Abstract: Objective To investigate the molecular mechanism in a case of ABO typing discrepancy. Methods A blood donor was enrolled on March 8, 2023 at the Shenzhen Blood Center. The ABO phenotype was identified using serological testing methods. Enzyme activity assay was performed to determine the activity of B-glycosyltransferase (GTB) in serum. ABO gene exons 1-7 and flanking sequences were amplified and subjected to Sanger sequencing. Haplotypes were determined by isolating haploid DNA using TA cloning technology and subsequent sequencing. Results Serological analysis revealed the forward type as O and the reverse type as O (difference in titer≥2). Enzyme activity assay conducted in vitro did not detect any GTB activity. Haplotype cloning and sequencing analysis identified the ABO allelic genotype of the participant as c.213-217delC in ABO*B.01/ABO*O.01.02. A single-base deletion, c.213-217delC, was observed in the ABO*B.01 allele gene, resulting in the substitution of glutamine with serine at position 73 of GTB (p.Gln73Ser) and premature termination codon appearance (73fs+3aaX). This variation has not been reported previously. Conclusion The frame-shift mutation caused by the single-base deletion c.213-217delC on the ABO*B.01 allele gene results in the loss of B antigen.

Key words: ABO blood group, Gene sequencing, Single-base deletion