ABO*A1-like allele (c.29-5T>C)
Discrepant serological findings in ABO blood group typing often are the results of ABO gene variants, influencing the ABO transferase activity causing unusual ABO phenotypes. In a sample with aberrant ABO blood group A phenotype, a novel ABO allele was identified. Material and methods ABO blood groups were determined with standard serologic and gel matrix techniques (Bio-Rad). Haplotype specific sequence analyses of the ABO allele covering exons 2 to 7, including the 3´region of intron 1 and the 3´untranslated region of the gene were performed by allele-specific long-range PCR (Peqlab Biotechnology) and direct sequencing (AB 3500 Genetic analyzer, Applied Biosystems). The regulatory regions of ABO (enhancer, promoter, Intron 1 +5.8 kb Gata site) were analyzed. Results The ABO antigen forward typing detected a mixed-field reaction with anti-A and anti-AB antiserum and no reaction with anti-B, indicating an unusual A phenotype. Allele-specific sequencing detected a variation in intron 1 at nucleotide position 12978 at the junction of intron 1 and exon 2 [c.29 – 5T>C], suggesting the presence of a splice site mutation. By analyzing ABO mRNA, multiple transcript variants were identified (n=6) and a cDNA variant, characterized by a large deletion including exon 2 and exon 3, was found. Conclusion: Investigation of ABO mRNA identified a deletion of exons 2 and 3 in an ABO*A1-like mutated transcript variant. The identified variant was associated with a splicing defect and is most likely to be responsible for the aberrant ABO blood group phenotype observed.