Association between ABO haplotypes and the risk of venous thrombosis: impact on disease risk estimation.

Genetic risk score (GRS) analysis is a popular approach to derive individual risk prediction models for complex diseases. In venous thrombosis (VT), such type of analysis shall integrate information at the ABO blood group locus, which is one of the major susceptibility loci. However, there is no consensus about which single nucleotide polymorphisms (SNPs) must be investigated when properly assessing association between ABO locus and VT risk. Using comprehensive haplotype analyses of ABO blood group tagging SNPs in 5425 cases and 8445 controls from 6 studies, we demonstrate that using only rs8176719 (tagging O1) to correctly assess the impact of ABO locus on VT risk is suboptimal, because 5% of rs8176719-delG carriers do not have an increased risk of developing VT. Instead, we recommend the use of 4 SNPs, rs2519093 (tagging A1), rs1053878 (A2), rs8176743 (B), and rs41302905 (O2), when assessing the impact of ABO locus on VT risk to avoid any risk misestimation. Compared with the O1 haplotype, the A2 haplotype is associated with a modest increase in VT risk (odds ratio, âˆ¼1.2), the A1 and B haplotypes are associated with an âˆ¼1.8-fold increased risk, whereas the O2 haplotype tends to be slightly protective (odds ratio, âˆ¼0.80). In addition, although the A1 and B blood groups are associated with increased von Willebrand factor and factor VIII plasma levels, only the A1 blood group is associated with ICAM levels, but in an opposite direction, leaving additional avenues to be explored to fully understand the spectrum of biological effects mediated by ABO locus on cardiovascular traits.

Frequency and characterization of RHD and RHCE variants in the Noir Marron population from French Guiana.

BACKGROUND: The RH system is one of the most polymorphic blood group systems due to the proximity and opposite orientation of RHD and RHCE genes. Numerous alleles are described and can affect Rh protein expression. This complexity is especially evident in populations of African origin. We performed RHD and RHCE genotyping of the Noir Marron population in French Guiana. This population belongs to the Maroon community who are direct descendants of African slaves, who escaped from Dutch plantations, in the current day Suriname, during the 17th century. They represent an original ethnic group with highly blended culture. METHODS AND MATERIALS: A total of 89 DNA samples were collected from four different ethnic groups of the Noir Marron population of French Guiana. RHD and RHCE genotyping was performed using DNA microarray and/or sequencing. RESULTS AND DISCUSSION: Significant allelic diversity was shown, with 45% of individuals presenting an RHD gene variant (most common: RHD*DAU, RHD*DIVa, and RHD*DIIIa allele) and 9.4% with a partial D phenotype. Likewise, 85% presenting an RHCE gene variant and 9% a partial RH2 antigen. One original allele was identified in two D+ Noir Marron individuals: a hybrid RHD*DIIIa-CE(9)-D allele, encoding probably a partial D antigen and associated with an RHCE*ce(48C,733G,1006T) allele. The African diversity of RHD and RHCE genes is found in this population with preserved genetic but mixed cultural backgrounds. These data allow us to describe the characteristics of the RH system antigen and highlights a significant number of partial antigens with a risk of alloimmunization.

The Comoros Show the Earliest Austronesian Gene Flow into the Swahili Corridor.

At the dawn of the second millennium, the expansion of the Indian Ocean trading network aligned with the emergence of an outward-oriented community along the East African coast to create a cosmopolitan cultural and trading zone known as the Swahili Corridor. On the basis of analyses of new genome-wide genotyping data and uniparental data in 276 individuals from coastal Kenya and the Comoros islands, along with large-scale genetic datasets from the Indian Ocean rim, we reconstruct historical population dynamics to show that the Swahili Corridor is largely an eastern Bantu genetic continuum. Limited gene flows from the Middle East can be seen in Swahili and Comorian populations at dates corresponding to historically documented contacts. However, the main admixture event in southern insular populations, particularly Comorian and Malagasy groups, occurred with individuals from Island Southeast Asia as early as the 8th century, reflecting an earlier dispersal from this region. Remarkably, our results support recent archaeological and linguistic evidence-based suggestions that the Comoros archipelago was the earliest location of contact between Austronesian and African populations in the Swahili Corridor.

