycoprotein (GP.) Mur is the most common glycophorin variant phenotype expressing those three immunogens. The aim of this study was to detect MNS system glycophorin variant phenotypes (GP. Mur, GP. Hop, GP. Bun, GP. HF, and GP. Hut) among Malaysian blood donors.

MATERIALS AND METHODS

In this cross-sectional study, 144 blood donors were selected under stratified random sampling. The deoxyribonucleic acid was extracted from whole blood samples, followed by a polymerase chain reaction assay. Sanger sequencing was used to identify the specific MNS variants and then validated by a serological crossmatch with known anti-Mur and anti-MUT.

RESULTS

GP. Mur was identified among Malaysian blood donors with a prevalence of 6.94%, and no other variants of the MNS system were found.

CONCLUSION

The present study substantiates that GP. Mur is the main variant of the MNS system glycophorin (B-A-B) hybrid in Malaysian blood donors. GP. Mur-negative red blood cells must therefore be considered in the current transfusion policy in order to prevent alloimmunization and immune-mediated transfusion reactions, particularly in transfusion-dependent patients.

Molecular genetic analysis of Mia -positive hybrid glycophorins revealed two novel alleles of GP.Vw and multiple variant transcripts of GYPB existing in both the homozygous GP.Mur and wild-type GPB individuals

BACKGROUND

The hybrid glycophorins of MNS blood group system express a series of low incidence antigens including Mi^a , which are commonly found in Southeast Asian populations. In this study, the molecular basis of Mi^a -positive hybrid glycophorins was firstly clarified in the Chinese Southern Han population. RNA transcripts of GYPB gene in the homozygous GP.Mur individuals were also analyzed.

STUDY DESIGN AND METHODS

DNAs were extracted from the whole blood samples of 111 Mi^a -positive donors. Then, high-resolution melting (HRM) analysis for GYP(B-A-B) was used to analyze the genotypes. Sequencing of GYPB pseudoexon 3 was conducted in the samples with variant melting curves. TA-cloning and subsequent sequencing of GYPA exons 2-4 were performed in the Mi^a -positive samples with normal GYPB/GYPB genotype by HRM. The transcript analysis of GYPB was conducted in homozygous GP.Mur and wild-type glycophorin B (GPB) individuals using RNA extracted from the cultured erythroblast.

RESULTS

The heterozygous GYP*Mur/GYPB (n = 101), homozygous GYP*Mur/GYP*Mur (n = 7) including one novel GYP*Mur allele with an extra GYPA/GYPE specific nucleotide substitution (c.229+110A>T), heterozygous GYP*Bun/GYPB (n = 1) and GYP*Vw/GYPA (n = 2) with two novel GYP*Vw alleles were identified. RNA transcript analysis revealed multiple transcripts of GYPB existing in both homozygous GP.Mur and normal GPB individuals.

CONCLUSION

The results showed the genetic diversity of hybrid glycophorins in the Chinese population. Besides, the successful analysis of GYPB transcripts indicates that the cultured erythroblast is a good source for RNA transcript analysis for the protein only expressed on the red blood cells.

Universal Detection of Mia Antigen and Frequencies of Glycophorin Hybrids among Blood Donors in Taiwan by Human Monoclonal Antibodies against Mia (MNS7), Mur (MNS10), and MUT (MNS35) Antigens

Glycophorin hybrids such as GP.Mur are common in Southeast Asians. In Taiwan, clinically significant alloantibodies to the GP.Mur phenotype are the most important issue in blood banks. A large-scale screening of glycophorin hybrids in the Taiwanese population is urgently needed to ensure transfusion safety. Four clones of human hybridomas that secrete anti-Mi^a, anti-MUT, and anti-Mur were established by fusing human B-lymphocytes and myeloma cells (JMS-3). The specificity of each monoclonal antibody (MoAb) was characterized. Three MoAbs were applied on an Automated Pretransfusion Blood Testing Analyzer (PK7300/PK7400) for donor screening. Genotyping was performed to determine the detailed subgrouping of glycophorin hybrids. Four MoAbs are IgM antibodies. Anti-Mi^a (377T) binds to ⁴⁶DXHKRDTYA⁵⁴, ⁴⁸HKRDTYAAHT⁵⁷ peptides, and anti-Mi^a (367T) binds to ⁴³QTNDXHKRD⁵¹ peptides (X indicates T, M, or K). Anti-Mur is reactive with ⁴⁹KRDTYPAHTA⁵⁸ peptides. Anti-MUT is reactive with ⁴⁷KHKRDTYA⁵⁴. A total of 78,327 donors were screened using three MoAbs, and 3690 (4.71%) were GP.Mur, 20 (0.025%) were GP.Hut, and 18 (0.022%) were GP.Vw. When the Mi^a antigen was introduced as routine screening, the frequency of Mi(a+) among blood donors in Taiwan was 4.66% (67,348/1,444,541). Mi^a antigen was implemented as a routine blood testing, and the results were labeled on all red blood cell (RBC) units.

