LAUSR

The ABO blood group system is the most clinically important in blood transfusion. The decreased expression levels of A or B antigens of the ABO subtype often present difficulties in blood typing and cross-matching for clinical transfusion. B3 is the most common B subtype, which has a frequency of approximately 1 in 900 in the Chinese population. The underlying mechanisms of the B3 phenotype were diversified. Several mutations in the exons, splicing site, and mutations in the promoter have been reported for B3. 1,2 Recently, a regulatory element was identified in the first intron of the ABO gene with a functional GATA-1 erythroid transcription factor binding site. Studies have shown that mutations in the erythroid cell–specific regulatory element (15.8 kb) can cause variant ABO phenotypes. Here, we report a novel single-nucleotide substitution within the GATA motif (C>T substitution at Position c.28 1 5885) in the 15.8-kb site on the B allele in one individual with the B3 phenotype.