RHD variants in Polish blood donors routinely typed as D-

Weak or partial D: Importance of molecular characterization of D variants

This case report presents first case of RHD*weak D type 9 in a 38-year-old Indian patient with severe osteoarthritis of the left hip joint scheduled for total hip replacement surgery. During routine blood grouping, an unexpected weak reaction with anti-D was observed. Serological characterization using an extended partial D typing kit characterized the variant as DV. The patient was successfully transfused with a O RhD negative compatible unit as per transfusion guidelines after surgery, without any observed transfusion reactions. The blood sample was sent to the ICMR-National Institute of Immunohematology, Mumbai, where molecular characterization revealed the presence of an RHD* 01 W.9 allele, as the underlying cause of weak expression of the RhD antigen. Serology can at best lead to the detection of the presence of a variant but characterization requires the help of molecular techniques.

Single-exon fetal RHD genotyping: a 31-month follow up in the obstetric population of Western Sweden

BACKGROUND

The Rh blood group system is highly complex, polymorphic, and immunogenic. The presence of RHD gene variants in RhD negative pregnant women is a challenge in fetal RHD genotyping as it may influence the antenatal management of anti-D prophylaxis. The aim of this study was to determine the efficiency of a non-invasive single-exon approach in the obstetric population of Western Sweden in a 31-month follow up. The frequency and type of maternal RHD variants were explored and the relation to the ethnicity was elucidated. Discrepant results between fetal RHD genotyping and serological blood group typing of newborns were investigated and clarified.

MATERIALS AND METHODS

RHD exon 4 was analysed with quantitative real-time PCR technique in a total of 6,948 blood samples from RhD negative women in early pregnancy. All cases with suspected maternal RHD gene and discrepant results observed in newborn samples, were further investigated using both serological and molecular technologies.

RESULTS

A total of 43 samples (0.6%) had inconclusive fetal genotyping result due the presence of a maternal RHD gene. These findings were in most cases (>66%) observed in pregnant women of non-European ancestry. Additionally, two novel RHD alleles were found. Seven discrepant results between fetal RHD genotype and serological RhD type of the newborns, were shown to be related to D antigen variants in newborns. Assay sensitivity was 99.95%, specificity 100%, and accuracy 99.97%.

DISCUSSION

The single-exon approach for fetal RHD screening early in pregnancy is an appropriate choice in the population of Western Sweden, with a very low frequency of inconclusive results caused by the presence of maternal RHD gene variants. Due to the high sensitivity, specificity, and accuracy of the test, serological typing of neonates born to RhD negative women has no longer been performed at our laboratory since June 2023.

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

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

Standardization of a multiplex assay to identify weak D types in a mixed-race Brazilian population

RH allele variability is caused by several types of variants, resulting in altered RhD and RhCE phenotypes. Most of the weak D phenotypes in European-derived populations are weak D types 1, 2, or 3, which are not involved in alloimmunization episodes. However, the Brazilian population is racially diverse, and the accuracy of molecular and serologic tests developed in recent years has allowed for the identification of other RH variants, that are common in the Brazilian population, such as weak D type 38 or weak partial 11, the latter involved in alloimmunization cases. Furthermore, patients with these two weak D variants must be transfused with D- red blood cell units, as do patients with weak D type 4 or DAR, which are also common D variants in Brazil. Weak D type 38 and weak partial 11 can be serologically misclassified as weak D types 1, 2, or 3 in patients, based on European experience, or as D- in donors. Additionally, pregnant women may unnecessarily be identified as requiring Rh immune globulin. RhCE phenotypes are reliable indicators of RhD variants. For individuals with the Dce phenotype, the preferred approach is to specifically search for RHD*DAR. However, when encountering DCe or DcE phenotypes, we currently lack a developed method that assists us in rapidly identifying and determining the appropriate course of action for the patient or pregnant woman. Two multiplex assays were proposed: one for the identification of RHD*weak partial 11, RHD*weak D type 38, and RHD*weak D type 3 and another for RHD*weak D type 2 and RHD*weak D type 5. The multiplex assays were considered valid if the obtained results were equivalent to those obtained from sequencing. Expected results were obtained for all tested samples. The proposed multiplex allele-specific polymerase chain reaction assays can be used in the molecular investigation of women of childbearing age, patients, and blood donors presenting a weak D phenotype with DCe or DcE haplotypes in a mixed-race population, such as Brazil.

DEL in China: the D antigen among serologic RhD-negative individuals

BACKGROUND

Providing RhD-negative red cell transfusions is a challenge in East Asia, represented by China, Korea, and Japan, where the frequency of RhD-negative is the lowest in the world.

