Systemic analysis and zygosity determination of the RHD gene in a D-negative Chinese Han population reveals a novel D-negative RHD gene

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.

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.

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.

Genotyping of RHD c.1227G>A allele by melting curve analysis

BACKGROUND

DEL is the weakest known D-positive phenotype and is detectable only by adsorption and elution tests. RHD c.1227G>A is an important marker for DEL phenotype in East Asians. The aim of this study was to develop a method for RHD c.1227G>A genotyping by single-tube PCR with melting curve analysis.

METHODS

Two GC-rich tails of different lengths were attached to the 5'-end of allele-specific primers for RHD 1227G and 1227A alleles, such that RHD c.1227G>A could be distinguished by the melting temperature. A total of 145 D-negative Chinese Han blood donors were genotyped for RHD c.1227G>A by melting curve analysis, conventional polymerase chain reaction with sequence-specific primers (PCR-SSP), and sequencing.

RESULTS

In 143 subjects (143/145, 98.6%), PCR-SSP and melting curve analysis produced consistent results with RHD exon 9 sequencings. Two samples were genotyped as RHD 1227G/A by PCR-SSP, but as RHD 1227A/A or A/- by melting curve analysis. These two samples were confirmed to be RHD 1227A/A or A/-. Based on RHD exon 9 sequencing, the accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of the melting curve analysis for detecting both RHD 1227A and 1227G were all 100%. In contrast, the accuracy, specificity and positive predictive value of PCR-SSP for RHD 1227G detection were 98.62%, 98.21% and 94.29%, respectively, which were lower than those observed with the melting curve analysis.

CONCLUSION

Melting curve analysis for RHD c.1227G>A genotyping is a simple, rapid, and reliable method, superior to conventional PCR-SSP.

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.

RHD Genotyping by Molecular Analysis of Hybrid Rhesus box in RhD-Negative Blood Donors from Iran

D antigen is the most important and immunogenic antigen of the Rh blood group. The RhD-negative phenotype has different genetic backgrounds with variable distribution in different populations. Hybrid Rhesus box, resulting from RHD gene deletion, is used in genotyping studies of the Rh blood group as a marker to identify the RHD gene deletion. This study for the first time identified genetic mechanisms for the occurrence of RhD-negative phenotype among the Iranian population. 200 RhD-negative blood donors were randomly selected from Tehran Blood Transfusion Center. The phenotype of D, C, Ε, e and c antigens was serologically identified, and DNA was extracted from buffy coat. The molecular analysis of hybrid Rhesus box was performed by PCR-SSP and PCR-RFLP. Moreover, the presence of different exons of RHD gene was investigated by real-time PCR on extracted DNA. Hybrid Rhesus box was detected in all samples, and PCR-RFLP confirmed that 198 (99%) were homozygous for an RHD gene deletion and 2 were heterozygous for hybrid Rhesus box in which one (0.5%) had a weak D type 11 and the other one (0.5%) had a RHD-CE (2-9)-D₂ hybrid allele. Similar to Caucasians, the frequency of RHD gene deletion was high among the Iranian population studied in this investigation, so hybrid Rhesus box can be used as an efficient marker to detect RHD gene deletion in our population.

RHD-Positive Alleles among D- C/E+ Individuals from India

Background

Molecular bases of blood group systems, including Rh blood group, have been poorly studied in the Indian population so far, while specificities of Europeans, East Asians and Africans have been well known for years. In order to gain insights into the molecular bases of this population, we sought to characterize the RHD allele in D- Indian donors expressing C and/or E antigen(s).

Methods

RHD gene was analyzed in 171 serologically D-, C/E+ samples by standard molecular methods such as quantitative, multiplex PCR of short fluorescent fragments (QMPSF) and direct sequencing when necessary.

Results

RHD whole gene deletion at the homozygous state was found to be the most common genotype associated with D- phenotype (118/171, 69.0%). Nonfunctional, negative hybrid genes with reported molecular backgrounds were observed in approximately one-third of the samples, while only four samples carry single-nucleotide variations, including one novel nonsense (RHD(Y243X)), one novel frameshift (RHD(c.701delG)), and two missense (RHD(T148R) and RHD(T148R, T195M)) alleles.

Conclusion

Overall we report for the first time the molecular bases of D antigen negativity in the D-, C/E+ Indian population, which appears to be qualitatively similar to other populations, but with a population-specific, quantitative distribution of D-- alleles.

