A novel ABO O allele caused by a large deletion covering two exons of the ABO gene identified in a Caucasian family showing discrepant ABO blood typing results.

BACKGROUND: The presence of ABO subgroup alleles and unusual O alleles often is associated with discrepant serologic findings in ABO blood group typing. In the ABO gene of a Caucasian female and her daughters who had aberrant ABO phenotypes, a novel ABO O allele characterized by a large deletion that included two exons was identified. METHODS: ABO phenotypes were determined by standard agglutination tests and adsorption-elution studies. Allele-specific sequencing analyses of the ABO gene as well as messenger RNA transcripts were carried out. RESULTS: All three samples showed the same discrepant ABO blood typing results lacking A and B antigens, indicating Blood Group O, whereas anti-A1 and anti-A2 isoagglutinins were not detectable in reverse typing. Analyses of the ABO gene revealed a novel allele characterized by a deletion of 2169 base pairs, including sequences of Intron 1, Exon 2, Intron 2, Exon 3, and Intron 3. Exon 1 was directly joined to Exon 4 in the ABO transcript. CONCLUSION: Because the novel allele was associated with a well-described O allele, the absence of A-antigens in the inherited ABO subtype phenotype may be due to the identified mutation affecting the transmembrane-spanning domain of the encoded protein and impairing the transferase activity.