High frequency of partial DIIIa and DAR alleles found in sickle cell disease patients suggests increased risk of alloimmunization to RhD

Transfusion management of Africans with RHD variants in China

The presence of D variant among minorities could produce a higher rate of alloimmunization observed in patients from this group. This is partly due to the ethnic and racial specificity of RHD variants and the limited availability of Rh-matched blood donors. Approximately half a million African migrants in China carrying distinct Rh blood type composition have presented to the health care system with an imperative safety requirement of blood transfusion among 1.3 billion Chinese individuals. We depict the clinically significant RHD alleles among African migrants living in China and identify the genetic similarities and disparities to Chinese. We discussed practical strategies to manage the unique transfusion needs of African migrants in China.

Systematic RHD genotyping in Brazilians reveals a high frequency of partial D in transfused patients serologically typed as weak D

BACKGROUND

The discrimination between weak D types and partial D can be of clinical importance because carriers of partial D antigen may develop anti-D when transfused with D-positive red blood cell units. The aim of this study was to determine by molecular analysis the type of D variants among Brazilian patients requiring transfusions with serologic weak D phenotypes.

MATERIAL AND METHODS

Samples from 87 patients (53 with sickle cell disease, 10 with thalassemia and 24 with myelodysplastic syndrome), serologic typed as weak D by manual tube indirect antiglobulin test or gel test were first RHD genotyped by using the RHD BeadChip Kit (BioArray, Immucor). Sanger sequencing was performed when necessary.

RESULTS

RHD molecular analysis revealed 32 (36.8 %) variant RHD alleles encoding weak D phenotypes and 55 (63.2 %) alleles encoding partial D antigens. RHD variant alleles were present in the homozygous state or as a single RHD allele, one variant RHD allele associated with the RHDΨ allele, or two different variant RHD alleles in compound heterozygosity with each other in 70 patients, 4 patients and 13 patients, respectively. Alloanti-D was found in 9 (16.4 %) cases with RHD alleles predicting a partial D.

DISCUSSION

The frequency of partial D was higher than weak D types in Brazilian patients serologically typed as weak D, showing the importance to differentiate weak D types and partial D in transfused patients to establish a transfusion policy recommendation.

Impact of RHD genotyping on transfusion practice in Denmark and the United States and identification of novel RHD alleles

BACKGROUND

Reduced D antigen on red blood cells (RBCs) may be due to "partial" D phenotypes associated with loss of epitope(s) and risk for alloimmunization or "weak" D phenotypes that do not lack major epitopes with absence of clinical complications. Genotyping of samples with weak and discrepant D typing is recommended to guide transfusion and RhIG prophylaxis. The goal was to compare the impact of RHD genotyping on transfusion practice in two centers serving different populations.

STUDY DESIGN AND METHODS

Fifty-seven samples from Denmark and 353 from the United States with weak or discrepant D typing were genotyped. RBC typing was by multiple methods and reagents. DNA isolated from white blood cells was tested with RBC-Ready Gene D weak or CDE in Denmark or RHD BeadChip in the United States. RHD was sequenced for those unresolved.

RESULTS

Of Caucasian samples from Denmark, 90% (n = 51) had weak D types 1, 2, or 3; two had other weak D, two partial D, and two new alleles. In diverse ethnic U.S. samples, 44% (n = 155) had weak D types 1, 2, or 3 and 56% (n = 198) had other alleles: uncommon weak D (n = 13), weak 4.0 (n = 62), partial D (n = 107), no RHD (n = 9), and new alleles (n = 7).

CONCLUSION

Most samples with weak or variable D typing from Denmark had alleles without risk for anti-D. In U.S. samples, 48% could safely be treated as D+, 18% may require consideration if pregnancy possible, and 34% could potentially benefit from being treated as D-. Black and multiracial ethnicities were overrepresented relative to population.

Molecular characterisation of RhD variants in North Indian blood donor population

OBJECTIVES

A molecular analysis of serologically RhD variant samples was conducted to find the incidence of various D variants in our blood donor population.

