Abstract: Objective To analyze a discrepancy in results of forward/reverse ABO blood grouping with molecular analysis and provide knowledge for safe blood transfusion.Methods Column gel testing was used for serological ABO blood grouping. Genomic DNA was extracted from whole blood and PCR-SSP was used for ABO genotyping. PCR was performed to amplify ABO exons 1 to 7 and the amplification products were sequenced directly. The obtained sequences were compared with wild type A101 to identify sequence variation.Results Blood grouping indicated the discrepant results of forward/reverse ABO typing. Forward typing produced blood group O,while reverse typing produced blood group A as only anti-B isoagglutinins were present. A monoclonal anti-AB antibody detection revealed a weak agglutination with patient's RBCs. ABO genotyping with PCR-SSP indicated a heterozygous O1/A type,and further PCR and ABO exons sequencing identified a new 248A>G missense mutation in exon 6,which led to the replacement of Aspartate at position 83 with glycine. PCR-SSP using newly designed 248A>G mutation-specific primer was performed to investigate the frequency of this new mutation among regular blood donors but none turned out to be positive.Conclusion sThis ABO gene 248A>G mutation is associated with the absence of anti-A isoagglutinins and weak A antigen expression.

Key words: ABO blood group, Genotyping, PCR-SSP, DNA sequencing, Gene variant