RHD Genotyping from Maternal Plasma: Guidelines and Technical Challenges

Prevalence and determinants of RH alloimmunization in Rh-negative women in teaching hospitals of Addis Ababa, Ethiopia: a hospital-based cross-sectional study

Background

Despite the implementation of immunization with an anti-D antigen for pregnant women, adverse pregnancy outcomes continue to occur in Ethiopia and most Sub-Saharan African countries. Consequently, the woman's obstetric care is compromised, and there is an increase in perinatal morbidity and mortality. In Ethiopia, the burden of the disease is not well understood, and no research has been conducted in the study area. Therefore, this study aims to determine the prevalence and determinants of Rh alloimmunization in Rh-negative women receiving care at Addis Ababa teaching hospitals.

Methods

An institutional-based cross-sectional study was conducted from 5 October 2020 to 5 May 2021, among 328 Rh-negative pregnant women who received antenatal care and delivery services at Teaching Hospitals under Addis Ababa University. Face-to-face interviews were used to gather data using a pre-tested structured questionnaire, and a chart review was performed using a checklist. The data were entered into Epidata version 3.1 and analyzed using SPSS version 22. Multivariable analysis and logistic regression were used to evaluate the predictors, and the results were presented as an adjusted odds ratio (AOR) with a 95% confidence interval. Statistical significance was declared at a p-value < 0.05.

Results

Among Rh-D negative individuals, 56(17.1%) were alloimunized with 95% CI (15.1%, 19.23%). The prevalence of Rh-D negative was 2.1% with 95% CI (1.56%, 2.76%). Factors such as unemployment [AOR = 2.28, 95% CI: 1.21, 4.28], failure to use anti-D prophylaxis in previous pregnancy [AOR = 2.08, 95% CI: 1.10, 3.92), and the presence of sensitizing events [AOR = 0.52, 95% CI: 0.27, 0.84] were statistically significant with the outcome variables.

Conclusions

This study pointed out that the prevalence of Rh was relatively large and that almost one in every five pregnant women was alloimunized. Factors such as unemployment and failure to use anti-D prophylaxis in a previous pregnancy were found to be associated with outcome variables. Therefore, all stakeholders and concerned entities should prioritize enhancing access and affordability to anti-D prophylaxis to prevent the occurrence of Rh alloimmunization and its associated adverse outcomes.

Non-invasive prenatal diagnosis of single gene disorders by paternal mutation exclusion: 3 years of clinical experience

OBJECTIVES

Cell-free fetal DNA (cffDNA) analysis is performed routinely for aneuploidy screening, RhD genotyping or sex determination. Although applications to single gene disorders (SGD) are being rapidly developed worldwide, only a few laboratories offer cffDNA testing routinely as a diagnosis service for this indication. In a previous report, we described a standardised protocol for non-invasive exclusion of paternal variant in SGD. Three years later, we now report our clinical experience with the protocol.

DESIGN

Descriptive study.

SETTING

Multi-centre French.

POPULATION

Indications for referral included pregnancies at risk of 25% or 50% of paternally inherited SGD, and pregnancies associated with an increased risk of SGD due to a de novo variant, either from strongly suggestive ultrasound findings or from a possible parental germinal mosaicism in the context of a previously affected child.

METHODS

Non-invasive prenatal diagnosis was performed using custom assays for droplet digital PCR. Feasibility, diagnostic performance and turn-around time were evaluated.

RESULTS

Mean time for a new assay design and validation was evaluated at 14 days, and mean result reporting time was 6 days. All referred pathogenic variants could be targeted except one located in a complex genomic region. A result was obtained for every 198 referrals except two.

CONCLUSION

This service was successfully implemented as a routine laboratory practice. It has been widely adopted by French clinicians and patients for paternal variant exclusion in various disorders.

Fetal Rhesus D Genotyping and Sex Determination from Maternal Plasma of Rhesus D-Negative Antenatal Population: The Usefulness of Conventional Polymerase Chain Reaction in Resource-limited Settings

Background

This prospective cohort study evaluated the usefulness of conventional PCR in genotyping fetal Rhesus D (RhD) and sex from the maternal plasma of RhD-negative (RhD−) antenatal population in resource-limited settings.

Methods

Thirty apparently healthy RhD− pregnant women with RhD positive (RhD+) partners were included. Blood samples were collected from each participant (in the third trimester of pregnancy) for DNA extraction/purification and fetal RhD genotyping.

