An exonic missense mutation c.28G>A is associated with weak B blood group by affecting RNA splicing of the ABO gene

Serological and genetic analysis of a B3 phenotype caused by c.259G > T in the ABO gene

BACKGROUND

Mixed agglutination is a serological pattern in some ambiguous ABO blood type identification. This study focused on the serological and molecular genetic characteristics of a B3 phenotype induced by a c.259G > T mutation in the ABO gene.

STUDY DESIGN AND METHODS

Serological methods such as gel cards and tubes were used to identify the ABO blood type of the patient, with fluorescent PCR for ABO genotyping and Sanger sequencing for analysing the ABO exons. Protein 3D Structure was simulated and further analysed using SWISS-MODLE and PyMOL. Both the wild-type (VAL-87, ABO*B.01) and the mutant (p.Val87Leu) plasmids were transfected into Hela cells to assess the agglutination intensity of the transfected cells with anti-B antibodies.

RESULTS

Serological testing showed weak expression of the B antigen and mixed agglutination with anti-B antibodies. ABO genotyping indicated the presence of a B allele, but exon sequencing revealed an additional c.259G > T mutation in exon 6 based on the ABO*B.01 allele. The simulated three-dimensional structures of the proteins showed increased steric hindrance with mutations, leading to a relatively loose structure. The transfected Hela cells with the mutant (p.Val87Leu) plasmid exhibited a significantly reduced agglutination intensity with anti-B antibodies.

CONCLUSION

Based on comprehensive serological, genetic, and simulation analyses, it is concluded that the c.259G > T mutation in exon 6 of the ABO*B.01 allele results in an amino acid change within the enzymatic active site. This alteration likely impacts protein stability and reduces B antigen expression, leading to the B3 subtype phenotype.

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.

Serologic and molecular identification of the variation on ABO*B.01 gene in ABO glycosyltransferases associated with Bw phenotype: a case report

AB antigen is formed by glycosyltransferase enzyme, which catalyzes the corresponding substrates to be connected to the galactose of the precursor substance H antigen. To study the effect of the α-1,3-D galactosyltransferase (GTB) gene mutation on B antigen expression, we explored its molecular mechanism by combining molecular biological methods with bioinformatics. The ABO blood type of the patients was identified using conventional serologic methods, and the polymerase chain reaction (PCR) products of exons 1-7 of the ABO gene were directly sequenced using gene-specific primers and direct sequencing. Proteins in the secretory supernatant of transfected cells were collected in vitro, and GTB content was quantitatively analyzed using western blotting. Bioinformatics software was used to simulate the 3-dimensional structure of the mutant protein. In this case, the patient's serologic test results revealed subtype B. Gene sequencing results confirmed a mutation at base 278 of exon 6. The mutation (c.278C>T) changed the 93rd amino acid of the protein polypeptide chain from proline to leucine (p.P93L). The variant p.P93L did not affect the expression and secretion of GTB, but affected enzyme activity and stability, ultimately manifesting as weakened expression of the B antigen and reduced affinity.

One novel single nucleotide polymorphism c.424A>G on A1.02 allele in ABO glycosyltransferases leads to Aweak phenotype

BACKGROUND

The dysfunction of the ABO glycosyltransferase (GT) enzyme, which is caused by mutations in the ABO gene, can lead to weak ABO phenotypes. In this study, we have discovered a novel weak ABO subgroup allele and investigated the underlying mechanism to causing its Aweak phenotype.

MATERIALS AND METHODS

The ABO phenotyping and genotyping were performed by serological studies and direct DNA sequencing of ABO gene. The role of the novel single nucleotide polymorphism (SNP) was evaluated by 3D model, predicting protein structure changes, and in vitro expression assay. The total glycosyltransferase transfer capacity in supernatant of transfected cells was examined.

RESULTS

The results of serological showed the subject was Aweak phenotype. A novel SNP c.424A > G (p. M142V) based on ABO∗A1.02 was identified, and the genotype of the subject was AW-var/O.01 according to the gene analysis. In silico analysis showed that the SNP c.424A > G on the A allele may change the local conformation by damaging the hydrogen bonds and reduce the stability of GT. In vitro expression study showed that SNP p.M142V impaired H to A antigen conversion, although it did not affect the generation of A glycosyltransferase (GTA).

