Establishment of a medium-throughput approach for the genotyping ofRHDvariants and report of nine novel rare alleles

Autoimmune anti-D in an RhD-positive young infant: Learning from a rare case

BACKGROUND AND OBJECTIVES

Anti-D is usually immune in nature and is formed in individuals lacking D antigen or having variants/altered D phenotypes. In the Indian population, 93.8% are RhD positive, and R1 R1 is the commonest Rh phenotype. Here we report a rare and interesting case of autoimmune anti-D in an RhD-positive 3-month-old infant leading to warm autoimmune haemolytic anaemia.

STUDY DESIGN AND METHODS

Auto-anti-D was detected serologically by immunohaematological techniques such as direct antiglobulin test, antibody detection and identification, dithiothreitol, enzyme treatment, antibody titration and elution. Molecular studies were performed to rule out genetic variants of RhD.

RESULTS

Anti-D was confirmed in eluate and blood group post elution was B RhD positive. On genotyping using the Indian-specific RHD genotyping assay, the sample was found to be negative for the RHD*01W.150 (most common RhD variant in Indians) but positive for RHD exon 5 and RHD exon 10 along with glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The sample was further sequenced for RHD exons 1-10 by Sanger sequencing and found to be a wild type, thus, ruling out the presence of an RhD variant.

CONCLUSION

This case is of interest because of the rare occurrence of autoimmune anti-D in an RhD-positive patient of such a young age (3 months). To the best of our knowledge, only two case reports have been published on autoimmune anti-D in infancy (in 1961 and 1964).

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.

RHD alleles contributing to serologically weak D phenotypes in China: A single-centre study over 10 years

BACKGROUND AND OBJECTIVES

In cases of serologically weak D phenotypes, RHD genotyping may identify discrepant serotyping results and protect the patient against allogeneic immunization. This study aimed to conduct a comprehensive analysis of weak D alleles in China.

MATERIALS AND METHODS

We collected samples carrying weak D antigen during a 10-year period from 2005 to 2014. The intensity and epitopes of D were analysed serologically. Genomic DNA was extracted and used for RHD sequencing and heterozygote analysis. In particular, an in vitro expression method for functional verification of the rare and novel in-frame deletion mutation was developed and then combined with homologous modelling results for analysis.

RESULTS

We studied a total of 283 weak D samples from volunteer blood donors and identified 45 RHD alleles among them, 11 of which were reported for the first time. Ten (3.5%) samples surprisingly carried DEL allelic variants and as many as 40 (14.1%) carried the wild-type RHD genotype. Combination of the results of functional experiments and in silico analysis suggested that the rare in-frame deletion mutation may reduce the expression of D antigen by affecting the RhD protein structure.

CONCLUSIONS

This study provides an enhanced overview of the distribution characteristics of RHD alleles in Chinese subjects with serologically weak D. An in vitro method to predict the biological significance of variant RHD alleles was also provided. We found inconsistent genotyping and phenotypic results in some samples, indicating the existence of additional regulatory mechanisms.

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.

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

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

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.

Nation-wide investigation of RHD variants in Thai blood donors: Impact for molecular diagnostics

BACKGROUND

Knowledge of the molecular determinants driving antigen expression is critical to design, optimize, and implement a genotyping approach on a population-specific basis. Although RHD gene variability has been extensively reported in Caucasians, Africans, and East-Asians, it remains to be explored in Southeast Asia. Thus the molecular basis of non-D+ blood donors was investigated in Thailand.

STUDY DESIGN AND METHODS

First, 1176 blood samples exhibiting an inconclusive or negative result by automated serological testing were collected in the 12 Regional Blood Centres of the Thai Red Cross located throughout Thailand. Second, the RHD gene was analyzed in all samples by 1) quantitative multiplex PCR of short fluorescent fragments, and 2) direct sequencing, when necessary, for identifying structural variants and single nucleotide variants, respectively.

RESULTS

Additional serological typing yielded 51 and 1125 samples with weak/partial D and D-negative (D-) phenotype, respectively. In the first subset, partial RHD*06.03 was the most common variant allele (allele frequency: 18.6%). In the second subset, the whole deletion of the gene is largely the most frequent (allele frequency: 84.9%), followed by the Asian DEL allele found in 15.6% of the samples. Eight novel alleles with various mutational mechanisms were identified.

CONCLUSION

We report, for the first time at the national level, the molecular basis of weak/partial D and serologically D- phenotypes in Thai blood donors. The design and implementation of a dedicated diagnostic strategy in blood donors and patients are the very next steps for optimizing the management and supply of RBC units in Thailand.

