Weak D and DEL alleles detected by routine SNaPshot genotyping: identification of four novel RHD alleles

Resolution of RHCE Haplotype Ambiguities in Transfusion Settings

Red blood cell (RBC) transfusion, limited by patient alloimmunization, demands accurate blood group typing. The Rh system requires specific attention due to the limitations of serological phenotyping methods. Although these have been compensated for by molecular biology solutions, some RhCE ambiguities remain unresolved. The RHCE mRNA length is compatible with full-length analysis and haplotype discrimination, but the RHCE mRNA analyses reported so far are based on reticulocyte isolation and molecular biology protocols that are fastidious to implement in a routine context. We aim to present the most efficient reticulocyte isolation method, combined with an RT-PCR sequencing protocol that embraces the phasing of all haplotype configurations and identification of any allele. Two protocols were tested for reticulocyte isolation based either on their size/density properties or on their specific antigenicity. We show that the reticulocyte sorting method by antigen specificity from EDTA blood samples collected up to 48 h before processing is the most efficient and that the combination of an RHCE-specific RT-PCR followed by RHCE allele-specific sequencing enables analysis of cDNA RHCE haplotypes. All samples analyzed show full concordance between RHCE phenotype and haplotype sequencing. Two samples from the immunohematology laboratory with ambiguous results were successfully analyzed and resolved, one of them displaying a novel RHCE allele (RHCE*03 c.340C>T).

Rh flow cytometry: An updated methodology for D antigen density applied to weak D types 164 and 165

BACKGROUND

An original methodology for determining the D antigen density on red cells was published in 2000 and has been applied in many publications since. This flow cytometry-based assay remained largely unrevised utilizing monoclonal anti-Ds that are not readily available anymore. We updated the methodology to quantify erythrocyte D antigen sites using microspheres and monoclonal anti-Ds that are commercially available today.

METHODS

The absolute D antigen density of a frozen standard CcDEe cell, drawn in 2003, a fresh blood donation from the same individual, drawn in 2022, and an internal control CcDEe cell, was quantified by flow cytometry using fluorescence-labeled microspheres. The internal control CcDEe cell was used in conjunction with 9 commercial anti-Ds to determine D antigen densities of 7 normal D, 4 partial D, and 11 weak D type samples, including 2 novel alleles.

RESULTS

The reproducibility of the updated assay was evaluated with red cells of published D antigen densities. The current results matched the known ones closely. The new weak D types 164 and 165 carried 4500 and 1505 D antigens/red cell, respectively. The absolute D antigen density decreased from 27,231 to 26,037 in an individual over 19 years.

DISCUSSION

The updated assay gave highly reproducible results for the D antigen densities of Rh phenotypes. Readily available anti-Ds allowed for the determination of the D antigen densities of 7 weak D types. The assay is suitable to evaluate the effects of distinct amino acid substitutions on the RhD phenotype.

DEL variants: review of molecular mechanisms, clinical consequences and molecular testing strategy

Patients with DEL phenotype, a D variant with a low number of D antigens per red blood cell, are routinely typed as RhD-negative in serology testing and are detectable only by adsorption and elution techniques or molecular methods. DEL is of clinical importance worldwide, as indicated by its genotype-phenotype discrepancies among different populations and its potential to cause anti-D alloimmunization when DEL phenotype individuals are inadvertently managed as RhD-negative. This narrative review summarized the DEL alleles causing DEL phenotype and the underlying mechanisms. The clinical consequences and current molecular testing approach were discussed to manage the transfusion needs of patients and donors with DEL phenotype.

Molecular and serological analysis of the D variant in the Chinese population and identification of seven novel RHD alleles

BACKGROUND

The molecular basis of the D variant phenotype in the Chinese differs greatly from that of the Caucasian. Adapting a specific D typing strategy to the spectrum of prevalent RHD variant alleles is necessary.

STUDY DESIGN AND METHODS

Blood samples with ambiguous D phenotypes were collected in the Southern Chinese population. A special three-step typing strategy was applied. First, the common DVI type 3 was identified from epitope profiles of D antigen. Then, another common weak D type 15 (RHD*845A) was identified by epitope profiles of D antigen and Sanger sequencing of RHD exon 6. Finally, the remaining D variants were genotyped mainly by Sanger sequencing. For the novel RHD alleles in the coding region and exon-intron junction, in vitro transfection and minigene splicing assays were performed, respectively. The anti-D investigation was performed.

