A clinically applicable method for determining the three major alleles at the Duffy (FY) blood group locus using polymerase chain reaction with allele-specific primers

Transfusing children with sickle cell disease using blood group genotyping when the pool of Black donors is limited

BACKGROUND

Red blood cell transfusion is an effective treatment for patients with sickle cell disease (SCD). Alloimmunization can occur after a single transfusion, limiting further usage of blood transfusion. It is recommended to match for the ABO, D, C, E, and K antigens to reduce risks of alloimmunization. However, availability of compatible blood units can be challenging for blood providers with a limited number of Black donors.

STUDY DESIGN AND METHODS

A prospective cohort of 205 pediatric patients with SCD was genotyped for the RH and FY genes. Transfusion and alloimmunization history were collected. Our capacity to find RhCE-matched donors was evaluated using a database of genotyped donors.

RESULTS

Nearly 9.8% of patients carried a partial D variant and 5.9% were D-. Only 45.9% of RHCE alleles were normal, with the majority of variants affecting the RH5 (e) antigen. We found an alloimmunization prevalence of 20.7% and a Rh alloimmunization prevalence of 7.1%. Since Black donors represented only 1.40% of all blood donors in our province, D- Caucasian donors were mostly used to provide phenotype matched products. Compatible blood for patients with rare Rh variants was found only in Black donors. A donor with compatible RhCE could be identified for all patients.

CONCLUSION

Although Rh-compatible donors were identified, blood units might not be available when needed and/or the extended phenotype or ABO group might not match the patient. A greater effort has to be made for the recruitment of Black donors to accommodate patients with SCD.

The highest Duffy (FYX) allele frequency ever reported for Scottish population: A cross-sectional study

Background and Aim

The Duffy (FY) blood group system has six known antigens among which the Fy^a and Fy^b are known as major antigens. Fy^x phenotype forms as a result of two point mutations in the FYB allele leading to instability of Duffy protein and so reduction of Duffy antigen expression in the cells. This study aimed to investigate the FYX allele frequency in the Scottish population.

Methods

The Duffy blood group system was serologically and molecularly investigated in 222 samples collected from donors of Aberdeen Regional Blood Transfusion Center (BTC). The haemagglutination and BeadChip microarray chemistry methods were used for phenotyping and genotyping. Confirmatory tests were also used to check the discrepant results.

Results

In this study, the frequency of Duffy blood group phenotypes including Fy^a+, Fy^a+b+, and Fy^b+ were 17.57%, 42.79%, and 39.64%, respectively. Furthermore, the frequency of FYA/FYA, FYA/FYB, and FYB/FYB genotypes was estimated to be 14.41%, 45.95%, and 39.64%, respectively, using the Bioarray method. In the present study, based on Duffy DNA sequencing results, 12 samples (5.41%) had just one FYX allele.

Conclusion

The frequency of the FYX allele in this study was estimated to be 0.0270% which is more than the results reported so far.

Improving the Molecular Diagnosis of Malaria: Droplet Digital PCR-Based Method Using Saliva as a DNA Source

Malaria is an acute febrile disease caused by a protozoan of the genus Plasmodium. Light microscopy (LM) is the gold standard for the diagnosis of malaria. Despite this method being rapid and inexpensive, it has a low limit of detection, which hampers the identification of low parasitemia infections. By using multicopy targets and highly sensitive molecular techniques, it is possible to change this scenario. In this study, we evaluated the performance of droplet digital PCR (ddPCR) to detect Plasmodium DNA obtained from saliva samples (whole saliva and buccal swab) of 157 individuals exposed to malaria transmission from the Brazilian Amazon region. We used the highly sensitive ddPCR method with non-ribosomal multicopy targets for Plasmodium vivax (Pvr47) and Plasmodium falciparum (Pfr364). There was good concordance between the quantitative real-time PCR (qPCR) results from the saliva and blood, except for mixed-species infections. The sensitivity of qPCR was 93% for blood, 77% for saliva, and 47% for swabs. Parasite DNA was not detected in saliva samples in low-density infections compared with the detection in blood samples. ddPCR showed increased sensitivity for detecting Plasmodium in the blood and swabs (99% in blood, 73% in saliva, and 59% in swabs). Notably, ddPCR detected more mixed infections in the blood (15%), saliva (9%), and swabs (18%) than qPCR. Our data showed that the differences between ddPCR and qPCR were the result of a higher number of P. falciparum infections detected by ddPCR. Overall, there was a moderate correlation between parasite densities estimated by the different methods in the blood. Our findings highlight the possibility of using non-invasive sample collection methods for malaria diagnosis by targeting multicopy sequences combined with highly sensitive molecular methods.

Genotyping of ABO and Duffy blood groups among malaria patients in Thailand

ABO blood groups have been proposed to influence malaria parasite infection and disease severity in individuals residing in different geographical areas. In Thailand, genetic polymorphisms of blood groups and susceptibility to malaria infection have rarely been investigated. The aim of this study was to assess the genotype frequencies of ABO and Duffy blood groups and susceptibility to malaria infection in two populations residing in malaria-endemic areas of Thailand. 1100 malaria samples and an identical number of samples from healthy subjects were collected from Thai-Malaysian and Thai-Myanmar areas. Genotyping of ABO and Duffy blood groups was performed by sequence specific primer-polymerase chain reaction. The distribution of ABO and Duffy blood groups was similar in malaria-positive and negative subjects. Blood group O was prevalent in both populations followed by blood group B (BO genotype) and A (AO genotype), respectively. In Plasmodium falciparum infections, blood group A frequency was significantly higher in Thai-Malaysian samples (P = 0.042) whereas blood group B frequency was significantly higher in Thai-Myanmar samples (P = 0.022). FY*A/*A frequency was significantly higher in Plasmodium vivax infection (P = 0.036) while FY*A/*B frequency was significantly higher in healthy subjects (P = 0.005). The different ABO blood group frequencies in the two populations may contribute to susceptibility to P. falciparum infection and the high prevalence of FY*A/*A can confer a risk of P. vivax infection. Further research in various ethnic groups is needed to clarify the association between blood groups and pathogenesis of malaria.

Children with Plasmodium vivax infection previously observed in Namibia, were Duffy negative and carried a c.136G > A mutation

Background

In a previous study, using a molecular approach, we reported the presence of P. vivax in Namibia. Here, we have extended our investigation to the Duffy antigen genetic profile of individuals of the same cohort with and without Plasmodium infections.

Methods

Participants with P. vivax (n = 3), P. falciparum (n = 23) mono-infections and co-infections of P. vivax/P. falciparum (n = 4), and P. falciparum/P. ovale (n = 3) were selected from seven regions. Participants with similar age but without any Plasmodium infections (n = 47) were also selected from all the regions. Duffy allelic profile was examined using standard PCR followed by sequencing of amplified products. Sequenced samples were also examined for the presence or absence of G125A mutation in codon 42, exon 2.

Results

All individuals tested carried the − 67 T > C mutation. However, while all P. vivax infected participants carried the c.G125A mutation, 7/28 P. falciparum infected participants and 9/41 of uninfected participants did not have the c.G125A mutation. The exon 2 region surrounding codon 42, had a c.136G > A mutation that was present in all P. vivax infections. The odds ratio for lack of this mutation with P. vivax infections was (OR 0.015, 95% CI 0.001–0.176; p = 0.001).