A DEL phenotype attributed to RHD Exon 9 sequence deletion: slipped-strand mispairing and blood group polymorphisms

BACKGROUND

The RhD blood group antigen is extremely polymorphic and the DEL phenotype represents one such class of polymorphisms. The DEL phenotype prevalent in East Asian populations arises from a synonymous substitution defined as RHD*1227A. However, initially, based on genomic and cDNA studies, the genetic basis for a DEL phenotype in Taiwan was attributed to a deletion of RHD Exon 9 that was never verified at the genomic level by any other independent group. Here we investigate the genetic basis for a Caucasian donor with a DEL partial D phenotype and compare the genomic findings to those initial molecular studies.

STUDY DESIGN AND METHODS

The 3'-region of the RHD gene was amplified by long-range polymerase chain reaction (PCR) for massively parallel sequencing. Primers were designed to encompass a deletion, flanking Exon 9, by standard PCR for Sanger sequencing. Targeted sequencing of exons and flanking introns was also performed.

RESULTS

Genomic DNA exhibited a 1012-bp deletion spanning from Intron 8, across Exon 9 into Intron 9. The deletion breakpoints occurred between two 25-bp repeat motifs flanking Exon 9 such that one repeat sequence remained.

CONCLUSION

Deletion mutations bordered by repeat sequences are a hallmark of slipped-strand mispairing (SSM) event. We propose this genetic mechanism generated the germline deletion in the Caucasian donor. Extensive studies show that the RHD*1227A is the most prevalent DEL allele in East Asian populations and may have confounded the initial molecular studies. Review of the literature revealed that the SSM model explains some of the extreme polymorphisms observed in the clinically significant RhD blood group antigen.

RHD positive among C/E+ and D-negative blood donors in Tunisia

PURPOSE OF THE STUDY

The aim of this study was to investigate RHD alleles among Tunisian blood donors with D-negative phenotype and positive for C and/or E antigen.

PATIENTS AND METHODS

A total of 100 D-negative and C/E+ samples were analyzed by RHD genotyping using an initial test for RHD exon 10. In case of a positive reaction, further molecular investigations including real time quantitative PCR, allele specific PCR and nucleotide sequencing were done to elucidate the RHD involved mechanisms.

RESULTS

Seventy-five percent of the studied samples lacked the RHD gene. Twenty-three percent carried the hybrid RHD-CE-D alleles (16 RHD-CE(3-7)-D, 5 RHD-CE(4-7)-D, 1 RHD-CE(4-8)-D, 1 RHD-CE(3-8)-D) and 2% were weak D (1 weak D type 1 and 1 weak D type 5).

CONCLUSION

Our study proved the high frequency of RHD gene among serologically D-negative samples, positive for C and/or E antigen. Thus achieving systematically RHCE phenotyping in all transfusion centers on the Tunisian territory and considering blood donated from D-negative C/E+ persons as D-positive will be recommended to reduce anti-D allo-immunization.

Molecular basis of DEL phenotype in the Chinese population

Background

Rh blood group system is the most complex and immunogenetic blood group system. Prevalent RHD alleles vary in different populations. We conducted the present study to examine the genotype of DEL individuals and to elucidate whether novel alleles exist in the Chinese population.

Methods

DEL phenotype was identified by a serologic adsorption-elution method. The nucleotide sequences of ten RHD exons and exon-intron boundary regions were evaluated by RHD gene-specific PCR-SSP and sequencing.

Results

Of 42306 samples from individual donors and patients, 165 samples were typed as D-negative. Among these D-negative samples, 41 DEL individuals were observed. Thirty-seven DELs were confirmed to have the RHD1227A allele. Two DELs seemed to have RHD-CE-D hybrid alleles, including one RHD-CE (4–7)-D and one RHD-CE (2–5)-D. Two novel RHD alleles were found among the rest of the DEL samples, including one RHD93T > A and one RHD838G > A.

Conclusion

In this study, about 24.85% (41/165) of the apparent D-negative Chinese individuals were DEL. RHD1227G > A is the most frequent allele in Chinese DEL phenotypes, accounting for 90.24% (37/41). The RHD-CE-D hybrid allele might be the second most frequent DEL allele in the Chinese population. Our study would contribute to the understanding of the molecular mechanism underlying D antigen expression of DEL individuals and provide useful information for designing suitable genotyping strategies in RhD-negative individuals in Asia.

Analysis of density and epitopes of D antigen on the surface of erythrocytes from DEL phenotypic individuals carrying the RHD1227A allele

BACKGROUND

The characteristics of the D antigen are important as they influence the immunogenicity of D variant cells. Several studies on antigenic sites have been reported in normal D positive, weak D and partial D cases, including a comprehensive analysis of DEL types in Caucasians. The aim of this study was to assess D antigen density and epitopes on the erythrocyte surface of Asian type DEL phenotypic individuals carrying the RHD1227A allele in the Chinese population.

