Abstract: Objective To identify the Bel subtype of c.586T>C mutation by third-generation technology, and analyze the serological characteristics of the Bel subtype blood group system. Methods The ABO blood type phenotyping examination relies on serological methods. In cases where there is a discrepancy between the ABO forward and reverse typing in a familial sample, the ABO gene's 6th and 7th exons are sequenced using Sanger sequencing. The full-length haplotype analysis of ABO gene was performed in 3 samples of proband and her children using the PacBio third-generation technology. Results The proband's serological phenotype is identified as the Bel subtype. Sequence analysis reveals a mutation at position c.586T>C in the 7th exon of the ABO gene. The haplotype analysis through third-generation technology confirms the proband's ABO genotypes as ABO*BEL (c.586T>C)/O01.02. As for their eldest son and daughter, their genotypes are determined as ABO*A1.02/BEL (c.586T>C) and ABO*B.01/ BEL (c.586T>C), respectively. Conclusion The c.586T>C mutation at the site is responsible for the molecular basis of the Bel phenotype in this case. PacBio third-generation technology enables accurate identification of ABO subtype haplotypes.

Key words: The Bel subtype, Blood group serology, Molecular mechanism, Haplotype identification, PacBio third-generation technology