CONCLUSION: The ABO intron 1 variants revealed significant association with the ABO*A1 allele and the A phenotype. However, the intron 1 genotype does not exclude variant alleles causing weak A phenotypes. With the introduction of reliable tag, single nucleotide variants for the A(1), A(2), B, and O blood groups and the genotyping instead of phenotyping of the ABO blood group are getting more feasible on a routine …