Analysis of weak expression of A antigen induced by ABO gene mutation

Objective This study aims to perform blood group genotyping on patients with weak antigen expression detected by ABO serology and analyze the causes of weak antigen expression. Methods Serological detection was carried out by the microcolumn gel method. Blood group genotyping was conducted by PCR combined with direct sequencing. The enhancer, promoter, exons 1-7, and adjacent intron regions of the ABO blood group gene in the patients were tested. The software PolyPhen-2 was used to predict the nucleotide function of mutations and to generate a 3D structural model. Results In one male patient, the red blood cells showed weak agglutination with anti-A antibody (2+) and agglutination with anti-B antibody (4+). The patient’s serum showed weak agglutination with A1 cells (2+), and no agglutination with B cells and O cells. The serological phenotype of the ABO blood group was AweakB, with both the direct antiglobulin test and antibody screening test being negative. The results of DNA sequencing showed that there were c.297 A>G mutation in exon 6, and c.526 C>G, c.657 C>T, c.703 G>A, c.796 C>A, c.803 G>C, c.930 G>A and c.940 A>G mutations in exon 7. According to the International Blood Transfusion Association database, the c.940 A>G mutation leads to p.Lys314Glu mutation in the ABO gene-encoded glycosyl transferase A (GTA), resulting in decreased A enzyme activity. The patient’s genotype was ABO*AW.37/B.01. Conclusions In this patient, exon 7 of the ABO blood group gene has a c.940 A>G mutation. This mutation site can change the encoded amino acid, namely p.Lys314Glu, resul-ting in weak expression of A antigen.