RHC and RHc genotyping in different ethnic groups

Accuracy of RHC/c genotyping in Chinese Han population

BACKGROUND AND OBJECTIVES

The RHCE gene plays an important role in the complex and polymorphic Rh blood group system. RHCE genotyping holds significant clinical and transfusion-related implications. The objective of this study was to evaluate the accuracy of RHC/c genotyping in the Chinese Han population.

MATERIALS AND METHODS

Blood samples were obtained from 653 Chinese Han blood donors. The serological RhD and RhCcEe types were determined using monoclonal antibodies. Subsequently, multiplex real-time polymerase chain reaction (PCR) analysis was performed for RHC and RHc genotyping. Additionally, exon 2 of RHCE and exon 1 of RHD were sequenced.

RESULTS

The analysis in this study found 443 RhD-positive donors and 210 RhD-negative donors. Among the 653 total donors, discrepancies between the RHC genotyping results and the serological results were found in 37 individuals. Specifically, 6 false-positive RhC results in RhD-positive donors and 28 false-positive RhC results in RhD-negative donors were identified based on c.48C in RHCE exon 1. Additionally, 3 false-negative RhC results were observed in the RhD-positive donors due to a 109 bp insertion in RHCE intron 2. RHc typing demonstrated complete consistency between the real-time PCR and the serological results.

CONCLUSION

In the Chinese Han population, RHC genotyping was reliable when consistent results were achieved by both c.48C-based and 109 bp insertion-based genotyping. Moreover, RHc genotyping based on c.203A and c.307C polymorphic loci demonstrated dependable performance.

RHC genotyping in Chinese Han population

BACKGROUND

The Rh blood group system is characterized by its complexity and polymorphism, encompassing 56 different antigens. Accurately predicting the presence of the C antigen using genotyping methods has been challenging. The objective of this study was to evaluate the accuracy of various genotyping methods for predicting the Rh C and to identify a suitable method for the Chinese Han population.

METHODS

In total, 317 donors, consisting 223 D+ (including 20 with the Del phenotype) and 94 D- were randomly selected. For RHC genotyping, 48C and 109bp insertion were detected on the Real-time PCR platform and -292 substitution was analyzed via restriction fragment length polymorphism (RFLP). Moreover, the promoter region of the RHCE gene was sequenced to search for other nucleotide substitutions between RHC and RHc. Agreement between prediction methods was evaluated using the Kappa statistic, and comparisons between methods were conducted via the χ2 test.

RESULTS

The analysis revealed that the 48C allele, 109bp insertion, a specific pattern observed in RFLP results, and wild-type alleles of seven single nucleotide polymorphisms (SNPs) were in strong agreement with the Rh C, with Kappa coefficients exceeding 0.8. However, there were instances of false positives or false negatives (0.6% false negative rate for 109bp insertion and 5.4-8.2% false positive rates for other methods). The 109bp insertion method exhibited the highest accuracy in predicting the Rh C, at 99.4%, compared to other methods (P values≤0.001). Although no statistical differences were found among other methods for predicting Rh C (P values>0.05), the accuracies in descending order were 48C (94.6%) > rs586178 (92.7%) > rs4649082, rs2375313, rs2281179, rs2072933, rs2072932, and RFLP (92.4%) > rs2072931 (91.8%).

CONCLUSIONS

None of the methods examined can independently and accurately predict the Rh C. However, the 109bp insertion test demonstrated the highest accuracy for predicting the Rh C in the Chinese Han population. Utilizing the 109bp insertion test in combination with other methods may enhance the accuracy of Rh C prediction.

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).

Polymorphisms in the promoter regions of RHD and RHCE genes in the Chinese Han population

BACKGROUND AND OBJECTIVES

The Rh blood group system is the most polymorphic human blood group system. Previous studies have investigated variants in the RHD and RHCE promoter. The relevance of these variants to the Chinese Han population is further clarified in this study.

MATERIALS AND METHODS

In total, 317 donors (223 Rh D-positive [D+], including 20 Del and 94 Rh D-negative [D-]) were randomly selected. The promoter regions and exon 1 of RHD and RHCE were amplified through polymerase chain reaction (PCR) whose products were directly sequenced using forward and reverse primers.