Successful prenatal management of two foetuses affected by antibodies against GP.Mur with prenatal genotyping analysis and a literature review

BACKGROUND

GP.Mur belongs to the GP(B-A-B) hybrid glycophorin family, which is the most common hybrid glycophorin in Southeast Asia. Antibodies against GP.Mur may cause a clinically significant haemolytic disease of the foetus and newborn (HDFN) although, so far, not many cases have been reported in mainland China.

MATERIALS AND METHODS

Two Chinese women with a history of severe hydrops foetalis were seen in our centre. Alloantibody identification and GYP.Mur genotyping analysis were used for prenatal evaluation. Intrauterine transfusion was performed in two pregnancies in case 1. The features of these two women are described and literature-reported cases of HDFN related to antibodies against GP.Mur are summarised.

RESULTS

The phenotype of both mothers was Mi^a- Mur-, while the fathers' was Mi^a+ Mur+ with a heterozygous GYP.Mur hybrid gene as determined by a high-resolution melting method of genotyping. In case 1, the antibodies against GP.Mur were detected in the mother's serum and the cord blood of two foetuses. Fortunately, the latest foetus was successfully saved after intrauterine transfusion. In case 2, hydrops foetalis occurred in the first two pregnancies, but the risk of HDFN was excluded for the third foetus because of the GP.Mur negative phenotype. The literature review showed that 68.8% (11/16) of the reported cases of HDFN related to antibodies against GP.Mur occurred in the Chinese population, and that 37.5% (6/16) of them were cases of severe HDFN.

DISCUSSION

More cases of severe HDFN caused by antibodies against GP.Mur are presumably undetected as GP.Mur cells are not included in the panel of obligatory screening tests in most Southeast Asian countries including mainland China. The high-resolution melting method for GYP.Mur genotyping and zygosity detection is helpful in prenatal management.

Hybrid glycophorin and red blood cell antigen genotyping in Asian American type O blood donors with Mia phenotype

BACKGROUND

The GP.Mur glycophorin with Mi^a phenotype is relatively common and clinically significant in the Southeast Asian populations. The aim of this study is to genotype Mi^a -positive Asian American type O blood donors. Red blood cell (RBC) minor antigens were also determined in the same cohort.

STUDY DESIGN AND METHODS

Asian American blood donors of the Gulf Coast Regional Blood Center (Houston, TX) were screened using a typing reagent (NOVACLONE Anti-Mi^a Monoclonal IgG Typing Reagent, Dominion Biologicals Ltd) from March 2016 to July 2018. Aliquots of Mi^a -positive blood from type O donors were subjected to serologic confirmation using Mi^a - and/or Mur-specific GAMA210 and 64D6 monoclonal antibodies, and two human antisera. Extracted genomic DNA was amplified by polymerase chain reaction (PCR) using GYP hybrid gene/allele-specific primers followed by bidirectional Sanger sequencing. Zygosity for GYP*Mur and GYP*Bun was determined using TaqMan real-time PCR assay. Phenotypes of 35 RBC antigens and three phenotypic variants were determined with use of an in vitro diagnostic test, PreciseType HEA Molecular BeadChip Test (Immucor).

RESULTS

By screening 4600 blood donations in the Houston metropolitan area, 209 samples from 103 unique donors were identified to be Mi^a -positive. By PCR and sequencing analysis, 97 of the 103 Mi^a -positive donors carried hybrid genes GYP*Mur (89.7% including two homozygotes), GYP*Bun (6.2%), GYP*Vw (3.1%) and GYP*Hut (1.0%). Concordance between serology and DNA analysis was 98%, 99%, and 100% for the GAMA210, 64D6, and human antisera, respectively. Genotyping of RBC antigens showed that the Mi^a -positive donors were predominantly associated M+ N- S- s+ (48.5%) and M+ N+ S- s+ (38.1%) phenotypes.

CONCLUSIONS

The GP.Mur glycophorin is most prevalent in the Mi^a -positive Asian American type O blood donors.

