Sequence variants in the proximal promoter and +5.8-kb site of ABO in Koreans with weak B phenotypes

Background and Objectives: Several studies on Chinese and Japanese populations have revealed that a substantial proportion of weak B subgroups are caused by variants in the major regulatory regions of ABO, the proximal promoter, CCAAT-binding factor/NF-Y binding site and +5.8-kb site. We performed molecular analyses of these regions in Koreans with weak B phenotypes. Materials and Methods: This study included 16 samples with weak B phenotypes (4 B₃, 1 B_w, 5 A₁B₃ and 6 A₁B_w) harbouring no subgroup-causing variants in ABO exons 6 and 7. These samples were subjected to sequencing analysis of exons 1–5 and the major regulatory regions of ABO. Results: Of the 16 samples, 14 were found to carry a sequence variant either in the proximal promoter (g.4991_5008del [n = 3]) or the +5.8-kb site (g.10893G>A [n = 4] and g.10925C>T [n = 7]). The remaining two samples were found to contain no subgroup-causing variants. Conclusion: Our study demonstrates that sequence variants in the proximal promoter and +5.8-kb site account for a substantial proportion of weak B subgroups in Koreans, suggesting that molecular analysis of these regions is essential for the accurate determination of ABO genotypes in Koreans with weak B phenotypes.