Splicing analysis of SLC40A1 missense variations and contribution to hemochromatosis type 4 phenotypes

Hemochromatosis type 4, or ferroportin disease, is considered as the second leading cause of primary iron overload after HFE-related hemochromatosis. The disease, which is predominantly associated with missense variations in the SLC40A1 gene, is characterized by wide clinical heterogeneity. We tested the possibility that some of the reported missense mutations, despite their positions within exons, cause splicing defects. Fifty-eight genetic variants were selected from the literature based on two criteria: a precise description of the nucleotide change and individual evidence of iron overload. The selected variants were investigated by different in silico prediction tools and prioritized for midigene splicing assays. Of the 15 variations tested in vitro, only two were associated with splicing changes. We confirm that the c.1402G>A transition (p.Gly468Ser) disrupts the exon 7 donor site, leading to the use of an exonic cryptic splicing site and the generation of a truncated reading frame. We observed, for the first time, that the p.Gly468Ser substitution has no effect on the ferroportin iron export function. We demonstrate alternative splicing of exon 5 in different cell lines and show that the c.430A>G (p.Asn144Asp) variant promotes exon 5 inclusion. This could be part of a gain-of-function mechanism. We conclude that splicing mutations rarely contribute to hemochromatosis type 4 phenotypes. An in-depth investigation of exon 5 auxiliary splicing sequences may help to elucidate the mechanism by which splicing regulatory proteins regulate the production of the full length SLC40A1 transcript and to clarify its physiological importance.

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

BACKGROUND

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

STUDY DESIGN AND METHODS

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

RESULTS

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

CONCLUSION

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

RHD genotyping of serological weak D phenotypes in the Iranian blood donors and patients

BACKGROUND

Most prevalent weak D types in the Caucasians molecularly defined weak D types 1, 2 or 3 and can be managed safely as RhD-positive, conserving limited supplies of RhD-negative RBCs. Therefore, identification of RHD alleles prevalence in each population could improve the policies related to accuracy of RhD typing. The aim of this study was to determine the frequency of RHD variant alleles among donors and patients for the first time in Iran.

MATERIALS AND METHODS

RHD genotyping was performed on 100 blood donor and patient samples with weak D phenotype. PCR-SSP and DNA sequencing were used to identify the RHD alleles.

RESULTS

Molecular analysis showed only 15 samples were RHD*weak D 1(n = 13) and RHD*weak D 3(n = 2), and no cases of RHD*weak D 2 were detected. RHD*weak 15 (n = 43) was determined as the most prevalent D variants in our population and the other weak D types follows: RHD*weak 4, 5, 80 and one case of each one: RHD*weak 8, 11, 14, 100 and 105. Partial D variants also was identified in 18 samples as follows: RHD*partial DLO, DBT1, DV2, DHK and DAU-1.

CONCLUSION

The results of this study highlight the specific pattern of RHD status in the Iranian population. The weak D types 15 was the most common weak D type in the Iranian population. However, the screening for weak D types 1, 2 and 3 with 15 % frequency is also necessary for accurate RhD typing and developing clinical strategy of blood transfusion in weak D patients.

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.

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

BACKGROUND AND OBJECTIVES

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

METHODS

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

RESULTS AND CONCLUSION

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

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-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.

Screening for DEL phenotype in RhD negative Indians

BACKGROUND

DEL phenotype represents a very weak form of D variant detected only by adsorption and elution technique. DEL phenotype individuals mistyped as RhD-negative can lead to alloimmunization after transfusion or pregnancy. Molecular techniques have now been used to identify DEL variants. They are commonly encountered in the East Asian population with RHD(K409K) being the most frequent allele. RHD(M295I) is the most common DEL allele in Caucasians. As there is a paucity of data on DEL phenotype in the Indian population, the study aims to screen RhD negative individuals for two most common DEL mutations.

MATERIAL AND METHODS

EDTA blood was collected from 900 RhD negative individuals. Serological analysis included testing for the five major Rh antigens- C, c, D, E, and e by tube technique. Samples showing negative reaction for the presence of D antigen by Indirect Antiglobulin test were further tested for DEL phenotype by adsorption and elution technique. Molecular analysis involved DNA extraction and testing by PCR-SSP for RHD(K409K) and RHD(M295I) DEL alleles.

RESULTS

Rh phenotyping showed 153 Rh negative individuals with r'r, ten with r''r and 737 with rr phenotype. All the samples tested negative for RhD antigen by adsorption and elution method. The two common DEL mutations RHD(K409K) and RHD(M295I) were also not detected in the study population.

CONCLUSION

The study population showed the absence of the two common DEL alleles, concluding the variant to be rare. A comprehensive study with a larger sample size to look for other DEL mutations should be performed.

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).

Insights into RHCE Molecular Analysis in Samples with Partial D Variants: the Experience of Western France

BACKGROUND

Although systematic blood group genotyping of patients/donors is virtually possible, serological studies remain the gold standard to identify samples of clinical interest that may be further genotyped. In this context, we sought to identify variant D alleles that are likely to be clinically relevant in terms of other Rh antigens in a subset of population genotyped in Western France.

METHODS

Samples presenting with the RHD*weak D type 4.2.2 allele (n = 47) were selected for the study. RHCE exons 1-7 were directly sequenced, and expression of Rh antigens was predicted on the basis of the molecular data.

