Abstract: Objective To analyze the serological and molecular biological characteristics of Bweak subtype probands and their families, and to explore the molecular mechanism and genetic characteristics of Bw27 variant. Methods Serological methods were used to detect ABO blood group antigens and antibodies in the proband and family members. Further serological detection was conducted by absorption and elution. Fluorescence PCR was employed for genotyping, and the 6th and 7th exons of the ABO gene were amplified and sequenced. Results The proband's ABO serological test showed inconsistent in p forward and reverse typing, and the absorption and elution test detected weak B antigen on the proband's red blood cells, with a serological phenotype similar to Bel. The genotyping result was B/O1, and gene sequencing revealed a c.905A>G mutation in the 7th exon of the ABO gene, with a genotype of ABO*BW.27/ABO*O.01.01. Pedigree testing results showed that the proband's mother carried the ABO*BW.27 allele, consistent with familial genetic characteristics. Conclusion The c.905A>G mutation in the 7th exon of the ABO gene leads to the substitution of aspartic acid at position 302 with glycine, resulting in weak expression of B antigen, which is a characteristic mutations of ABO*BW.27 that can be distinguished from Bel by gene sequencing. A single nucleotide point mutations can cause specific changes in glycosyltransferase and can be inherited to produce specific serological phenotypes in offspring. Blood types should be comprehensively determined based on serological results with genotyping and DNA sequencing results.

Key words: Bweak subtype, ABO*BW.27, Absorption and elution, Gene sequencing