Evaluation of the applicability and effectiveness of a molecular strategy for identifying weak D and DEL phenotype among D- blood donors of mixed origin exhibiting high frequency ofRHD*Ψ

Genotype analysis to clarify RhD variants in discrepant samples of Chilean population

Introduction

The D antigen variants are classified as weak, partial, and extremely weak (DEL) and can be differentiated using molecular tests. In Chile, the laboratories of local blood centers do not identify variants of the D antigen, referring them for study to the Reference Laboratory of the Public Health Institute of Chile. So, our aim was to talk about the results of the molecular analysis of variants of the D antigen in samples that had different results in the serological classification.

Methods

In the D antigen classification of the Rh system, 479 samples with serological discrepant results were sent for molecular analysis. The Rh phenotype was performed with monoclonal anti-C, anti-c, anti-E, and anti-e antisera by direct agglutination. To find the D antigen, researchers used direct agglutination with monoclonal antisera and indirect antiglobulin testing with the column (gel) agglutination method. Molecular analysis was performed with a polymerase chain reaction with sequence-specific primers (SSP-PCR) and sequencing.

Results and discussion

The presence of D antigen variants was confirmed in 332 samples (69.3%), with an initial discrepancy in serological classification. In this group of discrepant samples, the frequency of weak RhD variants was 66% (219/332), that of extremely weak RhD was 28% (93/332), and that of partial RhD was 6% (20/332). The weak variants type 2 (27.4%), type 3 (8.4%), type 48 (8.4%), and type 1 (8.1%) were the next most prevalent variants after RHD*DEL43 (28%). The ccEe (R2r) phenotype was the most frequently detected (38.4%) and is present in 87% of the RHD*DEL43 samples. The E antigen is associated with the presence of this variant. Our analyses give the first description of D antigen variants in Chile. The most common variants are DEL type (RHD*DEL43) and weak (weak type 2), which are linked to the ccDEe (R2r) phenotype. These findings allow us to characterize the variants of the D antigen in Chile and, according to the obtained data, to design strategies for the management of donors, patients, and pregnant women.

Serological and molecular characterisation of the most prevalent weak D variants in Croatian population

INTRODUCTION

Existence of hundreds of RHD gene variants contributes to variable D antigen expression and inconsistencies in reporting the RHD results. The aim of the study was to determine the serological and molecular characteristics of the most prevalent RHD alleles encoding serologically weak D variants.

MATERIAL AND METHODS

Blood donors (n = 145 924) were typed for D antigen using the direct serologic micromethod. Nonreactive samples were analysed in IAT method with the IgM/IgG anti-D monoclonal blend, and 0,2% (n = 263) confirmed weak D antigen expression. After genomic DNA extraction (Qiaqen, Germany), RHD genotyping was performed using in house reagents and PCR-SSP kits (Inno-Train, Germany).

RESULTS

The prevalence of serologically weak D in blood donor population was 0.2% (n = 263). RHD genotyping confirmed weak D allele in 92.4% and partial D allele in 7.6%. The most common was weak D type 1 (49.7%) followed by weak D type 3 (24.7%) and type 2 (9.5%). Relatively high frequency was detected for weak D type 14 (4.6%) and type 64 (2.3%). In the category of partial D phenotypes, only DVI variant was found. Direct typing has shown great variability in the strength of reactions with different clones of anti-D reagents.

CONCLUSION

Weak D type 1 is the most common weak D variant in Croatian blood donor population. The frequency of D variants and distribution of Rh phenotypes in our study was in concordance with other studies. It has been shown that serological methods and the combination of clones used, cannot distinguish variant D types, which justifies the use of molecular methods.

Insights into anti-D formation in carriers of RhD variants through studies of 3D intraprotein interactions

BACKGROUND

Many RhD variants associated with anti-D formation (partial D) in carriers exposed to the conventional D antigen carry mutations affecting extracellular loop residues. Surprisingly, some carry mutations affecting transmembrane or intracellular domains, positions not thought likely to have a major impact on D epitopes.