RESULTS

DVI type 3 (65/253, 25.7%) and weak D type 15 (62/253, 24.5%) were common Chinese D variants, and RHD*960A, DFR, RHD*weak D type 25, 72, and 136 were frequent variant RHD alleles. Besides, twenty-two sporadic and seven novel RHD alleles (RHD*188A; RHD*688C; RHD*782 T; RHD*1181C; RHD*165 T, 993A; RHD*148 + 3G > T and RHD*1227 + 5G > C) were identified. The deleterious effect of the novel RHD alleles on D antigen or mRNA expression was confirmed. Anti-D was detected in two DVI type 3 pregnant women.

DISCUSSION

The three-step typing strategy provides an effective approach for Chinese D variant typing. It can be anticipated that commercially available RHD genotyping kits have limitations for testing Chinese D variants, as some of the frequent variants are not interrogated.

Missense RHD single nucleotide variants induce weakened D antigen expression by altering splicing and/or protein expression

BACKGROUND

Although D variant phenotype is known to be due to genetic defects, including rare missense single nucleotide variants (SNVs), within the RHD gene, few studies have addressed the molecular and cellular mechanisms driving this altered expression. We and others showed previously that splicing is commonly disrupted by SNVs in constitutive splice sites and their vicinity. We thus sought to investigate whether rare missense SNVs located in "deep" exonic regions could also impair this mechanism.

STUDY DESIGN AND METHODS

Forty-six missense SNVs reported within exons 6 and 7 were first selected from the Human RhesusBase. Their respective effect on splicing was assessed by using an in vitro assay. An RhD-negative cell model was further generated by using the CRISPR-Cas9 approach. RhD-mutated proteins were overexpressed in the newly created model, and cell membrane expression of the D antigen was measured by flow cytometry.

RESULTS

Minigene splicing assay showed that 14 of 46 (30.4%) missense SNVs alter splicing. Very interestingly, further investigation of two missense SNVs, which both affect codon 338 and confer a weak D phenotype, showed various mechanisms: c.1012C>G (p.Leu338Val) disrupts splicing only, while c.1013T>C (p.Leu338Pro) alters only the protein structure, in agreement with in silico prediction tools and 3D protein structure visualization.

CONCLUSION

Our functional data set suggests that missense SNVs damage quantitatively D antigen expression by, at least, two different mechanisms (splicing alteration and protein destabilization) that may act independently. These data thereby contribute to extend the current knowledge of the molecular mechanisms governing weakened D expression.

Frequency of RHD variants in serologically weak D Turkish blood donors

BACKGROUND

RhD typing has remained of primary importance, as being the leading cause of hemolytic disease of the newborn. Among Rh system's 55 blood group antigens, RhD is the most immunogenic. We aimed with this study to determine weak D/partial D variant frequency in blood donors who were admitted to our blood center and have serologically designated blood group weak D.

MATERIALS AND METHODS

We screened blood donors who admitted between 2011 and 2017 to our blood center. Sixty-seven serologically weak D phenotyped donors have participated in the study. These donors' samples were studied further by Polymerase Chain Reaction Sequence- Specific Primers (PCR-SSP) for determining D variants.

RESULTS

Weak D phenotype was detected in 228(0.12 %) out of 177,554 donors. Sixty-seven of them agreed to take part in the study. The frequency of weak D and partial D was 68.7 % (n = 46), and 22.4 % (n = 15), in order. The most encountered weak D and partial D variant was type 15 and DFR type, respectively.

CONCLUSIONS

The prevalence of serologically weak D phenotypes varies by race and ethnicity. Turkey is a country covering a mixture of European and Asian DNA with different ethnic groups. Thus, our research as giving the overall distribution of RHD variants from the largest city of Turkey, which may reflect the general ethnic background of the country, would help to the establishment of a databank for blood banking. This paper is the first molecular study on RHD variants in Turkey. New molecular research would be more reliable and precise.

