[Molecular basis of the B(A) phenotype].

OBJECTIVE: To explore the serological and molecular characteristics of a female with the B(A) phenotype and safety issues related to her blood transfusion.

METHODS: The B(A) phenotype of the proband was confirmed by serological testing. Her genotype was determined by using polymerase chain reaction-sequence specific primer (PCR-SSP) and direct sequencing of exons 6 and 7 of the ABO locus. Clinical condition of her blood transfusion was also reviewed.

RESULTS: Both A and B antigens were detected on the red blood cells derived from the proband, while anti-A antibody was detected in her serum. The result of PCR-SSP suggested that she has a B/O02 phenotype. DNA sequencing revealed presence of 297A>G, 526C>G, 657C>T, 700C>G, 703G>A, 796C>A, 803G>C and 930G>A mutations. The genotype of the proband was deduced as B(A) 02/O02. Compared with the B101 allele, the B(A)02 allele has a nucleotide change (C>G) at position 700, which resulted in substitution of an amino acid (P234A). The result of cross match testing between the proband and two donors with an A2 B phenotype was consistent. No adverse reaction was observed after the transfusion.

CONCLUSION: 700G>C of B allele can result in the B(A) phenotype, which is similar to A2 B. Blood donors for individuals with the B(A) phenotype should include those with an A2 B phenotype.