Conclusion

We conclude that P. vivax infections previously reported in Namibia, occurred in Duffy negative participants, carrying the G125A mutation in codon 42. The role of the additional mutation c.136 G > A in exon 2 in P. vivax infections, will require further investigations.

High frequency of the Duffy-negative genotype and absence of Plasmodium vivax infections in Ghana

Background

Recent studies from different malaria-endemic regions including western Africa have now shown that Plasmodium vivax can infect red blood cells (RBCs) and cause clinical disease in Duffy-negative people, though the Duffy-negative phenotype was thought to confer complete refractoriness against blood invasion with P. vivax. The actual prevalence of P. vivax in local populations in Ghana is unknown and little information is available about the distribution of Duffy genotypes. The aim of this study was to assess the prevalence of P. vivax in both asymptomatic and symptomatic outpatients and the distribution of Duffy genotypes in Ghana.

Methods

DNA was extracted from dried blood spots (DBS) collected from 952 subjects (845 malaria patients and 107 asymptomatic persons) from nine locations in Ghana. Plasmodium species identification was carried out by nested polymerase chain reaction (PCR) amplification of the small-subunit (SSU) rRNA genes. For P. vivax detection, a second PCR of the central region of the Pvcsp gene was carried out. Duffy blood group genotyping was performed by allele-specific PCR to detect the presence of the FY^ES allele.

Results

No cases of P. vivax were detected in any of the samples by both PCR methods used. Majority of infections (542, 94.8%) in the malaria patient samples were due to P. falciparum with only 1 infection (0.0017%) due to Plasmodium malariae, and 2 infections (0.0034%) due to Plasmodium ovale. No case of mixed infection was identified. Of the samples tested for the FY^ES allele from all the sites, 90.5% (862/952) had the FY^ES allele. All positive samples were genotyped as FY*B-33/FY*B-33 (Duffy-negative homozygous) and therefore classified as Fy(a−b−).

Conclusions

No cases of P. vivax were detected by both PCRs and majority of the subjects tested carried the FY^ES allele. The lack of P. vivax infections observed can be attributed to the high frequency of the FY^ES allele that silences erythroid expression of the Duffy. These results provide insights on the host susceptibility for P. vivax infections that had not been investigated in Ghana before.

Prospective assessment of malaria infection in a semi-isolated Amazonian indigenous Yanomami community: Transmission heterogeneity and predominance of submicroscopic infection

In the Amazon basin, indigenous forest-dwelling communities typically suffer from a high burden of infectious diseases, including malaria. Difficulties in accessing these isolated ethnic groups, such as the semi-nomadic Yanomami, make official malaria data largely underestimated. In the current study, we longitudinally surveyed microscopic and submicroscopic malaria infection in four Yanomami villages of the Marari community in the northern-most region of the Brazilian Amazon. Malaria parasite species-specific PCR-based detection of ribosomal and non-ribosomal targets showed that approximately 75% to 80% of all malaria infections were submicroscopic, with the ratio of submicroscopic to microscopic infection remaining stable over the 4-month follow-up period. Although the prevalence of malaria infection fluctuated over time, microscopically-detectable parasitemia was only found in children and adolescents, presumably reflecting their higher susceptibility to malaria infection. As well as temporal variation, the prevalence of malaria infection differed significantly between villages (from 1% to 19%), demonstrating a marked heterogeneity at micro-scales. Over the study period, Plasmodium vivax was the most commonly detected malaria parasite species, followed by P. malariae, and much less frequently P. falciparum. Consecutive blood samples from 859 out of the 981 studied Yanomami showed that malaria parasites were detected in only 8% of the previously malaria-positive individuals, with most of them young children (median age 3 yrs). Overall, our results show that molecular tools are more sensitive for the identification of malaria infection among the Yanomami, which is characterized by heterogeneous transmission, a predominance of low-density infections, circulation of multiple malaria parasite species, and a higher susceptibility in young children. Our findings are important for the design and implementation of the new strategic interventions that will be required for the elimination of malaria from isolated indigenous populations in Latin America.

Ribosomal and non-ribosomal PCR targets for the detection of low-density and mixed malaria infections

Background

The unexpected high proportion of submicroscopic malaria infections in areas with low transmission intensity challenges the control and elimination of malaria in the Americas. The current PCR-based assays present limitations as most protocols still rely on amplification of few-copies target gene. Here, the hypothesis was that amplification of different plasmodial targets—ribosomal (18S rRNA) and non-ribosomal multi-copy sequences (Pvr47 for Plasmodium vivax and Pfr364 for Plasmodium falciparum)—could increase the chances of detecting submicroscopic malaria infection.

Methods

A non-ribosomal real-time PCR assay targeting Pvr47/Pfr364 (NR-qPCR) was established and compared with three additional PCR protocols, two of them based on 18S rRNA gene amplification (Nested-PCR and R-qPCR) and one based on Pvr47/Pfr364 targets (NR-cPCR). The limit of detection of each PCR protocol, at single and artificial mixed P. vivax/P. falciparum infections, was determined by end-point titration curves. Field samples from clinical (n = 110) and subclinical (n = 324) malaria infections were used to evaluate the impact of using multiple molecular targets to detect malaria infections.

Results

The results demonstrated that an association of ribosomal and non-ribosomal targets did not increase sensitivity to detect submicroscopic malaria infections. Despite of that, artificial mixed-malaria infections demonstrated that the NR-qPCR was the most sensitive protocol to detect low-levels of P. vivax/P. falciparum co-infections. Field studies confirmed that submicroscopic malaria represented a large proportion (up to 77%) of infections among asymptomatic Amazonian residents, with a high proportion of infections (~ 20%) identified only by the NR-qPCR.

Conclusions

This study presents a new species-specific non-ribosomal PCR assay with potential to identify low-density P. vivax and P. falciparum infections. As the majority of subclinical infections was caused by P. vivax, the commonest form of malaria in the Amazon area, future studies should investigate the potential of Pvr47/Pfr364 to detect mixed-malaria infections in the field.

Electronic supplementary material

The online version of this article (10.1186/s12936-019-2781-3) contains supplementary material, which is available to authorized users.

Molecular genotyping of G6PD mutations and Duffy blood group in Afro-descendant communities from Brazilian Amazon

Glucose-6-phosphate dehydrogenase deficiency (G6PDd) and Duffy-negative blood group are two red blood cells variants that confer protection against malaria. In this study, the distribution of the most common G6PD variants (G6PD*A-, GGPD*A and G6PD Mediterranean) and the major alleles of the Duffy blood group (FY*A, FY*B and FY*BES) were investigated in an Afro-descendant population from state of Pará, Brazilian Amazon. G6PD variants and Duffy blood group alleles were determined by TaqMan SNP genotyping assay. Overall, molecular genotyping revealed the presence of G6PD variants in 126 (24%) of the individuals studied (5% male and 19% female), and frequencies of the G6PD*A- and G6PD*A alleles were 0.061 and 0.104, respectively. Duffy blood group genotyping showed that 24.3% of people were Duffy-negative and 41.3% were heterozygous for FY*BES. The frequency of allele FY*BES was 41.0%. The results emphasize the need to monitor G6PD deficiency for the use of primaquine in the routine care of the Afro-descendant communities of the Trombetas, Erepecuru and Cumná rivers, evaluating the risks of hemolytic crisis in case of recurrence of malaria in the region. In addition, the possible greater protection against malaria conferred by these erythrocyte polymorphisms deserves to be better investigated and explored among these Afro-descendants.