RESULTS

Expected PCR products of the RHD promoter and exon 1 were amplified in 223 D+ individuals, including 20 Del individuals, and were absent in 81 of 94 D- individuals. Expected PCR products of RHCE were observed in all donors. Two single nucleotide variants (SNVs) were observed in the RHD promoter region. Moreover, 11 SNVs were observed in the promoter and exon 1 of RHCE. rs4649082, rs2375313, rs2281179, rs2072933, rs2072932, rs2072931 and rs586178 with strong linkage disequilibria were significantly different between the D+ and D- groups. [A;C] was the most common haplotype in the RHD promoter (NC_000001.11:g.[-1033A>G;-831C>T]). [G;T;T;A;T;A;C;G;A;C;G] was the most predominant haplotype in both total and D- groups. In D+ individuals, [A;C;T;G;C;G;C;G;C;C;C] was the most frequent haplotype in the RHCE promoter (NC_000001.11:g.[-1080A>G;-958C>T;-390T>C;-378G>A;-369C>T;-296G>A;-144C>G;-132G>A;-122C>A;28C>T;48C>G]).

CONCLUSION

We speculate that the SNVs/haplotypes found in this article cannot significantly affect gene expression. The present study findings should help elucidate the molecular basis of the polymorphic expression of RHD and RHCE promoter regions.

Variant genotypes associated with reduced expression of RhCE antigens among Brazilian blood donors

BACKGROUND

The genetic diversity of the RHCE gene locus has been explored in diverse populations of different racial backgrounds. Data referring to the diversity of RHCE encoding weakened expression of C, c, E, and e in multiethnic populations is still incomplete.

METHODS

Samples from Brazilian blood donors presenting reduced expression of C, c, E, or e on gel method were selected for the study. All exons and flanking introns of RHCE were genotyped though direct Sanger sequencing for the included donors.

RESULTS

Sixty-six donors were included: 23 with weak C, 22 with weak c, 6 with weak E, 14 with weak e, and 1 with weak c and E. Among the samples with weak C, the following altered RH*C were encountered: RHCE*CeMA (n = 3), RHCE*Ce941C (n = 1), and RHCE*CeVA (n = 1). RHD*D-CE(4-7)-D was detected in six cases, RHCE*CE was presumably present in five cases, and seven cases were unexplained. Two altered alleles underlay the weak c phenotype: RHCE*ceJAL (n = 20) and RHCE*ce340T (n = 2), and two altered RHCE justified weak e: RHCE*ceMO (n = 6) and RHCE*ceJAL (n = 8). Three variant RHCE were associated with weak E: RHCE*cEJU (n = 4), RHCE*cE382C (n = 1), and RHCE*cEIV (n = 1). The RHCE*cE905A justified one case of weak c and E.

CONCLUSION

We describe the distribution of RHCE variants found in association with weak expression of C, c, E, and e in blood donors of multiethnic origin, which differs in comparison to that previously reported for people of African or Caucasian descent.

Effectiveness of strategies to screen for blood donors with RH variants in a mixed population

INTRODUCTION

Patients with RH variants presenting antibodies directed to RH high frequency antigens or multiple RH antibodies might, in some occasions, be better served with RH genotype-matched units, requiring screening for RH variants among blood donors. To date, strategies to identify donors with RH variants were restricted to selecting individuals of African descent based on self-reported race, what can be inaccurate in racially mixed population. Our goal was to: 1) Screen for donors with RH variants in a mixed population using self-declared race and Rh phenotype as selection criteria; and 2) Verify if including the Duffy null genotype in the screening algorithm increases its effectiveness.

METHODS

Brazilian donors were included if self-declared as black and phenotyped as R0r or R1r. All individuals were genotyped for RHCE exons 1, 5, 6 and 7 and for the FY*B c.-67 T > C polymorphism in order to determine the Duffy null genotype. RHD variants were searched for in cases of altered RHCE.

RESULTS

Among 2500 blood donors, 217 fulfilled the inclusion criteria and were enrolled. Fifty-three (24.4 %) had a predicted clinically relevant Rh phenotype (partial antigens or lack of high frequency antigens). Twelve donors (5.5 %) had a predicted RhCE phenotype lacking either hrB or hrS. Most cases with predicted lack of high frequency antigens (66.7 %) occurred in donors with the Duffy null genotype.

