Molecular basis of the D variant phenotypes DNU and D^II allows localization of critical amino acids required for expression of Rh D epitopes epD3, 4 and 9 to the sixth external domain of the Rh D protein

Abstract

Summary. The discovery of Rh partial D variant red cells by discrepant reactions with different monoclonal anti-D hasdemonstrated the range of Rh D epitopes that have arisen due to alterations in Rh D protein structure. There are two current classification systems, one which uses a nine epitope model (epD1-epD9) whereas a more recent model proposes 30 different epitopes. We describe here the molecular basis of two D variants which lack epD4 and epD9 namely the DNU and D II phenotypes. These would have both been originally classified as D II phenotype individuals, but we have revealed subtle differences in the serological profile of these erythrocytes. Such a differential reactivity and determination of the molecular bases of these phenotypes allows us to predict critical amino acids for epD3, epD4 and epD9 expression. The DNU phenotype arises from a single point mutation in the RHD gene resulting in a single amino acid change (Gly353Arg). Sequence analysis of exon 7 of the RHD gene derived from the D II propositus indicates that there is a single point mutation in this exon resulting in a single amino acid change (Ala354Asp). It is likely that this point mutation gives rise to the D II phenotype. Both mutations result in the change to Rh D-specific residues. Our results indicate that the following amino acids are crucial for epD3a

The Rhesus Site

“…Initial contributions were the frequency of the D category VI (today known as DVI) in the German population [14]; characterization of the partial D DNU [15]; and of a third molecular basis for DVI [16], which proved that the low antigen density of many DVI could not be explained by the loss of D epitopes. Based on these contributions, the German Guidelines for Blood Group Determination and Blood Transfusion were changed in 1996 [17]: the use of monoclonal anti-D with distinct characteristics was implemented for determination of the D antigen; the concept of ‘D u ' carriers considered as D-positive blood donors and D-negative transfusion recipients was replaced by distinct recommendations for weak D (D-positive transfusion strategy) and partial D carriers (D-negative transfusion strategy, especially for DVI).…”

Polymorphisms of RhD^Va and a New RhD^Va–Like Variant Found in Japanese Individuals

“…Some D variants have a specific part of the RHD polypeptide fragment replaced by the equivalent RHCE polypeptide, and are designated D–CE–D [6, 7, 8, 9, 10, 11, 12, 13]. Others have a point mutation causing an amino acid change in an extracellular domain of the RHD polypeptide [4, 5, 14]. …”

“…D variants lack some of the D epitopes and a lack of specific epitopes defines D category phenotypes (D II–VII , DFR, DBT, DHMi, DHMii, DNU, and DHR) [2, 3, 4, 5]. Some D variants have a specific part of the RHD polypeptide fragment replaced by the equivalent RHCE polypeptide, and are designated D–CE–D [6, 7, 8, 9, 10, 11, 12, 13].…”

Rh and RHAG Blood Group Systems

“…The rediscovery of the original Category II propositus led to the subdivision of epD3 [209] . DNU (Gly353Arg) [159] and DNB (Gly355Ser) [168] are D variants with similar epitope profi les to DII. DNU (Gly353Arg) [159] and DNB (Gly355Ser) [168] are D variants with similar epitope profi les to DII.…”