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.

Duffy blood group system: New genotyping method and distribution in a Brazilian extra-Amazonian population

Duffy blood group system is of interest in several fields of science including transfusion medicine, immunology and malariology. Although some methods have been developed for Duffy polymorphism genotyping, not all of them have been sufficiently described and validated, and all present limitations. At the same time, the frequency of Duffy alleles and antigens in some densely populated regions of the world are still missing. In this study we present new tests for genotyping the major alleles of the Duffy blood system and describe Duffy alleles and antigens in blood donors and transfusion-dependent patients in Minas Gerais, Brazil. A simple and reproducible strategy was devised for Duffy genotyping based on real-time PCR that included SNPs rs12075 and rs2814778. No significant differences between the allele frequencies were observed comparing blood donors and patients. Among the blood donors, the phenotype Fy(a-b+) was the most common and the Fy(a-b-) phenotype, associated with populations of African descent, was remarkably less common among subjects who self-identified as black in comparison to other ethnoracial categories. However, the African ancestry estimated by molecular markers was significantly higher in individuals with the allele associated to the Duffy null phenotype. The genotyping method presented may be useful to study Duffy genotypes accurately in different contexts and populations. The results suggest a reduced risk of alloimmunization for Duffy antigens and increased susceptibility for malaria in Minas Gerais, considering the high frequency of Duffy-positive individuals.

Duffy blood group genotyping in Thai blood donors

Background

Duffy (FY) blood group genotyping is important in transfusion medicine because Duffy alloantibodies are associated with delayed hemolytic transfusion reactions and hemolytic disease of the fetus and newborn. In this study, FY allele frequencies in Thai blood donors were determined by in-house PCR with sequence-specific primers (PCR-SSP), and the probability of obtaining compatible blood for alloimmunized patients was assessed.

Methods

Five hundred blood samples from Thai blood donors of the National Blood Centre, Thai Red Cross Society, were included. Only 200 samples were tested with anti-Fy^a and anti-Fy^b using the gel technique. All 500 samples and four samples from a Guinea family with the Fy(a-b-) phenotype were genotyped by using PCR-SSP. Additionally, the probability of obtaining antigen-negative red blood cells (RBCs) for alloimmunized patients was calculated according to the estimated FY allele frequencies.

Results

The FY phenotyping and genotyping results were in 100% concordance. The allele frequencies of FY^*A and FY^*B in 500 central Thais were 0.962 (962/1,000) and 0.038 (38/1,000), respectively. Although the Fy(a-b-) phenotype was not observed in this study, FY^*B^ES/FY^*B^ES was identified by PCR-SSP in the Guinea family and was confirmed by DNA sequencing.

Conclusions

Our results confirm the high frequency of the FY^*A allele in the Thai population, similar to that of Asian populations. At least 500 Thai blood donors are needed to obtain two units of antigen-negative RBCs for the Fy(a-b+) phenotype.

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.

Molecular identification of rare FY*Null and FY*X alleles in Caucasian thalassemic family from Sardinia

Molecular genetic studies on Duffy blood group antigens have identified mutations underlying rare FY*Null and FY*X alleles. FY*Null has a high frequency in Blacks, especially from sub-Saharan Africa, while its frequency is not defined in Caucasians. FY*X allele, associated with Fy(a-b+w) phenotype, has a frequency of 2-3.5% in Caucasian people while it is absent in Blacks. During the project of extensive blood group genotyping in patients affected by hemoglobinopathies, we identified FY*X/FY*Null and FY*A/FY*Null genotypes in a Caucasian thalassemic family from Sardinia. We speculate on the frequency of FY*X and FY*Null alleles in Caucasian and Black people; further, we focused on the association of FY*X allele with weak Fyb antigen expression on red blood cells and its identification performing high sensitivity serological typing methods or genotyping.

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.

Submicroscopic malaria parasite carriage: how reproducible are polymerase chain reaction-based methods?

The polymerase chain reaction (PCR)-based methods for the diagnosis of malaria infection are expected to accurately identify submicroscopic parasite carriers. Although a significant number of PCR protocols have been described, few studies have addressed the performance of PCR amplification in cases of field samples with submicroscopic malaria infection. Here, the reproducibility of two well-established PCR protocols (nested-PCR and real-time PCR for the Plasmodium 18 small subunit rRNA gene) were evaluated in a panel of 34 blood field samples from individuals that are potential reservoirs of malaria infection, but were negative for malaria by optical microscopy. Regardless of the PCR protocol, a large variation between the PCR replicates was observed, leading to alternating positive and negative results in 38% (13 out of 34) of the samples. These findings were quite different from those obtained from the microscopy-positive patients or the unexposed individuals; the diagnosis of these individuals could be confirmed based on the high reproducibility and specificity of the PCR-based protocols. The limitation of PCR amplification was restricted to the field samples with very low levels of parasitaemia because titrations of the DNA templates were able to detect < 3 parasites/µL in the blood. In conclusion, conventional PCR protocols require careful interpretation in cases of submicroscopic malaria infection, as inconsistent and false-negative results can occur.

Genotyping of the Duffy blood group among Plasmodium knowlesi-infected patients in Malaysia

The Duffy blood group is of major interest in clinical medicine as it plays an important role in Plasmodium knowlesi and Plasmodium vivax infection. In the present study, the distribution of Duffy blood group genotypes and allelic frequencies among P. knowlesi infected patients as well as healthy individuals in Peninsular Malaysia were determined. The blood group of 60 healthy blood donors and 51 P. knowlesi malaria patients were genotyped using allele specific polymerase chain reaction (ASP-PCR). The data was analyzed using Fisher's exact test in order to assess the significance of the variables. Our results show a high proportion of the FY*A/FY*A genotype (>85% for both groups) and a high frequency of the FY*A allele (>90% for both groups). The FY*A/FY*A genotype was the most predominant genotype in both infected and healthy blood samples. The genotype frequency did not differ significantly between the donor blood and the malaria patient groups. Also, there was no significant correlation between susceptibility to P. knowlesi infection with any Duffy blood genotype.

A New Method for Analyzing the Duffy Blood Group Genotype by TaqMan Minor Groove Binding Probes

BACKGROUND

Duffy blood group genotyping is useful to ensure transfusion safety and determine the association of Duffy blood group polymorphism with diseases, and therefore has its clinical significance. In order to improve the existing methods for genotyping of Duffy blood group, which normally require post-PCR manipulation, a new method was developed by using 5'-nuclease assay (NA) with TaqMan minor groove binding (MGB) probes.

METHODS

Primers and TaqMan-MGB probes were designed and synthesized to genotype FY*A and FY*B alleles at Duffy blood group locus on a real-time PCR platform. A total of 120 samples were genotyped by using the new 5'-NA and conventional polymerase chain reaction with allele-specific primers (PCR-ASP). The results obtained by the two methods were compared.

RESULTS

There was a complete concordance of results for all samples genotyped by 5'-NA and PCR-ASP. The retesting results of 5'-NA were consistent with those of the initial testing. The detection limit of 5'-NA was determined as 100 pg per reaction. The FY*A and FY*B allelic frequencies were 93.3% and 6.7% respectively in the Chinese Han population in Dalian.

CONCLUSIONS

The 5'-NA for genotyping of Duffy blood group is simple, rapid, reliable, reproducible, sensitive, and high-throughput and is superior to PCR-ASP used in routine genotyping.