Molecular and computational analysis of 45 samples with a serologic weak D phenotype detected among 132,479 blood donors in northeast China

Background

RH1 is one of the most clinically important blood group antigens in the field of transfusion and in the prevention of fetal incompatibility. The molecular analysis and characterization of serologic weak D phenotypes is essential to ensuring transfusion safety.

Methods

Blood samples from a northeastern Chinese population were randomly screened for a serologic weak D phenotype. The nucleotide sequences of all 10 exons, adjacent flanking intronic regions, and partial 5′ and 3′ untranslated regions (UTRs) were detected for RHD genes. Predicted deleterious structural changes in missense mutations of serologicl weak D phenotypes were analyzed using SIFT, PROVEAN and PolyPhen2 software. The protein structure of serologic weak D phenotypes was predicted using Swiss-PdbViewer 4.0.1.

Results

A serologic weak D phenotype was found in 45 individuals (0.03%) among 132,479 blood donors. Seventeen distinct RHD mutation alleles were detected, with 11 weak D, four partial D and two DEL alleles. Further analyses resulted in the identification of two novel alleles (RHD weak D 1102A and 399C). The prediction of a three-dimensional structure showed that the protein conformation was disrupted in 16 serologic weak D phenotypes.

Conclusions

Two novel and 15 rare RHD alleles were identified. Weak D type 15, DVI Type 3, and RHD1227A were the most prevalent D variant alleles in a northeastern Chinese population. Although the frequencies of the D variant alleles presented herein were low, their phenotypic and genotypic descriptions add to the repertoire of reported RHD alleles. Bioinformatics analysis on RhD protein can give us more interpretation of missense variants of RHD gene.

Effects of RHD gene polymorphisms on distinguishing weak D or DEL from RhD- in blood donation in a Chinese population

BACKGROUND

Weak D or DEL red blood cell units may be mistyped as RhD- by current serology assays, which can lead to incompatible transfusion to RhD- recipients and further cause anti-D immunization. Molecular RHD blood group typing is a very effective method for overcoming current technical limits. The purpose of this study was to identify RHD single-nucleotide polymorphisms (SNPs) and compare the genotype prevalence among confirmed RhD- individuals in a Chinese population as well as explore effective biomarkers for current weak D or DEL detection before blood transfusion.

METHODS

In the present study, 125 weak D (1, 2, 3, and 4.1) or DEL and 185 RhD- blood samples from donors detected by current standard serology were collected. Genotyping system was used to analyze the SNPs of RHD in each sample.

RESULTS

Seven SNPs (rs592372, rs11485789, rs6669352, rs3118454, rs1053359, rs590787, and rs3927482) were detected in the RHD region. Rs3118454, rs1053359, rs590787, and rs3927482 showed significant differences between the weak D (1, 2, 3 and 4.1) or DEL and RhD- groups. Further combined analysis of the allelic distribution of these four SNPs revealed their higher frequencies in the RhD- group.

CONCLUSION

The SNPs rs3118454, rs1053359, rs590787, and rs3927482 in RHD showed a significantly higher frequency among an RhD- Chinese population and are potential biomarkers.

Comprehensive Molecular Analysis of Serologically D-Negative and Weak/Partial D Phenotype in Thai Blood Donors

Background

Molecular genetics of the Rh system has been extensively studied in Caucasians, Black Africans, East Asians, and Indians more recently. In this work, we sought to investigate the molecular basis of variant D expression in the Thai population, which remains unknown.

Materials and Methods

Blood samples from 450 Thai donors showing the variant D phenotype were collected. The RHD gene was analyzed by quantitative multiplex polymerase chain reaction of short fluorescent fragments and/or Sanger sequencing.

Results

The most frequent alleles in 200 D-negative and 121 DEL samples were the whole RHD gene deletion and the Asian DEL alleles, respectively. In 129 weak/partial D samples, 36 variant alleles were identified, including eight novel alleles. RHD*06.03, which is common in variant D samples from South China, is the most prevalent variant allele, followed by the recently reported Indian RHD*01W.150 allele.

