Genotyping for red blood cell polymorphisms

Molecular Blood Group Screening in Donors from Arabian Countries and Iran Using High-Throughput MALDI-TOF Mass Spectrometry and PCR-SSP

Background and Aims

Only little is known about blood groups other than ABO blood groups and Rhesus factors in Arabian countries and Iran. During the last years, increased migration to Central Europe has put a focus on the question how to guarantee blood supply for patients from these countries, particularly because hemoglobinopathies with the need of regular blood support are more frequent in patients from that region. Therefore, blood group allele frequencies should be determined in individuals from Arabian countries and Iran by molecular typing and compared to a German rare donor panel.

Methods

1,111 samples including 800 individuals from Syria, 147 from Iran, 123 from the Arabian Peninsula, and 41 from Northern African countries were included in a MALDI-TOF MS assay to detect polymorphisms coding for Kk, Fy(a/b), Fy_null, C_w, Jk(a/b), Jo(a+/a-), Lu(a/b), Lu(8/14), Ss, Do(a/b), Co(a/b), In(a/b), Js(a/b), Kp(a/b), and variant alleles RHCE*c.697C>G and RHCE *c.733C>G. Yt(a/b), S-s-U-, Vel_null, Co_null, and RHCE *c.667G>T were tested by PCR-SSP.

Results

Of the Arabian donors, 2% were homozygous for the FY *02.01N allele (Fy_null), and 15.7% carried the heterozygous mutation. However, 0.8% of the German donors also carried 1 copy of the allele. 3.6% of all and 29.3% of Northern African donors were heterozygous for the RHCE *c.733C>G substitution, 0.4% of the Syrian probands were heterozygous for DO *01/DO *01.-05, a genotype that was lacking in German donors. Whereas the KEL *02.06 allele coding for the Js(a) phenotype was missing in Germans; 0.8% of the Syrian donors carried 1 copy of this allele. 1.8% of the Syrian but only 0.3% of the German donors were negative for YT *01. One donor from Northern Africa homo-zygously carried the GYPB *270+5g>t mutation, inducing the S-s-U+^w phenotype, and in 2 German donors a GYPB *c.161G>A exchange, which induces the Mit+ phenotype, caused a GYPB *03 allele dropout in the MALDI assay. The overall failure rate of the Arabian panel was 0.4%.

Conclusions

Some blood group alleles that are largely lacking in Europeans but had been described in African individuals are present in Arabian populations at a somewhat lower frequency. In single cases, it could be challenging to provide immunized Arabian patients with compatible blood.

Low-Frequency Blood Group Antigens in Switzerland

Background

High-frequency blood group antigens (HFA) are present in >90% of the human population, according to some reports even in >99% of individuals. Therefore, patients lacking HFA may become challenging for transfusion support because compatible blood is hardly found, and if the patient carries alloantibodies, the cross-match will be positive with virtual every red cell unit tested.

Methods

In this study, we applied high-throughput blood group SNP genotyping on >37,000 Swiss blood donors, intending to identify homozygous carriers of low-frequency blood group antigens (LFA).

Results

326 such individuals were identified and made available to transfusion specialists for future support of patients in need of rare blood products.

Conclusion

Thorough comparison of minor allele frequencies using population genetics revealed heterogeneity of allele distributions among Swiss blood donors which may be explained by the topographical and cultural peculiarities of Switzerland. Moreover, geographically localized donor subpopulations are described which contain above-average numbers of individuals carrying rare blood group genotypes.

Evolution of technology for molecular genotyping in blood group systems

The molecular basis of the blood group antigens was identified first in the 1980s and 1990s. Since then the importance of molecular biology in transfusion medicine has been described extensively by several investigators. Molecular genotyping of blood group antigens is one of the important aspects and is successfully making its way into transfusion medicine. Low-, medium- and high-throughput techniques have been developed for this purpose. Depending on the requirement of the centre like screening for high- or low-prevalence antigens where antisera are not available, correct typing of multiple transfused patients, screening for antigen-negative donor units to reduce the rate of alloimmunization, etc. a suitable technique can be selected. The present review discusses the evolution of different techniques to detect molecular genotypes of blood group systems and how these approaches can be used in transfusion medicine where haemagglutination is of limited value. Currently, this technology is being used in only a few blood banks in India. Hence, there is a need for understanding this technology with all its variations.