DO/ART4 gene sequencing in sub-Saharan cohorts and African migrants: useful data describing the diversity and spreading of rare variants.

BACKGROUND: Due to the unavailability of immunological reagents, the Dombrock blood group is insufficiently explored in African populations and can be a source of alloimmunization. A large study including pygmoid and nonpygmoid ethnic groups from East, Central, and West continental Africa, together with African migrants like Comorians, Afro-Caribbean from Martinique, and Maroons from French Guiana would be helpful to increase transfusion safety. STUDY DESIGN AND METHODS: Using genomic DNA extracted from blood samples collected from 336 nonpygmoid and 51 pygmoid Africans as well as 268 samples of African descent, DO coding regions were PCR-amplified and sequenced. RESULTS: DO*A and DO*B alleles were detected in almost all groups, with a clear predominance of DO*B in every cohort tested. DO*JO and DO*HY allele frequencies reached 10% or more in several ethnic groups. DO*B-SH-Gln149Lys, DO*B-Ile5Thr, and DO*DODE variants were identified both in African ethnic groups and outside Africa. Twelve novel variants were characterized on a DO*A or a DO*B background. Five of them were found in both African and migrant cohorts, the others were restricted to either within or outside Africa. No DO*DOYA, DO*DOLG, DO*DOLC, nor DO*DOMR variants were observed. A first phylogenetic tree was proposed including all variant alleles. CONCLUSION: This study across continental Africa and countries with African migrants provides a useful overview of Dombrock allele diversity and distribution. The identification of 12 new alleles underlines the importance of genotyping for Dombrock alleles, particularly to improve transfusion safety in countries hosting migrant populations of African descent.

Multiplex Lateral Flow Assay for Rapid Visual Blood Group Genotyping.

Conventional blood group phenotyping by hemagglutination assays, carried out pretransfusion, is unsuitable in certain clinical situations. Molecular typing offers an alternative method, allowing the deduction of blood group phenotype from genotype. However, current methods require a long turnaround time and are not performed on-site, limiting their application in emergency situations. Here, we report the development of a novel, rapid multiplex molecular method to identify seven alleles in three clinically relevant blood group systems (Kidd, Duffy, and MNS). Our test, using a dry-reagent allele-specific lateral flow biosensor, does not require DNA extraction and allows easy visual determination of blood group genotype. Multiplex linear-after-the-exponential (LATE)-PCR and lateral flow parameters were optimized with a total processing time of 1 h from receiving the blood sample. Our assay had a 100% concordance rate between the deduced and the standard serological phenotype in a sample from 108 blood donors, showing the accuracy of the test. Owing to its simple handling, the assay can be operated by nonskilled health-care professionals. The proposed assay offers the potential for the development of other relevant single nucleotide polymorphism (SNP) panels for immunohematology and new applications, such as for infectious diseases, in the near future.

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

BACKGROUND: RhD phenotypes that express a significantly reduced amount of RhD antigen per red blood cell may be mistyped as RhD-negative by standard serologic methods. The molecular identification of weak D Type 1, 2, or 3 carriers allows managing them as RhD-positive and, thus, rationalizes the use of RhD-negative stock units and the administration of Rh-immunoglobulin prophylaxis, avoiding unnecessary costs and possible side effects. STUDY DESIGN AND METHODS: One sample was investigated for confirming a D-C-E+c+e- phenotype. Rh phenotyping was performed with the microplate direct hemagglutination test. DNA array analysis was performed using the BeadChip wRhD kit, and the RHD gene was explored by sequencing to determine the molecular background associated with RhD-negative phenotype. RESULTS: Molecular investigations showed a lack of amplification of Exons 3 through 7 and c.1154G>T transversion in Exon 9, suggesting an RHD-CE-D composite on a weak D Type 2 background. We attempted to precisely identify the two recombination sites generating this hybrid allele. The 5' and 3' breakpoints were located in Introns 2 and 7, which showed concentration of mobile Alu sequences most likely involved in the RHD-cE(3-7)-weak D Type 2 allele. CONCLUSION: Altogether, we identified the first example of an RHD-CE-D large hybrid allele on a weak D Type 2 background associated with an RhD-negative phenotype. By investigating the RHCE-D breakpoint zones, we suggest a mobile element-mediated recombination.