Discussion

For the first time, a comprehensive overview of the nature and distribution of variant RHD alleles in Thailand is reported. It is a milestone to pave the way towards improvement of the current screening strategy to identify DEL donors accurately. The next step will be the design and implementation of a simple molecular test for screening the most frequent alleles, specifically in this population.

Rapid rare ABO blood typing using a single PCR based on a multiplex SNaPshot reaction

BACKGROUND

ABO subgroups would be considered when discrepancies in ABO grouping occur. Serological methods including adsorption-elution test, salivary ABH inhibition test, and anti-A1 (lectin) saline method could be used. However, these serological methods are laboring and obscure. Therefore, reliable and affordable method to assess the ABO subgroups is of particular interest.

METHODS

To solve this problem, the multiplex SNaPshot-based assays were designed to determine rare A and B subgroups. Primers used as probes for determination of rare ABO blood groups known in Taiwanese population were designed. Many ABO subtype samples were used to validate the accuracy and reproducibility of our SNaPshot panel.

RESULTS

A panel of primer probes were successfully designed in determining 8 SNP sites (261, 539, 838, 820, 745, 664, IVS6 +5, and 829 in exon 6 and 7) for A phenotype and 6 SNP sites (261, 796, IVS3 +5, 247, 523, and 502 in exon 2, 6 and 7 and intron 3) for B phenotype. SNaPshot analysis for defining blood group A alleles (A₁, A₂, A₃, A_m and A_el) and blood group B alleles (B₁, B₃, B_w and B_el) was therefore available.

CONCLUSION

SNaPshot analysis could be used in reference laboratories for typing known rare subgroups of A and B without DNA cloning and traditional sequencing. Moreover, this method would help to construct databases of genotyped blood donors, and it potentially plays a role in determining fetal-maternal ABO incompatibility.

Two large deletions extending beyond either end of the RHD gene and their red cell phenotypes

Only two partial deletions longer than 655 nucleotides had been reported for the RHD gene, constrained within the gene and causing DEL phenotypes. Using a combination of quantitative PCR and long-range PCR, we examined three distinct deletions affecting parts of the RHD gene in three blood donors. Their RHD nucleotide sequences and exact boundaries of the breakpoint regions were determined. DEL phenotypes were caused by a novel 18.4 kb deletion and a previously published 5.4 kb deletion of the RHD gene; a D-negative phenotype was caused by a novel 7.6 kb deletion. Examination of the deletion-flanking regions suggested microhomology-mediated end-joining, replication slippage, and non-homologous end-joining, respectively, as the most likely mechanisms for the three distinct deletions. We described two new deletions affecting parts of the RHD gene, much longer than any previously reported partial deletion: one was the first deletion observed at the 5' end of the RHD gene extending into the intergenic region, and the other the second deletion observed at its 3' end. Large deletions present at either end are a mechanism for a much reduced RhD protein expression or its complete loss. Exact molecular characterization of such deletions is instrumental for accurate RHD genotyping.

The synonymous nucleotide substitution RHD 1056C>G alters mRNA splicing associated with serologically weak D phenotype

BACKGROUND

D antigen is one of the most clinically significant blood group antigens. Variation of the RHD gene can cause weak D or partial D phenotypes. While most variations are missense substitutions with amino acid changes, those without are called "silent" or "synonymous" substitutions. Synonymous substitutions often have little effect on the protein, not altering the phenotype. However, effect on splicing can affect end-product protein. We report a new synonymous variation, RHD 1056C>G, that resulted in weak D phenotype, and predicted its effect with various in silico methods.

METHODS

Serologic testing of the D antigen with full sequencing of the RHD gene was done. Human Splice Finder was used to predict the effect of this variation, and validation of this method was done with all known RHD variations reported in the literature.

RESULTS

RHD 1056C>G was predicted to cause the formation of an exonic splicing silencer (ESS) site. The creation of new ESS site potentially inhibits the splicing event, resulting alteration of splicing. This is similar to remodeling of splice acceptor or donor site, as this kind of deep exonic variation could affect the D antigen's quality or quantity. This is in concordance with serologic results, which showed only delayed weak agglutination to anti-D reagents.