CONCLUSION

Selecting donors based on self-declared race, Rh phenotype and Duffy null genotype is feasible and effective in identifying RH variants lacking Rh high frequency antigens among racially mixed donors.

Non-invasive Prenatal Testing Using Fetal DNA

Non-invasive prenatal diagnosis (NIPD) is based on fetal DNA analysis starting from a simple peripheral blood sample, thus avoiding risks associated with conventional invasive techniques. During pregnancy, the fetal DNA increases to approximately 3-13% of the total circulating free DNA in maternal plasma. The very low amount of circulating cell-free fetal DNA (ccffDNA) in maternal plasma is a crucial issue, and requires specific and optimized techniques for ccffDNA purification from maternal plasma. In addition, highly sensitive detection approaches are required. In recent years, advanced ccffDNA investigation approaches have allowed the application of non-invasive prenatal testing (NIPT) to determine fetal sex, fetal rhesus D (RhD) genotyping, aneuploidies, micro-deletions and the detection of paternally inherited monogenic disorders. Finally, complex and innovative technologies such as digital polymerase chain reaction (dPCR) and next-generation sequencing (NGS) (exhibiting higher sensitivity and/or the capability to read the entire fetal genome from maternal plasma DNA) are expected to allow the detection, in the near future, of maternally inherited mutations that cause genetic diseases. The aim of this review is to introduce the principal ccffDNA characteristics and their applications as the basis of current and novel NIPT.

Rh-Matched Transfusion through Molecular Typing for β-Thalassemia Patients Is Required and Feasible in Chinese

Background

Molecular typing for RHCE blood group alleles has been established in many countries for patients and blood donors. In the Chinese literature nearly 80% of transfused patients with alloimmunization have antibodies specific for antigens of the Rh blood group system. We investigated if it is feasible to match packed red blood cells (RBCs) for Chinese β-thalassemia patients by RHCE genotyping.

Methods

In this study, 481 patients with β-thalassemia were enrolled. They were genotyped for RHCE alleles by a simple PCR method with sequence-specific primers (PCR-SSP). Among these patients, 203 continuously received RBCs of the identical Rh subgroups according to the genotyping results for at least 3 months. Subsequently, their phenotypes were tested through a micro-column gel card method. For validation purposes, 400 donors were serologically typed with the same technology, of which 164 were genotyped too. Finally, the C, c, E, and e frequencies and the feasibility of the simple genotyping method were analyzed.

Results

All patients showed mixed-field agglutination in the Rh subgroup gel cards before the same Rh subgroups in blood donors were selected for blood transfusion. The results, however, lacked mixed-field agglutination in all 203 cases after transfusion with RBC concentrates selected for the patient's C, c, E, and e antigens for at least 3 months. The genotyping results of 164 donors were all consistent with the serological results. Whole coding regions of RHCE were sequenced in 7 individuals with weak c, E, or e antigens. In only one sample we observed a 1059G>A nucleotide mutation coding for a truncated RhCE polypeptide (GenBank KT957625), in the other 6 samples no sequence variant was found. Both patients and donors were predominantly CcEe and CCee, with a prevalence of 55.3% and 24.9% for patients or 49.3% and 31.3% for donors, respectively. It revealed that about 80% of Chinese could receive Rh-matched RBCs easily.

Conclusion

A simple RHCE genotyping technique is safe enough for Rh-matched transfusion of β-thalassemia patients in Chinese Han.

High frequency of variant RHD genotypes among donors and patients of mixed origin with serologic weak-D phenotype

BACKGROUND

The current transfusion policy recommended for individuals with serologic weak-D phenotype is based on data derived from European-descent populations. Data referring to the distribution of RH alleles underlying weak-D phenotype among people of mixed origin are yet incomplete, and the applicability of European-based transfusion guidelines to this specific population is questionable.

GOAL

To evaluate the distribution of RHD variant genotype among individuals with serologic weak-D phenotype of both African and European descent.

METHODS

Donors and patients of mixed origin and with serologic weak-D phenotype were selected for the study. They were investigated using conventional RHD-PCR assays and RHD whole-coding region direct sequencing.