CONCLUSION

One novel AW allele was identified and the SNP c.424A > G (p.M142V) can cause the Aweak phenotype through damaging the hydrogen bonds and reducing stability of the GTA.

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.

Prevalence and distribution of serological characteristics of weak ABO subgroups in the Chinese population

OBJECTIVES

This study aimed to determine the true frequency of weak ABO subgroups and to investigate the serological characteristics of various subgroup alleles in the Chinese population.

METHODS

A total of 2,945,643 blood samples were collected from January 2009 to December 2017. After initial screening and re-examination using automatic blood group analyzers, all ABO-discrepant samples were confirmed by standard serological analysis and molecular detection by DNA sequencing. The true frequency of weak ABO subgroups was determined by the number of ABO subgroup donors and the missed detection rate. The ABO antigen expressions corresponding to subgroup alleles were analyzed by the agglutination intensity of red blood cells.

RESULTS

The detection rate of ABO subgroups was 0.031 % (927/2,945,643). Considering the missed detection rate (27.81 %), the true frequency of ABO subgroups in the Chinese population was 0.044 %. The three most common genetic variations among blood donors in Shanghai were BA.04, BW.12 and BA.02. BW.03 showed the weakest B antigen expression (6.00 ± 1.97) and Bvar-1 the strongest (9.20 ± 1.10).

CONCLUSION

Many ABO subgroups were missed. BA.04 was found to be the most common subgroup allele in the Chinese population. Different ABO subgroup alleles exhibit different ABO antigen expression patterns.

Molecular genetic analysis of two novel a allele to cause Ax phenotype in Chinese

BACKGROUND

Mutations of ABO gene may cause the dysfunction of ABO glycosyltransferase (GT) that can result in weak ABO phenotypes. Here, we identified two novel weak ABO subgroup alleles and explored the mechanism that caused Ax phenotype.

MATERIALS AND METHODS

The ABO phenotyping and genotyping were performed by serological studies and direct DNA sequencing of ABO gene. The role of the mutations was evaluated by 3D model, predicting protein structure changes, and in vitro expression assay. The total glycosyltransferase transfer capacity in supernatant of transfected cells was examined.

RESULTS

The results of serological showed the subject RJ23 and RJ52 both were Ax phenotypes. The novel A alleles, Avar-1 and Avar-2 were identified according to the gene analysis. Both Avar-1 and Avar-2 harbored recombinant heterozygous alleles, specifically A2.05 and O.01.02. These alleles showcased substitutions at positions c.106G > T, c.189C > T, c.220C > T, and c.1009A > G in their respective exons. It is worth noting that the crossing-over regions of these two alleles differed from each other. In vitro expression study showed that GTA mutant impaired H to A antigen conversion, and the mutant did not affect the production of GTA though the Western bolt. In silico analysis showed that GTA mutant may change the local conformation and the stability of GT.

CONCLUSIONS

The Avar-1 and Avar-2 alleles were identified, which could cause the Ax phenotype through changing the local conformation and reducing stability of the GTA.

Identification of a novel variant c.761C>T on ABO*B.01 gene in ABO glycosyltransferases associated with Bweak phenotype

BACKGROUND AND OBJECTIVES

ABO antigens are produced from H antigen by the activity of glycosyltransferase enzyme encoded by the ABO gene. Variants in the ABO gene can produce a weak ABO phenotype. In this study, we identify a novel ABO*BW allele and investigate the underlying mechanism leading to the Bweak phenotype.

MATERIALS AND METHODS

The ABO phenotype and genotype of the sample were determined using serological and direct DNA sequencing methods. We assessed the impact of the novel variant by three-dimensional modelling to predict protein stability changes (ΔΔG), and carried out an in vitro expression assay. The total glycosyltransferase transfer capacity in the supernatant of transfected cells was also examined.

RESULTS

Serological analysis confirmed the Bweak phenotype in the subject, and gene sequencing identified a novel variant c.761C>T (p.A254V) on the ABO*B.01 allele, resulting in a BW-var/O.01.02 genotype. In silico analysis suggested that the p.A254V variant on the B allele may reduce the stability of glycosyltransferase B (GTB), as indicated by the ΔΔG values. In vitro expression studies showed that the variant p.A254V impaired H to B antigen conversion, although it did not affect the expression of GTB.

