Identification and analysis of a novel A allele with a c.565A > G variant on the ABO*A1.02 allele leading to subtype A: A case report.

RATIONALE: The ABO blood group system typically includes 4 phenotypes: type A, type B, type O, and type AB. ABO subtypes refer to further subdivisions within these 4 blood types. We report a case of subtype A, focusing on elucidating the molecular mechanisms of this rare genotype.

PATIENT CONCERNS: The patient is a 34-year-old pregnant woman at 39 weeks gestation presenting with preterm labor. She exhibits forward and reversed stereotypic incompatibility.

DIAGNOSES: All exons of ABO were amplified by PCR and sequenced using Sanger sequencing. Furthermore, only the seventh exon was sequenced by TA cloning for haplotype analysis. Sequencing analysis revealed that the genotypes ABO*A1.02 and ABO*O.01.02, and the mutation c.565A > G, which has never been reported for the A allele, occurred based on ABO*A1.02.

INTERVENTIONS: In addition to serological test, the patient underwent further molecular biology test.

OUTCOMES: It led to identify a novel allele with subtype A serological characteristics, caused by the c.565A > G variant, which leads to a weakened A antigen.

LESSONS: Given its rarity, it is advisable to employ dual serological and molecular biological testing mechanisms during complex ABO blood typing to prevent missed detection and misclassifications, thereby effectively promoting transfusion and compatibility safety.