Abstract: Objective To investigate the genetic background of ABO blood group-incompatible specimens in 4 cases. Methods The blood group serological test was used to identify the subtypes of ABO positive and negative stereotyping inconsistency; PCR was used to amplify 7 exons of the ABO gene; the sequence analysis was directly performed for 7 exons. Results The blood group serology test indicated that 4 specimens were ABO subtypes, namely Bx (1 case); ABx(1 case); Ax (2 cases). The genes by direct sequencing revealed that Bx and ABx change were not detected in exons 1~6 on the molecular basis of ABO^*B.01, only the mutation at position 449A>G in exon 7 of B allele. The exons 1~6 change of 2 Ax cases were not detected on the molecular basis of ABO^*A1.01, only the mutation at position 467C>T and the insertion of a base T at position 798 in exon 7 of A allele. Changes in above gene loci resulted in changes in the serological phenotype of the ABO blood groups, which manifested as ABO subtype. Conclusion The study revealed the molecular genetic background of ABO subtypes in 4 cases. Two novel ABO alleles were found, namely c.449A>G single locus mutation, c.467C>T mutation and c.798insT single base insertion.

Key words: ABO subtype, Blood group serology, Direct sequencing, Gene mutation