RHD allelic identification among D-Brazilian blood donors as a routine test using pools of DNA

Serologic profiling of D variants in donor routine: unveiling the impact on false-negative results and alloimmunization

The high number of D variants can lead to the unnecessary use of Rh immune globulin, overuse of D- RBC units, and anti-D allommunization. D variant prevalence varies among ethnic groups, and knowledge of the main variants present in a specific population, their behavior in serologic tests, and their impact on clinical practice is crucial to define the best serologic tests for routine use. The present study aimed to explore the serologic profile of D variants and to determine which variants are most associated with false-negative D typing results and alloimmunization. Donor samples were selected in two study periods. During the first period, D typing was performed on a semi-automated instrument in microplates, and weak D tests were conducted in tube or gel tests. In the second period, D typing was carried out using an automated instrument with microplates, and weak D tests were performed in solid phase. Samples from patients typed as D+ with anti-D were also selected. All samples were characterized by molecular testing. A total of 37 RHD variants were identified. Discrepancies and atypical reactivity without anti-D formation were observed in 83.4 percent of the samples, discrepant D typing results between donations were seen in 12.3 percent, and D+ patients with anti-D comprised 4.3 percent. DAR1.2 was the most prevalent variant. Weak D type 38 was responsible for 75 percent of discrepant samples, followed by weak D type 11, predominantly detected by solid phase. Among the D variants related to alloimmunization, DIVa was the most prevalent, which was not recognized by serologic testing; the same was true for DIIIc. The results highlight the importance of selecting tests for donor screening capable of detecting weak D types 38 and 11, especially in populations where these variants are more prevalent. In pre-transfusion testing, it is crucial that D typing reagents demonstrate weak reactivity with DAR variants; having a serologic strategy to recognize DIVa and DIIIc is also valuable.

Standardization of a multiplex assay to identify weak D types in a mixed-race Brazilian population

RH allele variability is caused by several types of variants, resulting in altered RhD and RhCE phenotypes. Most of the weak D phenotypes in European-derived populations are weak D types 1, 2, or 3, which are not involved in alloimmunization episodes. However, the Brazilian population is racially diverse, and the accuracy of molecular and serologic tests developed in recent years has allowed for the identification of other RH variants, that are common in the Brazilian population, such as weak D type 38 or weak partial 11, the latter involved in alloimmunization cases. Furthermore, patients with these two weak D variants must be transfused with D- red blood cell units, as do patients with weak D type 4 or DAR, which are also common D variants in Brazil. Weak D type 38 and weak partial 11 can be serologically misclassified as weak D types 1, 2, or 3 in patients, based on European experience, or as D- in donors. Additionally, pregnant women may unnecessarily be identified as requiring Rh immune globulin. RhCE phenotypes are reliable indicators of RhD variants. For individuals with the Dce phenotype, the preferred approach is to specifically search for RHD*DAR. However, when encountering DCe or DcE phenotypes, we currently lack a developed method that assists us in rapidly identifying and determining the appropriate course of action for the patient or pregnant woman. Two multiplex assays were proposed: one for the identification of RHD*weak partial 11, RHD*weak D type 38, and RHD*weak D type 3 and another for RHD*weak D type 2 and RHD*weak D type 5. The multiplex assays were considered valid if the obtained results were equivalent to those obtained from sequencing. Expected results were obtained for all tested samples. The proposed multiplex allele-specific polymerase chain reaction assays can be used in the molecular investigation of women of childbearing age, patients, and blood donors presenting a weak D phenotype with DCe or DcE haplotypes in a mixed-race population, such as Brazil.

Molecular basis of RhD-negative phenotype in North Indian blood donor population

Background & objectives

RHD gene typing is highly complex due to homology with RHCE genes. Molecular polymorphism of the RHCE and RHD genes have been characterized among various populations, but no studies have been undertaken among Indians. This study was undertaken to assess the genetic basis of RHD-negative phenotype in Indian blood donor population.