New KEL*01M and KEL*02M alleles: structural modeling to assess the impact of amino acid changes.

BACKGROUND: The KELL antigens are carried by the well-folded and highly polymorphic glycoprotein KELL, belonging to the M13 family of metalloproteases. Anti-KEL, particularly anti-KEL1, are clinically significant. We retrospectively investigated genomic DNA from samples with uncertain KEL1 or KEL2 phenotype and identified six novel Kmod alleles. We then considered a model of the protein three-dimensional (3D) structure to assess the impacts of the amino acid changes. STUDY DESIGN AND METHODS: The 19 exons of the KEL gene were polymerase chain reaction amplified and sequenced. Modeling was performed using the experimental 3D structure of human endothelin-converting enzyme-1 in the presence of the metabolite phosphoramidon. RESULTS: We identified four novel KEL*01M alleles with amino acid substitutions p.Arg447Trp, p.Gly641Arg, p.Ala645Val, and p.Gly703Arg found buried within helices of the ectodomain catalytic lobe. We also revealed one new KEL*02M allele with p.Gly263Glu in contact with solvent (water) located within the second lobe of the ectodomain. One sample with c.575G>C transversion (p.Arg192Pro) on a KEL*02 background showed a weakened reactivity for KEL1. According to our 3D modeling, these amino acid substitutions may have a profound impact on the protein structure. CONCLUSION: This study is especially interesting with regard to the description of four new KEL*01M alleles. Indeed, to date only two KEL*01M alleles have been described and our data suggest a nonnegligible incidence of KEL1 variants. Serologic KEL2-negative results as well as any ambiguity implying either KEL1 or KEL2 in donors should always be confirmed by means of genotyping analysis and discrepancies between these methods require sequencing of KEL gene.

Sub-Saharan red cell antigen phenotypes and glucose-6-phosphate dehydrogenase deficiency variants in French Guiana.

BACKGROUND: The treatment of Plasmodium vivax infections requires the use of primaquine, which can lead to severe haemolysis in glucose-6-phosphate dehydrogenase (G6PD)-deficient individuals. However, most of the Latin American countries, which are still endemic for vivax malaria, lack information on the distribution of G6PD deficiency (G6PDd). No survey has been performed so far in French Guiana. Herein, 80 individuals of the French Guianan Noir Marron population were scrutinized for red cell surface antigens of six blood group systems (ABO, Rh, Kell, Kidd, Duffy and MNS) and G6PD genetic polymorphisms. First, the sub-Saharan origin of the red cell phenotypes was assessed in relation with the literature. Then, given that the main sub-Saharan G6PDd variants are expected to be encountered, only the G6PD sequences of exons 4, 5, 6 and 9 were screened. This work aims at appraising the G6PD gene variation in this population, and thus, contributing to the G6PD piecemeal information in Latin America. RESULTS: Ninety-seven percent (97 %) of the red cells are Fy(a- b-), either D+ C- E- c+ e+ or D+ C+ E- c+ e+ and 44 % exhibited the Fya-/Jkb-/S- combined phenotype. Noteworthy is the detection of the G6PD(Val68Met) variant characterized by c.202G > A transition, G6PD(Asn126Asp) variant characterized by c.376A>G transition and G6PD(Asp181Val) variant characterized by c.542A>T transversion of the G6PD gene in 22.5 % of the sample, characteristic of the A(-(202)), A and Santamaria G6PDd variants, respectively. CONCLUSIONS: French Guianan Noir Marron population represents a pool of Rh-D antigen positive, Duffy-negative and G6PD-deficient erythrocytes, the latter accounting for one in every eight persons. The present study provides the first community-based estimation of the frequency of G6PDd polymorphisms in French Guiana. These results contribute to the G6PD genetic background information puzzle in Latin America.

