The serological and genetic basis of the cis-AB blood group in Korea

Molecular analysis and transfusion management in a rare case of cis-AB blood group: A report from India

Molecular characterization of a rare cis-AB blood group has not been done in the Indian subcontinent. Herein, we report a case of A2B3 blood group in an Indian patient which was subsequently confirmed to be a case of cis-AB phenotype. Blood grouping was performed by the column agglutination technique (CAT), conventional tube technique (CTT) and subsequently, whole exome sequencing for molecular analysis. The patient was initially typed as AB, RhD positive in forward grouping. However, serum grouping showed agglutination (2+) with the B red cells in CAT. In CTT, an extra reaction was observed with A1 red cells and a strong agglutination was seen with Anti-H lectin. Thus, the blood group was identified serologically as A2B3. During the next-generation sequencing, a total of 10 exonic variants in the ABO gene were filtered, of which 2 (rs8176747 and rs7853989) were found to be non-synonymous and occurring on the same allele. The other allele was found to be ABO*A1.01. The sample analyzed in the study was found to carry two previously reported nucleotide changes of cis-AB (c.803G > C and c.526C > G) on the same allele which had not been reported before. Transfusion requirement was managed with type O red cells and type AB plasma.

Investigation of Discrepant ABO Blood Grouping Results from an Autoanalyzer

Background

A paucity of studies evaluating failed cases of ABO grouping using autoanalyzers exists. We investigated autoanalyzer rejected cases, including serologically suspicious ABO subgroups and discrepant ABO blood grouping results from Erytra Eflexis (Grifols, Spain), to demonstrate efficient use of autoanalyzers for ABO grouping.

Methods

Samples requested for ABO grouping throughout 2020 were tested using two Eflexis instruments and standard ABO RhD and reverse grouping cards. Neonatal cards were not used. When necessary, a conventional tube technique (TUBE) was used to resolve rejected/discrepant Eflexis ABO grouping results.

Results

The overall sample rejection rate (RR) was 3.2% (628/19,466), 1.3% of which were due to various error flags and 1.9% for discrepant results. Cases from neonates ≤1 year old accounted for 35.3% of the rejected cases based on Eflexis results. The ABO groups with the highest and lowest RR (excluding neonates) were A and O, respectively. The 628 samples resulted in 682 rejections, which were frequently associated with reverse grouping, including 28.4% against A₁ and 54.5% for B red cells. Among 14 serologically weakened A and/or B blood groups, six A₂BW and two ABw, which had been missed by Eflexis, were detected using TUBE and our follow-up laboratory criteria.

Conclusions

The ABO group and a proportion of neonatal samples influenced the RR due to weak reverse grouping reactivity, especially toward B red cells. Confirmatory ABO grouping by TUBE in a new patient and/or extra rejection criteria for forward grouping are needed to detect cis-AB, which is relatively common in Korea.

Application of Blood Group Genotyping by Next-Generation Sequencing in Various Immunohaematology Cases

BACKGROUND

Next-generation sequencing (NGS) technology has been recently introduced into blood group genotyping; however, there are few studies using NGS-based blood group genotyping in real-world clinical settings. In this study, we applied NGS-based blood group genotyping into various immunohaematology cases encountered in routine clinical practice.

METHODS

This study included 4 immunohaematology cases: ABO subgroup, ABO chimerism, antibody to a high-frequency antigen (HFA), and anti-CD47 interference. We designed a hybridization capture-based NGS panel targeting 39 blood group-related genes and applied it to the 4 cases.

RESULTS

NGS analysis revealed a novel intronic variant (NM_020469.3:c.29-10T>G) in a patient with an Ael phenotype and detected a small fraction of ABO*A1.02 (approximately 3-6%) coexisting with the major genotype ABO*B.01/O.01.02 in dizygotic twins. In addition, NGS analysis found a homozygous stop-gain variant (NM_004827.3:c.376C>T, p.Gln126*; ABCG2*01N.01) in a patient with an antibody to an HFA; consequently, this patient's phenotype was predicted as Jr(a-). Lastly, blood group phenotypes predicted by NGS were concordant with those determined by serology in 2 patients treated with anti-CD47 drugs.

