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

BACKGROUND: 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. MATERIALS AND METHODS: 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. RESULTS: 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 a-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. DISCUSSION: 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.

[Study of the molecular characteristics of a Bweak phenotype due to a novel c.398T>C variant of the ABO gene].

OBJECTIVE: To explore the molecular mechanism for an individual with Bweak subtype. METHODS: Serological methods were used to identify the proband's phenotype. In vitro enzyme activity test was used to determine the activity of B-glycosyltransferase (GTB) in her serum. The genotype was determined by PCR amplification and direct sequencing of exons 5 to 7 and flanking sequences of the ABO gene. T-A cloning technology was used to isolate the haploids. The primary physical and chemical properties and secondary structure of the protein were analyzed with the ProtParam and PSIPRED software. Three software, including PolyPhen-2, SIFT, and PROVEAN, was used to analyze the effect of missense variant on the protein. RESULTS: Serological results showed that the proband's phenotype was Bweak subtype with anti-B antibodies presented in her serum. In vitro enzyme activity assay showed that the GTB activity of the subject was significantly reduced. Analysis of the haploid sequence revealed a c.398T>C missense variant on the B allele, which resulted in a novel B allele. The 398T>C variant has caused a p.Phe133S substitution at position 133 of the GTB protein. Based on bioinformatic analysis, the amino acid substitution had no obvious effect on the primary and secondary structure of the protein, but the thermodynamic energy of the variant protein has increased to 6.07 kcal/mol, which can severely reduce the protein stability. Meanwhile, bioinformatic analysis also predicted that the missense variant was harmful to the protein function. CONCLUSION: The weak expression of the Bweak subtype may be attributed to the novel allele of ABO*B.01-398C. Bioinformatic analysis is helpful for predicting the changes in protein structure and function.

The Significance of RHD Genotyping and Characteristic Analysis in Chinese RhD Variant Individuals.

Background: RhD is the most important and complex blood group system because of its highly polymorphic and immunogenic nature. RhD variants can induce immune response by allogeneic transfusion, organ transplantation, and fetal immunity. The transfusion strategies are different for RhD variants formed by various alleles. Therefore, extensive investigation of the molecular mechanism underlying RhD variants is critical for preventing immune-related blood transfusion reactions and fetal immunity. Methods: RhD variants were collected from donors and patients in Zhejiang Province, China. The phenotypes were classified using the serologic method. The full coding regions of RHD gene were analyzed using the PCR-SBT method. The multiplex ligation-dependent probe amplification (MLPA) assay was used to analyze the genotype and gene copy number. SWISS-MODLE and PyMOL software were used to analyze 3D structures of RhD caused by the variant alleles. The effect of non-synonymous substitutions was predicted using Polymorphism Phenotyping algorithm (PolyPhen-2), Sorting Intolerant From Tolerant (SIFT), and Protein Variation Effect Analyzer (PROVEAN) software. Results: In the collected RhD variants, 28 distinct RHD variant alleles were identified, including three novel variant alleles. RH-MLPA assay is advantageous for determining the copy number of RHD gene. 3D homology modeling predicted that protein conformation was disrupted and may explain RhD epitope differential expression. A total of 14 non-synonymous mutations were determined to be detrimental to the protein structure. Discussion: We revealed the diversity of RHD alleles present in eastern Chinese RhD variants. The bioinformatics of these variant alleles extended our knowledge of RhD variants, which was crucial for evaluating their impact to guide transfusion support and avoid immune-related blood transfusion reactions.

[Analysis of erythroid-specific blood group genes using un-mobilized peripheral stem cells cultured in vitro].

OBJECTIVE: To analyze specific expression of blood group genes using nucleated erythroid cells cultured from un-mobilized peripheral stem cells in vitro. METHODS: Hematopoietic stem cells(HSC) bearing the CD34 antigen were isolated from peripheral blood by centrifugation and magnetic beads sorting, followed by suspension culture in vitro. Cells were collected from medium on various stages and analyzed by immunofluorescence. The RNA transcription of RH and ABO blood group genes was analyzed using culture cells on day 12. RESULTS: A total of(3.19±0.13) ×10 (4) CD34+cells were isolated from about 50 mL peripheral blood with a recovery rate of 67.3%±2.7%. The cells amount in erythroid-lineage culture system on day 9 reached a plateau of a 237.1±15.5-fold amplification of the initial cell input. The stem cell-specific CD34 antigen was dropped off, while the erythroid-specific CD235a and CD240D antigens were increased in culture period. RHD/CE and ABO genes can be amplified using RNA extracted from culture cells on day 12, and genotypes of Rh and ABO systems by DNA sequencing were consistent with their serologic phenotypes. CONCLUSION: A method was established to analyze the gene expression of erythroid blood group derived from un-mobilized peripheral stem cells cultured in vitro. It can be used to study the expression of various erythroid-specific genes.

[A rare p phenotype caused by a 26-bp deletion in α 1,4-galactosyltransferase gene].

OBJECTIVE: To delineate serological features and genetic basis for a rare p phenotype of P1Pk blood group system found in a Chinese individual. METHODS: Serological assaying was carried out for a proband with unexpected antibody found in his serum using specific antibodies and panel cells. Coding regions and flanking introns of α 1,4-galactosyltransferase gene (A4GALT) associated with the p phenotype were screened with polymerase chain reaction and DNA sequencing. RESULTS: A rare p phenotype of the P1Pk blood group system has been identified with red blood cells from the proband, whose serum contained anti-Tja antibody which can agglutinate and hemolyze with other common red blood cells. Other members of the proband's family were all normal with P1 or P2 phenotype. DNA sequencing has identified in the proband a homozygous 26 bp deletion at position 972 to 997 of the A4GALT gene. The deletion has caused a shift of the reading frame, resulting in a variant polypeptide chain with additional 83 amino acid residues compared with the wild-type protein. Other family members were either heterozygous for above deletion or non-deleted. CONCLUSION: A 26 bp deletion at position 972 to 997 of the A4GALT gene has been identified in a Chinese individual with p phenotype.