Weak D alleles express distinct phenotypes

Weak and partial D phenotyping: a comparison study between molecular and serologic results

Variant D antigens can cause variable serologic results when typing with Anti-D reagents. There is limited information regarding the ability of Anti-D reagents to differentiate between D variants defined by RHD genotyping. This study was performed to determine if a panel of 20 U.S. Food and Drug Administration-licensed Anti-D reagents can identify molecularly defined D variants. Red blood cells from 119 donors carrying variant RHD alleles were tested at immediate spin (IS) and/or by the indirect antiglobuin test (IAT) using conventional test tube and/or column agglutination technology. Reaction strength at IS and IAT was reviewed to determine whether a pattern of reactivity could be correlated with a specific D variant. Agglutination results from each sample with each Anti-D reagent were combined to assess overall reactivity. The sample set consisted of 21 D variants, based on prior RHD genotyping. Of these variants, nine categories had three or more samples used for analysis (N = 102); 25 RHD*01W.1, 15 RHD*01W.2, 14 RHD*01W.3, 17 RHD*09.01, 14 RHD*09.03, 4 RHD*01W.4, 23 RHD*07, 4 RHD*10.05, and 6 reference allele RHD*01. As expected, IS showed more negative or weak reactions, and IAT produced more positive reactions with 3+/4+ agglutination strength. RHD*01W.3 samples showed strongest reactivity at IS and IAT. Greatest variation in reactivity was observed with RHD*01W.2, showing weakest overall reactivity at IS. All weak D types had at least one sample that yielded a negative result and one sample with 4+ agglutination at IS. Although there were general patterns of reactivity for each variant tested, no one pattern defined all samples carrying the same RHD allele. This study demonstrated that even with 20 different Anti-D reagents, serologic testing alone is insufficient to define weak or partial D types, characterize the risk for alloanti-D, or determine candidacy for Rh immune globulin. The results illustrate how multiple Anti-D reagents can be used to identify samples that should be reflexed to molecular testing.

A Bioinformatically Initiated Approach to Evaluate GATA1 Regulatory Regions in Samples with Weak D, Del, or D- Phenotypes Despite Normal RHD Exons

Introduction

With over 360 blood group antigens in systems recognized, there are antigens, such as RhD, which demonstrate a quantitative reduction in antigen expression due to nucleotide variants in the non-coding region of the gene that result in aberrant splicing or a regulatory mechanism. This study aimed to evaluate bioinformatically predicted GATA1-binding regulatory motifs in the RHD gene for samples presenting with weak or apparently negative RhD antigen expression but showing normal RHD exons.

Methods

Publicly available open chromatin region data were overlayed with GATA1 motif candidates in RHD. Genomic DNA from weak D, Del or D- samples with normal RHD exons (n = 13) was used to confirm RHD zygosity by quantitative PCR. Then, RHD promoter, intron 1, and intron 2 regions were amplified for Sanger sequencing to detect potential disruptions in the GATA1 motif candidates. Electrophoretic mobility shift assay (EMSA) was performed to assess GATA1-binding. Luciferase assays were used to assess transcriptional activity.

Results

Bioinformatic analysis identified five of six GATA1 motif candidates in the promoter, intron 1 and intron 2 for investigation in the samples. Luciferase assays showed an enhancement in transcription for GATA1 motifs in intron 1 and for intron 2 only when the R 2 haplotype variant (rs675072G>A) was present. GATA1 motifs were intact in 12 of 13 samples. For one sample with a Del phenotype, a novel RHD c.1-110A>C variant disrupted the GATA1 motif in the promoter which was supported by a lack of a GATA1 supershift in the EMSA and 73% transcriptional activity in the luciferase assay. Two samples were D+/D- chimeras.

Conclusion

The bioinformatic predictions enabled the identification of a novel DEL allele, RHD c.1-110A>C, which disrupted the GATA1 motif in the proximal promoter. Although the majority of the samples investigated here remain unexplained, we provide GATA1 targets which may benefit future RHD regulatory investigations.

Obstetric and Newborn Weak D-Phenotype RBC Testing and Rh Immune Globulin Management Recommendations: Lessons From a Blinded Specimen-Testing Survey of 81 Transfusion Services

CONTEXT.—

Modern RHD genotyping can be used to determine when patients with serologic weak D phenotypes have RHD gene variants at risk for anti-D alloimmunization. However, serologic testing, RhD interpretations, and laboratory management of these patients are quite variable.