CONCLUSION

We identified a novel BW allele and demonstrated that the variant c.761C>T (p.A254V) can cause the Bweak phenotype by reducing the stability of GTB.

Generation of hiPSCs with ABO c.767T>C substitution: resulting in splicing variants

Introduction: The ABO blood group system has important clinical significance in the safety of blood transfusion and organ transplantation. Numerous ABO variations, especially variations in the splice sites, have been identified to be associated with some ABO subtypes. Methods: Here, we performed the c.767T>C substitution of the ABO gene in human induced pluripotent stem cells (hiPSCs) by the adenosine base editor (ABE) system and described its characteristics at the genome level in detail. Results: The hiPS cell line with c.767T>C substitution maintained a normal karyotype (46, XX), expressed pluripotency markers, and showed the capability to spontaneously differentiate into all three germ layers in vivo. The genome-wide analysis demonstrated that the c.767T>C substitution in the ABO gene did not cause any detected negative effect in hiPSCs at the genome level. The splicing transcript analysis revealed that splicing variants were observed in the hiPSCs with ABO c.767T>C substitutions. Conclusion: All these results indicated that some splicing variants occurred in hiPSCs with c.767 T>C substitution of ABO gene, which probably had a significant effect on the formation of the rare ABO*Ael05/B101 subtype.

A Novel Methodology for Detecting Variations in Cell Surface Antigens Using Cell-Tearing by Optical Tweezers

The quantitative analysis of cell surface antigens has attracted increasing attention due to the antigenic variation recognition that can facilitate early diagnoses. This paper presents a novel methodology based on the optical "cell-tearing" and the especially proposed "dilution regulations" to detect variations in cell surface antigens. The cell attaches to the corresponding antibody-coated slide surface. Then, the cell-binding firmness between a single cell and the functionalized surface is assayed by optically tearing using gradually reduced laser powers incorporated with serial antibody dilutions. Groups B and B3 of red blood cells (RBCs) were selected as the experiment subject. The results indicate that a higher dilution called for lower power to tear off the cell binding. According to the proposed relative-quantitative analysis theory, antigenic variation can be intuitively estimated by comparing the maximum allowable dilution folds. The estimation result shows good consistency with the finding in the literature. This study suggests a novel methodology for examining the variation in cell surface antigens, expected to be widely capable with potential sensor applications not only in biochemistry and biophysics, but also in the micro-/nano- engineering field.

Molecular genetic mechanism analysis and pedigree investigation of rare Bweak subgroup

OBJECTIVE

To analyze the molecular mechanism of rare B_weak subgroup in the ABO blood group system and conduct pedigree investigations.

METHODS

The blood group was detected by conventional serological method, and ABO gene of proband and her family was amplified and sequenced by polymerase chain reaction method.

RESULTS

The study showed that the proband was a B_weak phenotype by conventional serological method. Her family's serological results were as follows, her father and eldest brother were B_weak subgroup while her mother and second eldest brother were O group. The proband's ABO gene sequencing result was ABO*BW.27/ABO*O.01.02. Her father, mother and two elder brothers were ABO*BW.27/ABO*O.01.01, ABO*O.01.01/ABO*O.01.02, ABO*BW.27/ABO*O.01.02, ABO*O.01.01/ABO*O.01.02.

CONCLUSION

Conventional blood group serology combined with molecular diagnostic technology can accurately identify the B_weak subgroup, and the pedigree investigation analysis showed that the proband's allelic mutation came from her father. She has gained a point mutation of c.905A>G on the basis of ABO*B.01.

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.

Six splice site variations, three of them novel, in the ABO gene occurring in nine individuals with ABO subtypes

Background

Nucleotide mutations in the ABO gene may reduce the activity of glycosyltransferase, resulting in lower levels of A or B antigen expression in red blood cells. Six known splice sites have been identified according to the database of red cell immunogenetics and the blood group terminology of the International Society of Blood Transfusion. Here, we describe six distinct splice site variants in individuals with ABO subtypes.