MATERIALS AND METHODS

A total of 154 DEL phenotypic individuals carrying the RHD1227A allele were identified through adsorption and elution tests and polymerase chain reaction analysis with sequence-specific primers in the Chinese population. D antigen density on the erythrocyte surface of these individuals was detected using a flow cytometric method. An erythrocyte sample with known D antigen density was used as a standard. Blood samples from D-negative and D-positive individuals were used as controls. In addition, D antigen epitopes on the erythrocyte surface of DEL individuals carrying the RHD1227A allele were investigated with 18 monoclonal anti-D antibodies specific for different D antigen epitopes.

RESULTS

The means of the median fluorescence intensity of D antigen on the erythrocyte membrane surface of D-negative, D-positive and DEL individuals were 2.14±0.25, 193.61±11.43 and 2.45±0.82, respectively. The DEL samples were estimated to have approximately 22 D antigens per cell. The samples from all 154 DEL individuals reacted positively with 18 monoclonal anti-D antibodies specific for different D antigen epitopes.

DISCUSSION

In this study, D antigen density on the erythrocyte surface of DEL individuals carrying the RHD1227A allele was extremely low, there being only very few antigenic molecules per cell, but the D antigen epitopes were grossly complete.

A comprehensive investigation of RHD polymorphisms in the Chinese Han population in Xi'an

BACKGROUND

This study is a comprehensive analysis of RHD in D-negative phenotypes in saline, in Xi'an, Shanxi province, central China.

MATERIAL AND METHODS

DCcEe in saline was measured for each blood sample from every donor between January 2008 and June 2012 in the Xi'an Blood Centre, China. D-negative results were confirmed by an indirect antiglobulin test and further investigated by adsorption-elution as required. The initial step of molecular analysis was RHD zygosity testing. Then RHD was detected by a sequence-specific polymerase chain reaction system for RHD(1227G>A), weak D type 15, and RHD(711delC) alleles for the samples carrying at least one RHD. For the remaining non-identified samples, ten RHD exons were amplified using a previously widely used RHD coding region sequencing method. Some RHD/RHCE conversion alleles were identified while those remaining were submitted to direct sequencing.

RESULTS

Overall, 2,493 D-negative samples in saline were detected in a total of 890,403 donors (D-negative rate, 0.28%). Among the D-negative individuals, RHD deletion (d/d) was assessed in 1685 donors (67.59%). Non-functional RHD alleles were detected in 184 donors (7.38%), the most common being the RHD-CE(2-9)-RHD and RHD(711delC) alleles. Two new alleles were observed and family investigations were performed; RHD(1227G>A) DEL was detected in 516 individuals (20.70%), and weak D or partial D variants were identified in 108 donors (4.33%). The most common alleles were weak D type 15, D(VI) type 3 and D(V) type 2. Four new weak D alleles were noted, and two cases of RHD(1227G>A)/weak D type 15 heterozygosity were confirmed.

CONCLUSIONS

Currently, it seems to be difficult to observe any new RHD alleles in the Han Chinese population. D prediction in this population is easier because popular alleles are dominant, accounting for about 99.80% of alleles in D-negative people. Weak D types and partial D variants are rare and occur in approximately 0.01% of the population.

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.

DEL RBC transfusion should be avoided in particular blood recipient in East Asia due to allosensitization and ineffectiveness

Previously, both primary and secondary anti-D alloimmunizations induced by "Asian type" DEL (RHD1227A allele) were observed in two incidents. We investigated how often these alloimmunization events occur. The transfusions of any D-negative patients were investigated in the First Affiliated Hospital of Xi'an Jiaotong University Medical College, China, during the entire 2009. The antigens of D, C, c, E, and e were routinely serotyped. The "Asian type" DEL variant was genotyped and the RHD heterozygote was determined through two published methods. The changes in anti-D levels were monitored by the indirect antiglobulin test (IAT) and flow cytometry. Thirty D-negative transfused patients were included in the study. We focused on 11 recipients who were transfused with packed red blood cells (RBCs) from DEL donors at least one time. Of those 11 recipients, seven were anti-D negative before transfusion and four were anti-D positive (one patient with an autoantibody). One of the seven pre-transfusion anti-D negative patients produced a primary-response anti-D after being transfused with 400 ml of DEL blood twice. All four pre-transfusion antibody positive patients were not observed hemoglobin (Hb) levels increased, as expected after transfusions. Two patients had an increase in anti-D from 1:8 to 1:64 by IAT, which was also shown by flow cytometry. None of the patients experienced an acute hemolytic episode. Our data indicated that the primary anti-D induced by DEL transfusion or the secondary anti-D elevated by DEL in a truly D-negative patient might not be unusual. We suggest that a truly D-negative childbearing-aged woman should avoid DEL transfusion to protect her from primary anti-D allosensitization. In addition, anti-D positive recipients should also avoid DEL red cell transfusion due to the delayed hemolytic transfusion reaction (DHTR).

