RESUMO
OBJECTIVE: To investigate the identification and molecular biological mechanism of a case of B(A)04 allele. METHODS: The ABO blood groups of the proband and his nine family members were analyzed serologically and DNA sequencing was used to accurately determine the genotypes of these ten specimens. The cartoon models of local active center of enzymes of the GTA,GTB and the GTB mutant were constructed to explore the possible molecular mechanism leading to abnormal enzyme-catalyzed A antigen synthesis. RESULTS: The serological results suggested that the ABO blood groups of the proband, his elder brother and his maternal grandmother were AweakB or B(A); the ABO blood group of his mother was type AB, his uncle and elder aunt were type B, and his father was type O. ABO blood group gene sequencing results showed that 6 out of 10 members of the family carried the B(A)04 allele. Molecular structure models suggested that the spatial distance of critical amino acid residues in the catalytic center of the GTB mutant enzyme was greater than that of GTB, which might cause the enzyme to abnormally catalyze the synthesis of A antigen. CONCLUSION: The characteristics of serological reactions of B(A) blood subgroup are complicated, and its identification needs to be combined with molecular biology and pedigree investigation. It is speculated that the B(A) phenotype may be associated with a larger volume of the catalytic center in the GTB mutant.
