Mutation of ABO gene in Thai blood donors with A₃ phenotype

The ABO system is the most important of all blood group systems in transfusion practice. The subgroup gives a weak reaction when treated with anti-A or anti-B. The most common subgroup found in Thai blood donors is subgroup A₃, which is characterized by mixed-field agglutination when reacted with anti-A and anti-A,B, was caused by mutation in the ABO gene, especially in the exon 7. In the present study mutation in A₃ were charactered in exon 7 of the ABO gene in 10 A₃ phenotype Thai blood donors from the National Blood Centre, Thai Red Cross Society by PCR amplification and DNA sequencing. Mutations in exon 7 were identified in the A allele of six cases. In four cases, mutations were detected at positions 646T>A, 681G>A, 771C>T and 829G>A. One case showed a double mutations at positions 467C>T and 745C>T and one case showed a mutation at position 467C>T. Four cases showed wild type exon 7 as A101 allele. These mutations were previously reported in BGMUT database and no novel mutation was identified. These data suggest genetic heterogeneity in A₃ phenotype in Thai blood donors.