Serology and gene sequence analysis of rare subgroup A₃ blood group

To investigate the serological phenotypic characteristics and possible mechanism of subgroup A₃, a blood donor's ABO phenotypes were detected by the conventional microcolumn gel method and classic tube method. N-acetylgalactosaminyl transferase activity was detected by the non-radioactive phosphate coupling method. ABO subtype genotyping was determined by PCR-SSP and exons 1-7 of ABO gene were analyzed by Sanger sequencing. The donor's blood type was subgroup A₃ as evaluated by serological test. There was no N-acetylgalactosaminyl transferase activity in the red blood cells and weak N-acetylgalactosaminyl transferase activity in the plasma. The ABO blood group genotyping result was ABO*AO1, and the gene sequencing result was confirmed as A221/O01. Sequencing results showed two mutations, 467C>T and 607G>A in exon 7 in ABO*A allele. In conclusion, it is suggested that the ABO blood group of the donor be subgroup A₃, which may be induced by mutations 467C>T and 607G>A, and led to a decrease in N-acetylgalactosaminyl transferase activity and resulted in weakened A antigen.