RESULTS

One hundred and six donors and 58 patients were included. There were 47 donors and 29 patients with partial-D genotype (47/106, 44.3%, and 29/58, 50%, respectively). RHD*DAR and RHD*weak D type 38 represented the most common altered RHD alleles among donors (joint frequency of 39.6%), while weak D types 1-3 accounted for 10.4% of the total D variant samples. RHD*DAR was the most common allele identified in the patient group (frequency of 31%), and weak D types 1-3 represented 29.3% of the total.

CONCLUSION

The frequency of partial D among mixed individuals with serologic weak-D phenotype is high. They should be managed as D-negative patients until molecular tests are complete.

Molecular basis of Rh blood group system in the Malaysian population

BACKGROUND

Rh molecular studies have been previously mainly conducted in Caucasians and African population. There is a limited data on the molecular basis for Rh genotypes among Asians.

AIMS

This study aims to characterize the Rh genes and frequency of the various RH genotypes among blood donors in National Blood Centre (NBC), Kuala Lumpur.

MATERIALS AND METHODS

A total of 1014 blood samples were obtained from blood donors from four different ethnic groups (360 Malays, 434 Chinese, 164 Indians and 56 others). Serological and molecular analysis of all 1014 blood samples were performed. An automated deoxyribonucleic acid sequencing analysis was performed.

RESULTS

Rh phenotypes and RH genotypes showed heterogeneity and significant association with ethnicities. Discrepancies in allele D, C/c and E/e between phenotypes and genotypes results were observed. Discrepancy results in allele D showed significant association with the ethnic groups of the blood donors in NBC. There were multiple novel mutations (23) and published mutations (5) found in this study. Significant associations between discrepancy results and mutations were found in allele D and C/c.

CONCLUSION

Performing RH molecular analysis in Malaysian population provided the basic database for the distribution of Rh genotypes of donors from major ethnic groups in Malaysia.

WITHDRAWN: Rh genotypes among Malaysian blood donors

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Routine use of DNA testing for red cell antigens in blood centres

During the last decade a number of blood establishments started using molecular methods for typing a subset of their blood donors for minor red cell antigens as a part of their routine work. It can be expected that this development will continue and that DNA testing will take a significant role in future. A sufficient number of antigen-typing in the donor-database allows for the efficient supply of red cell units for patients who carry irregular antibodies directed to red cell antigens. Therefore blood centres often operate antigen typing programs for a subset of their repeat donors. Large-scale donor typing programs are labour-intensive and costly. DNA testing is a feasible alternative to standard serological assays. The most important advantage is the easy access to a spectrum of hundreds of antigens independent of the availability of serological reagents. Besides, that there are both positive, but also less favourable aspects, which are related to the different particular methods and platforms available for molecular testing. Several of them enable medium- and high-throughput applications and some are more cost-efficient than serology.

Molecular genetics and clinical applications for RH

Rhesus is the clinically most important protein-based blood group system. It represents the largest number of antigens and the most complex genetics of the 30 known blood group systems. The RHD and RHCE genes are strongly homologous. Some genetic complexity is explained by their close chromosomal proximity and unusual orientation, with their tail ends facing each other. The antigens are expressed by the RhD and the RhCE proteins. Rhesus exemplifies the correlation of genotype and phenotype, facilitating the understanding of general genetic mechanisms. For clinical purposes, genetic diagnostics of Rhesus antigens will improve the cost-effective development of transfusion medicine.

Blood group genotyping: from patient to high-throughput donor screening

Blood group antigens, present on the cell membrane of red blood cells and platelets, can be defined either serologically or predicted based on the genotypes of genes encoding for blood group antigens. At present, the molecular basis of many antigens of the 30 blood group systems and 17 human platelet antigens is known. In many laboratories, blood group genotyping assays are routinely used for diagnostics in cases where patient red cells cannot be used for serological typing due to the presence of auto-antibodies or after recent transfusions. In addition, DNA genotyping is used to support (un)-expected serological findings. Fetal genotyping is routinely performed when there is a risk of alloimmune-mediated red cell or platelet destruction. In case of patient blood group antigen typing, it is important that a genotyping result is quickly available to support the selection of donor blood, and high-throughput of the genotyping method is not a prerequisite. In addition, genotyping of blood donors will be extremely useful to obtain donor blood with rare phenotypes, for example lacking a high-frequency antigen, and to obtain a fully typed donor database to be used for a better matching between recipient and donor to prevent adverse transfusion reactions. Serological typing of large cohorts of donors is a labour-intensive and expensive exercise and hampered by the lack of sufficient amounts of approved typing reagents for all blood group systems of interest. Currently, high-throughput genotyping based on DNA micro-arrays is a very feasible method to obtain a large pool of well-typed blood donors. Several systems for high-throughput blood group genotyping are developed and will be discussed in this review.