Improved allele-specific PCR technique for Kidd blood group genotyping

BACKGROUND

We developed an allele-specific polymerase chain reaction (AS-PCR) technique for Kidd blood group genotyping.

METHODS

Altogether, 340 blood samples from Thai blood donors at the National Blood Centre, Thai Red Cross Society, were tested with anti-Jk(a) and anti-Jk(b) using the gel technique and the direct urea lysis test was used for screening Jk(a-b-) phenotype. For AS-PCR technique, different types of primers were used for JK*01 and JK*02 allele detections in known DNA controls.

RESULTS

Regarding JK*02 allele detection, the pseudopositve amplification products were found when using correctly matched forward primer and a single mismatch forward primer. Interestingly, one type of two mismatch pairing at the 3' end of the forward primer can be used together with the newly designed reverse primer for Kidd blood group genotyping. It was found that the typing results in all samples obtained by serological techniques and newly developed AS-PCR technique were in agreement and this PCR technique also gave 100% concordance of results in 30 samples randomly tested twice and demonstrated reproducible results.

CONCLUSION

This study shows that the in-house AS-PCR is simple, cost-effective, and convenient for Kidd blood group genotyping in routine laboratories, especially, in resolving serologic investigations.

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

BACKGROUND

RHD alleles leading to a reduced expression of D antigen of the red blood cell (RBC) surface may be erroneously typed as D- by serology and may cause anti-D immunizations when transfused to recipients.

METHODS

To determine the occurrence of such alleles among apparent D- blood donors, molecular typing was implemented as a routine test using a pool of DNA. A total of 2,450 pretyped D- samples were tested in pools of 10 for the RHD-specific polymorphism in intron 4 and exon 7. Samples in polymer chain reaction (PCR) positive pools were individually reevaluated by exon-specific PCRs, sequencing, and serologic methods.

RESULTS

Among 2,450 serologically D- blood donor samples tested, 101 (4.1%) carried the RHD gene. Nonfunctional RHD (RHDψ, RHD*CE(2-9)-D, and RHD*CE(3-7)-D), different weak D alleles such as RHD*weak D type 1, RHD*weak D type 4.3, RHD*weak D type 5, RHD*weak D type 38, and RHD*DEL were identified.

CONCLUSION

We employed a PCR-based assay for RHD as a routine test using pools of ten DNA blood donor samples. The integration of RHD genotyping into the routine screening program using pools of DNA samples was straightforward. As a consequence, 19 (0.8%) blood donors carrying a weak D and Del phenotypes with the potential of causing anti-D immunizations in recipients were reclassified as D+. For each population, it would be necessary to adapt the RHD genotyping strategy to the spectrum of prevalent alleles.

Molecular bases of unexpressed RHD alleles in Chinese D- persons

BACKGROUND

The aim of this study was to use a systematic survey to analyze RHD alleles in Chinese D- donors who do not express D antigen or who lack functional RhD protein.

STUDY DESIGN AND METHODS

A total of 733 D-Chinese donors, not including Del phenotypes, were investigated by RHD polymorphism–specific polymerase chain reaction (PCR), Rhesus box PCR-PstI digestion, and RHD sequencing. The frequencies of identified alleles were calculated.

RESULTS

Three genetic mechanisms and eight alleles were found associated with the Chinese D- phenotype. One new RHD/CE hybrid allele and one novel mutation were also found. The rates of total deletion and the most frequent hybrid allele RHD(1)-CE(2-9)-D(10) were similar to those found in previous studies. A previously reported mutation RHD(711delC) was found to be the predominant cause of aberrant RHD alleles.

CONCLUSION

Informative population-based data for improving molecular diagnostic strategies for Chinese D- persons are suggested by this study. This type of systematic knowledge is important for the development of typing and transfusion strategies for the Chinese population.

Establishing RHD zygosity in India: a step into the future of foetal and neonatal haemolytic disease prevention

BACKGROUND

Determination of RHD zygosity is important for the prevention of haemolytic disease of foetus and neonate. There is no data from India regarding the prevalence of RHD genotypes.