Reticulocytes from cryopreserved erythroblasts support Plasmodium vivax infection in vitro

Plasmodium vivax is the most widely distributed human malaria parasite. Despite its importance, both clinical research and basic research have been hampered by lack of a convenient in vitro culture system, in part due to the parasite's infection preference of reticulocytes rather than mature erythrocytes. The use of reticulocyte-producing hematopoietic stem cell culture has been proposed for the maintenance of the parasite, but good numbers of reticulocytes and P. vivax parasites sufficient for practical use in research have been difficult to produce from this system. Here, we report an improved method of hematopoietic stem cell culture for P. vivax infection, which requires less time and produces higher or equivalent percentage of reticulocytes than previously reported systems. Reticulocytes were cultured from cryopreserved erythroblasts that were frozen after 8day-cultivation of purified CD34+ cells from human umbilical cord blood. This method of production allowed the recovery of reticulocytes in a shorter time than with continuous stem cell culture. We obtained a relatively high percentage of peak reticulocyte production by using co-cultivation with a mouse stromal cell line. Using P. vivax mature stage parasites obtained from infected Aotus monkeys, we observed substantial numbers (up to 0.8% of the total number of the cells) of newly invaded reticulocytes 24h after initial cultivation. The addition of fresh reticulocytes after 48h culture, however, did not result in significant increase of second cycle reticulocyte invasion. Assays of invasion inhibition with specific antibodies were successful with this system, demonstrating potential for study of biological processes as well as the conditions necessary for long-term maintenance of P. vivax in vitro.

DNA biosensor/biochip for multiplex blood group genotyping

At present, 33 blood groups representing over 300 antigens are listed by the International Society of Blood Transfusion (ISBT). Most of them result from a single nucleotide polymorphism (SNP) in the corresponding DNA sequence, i.e. approx. 200 SNPs. In immunohematology laboratories, blood group determination is classically carried out by serological tests, but these have some limitations, mostly in term of multiplexing and throughput. Yet, there is a growing need of extended blood group typing to prevent alloimmunization in transfused patients and transfusion accidents. The knowledge of the molecular bases of blood groups allows the use of molecular biology methods within immunohematology laboratories. Numerous assays focused on blood group genotyping were developed and described during the last 10 years. Some of them were real biochips or biosensors while others were more characterized by the particular molecular biology techniques they used, but all were intending to produce multiplex analysis. PCR techniques are most of the time used followed by an analytical step involving a DNA biosensor, biochip or analysis system (capillary electrophoresis, mass spectrometry). According to the method used, the test can then be classified as low-, medium- or high-throughput. There are several companies which developed platforms dedicated to blood group genotyping able to analyze simultaneously various SNPs or variants associated with blood group systems. This review summarizes the characteristics of each molecular biology method and medium-/high-throughput platforms dedicated to the blood group genotyping.

Detection of alloimmunization to ensure safer transfusion practice

BACKGROUND

Serological safety is an integral part of overall safety for blood banks. Emphasis is on the use of routinue Red Blood Cell (RBC) antibody screen test, at set time intervals, to reduce risks related to alloantibodies. Also emphasis is on importance of issuing antigen negative blood to alloantibody positive patients. Effect of using leucodepleted blood on the rate of alloimmunization is highlighted. The concept of provision of phenotypically matched blood is suggested.

MATERIALS AND METHODS

Antibody screen test is important to select appropriate blood for transfusion. Repeat antibody screen testing, except if time interval between the earlier and subsequent transfusion was less than 72 hours, followed by antibody identification, if required, was performed in patients being treated with repeat multiple blood transfusions. Between February 2008 and June 2009, repeat samples of 306 multi-transfused patients were analyzed. Search for irregular antibodies and reading of results was conducted using RBC panels (three-cell panel of Column Agglutination Technology (CAT) and two cell panel of the Solid Phase Red Cell Adherence Technology (SPRCAT). Specificities of antibodies were investigated using appropriate panels, 11 cell panel of CAT and 16 cell panel of SPRCA. These technologies, detecting agglutination in columns and reactions in solid phase, evaluate the attachment of irregular incomplete antibody to antigen in the first phase of immunological reaction more directly and hence improve the reading of agglutination. Three to four log leuco reduced red blood cells were transfused to patients in the study using blood collection bags with integral filters.

RESULTS

Alloimmunization rate of 4.24% was detected from 306 multiply transfused patients tested and followed up. The Transfusion therapy may become significantly complicated.

CONCLUSION

Red cell antibody screening and identification and subsequent issue of antigen negative blood have a significant role in improving blood safety. Centers that have incorporated antibody screen test and identification have ensured safe transfusion. Identified patients should be flagged in a database and information shared. Such patients can be given carry-on cards and educated about the names of the identified antibodies. Full red cell phenotyping of individuals, patients and donors, can be feasibility.

Plasmodium vivax infection in Anajás, State of Pará: no differential resistance profile among Duffy-negative and Duffy-positive individuals

Background

There is large body of evidence that states that invasion of Plasmodium vivax requires the Duffy antigen, but the universality of this specificity is certainly now under question with recent reports showing that in some parts of the world P. vivax infects and causes disease in Duffy-negative people. These findings reinforce the idea that this parasite is rapidly evolving, being able to use other receptors than Duffy to invade the erythrocytes, which may have an enormous impact in P. vivax current distribution. The presence of P. vivax infection in Duffy-negative individuals was investigated in a cross-sectional study conducted in Anajás, Archipelago of Marajó, State of Pará, which is an area of malaria transmission in the Brazilian Amazonia.

Methods

Duffy genotyping and Plasmodium species diagnostic assays were performed successfully in 678 individuals. An allele-specific primer polymerase chain reaction (PCR) technique was used for Duffy blood group genotyping. Identification of Plasmodium species was achieved by conventional blood smear light microscopy and a TaqMan-based real-time PCR method to detect mitochondrial genome of Plasmodium falciparum and P. vivax.

Results

Plasmodium spp. infection was detected in 137 samples (20.2%). Prevalence of each Plasmodium species was 13.9% P. vivax, 5.8% P. falciparum, and 0.6% P. vivax plus P. falciparum. Overall, 4.3% (29/678) were genotyped as Duffy-negative (FY*B^ES/*B^ES). Among Duffy-negative individuals 6.9% were P. vivax PCR positive and among Duffy-positive 14.2% were P. vivax PCR positive. Although lower, the risk of Duffy-negatives to experience a P. vivax blood stage infection was not significantly different to that of Duffy-positives. Furthermore, the genotypic and allelic frequencies of the Duffy blood group among P. vivax-infected patients and in the control group did not differ significantly, also suggesting no reduction in infection rates among the carriers of FY*B^ES allele.

Conclusions

The data obtained in Anajás showed no differential resistance vivax malaria among Duffy-negative and Duffy-positive individuals. This result needs additional confirmation through a deeper evaluation in a larger sample of patients with P. vivax malaria and molecular parasite characterization. Nonetheless, this genetic profile of the parasite may be contributing to the high incidence of malaria in the municipality.