CONCLUSION

NGS-based blood group genotyping can be used for identifying ABO subgroup alleles, low levels of blood group chimerism, and antibodies to HFAs. Furthermore, it can be applied to extended blood group antigen matching for patients treated with anti-CD47 drugs.

Molecular basis of weak A subgroups in the Korean population: Identification of three novel subgroup-causing variants in the ABO regulatory regions

BACKGROUND

Recent studies on Chinese and Japanese populations have shown that weak ABO subgroups could be caused by variants in the major regulatory regions of ABO, the proximal promoter, +5.8-kb site, and CCAAT-binding factor/NF-Y binding site. We investigated the molecular basis of weak A subgroups in the Korean population.

STUDY DESIGN AND METHODS

This study included 11 samples suspected to have a weak A subgroup. These samples were subjected to sequencing analysis of ABO exons 6 and 7. If no subgroup-causing variants were detected in this region, exons 1-5 and three major regulatory regions were sequenced.

RESULTS

Sequencing analysis of exons 6 and 7 detected two known subgroup alleles (ABO*AW.10, n = 5; ABO*AEL.02, n = 2). The remaining four samples contained a sequence variant in the proximal promoter (g.4944C>T, n = 1; g.4954G>T, n = 1) or +5.8-kb site (g.10843T>C, n = 1; g.10935C>T, n = 1). Notably, three of the four variants (g.4944C>T, g.4954G>T, and g.10843T>C) have not been reported previously in weak ABO subgroups.

CONCLUSION

This study provides the first evidence that alterations in the proximal promoter and + 5.8-kb site could account for a substantial proportion of weak A subgroups in the Korean population.

Accurate cisAB typing is essential to ensure the safety of a transfusion: A case of a cisAB01 neurosurgery pediatric patient and family study

The rare cisAB subgroups inherited from a single parent are characterized by the activities of dual A and B glycosyltransferases encoded by a gene on one chromosome. The serological complexity of cisAB challenges clinical blood transfusion practice because of misclassification in ABO grouping.

Sequence variants in the proximal promoter and +5.8-kb site of ABO in Koreans with weak B phenotypes

BACKGROUND AND OBJECTIVES

Several studies on Chinese and Japanese populations have revealed that a substantial proportion of weak B subgroups are caused by variants in the major regulatory regions of ABO, the proximal promoter, CCAAT-binding factor/NF-Y binding site and +5.8-kb site. We performed molecular analyses of these regions in Koreans with weak B phenotypes.

MATERIALS AND METHODS

This study included 16 samples with weak B phenotypes (4 B₃ , 1 B_w , 5 A₁ B₃ and 6 A₁ B_w ) harbouring no subgroup-causing variants in ABO exons 6 and 7. These samples were subjected to sequencing analysis of exons 1-5 and the major regulatory regions of ABO.

RESULTS

Of the 16 samples, 14 were found to carry a sequence variant either in the proximal promoter (g.4991_5008del [n = 3]) or the +5.8-kb site (g.10893G>A [n = 4] and g.10925C>T [n = 7]). The remaining two samples were found to contain no subgroup-causing variants.

CONCLUSION

Our study demonstrates that sequence variants in the proximal promoter and +5.8-kb site account for a substantial proportion of weak B subgroups in Koreans, suggesting that molecular analysis of these regions is essential for the accurate determination of ABO genotypes in Koreans with weak B phenotypes.

Analysis of ABO grouping discrepancies among patients from a tertiary hospital in Korea

BACKGROUND

Accurate ABO typing is essential for preventing ABO incompatibility reactions. However, the causes of ABO grouping discrepancy has not been sufficiently studied, and it may vary among different ethnic populations. Thus, the aim of this retrospective study was to investigate the causes of ABO discrepancy in the East Asian population.

