Identification of a novel A² allele derived from the A transferase gene through a nucleotide substitution G539C

Background and Objectives: The A₂ is a very rare phenotype in the ABO blood group system in the Oriental population. It corresponds to a special ABO allele encoding a glycosyltransferase that is capable of synthesizing A₂ antigens, which is weaker than the typical A antigen. In this study, we report a novel A² allele in two unrelated Taiwanese individuals. Materials and Methods: Two individuals were identified as the A₂ phenotype based on the standard ABO serological test. For analysing the A² allele, both direct sequencing and gene cloning of the ABO gene were performed. Results: The ABO gene of the two A₂ individuals was composed of O¹ and A² alleles, and the novel A² allele has a 539G > C that results in the amino acid change Arg18OPro. The mutation was not detected in the general group A population. Conclusion: We report for the first time that a 539G > C mutation represents a new molecular basis for the A₂ blood type. The amino acid substitution from arginine to proline may have effect on the expression of A antigen.