Serological and molecular characterization of novel ABO variants including an interesting B(A) subgroup

BACKGROUND

ABO grouping is the most important pretransfusion testing that is directly related to the safety of blood transfusion. A weak ABO subgroup is one of the important causes of an ABO grouping discrepancy. Here, we investigated the characterization of four novel ABO variants including a novel B(A) subgroup.

STUDY DESIGN AND METHODS

RBCs were phenotyped by standard serology methods. The full coding regions of the ABO gene and the erythroid cell-specific regulatory elements in intron one were sequenced. The effect of the possible splice site variant was predicted by Alamut software. The 3D structural modeling of three relative B(A) enzymes (p.Met214Thr, p.Met214Val, and p.Met214Leu) were performed by PyMOL software.

RESULTS

Four novel ABO alleles were identified with weak ABO expression in this study, in which two would lead to premature terminations, and two resulted in amino acid changes. In silico analysis revealed that the splice site variant c.155G>T had the potential to alter splice transcripts. 3D structural view shown that the variant amino acid position 214 was spatially adjacent to the donor recognition pocket residues (266Met and 268Ala) and just next to the 211DVD213 motif. The size of the side chain of Thr and Val is the smallest, Leu is medium, and Met is the largest, and the size changes in the critical position 214 may affect the donor recognition pocket.

CONCLUSION

Four ABO subgroup alleles were newly linked to different kinds of ABO variants and the possible mechanism through which they produce weak ABO subgroups was analyzed in silico.

Detecting serologically difficult ABO blood groups using single-molecule real-time sequencing technology

BACKGROUND AND OBJECTIVES

Recently, third-generation long-read sequencing technology has been increasingly applied to the detection of various blood group systems. Because of its long read length and use of single-molecule sequencing, it is capable of obtaining the sequences of blood group genes in their entirety as well as of distinguishing haplotypes. Therefore, here, we collected ABO blood group samples that were difficult to classify serologically and analysed the sequences of the coding regions of the ABO genes as well as the sequences upstream and downstream of the coding regions.

MATERIALS AND METHODS

Samples with ABO antigen typing and reverse serum typing discrepancies were screened in a total of 21 patients. All samples were subjected to serological testing and preliminary ABO genotyping (polymerase chain reaction with sequence-specific primers [PCR-SSP]), followed by single-molecule real-time (SMRT) sequencing to obtain complete ABO gene sequences. PCR sequence-based typing (PCR-SBT) was performed to validate the results.

RESULTS

Of the 21 samples, 15 had common ABO types, and 6 had rare ABO subtypes. One new allele, ABO*B.NEW (c.861C>T), and one allelic base recombination event was identified. Forty-two haplotype sequences were obtained via SMRT sequencing with intronic single-nucleotide variants (SNVs) specific to the ABO allele, and all of the exon region sequences were consistent with the PCR-SBT results.

CONCLUSION

SMRT sequencing is capable of accurately obtaining complete ABO gene sequences, distinguishing haplotypes and identifying allelic recombination.

Review of ABO Expression and Variations based on Transcriptional Regulation of the ABO Blood Group Gene

Background and Summary

We review the transcriptional regulation of ABO expression and discuss variants in the promoter and erythroid cell-specific regulatory region in individuals with weak ABO phenotypes such as Bm, Am, B3, and A3. We also review the molecular mechanisms responsible for variations in ABO expression in development and disease including the cell type-specific expression of ABO during erythroid cell differentiation, and reduction of A- or B-antigens in cancer cells or on red blood cells in patients with leukemia. Although the relationship between ABO blood group antigens and diseases has been characterized, the physiological significance of the ABO blood group system remains unclear.

Key Messages

This review discusses accumulated knowledge of the ABO gene regulation and potential reasons for conservation of ABO during evolution.