MATERIALS AND METHODS

A retrospective observational study on ABO typing discrepancy among patients in a tertiary hospital was carried out using the electronic medical record database of Samsung Medical Center (Seoul, Korea) between July 2016 and May 2019.

RESULTS

ABO grouping was performed on 551,959 blood samples during the study period; 1468 events of serologic ABO discrepancy were determined from 1334 (0.24 %) samples. A total of 134 samples (0.02 %) presented multiple causes of ABO discrepancy. Weak/missing serum reactivity (594, 40.5 %) was the most frequent reason for ABO discrepancy, followed by extra serum reactivity (370, 25.2 %), weak/missing red cell reactivity (267, 18.2 %), mixed-field red cell reactivity (176, 12.0 %), and extra red cell reactivity (61, 4.2 %). In the category of weak/missing red cell reactivity, ABO subgroup was the most common reason, and using ABO genotyping, 26.2 % of the cases genotyped were found to be related to the cis-AB allele.

CONCLUSIONS

Our results suggest that the incidence and cause of ABO typing discrepancies vary among institutes and ethnic groups. Our data helps to better understand and facilitate the resolution of ABO typing discrepancies in patients.

ABO maternal-child discordance: Evidence of variable allelic expression and considerations for investigation

BACKGROUND

We report a case of apparent mother-child ABO group noninheritance. A Caucasian mother initially typed as group O and her infant group AB. Investigation ruled out preanalytical causes such as mislabeled samples and in vitro fertilization.

MATERIALS AND METHODS

Red blood cells were characterized by routine serologic testing. Genomic data were analyzed by targeted polymerase chain reaction-restriction fragment length polymorphism and Sanger sequencing. Transferase structures were modeled using PyMOL molecular visualization software.

RESULTS

Serologic testing initially demonstrated the mother was group O, father group AB, and infant group AB. Further testing of the maternal sample with anti-A,B demonstrated weak A expression. Molecular testing revealed the maternal sample had an ABO*O.01.01 allele in trans to an A allele, ABO*AW.29 (c.311T>A, p.Ile104Asn), determined by gene sequencing. The sample from the infant carried the same ABO*AW.29 allele in trans to a B allele, ABO*B.01.

CONCLUSION

ABO genotyping revealed an A transferase encoded by ABO*AW.29, with apparent variable activity. Although A antigen expression is well known to be weak in newborns, it was robust on the red blood cells (RBCs) of the AB infant and undetectable with anti-A on the mother. Variable expression of weak subgroups may reflect competition or enhancement by a codominant allele, as well as glycan chain maturation on red cells. Previous examples in group AB mothers with A_weak infants suggested that the decreased expression is primarily due to glycan immaturity. To our knowledge, this is the first reported case of the ABO*AW.29 allele presenting with weak A expression in a group A_weak mother and robust A expression in a group AB infant, suggesting the in trans allele is an important factor in determining transferase activity and may override age-related effects.

Developing a Standardization Algorithm for Categorical Laboratory Tests for Clinical Big Data Research: Retrospective Study

Background

Data standardization is essential in electronic health records (EHRs) for both clinical practice and retrospective research. However, it is still not easy to standardize EHR data because of nonidentical duplicates, typographical errors, or inconsistencies. To overcome this drawback, standardization efforts have been undertaken for collecting data in a standardized format as well as for curating the stored data in EHRs. To perform clinical big data research, the stored data in EHR should be standardized, starting from laboratory results, given their importance. However, most of the previous efforts have been based on labor-intensive manual methods.

Objective

We aimed to develop an automatic standardization method for eliminating the noises of categorical laboratory data, grouping, and mapping of cleaned data using standard terminology.

Methods

We developed a method called standardization algorithm for laboratory test–categorical result (SALT-C) that can process categorical laboratory data, such as pos +, 250 4+ (urinalysis results), and reddish (urinalysis color results). SALT-C consists of five steps. First, it applies data cleaning rules to categorical laboratory data. Second, it categorizes the cleaned data into 5 predefined groups (urine color, urine dipstick, blood type, presence-finding, and pathogenesis tests). Third, all data in each group are vectorized. Fourth, similarity is calculated between the vectors of data and those of each value in the predefined value sets. Finally, the value closest to the data is assigned.

