ABO Genotyping Research Articles

Genetic and mechanistic evaluation of an individual with para-Bombay phenotype associated with a compound heterozygote comprising two novel FUT1 variants.

As is well documented, the para-Bombay phenotype is typically characterized by the reduction or absence of ABH antigens on red blood cells but the presence of corresponding antigens in saliva. Herein, the underlying molecular mechanism of an individual with para-Bombay AB phenotype combined with two novel variants of the FUT1 gene was investigated. ABH antigens and antibodies were detected in the serum of the proband using conventional serological methods. The coding region nucleotides of the ABO, FUT1, and FUT2 genes were directly sequenced by polymerase chain reaction. Moreover, the FUT1 haploid type in the proband was analyzed by TA clone sequencing. The 3D structure of wild-type and mutant fucosyltransferases were simulated and analyzed using Phyre2 and Pymol software. Lastly, the effect of missense substitution on the function of fucosyltransferase was predicted by the Polymorphism Phenotyping algorithm (PolyPhen-2) and MutationTaster. ABH antigens were noted to be absent on the surface of red blood cells of the proband. The ABO genotype was ABO*A1.02/ABO*B.01, while the FUT2 genotype was FUT2*01/FUT2*c.357T. Interestingly, two novel missense variants (c.289G>A, p.Ala97Thr and c.575G>C, p.Arg192Pro) and one synonymous SNP (c.840G>A) were identified in the FUT1 gene. Furthermore, c.289G>A was detected in one haploid type, whereas c.575G>C and c.840G>A were discovered in another haploid type. Meanwhile, in silico analysis revealed that amino acid substitution caused by missense variants altered the partial spatial structure of the α-helices where residues 97 and 298 were located using 3D homology modeling software. Finally, both missense variants were defined as probably damaging based on PolyPhen-2 prediction. Two novel FUT1 variants were identified in a Chinese individual with para-Bombay AB phenotype, which can expand our understanding of the molecular mechanism underlying the para-Bombay phenotype and contribute to improving the safety of blood transfusion.

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

BackgroundMutations 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 methodsThe 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. ResultsThe 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. ConclusionsThe 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.

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

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

Identification of Novel Variations in Exon 1 of ABO Blood Group Gene

Serological and molecular biology methods were used to identify the blood type of a patient with forward and reverse ABO typing inconsistency, and to explore the genetic characteristics of this blood type. The ABO phenotype of the proband was identified by tube method, and the ABO blood group genotype of the proband and her parents was determined by fluorescent PCR. The 7 exons of the ABO gene were directly sequenced and analyzed. According to preliminary serological identification, the ABO phenotype of this patient was Bel subtype. Genotyping tests showed that the ABO genotype of the proband and her father was B/O1 , and her mother was O1/O1. Sequencing of exons revealed novel heterozygous variations in exon 1: c.16_17delinsTGTTGCA. The Novel variations in exon 1 led to Bel subtype in the ABO blood group of the proband, and these variations are heritable.

ABO Blood Type and Urinary Bladder Cancer: Phenotype, Genotype, Allelic Association with a Clinical or Histological Stage and Recurrence Rate.

Background Previous research on connection between the ABO blood group and bladder cancer has been based on determining the ABO phenotype. This specific research is extended to the molecular level, providing more information about particular ABO alleles. Aim To investigate the impact of the ABO blood group genotype or phenotype as a risk factor for urinary bladder cancer. Materials and Methods In the case-control study, we included 74 patients who underwent surgery for a urinary bladder tumor at the Urology Clinic, Clinical Hospital Centre Zagreb, in 2021 and 2022. The control group comprised 142 asymptomatic and healthy blood donors. ABO genotyping to five basic alleles was done using a polymerase chain reaction with sequence-specific primers. We compared ABO phenotypes, genotypes, and alleles between patients and the healthy controls and investigated their distribution according to the clinical and histological stage and recurrence rate. Results No statistically significant difference was found among the groups, nor for the observed disease stages in terms of the phenotype and genotype. At the allele level, the results show a significantly lower proportion of malignancy in O1 ( p < 0.001), A1 ( p < 0.001), and B ( p = 0.013), and a lower proportion of metastatic disease in A2 (0%, p = 0.024). We also found significantly higher proportions of high-grade tumors in patients with O1 (71.4%, p < 0.001), A1 (70.1%, p = 0.019), of nonmuscle invasive tumors in patients with O1 (55.1%, p < 0.001), O2 (100%, p = 0.045), and recurrent tumors in patients with O1 (70.2%, p < 0.001) and A1 (74.2%, p = 0.007) alleles. Conclusion We did not find an association between the ABO blood group genotype or phenotype as a genetic risk factor for urinary bladder cancer. However, an analysis at the allelic level revealed a statistically significant association between certain alleles of the ABO blood group system and urinary bladder tumors, clinical or histological stage, and recurrence rate, respectively.