Methods

Sample from a total of 200 phenotypically RhD-negative blood donors were analyzed for presence of RHD gene using polymerase chain reaction (PCR). RHD genotyping was done using three primer sets designed for exons 4 and 10 and one set for identification of pseudo (RHDΨ) gene between introns (int) 3 and 4. Amplified PCR products were analyzed by gel-electrophoresis (XY Loper, Uvitech, Cambridge) and confirmed by nucleotide sequencing (ABI 3730 xl 96 capillary system).

Results

No PCR product was found in 195/200 (97.5%) of study samples indicating homozygous gene deletion. Of the 5/200 (2.5%) showing RHD gene polymorphisms, 4/200 (2%) were positive for presence of exon 10 only (RHD-CE-D hybrid). RHDΨ gene was not detected in any of the samples tested. One sample showed presence of all three tested regions and was negative for RHDΨ gene.

Interpretation & conclusions

RHD gene deletion was found to be the most common cause of an RHD-negative phenotype while RHDΨ gene was, reported to be present in up to 39 per cent of various ethnic populations, but was not detected. RHD-CE-D hybrid gene (found in 2.5% individuals) is important for predicting the requirement of Rh prophylaxis during the antenatal period.

DEL in China: the D antigen among serologic RhD-negative individuals

BACKGROUND

Providing RhD-negative red cell transfusions is a challenge in East Asia, represented by China, Korea, and Japan, where the frequency of RhD-negative is the lowest in the world.

FINDINGS

Among 56 ethnic groups in China, the RhD-negative frequency in Han, the prevalent ethnicity, is 0.5% or less, similar to most other ethnic groups. The Uyghur ethnic group has the highest reported RhD-negative frequency of up to 4.7%, as compared to 13.9% in the US. However, an estimated 7.15 million RhD-negative people live in China. The RhD-negative phenotype typically results from a loss of the entire RHD gene, causing the lack of the RhD protein and D antigen. The DEL phenotype carries a low amount of the D antigen and types as RhD-negative in routine serology. The DEL prevalence in RhD-negative individuals averages 23.3% in the Han, 17% in the Hui and 2.4% in the Uyghur ethnicities. The Asian type DEL, also known as RHD*DEL1 and RHD:c.1227G > A allele, is by far the most prevalent among the 13 DEL alleles observed in China.

CONCLUSION

The purpose of this review is to summarize the data on DEL and to provide a basis for practical strategy decisions in managing patients and donors with DEL alleles in East Asia using molecular assays.

A Review of the Literature Organized Into a New Database: RHeference

Hundreds of articles containing heterogeneous data describe D variants or add to the knowledge of known alleles. Data can be difficult to find despite existing online blood group resources and genetic and literature databases. We have developed a modern, elaborate database for D variants, thanks to an extensive literature search with meticulous curation of 387 peer-reviewed articles and 80 abstracts from major conferences and other sources. RHeference contains entries for 710 RHD alleles, 11 RHCE alleles, 30 phenotype descriptions (preventing data loss from historical sources), 35 partly characterized alleles, 3 haplotypes, and 16 miscellaneous entries. The entries include molecular, phenotypic, serological, alloimmunization, haplotype, geographical, and other data, detailed for each source. The main characteristics are summarized for each entry. The sources for all information are included and easily accessible through doi and PMID links. Overall, the database contains more than 10,000 individual pieces of data. We have set up the database architecture based on our previous expertise on database setup and biocuration for other topics, using modern technologies such as the Django framework, BioPython, Bootstrap, and Jquery. This architecture allows an easy access to data and enables simple and complex queries: combining multiple mutations, keywords, or any of the characteristics included in the database. RHeference provides a complement to existing resources and will continue to grow as our knowledge expands and new articles are published. The database url is http://www.rheference.org/.

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.