RH diversity in Mali: characterization of a new haplotype RHD*DIVa/RHCE*ceTI(D2).

BACKGROUND: Knowledge of RH variants in African populations is critical to improving transfusion safety in countries with populations of African ancestry and to providing valuable information and direction for future development of transfusion in Africa. The purpose of this report is to describe RH diversity in individuals from Mali. STUDY DESIGN AND METHODS: Blood samples collected from 147 individuals self-identified as Dogon and Fulani were analyzed for Rh antigens and alleles. RESULTS: The most common RHD allele variant was RHD*DAU0. Five predicted partial-D phenotypes were attributed to RHD*DAU3 or RHD*DIVa. Neither RHD*DAR nor RHD*DIIIa was found. Investigation of RHCE revealed three predicted partial-e antigens encoded by RHCE*ce(254G) in trans to RHCE*cE. Regarding C antigen, 28 Fulani typed as C+ and 16 of 28 harbored at least one RHCE*Ce-D(4)-ce, two being homozygous and predicted to show a rare RH:32,-46 phenotype. A new RHCE*ceTI with replacement of Exon 2 by RHD (RHCE*ceTI(D2)) was identified in Dogon and was identified by inheritance study to be in cis to RHD*DIVa. These samples typed C- with anti-C polyclonal antibody and monoclonal antibodies (MoAbs) MS24, P3X2551368+MS24, and MS273, but positive with anti-RhCe MoAb-BS58. The same pattern was observed in sample with RHD*DIVa/RHCE*ceTI. CONCLUSION: Our survey indicated an uneven distribution of RH variant alleles between Dogon and Fulani, suggesting that study in well-documented cohorts is warranted. A high incidence of predicted partial-C phenotype encoded by RHCE*Ce-D(4)-ce was found in Fulani. Further study will also be needed to clarify the clinical significance of the new DIVa/ceTI(D2) haplotype encoding partial D and variant ce antigens.

Sequencing of the ART4 gene in sub-Saharan cohorts reveals ethnic differences and two new DO alleles: DO*B-Ile5Thr and DO*B-Trp266Arg.

BACKGROUND: Given the high heterogeneity of sub-Saharan populations especially between nonpygmoids and pygmoids, differences are expected during investigation of the DO/ART4 gene. STUDY DESIGN AND METHODS: Using genomic DNA extracted from blood samples collected from 77 Tswa pygmoids and 39 Teke and seven San nonpygmoids, DO coding regions were amplified and sequenced. A tetra-primer amplification refractory mutation system-polymerase chain reaction method was developed to specifically detect the DO*B-SH-Gln149Lys variant. Membrane expression of newly identified variant alleles in K562-transduced cells was studied by flow cytometry. RESULTS: Extensive polymorphism was confirmed in Teke or San nonpygmoids and Tswa pygmoids with, respectively, 12, zero, and 24 DO*A; 54, 10, and 115 DO*B or DO*B-WL; five, zero, and 14 DO*HY; and six DO*JO alleles in Teke only. The DO*B-SH-Gln149Lys variant was observed as the third most frequent after the DO*HY and DO*JO alleles. Two novel DO*B alleles were identified in the San samples, that is, DO*B-Ile5Thr and DO*B-Trp266Arg. Study of K562-transduced cells showed that compared to the DO*B allele, DO*B-Ile5Thr was expressed more strongly while DO*B-Trp266Arg variant was expressed to a lesser extent and was not recognized by MIMA-123 monoclonal antibodies. CONCLUSION: Sequencing analysis showed more allelic combinations in nonpygmoids than in pygmoids with high frequencies of DO*HY, DO*JO, and DO*B-SH-Gln149Lys variant alleles. This finding underlines the importance of including DO*HY and DO*JO single-nucleotide polymorphisms in genotyping tests to improve transfusion safety. Characterization of two novel DO*B alleles highlights the value of testing selected ethnic groups in understanding DO allele diversity.