OBJECTIVES

We conducted this study to investigate RHD zygosity in phenotypically RhD positive (RhD+) Indians. We have also investigated the utility and concordance of two different genotyping techniques.

METHODS

Hundred serologically RhD+ Indians were genotyped at the RHD gene using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and polymerase chain reaction-sequence-specific primer (PCR-SSP) techniques.

RESULTS

Of the 100 RhD+ individuals, 26 (25%) were D heterozygous by both methods and 74 (71·2%) were D homozygous. There was no discordance in the results from the two techniques.

CONCLUSION

At least 25% of RhD+ Indians are heterozygous at the RHD gene. Both the genotyping techniques were equally robust and their complete concordance indicates RHD deletion as the main mechanism underlying RhD negativity in Indians.

Aberrant RNA splicing in RHD 7-9 exons of DEL individuals in Taiwan: a mechanism study

BACKGROUND

The Rh blood D group provides a clinically important model of aberrant splicing with skipped exons. Approximately 30% of serologically D-negative Chinese individuals have an intact RHD gene (DEL phenotype) and induce allo-immunization in transfusions. The RHD1227GNA polymorphism occurs in >95% DEL phenotype of Asian descent. The effects of RHD 1227A and a novel allele on exon 9 splicing were examined.

RESULTS

Amplified DEL RNA products revealed that 3 transcripts involved skipping of exons 8-9, exon 9, or exon 9 with an inserted 170-bp cryptic exon located between exons 7 and 8. A novel, single nucleotide polymorphism was identified in the 7th intron, (IVS7) 923C>T, and present in all DEL patients. The odds ratio of RHD1227G>A allele with DEL phenotype was 2711. Splicing analysis of transcripts from minigenes containing the 1227GNA allele, but not the (IVS7) 923C>T allele, demonstrated aberrant exon 9 skipping.

CONCLUSIONS

A combined haplotype of 1227G>A and IVS7 923C>T alleles was apparent in >95% DEL Chinese individuals. RHD1227A mutation significantly increased aberrant mRNA splicing, producing a hybrid RHD mRNA lacking exon 9. These results provide a molecular basis of the DEL phenotype in the Chinese population.

Non-invasive foetal RHD genotyping via real-time PCR of foetal DNA from Chinese RhD-negative maternal plasma

BACKGROUND

A majority of studies predicting the foetal RhD blood group in free foetal DNA from RhD-negative maternal plasma have been conducted in Caucasian populations, whereas limited data have been accumulated for Asian populations. In this study, we assessed the feasibility of prenatal genotyping of RHD in RhD-negative Chinese pregnant women.

MATERIALS AND METHODS

Cell-free plasma DNA was extracted from 78 RhD-negative Chinese women carrying a singleton foetus (gestation between 14 and 40 weeks). Foetal DNA was confirmed by testing SRY or nine different polymorphic STR loci in the maternal plasma and buffy coat. Foetal RHD exons 5, 7 and 10 and intron 4 were successfully amplified with RQ-PCR. The RHD1227A allele was examined in all RhD-positive individuals. The foetal RHD genotyping results were compared with the infant cord blood serological analysis.

RESULTS

Among the 78 specimens, RHD genotyping results of 70 cases were in complete concordance with serological results from foetal umbilical cord blood. Sixty of these cases were identified as RhD-positive, and 10 cases were typed as RhD-negative. In addition, five cases were 'false-positives', while three cases were considered inconclusive. The detection rate was 89.7% (70/78). In four of the five 'false-positive' cases, the RhDel phenotype was assessed by detecting the RHD1227A allele. Thus, this method yielded a 94.9% (74/78) accuracy rate.

CONCLUSIONS

The correct foetal RhD phenotype may be accurately predicted from RhD-negative maternal plasma in Chinese subjects. The RHD1227A allele proved to be an important genetic marker in the RhDel Chinese population.

Molecular basis of the RHD gene in blood donors with DEL phenotypes in Shanghai

BACKGROUND AND OBJECTIVES

The purpose of the work was to analyse the genotype of D-elute (DEL) samples and to elucidate whether there were novel DEL alleles in Chinese population.

MATERIALS AND METHODS

D-negative samples were identified by an indirect antiglobulin test (IAT), and absorption\elution tests to screen weak D, partial D and DEL phenotypes. DELs were further analysed by multiplex PCR, PCR-sequence-specific primers (PCR-SSP) and sequencing. Some of the DEL samples were determined to show RHD zygosity by PCR-restriction fragment length polymorphism or real-time quantitative PCR.