CONCLUSIONS

The analytic methods we applied showed good correlation with the actual phenotype, along with concordant results when analyzing other known variants reported in the literature. We conclude that RHD 1056C>G results in serologic weak D phenotype.

First description of a D-CE-D hybrid gene on a weak D Type 2 molecular background

BACKGROUND

RhD phenotypes that express a significantly reduced amount of RhD antigen per red blood cell may be mistyped as RhD-negative by standard serologic methods. The molecular identification of weak D Type 1, 2, or 3 carriers allows managing them as RhD-positive and, thus, rationalizes the use of RhD-negative stock units and the administration of Rh-immunoglobulin prophylaxis, avoiding unnecessary costs and possible side effects.

STUDY DESIGN AND METHODS

One sample was investigated for confirming a D-C-E+c+e- phenotype. Rh phenotyping was performed with the microplate direct hemagglutination test. DNA array analysis was performed using the BeadChip wRhD kit, and the RHD gene was explored by sequencing to determine the molecular background associated with RhD-negative phenotype.

RESULTS

Molecular investigations showed a lack of amplification of Exons 3 through 7 and c.1154G>T transversion in Exon 9, suggesting an RHD-CE-D composite on a weak D Type 2 background. We attempted to precisely identify the two recombination sites generating this hybrid allele. The 5' and 3' breakpoints were located in Introns 2 and 7, which showed concentration of mobile Alu sequences most likely involved in the RHD-cE(3-7)-weak D Type 2 allele.

CONCLUSION

Altogether, we identified the first example of an RHD-CE-D large hybrid allele on a weak D Type 2 background associated with an RhD-negative phenotype. By investigating the RHCE-D breakpoint zones, we suggest a mobile element-mediated recombination.

Prevalence of RhD status and clinical application of non-invasive prenatal determination of fetal RHD in maternal plasma: a 5 year experience in Cyprus

BACKGROUND

After the discovery that cell-free fetal DNA (cffDNA) is circulating in the maternal plasma of pregnant women, non-invasive prenatal diagnosis for fetal RhD in maternal plasma in RhD negative women at risk for haemolytic disease of the newborn (HDN) was clinically established and used by many laboratories. The objectives of this study are: (a) to assess the feasibility and report our experiences of the routine implementation of fetal RHD genotyping by analysis of cffDNA extracted from maternal plasma of RhD negative women at risk of HDN, and (b) to estimate the RhD phenotype frequencies, the RHD genotype frequencies and the RhD zygosity in the Cypriot population.

METHODS

cffDNA was extracted from maternal plasma of 73 RhD negative pregnant women. Real-Time Multiplex-PCR was used to amplify regions of RHD gene in exons 4, 5 and 10. RhD phenotypes were determined on 445 random samples using conventional agglutination slide test.

RESULTS

The fetus was predicted to be positive in 53 cases and negative in 18 cases. Two of cases were identified as D-variants, weak D type-1 and 11. The frequency of RhD negative homozygosity in the Cypriot population was estimated to be 7.2%, while the frequencies of RHD hemizygosity and RhD positive homozygosity was calculated to be 39.2 and 53.6%, respectively.

CONCLUSION

Fetal RHD genotyping can be accurately determined using cffDNA from maternal plasma. The implementation of the test has eliminated all use of unnecessary anti-D and reduced the total use of anti-D by 25.3% while achieving appropriate management of the RhD negative pregnancies.

Molecular RHD-RHCE Analysis by Multiplex PCR of Short Fluorescent Fragments

Several hundred variant alleles have been reported within the homologous RHD and RHCE genes that encode the antigens involved in the human Rh blood group system, which is of the main interest in the field of both transfusion and obstetrical medicine. Although these variants can be mostly characterized at the molecular level by sequence-specific primer polymerase chain reaction (SSP-PCR) and/or direct sequencing, some allelic combinations remain unresolved by conventional methods. Typically exon deletion or hybrid genes may be difficult to assess in a heterozygous context. Here we describe a qualitative and quantitative method to resolve copy number variations in the RH gene exons by quantitative multiplex polymerase chain reaction (PCR) of short fluorescent fragments (QMPSF).

