Prenatal genotyping of the Duffy blood group system by allele-specific polymerase chain reaction

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.

A novel FY*A allele with the 265T and 298A SNPs formerly associated exclusively with the FY*B allele and weak Fy(b) antigen expression: implication for genotyping interpretative algorithms

BACKGROUND AND OBJECTIVES

An Australian Caucasian blood donor consistently presented a serology profile for the Duffy blood group as Fy(a+b+) with Fy(a) antigen expression weaker than other examples of Fy(a+b+) red cells. Molecular typing studies were performed to investigate the reason for the observed serology profile.

MATERIAL AND METHODS

Blood group genotyping was performed using a commercial SNP microarray platform. Sanger sequencing was performed using primer sets to amplify across exons 1 and 2 of the FY gene and using allele-specific primers.

RESULTS

The propositus was genotyped as FY*A/B, FY*X heterozygote that predicted the Fy(a+b+(w) ) phenotype. Sequencing identified the 265T and 298A variants on the FY*A allele. This link between FY*A allele and 265T was confirmed by allele-specific PCR.

CONCLUSION

The reduced Fy(a) antigen reactivity is attributed to a FY*A allele-carrying 265T and 298A variants previously defined in combination only with the FY*B allele and associated with weak Fy(b) antigen expression. This novel allele should be considered in genotyping interpretative algorithms for generating a predicted phenotype.

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.

Fetal anemia due to non-Rhesus-D red-cell alloimmunization

Although anti-RhD was once the major etiology of hemolytic disease of the fetus/newborn (HDFN), the widespread adoption of antenatal and postpartum Rhesus immune globulin has resulted in a marked decrease in the prevalence of alloimmunization to the RhD antigen in pregnancy. Maternal alloimmunization to other red cell antigens continues to play a role as the cause of fetal disease since no prophylactic immune globulins are available to prevent the formation of these antibodies. An increasing incidence of the Kell (anti-K1) antibody has been noted in the United States. Guidelines for intervention in cases of irregular red cell antibodies are limited by the bias of anecdotal reports in the literature in favor of severe cases of HFDN. Although most diagnostic protocols used in the management of the RhD-alloimmunized pregnancy can be applied in cases of non-RhD sensitization, Kell (K1 and K2) alloimmunization should be managed more conservatively.

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.

Red Blood Cell Alloimmunization in Pregnancy

Red blood cell (RBC) alloimmunization in pregnancy continues to occur despite the widespread use of both antenatal and postpartum Rhesus immune globulin (RhIG), due mainly to inadvertent omissions in administration as well as antenatal sensitization prior to RhIG given at 28 weeks' gestation. Additional instances are attributable to the lack of immune globulins to other RBC antigens. Evaluation of the alloimmunized pregnancy begins with the maternal titer. Once a critical value [32 for anti-Rh(D) and other irregular antibodies; 8 for anti-K and -k] is reached, fetal surveillance using serial Doppler ultrasound measurements of the peak velocity in the fetal middle cerebral artery (MCA) is standard. In the case of a heterozygous paternal phenotype, amniocentesis can be performed to detect the antigen-negative fetus that requires no further evaluation. MCA velocities greater than 1.5 multiples of the median necessitate cordocentesis, and if fetal anemia is detected, intrauterine transfusion therapy is initiated. A perinatal survival of greater than 85% with normal neurologic outcome is now expected. Future therapies will target specific immune manipulations in the pregnant patient.

Amniotic fluid: not just fetal urine anymore

Amniotic fluid (AF) is a complex substance essential to fetal well-being. This article reviews recent discoveries and the current understanding of the origin and circulation of AF and its nutritive, protective, and diagnostic functions. Future directions for AF research are also discussed.

Detection of genomic polymorphisms associated with venous thrombosis using the invader biplex assay

A multi-site study to assess the accuracy and performance of the biplex Invader assay for genotyping five polymorphisms implicated in venous thrombosis was carried out in seven laboratories. Genotyping results obtained using the Invader biplex assay were compared to those obtained from a reference method, either allele-specific polymerase chain reaction (AS-PCR), restriction fragment length polymorphism (PCR-RFLP) or PCR-mass spectrometry. Results were compared for five loci associated with venous thrombosis: Factor V Leiden, Factor II (prothrombin) G20210A, methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C, and plasminogen activator inhibitor (PAI-1) 4G/5G. Of a total of 1448 genotypes tested in this study, there were 22 samples that gave different results between the Invader biplex assay and the PCR-based methods. On further testing, 21 were determined to be correctly genotyped by the Invader Assay and only a single discrepancy was resolved in favor of the PCR-based assays. The compiled results demonstrate that the Invader biplex assay provides results more than 99.9% concordant with standard PCR-based techniques and is a rapid and highly accurate alternative to target amplification-based methods.

Duffy antigen receptor and genetic susceptibility of African Americans to acute rejection and delayed function

BACKGROUND

The unique distribution of the alleles for the Duffy antigen receptor complex (DARC) that binds to chemokines may be associated with the rates of acute rejection and delayed allograft function (DGF) among African Americans.

METHODS

A prospective, multicenter cohort study enrolled 222 African American recipients of cadaveric renal allografts from eight adult transplant centers. Subjects were typed by allele-specific polymerase chain reaction (ASPCR) for the polymorphism at position 535 that determines the level of transcription. Associations of DARC genotypes were examined in Cox hazards models with episodes of acute rejection and in logistic regression models with the development of DGF.