RESULTS

Of 400 253 samples from individual donations, 1585 (0.40%) were typed as D negative. Among these D-negative samples, 279 DELs were observed. Two hundred and sixty-eight DELs were confirmed to have the RHD (K409 K) allele. Three DELs seemed to have RHD-CE-D hybrid alleles, including one RHD-CE(4-9)-D, one RHD-CE(2-5)-D and one suspected RHD(1-9)-CE. Five novel RHD alleles were found among the rest of the DEL samples, including four RHD 3 g > a, one RHD (R10W), one RHD (L18P), one RHD (L84P) and one RHD (A137E). Eighty-four DELs were analysed for Rhesus box zygosity, there were 77 RHD+/RHD-and seven RHD+/RHD+.

CONCLUSION

About 4.35% apparent D negative Chinese individuals were weak D or partial D, while 17.60% were DEL. Novel DEL alleles are rare, and all but 11 of the 279 DELs were due to the most common DEL allele, RHD (K409 K). The RHD 3G > A might be the second most frequent DEL allele in Chinese. Exploration of a complete molecular basis for DEL in Chinese ethnic groups is a long-term endeavour.

Molecular and family analyses revealed two novel RHD alleles in a survey of a Chinese RhD-negative population

BACKGROUND AND OBJECTIVES

RHD alleles are considered variable in the Chinese RhD-negative persons. The purpose of the present work was to elucidate the molecular bases of two novel RHD alleles identified in a survey of a Chinese RhD-negative population.

MATERIALS AND METHODS

A total of 163 RhD-negative blood samples were investigated. The sequences of RHD exons were examined by RHD exon specific multiplex polymerase chain reaction (PCR) and PCR with sequence-specific primers (PCR-SSP). Characterizations of RHD intron 2 and Rhesus box were performed by PCR-PstI digestion. The DNA and cDNA sequences of the novel alleles were determined by PCR and reverse transcriptase-PCR (RT-PCR) sequencing analysis. A family study was performed to investigate the segregation of a novel RHD allele.

RESULTS

One hundred and twenty-nine samples (79.1%) had no RHD gene. Twenty-seven samples (16.6%) carried RHD-CE-D hybrid alleles. The remainder seven samples (4.3%) appeared to have an intact RHD gene. Three of them were sequenced for RHD gene and two novel alleles, RHD 325del and RHD intron 2 1A, were identified. The deletion of a nucleotide A at position 325 in the allele RHD 325del resulted in a stop codon at amino acid position 118. The RHD intron 2 1A allele was generated from a splice mutation and its transcript sequence had no exon 2. Family study indicated that the RHD 325del allele was inherited with a Ce haplotype.

CONCLUSION

This study provides the molecular bases of RHD alleles RHD 325del and RHD intron 2 1A. The existences of RHD 711del, RH (D1 CE2-9 D10), and RH (D1 CE2-9 D10) alleles in the Chinese population were confirmed. A PCR-SSP-based assay for rapid detection of RHD 325del and RHD intron 2 1A alleles was established and it could be used to predict the RHD genotype in the Chinese RhD-negative subjects.

Molecular basis of D variants in Chinese persons

BACKGROUND

Most studies of the molecular basis of D variants have been conducted in Caucasian and African populations. There are limited data on the molecular basis for D variants in Chinese populations.

STUDY DESIGN AND METHODS

With a blended monoclonal anti-D and a sequential slide and tube typing protocol, red blood cells from greater than 99 percent of Han Chinese were tested for the D antigen. Samples that agglutinated weakly by tube method or that reacted only by indirect antiglobulin test (IAT) were classified as D variants. The D variant was tested by an RHD polymerase chain reaction with sequence specific primers and by gene sequencing to distinguish and characterize weak D and partial D alleles.

RESULTS

Of 305,572 samples from individual donations (305,475 [99.97%] were ethnic Han and 97 [0.032%] were ethnic minorities), 304,134 (99.53%) typed as D+. Five (0.0016%) typed as D variants (weak agglutination by tube). By IAT an additional 32 (0.0105%) typed as D variants and 1401 (0.46%) typed as D-. Weak D type 15 and RHD(K409K) alleles represented 72.7 percent of all weak D phenotypes. All partial D phenotypes were DVI Type 3 or DV. Three new weak D alleles carrying 594A>T and 602C>G (weak D Type 51), 92T>C (weak D type 52), and 740T>G (weak D type 53) mutations, respectively, were identified.