Molecular Detection of Glycophorins A and B Variant Phenotypes and their Clinical Relevance

Crossover or conversion between the homologous regions of glycophorin A (GYPA) and glycophorin B (GYPB) gives rise to several different hybrid glycophorin genes encoding a number of different glycophorin variant phenotypes which bear low prevalence antigens in the MNS blood group system. GP.Mur is the main glycophorin variant phenotype which causes hemolytic transfusion reaction (HTR) and hemolytic disease of the fetus and newborn (HDFN) in East and Southeast Asians. The detection of glycophorin variant phenotypes using serological methods is limited to phenotyping reagents that are not commercially available. Moreover, the red blood cells used for antibody identification are usually of the GP.Mur phenotype. The current Polymerase Chain Reaction (PCR)-based methods and loop-mediated isothermal amplification (LAMP) are available alternatives to phenotyping that allow for the specific detection of glycophorin variant phenotypes. This review highlights the molecular detection method for glycophorins A and B variant phenotypes and their clinical relevance.

Molecular Pathology in Transfusion Medicine: New Concepts and Applications

Virtually all the red blood cell and platelet antigen systems have been characterized at the molecular level. Highly reliable methods for red blood cell and platelet antigen genotyping are now available. Genotyping is a useful adjunct to traditional serology and can help resolve complex serologic problems. Although red blood cell and platelet phenotypes can be inferred from genotype, knowledge of the molecular basis is essential for accurate assignment. Genotyping of blood donors is an effective method of identifying antigen-negative and/or particularly rare donors. Cell-free DNA analysis provides a promising noninvasive method of assessing fetal genotypes of blood group alloantigens.

Selection of GP. Mur antigen-negative RBC for blood recipients with anti-'Mia ' records decreases transfusion reaction rates in Taiwan

OBJECTIVES

To evaluate the clinical significance of GP. Mur antigen-negative blood selection for transfusion in patients with anti-'Mi^a ' records.

BACKGROUND

The GP. Mur RBC phenotype is prevalent (7·3%) in Taiwan. Antibodies against GP. Mur (anti-'Mi^a ') are identified in 1·24% of our population, and anti-'Mi^a ' screening using GP. Mur RBC has been routine for Taiwan's blood banks. However, due to the lack of commercial antibodies, only cross-matching was used to prevent transfusion of GP. Mur-positive blood to patients with anti-'Mi^a ' in most hospitals. There is still a risk of GP. Mur-positive RBC exposure and subsequent anti-'Mi^a '-related transfusion reactions.

METHODS

Since February 2014, GP. Mur antigen-negative RBCs identified by reaction with anti-'Mi^a '-positive serum were selected for blood recipients with anti-'Mi^a ' records. The transfusion reactions between January 2013 and January 2014 were compared with those that occurred between February 2014 and July 2015.

RESULTS

The transfusion reaction rate was significantly higher in anti-'Mi^a '-positive blood recipients compared to total subjects receiving an RBC transfusion before GP. Mur-negative donor RBC selection. After antigen-negative RBC selection, the transfusion reaction frequency in subjects with anti-'Mi^a ' became similar to total blood recipients. IgG form anti-'Mi^a ' antibodies were present in all cases of probable anti-'Mi^a '-related transfusion reactions. The time required for anti-'Mi^a ' boosting after transfusion was around 4-21 days.

CONCLUSION

Selection of GP. Mur-negative RBC for transfusion to patients with anti-'Mi^a ' records could decrease the rate of transfusion reaction and antibody boosting. This procedure should be incorporated into blood bank routines in areas where anti-'Mi^a ' is prevalent.

MNSs blood group glycophorin variants in Taiwan: a genotype-serotype correlation study of 'Mi(a)' and St(a) with report of two new alleles for St(a)

Background

Glycophorin variants of the MNSs blood group are important in Taiwan. For more than 20 years, screening for the most frequent irregular antibody, anti-‘Mi^a’, has been conducted by using ‘Mi^a’(+) RBCs, with a significant success. However, the sensitivity and the specificity of this screening strategy have never been validated, and the true incidences of different glycophorin variants in Taiwan have been in controversy. Also, the significance of another less frequent and usually separately reported variant, St^a, has never been evaluated.

