Early detection of RhD status in pregnancies at risk of hemolytic disease of the newborn

RHD Genotyping of Rh-Negative and Weak D Phenotype among Blood Donors in Southeast Iran

Background: The D antigen is a subset of Rh blood group antigens involved in the hemolytic disease of the newborn [HDFN] and hemolytic transfusion reaction [HTR]. The hybrid Rhesus box that was created after RH gene deletion, was known as a mechanism of the Rh-negative phenotype. Hybrid marker identification is used to confirm the deletion of the RHD gene and to determine zygosity. This study aims to detect this marker in Rh-negative and weak D phenotype blood donors of the southeast of Iran.

Materials and Methods: The molecular analysis of the hybrid Rhesus box was performed on the 200 Rh-negative blood donors in Sistan and Baluchestan province, southeast Iran. The presence of alleles responsible for the D variants was assessed by DNA sequencing in 26 weak D phenotype donors.

Results: Of the 200 Rh-negative blood samples, 198 samples were homozygous (99%), and two samples were heterozygous (1%). Heterozygous samples had RHD*01N.73 allele and the RHD*01N.18 allele. Of the 26 samples with weak D phenotype, 16 partial DLO (61%), 4 partial DBT1 (15.3%), 2 partial DV type 2 (7.7%), 1 weak D type 1, 1 weak D type 4.2.3, 1weak D type 105 and 1 RHD (S103P) (4%) were determined.

Conclusion: Since RHD gene deletion is the main mechanism of the Rh-negativity in Sistan and Baluchestan provinces, a hybrid Rhesus box marker can be used in resolving RhD typing discrepancies by RHD genotyping methods.

The Most Favourable Procedure for the Isolation of Cell-Free DNA from the Plasma of Iso-Immunized RHD-Negative Pregnant Women

BACKGROUND

The ability to achieve quality recovery of cell-free foetal DNA is important for making non-invasive prenatal diagnoses. In this study, we performed quantitative and qualitative analyses of isolated DNA from maternal plasma, using different DNA-isolation methods.

METHOD

DNA was isolated from 30 iso-immunized women via the QIAamp column-based method, using four different elution volumes and two conventionally based methods. Real-time polymerase chain-reaction quantification of RHD and β-globin genes was performed in order to determine foetal-specific sequences and total genome equivalents, respectively.

RESULTS

The column-based method at a 3 μl elution volume yielded the highest quality and quantity of total DNA (67.0±0.6 ng/μL). At a 3 μl elution volume, the β-globin and RHD-gene sequences were estimated to be the highest among all isolation procedures, with 2778.13±1.5 and 66.9±0.6 GEq/mL, respectively, and a 100% sensitivity for RHD-gene sequence detection. Among the two conventional manual methods, the boiling lysis method yielded a higher DNA concentration (53.8±0.8 ng/μL) and purity (1.73±0.05). In addition, the method's sensitivity for foetal-detection sequences was only 80%, whereas the salting-out method's sensitivity was just 70%.

CONCLUSIONS

This study confirms the theory that the QIAamp method is a specific and sensitive approach for purifying and quantifying plasma DNA, when used in the minimum elution volume.

Comparison of PCR methods for detecting fetal RhDin maternal plasma

BACKGROUND

Aim of this study was to establish the method yielding the highest sensitivity routinely used to determine fetal RhD type and gender from maternal cell-free plasma DNA in different periods of gestation.

METHODS

Plasma DNA concentrations were measured from 46 pregnant women in different gestational periods and tested for RhD using three different PCR methods on exon 7: Thermal Cycler, Taqman method on LightCycler, and melting curve analysis on LightCycler. In addition, fetal gender was determined by PCR. Cell-free plasma DNA was measured in 100 healthy volunteers as a reference group.

RESULTS

The mean value of cell-free plasma DNA in the reference group was 10.9 pg/microL mean, (standard deviation (SD): 3.66) in 50 healthy women and 12.7 pg/microL (SD: 8.2) in 50 healthy men. In the first trimester of pregnancy cell-free plasma DNA was 14.9 pg/microL mean, (SD: 4.2), in the second trimester 15.4 pg/microL mean, (SD: 4.96), and the maximum was achieved in the third trimester of pregnancy 15.6 pg/microl mean, (SD: 6.49). TaqMan probes had the same accuracy, when compared with Thermal Cycler technology (46 samples, 6 failures). Using real-time PCR with melting curve analysis 12 of 17 samples were correctly tested. Gender determination was correctly in 41 of 46 samples.

CONCLUSION

RhD determinations with TaqMan and Thermal Cycler technology are useful methods for fetal RhD prediction. To increase the accuracy of RhD determination it is necessary to test on other exons in addition.

Prenatal determination of the fetal RhD blood group by multiplex PCR: a 7-year Portuguese experience

OBJECTIVES

This is a retrospective study to evaluate the efficacy and accuracy of the multiplex polymerase chain reaction (PCR) amplification, for early detection of fetuses at risk for hemolytic disease, in the population living in Portugal, and to characterize the RhD-negative individuals at serologic and molecular level.

