Introduction - The transcription of ABO gene is known to be regulated by a promoter and other transcription factor. Here, we identified two weak ABO subgroup alleles associated with -72G>A in the ABO promoter and explored the mechanisms that leads to A3B and B3 phenotype.
Materials and methods - Serology studies were performed to investigate the phenotype. The DNA sequence of ABO gene was analyzed to identified the genotype of the individuals. And the pedigree analysis was carried out to validate the hereditary background of the mutation and phenotype. The promoter activity was evaluated by reporter assays.
Results - Two individuals showed a discrepancy between the forward and reverse typing according to the serological results. The subject 1 was suspected to be A3B phenotype and subject 2 was B3 phenotype. According to the results of the direct sequencing and pedigree analysis, we identified a same mutation -72G>A in the ABO promoter on A allele in one A3B individual and on B allele in a B3 individual. The reporter assays showed the mutation -72G>A could reduce the promoter activity by 70% compared to the activity of the wild-type promoter and resulting in strong mixed-field agglutination.
Conclusion - Two “3” alleles were identified, and both associated with -72G>A in the ABO promoter. The substitution -72G>A can impair the transcription of ABO gene by reducing the promoter activity.
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