Novel regulatory variant in ABO intronic RUNX1 binding site inducing A3 phenotype

BACKGROUND AND OBJECTIVES

Mixed-field agglutination in ABO phenotyping (A3, B3) has been linked to genetically different blood cell populations such as in chimerism, or to rare variants in either ABO exon 7 or regulatory regions. Clarification of such cases is challenging and would greatly benefit from sequencing technologies that allow resolving full-gene haplotypes at high resolution.

MATERIALS AND METHODS

We used long-read sequencing by Oxford Nanopore Technologies to sequence the entire ABO gene, amplified in two overlapping long-range PCR fragments, in a blood donor presented with A3B phenotype. Confirmation analyses were carried out by Sanger sequencing and included samples from other family members.

RESULTS

Our data revealed a novel heterozygous g.10924C>A variant on the ABO*A allele located in the transcription factor binding site for RUNX1 in intron 1 (+5.8 kb site). Inheritance was shown by the results of the donor's mother, who shared the novel variant and the anti-A specific mixed-field agglutination.

CONCLUSION

We discovered a regulatory variant in the 8-bp RUNX1 motif of ABO, which extends current knowledge of three other variants affecting the same motif and also leading to A3 or B3 phenotypes. Overall, long-range PCR combined with nanopore sequencing proved powerful and showed great potential as an emerging strategy for resolving cases with cryptic ABO phenotypes.

Detection and phenotype analysis of a novel Ael blood group allele

BACKGROUND AND OBJECTIVES

The presence of blood subtypes may lead to difficulties in blood group identification; however, third-generation sequencing (TGS) can help in accurately identifying difficult blood groups, and study the serological characteristics and molecular mechanism of Ael subtypes.

MATERIALS AND METHODS

ABO blood group was identified by the standard serological technique, weak blood group antigen was identified by adsorption-elution experiments, ABH substance in the saliva was determined and glycosyltransferase activity of A and B was detected. The ABO gene full-length sequence and promoter region were amplified by specific primers using single-molecule real-time sequencing, with the amplified products being sequenced directly and analysed in real time.

RESULTS

The patient was serologically identified as Ael subtype, and TGS analysis revealed new intron mutations in Ael patients (c.467C>T; c.29-10T>A).

CONCLUSION

The discovery of the new allele and the identification of ABO subtypes can be combined with serological characterization and molecular biological methods.

Analysis of the Genomic Sequence of ABO Allele Using Next-Generation Sequencing Method

Background

Although many molecular diagnostic methods have been used for ABO genotyping, there are few reports on the full-length genomic sequence analysis of the ABO gene. Recently, next-generation sequencing (NGS) has been shown to provide fast and high-throughput results and is widely used in the clinical laboratory. Here, we established an NGS method for analyzing the sequence of the start codon to the stop codon in the ABO gene.

Study Design and Methods

Two pairs of primers covering the partial 5’-untranslated region (UTR) to 3’-UTR of the ABO gene were designed. The sequences covering from the start codon to the stop codon of the ABO gene were amplified using these primers, and an NGS method based on the overlap amplicon was developed. A total of 110 individuals, including 88 blood donors with normal phenotypes and 22 ABO subtypes, were recruited and analyzed. All these specimens were first detected by serological tests and then determined by polymerase chain reaction sequence-based typing (PCR-SBT) and NGS. The sequences, including all the intron regions for the specimens, were analyzed by bioinformatics software.

Results

Among the 88 blood donors with a normal phenotype, 48 homozygous individuals, 39 heterozygous individuals, and one individual with a novel O allele were found according to the results of the PCR-SBT method. Some single-nucleotide variants (SNV) in intronic regions were found to be specific for different ABO alleles from 48 homozygous individuals using the NGS method. Sequences in the coding region of all specimens using the NGS method were the same as those of the PCR-SBT method. Three intronic SNVs were found to be associated with the ABO subtypes, including one novel intronic SNV (c.28+5956T>A). Moreover, six specimens were found to exhibit DNA recombination.

Conclusion

An NGS method was established to analyze the sequence from the start codon to the stop codon of the ABO gene. Two novel ABO alleles were identified, and DNA recombination was found to exist in the ABO alleles.