Methodology/Principal Findings

We ran a population-based screening (from unselected patients in our hospital) for MNSs blood group glycophorin variants by PCR-sequencing method. GP.Mur (Mil.III) was confirmed by sequence from 57 out of 1027 samples (5.6%), and there was no other Miltenberger subtype glycophorin variant found. Glycophorin variant St^a was found from 35 out of 1027 samples (3.4%). In contrast to anti-‘Mi^a’, which is the most frequently identified irregular antibody in Taiwan, the prevalence of anti-St^a was only 0.13% as determined by serologic method. In addition, two new alleles for St^a were found and reported.

Conclusion/Significance

We confirm the long-standing assumption that GP.Mur is the only prevalent Miltenberger subtype in Taiwan. The current anti-‘Mi^a’ screening method used in Taiwan, although neither sensitive nor specific, is still a suitable practice. Although St^a antigen has a high prevalence in Taiwan, routine screening for anti-St^a is not warranted based on current evidence.

Molecular pathology in transfusion medicine

This article provides an overview of the application of molecular diagnostic methods to red cell and platelet compatibility testing. The advantages and limitations of molecular methods are evaluated compared with traditional serologic methods. The molecular bases of clinically significant red cell and platelet antigens are presented. Current recommendations for reporting molecular assay results and distinctions between genotype and phenotype are discussed.

A direct blood polymerase chain reaction approach for the determination of GP.Mur (Mi.III) and other Hil+ Miltenberger glycophorin variants

BACKGROUND

GP.Mur (Mi.III) is a glycophorin B-A-B hybrid sialoglycoprotein expressing several potent immunogens, including Mi(a), Mur, and Hil. GP.Mur is considered one of the most important red blood cell (RBC) phenotypes in blood banking in Southeast Asia. However, there are no antibodies commercially available for the screening of GP.Mur RBCs.

STUDY DESIGN AND METHODS

To develop a direct blood polymerase chain reaction (PCR) approach for the screening of GP.Mur cells, we first confirmed the genomic sequence differences among four GP.Mur and three Mi(a-) samples by sequencing their GYP.Mur and GYPB genes. With these data, we designed PCR primers that best discriminate GYPB and GYP.Mur. Our primer design also allows the detection of other Hil+ glycophorin variants. We also constructed two plasmids--pGBi2i3 and pMiIIIi2i3--which serve as the negative and positive control DNA, respectively, for the PCR procedure. Additionally, we designed a control PCR to be run side by side with the typing PCR.

RESULTS

Because of the high specificity of our primers, we found it unnecessary to extract DNA from blood samples for PCR. We have tested this PCR method on 379 fresh and frozen blood samples. The results were further validated by serology and DNA sequencing and were shown to be completely accurate in our hand. We also found that the rapid genotyping method--high-resolution melting--can be a timesaving alternative for DNA sequencing.

CONCLUSION

This direct blood PCR approach for determination of GP.Mur and related Hil+ phenotypes is reliable and economical and is expected to be useful for blood banking in Southeast Asia.

Sixty years of antibodies to MNS system hybrid glycophorins: what have we learned?

The MNS system was the second blood group system discovered and at least 16 of the 46 antigens in the MNS system result from genetic recombination, producing a hybrid glycophorin. The incidence of these hybrid glycophorins is highest in East Asian populations. MNS system antigens defined by hybrid glycophorins are immunogenic with alloimmune IgG responses developing after transfusion or pregnancy; with reports originating from Asia, Europe, the Americas, and Australia. This demonstrates the global nature of problems associated with these antibodies. Since the initial report that production of anti-Mi(a) was a cause of hemolytic disease of the fetus and newborn (HDFN), antibodies to antigens defined by hybrid glycophorins have been reported in 27 cases of HDFN (1 fatal) and 8 cases of hemolytic transfusion reaction (HTR) (1 fatal). In at least 40% of these clinical cases, the disease was reported as severe. Hyporegenerative fetal anemia is a common feature of the reported HDFN cases. In all published cases, the causative antibodies were identified by reference laboratory investigative tests following clinical presentation. The failure to detect these antibodies by routine testing highlights the need for consideration of the medical importance of these antibodies when defining antibody screening practices and reagents. The aim of this review is to raise awareness of severe disease caused by antibodies to MNS antigens defined by hybrid glycophorins and, thus, to improve diagnosis and patient management.

Anti-"Mi(a)" immunization is associated with HLA-DRB1*0901

BACKGROUND

Anti-"Mi(a)" is one of the most important irregular red blood cell antibodies found in Taiwan. The aim of this study was to investigate whether specific HLA-DRB1 alleles are associated with anti-"Mi(a)" production.

