Polymorphisms at the ABO locus in subgroup A individuals

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Abstract
Background: The common ABO allele sequences are known, but little or no genetic information is available on the rare but important A subgroups. Study Design and Methods: Blood group ABO polymorphism was analyzed in genomic DNA from 45 rare subgroup A individuals by sequence‐specific primer polymerase chain reaction and amplified fragment length polymorphism investigating exons VI and VII in the ABO genes. These methods are used to detect specific mutations only, and not all changes that might be present can be detected. ABO genotypes discriminating six alleles (A1, A2, B, O1, O1var, and O2) were determined. Results: The C→T substitution at nucleotide position 467 (C467T) is not restricted to A2 and cis‐AB individuals, but was found also in some A subgroups. Detection of the functionally more relevant C1060‐single‐point deletion in A2 was accomplished by a novel sequence‐specific primer polymerase chain reaction approach. A 100‐percent correlation between the C467T and the C1060‐mutations was found. Fifteen of 17 samples showing the T646A mutation (described earlier in one case of Ax) showed a positive correlation with the C771T mutation in a frequently occurring O1var allele. The two exceptions were defined serologically as Ax. Conclusion: Indications have been found of an evolutionary relationship between A1 alleles and Ael and A3 subgroups as well as between A2 alleles and Aend and Aweak subgroups. Genetic heterogeneity within the Ax and Aint subgroups was also seen.