Molecular Genetic Analysis of the ABO Blood Group System: 2. Cis-AB Alleles

We have determined the nucleotide sequence of the coding region in the last two coding exons of ABO genes from two cis-AB individuals (genotype cis-AB/O) with no consanguinity. In this region, cis-AB alleles from these 2 individuals were identical to one another while different from the A1 allele by two nucleotide substitutions. Both of these nucleotide substitutions result in amino acid substitutions. The first substitution is identical to the one previously found in the A2 allele. The other substitution is found at the fourth position of the four amino acid substitutions which discriminate A1 and B transferases.