ABO gene mutation c.815_816insG in an African individual forms a novel Ael allele

Serological and molecular characterization of novel ABO variants including an interesting B(A) subgroup

BACKGROUND

ABO grouping is the most important pretransfusion testing that is directly related to the safety of blood transfusion. A weak ABO subgroup is one of the important causes of an ABO grouping discrepancy. Here, we investigated the characterization of four novel ABO variants including a novel B(A) subgroup.

STUDY DESIGN AND METHODS

RBCs were phenotyped by standard serology methods. The full coding regions of the ABO gene and the erythroid cell-specific regulatory elements in intron one were sequenced. The effect of the possible splice site variant was predicted by Alamut software. The 3D structural modeling of three relative B(A) enzymes (p.Met214Thr, p.Met214Val, and p.Met214Leu) were performed by PyMOL software.

RESULTS

Four novel ABO alleles were identified with weak ABO expression in this study, in which two would lead to premature terminations, and two resulted in amino acid changes. In silico analysis revealed that the splice site variant c.155G>T had the potential to alter splice transcripts. 3D structural view shown that the variant amino acid position 214 was spatially adjacent to the donor recognition pocket residues (266Met and 268Ala) and just next to the 211DVD213 motif. The size of the side chain of Thr and Val is the smallest, Leu is medium, and Met is the largest, and the size changes in the critical position 214 may affect the donor recognition pocket.

CONCLUSION

Four ABO subgroup alleles were newly linked to different kinds of ABO variants and the possible mechanism through which they produce weak ABO subgroups was analyzed in silico.

A report on a modified protocol for flow cytometry-based assessment of blood group erythrocyte antigens potentially suitable for analysis of weak ABO subgroups

BACKGROUND

Flow cytometry (FC) has proven its utility in scrutinizing AB antigen expression in red blood cells (RBCs), cooperating with serological tests for accurate blood group typing. However, technical difficulties may impair the characterization of weak ABO subtypes when background noises appear at non-negligible levels.

STUDY DESIGN AND METHODS

We sought to establish an FC method that could prevent antibody-induced hemagglutination and an increase in cellular autofluorescence, two major issues inherent to RBC-FC analysis of AB expression. We optimized fixatives, multicolor-staining protocols, and sequential gating strategies. Blood samples from weak ABO subtype cases, B_m and A_el , were analyzed with the established protocol.

RESULTS

The optimized mixture of glutaraldehyde and formaldehyde successfully generated fixed RBCs resistant to agglutination while maintaining low autofluorescence. These features allowed co-staining of leukocyte- and erythrocyte-markers, which enabled sequential gating strategies facilitating the precise AB antigen analysis in purely single RBCs with minimum background noises. By the established FC analysis, we could detect in the B_m sample a small RBC population exhibiting weak B antigen expression. The assay also proved it feasible to identify a small population (0.04%) of RBCs weakly expressing the A antigen in the A_el sample confirmed as harboring a rare c.816dupG ABO variant allele.

CONCLUSION

The RBC-FC analysis described here allows the detection of AB antigens weakly expressed in RBCs while achieving minimum background noise levels in negative control samples. Overall, the modified protocol provides a quick and reliable assay valuable in transfusion medicine and is potentially applicable to the characterization of rare weak ABO variants.