Association between ABO genotypes and risk of dementia and neuroimaging markers: roles of sex and APOE status.

Whether the relationships between ABO blood genotypes (AA, AO, BB, BO, AB, and OO) and dementia are modified by gender and APOE status has been unclear. We used data from the UK Biobank, a population-based cohort study of 487,425 individuals. Cox proportional hazards models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CI) between ABO genotypes and risk of dementia. Multivariable linear regression models were used to estimate the relationship between ABO genotypes and MRI-based brain indices. Overall, 487,425 participants were included at baseline. After 34 million person-years follow up, 7,548 patients developed all-cause dementia. Before stratifying by sex and APOE status, compared to OO genotype, BB genotype was associated with increased risk of all-cause dementia (1.36, 1.03-1.80) and other types dementia (1.65, 1.20-2.28). After stratifying by sex, only in males, BB genotype was associated with higher risk of all-cause dementia (1.44, 1.02-2.09) and other types of dementia (1.95, 1.30-2.93). AB genotype in males was also associated with increased AD (1.34, 1.04-1.72). After further stratifying by APOE e4 status, BB genotype with two APOE e4 alleles showed even stronger association with all-cause dementia 4.29 (1.57, 11.72) and other types dementia (5.49, 1.70-17.69) in males. Also in males, AA genotype with one APOE e4 was associated with increased risks of all-cause dementia (1.27, 1.04-1.55), AD (1.45, 1.09-1.94) and other types dementia (1.40, 1.08-1.81). Linear regression models showed that in both sexes with APOE e4, AA genotype was associated with reduced total grey matter volume. Sex and APOE e4 carrier status modified the association between ABO genotypes and risk of dementia. In males, BB genotype was consistently associated with increased risk of dementia, especially in those with two APOE e4 alleles. Also, in males with one APOE e4, AA genotype might be linked to higher risk of dementia.

(356) - ABO Genotype and its Relation on Histo-Blood Antigen Expression and Regeneration Following Removal - Potential Significance in ABO Incompatible Transplantation

(356) - ABO Genotype and its Relation on Histo-Blood Antigen Expression and Regeneration Following Removal - Potential Significance in ABO Incompatible Transplantation

ABO*A2.08 Subtype Allele Identification and Protein Structure Analysis in Newborns

To study the serological characteristics of ABO*A2.08 subtype and explore its genetic molecular mechanism. ABO blood group identification was performed on proband and her family members by routine serological methods. ABO genotyping and sequence analysis were performed by polymerase chain reaction-sequence specific primer (PCR-SSP), and direct sequencing of PCR products from exons 6 and 7 of ABO gene were directly sequenced and analyzed. The effect of gene mutation in A2.08 subtype on structural stability of GTA protein was investigated by homologous protein conserved analysis, 3D molecular modeling and protein stability prediction. The proband's serological test results showed subtype Ax, and ABO genotyping confirmed that the proband's genotype was ABO*A207/08. Gene sequencing of the proband's father confirmed the characteristic variation of c.539G>C in the 7th exon of ABO gene, leading to the replacement of polypeptide chain p.Arg180Pro (R180P). 3D protein molecular modeling and analysis suggested that the number of hydrogen bonds of local amino acids in the protein structure was changed after the mutation, and protein stability prediction showed that the mutation had a great influence on the protein structure stability. The mutation of the 7th exon c.539G>C of ABO gene leads to the substitution of polypeptide chain amino acid, which affects the structural stability of GTA protein and leads to the change of enzyme activity, resulting in the A2.08 phenotype. The mutated gene can be stably inherited.

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

BackgroundThe 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 methodsThe 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. ResultsThe 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). ConclusionOne 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.

