From genetic variability to phenotypic expression of blood group systems.

More than 300 red blood cell (RBC) antigens belonging to 36 blood group systems have been officially reported in humans by the International Society of Blood Transfusion (ISBT). Phenotypic variability is directly linked to the expression of the 41 blood group genes. The Rh blood group system, which is composed of 54 antigens, is the most complex and polymorphic system. Many rare genetic variants within the RH (RHD and RHCE) genes, involving various mutational mechanisms (single-nucleotide substitutions, short insertions/deletions, rearrangements, large deletions), have been reported in the literature and reference databases. Expression of the variants induces variable clinical outcomes depending on their nature and impact on antigen structure. Their respective molecular and cellular effects remain however poorly studied. Biological resources to conduct this research are also barely available. We have paid a specific attention to three different classes of single-nucleotide substitutions: 1/ splice site variants in the Rh, Kell, Kidd, Junior and Langereis systems by the minigene splicing assay developed locally; 2/ missense variants in the RhD protein and their effect on intermolecular interaction with its protein partner RhAG, intracellular trafficking and plasma membrane integration; and 3/ synonymous variants in the RHD gene. Overall not only this project has fundamental objectives by analyzing the functional effect of variants in order to make genotype-phenotype correlation, but the aim is also to develop/engineer molecular tools and cell models to carry out those studies.