The nature of diversity and diversification at the ABO locus.

In this study we analyzed the complete genomic sequences, except intron 1, and 2 regulatory regions of 6 common (ABOA101, ABOA201, ABOB101, ABOO01, ABOO02, and ABOO03) and 18 rare ABO alleles, 3 of which were new. This was done by phylogenetic analysis and correlating sequence data with the ABO phenotypes. The study revealed multiple polymorphisms in noncoding regions. The intron-based phylogenetic analysis revealed 5 main lineages: ABOA, ABOB, ABOO01, ABOO02, and ABOO03. The genomic sequences of most rare ABO alleles differed slightly from those of the common alleles. Singular mutations or hybrid alleles were most common, but a few exhibited mosaic sequence pattern containing multiple exon and/or intron motifs from other ABO lineages. Thus, both an accumulation of mutations as well as an assortment of the mutations by recombination seems to be responsible for the ABO gene diversity. The prevalence of replacement mutations indicates positive selection for allelic diversity. Phenotype-genotype correlation showed that sequence variations within the complete coding sequence can affect A- and B-antigen expression. All variant ABOA/B alleles and one new ABO*O03-like allele were associated with weak ABO phenotypes. These findings are suggestive of the requirement of a comprehensive coding sequence database for sequence-based phenotype prediction.