Methods

The ABO phenotype was examined using a conventional serological method. A polymerase chain reaction sequence-based typing method was used to examine the whole coding sequence of the ABO gene. The ABO gene haplotypes were studied using allele-specific primer amplification or cloning technology. In silico analytic tools were used to assess the functional effect of splice site variations.

Results

Six distinct variants in the ABO gene splice sites were identified in nine individuals with ABO subtypes, including c.28 + 1_2delGT, c.28 + 5G > A, c.28 + 5G > C, c.155 + 5G > A, c.204-1G > A and c.374 + 5G > A. c.28 + 1_2delGT was detected in an A_w individual, while c.28 + 5G > A, c.28 + 5G > C, and c.204-1G > A were detected in B_el individuals. c.155 + 5G > A was detected in one B₃ and two AB₃ individuals, whereas c.374 + 5G > A was identified in two A_el individuals. Three novel splice site variants (c.28 + 1_2delGT, c.28 + 5G > A and c.28 + 5G > C) in the ABO gene were discovered, all of which resulted in low antigen expression. In silico analysis revealed that all variants had the potential to alter splice transcripts.

Conclusions

Three novel splice site variations in the ABO gene were identified in Chinese individuals, resulting in decreased A or B antigen expression and the formation of ABO subtypes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03141-5.

Two novel mutations p. L319V and p. L91P in ABO glycosyltransferases lead to Ael and Bel phenotypes

BACKGROUND

Mutations of the ABO gene may cause the dysfunction of ABO glycosyltransferase (GT) that can result in weak ABO phenotypes. Here, we identified two novel weak ABO subgroup alleles and explored their mechanisms that caused A_el and B_el phenotypes.

MATERIALS AND METHODS

The ABO phenotyping and genotyping were performed by serological studies and direct DNA sequencing of the ABO gene. The role of the novel mutations were evaluated by a three-dimensional model, predicting protein structure changes, and in vitro expression assay. The total glycosyltransferase transfer capacity in supernatant of transfected cells was examined.

RESULTS

We identified a mutation c. 955C>G (p. L319V) of A allele in an A_el subject and a mutation c. 272T>C (p. L91P) of B allele in a B_el subject. In silico analysis showed that the mutation p. L319V of the A allele and p. L91P of the B allele may change the local conformation of GT and impair the catalysis of H to A or B antigen conversion. In vitro expression study showed that mutation p. L319V impaired H to A antigen conversion, although it did not affect the expression of glycosyltransferase A.

CONCLUSIONS

Two novel "el"-type ABO subgroup alleles were identified. Both of the two novel mutations can change the local conformation of GTs and reduce protein stability. GTA mutation p. L319V can impair the conversion from H to A antigen and causes the A_el phenotype.

p.R180C mutation of glycosyltransferase B leads to B subgroup, an in vitro and in silico study

BACKGROUND AND OBJECTIVES

Dysfunctional glycosyltransferase A or B may lead to incomplete glycosylation of H antigen and atypical ABO blood group with weak A or B phenotypes, posing challenges for blood typing for transfusion.

MATERIALS AND METHODS

Serological studies and ABO gene analysis were performed. Flow cytometry was performed on HeLa cells transfected glycosyltransferase B expressing plasmids. Agglutination of transfected cells and total glycosyltransferase B transfer capacity were examined. Molecular dynamics simulations were used to explore possible dynamic conformational changes around the binding pocket.

RESULTS

We identified a mutation c.538C>T (p. R180C) of B allele in a Chinese donor and his father with ABw phenotype. In vitro expression study showed that mutation p.R180C, although not affecting expression of glycosyltransferase B, impaired H to B antigen conversion. The in silico analyses found that the residue Arg180 on the internal loop next to the entry of the binding pocket may have its long side chain salt-bridged with the highly flexible C-terminal carboxyl and contribute to the catalysis of H to B antigen conversion.

CONCLUSION

The p.R180C mutation impairs the conversion from H to B antigen and leads to weak B phenotype. Dynamic interaction between Arg180 and C-terminal of glycosyltransferase B may stabilize its binding with UDP-galactose and facilitate H/B antigen conversion.