Results

Out of the 30 samples, 26 (86.7%) were found to be RhD+ while 4 (13.3%) were RhD−. The RhD+ comprised 24 (80.0%) RhD+ based on exons 5, 7, and 10 combined. Exons 5 and 7 were detected in two additional samples but not exon 10. Serological phenotyping of neonatal blood confirmed 26 RhD+ and 4 RhD−. There was a perfect agreement between the fetal RhD genotype and neonatal RhD phenotyping after delivery for exons 5 and 7 (concordance = 100%, κ = 100.0%, diagnostic accuracy = 100%, p < 0.0001) while exon 10 presented with an almost perfect agreement (concordance = 93.3%, κ = 76.2%, diagnostic accuracy = 93.3%, p < 0.0001). Regarding the prenatal test for the SRY gene, 9 (30.0%) were predicted to be males and the remaining 21 (60.0%) were females. All the 9 and 21 anticipated males and females, respectively, were confirmed after delivery (concordance = 100%, κ = 100.0%, diagnostic accuracy = 100%).

Conclusion

Our study suggests that conventional PCR using the SRY, RhD exons 5 and 7 could be useful for predicting fetal sex and RhD from maternal peripheral blood in resource-limited settings.

Considerations for whole exome sequencing unique to prenatal care

Whole exome sequencing (WES) is increasingly being used in the prenatal setting. The emerging data support the clinical utility of prenatal WES based on its diagnostic yield, which can be as high as 80% for certain ultrasound findings. However, detailed practice and laboratory guidelines, addressing the indications for prenatal WES and the surrounding technical, interpretation, ethical, and counseling issues, are still lacking. Herein, we review the literature and summarize the most recent findings and applications of prenatal WES. This review offers specialists and clinical genetic laboratorians a body of evidence and expert opinions that can serve as a resource to assist in their practice. Finally, we highlight the emerging technologies that promise a future of prenatal WES without the risks associated with invasive testing.

Prenatal non-invasive foetal RHD genotyping: diagnostic accuracy of a test as a guide for appropriate administration of antenatal anti-D immunoprophylaxis

BACKGROUND

Foetal RHD genotyping can be predicted by real-time polymerase chain reaction (qPCR) using cell-free foetal DNA extracted from maternal plasma. The object of this study was to determine the diagnostic accuracy and feasibility of non-invasive RHD foetal genotyping, using a commercial multiple-exon assay, as a guide to appropriate administration of targeted antenatal immunoprophylaxis.

MATERIAL AND METHODS

Cell-free foetal DNA was extracted from plasma of RhD-negative women between 11-30 weeks of pregnancy. The foetal RHD genotype was determined non-invasively by qPCR amplification of exons 5, 7 and 10 of the RHD gene using the Free DNA Fetal Kit^® RhD. Results were compared with serological RhD cord blood typing at birth. The analysis of diagnostic accuracy was restricted to the period (24-28⁺⁶ weeks) during which foetal genotyping is usually performed for targeted antenatal immunoprophylaxis.

RESULTS

RHD foetal genotyping was performed on 367 plasma samples (24-28⁺⁶ weeks). Neonatal RhD phenotype results were available for 284 pregnancies. Foetal RHD status was inconclusive in 9/284 (3.2%) samples, including four cases with RhD maternal variants. Two false-positive results were registered. The sensitivity was 100% and the specificity was 97.5% (95% CI: 94.0-100). The diagnostic accuracy was 99.3% (95% CI: 98.3-100), decreasing to 96.1% (95% CI: 93.9-98.4) when the inconclusive results were included. The negative and positive predictive values were 100% (95% CI: 100-100) and 99.0% (95% CI: 97.6-100), respectively. There was one false-negative result in a sample collected at 18 weeks. After inclusion of samples at early gestational age (<23⁺⁶ week), sensitivity and accuracy were 99.6% (95% CI: 98.7-100) and 95.5% (95% CI: 93.3-97.8), respectively.

DISCUSSION

This study demonstrates that foetal RHD detection on maternal plasma using a commercial multiple-exon assay is a reliable and accurate tool to predict foetal RhD phenotype. It can be a safe guide for the appropriate administration of targeted prenatal immunoprophylaxis.

