A novel A allele with 664G>A mutation identified in a family with the Am phenotype

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.

Rapid rare ABO blood typing using a single PCR based on a multiplex SNaPshot reaction

BACKGROUND

ABO subgroups would be considered when discrepancies in ABO grouping occur. Serological methods including adsorption-elution test, salivary ABH inhibition test, and anti-A1 (lectin) saline method could be used. However, these serological methods are laboring and obscure. Therefore, reliable and affordable method to assess the ABO subgroups is of particular interest.

METHODS

To solve this problem, the multiplex SNaPshot-based assays were designed to determine rare A and B subgroups. Primers used as probes for determination of rare ABO blood groups known in Taiwanese population were designed. Many ABO subtype samples were used to validate the accuracy and reproducibility of our SNaPshot panel.

RESULTS

A panel of primer probes were successfully designed in determining 8 SNP sites (261, 539, 838, 820, 745, 664, IVS6 +5, and 829 in exon 6 and 7) for A phenotype and 6 SNP sites (261, 796, IVS3 +5, 247, 523, and 502 in exon 2, 6 and 7 and intron 3) for B phenotype. SNaPshot analysis for defining blood group A alleles (A₁, A₂, A₃, A_m and A_el) and blood group B alleles (B₁, B₃, B_w and B_el) was therefore available.

CONCLUSION

SNaPshot analysis could be used in reference laboratories for typing known rare subgroups of A and B without DNA cloning and traditional sequencing. Moreover, this method would help to construct databases of genotyped blood donors, and it potentially plays a role in determining fetal-maternal ABO incompatibility.

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.

Blood group B gene is barely expressed in in vitro erythroid culture of Bm-derived CD34+ cells without an erythroid cell-specific regulatory element

BACKGROUND AND OBJECTIVES

Previously, a weak phenotype Am or Bm was assumed to be caused by a reduction of A or B gene expression in bone marrow cells, but not in mucus-secreting cells. However, ABO expression has not been examined in erythroid progenitor cells of Am or Bm individuals.

MATERIALS AND METHODS

We carried out in vitro erythroid differentiation of CD34(+) cells from peripheral blood of a Bm individual harbouring a 3.0-kb deletion including an erythroid cell-specific regulatory element, named the +5.8-kb site, in intron 1 of the human ABO blood group gene.

RESULTS

During the in vitro differentiation of CD34(+) cells from this Bm individual into erythroid cells, B-antigens were not detectable on the cultured cells by flow cytometric analysis, and allele-specific RT-PCR consistently detected the transcripts from the O allele, but not from the B allele. Moreover, chromatin immunoprecipitation assay demonstrated that both RUNX1 and GATA-2 or GATA-1 were bound to the +5.8-kb site in cultured erythroid cells expressing ABO.

CONCLUSION

It is likely that the +5.8-kb site enhances transcription from the ABO promoter in erythroid cells through binding of RUNX1 and GATA-2 or GATA-1.

Deletion of the RUNX1 binding site in the erythroid cell-specific regulatory element of the ABO gene in two individuals with the Am phenotype

BACKGROUND AND OBJECTIVES

An erythroid cell-specific regulatory element, referred to as the +5·8-kb site, had been identified in the first intron of the human ABO blood group gene. Subsequent studies revealed that either a 5·8-kb deletion including the +5·8-kb site or disruption of a GATA factor binding motif at the site was present in all Bm and ABm individuals examined. We investigated the molecular mechanism of the Am phenotype, which is analogous to the Bm phenotype.

MATERIALS AND METHODS

Genomic DNAs were prepared from peripheral blood of two Am individuals, and the nucleotide sequences were investigated using PCR and direct sequencing. Electrophoretic mobility shift assay (EMSA) and promoter assay with K562 cells were carried out.

RESULTS

A novel 23-bp nucleotide deletion was found at the +5·8-kb site in both individuals. EMSAs demonstrated binding of the transcription factor RUNX1 to the nucleotides within the deletion. Promoter assays showed that the deletion reduced the transcriptional activity of the +5·8-kb site.

CONCLUSION

Deletion of the 23-bp nucleotides including the RUNX1 binding site decreases transcription of the A allele, resulting in the reduction in A antigen expression in the Am phenotype.

Mutation of the GATA site in the erythroid cell-specific regulatory element of the ABO gene in a Bm subgroup individual

BACKGROUND

The ABO blood group is important in blood transfusion. Recently, an erythroid cell-specific regulatory element has been identified in the first intron of ABO using luciferase reporter assays with K562 cells. The erythroid cell-specific regulatory activity of the element was dependent upon GATA-1 binding. In addition, partial deletion of Intron 1 including the element was observed in genomic DNAs obtained from 111 Bm and ABm individuals, except for one, whereas the deletion was never found among 1005 individuals with the common phenotypes.

STUDY DESIGN AND METHODS

In this study, further investigation was performed to reveal the underlying mechanism responsible for reduction of B antigen expression in the exceptional Bm individual. Peptide nucleic acid-clamping polymerase chain reaction was carried out to amplify the B-related allele, followed by sequence determination. Electrophoretic mobility assays and promoter assays were performed to examine whether a nucleotide substitution reduced the binding of a transcription factor and induced loss of function of the element.

RESULTS

Sequence determination revealed one point mutation of the GATA motif in the element. The electrophoretic mobility shift assays showed that the mutation abolished the binding of GATA transcription factors, and the promoter assays demonstrated complete loss of enhancer activity of the element.

CONCLUSION

These observations suggest that the mutation in the GATA motif of the erythroid-specific regulatory element may diminish the binding of GATA transcription factors and down regulate transcriptional activity of the element on the B allele, leading to reduction of B antigen expression in erythroid lineage cells of the Bm individual.

Three missense mutations, including a novel 860C>T transition, and allelic enhancement phenomenon associated with ABO blood subgroups A in Taiwan

BACKGROUND

It was estimated that approximately 25 percent of Taiwanese residents were ABO blood group A. Many subgroups of A, however, revealed ambiguous serologic typing results. This study aimed to delineate the molecular basis of the A3, Ax, and weak A phenotypes.

STUDY DESIGN AND METHODS

Serologic analyses including adsorption and elution assay, serum transferases activity assay, and saliva test were performed to determine the unique phenotypes of these samples. DNA sequencing and polymerase chain reaction-restriction fragment length polymorphism were performed to further investigate the relationships between the genetic characteristics and phenotypic features of these samples.

RESULTS

Three single-nucleotide transitions (745C>T, 820G>A, and a novel 860C>T) were found in nine A3/A3B cases. In addition, the Ax and A3B subjects shared the same 860C>T mutation. This A(x) allele with 860C>T transition expressed A3B phenotype in A(x)/B101 heterozygote but Ax phenotype in A(x)/O01 heterozygote. This allelic enhancement was also observed in the weak A family with Aw05 allele, which was previously not found in Taiwan.

CONCLUSION

This allelic enhancement phenomenon was prone to cause serologic discrepancy between parents and children. Genotyping could help us to resolve this problem. Thus, a novel mutation is reported among Taiwanese blood donors.