RESULTS

Of the 47 samples tested, 19 (40.4%) were predicted to be of potential clinical interest. Moreover, we could show that selecting the samples to be genotyped by the nature of their variant D allele (i.e., RHD*weak D type 4.2.2 allele) rather than by their Duffy-null status appears to increase significantly the likelihood of identifying clinically relevant individuals for Rh status.

CONCLUSION

On the basis of our findings we suggest that all individuals genotyped as weak D type 4.2.2 should be systematically screened for RHCE variants by molecular analysis on a routine basis.

Duffy blood group phenotype-genotype correlations using high-resolution melting analysis PCR and microarray reveal complex cases including a new null FY*A allele: the role for sequencing in genotyping algorithms

BACKGROUND AND OBJECTIVES

Duffy blood group phenotypes can be predicted by genotyping for single nucleotide polymorphisms (SNPs) responsible for the Fy(a) /Fy(b) polymorphism, for weak Fy(b) antigen, and for the red cell null Fy(a-b-) phenotype. This study correlates Duffy phenotype predictions with serotyping to assess the most reliable procedure for typing.

MATERIALS AND METHODS

Samples, n = 155 (135 donors and 20 patients), were genotyped by high-resolution melt PCR and by microarray. Samples were in three serology groups: 1) Duffy patterns expected n = 79, 2) weak and equivocal Fy(b) patterns n = 29 and 3) Fy(a-b-) n = 47 (one with anti-Fy3 antibody).

RESULTS

Discrepancies were observed for five samples. For two, SNP genotyping predicted weak Fy(b) expression discrepant with Fy(b-) (Group 1 and 3). For three, SNP genotyping predicted Fy(a) , discrepant with Fy(a-b-) (Group 3). DNA sequencing identified silencing mutations in these FY*A alleles. One was a novel FY*A 719delG. One, the sample with the anti-Fy3, was homozygous for a 14-bp deletion (FY*01N.02); a true null.

CONCLUSION

Both the high-resolution melting analysis and SNP microarray assays were concordant and showed genotyping, as well as phenotyping, is essential to ensure 100% accuracy for Duffy blood group assignments. Sequencing is important to resolve phenotype/genotype conflicts which here identified alleles, one novel, that carry silencing mutations. The risk of alloimmunisation may be dependent on this zygosity status.

Distribution of Rhesus blood group antigens and weak D alleles in the population of Albania

BACKGROUND

Determination of Rhesus (Rh) status is of critical importance in the field of both transfusion and obstetric medicine. As the distribution of Rh phenotypes was unknown in the Albanian population, we investigated the donor population in Albania to estimate the prevalence of each phenotype, as well as to identify and characterise the variants at the molecular level.

MATERIALS AND METHODS

A total of 38,836 blood donors were phenotyped for Rh D, C, c, E and e antigens by routine serological methods, and samples with reduced D antigen expression underwent molecular characterisation by a Tm-shift genotyping method and direct sequencing.

RESULTS

Among all donors 89.00% and 10.86% were D-positive and D-negative, respectively, while 0.14% (n=55) of the donors were found to be weak D-positive. Overall 45/55 samples (81.8%) were resolved by Tm-shift screening, showing that approximately 67% of the variant D alleles were weak D type 1, while weak D type 3 (9.1%) and weak D type 2 (3.6%) were less common. A novel c.932A>G (p.Y311C) variant was also found in the heterozygous state by direct sequencing.

DISCUSSION

This extensive study reveals the distribution of Rh phenotypes in the Albanian population, the low prevalence of individuals with a weak D phenotype, and the specific pattern of distribution of the three most common variant alleles in this Caucasian population.

A convenient qualitative and quantitative method to investigate RHD-RHCE hybrid genes

BACKGROUND

Molecular biology techniques, such as single specific-primer polymerase chain reaction (PCR), denaturing-high performance liquid chromatography, direct sequencing, next-generation sequencing, and microarray platforms, contribute to the efficient genotyping of the human blood group RHD gene. However, some alleles remain undetermined in rare cases in DNA samples carrying two copies of the RHD gene, which challenge the identification of D-CE hybrid genes.

STUDY DESIGN AND METHODS

We set up, in a single-tube format, a qualitative and quantitative assay based on multiplex PCR of short fluorescent fragments (QMPSF) to simultaneously amplify all 10 RHD exons on the one hand and all 10 RHCE exons on the other hand.

RESULTS

The test proved to be useful to rapidly identify hybrid genes in hemizygous RHD samples carrying a hybrid D-CE gene and to resolve unknown genotypes by quantifying individual exons in compound heterozygous samples, but also unexpectedly helped to redefine the RHDΨ haplotype. While validating the test, two novel single-point variants, c.648G>C (p.L216F) and c.1048G>C (p.D350H), were found.

CONCLUSION

For the first time, a QMPSF-based method is reliable to individually quantify the exons of both RH genes, including hybrid D-CE genes in compound heterozygous samples and may help to investigate samples with unknown RHD and/or RHCE status.