Single base extension in multiplex blood group genotyping

Transfusion recipients who become alloimmunized to blood group antigens require antigen-negative blood to limit adverse transfusion reactions. An alternative strategy to phenotyping blood is to assay genomic DNA for the associated single nucleotide polymorphisms (SNPs). A multiplex PCR coupled with a single base oligonucleotide extension assay using genomic DNA can identify SNPs related to D, C/c, E/e, S/s, K/k, Kp(a/b), Fy(a/b), Fy0 (-33 promoter silencing polymorphism), Jk(a/b), Di(a/b), and HPA-1a/b. Using this technology, individual SNP call rates vary from 98 to 100%. The platform has the capacity to genotype thousands of samples per day. The suite of SNPs provides rapid data for both blood donors and transfusion recipients and is poised to change whose blood is provided for potential transfusion recipients. The potential to dramatically lower the incidence of alloimmunization and to avoid serious hemolytic complications of transfusions can be realized with the implementation of this technology.

Heterogeneous molecular background of the weak C, VS+, hr B-, Hr B- phenotype in black persons

BACKGROUND

The rare Hr(B)- phenotype is encoded by the (C)ce(s) haplotype when present at the homozygous state. This haplotype contains two altered genes: a hybrid RHD-CE-D(s) gene segregated with a ce(s) allele of RHCE (733C>G and 1006G>T substitutions in Exon 5 and Exon 7 respectively). The aim of this study was to further investigate the molecular background of the (C)ce(s) haplotype.

STUDY DESIGN AND METHODS

Twelve individuals with depressed C and/or depressed e phenotype were selected from their genomic DNA analysis showing both 733C>G and 1006G>T substitutions. Phenotypic expression of low- and high-prevalence Rh antigens was studied. Complete sequences of RHD and RHCE transcripts were analyzed when obtained.

RESULTS

A new hybrid RHD-CE-D(s) gene (Exons 1 and 2; complete Exon 3; Exons 8, 9, and 10 from RHD; and Exons 4 through 7 from RHCE) segregated with a ce(s) allele, which genomic organization was almost identical to that of the classical (C)ce(s) haplotype, is described. The two different (C)ce(s) haplotypes encoded two different patterns of Rh antigen expression. Although both encoded weak e, VS, and did not produce D, V, hr(B), or Hr(B) antigens, the new haplotype encoded a much weaker C antigen and red blood cells lacked expression of Rh42, in contrast to the classic (C)ce(s) haplotype.

CONCLUSION

The study showed the heterogeneity of the molecular background of the weak C, VS+, hr(B)-, Hr(B)- phenotype in the black population. The screening of blood donors in this population for hr(B)- or Hr(B)- phenotype should implement the molecular characterization of Rh genes.

Routine fetal RHD genotyping with maternal plasma: a four-year experience in Belgium

BACKGROUND

The objective was to evaluate the diagnostic value of RHD fetal genotyping from the plasma of D- mothers as soon as 10 weeks' gestation in a routine clinical practice in Belgium.

STUDY DESIGN AND METHODS

A prospective study was conducted between November 2002 and December 2006. DNA extraction was performed in an automated closed tube system. Fetal RHD/SRY genotypes were detected in the plasma of 563 pregnant mothers by real-time polymerase chain reaction (PCR) targeting multiple exons 4, 5, and 10 of the RHD gene and targeting an SRY gene sequence. These were compared to the D phenotypes determined in the 581 babies they delivered.

RESULTS

By combining amplification of three exons, the concordance rate of fetal RHD genotypes in maternal plasma and newborn D phenotypes at delivery was 100 percent (99.8% including one unusual false-positive). The presence of nonfunctional RHD genes and the absence of a universal fetal marker, irrespective of fetal sex, did not influence the accuracy of fetal RhD status prediction. The RHD genotyping from 18 twin pregnancies was also assessed. Five weak D women were excluded from the RHD fetal genotyping prediction. Three discrepant results (0.5%) between predicted fetal genotype and cord blood phenotype were not confirmed by the baby phenotypes from venipuncture blood.

