![]() The Rh system, with a large number of antigens, is one of the most polymorphic and immunogenic blood group systems and the cause of most alloimmunization following transfusions and pregnancy. Blood group antigens exhibit different immunogenicity, namely the ability to provoke an immune response when introduced into an immunocompetent host to whom it is foreign. It is important to note that a blood group system includes antigens defined by a human alloantibody, and they are frequently discovered in alloimmunized pregnant women or transfused patients. The SNPs indicate the presence, in the same population, of two or more alleles for a locus, each present at an appreciable frequency (>1%) some blood group systems are highly polymorphic (e.g., Rh, MNS). Schematic representation of the antigens on the erythrocyte membrane. Many specificities of blood groups are polymorphic, and this diversity is mainly caused by single nucleotide polymorphisms (SNPs), and by several other genetic mechanisms, as missense mutations, nonsense mutations, alternative splicing, deletion of a gene, exon or nucleotide, insertion of an exon or a nucleotide, chromosomal translocation, gene conversion. Unlike the antigens of the ABO, H, Le, and I systems, other non-ABO-non-Rh antigens are proteins and are primary products of a gene they can have one or more transmembrane domains or be bonded to the membrane by anchoring complexes (Figure 1).
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