Results

The performance of SALT-C was validated using 59,213,696 data points (167,938 unique values) generated over 23 years from a tertiary hospital. Apart from the data whose original meaning could not be interpreted correctly (eg, ** and _^), SALT-C mapped unique raw data to the correct reference value for each group with accuracy of 97.6% (123/126; urine color tests), 97.5% (198/203; (urine dipstick tests), 95% (53/56; blood type tests), 99.68% (162,291/162,805; presence-finding tests), and 99.61% (4643/4661; pathogenesis tests).

Conclusions

The proposed SALT-C successfully standardized the categorical laboratory test results with high reliability. SALT-C can be beneficial for clinical big data research by reducing laborious manual standardization efforts.

Cis-AB, the Blood Group of Many Faces, Is a Conundrum to the Novice Eye

Cis-AB, a rare ABO variant, is caused by a gene mutation that results in a single glycosyltransferase enzyme with dual A and B glycosyltransferase activities. It is the most frequent ABO subgroup in Korea, and it occurs more frequently in the East Asian region than in the rest of the world. The typical phenotype of cis-AB is A₂B₃, but it can express various phenotypes when paired with an A or B allele, which can lead to misclassification in the ABO grouping and consequently to adverse hemolytic transfusion reactions. While cis-AB was first discovered as having an unusual inheritance pattern, it was later found that both A and B antigens are expressed from the same allele inherited from a single parent; hence, the name cis-AB. Earlier studies relied on serological and familial investigation of cis-AB subjects, but its detection has become much easier with the introduction of molecular methods. This review will summarize the serological variety, genetic basis and inheritance pattern, laboratory methods of investigation, clinical significance, and the blood type of choice for transfusion for the cis-AB blood group.

ABO Mistyping of cis-AB Blood Group by the Automated Microplate Technique

Background

The cis-AB phenotype, although rare, is the relatively most frequent of ABO subgroups in Koreans. To prevent ABO mistyping of cis-AB samples, our hospital has applied a combination of the manual tile method with automated devices. Herein, we report cases of ABO mistyping detected by the combination testing system.

Methods

Cases that showed discrepant results by automated devices and the manual tile method were evaluated. These samples were also tested by the standard tube method. The automated devices used in this study were a QWALYS-3 and Galileo NEO. Exons 6 and 7 of the ABO gene were sequenced.

Results

13 cases that had the cis-AB allele showed results suggestive of the cis-AB subgroup by manual methods, but were interpreted as AB by either automated device. This happened in 87.5% of these cases by QWALYS-3 and 70.0% by Galileo NEO. Genotyping results showed that 12 cases were ABO*cis-AB01/ABO*O01 or ABO*cis-AB01/ABO*O02, and one case was ABO*cis-AB01/ ABO*A102.

Conclusion

Cis-AB samples were mistyped as AB by the automated microplate technique in some cases. We suggest that the manual tile method can be a simple supplemental test for the detection of the cis-AB phenotype, especially in countries with relatively high cis-AB prevalence.

Evaluation of kodecytes using function-spacer-lipid constructs as a survey material for external proficiency testing for ABO subgrouping

BACKGROUND

It is not easy to find natural red blood cells (RBCs) with weak A (A_w ) or weak B phenotype (B_w ) for use as quality controls in ABO subgroup testing (subgrouping). The aim of this study was to prepare RBC kodecytes with synthetic blood group A and/or B function-spacer-lipid (FSL) constructs and to evaluate the possibility of using such kodecytes as a survey material for an external proficiency test (PT) to improve the quality of subgroup analysis.

METHODS

Three types of survey samples, including O phenotype RBCs and A kodecytes with A_w (0.02 mg/mL FSL-A solution) and B kodecytes with B_w (0.15 mg/mL FSL-B solution) were sent to 53 laboratories for an educational trial of PT for subgrouping. Cell typing was done using the manual tube technique.

