Identification of a Novel B Allele with c.318C>T on the ABO*B.01 Background

The ABO blood group system is critical in transfusion medicine, organ transplantation, and neonatal hemolytic disease prevention. ABO antigen expression is regulated by the ABO gene, where single nucleotide polymorphisms (SNPs) may significantly alter antigenicity.

Two cases were analyzed: a 32-year-old pregnant woman (Proband 1) and a 71-year-old patient with respiratory failure (Proband 2). ABO serological typing was conducted using automated microcolumn glass bead and saline tube methods for forward and reverse typing. Genomic DNA was extracted using commercial kits, and the ABO gene was sequenced via PacBio RS and Sequel Systems (third-generation sequencing) to identify mutations.

Serological testing revealed weakened B antigen expression. Full-length ABO gene sequencing identified the A1.02 allele and a c.318C>T mutation on the B.01 allele. This synonymous substitution (p.Asn106Asn) did not alter the encoded amino acid. No additional mutations were detected in promoter, enhancer, or intronic regions. The sequence was deposited in GenBank (accession: PP836062).

This study reports the c.318C>T mutation in the B.01 allele as a potential contributor to weakened B antigen expression in two Chinese individuals.