CONCLUSION

Prenatal prediction of fetal RHD by targeting multiple exons from the maternal plasma with real-time PCR is highly sensitive and accurate. Over 4 years, this experience has highly modified our management of D- pregnant women.

The Dc(G48)e(s) haplotype is frequent among the Dce haplotypes within a white population

BACKGROUND

The absence of hybrid Rhesus boxes denotes an RHD homozygous status and helps to detect the presence of Dce haplotypes instead of dce. RHCE exon 1 C48, characteristic of RHC alleles, and RHCE exon 5 G733, responsible for VS antigenicity, have been noted in many RHce alleles but it was not clearly established whether they occurred in the same allele and/or cosegregate together with RHD.

STUDY DESIGN AND METHODS

Samples from 148 white trios (father, mother, and child) were studied. Rh phenotype was performed by hemagglutination. Hybrid Rhesus box, RHCE exon 1 G48C, RHCE exon 5 C733G, and RHC intron 2 polymorphisms were analyzed by polymerase chain reaction. Haplotypes were determined considering serologic, molecular, and segregation data.

RESULTS

RHCE exon 1 C48 and RHCE exon 5 G733 were present in RHce alleles that cosegregated with RHD forming Dce haplotypes. Both transversions were not frequently found in the same RHce allele. Of the 33 Dce haplotypes, 16 (48.5%) had a C at position 48 [Dc(C48)e], 11 (33.3%) had a G at position 48 with a G at position 733 [Dc(G48)e(s)], 5 (15.2%) had a G at position 48 [Dc(G48)e], and 1 (3.0%) had a C at position 48 with a G at position 733 [Dc(C48)e(s)].

CONCLUSIONS

The results show four molecular backgrounds for the Dce haplotype and reflect the contribution of African alleles to the genetic pool of the population under study. The molecular characterization of Dce and its frequency distribution may develop a better understanding of the phylogeny of Rh haplotypes.

Evaluation of prenatal RHD typing strategies on cell-free fetal DNA from maternal plasma

BACKGROUND

The discovery of cell-free fetal DNA in maternal plasma led to the development of assays to predict the fetal D status with RHD-specific sequences. Few assays are designed in such a way that the fetus can be typed in RHDpsi mothers and that RHDpsi fetuses are correctly typed. Owing to the limited knowledge about the mechanism responsible for the presence of fetal DNA in maternal plasma, precautions in developing prenatal genotyping strategies must be made.

STUDY DESIGN AND METHODS

Real-time quantitative (RQ)-polymerase chain reaction (PCR) assays were developed for prenatal diagnostic use with cell-free fetal DNA from maternal plasma. An RQ-PCR assay on RHD exon 5 (amplicon 361 bp), negative on RHDpsi, was developed with genomic DNA and evaluated with cell-free fetal DNA. A previously published RHD exon 5 RQ-PCR (amplicon 82 bp) was duplexed with an in-house developed RHD exon 7 RQ-PCR and evaluated with cell-free fetal DNA from pregnant D-RHDpsi+ women.

RESULTS

The RHD exon 5 361 bp assay showed on cell-free plasma DNA from D- women carrying a D+ fetus, low amplification levels, resulting in high Ct values and false-negative results. Owing to fragmentation of cell-free plasma DNA, too few DNA stretches of sufficient length (> 360 bp) are present. The RHD exon 5 82 bp and exon 7 RQ-PCR duplex was evaluated with RHDpsi+ cell-free plasma DNA and showed complete specificity and maximal sensitivity.

CONCLUSION

Assays designed for prenatal genotyping should be developed and evaluated on cell-free plasma DNA. Prenatal RHD typing is accurate with the RHD exon 5 82 bp and exon 7 duplex strategy.

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.