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.

New ABO intron 1 variant alleles

Unusual and discrepant ABO phenotypes are often due to genetic variants that lead to altered levels or activity of ABO transferases and consequently to altered expression of ABO antigens. This report describes eight genetic alterations found in 15 cases with reduced or undetectable expression of ABO antigens. Forward and reverse ABO grouping was performed by standard gel or tube methods. Adsorption-heat elution and saliva testing for H and A substances followed the AABB technical manual procedures. Genomic DNA extracted from whole blood was PCR-amplified to cover the entire ABO coding sequence, splice junctions, proximal promoter, and intron 1 enhancer. Amplification products were sequenced by next-generation or Sanger dideoxy methods, either directly or after cloning into a bacterial plasmid vector. Eight unreported alleles were found in the 15 cases analyzed. Alleles ABO*A(28+1C) and ABO*A(29-5G) harbor variants that alter the consensus sequence at the intron 1 donor and acceptor splice sites, respectively. The other alleles harbor variants that alter the consensus sequence at transcription factor-binding sites in the intron 1 enhancer: specifically, ABO*A(28+5792T), ABO*A(28+5859A), and ABO*A(28+5860G) at GATA-1 sites; ABO*B(28+5877T) and ABO*B(28+5878G) at a RUNX1 site; and ABO*A(28+5843A) at or near a C/EBP site. Molecular and serologic characterization of ABO alleles can help in their future identification and in the resolution of discrepancies.

Unusual and discrepant ABO phenotypes are often due to genetic variants that lead to altered levels or activity of ABO transferases and consequently to altered expression of ABO antigens. This report describes eight genetic alterations found in 15 cases with reduced or undetectable expression of ABO antigens. Forward and reverse ABO grouping was performed by standard gel or tube methods. Adsorption-heat elution and saliva testing for H and A substances followed the AABB technical manual procedures. Genomic DNA extracted from whole blood was PCR-amplified to cover the entire ABO coding sequence, splice junctions, proximal promoter, and intron 1 enhancer. Amplification products were sequenced by next-generation or Sanger dideoxy methods, either directly or after cloning into a bacterial plasmid vector. Eight unreported alleles were found in the 15 cases analyzed. Alleles ABO*A(28+1C) and ABO*A(29–5G) harbor variants that alter the consensus sequence at the intron 1 donor and acceptor splice sites, respectively. The other alleles harbor variants that alter the consensus sequence at transcription factor–binding sites in the intron 1 enhancer: specifically, ABO*A(28+5792T), ABO*A(28+5859A), and ABO*A(28+5860G) at GATA-1 sites; ABO*B(28+5877T) and ABO*B(28+5878G) at a RUNX1 site; and ABO*A(28+5843A) at or near a C/EBP site. Molecular and serologic characterization of ABO alleles can help in their future identification and in the resolution of discrepancies.

Reduction of blood group A antigen on erythrocytes in a patient with myelodysplastic syndrome harboring somatic mutations in RUNX1 and GATA2

BACKGROUND

Reduction of blood group ABO antigens on red blood cells (RBCs) is well known in patients with leukemias, and this reduction of ABO expression is strongly associated with DNA methylation of the ABO promoter. Previously, we reported a two-nucleotide deletion in RUNX1 encoding an abnormally elongated protein lacking the trans-activation domain in a patient with myelodysplastic syndrome (MDS) showing A-antigen loss on RBCs. This prompted us to investigate the underlying mechanism responsible for A-antigen reduction on RBCs in another patient with MDS.

STUDY DESIGN AND METHODS

Screening of somatic mutations was carried out using a targeted sequencing panel with genomic DNA from peripheral blood mononuclear cells from the patient and eleven MDS controls without A- or B-antigen loss. DNA methylation of the ABO promoter was examined by bisulfite genomic sequencing. Transient transfection assays were performed for functional evaluation of mutations.