Genetic variability of blood groups in southern Brazil

We evaluated genetic variability among the blood groups Kell (c.578C > T and c.1790T > C), Kidd (c.838A > G), Duffy (c.125A > G, c.265C > T and c.1-67T > C), Diego (c.2561C > T), MNS (c.143T > C) and Rh (c.676G > C) in Rio Grande do Sul in southern Brazil. Genetic profiling from 382 volunteer blood donors was performed through allelic discrimination assays using a hydrolysis probe (TaqMan®) with a real-time PCR system. The sample was divided into two groups: Euro-Brazilian and Afro-Brazilian. A comparison with studies from other regions of Brazil and the 1000 Genomes Database showed significant differences for almost all polymorphisms evaluated in our population. Population differentiation between the Euro- and Afro-Brazilian groups was low (FST value 0.055). However, when each locus was evaluated individually, KEL*06 and FY*02N.01 allele frequencies were significantly higher in the Afro-Brazilian group than in the Euro-Brazilian group. Ethnic classification that uses phenotypic criteria to find blood units with rare antigens may be important when there is a need to detect blood units with an absence of Duffy antigens. There is also a greater probability of finding donors in the Afro-Brazilian group. Taken together, the data indicate strong European and African contributions to the gene pool, with intense admixture.

Characterization of RHD alleles present in serologically RHD-negative donors determined by a sensitive microplate technique

BACKGROUND AND OBJECTIVES

Weak D phenotypes with very low antigen densities and DEL phenotype may not be detected in RhD typing routine and could be typed as D-negative, leading to D alloimmunization of D-negative recipients. The present study aimed to investigate the presence of RHD-positive genotypes in blood donors typed as D-negative by an automated system using the solid-phase methodology as a confirmatory test.

METHODS

Two screenings were performed in different selected donor populations. For the first screening, we selected 1403 blood donor samples typed as D-negative regardless of the CE status, and in the second screening, we selected 517 donor samples typed as D-negative C+ and/or E+. RhD typing was performed by microplate in an automated equipment (Neo-Immucor®), and the confirmatory test was performed by solid-phase technique using Capture R® technology. A multiplex PCR specific to RHD and RHDψ was performed in a pool of 6 DNA samples. Sequencing of RHD exons was performed in all RHD-positive samples, and a specific PCR was used to identify the D-CE(4-7)-D hybrid gene.

RESULTS AND CONCLUSION

No weak D type was found in either screening populations. Additionally, 353 (18·4%) D-negative samples presented previously reported non-functional RHD genes, 2 samples had a DEL allele, and 6 samples demonstrated new alleles, including one novel DEL allele. Our study identified six new RHD alleles and showed that the inclusion of a confirmatory test using serological methodology with high sensitivity can reduce the frequency of weak D samples typed as D-negative.

Recommendations Regarding Practical DEL Typing Strategies for Serologically D-Negative Asian Donors

Background

DEL, the weakest D variant, is mistyped as D-negative by routine serological assays. Transfusion of red blood cells expressing the DEL phenotype has the potential to elicit anti-D alloimmunization in D-negative recipients. The goal of this study was to recommend DEL typing strategies for serologically D-negative Asian donors.

Methods

RhCE phenotyping and the adsorption-elution test were performed on 674 serologically D-negative samples. RHD genotyping using real-time polymerase chain reaction and melting curve analysis were also undertaken to identify DEL alleles. Costs and turnaround time of RhCE phenotyping, the adsorption-elution test, and RHD genotyping were estimated.

Results

Sensitivity and specificity of the adsorption-elution test for serologically D-negative samples were 94.9% (93/98) and 91.5% (527/576), respectively. C+ phenotypes were detected in all 98 samples with DEL alleles. Despite comparable costs, RHD genotyping was more accurate and rapid than the adsorption-elution test.

Conclusions

Two practical DEL typing strategies using RhCE phenotyping as an initial screening method were recommended for serologically D-negative Asian donors. Compared with DEL typing using RHD genotyping, serological DEL typing using adsorption-elution test is predicted to increase the incidence of anti-D alloimmunization and decrease the D-negative donor pool without having any cost-competitiveness but can be used in laboratories where molecular methods are not applicable.

Determination of Fetal RHD Genotype Including the RHD Pseudogene in Maternal Plasma

OBJECTIVE

To examine the accuracy of fetal RHD genotype and RHD pseudogene determination in a multiethnical population.