Short duplication within the RHCE gene associated with an in cis deleted RHD causing a Rhnull amorph phenotype in an immunized pregnant woman with anti-Rh29.

BACKGROUND: The rare amorph Rhnull phenotype is caused by silent alleles at the RH locus and usually arises in consanguineous families. To date, only five molecular backgrounds have been identified in five unrelated families. Subjects with Rhnull red blood cells (RBCs) readily produce alloantibodies to high-prevalence Rh antigens. STUDY DESIGN AND METHODS: RBCs from a pregnant woman (G5P3) from Libya, with a positive indirect antiglobulin test were phenotyped by hemagglutination. RHD and RHCE genes were analyzed at the genomic level and mutation inheritance pattern was assessed in the patient's family. RESULTS: Hemagglutination testing showed a D-C-E-c-e- phenotype in the proposita associated with the presence of a high titer anti-Rh29 (4096). Molecular analysis revealed a deletion of RHD and presence of a novel RHCE allele with a 7-bp duplication in Exon 7. This duplication is predicted to introduce a frameshift after His350, a new C-terminal sequence, and a premature stop codon resulting in shortened predicted protein with only 402 amino acids. The mutated allele was found at homozygous state in the proposita and heterozygous state in her parents and one brother. CONCLUSION: This report describes a novel RHCE mutation causing the loss of RhCE antigen expression in association with RHD deletion, leading to an amorph Rhnull phenotype.

Synonymous nucleotide polymorphisms influence Dombrock blood group protein expression in K562 cells.

To gain further insight into ART4 (DO) gene alleles (DO*A, DO*JO1, DO*A-WL, DO*DOYA, DO*B, DO*B-WL, DO*B-SH-Q149K, DO*B-(WL)-I175N, DO*HY1, DO*HY2, DO*DOMR) and evaluate the impact of synonymous nucleotide polymorphisms on protein expression and mRNA accumulation of DO*A-HA, DO*A-SH and DO*B-SH alleles, human erythroleukaemic K562 cells were transducted with variant DO-lentiviral particles and analysed by flow cytometry and quantitative reverse transcription polymerase chain reaction. Monoclonal antibody (MoAb) detection of DO*A-HA and DO*JO1 transductants was lower than DO*A transductants, while detection of DO*A-SH, DO*A-WL and DO*DOYA transductants was higher. Variant DO*B alleles, i.e. DO*B-SH, DO*B-WL, DO*HY1, DO*HY2 and DO*DOMR, showed reduced MoAb binding. The unexpected modifications of protein expression of the DO*A-HA, DO*A-SH and DO*B-SH alleles that differ from the DO*A or DO*B alleles by a single synonymous polymorphism were abolished by reversion, thus implying involvement of these polymorphisms. Depending on the Leu208 codon used, detection level ranged from 1 to 4·14. In the variant alleles resulting from single synonymous polymorphism, mRNA accumulation correlated roughly with MoAbs detection levels, suggesting post-transcriptional regulation. Other than a few reports involving aberrant splicing, the experiments described herein provide the first evidence that synonymous nucleotide polymorphisms can influence Dombrock blood group expression. Such polymorphisms should be taken into account for molecular screening and potential impact on transfusion.

Heterogeneity of alleles encoding high- and low-prevalence red blood cell antigens across Africa: useful data to facilitate transfusion in African patients.