RESULTS

Screening of somatic mutations showed missense mutations in RUNX1 and GATA2 in the patient, while no mutation was found in exons of those genes in the controls. There was no significant difference in ABO promoter methylation between the patient and the controls. Transient transfection experiments into COS-7 and K562 cells suggested that the amino acid substitutions encoded by those mutations reduced or lost the trans-activation potential of the ABO expression.

CONCLUSION

Considering the discrepancy between the variant frequencies of these mutations and the ratios of the RBCs with A-antigens loss, the antigen reduction might be associated with these somatic mutations and hypermethylation of the ABO promoter.

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.

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.

A cell-specific regulatory region of the human ABO blood group gene regulates the neighborhood gene encoding odorant binding protein 2B

The human ABO blood group system is of great importance in blood transfusion and organ transplantation. ABO transcription is known to be regulated by a constitutive promoter in a CpG island and regions for regulation of cell-specific expression such as the downstream + 22.6-kb site for epithelial cells and a site in intron 1 for erythroid cells. Here we investigated whether the + 22.6-kb site might play a role in transcriptional regulation of the gene encoding odorant binding protein 2B (OBP2B), which is located on the centromere side 43.4 kb from the + 22.6-kb site. In the gastric cancer cell line KATOIII, quantitative PCR analysis demonstrated significantly reduced amounts of OBP2B and ABO transcripts in mutant cells with biallelic deletions of the site created using the CRISPR/Cas9 system, relative to those in the wild-type cells, and Western blotting demonstrated a corresponding reduction of OBP2B protein in the mutant cells. Moreover, single-molecule fluorescence in situ hybridization assays indicated that the amounts of both transcripts were correlated in individual cells. These findings suggest that OBP2B could be co-regulated by the + 22.6-kb site of ABO.

RUNX1 mutation in a patient with myelodysplastic syndrome and decreased erythrocyte expression of blood group A antigen

BACKGROUND

Loss of blood group ABO antigens on red blood cells (RBCs) is well known in patients with leukemias, and such decreased ABO expression has been reported to be strongly associated with hypermethylation of the ABO promoter. We investigated the underlying mechanism responsible for A-antigen reduction on RBCs in a patient with myelodysplastic syndrome.

STUDY DESIGN AND METHODS

Genetic analysis of ABO was performed by PCR and sequencing using peripheral blood. RT-PCR were carried out using cDNA prepared from total bone marrow (BM) cells. Bisulfite genomic sequencing was performed using genomic DNA from BM cells. Screening of somatic mutations was carried out using a targeted sequencing panel with genomic DNA from BM cells, followed by transient transfection assays.

RESULTS

Genetic analysis of ABO did not reveal any mutation in coding regions, splice sites, or regulatory regions. RT-PCR demonstrated reduction of A-transcripts when the patient's RBCs were not agglutinated by anti-A antibody and did not indicate any significant increase of alternative splicing products in the patient relative to the control. DNA methylation of the ABO promoter was not obvious in erythroid cells. Targeted sequencing identified somatic mutations in ASXL1, EZH2, RUNX1, and WT1. Experiments involving transient transfection into K562 cells showed that the expression of ABO was decreased by expression of the mutated RUNX1.

CONCLUSION

Because the RUNX1 mutation encoded an abnormally elongated protein without a transactivation domain which could act as dominant negative inhibitor, this frame-shift mutation in RUNX1 may be a genetic candidate contributing to A-antigen loss on RBCs.

Molecular Basis of ABO Variants Including Identification of 16 Novel ABO Subgroup Alleles in Chinese Han Population

Introduction

The characteristic of ABO blood subgroup is crucial for elucidating the mechanisms of such variant phenotypes and offering useful information in blood transfusion.

Methods

In total, 211 ABO variants including part of available family members were investigated in this study. The phenotypes of these individuals were typed with serologic methods. The full coding regions of ABO gene and the erythroid cell-specific regulatory elements in intron 1 of them were amplified with polymerase chain reaction and then directly sequenced. The novel alleles were confirmed by cloning and sequencing. Phylogenetic tree was made using CLUSTAL W software. 3D structural analyses of the glycosyltransferases (GTs) with some typical mutations were performed by PyMOL software.

