DAL: a new partial RHD phenotype

Many examples of partial D phenotypes in the RH blood group system have been described, and, in most cases, the molecular bases have been established.1,2 These phenotypes generally result from replacement of RHD-specific nucleotides by their RHCE counterparts at polymorphic positions (gene conversion or nucleotide substitution events), but mutations at nonpolymorphic positions may also occur. Another feature of partial D phenotypes is the occasional presence of low-frequency antigens, which are detected by specific antisera. Antibodies produced by persons with the partial D phenotype are of clinical significance, because they may trigger hemolytic transfusion reactions and HDN. Therefore, it is of clinical interest to detect partial D in recipients as well as in donors of blood units. Commercial reagents based on the nine epitope model of D cannot distinguish all polymorphisms responsible for partial D phenotypes. For a more accurate detection of these phenotypes, we developed a procedure that is based on the reactivity profile of RBCs with 14 IgG D MoAbs. At first, typical patterns of reactivity were established with a panel of variants available in our laboratory that were well characterized at the molecular level. Therefore, the identification of a new profile leaves us with two possibilities: 1) the variant is an already described partial D phenotype, but the profile has not been established previously, as the variant was not available; or 2) the sample is a new variant. In both cases, either the RHD transcript (from circulating reticulocytes) or all exons of the entire RHD gene are sequenced. With our procedure, we recently identified a L E T T E R S T O T H E E D I T O R