STUDY DESIGN AND METHODS

A wild-type Rh trimer (RhD₁ RhAG₂ ) was modeled by comparative modeling with the human RhCG structure. Taking trimer conformation, residue accessibility, and position relative to the lipid bilayer into account, we redefine the domains of the RhD protein. We generated models for RhD variants carrying one or two amino acid substitutions associated with anti-D formation in published articles (25 variants) or abstracts (12 variants) and for RHD*weak D type 38. We determined the extracellular substitutions and compared the interactions of the variants with those of the standard RhD.

RESULTS

The findings of the three-dimensional (3D) analysis were correlated with anti-D formation for 76% of RhD variants: 15 substitutions associated with anti-D formation concerned extracellular residues, and structural differences in intraprotein interactions relative to standard RhD were observed in the others. We discuss the mechanisms by which D epitopes may be modified in variants in which the extracellular residues are identical to those of standard RhD and provide arguments for the benignity of p.T379M (RHD*DAU0) and p.G278D (RHD*weak D type 38) in transfusion medicine.

CONCLUSION

The study of RhD intraprotein interactions and the precise redefinition of residue accessibility provide insight into the mechanisms through which RhD point mutations may lead to anti-D formation in carriers.

Effectiveness of strategies to screen for blood donors with RH variants in a mixed population

INTRODUCTION

Patients with RH variants presenting antibodies directed to RH high frequency antigens or multiple RH antibodies might, in some occasions, be better served with RH genotype-matched units, requiring screening for RH variants among blood donors. To date, strategies to identify donors with RH variants were restricted to selecting individuals of African descent based on self-reported race, what can be inaccurate in racially mixed population. Our goal was to: 1) Screen for donors with RH variants in a mixed population using self-declared race and Rh phenotype as selection criteria; and 2) Verify if including the Duffy null genotype in the screening algorithm increases its effectiveness.

METHODS

Brazilian donors were included if self-declared as black and phenotyped as R0r or R1r. All individuals were genotyped for RHCE exons 1, 5, 6 and 7 and for the FY*B c.-67 T > C polymorphism in order to determine the Duffy null genotype. RHD variants were searched for in cases of altered RHCE.

RESULTS

Among 2500 blood donors, 217 fulfilled the inclusion criteria and were enrolled. Fifty-three (24.4 %) had a predicted clinically relevant Rh phenotype (partial antigens or lack of high frequency antigens). Twelve donors (5.5 %) had a predicted RhCE phenotype lacking either hrB or hrS. Most cases with predicted lack of high frequency antigens (66.7 %) occurred in donors with the Duffy null genotype.

CONCLUSION

Selecting donors based on self-declared race, Rh phenotype and Duffy null genotype is feasible and effective in identifying RH variants lacking Rh high frequency antigens among racially mixed donors.

High frequency of variant RHD genotypes among donors and patients of mixed origin with serologic weak-D phenotype

BACKGROUND

The current transfusion policy recommended for individuals with serologic weak-D phenotype is based on data derived from European-descent populations. Data referring to the distribution of RH alleles underlying weak-D phenotype among people of mixed origin are yet incomplete, and the applicability of European-based transfusion guidelines to this specific population is questionable.

GOAL

To evaluate the distribution of RHD variant genotype among individuals with serologic weak-D phenotype of both African and European descent.

METHODS

Donors and patients of mixed origin and with serologic weak-D phenotype were selected for the study. They were investigated using conventional RHD-PCR assays and RHD whole-coding region direct sequencing.

RESULTS

One hundred and six donors and 58 patients were included. There were 47 donors and 29 patients with partial-D genotype (47/106, 44.3%, and 29/58, 50%, respectively). RHD*DAR and RHD*weak D type 38 represented the most common altered RHD alleles among donors (joint frequency of 39.6%), while weak D types 1-3 accounted for 10.4% of the total D variant samples. RHD*DAR was the most common allele identified in the patient group (frequency of 31%), and weak D types 1-3 represented 29.3% of the total.

CONCLUSION

The frequency of partial D among mixed individuals with serologic weak-D phenotype is high. They should be managed as D-negative patients until molecular tests are complete.