High-throughput molecular profiling of blood donors for minor red blood cell and platelet antigens

BACKGROUND

ABO and D phenotyping of both blood donors and patients receiving transfusions is routinely performed by blood banks to ensure compatibility. These analyses are performed by antibody-based agglutination assays. Blood is not tested for minor blood group antigens on a regular basis, however, because of cost and time constraints. This can result in alloimmunization of the patient against one to several minor antigens and may complicate future transfusions.

STUDY DESIGN AND METHODS

To address this problem, an assay has been generated on the GenomeLab SNPstream genotyping system to test simultaneously polymorphisms linked to 22 different blood antigens with donor's DNA isolated from minute amounts of white blood cells.

RESULTS

The results showed that both the error rate of the assay, as measured by the strand concordance rate, and the no-call rate were very low (0.1%). The concordance rate with the actual red blood cell (RBC) and platelet (PLT) serology data varied from 97 to 100 percent. Experimental or database errors as well as rare polymorphisms contributing to antigen conformation could explain the observed differences. These rates, however, are well above requirements because phenotyping and cross-matching will always be performed before transfusion.

CONCLUSION

Molecular profiling of blood donors for minor RBC and PLT antigens will give blood banks instant access to many different matched donors through the setup of a centralized data storage system.

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.

Noninvasive prenatal diagnosis of fetal Rhesus D: ready for Prime(r) Time

Rhesus (Rh) D blood group incompatibility between the pregnant woman and her fetus is a significant problem due to the possibility of maternal alloimmunization and consequent hemolytic disease of the newborn. The RhD-negative blood group is found in 15% of whites, 3-5% of black Africans, and is rare in Asians. Advances in both our understanding of the RHD locus and its variants, as well as technical improvements in the extraction and amplification of cell-free fetal DNA in maternal plasma, have led to incorporation of noninvasive diagnosis of RHD genotype into routine prenatal care in the United Kingdom, France, and the Netherlands. In this commentary we examine the experience to date with large-scale clinical trials performed in the European Union, describe approaches to reduce false-positive and false-negative results, and review ongoing research to standardize assays and reduce costs using automated assays. False-negative cases are mainly due to either a lack of fetal DNA in the maternal sample due to early gestation or insensitive methods. False-positive cases are due to genotypic variants observed in individuals of African ancestry. Noninvasive prenatal diagnosis of fetal Rhesus D genotype is sensitive and accurate and has been widely validated in Europe. The United States should begin to undertake clinical trials to bring this technology to patient care as soon as possible.

Utilisation en routine clinique du génotypage fœtal RHD sur plasma maternel : bilan de deux ans d’activité

OBJECTIVES

To evaluate the predictive value of RHD fetal genotype in maternal plasma of Rh D negative mothers after 10 weeks of gestation in a clinical use.

MATERIAL AND METHOD

Prospective, comparative study between fetal RHD genotyping in maternal plasma, with amplification of exons 4,5,10 of the RHD gene, by real-time multiplex PCR, and Rh D serology at birth, in 218 pregnancy and their 223 babies, between November 2002 and 2004.

RESULTS

Combining the amplification of three exons, the concordance rate of fetal Rh D genotyping in maternal plasma and baby phenotyping at delivery was 100%. Four women whose the babies were Rh D negative were positive for RHD exon 10 during pregnancy. This positivity was, in three cases, correlated with the presence of RHDpsi pseudogene and in last case, with a haplotype Cdes (r's). RHD genotyping was performed for five twin pregnancies.

CONCLUSION

Multiplex PCR using maternal plasma provides perfect prenatal prediction of fetal RHD gene. These results confirm that this non invasive procedure is the preferred method for assessing Rh D fetal status in Rh negative mothers. Using this method for two years in routine practice has led us to modify our management scheme for sensitized Rh D-negative pregnant women.

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

BACKGROUND AND OBJECTIVES

The aim of this study was to systemically analyse the genetic background of D negativity in a Chinese Han population.

MATERIALS AND METHODS

DNA of 74 D-negative samples was analysed by using an RHD multiplex polymerase chain reaction (MPX PCR) for the presence of RHD and by PCR-restriction fragment length polymorphism (PCR-RFLP) for RHD zygosity determination. Sixty-five samples were additionally analysed by using real-time quantitative PCR on RHD exon 7. RHD exon-specific sequencing was performed on discrepant samples.