RESULTS

Forty-three laboratories responded, and the re-activities of the survey samples varied from 0 to 4+ against anti-A and anti-B monoclonal reagents(MoAbs). Twenty-nine laboratories (67%) correctly grouped the B_w kodecytes as B_w . Fifteen (35%), 21 (48%), and 6 (13%) laboratories grouped the A_w kodecytes as A_w , A₂ , and O phenotypes, respectively. The anti-A MoAb clone affects the results of cell typing for A_w kodecytes. The stability of kodecytes was similar to that of natural O RBCs during storage.

CONCLUSION

Our kodecytes were useful as a survey material, and the survey results showed the necessity of materials for PT for subgrouping to improve the quality of laboratory analysis regardless of the different reactions according to the MoAb.

Sex-specific differences in the association between ABO genotype and gastric cancer risk in a Korean population

BACKGROUND

Although previous studies have demonstrated an association between ABO blood group and the risk of gastric cancer (GC), only one study has identified these associations using the ABO genotype; however, that study did not evaluate sex differences in this association. The aim of the present study was to investigate whether there are sex-specific differences in the ABO genotype-associated risk of GC. In addition, we explored the association of the ABO genotype and the clinicopathologic characteristics of GC in a Korean population.

METHODS

We conducted a large-scale case-control study of 3245 GC patients (2204 males, 1041 females) and 1700 controls (821 males, 879 females). The ABO genotype was determined by multicolor real-time polymerase chain reaction (PCR) using displacing probes.

RESULTS

As compared with genotype OO, genotypes AA and AO in females, but not in males, were associated with a significantly increased risk of GC (odds ratio [OR] 1.56 and 95 % confidence interval [CI] 1.08-2.26 for AA; OR 1.57 and 95 % CI 1.21-2.03 for AO). In a subgroup analysis, blood group A had a significantly increased risk of diffuse-type GC (OR 2.00, 95 % CI 1.43-2.78), but not of intestinal-type (OR 1.31, 95 % CI 0.96-1.79) or mixed-type GC (OR 1.43, 95 % CI 0.92-2.24).

CONCLUSION

The ABO genotypes AA and AO were significantly associated with GC only in females and only for diffuse-type GC. These data suggest that the association between ABO blood group and GC risk may differ according to sex and histological type.

[Resolution of ABO Discrepancies by ABO Genotyping.]

BACKGROUND

Before a blood transfusion, both red cell and serum typing need to be matched for ABO tests on the donor and patient (recipient). When a mismatch exists in the tests, additional ABO genotyping and serological tests are required for the resolution of the discrepancy. We performed ABO genotyping on a series of blood donors and patients with ABO discrepancies to assist in resolving their blood groups.

METHODS

We examined 46 samples with ABO discrepancies from a random pool of donors recruited at Gwangju-Chonnam Red Cross Blood Center and from patients at Chonnam National University Hospital between May 2004 and July 2005. ABO genotyping was performed on all samples with an allele specific polymerase chain reaction for differentiation of A, B,O, cis-AB, A(var) (784 G>A), and B(var) (547 G>A) alleles; routine serologic tests were also performed. Exon 6 and 7 of ABO gene from five samples were sequenced.

RESULTS

The genotypes of 18 donors/patients with weakened A or B antigen expressions consisted of 4 cases of cis-AB/O (3 A(2)B(3), 1 A(2)B); 5 cases of cis-AB/A (5 A(1)B(x or el)); 2 cases of A/O (1 O, 1 A(m or x)); 1 case of B/O (1 B(m or x)); 4 cases of A/B (1 A(2)B , 1 A(1)B(x or el), 2 A(1)B(3)); and 2 cases of A(var)/B (2 A(w)B). On the other hand, the genotypes of 28 samples with unexpected serum reactions included 18 cases of A/O (16 A(1), 2 A(int)); 7 cases of A/A (5 A(1), 1 A(1)B(x or el), 1 A(1)B(w)); and 3 cases of O/O (1 O, 2 B(w)).