STUDY DESIGN AND METHODS

A case-control retrospective study was performed on 68 patients showing presence of anti-"Mi(a)" and 219 unrelated control subjects from the Mackay Memorial Hospital. HLA-DRB1 genotyping was carried out using sequence-based typing method. Fisher's exact test using 2 x 2 contingency tables was used to analyze significance of the association between DRB1 polymorphisms and presence of anti-"Mi(a)" in patients.

RESULTS

HLA-DRB1*0901 allele frequency in the anti-"Mi(a)" group (30%) was significantly higher than in the control group (16%) with an odds ratio of 2.27 (95% confidence interval, 1.44-3.55; p = 0.0005; p(c) = 0.016).

CONCLUSION

HLA-DRB1*0901 is significantly more prevalent in the anti-"Mi(a)" patients group than in the control group. It is suggested that cells from DR9 individuals might present processed "Mi(a)" antigen-allospecific peptides more effectively than cells from individuals carrying other DR phenotypes. Finally, it was predicted that two epitopes, derived from the MiIII glycophorin amino acid sequence, were likely to bind preferentially with the DR9 molecule. Further work will be necessary to determine if these epitopes are responsible for anti-"Mi(a)" alloimmunization.

Haemolytic disease of the newborn due to maternal irregular antibodies in the Chinese population in Taiwan

From 1991 to 2000, amongst 23,886 full-term healthy Chinese babies delivered at our hospital, 2615 babies developed neonatal hyperbilirubinaemia. After excluding other causes of hyperbilirubinaemia and identifying the irregular antibodies, 15 cases of haemolytic disease of the newborn (HDN) due to maternal irregular antibodies were diagnosed; three cases were born in our hospital and 12 cases were referred. Amongst these 15 babies, six cases had HDN due to anti-E, three cases due to anti-E + c, three cases due to anti-D, one case due to anti-c and two cases due to 'Mi' antibodies reacting with MiIII phenotype cells (anti-Hil and anti-Mur). Although there were four cases of hydrops fetalis, only one of the patients expired. The prevalence of HDN caused by maternal irregular antibodies has been estimated to be 0.01%. Therefore, routine prenatal screening for irregular antibodies was not rational in the Chinese population in Taiwan. Anti-E and anti-E + c were the important irregular antibodies resulting in HDN. Although few cases of HDN due to anti-'Mi' have been reported, Anti-'Mi' is significant in regions with a high prevalence of the MiIII phenotype.

Hydrops foetalis caused by anti-Mur in first pregnancy--a case report

Anti-'Mia' is the most common alloantibody of potential clinical significance in the Taiwanese population. The Mi.III phenotype is rare among Caucasians but has a high incidence in various Oriental populations. We describe a nulliparous woman with no history of transfusions, who had hydrops foetalis at 28 weeks gestation. Foetal haemoglobin was 4.4 g dL-1, and a positive direct antiglobulin test was positive in the foetal blood. Intrauterine intravascular transfusion was given, and the baby was discharged healthy. Anti-'Mia' was identified in the maternal serum, the cord blood serum and the eluate from red cells of the cord blood. Anti-'Mia' in the maternal serum was confirmed to be anti-Mur. The polymerase chain reaction-restriction fragment length polymorphism method confirmed that both the baby and her father had the Mi.III gene. Therefore, our report documents that anti-Mur has the potential to cause hydrops foetalis.

A novel St(a) glycophorin produced via gene conversion of pseudoexon III from glycophorin E to glycophorin A gene

Stone (St(a)) is a variant antigen carried on human erythrocyte MNSs glycophorins (GPSt(a)) that are genetically associated with splicing mutations in GPA genes or with hybrid formation between GPA and GPB genes. Here we identify the first and rare gene conversion event in which GPE, the third member of the family, recombined with GPA, giving rise to a GPA-E-A hybrid gene encoding the St(a) antigen. Western blot detected expression in the proband of both GPA and GPSt(a) on the plasma membrane. Southern blot showed a new restriction fragment from the GPSt(a) gene, indicating an altered exon III-intron 3 junction. Sequencing of RT-PCR products identified one full-length and two shortened glycophorin cDNAs. The shortened forms were derived from GPSt(a) lacking one (exon III) and two exons (exon III and IV), respectively. To define the molecular basis for exon skipping, the genomic region spanning exon III of the GPSt(a) gene was amplified and sequenced. This revealed transfer from GPE to GPA of a DNA segment containing the pseudoexon III and its silent donor splice site. Thus, the inactivation of GPA exon III by conversion of a silent GPE donor splice site portrays a new molecular mechanism for St(a) antigen expression in human erythrocytes.