BACKGROUND

Determining a blood donor's RhD phenotype and genotype is important as transfusion of units with a weak D or partial D phenotype can result in immunisation of the recipients.

METHODS

Samples with discrepant D and weak D phenotypes identified on testing with at least five different monoclonal anti-D antisera were considered serological RhD variant and subjected to molecular testing (Massarray kit, Agena Bioscience, San Diego) for variant RHD gene.

RESULTS

A total of 39 samples, including 19 RhD discrepant samples and 20 weak D samples, were identified as serological RhD variant from a total of 4386 samples. Thirteen (13/39) samples carried variants leading to weak D phenotype, and eight samples had variants leading to partial D categories. Seven samples (7) could not be characterised, whereas 11 samples were identified as Rh negative (RHD*01N.01) after molecular testing. Overall incidence of D variants in the study population was 0.48%. RHD*weak D type 1(5, 0.1%) and RHD*DFR1 (5, 1%) were the most common variants identified.

CONCLUSIONS

Few samples with weak reaction on serological testing were found to be partial D variant and vice versa. Donor centres should develop a protocol for genotyping of samples with aberrant results on serological testing for assessing the actual RhD status of an individual as results of serological testing may be misleading.

Diversity of RH and transfusion support in Brazilian sickle cell disease patients with unexplained Rh antibodies

BACKGROUND

Genetic diversity in the RH genes among sickle cell disease (SCD) patients is well described but not yet extensively explored in populations of racially diverse origin. Transfusion support is complicated in patients who develop unexpected Rh antibodies. Our goal was to describe RH variation in a large cohort of Brazilian SCD patients exhibiting unexpected Rh antibodies (antibodies against RH antigens to which the patient is phenotypically positive) and to evaluate the impact of using the patient's RH genotype to guide transfusion support.

STUDY DESIGN AND METHODS

Patients within the Recipient Epidemiology and Evaluation Donor Study (REDS)-III Brazil SCD cohort with unexpected Rh antibodies were selected for study. RHD and RHCE exons and flanking introns were sequenced by targeted next-generation sequencing.

RESULTS

Fifty-four patients with 64 unexplained Rh antibodies were studied. The majority could not be definitively classified as auto- or alloantibodies using serologic methods. The most common altered RH were RHD*DIIIa and RHD*DAR (RHD locus) and RHCE*ce48C, RHCE*ce733G, and RHCE*ceS (RHCE locus). In 53.1% of the cases (34/64), patients demonstrated only conventional alleles encoding the target antigen: five of 12 anti-D (41.7%), 10 of 12 anti-C (83.3%), 18 of 38 anti-e (47.4%), and one of one anti-E (100%).

CONCLUSION

RHD variation in this SCD cohort differs from that reported for African Americans, with increased prevalence of RHD*DAR and underrepresentation of the DAU cluster. Many unexplained Rh antibodies were found in patients with conventional RH allele(s) only. RH genotyping was useful to guide transfusion to determine which patients could potentially benefit from receiving RH genotyped donor units.

The DAU Allele and Anti-D Alloimmunization Present With High Frequency in Brazilian Sickle Cell Disease Patients

Background

Antigens DIIIa, DAR and DAU are common in people of African descent and are involved in anti-D alloimmunization. Sickle cell disease (SCD) patients frequently need blood therapy and are vulnerable to alloimmunization.

Methods

The study included SCD patients from the Brazilian state of Bahia, which has the highest incidence of the disease in Brazil; 241 SCD patients and 220 healthy individuals were studied. Alleles were characterized by PCR-RFLP and PCR-SSP techniques.

Results

The DAU allele was found in 22.3% (43/193) of the SCD patients. Two (1%) patients had the DIIIa/D wild-type genotype, one (0.5%) had the DIIIa/D- genotype, 11 (5.7%) had the DAR/D wild-type genotype and three (1.6%) had the DAR/D- genotype. Two patients were positive for the 667T>G mutation and the 1136C>T mutation, one (0.5%) had the genotype DIIIa/DAU, and one (0.5%) had the genotype DAR/DAU.

