Molecular analysis of the O alleles at the blood group ABO locus in populations of different ethnic origin reveals novel crossing-over events and point mutations.

The blood group ABO genotypes of 138 group O individuals with three different ethnic origins in Brazil were determined, including Whites, Blacks and Amerindians. Several previously undescribed O alleles were found, predominantly in the Black group, in which about a third of the samples did not conform to previously known O allele structures. It has been well documented for the first time that some new alleles can arise from crossing-over events between known alleles in the ABO system. This was made possible by both restriction endonuclease analysis and direct sequencing of exons 3-7 in the ABO gene. The anticipated relatively high frequency of some of these new alleles in certain populations, necessitates great care when interpreting results from existing genotype screening methods.