Results

Forty-eight distinctly rare ABO alleles were identified in 211 Chinese variant individuals, including 16 novel ABO alleles. All of the alleles were categorized as 5 groups: 16 ABO*A alleles, 23 ABO*B alleles, 4 ABO*BA alleles, 4 ABO*cisAB alleles, and 1 ABO*O alleles. ABO*A2.08 and ABO*BA.02 were the relatively predominant A and B subgroup alleles, respectively. According to the phylogenetic tree, 28 alleles (5 common alleles and 23 alleles identified in our laboratory) were classified into 3 major allelic lineages. The structural analysis of 3D homology modeling predicted reduced protein stability of the mutant GTs and may explain the reduced ABO antigen expression.

Conclusions

The molecular basis of ABO variants was analyzed, and 16 novel ABO alleles were identified. The results extended the information of ABO variants and provided a basis for better transfusion strategies and helped to improve blood transfusion safety.

A novel mutation +5904 C>T of RUNX1 site in the erythroid cell-specific regulatory element decreases the ABO antigen expression in Chinese population

BACKGROUND

An erythroid cell-specific regulatory element (+5·8-kb) in the first intron of ABO is responsible for the antigen differential expression and the regulatory activity of the element was affected by the nucleotide mutation in the +5·8-kb region. Currently, many individuals with ABO subgroups were found in the Chinese population, but there was little information about the function of +5·8-kb region in these individuals. Here, we studied the mechanism of the mutation in the +5·8-kb region responsible for reducing of antigen expression in 30 ABO subtype Chinese individuals without mutation in the coding region or splicing site.

MATERIALS AND METHODS

The nucleotide sequence of the partial intron 1 covering the +5·8-kb site was amplified and directly sequenced. The haplotype with the novel mutation was obtained by the TOPO TA cloning. Both of the ABO promoter and the +5·8 kb regulatory element were subcloned into the basic luciferase reporter plasmid using the double endonuclease digestion. The promoter activity was examined by the dual-luciferase report vector with K562 cells.

RESULTS

A novel nucleotide substitution +5904 C>T located at RUNX1-binding site in the +5·8 kb site was identified from three individuals with B subtypes. +5890 T>G were found in three Bel and one Ael phenotypes. Cotransfection and luciferase assays demonstrated that the +5904 C>T could obviously reduce activity of the +5·8 kb site.

CONCLUSION

The study suggested that the transcriptional activity of the +5·8 kb site could be downregulated by the single point mutation of RUNX1 motif, leading to reduction in A or B antigen expression.

Effect on gene expression of three allelic variants in GATA motifs of ABO, RHD, and RHCE regulatory elements

BACKGROUND

Only a few genetic variants have been reported in regulatory elements of blood group genes. Most of them affect GATA motifs, binding sites for the GATA-1 transcription factor.

STUDY DESIGN AND METHODS

Samples from two patients and one donor with unusual or discrepant serology for ABO, RhD, and RhCE antigens were analyzed by DNA sequencing. Analyzed regions included the coding sequence and portions of regulatory elements. The effect of some variants on gene expression was evaluated in reporter gene assays.

RESULTS

Three new alleles were identified. Their key variants are located in the ABO Intron 1 enhancer, the RHD proximal promoter, and the RHCE proximal promoter. IVS1 + 5859A was found in an African American patient with a group O forward type and a group B reverse type. 5'UTR-115C was the only RHD variant sequence found in a mixed-race black and Caucasian prenatal patient showing mixed-field agglutination with anti-D. 5'UTR-83T was found in several black donors and patients in the context of the genetically related RHCE*ceBI and RHCE*ceSM alleles. Reporter assays of promoter constructs including 5'UTR-115C or 5'UTR-83T showed a significant reduction in RH gene expression.