Host genetic regulation of human gut microbial structural variation

Although the impact of host genetics on gut microbial diversity and the abundance of specific taxa is well established1–6, little is known about how host genetics regulates the genetic diversity of gut microorganisms. Here we conducted a meta-analysis of associations between human genetic variation and gut microbial structural variation in 9,015 individuals from four Dutch cohorts. Strikingly, the presence rate of a structural variation segment in Faecalibacterium prausnitzii that harbours an N-acetylgalactosamine (GalNAc) utilization gene cluster is higher in individuals who secrete the type A oligosaccharide antigen terminating in GalNAc, a feature that is jointly determined by human ABO and FUT2 genotypes, and we could replicate this association in a Tanzanian cohort. In vitro experiments demonstrated that GalNAc can be used as the sole carbohydrate source for F. prausnitzii strains that carry the GalNAc-metabolizing pathway. Further in silico and in vitro studies demonstrated that other ABO-associated species can also utilize GalNAc, particularly Collinsella aerofaciens. The GalNAc utilization genes are also associated with the host’s cardiometabolic health, particularly in individuals with mucosal A-antigen. Together, the findings of our study demonstrate that genetic associations across the human genome and bacterial metagenome can provide functional insights into the reciprocal host–microbiome relationship.

Distribution of ABO, RhD Blood Group among Secondary School Students at Bishops Girls Secondary School Rushere Kiruhura Southwestern Uganda

ABO and Rhesus blood group antigens are inherited genetic markers in human blood. Haemoglobin is an efficient transporter of oxygen from the lungs to the tissues and carbon dioxide from tissues to the lungs for exhalation. The study was to determine the distribution of ABO and Rhesus blood groups among secondary school female students. The blood samples of 107 secondary school students at Bishops girls’ Secondary School Rushere kiruhura Southwestern Uganda between July to August, 2023 were collected and their haemoglobin genotypes were determined using HemoTypeSC™ rapid test kit and ABO and Rhesus blood groups were determined by a standard tube method. Results. The frequencies of ABO blood groups among the study population were 20 (18.5%), 24 (22.5%), 06 (5.4%) and 57 (53.6%) for blood group A, B, AB, and O respectively. Also, the distribution of Rhesus (D) positive and Rhesus (D) negative were reported as 98 (91.6%) and 9 (8.4%) each. There was no association between ABO, Rhesus (D) and Hb genotypes observed. Data revealed that Rhesus (D) positive students were statistically higher in number compared to the Rhesus (D) negative students (p=0.000). The sequence of ABO distribution among the rural population in southwestern Uganda is; O &gt; A &gt; B &gt; AB. The frequency of Rhesus (D) negative is very low among secondary school students at Bishops’ Girls Secondary School Rushere Kiruhura Southwestern Uganda Keywords: blood groups, ABO blood group, Rh group, Haemolytic Disease of the Newborn

Rapid ABO genotyping method using loop-mediated isothermal amplification (LAMP) and real-time PCR.

Analyzing all biological evidence at a crime scene presents serious time, budget, and labor constraints. Therefore, selecting valid evidence is crucial for efficient screening. The ABO blood group is a marker that can serve as valid evidence for identifying investigative leads in criminal case. Conventional identification of ABO blood groups using serological methods has only been for blood and is difficult to apply to other body fluids. ABO genotyping was conducted by analyzing single nucleotide polymorphisms (SNP) representative of each blood group. However, this method is time-consuming, expensive, and requires sophisticated instruments. In this study, we developed rapid ABO genotyping method using loop-mediated isothermal amplification (LAMP) and multiplex real-time polymerase chain reaction (PCR). Three SNP sites in the ABO gene (nt 261, 526, and 803) were selected to classify the ABO genotypes. For the specificity test, we performed sequencing of 60 saliva samples to confirm that the genotyping. We conducted experiments to apply ABO genotyping using two amplification methods to mock forensic sample using cotton swab and filter paper. As a result, using LAMP, we successfully identified six ABO genotypes within 30min at a constant temperature (65 ℃). Moreover, by using multiple real-time PCR, it was possible to detect not only the major group but also the subgroup of the ABO genotype (ex. cis-AB). The amplification results using the new methods were in concordance with the sequencing results. Therefore, these ABO genotyping methods are expected to select valid evidence successfully and efficiently at the crime scene.