Prospective Evaluation of a Transfusion Policy of RhD-Positive Red Blood Cells into DEL Patients in China

BACKGROUND

The D antigen is highly immunogenic, requiring only a small quantity of transfused red blood cells (RBCs) to cause alloimmunization in D- immunocompetent recipients. DEL was reported arousing alloimmunization to true Rh- patients. Molecular studies of the RHD gene have revealed that DEL individuals retain a grossly intact RHD gene or have a portion of RHD in their genomes. Avoiding immunization with clinically important antibodies is a primary objective in transfusion medicine.

METHODS

In order to determine whether pregnant DEL women carrying an RhD+ fetus are at risk of anti-D alloimmunization, 808 Rh- pregnant women with a history of gestations or parturitions who regularly visited hospitals for their prenatal anti-D screening and postpartum care from January 2011 to December 2012 were investigated. Samples were analyzed for DEL by PCR with specific primers, PCR-sequence-specific primers (PCR-SSP), reverse transcription-PCR (RT-PCR), PCRrestriction fragment length polymorphism (PCR-RFLP), and by gene sequencing to characterize different alleles.

RESULTS

Among the 808 Rh- pregnant women of our sample, 178 (22.0%) were typed as DEL; 168 DEL samples were confirmed to have the RHD (1,227 G>A) allele, 8 DEL samples were characterized by one base mutation of the RHD (3G >A) allele, and the remaining two DEL samples were determined to carry RHD-CE(4-9)-D or RHD-CE(2-5)-D. The observation of allo-anti-D in two prominent D epitope loss cases confirmed the partial nature of these DEL phenotypes.

CONCLUSIONS

In conclusion, evidence is provided that different DEL genotypes code either for partial or complete D antigen expression. It is suggested that the use of RhD+ RBCs in complete D antigen DEL patients does not induce adverse reaction.

[Contribution of red blood group genotyping for recipients in immune-hematology through three years of activity at the EFS Alpes-Méditerranée]

AIM OF THE STUDY

Current knowledge of the molecular basis of most blood groups enables genetic testing for blood groups to overcome the limitations of agglutination. A retrospective review was carried out on genotyping assays performed between 2011 and 2013.

METHODS AND PATIENTS

The Molecular Hematology Laboratory of the EFS Alpes-Méditerranée implements commercially available tools (BioArray, Gen-Probe) and other techniques (TaqMan, tetra-primer ARMS-PCR, sequencing). It provides a high-level of expertise in molecular biology, complying with regulatory requirements and standards.

RESULTS

A total of 2382 genotyping assays was performed including 764 extended typings and 115 large extended typings essentially in cases involving multiple transfusion and suspected rare blood type. Phenotype discrepancies linked to the RH system accounted for 1501 genotypings. Discrepancies linked to the D and E were mainly related to an allele coding for weak antigen (weak D type 1, 2, 3 and EIV) while those linked to C, c and e antigens were related to an allele coding for a partial antigen (RN, ces(340), ceMo). A high prevalence of (C)ces haplotype in trans of a DAR allele was observed in Afro-Caribbean (54/62).

CONCLUSION

In transfusion medicine, red-cell genotyping can overcome the limitations of hemagglutination. It must be used only in situations where it provides a benefit either for the patient or resource management. For implementation of appropriate transfusional practices, this technique requires a sound knowledge of the genetic characteristics of blood groups and clinically relevant variants. It also requires competency with molecular biology tools and continuously updated scientific data.

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.

A new strategy to identify rare blood donors: single polymerase chain reaction multiplex SNaPshot reaction for detection of 16 blood group alleles

BACKGROUND

As an alternative to phenotyping, large-scale DNA-based assays, which are feasible for high-throughput donor red blood cell typing, were developed for determination of blood group polymorphisms. However, high-throughput genotyping platforms based on these technologies are still expensive and the inclusion of single nucleotide polymorphisms and analysis of the alleles depend on the manufacturer's determination. To overcome this limitation and in order to develop an assay to enable the screening of rare donors, we developed a SNaPshot assay for analysis of nine single nucleotide polymorphisms related to antigens that are difficult to assess using conventional serology.