Analysis for genotyping Duffy blood group in inhabitants of Sudan, the fourth cataract of the Nile

Background

Genetic polymophisms of the Duffy antigen receptor for the chemokines (DARC) gene successfully protected against blood stage infection by Plasmodium vivax infection. The Fy (a-, b-) phenotype is predominant among African populations, particularly those originating from West Africa, and it is rare among non-African populations. The aim of this study was to analyse the frequency of four Duffy blood groups based on SNPs (T-33C, G125A, G298A and C5411T) in two local tribes of Sudanese Arabs, the Shagia and Manasir, which are both from the region of the Fourth Nile cataract in Sudan.

Methods

An analysis of polymorphisms was performed on 217 individuals (126 representatives of the Shagia tribe and 91 of the Manasir). Real-time PCR and TaqMan Genotyping Assays were used to study the prevalence of alleles and genotypes.

Results

The analysis of allelic and genotype frequency in the T-33C polymorphisms demonstrated a significant dominance of the C allele and CC genotype (OR = 0.53 [0.32-0.88]; p = 0.02) in both tribes. The G125A polymorphism is associated with phenotype Fy(a-, b-) and was identified in 83% of Shagia and 77% of Manasir. With regard to G298A polymorphisms, the genotype frequencies were different between the tribes (p = 0,002) and no single AA homozygote was found. Based on four SNPs examined, 20 combinations of genotypes for the Shagia and Manasir tribes were determined. The genotype CC/AA/GG/CT occurred most often in Shagia tribe (45.9%) but was rare in the Manasir tribe (6.6%) (p < 0.001 Shagia versus Manasir). The FY*A^ES allele was identified in both analysed tribes. The presence of individuals with the FY*A/FY*A genotype was demonstrated only in the Shagia tribe.

Conclusion

This is probably the first report showing genotypically Duffy-negative people who carry both FY*B^ES and FY*A^ES. The identification of the FY*A^ES allele in both tribes may be due to admixture of the non-African genetic background. Taken as a whole, allele and genotype frequencies between the Shagia and the Manasir were statistically different. However, the presence of individuals with the FY*A/FY*A genotype was demonstrated only in the Shagia tribe.

The association between a Darc gene polymorphism and clinical outcomes in African American patients with acute lung injury

BACKGROUND

Acute lung injury (ALI) mortality is increased among African Americans compared with Americans of European descent, and genetic factors may be involved. A functional T-46C polymorphism (rs2814778) in the promoter region of Duffy antigen/receptor for chemokines (Darc) gene, present almost exclusively in people of African descent, results in isolated erythrocyte DARC deficiency and has been implicated in ALI pathogenesis in preclinical and murine models, possibly because of an increase in circulating Duffy-binding, proinflammatory chemokines like IL-8. We sought to determine the effect of the functional rs2814778 polymorphism, C/C genotype (Duffy null state), on clinical outcomes in African Americans with acute lung injury.

METHODS

Clinical data and biologic specimens from African American patients with ALI who enrolled in three randomized controlled trials were analyzed. Multivariate analysis accounted for proportion of African ancestry, sex, cirrhosis, and severity of illness on presentation.

RESULTS

Among 132 subjects, 88 (67%) were Duffy null (C/C genotype). The Duffy null state was associated with a 17% absolute risk increase (95% CI, 1.4%-33%) in mortality at 60 days, a median of 8 fewer ventilator-free days (95% CI, 1-18.5), and 4.5 fewer organ failure-free days (95% CI, 0-18) compared with individuals with the C/T or T/T genotypes (all P values < .05). Estimates were similar on multivariate analysis. In African Americans without the null variant, clinical outcomes were similar to those in patients of European descent. A subgroup analysis suggested that plasma IL-8 levels are increased in Duffy null individuals.

CONCLUSIONS

Our results provide evidence that the functional rs2814778 polymorphism in the gene encoding DARC is associated with worse clinical outcomes among African Americans with ALI, possibly via an increase in circulating IL-8.

4.1R-deficient human red blood cells have altered phosphatidylserine exposure pathways and are deficient in CD44 and CD47 glycoproteins

BACKGROUND

Protein 4.1R is an important component of the red cell membrane skeleton. It imparts structural integrity and has transmembrane signaling roles by direct interactions with transmembrane proteins and other membrane skeletal components, notably p55 and calmodulin.

DESIGN AND METHODS

Spontaneous and ligation-induced phosphatidylserine exposure on erythrocytes from two patients with 4.1R deficiency were studied, using CD47 glycoprotein and glycophorin C as ligands. We also looked for protein abnormalities in the 4.1R-based multiprotein complex.

RESULTS

Phosphatidylserine exposure was significantly increased in 4.1R-deficient erythrocytes obtained from the two different individuals when ligands to CD47 glycoprotein were bound. Spontaneous phosphatidylserine exposure was normal. 4.1R, glycophorin C and p55 were missing or sharply reduced. Furthermore there was an alteration or deficiency of CD47 glycoprotein and a lack of CD44 glycoprotein. Based on a recent study in 4.1R-deficient mice, we found that there are clear functional differences between interactions of human red cell 4.1R and its murine counterpart.

CONCLUSIONS

Glycophorin C is known to bind 4.1R, and we have defined previously that it also binds CD47. From our evidence, we suggest that 4.1R plays a role in the phosphatidylserine exposure signaling pathway that is of fundamental importance in red cell turnover. The linkage of CD44 to 4.1R may be relevant to this process.

The Duffy Antigen/Receptor for Chemokines (DARC) and prostate-cancer risk among Jamaican men

As an evolutionary response to prevent malaria infection, most Africans do not express the Duffy Antigen/Receptor for Chemokines (DARC) on their red blood cells. Results from experimental studies suggest that DARC expression inhibits prostate-tumor growth. We tested the hypothesis that men of African descent who lack DARC expression are at increased risk of prostate cancer. A case-control study involving 81 age-matched pairs was conducted in Jamaica. Participants were interviewed to collect data, and they donated blood for determination of DARC expression. Logistic regression was used to estimate associations with prostate cancer and aggressive disease. Little or no association was observed between erythrocyte DARC expression and prostate cancer or between DARC expression and aggressive disease. These associations changed little when adjusting for other potential confounders. Our results do not support an effect of erythrocyte DARC expression on the risk or progression of prostate cancer in men of African descent.

High-throughput red blood cell antigen genotyping using a nanofluidic real-time polymerase chain reaction platform

BACKGROUND

Serologic testing of donors to obtain antigen-negative blood for transfusion is limited by availability and quality of reagents. Where sequence variant information is available, molecular typing platforms can be used to determine the presence of a variant allele and offer a high-throughput format correlated to the blood group antigen. We have investigated a flexible high-throughput platform to screen blood donors for antigen genotypes in the African American population.

STUDY DESIGN AND METHODS

Genomic DNA from 427 African American donors was analyzed for single-nucleotide polymorphisms responsible for red blood cell (RBC) antigens E/e, Fy(a)/Fy(b), Fy gene promoter, Jk(a)/Jk(b), Lu(a)/Lu(b), K/k, Js(a)/Js(b), Do(a)/Do(b), Jo(a), and Hy using primer/probe sets (Taqman, Applied Biosystems) on a high-throughput genotyping platform (OpenArray, BioTrove). Where available, the phenotype obtained by serologic testing was compared to genotype data.

RESULTS

Serologic antigen types were available for 2037 of the 4270 genotypes generated. There were five discordant results. Three resolved with repeat serologic typing, one resolved after repeat genotyping, and one discordance was clarified by confirmation of the BioTrove genotype by Sanger sequencing. Triplicate determinations were made for each sample genotype and the results were identical more than 99% of the time.