METHODS

Prospective study involving D-negative pregnant women. Cell-free DNA was extracted from 1 ml of maternal plasma by an automated system (MagNA Pure Compact, Roche) and real-time PCR was performed in triplicate targeting the RHD gene exons 5 and 7. Inconclusive samples underwent RHD pseudogene testing by real-time PCR analysis employing novel primers and probe.

RESULTS

A positive result was observed in 128/185 (69.2%) samples and negative in 50 (27.0%). Umbilical cord blood phenotype confirmed all cases with a positive or negative PCR result. Seven (3.8%) cases were found inconclusive (exon 7 amplification only) and RHD pseudogene testing with both conventional and real-time PCR demonstrated a positive result in five of them, while two samples were also RHD pseudogene negative.

CONCLUSION

Real-time PCR targeting RHD exons 5 and 7 simultaneously in maternal plasma is an accurate method for the diagnosis of fetal D genotype in our population. The RHD pseudogene real-time PCR assay is feasible and is particularly useful in populations with a high prevalence of this allele.

Dried blood spots of pooled samples for RHD gene screening in blood donors of mixed ancestry

OBJECTIVES

In this study, we present a strategy for RHD gene screening based on real-time polymerase chain reaction (PCR) using dried blood spots of pooled samples.

BACKGROUND

Molecular analysis of blood donors may be used to detect RHD variants among the presumed D-negative individuals. RHD genotyping using pooled samples is a strategy to test a large number of samples at a more reasonable cost.

MATERIALS AND METHODS

RHD gene detection based on real-time PCR using dried blood spots of pooled samples was standardised and used to evaluate 1550 Brazilian blood donors phenotyped as RhD-negative. Positive results were re-evaluated by retesting single samples using real-time PCR and conventional multiplex PCR to amplify five RHD-specific exons. PCR-sequence-specific primers was used to amplify RHDψ allele.

RESULTS

We devised a strategy for RHD gene screening using dried blood spots of five pooled samples. Among 1550 serologically D-negative blood donors, 58 (3.74%) had the RHD gene. The non-functional RHDψ allele was detected in 47 samples (3.02%).

CONCLUSION

The present method is a promising strategy to detect the RHD gene among presumed RhD-negative blood donors, particularly for populations with African ancestry.

Cost-effective pooling of DNA from nasopharyngeal swab samples for large-scale detection of bacteria by real-time PCR

We investigated the potential of pooling DNA from nasopharyngeal specimens to reduce the cost of real-time PCR (RT-PCR) for bacterial detection. Lyophilization is required to reconcentrate DNA. This strategy yields a high specificity (86%) and a high sensitivity (96%). We estimate that compared to individual testing, 37% fewer RT-PCR tests are needed.

RHD genotyping and its implication in transfusion practice

BACKGROUND

The limitations of serology can be overcome by molecular typing. In order to evaluate the contribution of RH systematic genotyping and its implication in transfusion practice, a genotyping of D- blood donors was initiated.

METHODS

Blood samples were collected from 400 unrelated D- individuals. All samples were tested by RHD exon 10 PCR. In order to clarify the molecular mechanisms of RHD gene carrier, we applied molecular tools using different techniques: PCR-multiplex, and PCR-SSPs.

RESULTS

Among 400 D- subjects tested, 390 had RHD gene deletion; and 10 had RHD exon 10 of which seven were associated with the presence of the C or E antigens. Among D- carriers, we observed in five cases the presence of RHD-CE-Ds hybrid, in four cases the presence of pseudogene RHD ψ and in one case the presence of weak D type 4.

CONCLUSION

Since the majority of aberrant alleles were associated with C or E antigens and the preliminary infrastructure for molecular diagnostic were absent in all Tunisia territory, we recommend to reinforce transfusion practice to consider D- donors but C+/E+ antigens as D+ donors and the application of RHD molecular typing only to solve serologic problems.