CONCLUSION

There are significant differences in the frequencies and molecular characteristics of D variants among indigenous Chinese populations, compared to Caucasian and African populations, which must be considered when developing clinical practices related to D variant blood donors, transfusion recipients, or obstetrical patients.

An easy RHD genotyping strategy for D- East Asian persons applied to Korean blood donors

BACKGROUND

In East Asian populations RHD alleles are known to occur frequently among D- donors, requiring suitable genotyping strategies. The molecular basis of the "RHD(el)" allele previously reported in Taiwan to harbor a genomic 1013-bp deletion was questioned by several authors.

STUDY DESIGN AND METHODS

The presence of the RHD gene was investigated in 126 random serologic D- blood donors from Gwangju, southwest Korea. Four donors who typed weakly positive for the D antigen were also analyzed. RH alleles were determined by polymerase chain reaction (PCR) with sequence-specific priming (PCR-SSP) or nucleotide sequencing.

RESULTS

Seventy-five percent of the serologically D- samples lacked the RHD gene, 10 percent carried the hybrid RHD-CE(2-9)-D2 or RHD-CE(2-7)-D2 alleles, 13 percent represented the RHD(K409K), and 2 percent were weak D type 15 and type 17. Among the four donors typing weak D, two carried weak D type 15, one RHD(K409K), and one the novel weak D type 43. Critical molecular characteristics of RHD(K409K) and its population frequencies were indistinguishable to those reported for the RHDel allele.

CONCLUSION

Korean RHD allele frequencies are comparable to Chinese and Japanese frequencies. It is concluded that the RHDel allele may actually not exist but is identical to RHD(K409K). A practical RHD genotyping strategy applicable to D- donors in all East Asian populations was devised. The strategy requires four PCR-SSP procedures only for RHD intron 4 and exon 7 as well as RHD(K409K) and non-RHD(K409K).

Prevalence of RHD 1227A and hybrid Rhesus box in the general Chinese population

The Rhesus (Rh) blood group is the most polymorphic blood group system. Serological analyses revealed that only 0.1% to 0.4% of the Chinese population exhibited a D-negative phenotype. In contrast to D-negative Caucasian persons, who are mostly associated with a deletion of RHD between the upstream and downstream Rhesus boxes, approximately 30% of apparently D-negative Chinese were actually DEL, potentially harboring a grossly intact RHD gene. The authors' previous detection of the RHD 1227A allele in all DEL samples prompted the conclusion that the RHD 1227A gene is highly prevalent in DEL populations of Chinese ethnicity, which indicates that it may be a marker for the rapid detection of DEL. Currently, random surveys for RHD 1227 A allele and for hybrid Rhesus box were conducted among 399 Han Chinese in Taiwan. The estimated frequencies of RHD 1227G/G, RHD 1227A/G, RHD A/A, RHD 1227G/-, RHD 1227A/-, and RHD-/- were 0.89054, 0.0118, 0.00016, 0.0414, 0.00055, and 0.00192, respectively. These results were consistent with the prevalence of D-negative and DEL in persons of Chinese ethnicity. The authors conclude that detection of RHD 1227A and hybrid Rhesus box alleles is predictive of Rh phenotypes in the Chinese population.

How I manage donors and patients with a weak D phenotype

PURPOSE OF REVIEW

Since the adoption of molecular blood-group typing, the considerable heterogeneity of the serologic entities weak D and DEL at the molecular level has come to light. I offer an approach to the management of donors and patients expressing D antigen weakly and carrying any of the various molecular types of weak D and DEL.

RECENT FINDINGS

More than 50 distinct weak D alleles have been described. An internet-based survey of anti-D immunizations occurring in D-positive transfusion recipients reveals that no allo-anti-D has been observed in patients carrying prevalent weak D types. Allo-immunizations are documented for weak D types 4.2 (also known as DAR), 11 and 15. Anti-D immunizations have been reported in D-negative persons transfused with weak D and DEL red blood cells.

SUMMARY

Patients carrying any of the prevalent weak D types 1, 2, 3 or 4.1 are not prone to allo-anti-D immunization and may safely be transfused with D-positive red blood cells. Pregnant women with these weak D types need not receive RhIg. We should pay attention to weak D- or DEL-positive blood units that are labelled D-negative. The clinical benefit of removing DEL blood units from our supply of D-negative red blood cell units should be determined.

RHD(T201R, F223V) cluster analysis in five different ethnic groups and serologic characterization of a new Ethiopian variant DARE, the DIII type 6, and the RHD(F223V)

BACKGROUND

The RHD phylogeny in humans shows four main clusters of which three are predominantly observed in (African) black persons. Each of the African clusters is characterized by specific amino acid substitutions relative to the Eurasian RHD allele. RH phylogeny defines the framework for identification of clinically relevant aberrant alleles. This study focuses on the weak D type 4 cluster (characterized by RHD(T201R, F223V) (602C>G 667T>G)) in five ethnic groups.

