ABO*B.01-like c.239+5G>A. Aberrant ABO blood group phenotypes

At the ABO blood group gene locus a broad genetic diversity with polymorphisms associated with phenotypic variations has been reported. Here we describe a novel ABO*B.01-like allele, characterized by an nucleotide substitution in the coding sequence of the ABO gene identified in a patient with aberrant ABO phenotype. Serologic ABO blood group typing (Bio-Rad), allele-specific amplification of ABO Exon 1 to Exon 7 were carried out. Sequencing of the ABO gene and regulatory regions was done (AB 3500, Applied Biosystems). ABO blood grouping using monoclonal and human antibodies showed absence of A and B antigens in routine blood grouping indicating an ABO blood group O phenotype. Data concerning adsorption/elution studies of the individuals´ RBCs to detect residual expression B antigen were not available. Allele-specific sequence analysis revealed a novel ABO*B.01 - like allele with a c.239+5G>A substitution in Intron 5 inherited with an inactive ABO*O1.01.01 allele in trans. The novel insertion is located at the intron-exon junction and may result in aberrant ABO mRNA transcripts.