RESULTS

Forty-six samples (62%) showed the absence of RHD-specific exons by RHD MPX PCR and homozygous RHD negativity by PCR-RFLP. Twenty-two samples (30%) showed a 1227G>A mutation, characteristic for the Del phenotype. Five (7%) samples showed all characteristics of the RHD(1-2)-CE(3-9)-D(10) hybrid gene. One sample (1.4%) showed a novel 933C>A nonsense mutation in RHD exon 6, which resulted in a premature stop codon.

CONCLUSIONS

The RHD gene deletion, RHD-CE-D hybrid genes and one novel 93C>A mutation were found to be the three mechanisms that cause D negativity in our samples. The 1227G>A Del mutation was found to be the major cause of discrepant results between genotyping and phenotyping strategies, favouring genotyping of D-negative samples.

The highly variable RH locus in nonwhite persons hampers RHD zygosity determination but yields more insight into RH-related evolutionary events

BACKGROUND

Knowledge about paternal RHD hemi- or homozygosity is of clinical interest in alloimmunized pregnant women. D negativity in white persons is usually caused by deletion of the RHD gene. Recently, the physical structure of the RH locus and the mechanism causing the deletion of the RHD gene have been explored, enabling RHD zygosity determination in white persons by specific detection of a hybrid Rhesus box characteristic for the RHD- locus.

STUDY DESIGN AND METHODS

RHD zygosity was determined in 402 samples from five different ethnic groups by polymerase chain reaction (PCR)-restriction fragment length polymorphism and by a newly developed real-time quantitative PCR. The Rhesus boxes of samples showing discrepancies between both tests were cycle sequenced.

RESULTS

In nonwhite persons, several mutated Rhesus boxes exist that hamper zygosity determination by detection of the RHD- locus. Such mutated Rhesus boxes in D+RHD homozygous black persons have a frequency of 0.22. In white persons, no mutated Rhesus boxes were encountered so far.

CONCLUSIONS

Owing to the high frequency of the mutated Rhesus boxes, zygosity determination by detection of the RHD- locus is not feasible in nonwhite persons. The cosegregation of variant RHD genes (RHDpsi and (C)cdes) with specific mutated Rhesus boxes yields more insight into the evolutionary events concerning variant RHD genes and mutated Rhesus boxes.

Report of the First International Workshop on molecular blood group genotyping

The use of molecular genetic technology for blood group typing is becoming routine procedure in many reference laboratories worldwide. A First International Workshop was organized on behalf of the International Society of Blood Transfusion (ISBT) and the International Council for Standardization in Haematology (ICSH). Thirty laboratories that provide a molecular diagnostic service participated in the workshop. Six samples were distributed: two represented DNA from transfusion-dependent patients for testing for multiple polymorphisms; two represented fetal DNA prepared from amniotic fluid for RhD, Rhc and K-testing; and two represented plasma from RhD-negative pregnant women for fetal RhD testing. Error rates varied from 0 to 11% for different polymorphisms. A consensus arising from discussion on the workshop results between participants at a feedback meeting and by e-mail has resulted in seven recommendations for molecular blood group genotyping. Further international workshops will take place every 2 years, with a more limited exercise being organized in the intervening years.

Clinical applications of cell-free fetal DNA from maternal plasma

OBJECTIVE

To describe our clinical experience with detection and analysis of cell-free fetal DNA derived from maternal plasma for prenatal sexing and fetal rhesus-D typing.

METHODS

Real-time quantitative polymerase chain reactions (PCRs) of rhesus-D sequences and the SRY gene were validated and offered to patients with an enhanced risk for sex-linked fetal pathology and patients with rhesus-D antibodies.

RESULTS

In the validation group, 72 samples were analyzed. Sensitivity of the rhesus-D real-time quantitative PCR in maternal plasma was 100% (95% confidence interval [CI]91.8%, 100%) and specificity was 96.6% (95% CI 82.2%, 99.9%). Sensitivity of the SRY real-time quantitative PCR was 97.2% (95% CI 85.5%, 99.9%), and specificity was 100% (95% CI 88.1%, 100%). The technique was used successfully in a clinical setting in 24 women. Overall, invasive tests were avoided in 41.7% of these patients.

CONCLUSION

Detection of cell-free fetal DNA from maternal plasma is a reliable technique that can substantially reduce invasive prenatal tests.