Ethnic variations in red blood cell (RBC) antigens can be a source of alloimmunization, especially in migrant populations. To improve transfusion safety in continental Africa and countries with African migrants, we performed RBC genotyping to determine allele frequencies coding for high- and low-prevalence antigens. A total of 481 blood samples were collected in ethnic groups from West, Central and East Africa. Molecular typing was performed using a polymerase chain reaction - reverse sequence specific oligonucleotide method. Results demonstrated no DI*1, DI*3, YT*2, SC*2, LW*7, KN*2 alleles in any sample and the CO*2 allele was rare. The frequency of LU*1 was comparable to that of European-Caucasians (2%) except in Biaka pygmies (8%). The frequency of CROM*-1 was high in Mbuti pygmies (13%). High frequency of KN*7 and KN*6 may reflect selection pressure in the countries investigated. Analysis of Dombrock allele patterns confirmed uneven distribution of the DO*1 and DO*2 alleles with high frequencies of DO*-4 and DO*-5 in all groups. Altogether, findings demonstrated extensive allele-frequency heterogeneity across Africa and suggested that knowledge of patient ethnicity gives information about the high-prevalence antigens that may be lacking. These data are medically useful to support transfusion care of African migrants living in countries where the majority of the population is from a different ethnical background.

A comprehensive survey of both RHD and RHCE allele frequencies in sub-Saharan Africa.

BACKGROUND: The RH system is one of the most polymorphic blood group systems with numerous allele variants affecting Rh polypeptides expression. This complexity is at the origin of difficulties for transfusion of African patients especially sickle cell disease patients requiring chronic transfusion therapy with high risk of immunization. As a complete survey of RH variants is lacking in African populations, we performed red blood cell genotyping to determine the type and frequency of RHD and RHCE alleles in sub-Saharan African populations. STUDY DESIGN AND METHODS: A total of 347 blood samples were collected from individuals of six nonpygmoid and three pygmoid populations. RH typing was performed using two single-tube multiplex polymerase chain reaction amplifications (BioArray Solutions, Immucor). RESULTS: All six sub-Saharan nonpygmoid populations exhibited constant variety in both type and frequency of aberrant RHD and RHCE alleles. Predicted partial RH1 (1.8%) and RH5 (0.9%) phenotypes were less than expected. Conversely, predicted partial phenotype RH2 (5.5%) was frequent. Data confirmed the high frequency of samples positive for the non-clinically significant RH10/RH20 antigens (39.5%) and revealed a high frequency of RH54 (DAK, 8.1%). The pygmoid groups showed higher percentages of predicted partial RH antigens and greater heterogeneity reflecting wide genetic differentiation. CONCLUSION: Our data show that frequencies of aberrant RHD and RHCE alleles were similar, irrespective of location and ethnicity. In view of the predicted frequencies and relative clinical significance of both private antigens and high-prevalence antigens absent, the most relevant assays for individuals of African descent in a transfusion setting are for 1) partial RH2 in the patient and 2) RH54 (DAK) in the donor.

RHCE*cE734C allele encodes an altered c antigen and a suppressed E antigen not detected with standard reagents.

BACKGROUND: The RH blood group system has many RHCE variant alleles that have arisen through gene conversion or nucleotide changes. Two probands, with red blood cells (RBCs) that were D+C+E-c+(w) e+ were sent to our laboratories to resolve the weak c expression. STUDY DESIGN AND METHODS: Hemagglutination tests were performed by automated and manual procedures. Genomic DNA analysis was performed by sequencing of Exons 1 to 10 of RHCE and RHD. RESULTS: The probands' RBCs did not react with standard monoclonal anti-E reagents from Bio-Rad, Diagast, DiaMed, Immucor, Ortho, and Quotient. The RBCs reacted variably with anti-c reagents from Diagast, DiaMed, Immucor, or Ortho and did not react with the Quotient anti-c reagent. Surprisingly, sequencing results of RHCE showed the presence of C/G at Position 676 (E/e polymorphism) and the association of the E polymorphism with a 734T>C transition in Exon 5 of the RHCE, encoding a Leu245Pro amino acid substitution in the mature RhcE polypeptide. Replacement of leucine 245 by proline in the eighth transmembrane domain of the RhcE protein may have a steric effect on the protein such that most anti-E reagents do not bind and the interaction between anti-c and c antigen is also affected. CONCLUSION: We report a novel RHCE*cE allele, RHCE*cE734C, which was assigned the provisional ISBT allele name RHCE*cE.14 or RHCE*03.14. It was found in two probands whose RBCs had weakened c expression and typed E- with conventional anti-E reagents. These data, once again, highlight the fact that the genotype does not always reflect the phenotype.