CONCLUSIONS

The nanofluidic genotyping platform described here provides an accurate method for predicting blood group phenotypes. The user-specified array layout provides flexibility of target selection and number of replicate determinations and is suitable for screening antigen types.

Real-time PCR assays for high-throughput blood group genotyping

There are multiple situations in the context of transfusion medicine where the classic serologic methods are unable to provide an adequate response, for example, recently polytransfused patients, patients with positive direct human antiglobulin tests, and hemolytic disease of the newborn. The traditional polymerase chain reaction techniques are slow and sometimes difficult to carry out and interpret. Thus there is a need for the development and validation of rapid and effective molecular methods. The genetic basis of the main alleles of the most important blood groups are known, but the frequencies vary in the different populations, thus for the genetic techniques to be efficient it is important to evaluate them, in order to adapt the molecular approaches.

Failure to detect Plasmodium vivax in West and Central Africa by PCR species typing

Background

Plasmodium vivax is estimated to affect 75 million people annually. It is reportedly absent, however, from west and central Africa due to the high prevalence of the Duffy negative phenotype in the indigenous populations. Despite this, non-African travellers consistently return to their own countries with P. vivax malaria after visiting this region. An attempt was made, therefore, to detect the presence of P. vivax parasites in blood samples collected from the indigenous populations of west and central Africa.

Methods

Parasite species typing (for all four human malaria parasites) was carried out by PCR on 2,588 blood samples collected from individuals from nine African malaria-endemic countries.

Results

Most infections (98.5%) were Plasmodium falciparum, Plasmodium malariae was identified in 8.5% of all infections, and Plasmodium ovale in 3.9%. The prevalence of both parasites varied greatly by country. Only one case of P. vivax was detected from Sao Tome, an island off the west coast of Africa, confirming the scarcity of this parasite in Africa.

Conclusion

The prevalence of P. vivax in local populations in sub-Saharan Africa is very low, despite the frequent identification of this parasite in non-African travellers.

Distribution of the FYBES and RHCE*ce(733C>G) alleles in an Argentinean population: implications for transfusion medicine

BACKGROUND

The understanding of the molecular bases of blood groups makes possible the identification of red cell antigens and antibodies using molecular approaches, especially when haemagglutination is of limited value. The practical application of DNA typing requires the analysis of the polymorphism and allele distribution of the blood group genes under study since genetic variability was observed among different ethnic groups. Urban populations of Argentina are assumed to have a white Caucasian European genetic component. However, historical and biological data account for the influence of other ethnic groups. In this work we analyse FY and RH blood group alleles attributed to Africans and that could have clinical implications in the immune destruction of erythrocytes.

METHODS

We studied 103 white trios (father, mother and child, 309 samples) from the city of Rosario by allele specific PCRs and serological methods. The data obtained were analysed with the appropriate statistical test considering only fathers and mothers (n = 206).

RESULTS

We found the presence of the FY*BES and RHCE*ce(733C>G) alleles and an elevated frequency (0.0583) for the Dce haplotype. The number of individuals with a concomitant occurrence of both alleles was significantly higher than that expected by chance. We found that 4.68% of the present gene pool is composed by alleles primarily associated with African ancestry and about 10% of the individuals carried at least one RH or FY allele that is predominantly observed among African populations. Thirteen percent of Fy(b-) subjects were FY*A/FY*BES.

CONCLUSION

Taken together, the results suggest that admixture events between African slaves and European immigrants at the beginning of the 20th century made the physical characteristics of black Africans to be invisible nowadays. Considering that it was a recent historical event, the FY*BES and RHCE*ce(733C>G) alleles did not have time to become widespread but remain concentrated within families. These findings have considerable impact for typing and transfusion strategy in our population, increasing the pool of compatible units for Fy(b-) individuals requiring chronic transfusion. Possible difficulties in transfusion therapy and in genotyping could be anticipated and appropriately improved strategies devised, allowing a better management of the alloimmunization in the blood bank.

An extensive polymerase chain reaction-allele-specific polymorphism strategy for clinical ABO blood group genotyping that avoids potential errors caused by null, subgroup, and hybrid alleles

BACKGROUND

ABO genotyping is complicated by the remarkable diversity at the ABO locus. Recombination or gene conversion between common alleles may lead to hybrids resulting in unexpected ABO phenotypes. Furthermore, numerous mutations associated with weak subgroups and nondeletional null alleles should be considered. All known ABO genotyping methods, however, risk incorrect phenotype predictions if any such alleles are present.

STUDY DESIGN AND METHODS

An extensive set of allele-specific primers was designed to accomplish hybrid-proof multiplex polymerase chain reaction (PCR) amplification of DNA fragments for detection of ABO alleles. Results were compared with serologic findings and ABO genotypes defined by previously published PCR-restriction fragment length polymorphism/PCR-allele-specific polymorphism (ASP) methods or DNA sequencing.

RESULTS

Phenotypically well-characterized samples from blood donors with common blood groups and rare-subgroup families were analyzed. In addition to the commonly encountered alleles (A1, A1(467C>T), A2, B, O1, O1v, and O2), the new method can detect hybrid alleles thanks to long-range amplification across intron 6. Four of 12 PCR-ASP procedures are used to screen for multiple infrequent subgroup and null alleles. This concept allows for a low-resolution typing format in which the presence of, for example, a weak subgroup or cis-AB/B(A) is indicated but not further defined. In an optional high-resolution step, more detailed genotype information is obtained.

CONCLUSION

A new genotyping approach has been developed and evaluated that can correctly identify ABO alleles including nondeletional null alleles, subgroups, and hybrids resulting from recombinational crossing-over events between exons 6 and 7. This approach is clinically applicable and decreases the risk for erroneous ABO phenotype prediction compared to previously published methods.

Structural basis for red cell phenotypic changes in newly identified, naturally occurring subgroup mutants of the human blood group B glycosyltransferase

BACKGROUND

Four amino-acid-changing polymorphisms differentiate the blood group A and B alleles. Multiple missense mutations are associated with weak expression of A and B antigens but the structural changes causing subgroups have not been studied.

STUDY DESIGN AND METHODS

Individuals or families having serologically weak B antigen on their red cells were studied. Alleles were characterized by sequencing of exons 1 through 7 in the ABO gene. Single crystal X-ray diffraction, three-dimensional-structure molecular modeling, and enzyme kinetics showed the effects of the B allele mutations on the glycosyltransferases.

RESULTS

Seven unrelated individuals with weak B phenotypes possessed seven different B alleles, five of which are new and result in substitution of highly conserved amino acids: M189V, I192T, F216I, D262N, and A268T. One of these (F216I) was due to a hybrid allele resulting from recombination between B and O(1v) alleles. The two other alleles were recently described in other ethnic groups and result in V175M and L232P. The first crystal-structure determination (A268T) of a subgroup glycosyltransferase and molecular modeling (F216I, D262N, L232P) indicated conformational changes in the enzyme that could explain the diminished enzyme activity. The effect of three mutations could not be visualized since they occur in a disordered loop.

CONCLUSION

The genetic background for B(w) phenotypes is very heterogeneous but usually arises through seemingly random missense mutations throughout the last ABO exon. The targeted amino acid residues, however, are well conserved during evolution. Based on analysis of the resulting structural changes in the glycosyltransferase, the mutations are likely to disrupt molecular bonds of importance for enzymatic function.