Serology and genomic analysis of para-Bombay individuals in a hospital in Hunan Province

To investigate the serological and genetic characteristics of para-Bombay patients in a hospital in Hunan Province. A retrospective analysis was conducted on the blood type results of 175 439 hospitalized patients born in Hunan Province from the Third Xiangya Hospital, Central South University from 2016 to 2021. Phenotypes of ABO blood group was analyzed by blood group serology, and molecular biological methods were used to analyze the genotype, including ABO genotyping by polymerase chain reaction-sequence specific primers (PCR-SSP) and fucosyltransferase 1 (FUT1) and fucosyltransferase 2 (FUT2) gene sequencing. The results showed that 3 cases of Ah and 1 case of Bh were detected. FUT1 sequencing showed that there were 2 cases of h3h3, 1 case of h1h1 and 1 case of h302h1, of which h302 (c.302C>T) was the first discovered mutation. FUT2 sequencing revealed that 4 cases were all Se357Se357. The pedigree study showed that the inheritance of para-Bombay blood group was consistent with autosomal dominant inheritance. In conclusion, the FUT1 gene mutations leading to para-Bombay blood group mainly include h3, h1 and h302, of which h3 mutation is the most common.

Type-O Blood Is Not Associated With Elevated Mortality After Trauma: A North American Cohort Study.

Recent studies have presented contradictory findings on the relationship between blood type and mortality in trauma patients. Using the largest population in a study of this type to date, we hypothesized that ABO genotype and Rhesus status would influence trauma-related mortality and morbidity given the relationship between blood type and hemostasis. Data from all trauma patients admitted to level I and level II trauma centers in one city over a five-year period was retrospectively analyzed. Patients were stratified by ABO type. Patient demographics and outcomes were then assessed. Chi-squared and Fisher's exact tests were used to analyze categorical variables. Continuous variables were analyzed using ANOVA or Kruskal-Wallis tests as appropriate. Logistic regression was used to determine independent associations for 28-day mortality and complications. Of 5249 patients, severe injury (ISS >15) was present in 1469. Approximately one-quarter of patients with severe injury received blood products within the first 24 hours. There were no significant variations in demographics or complications between patients of different blood types. Univariate and multivariable regression analysis showed no association between blood type and mortality. However, penetrating injury, lower GCS, higher ISS, blood transfusion within 24 hours, and Asian descent were associated with higher overall mortality. In contrast to previous studies, we found no evidence of an association between blood type and mortality. However, our findings suggest that patients of Asian descent may be at higher risk for mortality following trauma. Further research is warranted to explore this observation.

P‐IG‐43 | Targeted Sequencing Resolves ABO Discrepancy in a Patient with Rare ABO Genotype

P‐IG‐43 | Targeted Sequencing Resolves ABO Discrepancy in a Patient with Rare ABO Genotype

Non-O ABO blood group genotypes differ in their associations with Plasmodium falciparum rosetting and severe malaria.

Blood group O is associated with protection against severe malaria and reduced size and stability of P. falciparum-host red blood cell (RBC) rosettes compared to non-O blood groups. Whether the non-O blood groups encoded by the specific ABO genotypes AO, BO, AA, BB and AB differ in their associations with severe malaria and rosetting is unknown. The A and B antigens are host RBC receptors for rosetting, hence we hypothesized that the higher levels of A and/or B antigen on RBCs from AA, BB and AB genotypes compared to AO/BO genotypes could lead to larger rosettes, increased microvascular obstruction and higher risk of malaria pathology. We used a case-control study of Kenyan children and in vitro adhesion assays to test the hypothesis that "double dose" non-O genotypes (AA, BB, AB) are associated with increased risk of severe malaria and larger rosettes than "single dose" heterozygotes (AO, BO). In the case-control study, compared to OO, the double dose genotypes consistently had higher odds ratios (OR) for severe malaria than single dose genotypes, with AB (OR 1.93) and AO (OR 1.27) showing most marked difference (p = 0.02, Wald test). In vitro experiments with blood group A-preferring P. falciparum parasites showed that significantly larger rosettes were formed with AA and AB host RBCs compared to OO, whereas AO and BO genotypes rosettes were indistinguishable from OO. Overall, the data show that ABO genotype influences P. falciparum rosetting and support the hypothesis that double dose non-O genotypes confer a greater risk of severe malaria than AO/BO heterozygosity.

Truncated glycosyltransferase coding regions in novel ABO alleles give rise to weak A or B blood group expression and discrepant typing results.