CONCLUSIONS

ABO genotyping is useful for differentiating the ABO discrepancies that were difficult to resolve by serological tests. The most frequent unusual red cell reactions were weak A and B antigen expressions, which were resulted from the ABO subgroup alleles including cis-AB allele, whereas the most frequent unusual serum reactions were caused by decreased anti-B titers.

Allelic Prevalence of ABO Blood Group Genes in Iranian Azari Population

INTRODUCTION

ABO blood group system is the most important blood group in transfusion and has been widely used in population studies. Several molecular techniques for ABO allele's detection are widely used for distinguishing various alleles of glycosyl transferase locus on chromosome 9.

METHODS

744 randomly selected samples from Azari donors of East Azerbaijan province (Iran) were examined using well-adjusted multiplex allele- specific PCR ABO genotyping technique.

RESULTS

The results were consistent for all individuals. The ABO blood group genotype of 744 healthy Azari blood donors was: 25.8% AA/AO (2), 7.6% AO (1), 1.6% BB, 11.3% B0 (1), 10% AB, 9.3% 0(1)0(1) and 15.3%0(1)0(2). The highest genotype frequency belonged to O01/O02 genotype (15.3%) and the lowest frequency belonged to A101/A102 genotype (0.4%).

CONCLUSIONS

The frequencies of ABO alleles didn't show significant differences between East Azerbaijan province population and that of other areas of the country. Meanwhile, statistical analysis of frequencies of A and B alleles between East Azerbaijan province population and neighbor countries showed significant differences whereas the frequency of allele O between them did not show significant difference (P>0.05).

CONCLUSIONS

The frequencies of ABO alleles didn't show significant differences between East Azerbaijan province population and that of other areas of the country. Meanwhile, statistical analysis of frequencies of A and B alleles between East Azerbaijan province population and neighbor countries showed significant differences whereas the frequency of allele O between them did not show significant difference (P>0.05).

A dispermic chimera with mixed field blood group B and mosaic 46,XY/47,XYY karyotype

Chimerism in humans is a rare phenomenon often initially identified in the resolution of an ABO blood type discrepancy. We report a dispermic chimera who presented with mixed field in his B antigen typing that might have been mistaken for the B3 subtype. The propositus is a healthy Korean male blood donor. Neither his clinical history nor initial molecular investigation of his ABO gene explained his mixed field agglutination with murine anti-B. Chimerism was suspected, and 9 short tandem repeat (STR) loci were analyzed on DNA extracted from blood, buccal swabs, and hair from this donor and on DNA isolated from peripheral blood lymphocytes from his parents. The propositus' red blood cells demonstrated mixed field agglutination with anti-B. Exon 6 and 7 and flanking intronic regions of his ABO gene were sequenced and revealed an O01/O02 genotype. B allele haplotype-specific PCR, along with exon 6 and 7 cloning and sequencing demonstrated a third ABO allele, B101. Four STR loci demonstrated a pattern consistent with a double paternal chromosome contribution in the propositus, thus confirming chimerism. His karyotype revealed a mosaic pattern: 32/50 metaphases were 46,XY and 18/50 metaphases demonstrated 47,XYY.

A new method for ABO genotyping to avoid discrepancy between genetic and serological determinations

In Japan and elsewhere, ABO genotyping is frequently used in forensic practice for identification of a decomposed body. However, the phenotype deduced from the genotyping data is occasionally inconsistent with the real phenotype. In this paper, we report a simple ABO genotyping method in which five single nucleotide polymorphism at nps 220, 261, 796, 802, and 803 are analyzed simultaneously to avoid discrepancies between genetic and serological determinations in ABO*A204, *O303, *O207, *cis-AB01 and *cis-AB02 alleles. This method can be used for the genotyping of badly decomposed remains or old bloodstains.