Conclusion

There was statistical significance when the allele frequencies were evaluated among SCD, sickle cell anemia (HbSS) patients and healthy individuals. The frequencies of the DIIIa, DAR and DAU alleles among SCD patients differ from those of healthy individuals from the same population, and a high frequency of the DAU variant was associated with anti-D alloimmunization in these patients.

Medical and economic implications of strategies to prevent alloimmunization in sickle cell disease

BACKGROUND

The pathogenesis of alloimmunization is not well understood, and initiatives that aim to reduce the incidence of alloimmunization are generally expensive and either ineffective or unproven. In this review, we summarize the current medical literature regarding alloimmunization in the sickle cell disease (SCD) population, with a special focus on the financial implications of different approaches to prevent alloimmunization.

STUDY DESIGN AND METHODS

A review of EMBASE and MEDLINE data from January 2006 through January 2016 was conducted to identify articles relating to complications of SCD. The search was specifically designed to capture articles that evaluated the costs of various strategies to prevent alloimmunization and its sequelae.

RESULTS

Currently, there is no proven, inexpensive way to prevent alloimmunization among individuals with SCD. Serologic matching programs are not uniformly successful in preventing alloimmunization, particularly to Rh antigens, because of the high frequency of variant Rh alleles in the SCD population. A genotypic matching program could offer some cost savings compared to a serologic matching program, but the efficacy of gene matching for the prevention of alloimmunization is largely unproven, and large-scale implementation could be expensive.

CONCLUSIONS

Future reductions in the costs associated with genotype matching could make a large-scale program economically feasible. Novel techniques to identify patients at highest risk for alloimmunization could improve the cost effectiveness of antigen matching programs. A clinical trial comparing the efficacy of serologic matching to genotype matching would be informative.

Serologic findings of RhD alleles in Egyptians and their clinical implications

INTRODUCTION

Serologic discrepancies caused by various reactivity of D variants can only be resolved by the use of RhD genotyping. However, this strategy cannot be applied routinely due to the cost and feasibility. It has been documented that D variants are demonstrated among individuals with positivity for at least C or E antigens. It is considered to be affordable for some countries to test D negative donors who are C or E positive for D variants. It was proposed that an algorithm could be found based on distinct serologic features that matches the Egyptian genetic frequency data, and correctly assigns donors and patients, using the least possible expenses.

MATERIALS AND METHODS

Samples with the most prevalent weak D and partial D were investigated for their RhCE phenotype. Routine D typing by immediate spin (IS) tube method was performed in parallel with an automated gel test, and the reactivity results of D variants with both techniques were compared.

RESULTS

Among 31 D variants, only 5 were C or E positive (16.1 %). R0r phenotype was associated with the remaining 26 samples (83.9%) and constituted weak D types 4.2 (38.5%), and 4.0/4.1 (11.5%), partial DIII (34.6%), and partial DV (15.4%). Gel reacted strongly with partial DIII and DV. Ten samples with DIII and DV typed as D positive with IS. All weak D were positive by indirect antiglobulin test (IAT), while all partial D were positive by gel and IAT.

CONCLUSION

Guidelines for RhD workup should be adjusted to match population data. Detection of D variants among C or E positive donors may not be an optimal strategy for Egyptians. Serology cannot discriminate weak D from partial D, but may provide a clue about the probable D variant to be tested molecularly with the appropriate kit. Reagent selection is important to correctly assign donors and patients with the DIII and DV types.

High prevalence of red blood cell alloimmunization in sickle cell disease despite transfusion from Rh-matched minority donors

Rh serologic phenotype–matched transfusions from minority donors do not prevent all Rh alloimmunization in patients with SCD. Variant RH genes are common in patients with SCD and contribute to Rh alloimmunization and transfusion reactions.

Serologic and molecular investigations of DAR1 (weak D Type 4.2), DAR1.2, DAR1.3, DAR2 (DARE), and DARA

BACKGROUND

The partial D variant DAR1 (weak D Type 4.2) is caused by three single-point mutations, 602C>G, 667T>G, and 1025T>C. Here we report a molecular study on different D variants belonging to the DAR category (DAR1, DAR1.2, DAR1.3, and DAR2) and their serologic data.