Emerging strategies of blood group genotyping for patients with hemoglobinopathies

Red cell alloimmunization is a serious problem in chronically transfused patients. A number of high-throughput DNA assays have been developed to extend or replace traditional serologic antigen typing. DNA-based typing methods may be easily automated and multiplexed, and provide reliable information on a patient. Molecular genotyping promises to become cheaper, being not dependent on serologic immunoglobulin reagents. Patients with hemoglobinopathies could benefit from receiving extended genomic typing. This could limit post transfusional complications depending on subtle antigenic differences between donors and patients. Patient/donor compatibility extended beyond the phenotype Rh/Kell may allows improved survival of transfused units of red blood cells (RBC) and lead to reduced need for blood transfusion and leading to less iron overload and reduced risk of alloimmunization. Here we discuss the advantages and limitations of current techniques, that detect only predefined genetic variants. In contrast, target enrichment next-generation sequencing (NGS) has been used to detect both known and de novo genetic polymorphisms, including single-nucleotide polymorphisms, indels (insertions/deletions), and structural variations. NGS approaches can be used to develop an extended blood group genotyping assay system.

Hemolytic disease of the fetus and newborn in the molecular era

Maternal-fetal red cell antigen incompatibility can lead to alloimmunization, maternal immunoglobulin transplacental transfer, and hemolytic disease of the fetus and newborn (HDFN). The use of routine antenatal anti-D prophylaxis (RAADP) has sharply decreased the incidence of and mortality from HDFN due to RhD allosensitization. The ability to identify pregnancies/fetuses at risk of HDFN has significantly improved due to paternal molecular RHD zygosity testing, and non-invasive fetal molecular diagnostics for detecting putative antigen(s) (notably RhD) in fetuses utilizing cff-DNA in maternal plasma. Fetal RHD genotyping using cff-DNA has become increasingly accurate for fetal RHD detection, prompting some countries to implement targeted RAADP through mass screening programs of RhD-negative pregnant women. Along with middle cerebral artery Doppler ultrasonography for predicting fetal anemia, non-invasive fetal molecular diagnostics have greatly decreased the need for invasive diagnostic procedures in pregnancies at risk for severe HDFN. This review highlights these molecular advancements in HDFN-related prenatal diagnostics.

Newborn screening and the era of medical genomics

Across the span of the last 75+ years, technological and conceptual advances in genetics have found rapid implementation at the beginning of human life. From karyotype testing, to molecular cytogenetics, to gene panel testing, and now to whole exome and whole genome sequencing, each iterative expansion of our capability to acquire genetic data on the next generation has been implemented quickly in the clinical setting. In tandem, our continuously expanding ability to acquire large volumes of genetic data has generated its own challenges in terms of interpretation, clinical utility of the information, and concerns over privacy and discrimination; for the first time, we are faced with the possibility of having complete access to our genetic data from birth, if not shortly after conception. Here, we discuss the evolution of the field toward this new reality and we consider the potentially far-reaching consequences and, at present, an unclear path toward developing best practices for implementation.

Considerations of red blood cell molecular testing in transfusion medicine

The field of transfusion medicine is on the threshold of a paradigm shift, as the technology for genotyping of red blood cell antigens, including US FDA-approved arrays, is now moving into standard practice. Access to cost-efficient, high-resolution genotyping has the potential to increase the quality of care by decreasing the risk for alloimmunization and incompatible transfusions in individuals on long-term blood transfusion protocols, including patient groups with hemoglobinopathies and other chronic diseases. Current and future applications of molecular methods in transfusion medicine and blood banking are discussed, with emphasis on indications for genotyping in various clinical scenarios. Furthermore, limitations of the current gold standard methodology and serology, as well as of contemporary molecular methodology, are examined.

Fetal Sex and RHD Genotyping with Digital PCR Demonstrates Greater Sensitivity than Real-time PCR

BACKGROUND

Noninvasive genotyping of fetal RHD (Rh blood group, D antigen) can prevent the unnecessary administration of prophylactic anti-D to women carrying RHD-negative fetuses. We evaluated laboratory methods for such genotyping.

METHODS

Blood samples were collected in EDTA tubes and Streck® Cell-Free DNA™ blood collection tubes (Streck BCTs) from RHD-negative women (n = 46). Using Y-specific and RHD-specific targets, we investigated variation in the cell-free fetal DNA (cffDNA) fraction and determined the sensitivity achieved for optimal and suboptimal samples with a novel Droplet Digital™ PCR (ddPCR) platform compared with real-time quantitative PCR (qPCR).