Weak D caused by a founder deletion in the RHD gene.

BACKGROUND: The RhD blood group system exemplifies a genotype-phenotype correlation by virtue of its highly polymorphic and immunogenic nature. Weak D phenotypes are generally thought to result from missense mutations leading to quantitative change of the D antigen in the red blood cell membrane or intracellularly. STUDY DESIGN AND METHODS: Different sets of polymerase chain reaction primers were designed to map and clone a deletion involving RHD Exon 10, which was found in approximately 3% of approximately 2000 RHD hemizygous subjects with D phenotype ambiguity. D antigen density was measured by flow cytometry. Transcript analysis was carried out by 3'-rapid amplification of complementary DNA ends. Haplotype analysis was performed by microsatellite genotyping. RESULTS: A 5405-bp deletion that removed nearly two-thirds of Intron 9 and almost all of Exon 10 of the RHD gene was characterized. It is predicted to result in the replacement of the last eight amino acids of the wild-type RhD protein by another four amino acids. The mean RhD antigen density from two deletion carriers was determined to be only 30. A consensus haplotype could be deduced from the deletion carriers based on the microsatellite genotyping data. CONCLUSION: The currently reported deletion was derived from a common founder. This deletion appears to represent not only the first large deletion associated with weak D but also the weakest of weak D alleles so far reported. This highly unusual genotype-phenotype relationship may be attributable to the additive effect of three distinct mechanisms that affect mRNA formation, mRNA stability, and RhD/ankyrin-R interaction, respectively.

Characterization of novel RHD alleles: relationship between phenotype, genotype, and trimeric architecture.

BACKGROUND: RH1 is one of the most clinically important blood group antigens in the field of transfusion and prevention of fetomaternal incompatibilities. New variant RHD alleles are regularly identified and their characterization is essential to ensuring patient safety. STUDY DESIGN AND METHODS: Blood samples with uncertain RhD phenotypes not resolved by our first-line SNaPshot assay were sequenced for all 10 RHD exons. RHD zygosity was investigated. Flow cytometry was performed to determine RhD antigen density and epitope pattern. RESULTS: Seven novel RHD alleles were identified. Six, that is, RHD(T55P), RHD(A85G), RHD(G132R), RHD(G132E), RHD(D403V), and DAR(T203A), resulted from nucleotide polymorphisms. The seventh, that is, RHD(S182WfsX46), resulted from a 4-bp deletion that led to a reading frame shift and the appearance of a premature stop codon. Study of RhD expression of the first five alleles at hemizygous state showed greatly reduced antigen densities ranging from 50 to 618 antigens per red blood cell (RBC). DAR(T203A) was classified as a partial D antigen with a weakened reactivity profile similar to that of DAR. As expected, no D antigen was detected on RBCs carrying the RHD(S182WfsX46) allele. In parallel, RhD expression of RHD(G336R)/weak D type 58, RHD(F410V), and suspected RHD(1-9)-CE was determined to be less than or equal to 50 antigens per RBC. RhAG/RhD(2) trimer model supports the observed phenotypes. CONCLUSION: Although the frequency of the new RHD alleles presented herein is low, their phenotypic and genotypic description adds to the repertoire of reported RHD alleles. These data can be useful for optimization of molecular screening tools.