A historical overview of advances in molecular genetic/genomic studies of the ABO blood group system

Comprehensive Annotation of Complete ABO Alleles and Resolution of ABO Variants by an Improved Full-Length ABO Haplotype Sequencing

BACKGROUND

Full-length ABO haplotype sequencing is crucial for accurate genotyping, reference gene annotation, and molecular mechanism analysis of its variants. However, there is currently a deficiency of comprehensive annotation for full-length ABO haplotypes, spanning from the 5' untranslated region (UTR) to the 3' UTR.

METHODS

Two sets of specimens (79 random blood donors and 47 ABO variants) were tested. The full-length ABO gene spanning the 5' UTR to the 3' UTR was amplified using an improved one-step ultra-long-range PCR with a pair of PCR suppression primers. A single-molecule real-time library was constructed, and ABO haplotype sequencing was performed. Data analysis including basecalling, aligning, variant calling, clustering, and variant annotation were performed.

RESULTS

The amplicon measured 26.1 kb without splicing, representing the most complete ABO gene reported to date. The complete ABO haplotype sequence was obtained via long-read sequencing. The comprehensive ABO reference alleles were obtained and the ABO sequence patterns within each allele in a Chinese population were further classified. The full-length ABO gene haplotype analysis technique effectively resolved ABO variants with structural variations (SVs), including large fragment deletions, inversions, recombination, and chimeras.

CONCLUSIONS

Full-length ABO haplotype sequencing filled a gap that was missing with respect to the 3' UTR sequences of ABO alleles and can advance blood group genomic analysis, aiding in ABO gene function analysis, evolutionary studies, and the resolution of ABO variants.

Chimerism analysis by ABO blood group genotyping with digital droplet PCR

OBJECTIVE

Chimerism analysis is an important post-transplant assessment for allogeneic hematopoietic stem cell transplant (HCT) recipients. Although various chimerism analysis techniques are already established, they are limited in terms of sensitivity, versatility, and turnaround time. Our objective was to develop a digital droplet polymerase chain reaction (ddPCR) assay for chimerism analysis using ABO gene polymorphisms as markers.

METHODS

Our new chimerism analysis method utilizes ddPCR to assess the ABO gene polymorphisms that encode the ABO blood genotype. ABO genotypes were determined in blood samples from 15 HCT recipients using the O panel (rs8176719) and B panel (rs8176746 and rs8176747).

RESULTS

The two panels distinguished six ABO genotypes (AA, AO, BB, BO, AB, and OO). The results of chimerism analysis using ABO genotypes with ddPCR were compatible with those of established methods, such as SRY gene analysis and the use of short tandem repeat markers via standard PCR. Our method could distinguish chimerism in 77% of donor and recipient combinations in the Japanese population.

CONCLUSIONS

We developed a sensitive and rapid chimerism analysis method for HCT using ABO gene polymorphisms in ddPCR.

Steps Forward to a Fair and Inclusive Blood Supply

Blood transfusions save lives. Scientific advancements in infectious disease testing, immunohematology, and blood processing, coupled with an altruistic blood donor model, blood transfusion has become a safe and effective therapeutic intervention. Blood establishments are an integral part of the health care continuum. However, challenges related to access to blood as well as diversity of blood donors can reflect the broader issues within our health care system. An awareness of the social injustices while using medical evidence-based data to support change will be essential for ensuring equitable access to life-saving treatments for all individuals and the communities we serve.

Disparities in ABO blood type determination across diverse ancestries: a systematic review and validation in the All of Us Research Program

OBJECTIVES

ABO blood types have widespread clinical use and robust associations with disease. The purpose of this study is to evaluate the portability and suitability of tag single-nucleotide polymorphisms (tSNPs) used to determine ABO alleles and blood types across diverse populations in published literature.

MATERIALS AND METHODS

Bibliographic databases were searched for studies using tSNPs to determine ABO alleles. We calculated linkage between tSNPs and functional variants across inferred continental ancestry groups from 1000 Genomes. We compared r2 across ancestry and assessed real-world consequences by comparing tSNP-derived blood types to serology in a diverse population from the All of Us Research Program.

RESULTS

Linkage between functional variants and O allele tSNPs was significantly lower in African (median r2 = 0.443) compared to East Asian (r2 = 0.946, P = 1.1 × 10-5) and European (r2 = 0.869, P = .023) populations. In All of Us, discordance between tSNP-derived blood types and serology was high across all SNPs in African ancestry individuals and linkage was strongly correlated with discordance across all ancestries (ρ = -0.90, P = 3.08 × 10-23).

DISCUSSION

Many studies determine ABO blood types using tSNPs. However, tSNPs with low linkage disequilibrium promote misinference of ABO blood types, particularly in diverse populations. We observe common use of inappropriate tSNPs to determine ABO blood type, particularly for O alleles and with some tSNPs mistyping up to 58% of individuals.

CONCLUSION

Our results highlight the lack of transferability of tSNPs across ancestries and potential exacerbation of disparities in genomic research for underrepresented populations. This is especially relevant as more diverse cohorts are made publicly available.

Novel missense mutation c.797T>C (p.Met266Thr) gives rise to the rare B(A) phenotype in a Chinese family

BACKGROUND AND OBJECTIVES

B(A) phenotype is usually formed by nucleotide mutations in the ABO*B.01 allele, with their products exhibiting glycosyltransferases (GTs) A and B overlapping functionality. We herein report a B(A) allele found in a Chinese family.

MATERIALS AND METHODS

The entire ABO genes of the probands, including flanking regulatory regions, were sequenced through PacBio third-generation long-read single-molecule real-time sequencing. 3D molecular models of the wild-type and mutant GTB were generated using the DynaMut web server. The effect of the mutation on the enzyme function was predicted by PROVEAN and PolyPhen2. The predictions of stability changes were performed using DynaMut and SNPeffect.

RESULTS

Based on serological and sequencing features, we concluded the two probands as possible cases of the B(A) phenotype. Crystallization analysis showed that Thr266 substitution does not disrupt the hydrogen bonds. However, some changes in interatomic contacts, such as loss of ionic interactions and hydrophobic contacts, and addition of weak hydrogen bonds, may have affected protein stability to some extent. This mutation was predicted to have a benign effect on enzyme function and slightly reduce protein stability.

CONCLUSION

The probands had the same novel B(A) allele with a c.797T>C (p.Met266Thr) mutation on the ABO*B.01 backbone.

Serological and molecular analysis of the B(A) subtype in China-A systematic review

OBJECTIVE

To study the serological and molecular biological characteristics of the B(A) subtype and its geographical distribution in China through case discussion and systematic review.

METHODS

A case of the B(A)02 subtype previously found in our laboratory was retrospectively analysed. The distribution characteristics and specific serological and genotypic characteristics of the B(A) subtype in China were systematically evaluated by searching four major Chinese databases.

RESULTS

In a previous case of an abnormal blood group, both the proband and her father were found to be genotype B(A)02/O02, while the mother was normal type B. After a systematic search, irrelevant studies were screened out, and 88 studies were included for analysis. The results showed that the B(A)04 subtype was significantly more frequently reported in the north than in the south, while the B(A)02 subtype was predominant in the southwest. The A antigen of the B(A)02 subtype reacts with monoclonal anti-A reagents in a wide range, while the A antigen of the B(A)04 subtype has a weak agglutination intensity of less than or equal to 2+.

CONCLUSION

The results showed that the B(A) subtype has specific characteristics in the Chinese population, and this study further enriched the serological and molecular biological characteristics of the B(A) subtype.