RESULTS

The cffDNA fraction was significantly larger for samples collected in Streck BCTs compared with samples collected in EDTA tubes (P < 0.001). In samples expressing optimal cffDNA fractions (≥4%), both qPCR and digital PCR (dPCR) showed 100% sensitivity for the TSPY1 (testis-specific protein, Y-linked 1) and RHD7 (RHD exon 7) assays. Although dPCR also had 100% sensitivity for RHD5 (RHD exon 5), qPCR had reduced sensitivity (83%) for this target. For samples expressing suboptimal cffDNA fractions (<2%), dPCR achieved 100% sensitivity for all assays, whereas qPCR achieved 100% sensitivity only for the TSPY1 (multicopy target) assay.

CONCLUSIONS

qPCR was not found to be an effective tool for RHD genotyping in suboptimal samples (<2% cffDNA). However, when testing the same suboptimal samples on the same day by dPCR, 100% sensitivity was achieved for both fetal sex determination and RHD genotyping. Use of dPCR for identification of fetal specific markers can reduce the occurrence of false-negative and inconclusive results, particularly when samples express high levels of background maternal cell-free DNA.

Use of Copy Number Deletion Polymorphisms to Assess DNA Chimerism

BACKGROUND

We describe a novel approach that harnesses the ubiquity of copy number deletion polymorphisms in human genomes to definitively detect and quantify chimeric DNA in clinical samples. Unlike other molecular approaches to chimerism analysis, the copy number deletion (CND) method targets genomic loci (&gt;50 base pairs in length) that are wholly absent from wild-type (i.e., self) background DNA sequences in a sex-independent manner.

METHODS

Bespoke quantitative PCR (qPCR) CND assays were developed and validated using a series of DNA standards and chimeric plasma DNA samples collected from 2 allogeneic kidney transplant recipients and 12 pregnant women. Assay performance and informativeness were assessed using appropriate statistical methods.

RESULTS

The CND qPCR assays showed high sensitivity, precision, and reliability for linear quantification of DNA chimerism down to 16 genomic equivalents (i.e., 106 pg). Fetal fraction (%) in 12 singleton male pregnancies was calculated using the CND qPCR approach, which showed closer agreement with single-nucleotide polymorphism–based massively parallel sequencing than the SRY (sex determining region Y) (Y chromosome) qPCR assay. The latter consistently underestimated the fetal fraction relative to the other methods. We also were able to measure biological changes in plasma nonself DNA concentrations in 2 renal transplant recipients.

CONCLUSIONS

The CND qPCR technique is suitable for measurement of chimerism for monitoring of rejection in allogeneic organ transplantation and quantification of the cell-free fetal DNA fraction in maternal plasma samples used for noninvasive prenatal genetic testing.

Non-Invasive Prenatal Testing Using Cell Free DNA in Maternal Plasma: Recent Developments and Future Prospects

Recent advances in molecular genetic technologies have facilitated non-invasive prenatal testing (NIPT) through the analysis of cell-free fetal DNA in maternal plasma. NIPT can be used to identify monogenic disorders including the identification of autosomal recessive disorders where the maternally inherited mutation needs to be identified in the presence of an excess of maternal DNA that contains the same mutation. In the future, simultaneous screening for multiple monogenic disorders is anticipated. Several NIPT methods have been developed to screen for trisomy. These have been shown to be effective for fetal trisomy 21, 18 and 13. Although the testing has been extended to sex chromosome aneuploidy, robust estimates of the efficacy are not yet available and maternal mosaicism for gain or loss of an X-chromosome needs to be considered. Using methods based on the analysis of single nucleotide polymorphisms, diandric triploidy can be identified. NIPT is being developed to identify a number of microdeletion syndromes including α-globin gene deletion. NIPT is a profoundly important development in prenatal care that is substantially advancing the individual patient and public health benefits achieved through conventional prenatal screening and diagnosis.