Performance evaluation study of ID CORE XT, a high throughput blood group genotyping platform

BACKGROUND

Traditionally, red blood cell antigens have been identified using serological methods, but recent advances in molecular biology have made the implementation of methods for genetic testing of most blood group antigens possible. The goal of this study was to validate the performance of the ID CORE XT blood group typing assay.

MATERIALS AND METHODS

One thousand independent samples from donors, patients and neonates were collected from three research institutes in Spain and the Netherlands. DNA was extracted from EDTA-anticoagulated blood. The data were processed with the ID CORE XT to obtain the genotypes and the predicted blood group phenotypes, and results were compared to those obtained with well-established serological and molecular methods. All 1,000 samples were typed for major blood group antigens (C, c, E, e, K) and 371-830 samples were typed for other antigens depending on the rarity and availability of serology comparators.

RESULTS

The incorrect call rate was 0%. Four "no calls" (rate: 0.014%) were resolved after repetition. The sensitivity of ID CORE XT for all phenotypes was 100% regarding serology. There was one discrepancy in E- antigen and 33 discrepancies in Fy^b- antigen. After bidirectional sequencing, all discrepancies were resolved in favour of ID CORE XT (100% specificity). ID CORE XT detected infrequent antigens of Caucasians in the sample as well as rare allelic variants.

DISCUSSION

In this evaluation performed in an extensive sample following the European Directive, the ID CORE XT blood genotyping assay performed as a reliable and accurate method for correctly predicting the genotype and phenotype of clinically relevant blood group antigens.

Challenges in the management of the blood supply

Although blood suppliers are seeing short-term reductions in blood demand as a result of initiatives in patient blood management, modelling suggests that during the next 5-10 years, blood availability in developed countries will need to increase again to meet the demands of ageing populations. Increasing of the blood supply raises many challenges; new approaches to recruitment and retainment of future generations of blood donors will be needed, and care will be necessary to avoid taking too much blood from these donors. Integrated approaches in blood stock management between transfusion services and hospitals will be important to minimise wastage--eg, by use of supply chain solutions from industry. Cross-disciplinary systems for patient blood management need to be developed to lessen the need for transfusion--eg, by early identification and reversal of anaemia with haematinics or by reversal of the underlying cause. Personalised medicine could be applied to match donors to patients, not only with extended blood typing, but also by using genetically determined storage characteristics of blood components. Growing of red cells or platelets in large quantities from stem cells is a possibility in the future, but challenges of cost, scaling up, and reproducibility remain to be solved.

DNA-based methods in the immunohematology reference laboratory

Although hemagglutination serves the immunohematology reference laboratory well, when used alone, it has limited capability to resolve complex problems. This overview discusses how molecular approaches can be used in the immunohematology reference laboratory. In order to apply molecular approaches to immunohematology, knowledge of genes, DNA-based methods, and the molecular bases of blood groups are required. When applied correctly, DNA-based methods can predict blood groups to resolve ABO/Rh discrepancies, identify variant alleles, and screen donors for antigen-negative units. DNA-based testing in immunohematology is a valuable tool used to resolve blood group incompatibilities and to support patients in their transfusion needs.

Overcoming methodical limits of standard RHD genotyping by next-generation sequencing

BACKGROUND AND OBJECTIVES

Molecular variations of the RHD gene may result in the reduced expression of the D antigen and altered Rh phenotypes. In many occasions, they cannot be typed reliably by standard serological methods. Sequence-based typing is the gold standard to determine rare and unknown RHD genotypes. For this pilot study, sequence-based typing by standard Sanger sequencing was compared to a newly established next-generation sequencing approach based on pyrosequencing.

MATERIALS AND METHODS

Twenty-six DNA samples were selected after primary serological testing exhibiting a weak reaction in Rh phenotype. Parallel sequence analysis of the complete coding sequence including adjacent intronic sequences allowed a comparison of the methodical potency in mutation detection of Sanger with next-generation sequencing.

RESULTS

Sanger sequencing revealed 39 RHD polymorphisms in 21 of 26 samples in the RHD coding region, while pyrosequencing detected all but two alterations resulting in a concordance rate of 94·9% and clearly revealed a heterozygous compound mutation in one sample with RHDψ and Weak D type 4 alleles. The resolution of cis/trans linkage of polymorphisms and exact characterization of a 37 bp duplication was achieved by next-generation sequencing.

CONCLUSION

Our data suggest that next-generation sequencing offers a new development for high-throughput and clonal sequencing for molecular RHD genotyping. However, further attempts in the methodical set-up have to be undertaken prior to validation and introduction as a routine service.