Real-time multiplex allele-specific polymerase chain reaction for genotyping of the Duffy antigen, the Plasmodium vivax invasion receptor

BACKGROUND AND OBJECTIVES

Duffy blood group is of major interest in clinical medicine as it is not only involved in blood-transfusion risks and occasionally in neonatal haemolytic disease, but it is also the receptor for the human malaria parasite Plasmodium vivax in the erythrocyte invasion. The aim of this study was to develop a rapid and inexpensive approach for high-throughput Duffy genotyping.

MATERIALS AND METHODS

This paper reported the development of a Duffy genotyping assay based on multiplex real-time polymerase chain reaction (PCR) using SYBR Green I fluorescent dye.

RESULTS

By using this approach for Duffy genotyping we obtained the same results as that for the conventional allele-specific PCR, however, in a high-throughput assay. The Duffy genotyping of field samples demonstrated that P. vivax-infected individuals showed a significantly higher prevalence of two functional alleles than Plasmodium falciparum-infected and non-infected individuals. This finding corroborates the hypothesis that the presence of two functional alleles increases the risk of P. vivax infection.

CONCLUSION

This methodology may be suitable for epidemiological studies, particularly for exploring the relationship between Duffy alleles and malaria susceptibility, and also for identification of transfusional incompatibility in blood banks.

Large scale blood group genotyping

Determination of predicted blood group phenotype by determination of genotype has been performed since the 1990s. This evolved due to the rapid accrual of information surrounding the molecular basis of blood group antigen expression, which started in 1990 with ABO and RH systems and has now resulted in the molecular description of 28 of the 29 blood groups. Blood group genotyping is currently performed mostly for fetal blood group incompatibility and for assessment of multi-transfused patients. Both of these clinical scenarios are either dangerous or technically difficult, respectively to define serologically. With the simultaneous development of mass scale genotyping platforms it has now permitted the application of them to blood group genotype determination. In this paper, I describe some recently published work that has demonstrated that mass scale genotyping approaches are feasible. These approaches may lead to more effective management of blood stocks and patient cross-matching by reducing the dependence on serology during the time critical pre-transfusion phase. It is most probable that large scale studies, perhaps involving many European Union and North American based blood suppliers, may drive the introduction of this technology and convince red cell serologists that this approach may allow their work to be more focussed.

FY*X real-time polymerase chain reaction with melting curve analysis associated with a complete one-step real-time FY genotyping

BACKGROUND AND OBJECTIVES

The Duffy (FY) blood group system is controlled by four major alleles: FY*A and FY*B, the Caucasian common alleles, encoding Fy(a) and Fy(b) antigens; FY*X allele responsible for a poorly expressed Fy(b) antigen, and FY*Fy a silent predominant allele among Black population. Despite the recent development of a real-time fluorescent polymerase chain reaction (PCR) method for FY genotyping FY*X genotyping has not been described by this method. This study focused on the real-time FY*X genotyping development associated with a complete, one-step real-time FY genotyping, based on fluorescence resonance energy transfer (FRET) technology.

MATERIALS AND METHODS

Seventy-two blood samples from Fy(a+b-) Caucasian blood donors were studied by real-time PCR only. Forty-seven Caucasian and Black individual blood samples, referred to our laboratory, were studied by PCR-RFLP and real-time PCR. For each individual, the result of the genotype was compared to the known phenotype.

RESULTS

The FY*X allele frequency calculated in an Fy(a+b-) Caucasian blood donors population was 0.014. With the Caucasian and Black patient samples we found a complete correlation between PCR-RFLP and the real-time PCR method whatever the alleles combination tested. When the known phenotype was not correlated to FY*X genotype, the presence of the Fy(b) antigen was always confirmed by adsorption-elution.

CONCLUSION

The real-time technology method is rapid and accurate for FY genotyping. From now, we are able to detect the FY*X allele in all the alleles combinations studied. Regarding its significant frequency, the detection of the FY*X allele is useful for the correct typing of blood donors and recipients considering the therapeutic use of blood units and the preparation of test red blood cells for antibody screening.

A clue to the basis of allelic enhancement: occurrence of the Ax subgroup in the offspring of blood group O parents

Apparent deviation from Mendelian rules of blood group inheritance is rarely observed. Blood group O parents with children expressing weak A subgroups have occasionally been described but not explained. A detailed serological investigation of such a family is described here. The ABO locus was analysed by PCR-ASP/restriction fragment length polymorphism genotyping and DNA sequencing. The propositus' RBCs were very weakly agglutinated with monoclonal anti-A but distinctly with polyclonal anti-A,B, i.e. typical for Ax. Serum anti-A1 (titre 4) and -B were present. Her parents' blood groups were both clearly O, with titres of serum anti-A1, and -A at 16 and 4, respectively. Adsorption/ elution studies demonstrated A antigen on the daughter's cells only. The ABO genotypes were: mother, AxO1; father, O1vO2; and propositus, AxO2. The Ax allele was an A1-O1v hybrid allele with a crossing-over breakpoint between positions 235 and 446 in intron 6 (Ax-4). Compared to the A1 glycosyltransferase, this allele predicts a protein with two amino acid substitutions (Phe216Ile and Met277Val) known to yield either weakly expressed or no A antigen on RBCs. This study suggests that the nature of the ABO allele in trans can influence A antigen expression, a phenomenon previously described as allelic enhancement (or reinforcement). Potential mechanisms for this are discussed.

The Abantu phenotype in the ABO blood group system is due to a splice-site mutation in a hybrid between a new O1-like allelic lineage and the A2 allele

BACKGROUND AND OBJECTIVES

Many phenotypic variations in the expression of blood group A have been explained by variations in gene structure, but unresolved samples are frequently encountered in the reference laboratory. Among ABO subgroups, A(bantu) has the highest frequency in a specified population. The molecular basis of this phenotype is now described.

MATERIALS AND METHODS

Blood from Black donors phenotyped as A(bantu) was subjected to genomic ABO screening and direct sequencing of polymerase chain reaction (PCR)-amplified ABO exons 1-7 and introns 2-6. Total RNA was extracted and ABO cDNA was synthesized by reverse transcription (RT)-PCR. Control material comprised Black South African, Swedish, Jordanian and Brazilian blood samples with common phenotypes.

RESULTS

Genomic ABO typing indicated the presence of an A(2) allele in each A(bantu) donor, in combination with an O allele. No previously reported mutations associated with weak A or B expression were found. Direct sequencing indicated the common A(2) sequence with a single nucleotide deletion (AGGT>AGT) at the exon 4/intron 4 junction, predicted either to disrupt the reading frame (resulting in a premature stop codon) or to cause erroneous splicing (resulting in the exclusion of exon 4 from the mRNA). O mRNA, but no transcripts from the A(bantu) allele, could be detected. Surprisingly, the splice-site mutation was also found in approximately 5% of O alleles in Black South Africans, but not in other blood donors, or in non-O(1) alleles. Utilizing intron polymorphisms, the A(bantu) allele was shown to be a recombination between a new allelic lineage (O(1bantu)) and A(2), with a cross-over region near exon 5.

CONCLUSION

The A(bantu) phenotype is caused by an O(1bantu)-A(2) hybrid at the ABO locus.