MATERIALS AND METHODS

The single polymerase chain reaction multiplex SNaPshot reaction was optimized to identify nine single nucleotide polymorphisms determining 16 alleles: KEL*3/KEL*4, KEL*6/KEL*7, DI*1/DI*2, DI*3/DI*4, YT*1/YT*2, CO*1/CO*2, DO*1/DO*2, DO*4, DO*5. We designed a single multiplex PCR with primers encompassing the blood group single nucleotide polymorphisms and performed an internal reaction with probe primers able to discriminate the alleles after fragment analysis. The SNaPshot assay was validated with 140 known alleles previously determined by PCR restriction fragment length polymorphism.

RESULTS

We were able to simultaneous detect nine single nucleotide polymorphisms defining 16 blood group alleles on an assay based on a multiplex PCR combined with a single base extension using genomic DNA.

DISCUSSION

This study demonstrates a robust genotyping strategy for conducting rare donor screening which can be applied in blood centers and could be an important tool for identifying antigen-negative donors and, therefore, for providing rare blood.

Weak D caused by a founder deletion in the RHD gene

BACKGROUND

The RhD blood group system exemplifies a genotype-phenotype correlation by virtue of its highly polymorphic and immunogenic nature. Weak D phenotypes are generally thought to result from missense mutations leading to quantitative change of the D antigen in the red blood cell membrane or intracellularly.

STUDY DESIGN AND METHODS

Different sets of polymerase chain reaction primers were designed to map and clone a deletion involving RHD Exon 10, which was found in approximately 3% of approximately 2000 RHD hemizygous subjects with D phenotype ambiguity. D antigen density was measured by flow cytometry. Transcript analysis was carried out by 3'-rapid amplification of complementary DNA ends. Haplotype analysis was performed by microsatellite genotyping.

RESULTS

A 5405-bp deletion that removed nearly two-thirds of Intron 9 and almost all of Exon 10 of the RHD gene was characterized. It is predicted to result in the replacement of the last eight amino acids of the wild-type RhD protein by another four amino acids. The mean RhD antigen density from two deletion carriers was determined to be only 30. A consensus haplotype could be deduced from the deletion carriers based on the microsatellite genotyping data.

CONCLUSION

The currently reported deletion was derived from a common founder. This deletion appears to represent not only the first large deletion associated with weak D but also the weakest of weak D alleles so far reported. This highly unusual genotype-phenotype relationship may be attributable to the additive effect of three distinct mechanisms that affect mRNA formation, mRNA stability, and RhD/ankyrin-R interaction, respectively.

Identification of RHCE and KEL alleles in large cohorts of Afro-Caribbean and Comorian donors by multiplex SNaPshot and fragment assays: a transfusion support for sickle cell disease patients

To lower the alloimmunization risk following transfusion in blacks, we developed two genotyping assays for large-scale screening of Comorian and Afro-Caribbean donors. One was a multiplex SNaPshot assay designed to identify ce(s) (340), ceMO/AR/EK/BI/SM, ce(s) , ce(s) (1006) and KEL*6/*7 alleles. The other was a multiplex fragment assay designed to detect RHD, RHDψ and RHCE*C and 455A>C transversion consistent with (C)ce(s) Type 1 and DIII Type5 ce(s) . Variant RHCE*ce alleles or RH haplotypes were detected in 58·69% of Comorians and 41·23% of Afro-Caribbeans. The ce(s) allele, (C)ce(s) Type 1, and DIII Type 5 ce(s) haplotypes were identified respectively in 39·13%, 14·67% and 4·88% of Comorians and 32·23%, 5·28% and 1·76% of Afro-Caribbeans. Genotypes consistent with partial D, C, c and/or e antigen expression were observed in 26·08% of Comorians and 14·69% of Afro-Caribbeans. No homozygous genotype corresponding to the RH:-18, -34, and -46 phenotypes were found. However, over 50% of genotypes produced low-prevalence antigens at risk for negative recipients, i.e., V, VS, JAL, and/or KEL6. One new variant RHCE*ce(s) (712) allele was identified. This is the first determination of variant RHCE and KEL allele frequencies. Results indicate the most suitable targets for molecular assay screening to optimize use of compatible blood units and lower immunization risk.