The RHD(1227G>A) DEL-associated allele is the most prevalent DEL allele in Australian D- blood donors with C+ and/or E+ phenotypes

BACKGROUND

Red blood cells (RBCs) with D antigen levels only detected by anti-D adsorption-elution and an antiglobulin test express a DEL phenotype. For two DEL types, including RHD(1227G>A), immunization of D- recipients has been reported. This study's aim was to measure the prevalence of DEL-associated RHD alleles in a cohort of Australian D- donors to develop a model to estimate alloimmunization risk.

STUDY DESIGN AND METHODS

D-, C+ and/or E+ blood donors were screened for RHD exons using quantitative polymerase chain reaction. Donors with RHD signals were DEL phenotyped with MCAD6 anti-D. RHD alleles were characterized via single-nucleotide polymorphism array or sequencing. Extended DEL phenotyping was performed with an anti-D panel.

RESULTS

Among 2027 donors, 39 carried RHD alleles that have been previously reported to associate with either the DEL or the weak D phenotype. An additional five donors carried previously unreported RHD alleles and exhibited the DEL phenotype: RHD(IVS2-2delA), RHD(IVS1+5G>C), RHD(ex9:del/CE), and RHD(ex8:del/CE) represented twice. In total, DEL/weak D-associated RHD alleles were detected in 44 of 2027 donors or 2.17% (95% confidence interval, 1.54%-2.81%). The RHD(1227G>A) DEL allele was the most frequent (n = 16). The risk of transfusing D- females not more than 40 years of age with an RHD(1227G>A) DEL RBC unit (when managed as D-) is estimated to be one in 149,109 transfusions (range, 100,680-294,490).

CONCLUSION

DEL/weak D-associated RHD alleles were found in 2.17% of Australian D-, C+ and/or E+ blood donors. This differs from previous European reports in that the clinically significant RHD(1227G>A) DEL allele is the most prevalent.

RHD variants in Polish blood donors routinely typed as D-

BACKGROUND

Blood donors exhibiting a weak D or DEL phenotypical expression may be mistyped D- by standard serology hence permitting incompatible transfusion to D- recipients. Molecular methods may overcome these technical limits. Our aim was to estimate the frequency of RHD alleles among the apparently D- Polish donor population and to characterize its molecular background.

STUDY DESIGN AND METHODS

Plasma pools collected from 31,200 consecutive Polish donors typed as D- were tested by real-time polymerase chain reaction (PCR) for the presence of RHD-specific markers located in Intron 4 and Exons 7 and 10. RHD+ individuals were characterized by PCR or cDNA sequencing and serology.

RESULTS

Plasma cross-pool strategy revealed 63 RHD+ donors harboring RHD*01N.03 (n = 17), RHD*15 (n = 12), RHD*11 (n = 7), RHD*DEL8 (n = 3), RHD*01W.2 (n = 3), RHD-CE(10) (n = 3), RHD*01W.3, RHD*01W.9, RHD*01N.05, RHD*01N.07, RHD*01N.23, and RHD(IVS1-29G>C) and two novel alleles, RHD*(767C>G) (n = 3) and RHD*(1029C>A). Among 47 cases available for serology, 27 were shown to express the D antigen

CONCLUSION

1) Plasma cross-pool strategy is a reliable and cost-effective tool for RHD screening. 2) Only 0.2% of D- Polish donors carry some fragments of the RHD gene; all of them were C or E+. 3) Almost 60% of the detected RHD alleles may be potentially immunogenic when transfused to a D- recipient.

RHD PCR of D-Negative Blood Donors

SUMMARY

RHD PCR of blood donors may be used to reveal weak D, partial D, DEL and chimeric D+/D- donors among presumed D-negative blood donors. Units donated by such donors pose a definite yet low risk for anti-D immunization of transfusion recipients. The frequency of DEL donors among D-negative donors is 1:350 to 1:2,000 in Europe and up to 1:5 in Asian countries. Different strategies for RHD PCR of blood donors have been used. Probably, the most cost-efficient implementation is replacement of sensitive D antigen testing with the indirect antiglobulin test by RHD PCR in pools which might even reduce total testing cost.