Weak blood group B phenotypes may be caused by variations in the CCAAT-binding factor/NF-Y enhancer region of the ABO gene.

BACKGROUND

Binding of CCAAT-binding factor NF-Y (CBF/NF-Y) to a 43-bp repeat unit in the minisatellite region in the 5' region of the ABO gene (CBF/NF-Y enhancer region) plays an important role in regulating the transcription of ABO genes. The common ABO alleles were found to have CBF/NF-Y enhancer regions with specific numbers of 43-bp minisatellite repeats.

MATERIAL AND METHODS

Blood samples from four healthy blood donors with weak B phenotypes were subjected to extensive ABO genotyping, including nucleotide sequencing of the 5' regulatory region containing the CBF/NF-Y enhancer.

RESULTS

The coding region of the ABO genes exhibited common ABOB101-heterozygous genotypes in all samples, but unexpected variations were observed in the CBF/NF-Y enhancer region. In two cases, the CBF/NF-Y enhancer motifs did not exhibit the expected ABO allele dependency. One, an AB(weak) sample was heterozygous for ABOA101 and ABOB101 but homozygous for the ABOB101-specific CBF/NF-Y motif. The second had a common ABOB101/ABOO01 genotype but was heterozygous for ABOA101- and ABOO01-specific enhancer motifs. In the other two samples, novel CBF/NF-Y motifs were found. One contained a shortened version of an otherwise ABOB101-specific CBF/NF-Y motif, and the other had a single-base substitution located 12 bp upstream from the beginning of the first 43-bp repeat of an ABOB101-specific CBF/NF-Y enhancer sequence.

CONCLUSION

The frequency of variations in the CBF/NF-Y region of the ABO gene in these samples with presumably common ABO*B101 alleles suggests that weak blood group B phenotypes may be caused by sequence variations in the CBF/NF-Y regulatory region.