Correct ABO blood-group matching between donor and patient is crucial for safe transfusions. We investigated the underlying reason causing inconclusive ABO serology in samples referred to our laboratory. Flow cytometric analysis, ABO genotyping, and sequencing were used to characterize ABO-discrepant blood samples (n = 13). ABOgene variants were inserted in a GFP-containing bicistronic vector to assess A/B expression following overexpression in HeLa cells. Seven novel alleles with nonsense mutations predicted to truncate the encoded ABO glycosyltransferases were identified. While these variants could represent O alleles, serology showed signs of ABO glycosyltransferase activity. ABO*A1.01-related alleles displayed remarkably characteristic percentages of A-positive cells for samples with the same variant: c.42C>A (p.Cys14*; 10%), c.102C>A (p.Tyr34*; 31%-32%, n = 2), c.106dup (p.Val36Glyfs*21; 16%-17%, n = 3) or c.181_182ins (p.Leu61Argfs*21; 12%-13%, n = 2). Transfection studies confirmed significantly decreased A expression compared to wild type. The remaining variants were found on ABO*B.01 background: c.1_5dup (pGly3Trpfs*20), c.15dup (p.Arg6Alafs*51) or c.496del (p.Thr166Profs*26). Although the absence of plasma anti-B was noted overall, B antigen expression was barely detected on erythrocytes. Overexpression confirmed decreased B in two variants compared to wildtype while c.1_5dup only showed a non-significant downward trend. Samples displaying aberrant ABO serology revealed seven principally interesting alleles. Despite the presence of truncating mutations, normally resulting in null alleles, low levels of ABO antigens were detectable where alterations affected ABO exons 1-4 but not exon 7. This is compatible with the previously proposed concept that alternative start codons in early exons can be used to initiate the translation of functional ABO glycosyltransferase.

Blood donor genotyping for prediction of blood group antigens: Results from 5 years' experience (2017-2022).

For 5 years, routine genotyping has been performed for selected blood groups of blood donors in the Copenhagen Capital Region, Denmark. The result is summarized in the following. Genotyping was carried out by an external service provider using the competitive allele specific PCR (KASP) technology. The genotypes were returned to the blood bank and translated into phenotypes by a proprietary IT application. In total, 65 alleles from 16 blood group systems (ABO, MNS, Rh, Lutheran, Kell, Duffy, Kidd, Diego, Yt, Dombrock, Colton, Landsteiner-Wiener, Cromer, Knops, Vel, secretor status) and the HPA1, HPA5 and HPA15 antigens were interrogated. After translation, phenotypes were imported into the laboratory information management system of the blood bank. The results from 31,538 genotyped blood donors were used to calculate the allele frequencies for a Danish blood donor population. ABO genotyping was done for sample ID purposes. Determination of the 1061delC single nucleotide polymorphism (SNP) (NM_020469.2), most frequently characteristic of ABO*A2, was validated against a series of 1287 samples with Dolichos biflorus lectin determination of the A1 phenotype. We report allele frequencies and phenotype frequencies for 16 blood groups from a total of 31,538 genotyped blood donors. Blood products were supplied from a total of 64,312 active blood donors, and of these active blood donors 25,396 (39.5%) were genotyped. These donors represent a valuable resource for patient treatment. This genotyping has enabled the provision of rare genotyped donor blood for patients with alloantibodies and rare reagent cells for serology.

Association between ABO blood group/genotype and COVID-19 in a Japanese population.

An association between coronavirus disease 2019 (COVID-19) and the ABO blood group has been reported. However, such an association has not been studied in the Japanese population on a large scale. Little is known about the association between COVID-19 and ABO genotype. This study investigated the association between COVID-19 and ABO blood group/genotype in a large Japanese population. All Japanese patients diagnosed with COVID-19 were recruited through the Japan COVID-19 Task Force between February 2020 and October 2021. We conducted a retrospective cohort study involving 1790 Japanese COVID-19 patients whose DNA was used for a genome-wide association study. We compared the ABO blood group/genotype in a healthy population (n = 611, control) and COVID-19 patients and then analyzed their associations and clinical outcomes. Blood group A was significantly more prevalent (41.6% vs. 36.8%; P = 0.038), and group O was significantly less prevalent (26.2% vs. 30.8%; P = 0.028) in the COVID-19 group than in the control group. Moreover, genotype OO was significantly less common in the COVID-19 group. Furthermore, blood group AB was identified as an independent risk factor for most severe diseases compared with blood group O [aOR (95% CI) = 1.84 (1.00-3.37)]. In ABO genotype analysis, only genotype AB was an independent risk factor for most severe diseases compared with genotype OO. Blood group O is protective, whereas group A is associated with the risk of infection. Moreover, blood group AB is associated with the risk of the "most" severe disease.

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

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. 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. 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. 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.