METHODS

2030 uncultured amniotic fluid samples and 2012 blood samples from the respective RhD-negative pregnant women were studied by multiplex PCR of intron 3/intron 4, exon 7 and 3'UTR. Amniocentesis was performed for a variety of medical indications. For quality control, serologic RhD blood groups were determined in the cord blood, after birth.

RESULTS

1361 fetal amniotic samples were RhD-positive (67%), 669 were RhD-negative. The average time for diagnosis was 2 days for uncultured amniocytes and the molecular versus serologic RhD typing (n = 809) had 99.5% concordance. Among the 2012 serologic RhD-negative mothers, 26 had an RhD-positive allele.

CONCLUSION

The multiplex PCR amplification used in this study was a rapid and accurate method to determine the RhD blood type in the population living in Portugal, being a great tool for management of pregnancies with fetuses at risk for alloimmune hemolytic disease. In this population, 1.3% of the serologic RhD-negative women have an RHD-positive allele.

Non-invasive fetal RHD exon 7 and exon 10 genotyping using real-time PCR testing of fetal DNA in maternal plasma

OBJECTIVE

In this prospective study, we assessed the feasibility of foetal RHD genotyping by analysis of DNA extracted from plasma samples of Rhesus (Rh) D-negative pregnant women using real-time PCR and primers and probes targeted toward exon 7 and 10 of RHD gene.

METHODS

We analysed 24 RhD-negative pregnant woman and 4 patients with weak D phenotypes at a gestational age ranging from 11th to 38th week of gestation and correlated the results with serological analysis of cord blood after the delivery.

RESULTS

Non-invasive prenatal foetal RHD exon 7 genotyping analyses of maternal plasma samples was in complete concordance with the serological analysis of cord blood in all 24 RhD-negative pregnant women delivering 12 RhD-positive and 12 RhD-negative newborns. RHD exon-10-specific PCR amplicons were not detected in 2 out of 12 studied plasma samples from women bearing RhD-positive foetus, despite the positive amplification in RHD exon 7 region observed in all cases. In 1 case red cell serology of cord blood revealed that the mother had D-C-E-c+e+ C(w)- and the infant D+C-E-c+e+ C(w)+ phenotypes. RhD exon 10 real-time PCR analysis of cord blood was also negative. These findings may reflect that DC(w)- paternally inherited haplotype probably possesses no RHD exon 10. In another case no cord blood sample has been available for additional studies. The specificity of both RHD exon 7 and 10 systems approached 100% since no RhD-positive signals were detected in women currently pregnant with RhD-negative foetus (n = 8). Using real-time PCR and DNA isolated from maternal plasma, we easily differentiated pregnant woman whose RBCs had a weak D phenotype (n = 4) from truly RhD-negative patients since the threshold cycle (C(T)) for RHD exon 10 or 7 amplicons reached nearly the same value like C(T) for control beta-globin gene amplicons detecting the total DNA present in maternal plasma. However in these cases foetal RhD status cannot be determined.

CONCLUSION

Prediction offoetal RhD status from maternal plasma is highly accurate and enables implementation into clinical routine. We suggest that safe non-invasive prenatal foetal RHD genotyping using maternal plasma should involve the amplification of at least two RHD-specific products.

Non-invasive fetal RHD and RHCE genotyping using real-time PCR testing of maternal plasma in RhD-negative pregnancies

We assessed the feasibility of fetal RHD and RHCE genotyping by analysis of DNA extracted from plasma samples of RhD-negative pregnant women using real-time PCR and primers and probes targeted toward RHD and RHCE genes. We analyzed 45 pregnant women in the 11th to 40th weeks of pregnancy and correlated the results with serological analysis of cord blood after delivery. Non-invasive prenatal fetal RHD exon 7, RHD exon 10, RHCE exon 2 (C allele), and RHCE exon 5 (E allele) genotyping analysis of maternal plasma samples was correctly performed in 45 out of 45 RhD-negative pregnant women delivering 24 RhD-, 17 RhC-, and 7 RhE-positive newborns. Detection of fetal RHD and the C and E alleles of RHCE gene from maternal plasma is highly accurate and enables implementation into clinical routine. We recommend performing fetal RHD and RHCE genotyping together with fetal sex determination in alloimmunized D-negative pregnancies at risk of hemolytic disease of the newborn. In case of D-negative fetus, amplification of another paternally inherited allele (SRY and/or RhC and/or RhE positivity) proves the presence of fetal DNA in maternal circulation.

Prevention and management of RhD isoimmunization

An Rh-negative woman is at risk for developing Rh isoimmunization upon exposure to RhD antigens from her Rh-positive baby through fetal-maternal hemorrhage. The incidence of Rh isoimmunization and fetal hemolytic disease has decreased substantially since Rh immune globulin was introduced in 1968. When RhD sensitization does occur, careful follow-up of these mothers and judicious intervention can result in good outcomes for most pregnancies. Both Doppler assessment of middle cerebral artery peak systolic velocity and spectral analysis of amniotic fluid at 450 nm (DeltaOD 450) are useful in the diagnosis and management of fetal anemia.