OBJECTIVE.—

To obtain interlaboratory comparisons of serologic testing, RhD interpretations, Rh immune globulin (RhIG) management, fetomaternal hemorrhage testing, and RHD genotyping for weak D-reactive specimens.

DESIGN.—

We devised an educational exercise in which 81 transfusion services supporting obstetrics performed tube-method RhD typing on 2 unknown red blood cell challenge specimens identified as (1) maternal and (2) newborn. Both specimens were from the same weak D-reactive donor. The exercise revealed how participants responded to these different clinical situations.

RESULTS.—

Of reporting laboratories, 14% (11 of 80) obtained discrepant immediate-spin reactions on the 2 specimens. Nine different reporting terms were used to interpret weak D-reactive maternal RhD types to obstetricians. In laboratories obtaining negative maternal immediate-spin reactions, 28% (16 of 57) performed unwarranted antiglobulin testing, sometimes leading to recommendations against giving RhIG. To screen for excess fetomaternal hemorrhage after a weak D-reactive newborn, 47% (34 of 73) of reporting laboratories would have employed a contraindicated fetal rosette test, risking false-negative results and inadequate RhIG coverage. Sixty percent (44 of 73) of laboratories would obtain RHD genotyping in some or all cases.

CONCLUSIONS.—

For obstetric and neonatal patients with serologic weak D phenotypes, we found several critical problems in transfusion service laboratory practices. We provide recommendations for appropriate testing, consistent immunohematologic terminology, and RHD genotype-guided management of Rh immune globulin therapy and RBC transfusions.

Demographics of Rhesus Phenotype of Blood Donors in Calabar: A Case Study of University of Calabar Teaching Hospital, Calabar, Cross River State, Nigeria

BACKGROUND

Rhesus antigens have been documented to cause haemolytic disease of the newborn as well as acute and delayed transfusion reactions. This study was performed to evaluate the frequency of rhesus antigens (C, c, D, E, and e) in the studied population.

METHOD

This study was a cross-sectional study involving 130 prospective blood donors attending University of Calabar Teaching Hospital (UCTH) donor clinic. Donors were grouped for Rh antisera (anti-E, anti-e, anti-C, anti-c, and anti-D) using the standard serologic technique.

RESULT

The most prevalent Rh antigen was "c" (98.5%), followed by "D" (97.7%), while the least was "C" (30.7%). The most prevalent phenotype was cDe/cDe (R0R0).

CONCLUSION

This work therefore concludes that the most prevalent rhesus antigen and rhesus phenotype was c and cDe/cDe among blood donors in University of Calabar Teaching Hospital.

Weak D types in the Egyptian population

Patients with the most common weak D types 1, 2, and 3 can be safely considered D positive. We evaluated 1,113 Rh-negative Egyptian samples for weak D expression to propose a cost-effective strategy related to D variant testing. D variants were tested using polymerase chain reaction with sequence-specific priming. Fifty samples were D variants (4.5%): weak D type 4.2 (32%), weak D type 4.0/4.1 (16%), and weak D type 15 (2%). Fifteen (62.5%) of 24 samples were identified serologically as partial D. We also studied the probability of the development of anti-D in 52 Rh-negative children with thalassemia who were receiving units for which weak D was not tested. Anti-D alloimmunization was observed in 63.5% of patients with thalassemia. It is prudent to implement weak D typing in Egyptian donors. Weak D variants of Egyptians are significantly different compared with Caucasians. Ethnicity must be taken into consideration when developing clinical and prenatal strategies related to D variants.

Prevalence of RhD variants, confirmed by molecular genotyping, in a multiethnic prenatal population

RhD determination in pregnant women is critical to facilitate Rh immune globulin prophylaxis for RhD-negative women. A single amino acid change in the RhD antigen can cause epitope loss, giving rise to "partial D" variants. Women with some partial D variants may develop anti-D against the missing epitope after pregnancy. RBCs with partial D may type as D-positive or D-negative depending on the reagent used. We screened routine blood bank samples from 501 prenatal patients for RhD variants by 3 commercially available serologic methods. Discordant serologic results were found in 11 cases. Weak D (n = 5) and partial D (n = 5) variants were confirmed by molecular genotyping in all but 1 case. RhD variants, confirmed molecularly, occur in 2.2% of our multiethnic population. Consideration of patients' ethnic background and close cooperation between pathologists and obstetric providers facilitate optimal prenatal care in these cases.