STUDY DESIGN AND METHODS

A total of 1702 samples were screened for the presence of 602C>G and 667T>G by sequence-specific polymerase chain reaction (PCR-SSP). Eighty samples were assigned to the weak D type 4 cluster and were molecularly characterized by PCR-SSP and RHD sequencing. Antigens of aberrant alleles were characterized with monoclonal anti-D according to the 37-epitope model when possible.

RESULTS

Five new aberrant alleles, DIII type 6, DIII type 7, DARE, RHD(T201R, F223V) (without 819G>A), and RHD(F223V), were identified and DIII type 6, DARE, and RHD(F223V) were serologically characterized with monoclonal anti-D. Both the DARE and RHD(F223V) showed epitope loss. It is postulated that the 1136C>T nucleotide substitution (characteristic for the DAU allele cluster) is present on the DVa(KOU) allele.

CONCLUSION

Identification of the new variant alleles refines the phylogeny of RHD in humans. The proposed DVa(KOU) allele with 1136C>T (DVa(KOU)T379M) is probably caused by conversion of the DAU0 allele and the DVa(KOU) allele, forming a phylogenetic link between the DV allele and the DAU cluster. By describing the RHD(F223V) (602C>G) and RHD(T201R, F223V) (602C>G and 667T>G) alleles formal proof is given for the origin of the non-Eurasian cluster.

Molecular genetics of RH and its clinical application

BACKGROUND

The RH genes RHD and RHCE encode two proteins that represent the clinically most important blood group system defined by the sequences of red cell membrane proteins. In the last five years the field has been moving from defining the underlying molecular genetics to applying the molecular genetics in clinical practice.

MATERIALS AND METHODS

The state of the current knowledge is briefly summarized using recent reviews and original work since 2000.

RESULTS

The RHD and RHCE genes are strongly homologous and located closely adjacent at the human chromosomal position 1p36.11. Part of the genetic complexity is explained by the clustered orientation of both genes with their tail ends facing each other. The SMP1 gene is located interspersed between both RH genes. Using additional genetic features of the RH gene locus, RHCE was shown to represent the ancestral RH position, while RHD is the duplicated gene. More than 150 alleles have been defined for RHD alone. They were classified based on antigenic and clinical properties into phenotypes like partial D, weak D and DEL. Among the D negative phenotype a large variety of non-functional alleles were found. The frequencies of these distinct alleles vary widely among human populations, which has consequences for clinical practice.

CONCLUSION

Rhesus is a model system for the correlation of genotype and phenotype, facilitating the understanding of underlying genetic mechanisms in clustered genes. With regard to clinical practice, the genetic diagnostics of blood group antigens will advance the cost-effective development of transfusion medicine.

Detection of RhD(el) in RhD-negative persons in clinical laboratory

The Rhesus (Rh) blood group is the most polymorphic human blood group system, and it is clinically significant in transfusion medicine. About 15% of Caucasoid people are RhD-negative, whereas in the Asian population, the RhD-negative blood type only occurs in 0.1% to 0.5%. However, approximately 30% of apparently RhD-negative Taiwanese people actually were RhD(el). Traditionally, we verify RhD(el) by a serologically adsorption-elution procedure with polyclonal anti-D. In our recent report, RhC phenotype is highly associated with RhD(el), and RHD1227A is a useful genetic marker for RhD(el). For setting up a rapid protocol to detect RhD(el) in clinical laboratory, a total number of 395 Taiwanese serological RhD-negative blood samples, those with RhC (+) phenotypes as selected by serological tests, were further screened by adsorption/elution tests and RHD1227A allele by specific sequence primer-polymerase chain reaction (SSP-PCR) for RhD(el). Among 395 blood samples collected from RhD-negative subjects, the incidence of RhC (+) was 43% (171/395). One hundred and twenty six of the 171 RhC (+) samples were positive for both adsorption/elution for RhD detection and SSP-PCR assay for RHD1227A. The sensitivity and specificity were 96.9% and 97.5%, respectively, for RHD1227A detection as compared with the traditional adsorption/elution test. Our results also indicated that RHD1227A was highly linked to Ce haplotypes (95.2%). In conclusion, combined RhC (+) phenotyping and RHD1227A analysis can be a simple and accurate laboratory screening protocol for RhD(el) detection in RhD-negative population.