Blood group genotype analysis for the quality improvement of reagent test red blood cells

BACKGROUND AND OBJECTIVES

Reagent red blood cells (RBCs) for antibody detection should express certain important antigens as a double dose, that is, the donors must be homozygous for the corresponding alleles. Traditionally, dose is determined by serological typing and known allele frequencies. However, RHD zygosity cannot be predicted serologically owing to the absence of an antithetical antigen, and FY zygosity is confounded by two variant haplotypes, FY*0 and FY*X. Furthermore, lack of reagents hampers our ability to type for some clinically important antigen pairs such as Do(a)/Do(b).

MATERIALS AND METHODS

Genomic DNA was isolated from reagent RBC samples. Established, validated methods were used to determine the RHD, FY, and DO genotypes.

RESULTS

Three of 52 D+ samples gave results that differed from the predicted genotype: two presumed R(1)R(1) samples and an R(2)R(2) sample were shown to be R(1)r' and R(2)r'', respectively. Five of 59 samples that were from presumed homozygotes for either FY*A or FY*B were heterozygous, together with either FY*X (three samples) or FY*0 (two samples). Seventy-five samples tested for DO were DO*A/A (n = 14), DO*A/B (n = 39), or DO*B/B (n = 22).

CONCLUSIONS

The results show that serologically determined RhD and Duffy phenotypes of reagent RBCs are unreliable and that antigens we thought were represented as a double dose were single dose. The addition of Dombrock genotyping provides information which is useful in antibody identification. We conclude that selected genotype analyses are a valuable quality assurance measure to ensure that reagent RBCs comply with national and international recommendations for test sensitivity.

A novel FY allele in Brazilians

The GATA box single nucleotide polymorphism (SNP) at position -33 (T>C) in Blacks silences the expression of FY*B in erythrocytes, and the substitution 265 C>T, together with 298 G>A, weakens the Fy(b) antigen (Fy(x)). Individuals with these phenotypes/genotypes who receive Fy(b+) blood are unlikely to be alloimmunized to Fy(b) because, in the presence of 265 T, the Fy(b) antigen is expressed, and in the case of -33 C, other tissues express Duffy protein and probably the Fy(b) antigen. We studied samples from 361 blood donors (182 of African ancestry and 179 of Caucasian ancestry) by haemagglutination and polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP). Forty Caucasian and 130 donors of African ancestry were serologically Fy(b-); among these, the majority of the donors of African ancestry had FY*B with the GATA SNP, while the majority of Caucasians typing Fy(b-) had FY*B with 265 T/298 A SNPs. Six of the Fy(b-) donors (three Africans and three Caucasians) had both GATA and 265/298 SNPs, and six donors of Caucasian ancestry apparently had a GATA SNP. Samples from two donors - one African and one Caucasian with an unusual MspA1I-RFLP pattern - were sequenced and found to have a novel SNP (145 G>T) co-existent with 265 C>T and 298 G>A SNPs. These findings highlight the importance of establishing the incidence and nature of molecular events that impact on Duffy expression in different populations.

ABO exon and intron analysis in individuals with the AweakB phenotype reveals a novel O1v-A2 hybrid allele that causes four missense mutations in the A transferase

Background

Since the cloning in 1990 of cDNA corresponding to mRNA transcribed at the blood-group ABO locus, polymorphisms due to ethnic and/or phenotypic variations have been reported. Some subgroups have been explained at the molecular level, but unresolved samples are frequently encountered in the reference laboratory.

Results

ABO blood grouping discrepancies were investigated serologically and by ABO genotyping [duplex polymerase-chain-reaction (PCR) – restriction-fragment-length-polymorphism (RFLP) and PCR – allele-specific-primer (ASP) across intron 6] and DNA sequencing of the ABO gene and its proposed regulatory elements. Blood samples from five individuals living in Portugal, Switzerland, Sweden and the USA were analysed. These individuals were confirmed to be of Black ethnic origin and had the unusual A_weakB phenotype but appeared to have the A²B genotype without previously reported mutations associated with weak A or B expression. Sequencing of this A allele (having 467C>T and 1061delC associated with the common A² [A201] allele) revealed three mutations regularly encountered in the O^1v [O02] allele: 106C>T (Val36Phe), 188G>A (Arg63His), 220C>T (Pro74Ser) in exons 3, 4 and 5, respectively. The additional presence of 46G>A (Ala16Thr) was noted, whilst 189C>T that normally accompanies 188G>A in O^1v was missing, as were all O^1v-related mutations in exons 6 and 7 (261delG, 297A>G, 646T>A, 681G>A, 771C>T and 829G>A). On screening other samples, 46G>A was absent, but two new O alleles were found, a Jordanian O¹ and an African O^1v allele having 188G>A but lacking 189C>T. Sequencing of introns 2, 3, 4 and 5 in common alleles (A¹ [A101], A², B [B101], O¹, O^1vand O² [O03]) revealed 7, 12, 17 and 8 polymorphic positions, respectively, suggesting that alleles could be defined by intronic sequences. These polymorphic sites allowed definition of a breakpoint in intron 5 where the O^1v-related sequence was fused with A² to form the new hybrid. Intron 6 has previously been sequenced. Four new mutations were detected in the hybrid allele and these were subsequently also found in intron 6 of A² alleles in other Black African samples.

Conclusions

A novel O^1v-A² hybrid was defined by ABO exon/intron analysis in five unrelated individuals of African descent with the A_weakB blood group phenotype.

Extended blood grouping of blood donors with automatable PCR-ELISA genotyping

BACKGROUND

In the past 10 years, PCR-based methods have been described to allow the detection of gene polymorphisms responsible for many blood group antigens. These methods are routinely used to test samples of fetal origin and to resolve serologic discrepancies. Another interesting application of blood group genotyping could be the extended typing of blood donors for minor antigens to facilitate the procurement of compatible blood for alloimmunized patients.

STUDY DESIGN AND METHODS

PCR-based tests have been modified to allow multiplex amplification of specific fragments of blood group genes and the convenient detection of hybridized amplicons by ELISA in a microplate format.

RESULTS

The results obtained show that fragments of the Rh (D, c, C, e, E), Kell (K, k), Duffy (Fya, Fyb), and Kidd (Jka, Jkb) genes could be amplified along with controls in multiplex PCR reactions. Labeling of amplicons with digoxigenin allowed their solid-phase detection in microplate wells previously coated with individual blood group-specific oligonucleotides. A comparative study performed with 100 individuals showed a 99.7 percent concordance between genotypes and phenotypes for the 11 antigens assayed, with only three discrepant Fyb genotypes.

CONCLUSION

Extended genotyping could be performed once on regular donors and confirmed when needed by standard serologic RBC assays. The format of these tests will allow easy automation of the procedure including the interpretation and downloading of the results with existing ELISA software.

Duffy blood group genotyping in French Basques using polymerase chain reaction with allele-specific primers (PCR-ASP)

Blood group antigens such as Duffy represent interesting models for population genetics studies. The distribution of the Duffy blood group was determined using PCR in a sample of Basque (n = 126) and non-Basque (n = 110) patients from the general hospital of the French Basque Country. The frequency of FY*A allele was significantly lower among autochthonous French Basques (P < 0.001). This result, obtained for the first time by PCR analysis in this population, was within the range of previous historical studies in various Basque subpopulations using traditional hemagglutination methods. When compared with European data, our Basque sample demonstrated the lowest FY*A/FY*B ratio, this fact confirming hemotypology data published before the molecular biology era. Our results with FY*X were quite similar to those reported in European populations.