RESULTS

FyB Null homozygosity was observed among 67% of the recipients. Fifteen percent of the study cohort experienced at least one episode of acute rejection, and the incidence of DGF was 42.5%. The number of FyB Null alleles and FyB Null homozygosity had no detectable association with the rate of acute rejection (P > 0.50) or with the development of DGF (P > 0.50).

CONCLUSION

The susceptibility of African American recipients to acute rejection and to DGF was not confirmed to be associated with DARC alleles or genotype. Future studies should exclude a potential role of donor-related DARC in transplant outcomes.

Rh genotyping: avoiding false-negative and false-positive results among individuals of African ancestry

High homology, variant alleles, and silent alleles have made the development of completely reliable genotyping assays for the RHD and RHC alleles difficult. An RHD pseudogene (RHDPsi) possessing a 37-bp insertion within exon 4 is common among serologically RhD-negative individuals of African descent and generates false-positive results in previously reported RhD genotyping assays. Genotyping RhC is problematic due to exon 2 homology between RHD and RHC; however, an RHC-specific 109-bp insertion within intron 2 has been reported useful for genotyping. Primers flanking the exon 4 insertion point were used for detection of RHD and RHDPsi among a total of 231 serotyped individuals: 134 African American, 85 Caucasian, and 12 RhD serotype-negative/genotype-positive, D-sensitized women. Primers flanking the RHC-specific intron 2 insertion were used to genotype 282 serotyped individuals (128 African American, 154 Caucasian) and were compared to RHC genotyping using the exon 1 RhC-specific nt48 cytosine polymorphism. Complete correlation was observed between genotyping with the RHDPsi primer pair and serotyping among 219 individuals and 10/12 previous RHD false-positive genotyping results were resolved. RHDPsi was detected in 19% (n = 4/21) of RhD seronegative African Americans and 4.4% (n = 5/113) of RhD seropositive African Americans. When using the 109-bp intron 2 insertion for genotyping of RHC, a 23.9% (n = 11/46) false-negative rate was observed among African American RhCc serotyped heterozygotes. Utilization of the exon 1 nt48 cytosine for indirect genotyping of RHC yielded a 7.2% (n = 4/55) and 56.3% (n = 45/80) false-positive rate among Rhcc Caucasians and African Americans, respectively. We conclude that these additional reactions, though not sufficient alone, can be useful supplements to existing Rh genotyping assays.

Non-anti-D antibodies in red-cell alloimmunization

OBJECTIVE

Review the fetal/neonatal outcome and management of pregnancies associated with alloimmunization to irregular anti-red-cell antibodies.

STUDY DESIGN

Computerized MEDLINE search using keywords that included hemolytic disease of the newborn (HDN) and the specific family of anti-red-cell antibody, such as anti-Kell antibody.

RESULTS

A review of the prevalence of antibodies associated with HDN in reproductive age women revealed a marked decrease in the incidence of anti-RhD. An increasing incidence of anti-K1 antibody has been noted in the US, a trend not seen in other countries. Guidelines for intervention in cases of irregular antibodies are limited by the bias of anecdotal reports in the literature in favor of severe cases of HDN.

CONCLUSIONS

In cases of Kell, M, Duffy and Kidd alloimmunization, DNA techniques using amniotic fluid can be used to exclude antigen-negative fetuses. Kell (K1 and K2) alloimmunization should be managed somewhat differently from RhD due to the unique ability of these antibodies to suppress the fetal erythropoietic response.

Genotyping of Factor V G1691A (Leiden) without the Use of PCR by Invasive Cleavage of Oligonucleotide Probes

Background: The factor V G1691A Leiden (FVL) mutation is the most common known hereditary risk factor for venous thrombosis.

Methods: Third Wave Technologies, Inc. (Madison, WI) has developed a new microtiter plate-based assay that does not require PCR, restriction digestion, or gel electrophoresis. This technology system, termed the InvaderTM assay, utilizes a 5′ “invading” oligonucleotide and a partially overlapping 3′ “signal” oligonucleotide, which together form a specific structure when bound to a complementary genomic DNA template. A thermostable flap endonuclease cleaves this structure, releasing the 5′ flap from the signal oligonucleotide. Increased temperature and an excess of the signal probe enable multiple probes to be cleaved for each target sequence present without temperature cycling. The cleaved probes then direct cleavage of a secondary probe, which is 5′ end-labeled with fluorescein but is quenched by an internal dye. Upon cleavage, the fluorescein-labeled product is detected using a standard fluorescence plate reader. Genotypes are determined by net wild-type/mutant signal ratio.

Results: Complete concordance was observed, after resolution of four discordances, when 1369 individuals (1264 wild type, 102 heterozygous, 3 homozygous) were FVL genotyped by both the Invader assay and by allele-specific PCR.

Conclusion: We conclude that FVL genotyping using invasive cleavage of oligonucleotide probes is a rapid and reliable alternative to genotyping by more traditional PCR-based methods.

Amniocentesis and chorionic villus sampling

Invasive prenatal diagnosis continues to be the gold standard for pregnancies at increased risk of chromosomal aneuploidy or other genetic disease. Chorionic villus sampling is the procedure of choice for the first trimester. Early amniocentesis has been shown to carry increased risks of pregnancy loss, amniotic fluid leakage and talipes equinovarus. Mid-trimester amniocentesis continues to be the most common form of invasive prenatal diagnosis, with post-procedural loss rates of between 0.5 and 1%. This present review summarizes information on technique risks, looks at new technology applied to invasive prenatal diagnosis testing, and reports on new diagnoses that could be made either by amniocentesis or chorionic villus sampling.