STUDY DESIGN AND METHODS

A total of 42 samples belonging to the DAR category were screened for the presence of the silent mutations 744C>T and 957G>A. The samples were phenotyped for RhD and RhCE, characterized for RhD epitope expression, and sequenced for RHD exons. Flow cytometry was performed to determine RhD antigen density.

RESULTS

The silent mutation 744C>T was found in all six samples previously typed as RHD*DAR2 (602C>G, 667T>G, 957G>A, 1025T>C). In addition to the three nucleotide changes originally reported for the RHD*DAR1 allele, the silent mutations 744C>T and 957G>A were found in 14 of 16 samples previously typed as RHD*DAR1. In the remaining two samples one additional silent mutation, 744C>T, was found. Serologically the DAR1.2 and DAR1.3 samples analyzed in this study showed no distinct difference in their anti-D reaction pattern compared to each other. The anti-D reaction pattern of DARA/DAR2 showed some distinct differences compared to those of DAR1.2 and DAR1.3.

CONCLUSION

RHD*DARA and RHD*DAR2 are the same allele. Furthermore, the alleles RHD*DAR1.2 and RHD*DAR1.3 both exist; however, the silent mutation 957G>A (V319) showed no influence on the RhD phenotype.

Red blood cell alloimmunization in sickle cell disease: pathophysiology, risk factors, and transfusion management

Red blood cell transfusions have reduced morbidity and mortality for patients with sickle cell disease. Transfusions can lead to erythrocyte alloimmunization, however, with serious complications for the patient including life-threatening delayed hemolytic transfusion reactions and difficulty in finding compatible units, which can cause transfusion delays. In this review, we discuss the risk factors associated with alloimmunization with emphasis on possible mechanisms that can trigger delayed hemolytic transfusion reactions in sickle cell disease, and we describe the challenges in transfusion management of these patients, including opportunities and emerging approaches for minimizing this life-threatening complication.

Relevance of RH variants in transfusion of sickle cell patients

Transfusion remains the main treatment of sickle cell disease patients. Red cell alloimmunization is frequent because of the antigen disparities between patients of African descent and donors of European ancestry. Alloimmunization is associated with severe hemolytic transfusion reaction, autoantibody formation, and difficulties in the management of transfusion compatibility. Beside common antigens, a number of different RH variant antigens found in individuals of African descent can be involved in alloimmunization. If some variants, such as Hr(S) negative antigens, are known to prone significant alloantibodies and delayed hemolytic transfusion reactions, it is not clear whether all the described variants represent a clinical risk for sickle cell disease patients. The knowledge of the clinical relevance of RH variants is a real issue. An abundance of molecular tools are developed to detect variants, but they do not distinguish those likely to prone immunization from those that are unlikely to prone immunization and delayed hemolytic transfusion reactions. A strategy of prevention, which generally requires rare red blood cells, cannot be implemented without this fundamental information. In this review, we discuss the relevance of RH variants in sickle cell disease, based on the published data and on our experience in transfusion of these patients.

Red cell genotyping and the future of pretransfusion testing

Over the past 20 years the molecular bases of almost all the major blood group antigens have been determined. This research has enabled development of DNA-based methods for determining blood group genotype. The most notable application of these DNA-based methods has been for determining fetal blood group in pregnancies when the fetus is at risk for hemolytic disease of the fetus and newborn. The replacement of all conventional serologic methods for pretransfusion testing by molecular methods is not straightforward. For the majority of transfusion recipients matching beyond ABO and D type is unnecessary, and the minority of untransfused patients at risk of alloimmunization who would benefit from more extensively blood group–matched blood cannot be identified reliably. Even if a method to identify persons most likely to make alloantibodies were available, this would not of itself guarantee the provision of extensively phenotype-matched blood for these patients because this is determined by the size and racial composition of blood donations available for transfusion. However, routine use of DNA-based extended phenotyping to provide optimally matched donations for patients with preexisting antibodies or patients with a known predisposition to alloimmunization, such as those with sickle cell disease, is widely used.