FINDINGS

Among 56 ethnic groups in China, the RhD-negative frequency in Han, the prevalent ethnicity, is 0.5% or less, similar to most other ethnic groups. The Uyghur ethnic group has the highest reported RhD-negative frequency of up to 4.7%, as compared to 13.9% in the US. However, an estimated 7.15 million RhD-negative people live in China. The RhD-negative phenotype typically results from a loss of the entire RHD gene, causing the lack of the RhD protein and D antigen. The DEL phenotype carries a low amount of the D antigen and types as RhD-negative in routine serology. The DEL prevalence in RhD-negative individuals averages 23.3% in the Han, 17% in the Hui and 2.4% in the Uyghur ethnicities. The Asian type DEL, also known as RHD*DEL1 and RHD:c.1227G > A allele, is by far the most prevalent among the 13 DEL alleles observed in China.

CONCLUSION

The purpose of this review is to summarize the data on DEL and to provide a basis for practical strategy decisions in managing patients and donors with DEL alleles in East Asia using molecular assays.

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.

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

Background

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

Methods

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

Results

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

Conclusion

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

A preliminary evaluation of next-generation sequencing as a screening tool for targeted genotyping of erythrocyte and platelet antigens in blood donors

BACKGROUND

Matching the compatibility of donor blood with the recipient's antigens prevents alloimmunisation. Next-generation sequencing (NGS) technology is a promising method for extensive blood group and platelet antigen genotyping of blood donors. It circumvents the limitations of detecting known alleles based on predefined polymorphisms and enables targeted sequencing on a massive scale. The aim of this study was to evaluate the NGS AmpliSeq application on the Ion Torrent platform as a screening tool for genotyping blood donors' erythrocyte/platelet antigens.

MATERIALS AND METHODS

Primers for regions encoding antigens RhD (exons 5, 7), Rhc, RhE/e, Fya/b, Jka/b, M/N, S/s, HPA-1, 2, 3, 5, 15 were designed with Ion AmpliSeq Designer with manual inclusion of RHCE*C primers. DNA libraries of 57 regular blood donors with determined phenotype/genotype (prepared using the Ion AmpliSeq Library Kit and 14 primer pairs) were sequenced on the Ion Torrent PGM using 316v2 chips and 200 bp chemistry.

RESULTS

Sequencing was successful in all but the MN and HPA-5 regions. Mean sequencing coverage in one experiment was 4,606 reads, except for the RHCE*C region (mean 568 reads). NGS results agreed with the known phenotype/genotype of donors except in one phenotypically Fy(a+b-) case in whom FY*A/FY*B alleles were found. Reading rates for homozygotes were 97-100%, while they were around 50% for heterozygotes. NGS of RHD regions led to identification of mutations in two RhD negative donors.

DISCUSSION

NGS can be performed as a screening test to determine erythrocyte/platelet antigens in blood donors. This method allowed testing of 48 donors for 14 features (200 bp long) with the depth of a few thousand reads simultaneously, and the estimation of natural chimerism or hemi/homozygotic status. NGS screening can be adjusted to the genetic background of a given tested population.

14 Years of Polish Experience in Non-Invasive Prenatal Blood Group Diagnosis

BACKGROUND

Blood cell antigens may cause maternal alloimmunization leading to fetal/newborn disorders. Non-invasive prenatal diagnostics (NIPD) of the blood group permits the determination of feto-maternal incompatibility.

AIM

To evaluate 14 years of blood group NIPD at the Institute of Hematology and Transfusion Medicine (IHTM) in Warsaw.

METHODS

Plasma DNA from 536 RhD-negative, 24 Rhc-negative, 26 RhE-negative, 43 K-negative, and 42 HPA-1a-negative pregnant women was examined by real-time PCR to detect RHD, RHCE*c, RHCE*E, RHCE*C, KEL*01 and HPA*1A, respectively. We tested for CCR5, SRY or bi-allelic polymorphisms and quantified the total or fetal DNA.

RESULTS

The results of fetal antigen status prediction by NIPD in all but one case (false-positive result of KEL*01) were correct taking neonate serology as a reference. It was confirmed that all negative results of NIPD contained fetal DNA except for four cases where there was no difference between the parents' polymorphisms.

CONCLUSIONS

A fetal genotype compatible with the mother was determined in 25% of all pregnancies tested at the IHTM for the fetal blood group. These cases were not at risk of disease, so it was possible to avoid invasive procedures.