An enhanced understanding of the Rhesus (Rh) system involved in hemolytic disease of the fetus and newborn (HDFN), including novel RHD allele variants, may help contribute to ongoing advancements in blood group diagnostics, according to findings from a study conducted in Austria and recently published in the journal Biomedicines.
In the field of transfusion medicine, the Rh blood group system includes the D antigen. Of note, the D antigen is considered to be the most immunogenic, because it triggers an immune response in the recipient that renders it most likely to lead to a transfusion reaction.
There are many alleles of the RHD gene that are linked to variant RhD phenotypes. When Rh incompatibility is present, some of these alleles can generate HDFN, as well as hemolytic transfusion reactions in which red blood cells rupture. Accurate blood group diagnostics are therefore essential. The performance of routine blood typing is a very formidable task, based on the high level of diversity that exists in the Rh system.
The researchers reported on the comprehensive evaluation of variant D phenotypes that were detected during routine pretransfusion testing in different blood samples. Ultimately, they were able “to identify novel RHD alleles characterized by variants spreading across several exons defining weak D and partial D variants.”
Read more about HDFN symptoms and risks
Overall, there were four novel RHD allele variants linked to weak D and partial D phenotypes that were revealed. For serologic typing, standard gel card matrix procedures with monoclonal and polyclonal anti-D antibodies were utilized. These were accompanied by the use of antigen density and D epitope evaluations. Additionally, genotyping via polymerase chain reaction with sequence-specific primers, in silico protein analysis, and genomic- and allele-specific Sanger sequencing was carried out.
During the performance of routine antigen typing, an unknown D status was detected in four individuals, which resulted in an additional serologic and molecular workup in an effort to resolve any inconclusive blood phenotyping findings among the patients and the donors.
One of the mutations discovered was predicted to disrupt the terminal stop codon and lead to an “elongated translation of the mutant D protein that phenotypically exhibits a loss of D epitopes.” Moreover, a hybrid gene that was formed with the homolog RHCE gene was delineated.
According to the authors, “[The identification of four] novel RHD gene variants associated with weak D and partial D phenotypes . . . enabled us to determine whether transfusion of D[-]positive or D[-]negative blood was most appropriate.” They concluded, “When D variants are suspected, accurate diagnostics are critical to selecting compatible red [blood] cells for transfusion so that immunization is avoided while the rarer D[-]negative blood is preserved.”