High-resolution melting analysis for genotyping Duffy, Kidd and Diego blood group antigens

High-resolution melting (HRM) analysis is a simpler genotyping method than allele-specific PCR, PCR-restriction fragment length polymorphism and multiplex PCR. Duffy, Kidd and Diego are clinically important blood group antigens. We used a novel method to genotype these three blood group antigens. Purified genomic DNA extracts of blood samples (354 Duffy, 347 Kidd and 457 Diego) were amplified using specific amplification primers. HRM curves were obtained by HRM analysis. Results were in complete concordance with those obtained for previous phenotypes and genotypes. Nucleotide substitutions for these blood group antigens were differentiated by the HRM curves. HRM analysis is a simple genotyping method and is an alternative to serological typing. Our results suggest that HRM analysis can also be used for genotyping blood group antigens whose allotype specificity is determined by single nucleotide substitutions.

Detection of blood-transmissible agents: can screening be miniaturized?

Transfusion safety relating to blood-transmissible agents is a major public health concern, particularly when faced with the continuing emergence of new infectious agents. These include new viruses appearing alongside other known reemerging viruses (West Nile virus, Chikungunya) as well as new strains of bacteria and parasites (Plasmodium falciparum, Trypanosoma cruzi) and finally pathologic prion protein (variant Creutzfeldt-Jakob disease). Genomic mutations of known viruses (hepatitis B virus, hepatitis C virus, human immunodeficiency virus) can also be at the origin of variants susceptible to escaping detection by diagnostic tests. New technologies that would allow the simultaneous detection of several blood-transmissible agents are now needed for the development and improvement of screening strategies. DNA microarrays have been developed for use in immunohematology laboratories for blood group genotyping. Their application in the detection of infectious agents, however, has been hindered by additional technological hurdles. For instance, the variability among and within genomes of interest complicate target amplification and multiplex analysis. Advances in biosensor technologies based on alternative detection strategies have offered new perspectives on pathogen detection; however, whether they are adaptable to diagnostic applications testing biologic fluids is under debate. Elsewhere, current nanotechnologies now offer new tools to improve the sample preparation, target capture, and detection steps. Second-generation devices combining micro- and nanotechnologies have brought us one step closer to the potential development of innovative and multiplexed approaches applicable to the screening of blood for transmissible agents.

Transfusion in the age of molecular diagnostics

DNA-based tests are increasingly being used to predict a blood group phenotype to improve transfusion medicine. This is possible because genes encoding 29 of the 30 blood group systems have been cloned and sequenced, and the molecular bases associated with most antigens have been determined. RBCs carrying a particular antigen, if introduced into the circulation of an individual who lacks that antigen (through transfusion or pregnancy), can elicit an immune response. It is the antibody from such an immune response that causes problems in clinical practice and the reason why antigen-negative blood is required for safe transfusion. The classical method of testing for blood group antigens and antibodies is hemagglutination; however, it has certain limitations, some of which can be overcome by testing DNA. Such testing allows conservation of antibodies for confirmation by hemagglutination of predicted antigen-negativity. High-throughput platforms provide a means to test relatively large numbers of donors, thereby opening the door to change the way antigen-negative blood is provided to patients and to prevent immunization. This review summarizes how molecular approaches, in conjunction with conventional hemagglutination, can be applied in transfusion medicine.

Applications and Experience with PCR-Based Assays to Predict Blood Group Antigens

DNA-based tests are increasingly being used to predict a blood group phenotype. This is possible because genes encoding 29 of the 30 blood group systems have been cloned and sequenced, and the molecular bases associated with most antigens have been determined. RBCs carrying a particular antigen, if introduced into the circulation of an individual who lacks that antigen, can elicit an immune response. It is the antibody from such an immune response that causes problems in clinical practice and the reason why antigen-negative blood is required for safe transfusion. The classical method of testing for blood group antigens and antibodies is hemagglutination; however, it has certain limitations, some of which can be overcome by testing DNA. Such testing allows conservation of antibodies for confirmation by hemagglutination of predicted antigen-negativity. High-throughput platforms provide a means to test relatively large numbers of donors, thereby opening the door to change the way antigen-negative blood is provided to patients. This chapter discusses how molecular approaches can be applied in transfusion medicine, and summarizes experiences of using laboratory developed tests and DNA arrays at the New York Blood Center.