The B allele with a 5·8 kb deletion in intron 1 of the ABO gene is the major allele in Japanese individuals with B m and A 1 B m phenotypes

B m and A 1 B m phenotypes are the most frequent ABO variants in the Japanese population. The B antigen on B m red blood cells is only detectable by adsorption and elution tests, and plasma B‐transferase activity is usually detected at half or less levels compared with that of common B. Recently, a B allele lacking an erythroid cell‐specific transcription enhancer in intron 1 of the ABO gene was identified from individuals with B m and A 1 B m phenotypes, which could explain the unique serologic properties of B m . In the Japanese Red Cross Society, eight Blood Centers tested blood samples from donors throughout Japan and collected blood samples from 888 B m and 415 A 1 B m individuals. DNA analysis revealed that 1300 of 1303 (99·77%) individuals had the B allele with a 5·8 kb deletion (c.28 + 5110_10889del), which included the enhancer element.