CONCLUSION

Three new alleles in the ABO, RHD, and RHCE genes consist of single-nucleotide changes within GATA motifs, emphasizing the key role of GATA transcription factors in the expression of blood group genes.

Histone deacetylase inhibitors suppress ABO transcription in vitro, leading to reduced expression of the antigens

BACKGROUND

The ABO system is of fundamental importance in the fields of transfusion and transplantation and has apparent associations with certain diseases, including cardiovascular disorders. ABO expression is reduced in the late phase of erythroid differentiation in vitro, whereas histone deacetylase inhibitors (HDACIs) are known to promote cell differentiation. Therefore, whether or not HDACIs could reduce the amount of ABO transcripts and A or B antigens is an intriguing issue.

STUDY DESIGN AND METHODS

Quantitative polymerase chain reactions were carried out for the ABO transcripts in erythroid-lineage K562 and epithelial-lineage KATOIII cells after incubation with HDACIs, such as sodium butyrate, panobinostat, vorinostat, and sodium valproate. Flow cytometric analysis was conducted to evaluate the amounts of antigen in KATOIII cells treated with panobinostat. Quantitative chromatin immunoprecipitation (ChIP) assays and luciferase assays were performed on both cell types to examine the mechanisms of ABO suppression.

RESULTS

HDACIs reduced the ABO transcripts in both K562 and KATOIII cells, with panobinostat exerting the most significant effect. Flow cytometric analysis demonstrated a decrease in B-antigen expression on panobinostat-treated KATOIII cells. ChIP assays indicated that panobinostat altered the modification of histones in the transcriptional regulatory regions of ABO, and luciferase assays demonstrated reduced activity of these elements.

CONCLUSION

ABO transcription seems to be regulated by an epigenetic mechanism. Panobinostat appears to suppress ABO transcription, reducing the amount of antigens on the surface of cultured cells.

Presence of nucleotide substitutions in the ABO promoter in individuals with phenotypes A3 and B3

Recently, the involvement of mutation and deletion of transcription regulatory elements in the Bm , Am , A3 and B3 phenotypes has been reported. In the present study, we carried out genetic analysis of individuals with A3 and B3 using peptide nucleic acid-clamping PCR to exclude amplification of O alleles. Two single-point mutations, -76G>C and -68G>T, were found in the ABO promoter on the A-allele in three A3 individuals and on the B allele in a B3 individual, respectively. Transient transfection of luciferase reporter plasmids carrying the same mutations into K562 cells revealed decreased luciferase activity in comparison with that carrying the wild-type promoter. These observations suggest that the mutations downregulate the promoter activity, leading to reduction in A- or B-antigen expression on red blood cells in individuals with the A3 and B3 phenotypes.

Genetic Sequencing Analysis of A307 Subgroup of ABO Blood Group

BACKGROUND The aim of this study was to investigate the serology and gene sequence characteristics of the A307 subgroup of the ABO blood group. MATERIAL AND METHODS Monoclonal anti-A and anti-B antibodies were used to detect the ABO antigens of a proband whose positive blood type was not consistent with the negative blood type of the ABO blood group. Standard A-, B-, and O-negative typing cells were used to test for ABO antibodies in the serum. Additionally, polymerase chain reaction with sequence-specific primer (PCR-SSP) was used to confirm the genotype, and subsequently, exons 6 and 7 of the ABO gene were detected by gene sequencing. Samples from the wife and daughters of the proband were also used for serological and genetic testing. RESULTS Red blood cells of the proband showed weak agglutination reaction with anti-A antibody, while anti-B antibody was detected in the serum. Moreover, PCR-SSP detected A307 and O02 alleles, while gene sequencing revealed mutation of c.745C>T in exon 7, which produced a polypeptide chain p.R249W. The A307 gene of the proband was not inherited by his daughters. CONCLUSIONS A mutation (c.745 C>T) in exon 7 of the ABO blood group gene resulted in low activity of a-1,3-N-acetyl-galactosaminyl transferase, producing A3 phenotype.