B/O blood group chimera identified by PacBio third-generation sequencing: a case report

[Objective] To determine the blood group of a patient with ABO forward and reverse typing discrepancies using PacBio third-generation sequencing (TGS) technology, and to explore the application of serological methods and molecular biological methods in identifying chimeric blood groups. [Methods] The blood group serology testing was utilized. PCR amplification and Sanger sequencing of exons 1-7 of the ABO gene were conducted. The full-length sequencing of the ABO gene and haplotype analysis were carried out by PacBio third-generation sequencing technology. Short tandem repeat typing was also performed. [Results] Serological testing suggested a suspected B subtype, which appeared mixed field of vision with anti-B antibodies and showed 2+mf strength agglutination. Sanger sequencing revealed a homozygous ABO* O. 01. 01 genotype with the c. 261delG mutation in exon 6. PacBio TGS identified a predominant ABO* O. 01. 01/ABO* O. 01. 01 genotype and a low proportion of ABO* B. 01. Nine locis of twenty short tandem repeat (STR) locis showed three or four types of genotypes in STR analysis, confirming chimerism. [Conclusion] The sample was a B/O blood group chimerism. The low proportion of ABO* B. 01 chimerism was the true cause for the serological mixed field of vision. The PacBio third-generation sequencing technology can not only determine the ABO gene haplotype but also detect a low proportion gene chimerism in ABO blood groups.