Three missense mutations, including a novel 860C>T transition, and allelic enhancement phenomenon associated with ABO blood subgroups A in Taiwan

BACKGROUND: It was estimated that approximately 25 percent of Taiwanese residents were ABO blood group A. Many subgroups of A, however, revealed ambiguous serologic typing results. This study aimed to delineate the molecular basis of the A3, Ax, and weak A phenotypes. STUDY DESIGN AND METHODS: Serologic analyses including adsorption and elution assay, serum transferases activity assay, and saliva test were performed to determine the unique phenotypes of these samples. DNA sequencing and polymerase chain reaction–restriction fragment length polymorphism were performed to further investigate the relationships between the genetic characteristics and phenotypic features of these samples. RESULTS: Three single-nucleotide transitions (745C>T, 820G>A, and a novel 860C>T) were found in nine A3/A3B cases. In addition, the Ax and A3B subjects shared the same 860C>T mutation. This Ax allele with 860C>T transition expressed A3B phenotype in Ax/B101 heterozygote but Ax phenotype in Ax/O01 heterozygote. This allelic enhancement was also observed in the weak A family with Aw05 allele, which was previously not found in Taiwan. CONCLUSION: This allelic enhancement phenomenon was prone to cause serologic discrepancy between parents and children. Genotyping could help us to resolve this problem. Thus, a novel mutation is reported among Taiwanese blood donors.