Kinetic studies on Korean serum cis-AB enzymes reveal diminished A and B transferase activities

BACKGROUND

cis-AB enzymes are rare glycosyltransferases that synthesize both blood group A and B antigens. We have identified a large cohort of Korean cis-AB blood donors and studied the N-acetylgalactosaminyltransferase (glycosyltransferase A, GTA) and galactosyltransferase (glycosyltransferase B, GTB) activity of their cis-AB serum enzymes.

MATERIALS AND METHODS

The cis-AB01 allele was identified by PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) in 60 donors collected at the Gwangju-Chonnam Red Cross Blood Center. Enzyme assays of this cis-AB enzyme were performed on available serum samples from 16 donors with the cis-AB01/O genotype and three with the cis-AB01/A genotype.

RESULTS

In cis-AB donors with an O allele, both the GTA and GTB activity of the cis-AB enzyme were markedly reduced compared to normal A and B controls (29% and 27%, respectively). This is consistent with the behaviour predicted from kinetic studies of a recombinant model of the corresponding AAAB enzyme.

CONCLUSION

Although variable, cis-AB enzymes feature reduced GTA and GTB activities.

SUMMARY

Cis-AB enzymes feature variable but reduced GTA and GTB activities with relatively weaker GTB activity, consistent with the weak agglutination present on forward typing with anti-B.

The genetic and phenotypic basis of blood group A subtypes in Koreans

A serological and genetic study of Korean blood donors with phenotypic group A subtypes was performed. There were 176 donors with phenotypic A subtypes identified. Exons 6 and 7 from 57 representative donors were sequenced. The A(var) allele (784 G > A) was cloned and sequenced, and a family study demonstrating its inheritance and unusual serological characteristics was performed. The A102 allele was the most frequently identified allele in phenotypically A2 (58%, 11/19) and A2B (68%, 17/25) donors. Anti-A1 was rarely present amongst A2 and A2B donors. The family study revealed that the A(var) allele was expressed as phenotype A(weak)B in A(var)/B heterozygote members, but as phenotype O in A(var)/O heterozygotes. The most frequent allele in Korean donors with the A2 phenotype differs from its Caucasian counterpart, as does the frequency of anti-A1. The A(var) allele demonstrates allelic enhancement in A(var)/B heterozygotes.

What a difference 2 nucleotides make: a short review of ABO genetics

ABO is the most important blood group system for transfusion and solid organ transplantation, but it is only over the past 15 years that the techniques for studying its molecular basis became mainstream. Many of its common and rare alleles are now well characterized and by using various expression systems, their effects on the resulting glycosyltransferases are being appreciated. As progress has been made in genetics and glycobiology, so too do reagents used to routinely type red blood cells in the clinical laboratory evolve. Monoclonal reagents are now widely used. This has created difficulties in nomenclature to describe subtype phenotypes as the names of some of these uncommon phenotypes were based on the red blood cell agglutination pattern using polyclonal reagents. In this brief review a discussion of the wild-type ABO allele and the enzymes it encodes is followed by a description of a selection of unusual and fascinating alleles-some that encode enzymes that create both A and B antigens and others that result from hybridization events. A short section on the techniques of ABO allele investigation describes some of the current methodologies used in both research and clinical laboratories.

A novel Bvar allele (547 G>A) demonstrates differential expression depending on the co-inherited ABO allele

BACKGROUND AND OBJECTIVES

Genetic analysis of group B donors in Korea was performed.

MATERIALS AND METHODS

Exons 6 and 7 were sequenced in 12 phenotypically B3 donors 6 B3, 6 A1B3.

RESULTS

Consensus sequences all B3 and 2/6 A1B3 donors were present. Four A1B3 donors demonstrated a novel B allele, B(var), in the context of A101/ or A102/B(var) genotypes. Family studies based on an A1B3 donor with the B(var) allele and on another unrelated subject with identical genotype and phenotype revealed B(var)/O01 genotypes with full B-antigen expression.

CONCLUSIONS

B(var) allele is subject to differential expression, depending on the co-inherited ABO allele.