Clinical applications of maternal plasma fetal DNA analysis: translating the fruits of 15 years of research

The collection of fetal genetic materials is required for the prenatal diagnosis of fetal genetic diseases. The conventional methods for sampling fetal genetic materials, such as amniocentesis and chorionic villus sampling, are invasive in nature and are associated with a risk of fetal miscarriage. For decades, scientists had been pursuing studies with goals to develop non-invasive methods for prenatal diagnosis. In 1997, the existence of fetal derived cell-free DNA molecules in plasma of pregnant women was first demonstrated. This finding provided a new source of fetal genetic material that could be obtained safely through the collection of a maternal blood sample and provided a new avenue for the development of non-invasive prenatal diagnostic tests. Now 15 years later, the diagnostic potential of circulating fetal DNA analysis has been realized. Fruitful research efforts have resulted in the clinical implementation of a number of non-invasive prenatal tests based on maternal plasma DNA analysis and included tests for fetal sex assessment, fetal rhesus D blood group genotyping and fetal chromosomal aneuploidy detection. Most recently, research groups have succeeded in decoding the entire fetal genome from maternal plasma DNA analysis which paved the way for the achievement of non-invasive prenatal diagnosis of many single gene diseases. A paradigm shift in the practice of prenatal diagnosis has begun.

Routine administration of Anti-D: the ethical case for offering pregnant women fetal RHD genotyping and a review of policy and practice

Background

Since its introduction in the 1960s Anti-D immunoglobulin (Anti-D Ig) has been highly successful in reducing the incidence of haemolytic disease of the fetus and newborn (HDFN) and achieving improvements to maternal and fetal health. It has protected women from other invasive interventions during pregnancy and prevented deaths and damage amongst newborns and is a technology which has been adopted worldwide. Currently about one third of pregnant women with the blood group Rhesus D (RhD) negative in the UK (approximately 40,000 women per year in England and Wales), receive antenatal Anti-D Ig in pregnancy when they do not require it because they are carrying a RhD negative fetus. Since 1997, a test using cell free fetal DNA (cffDNA) in maternal blood has been developed to identify the genotype of the fetus and can be used to predict the fetal RhD blood group.

Discussion

This paper considers whether it is ethically acceptable to continue administering antenatal Anti-D Ig to all RhD negative women when fetal RHD genotyping using maternal blood could identify those women who do not need this product.

Summary

The antenatal administration of Anti-D Ig to a third of RhD negative pregnant women who carry a RhD negative fetus and therefore do not need it raises important ethical issues. If fetal RHD genotyping using maternal blood was offered to all RhD negative pregnant women it would assist them to make an informed choice about whether or not to have antenatal Anti-D Ig.

Evaluation of sample stability and automated DNA extraction for fetal sex determination using cell-free fetal DNA in maternal plasma

OBJECTIVE

The detection of paternally inherited sequences in maternal plasma, such as the SRY gene for fetal sexing or RHD for fetal blood group genotyping, is becoming part of daily routine in diagnostic laboratories. Due to the low percentage of fetal DNA, it is crucial to ensure sample stability and the efficiency of DNA extraction. We evaluated blood stability at 4°C for at least 24 hours and automated DNA extraction, for fetal sex determination in maternal plasma.

METHODS

A total of 158 blood samples were collected, using EDTA-K tubes, from women in their 1st trimester of pregnancy. Samples were kept at 4°C for at least 24 hours before processing. An automated DNA extraction was evaluated, and its efficiency was compared with a standard manual procedure. The SRY marker was used to quantify cfDNA by real-time PCR.

RESULTS

Although lower cfDNA amounts were obtained by automated DNA extraction (mean 107,35 GE/mL versus 259,43 GE/mL), the SRY sequence was successfully detected in all 108 samples from pregnancies with male fetuses.

CONCLUSION

We successfully evaluated the suitability of standard blood tubes for the collection of maternal blood and assessed samples to be suitable for analysis at least 24 hours later. This would allow shipping to a central reference laboratory almost from anywhere in Europe.

Development and validation of multiplex real-time PCR assay for noninvasive prenatal assessment of fetal RhD status and fetal sex in maternal plasma

OBJECTIVE

Noninvasive prenatal detection of RhD status and fetal sex is becoming part of daily practice in clinical laboratories. We evaluated a high throughput procedure for automated DNA extraction and developed a multiplex real-time PCR (rt-PCR) for the simultaneous detection of three fetal loci in a single reaction to assess fetal sex and RhD status in maternal plasma.

METHODS

An automated DNA extraction method was evaluated together with a new multiplex rt-PCR assay for the simultaneous detection of exons 5 and 7 of the RHD gene together with the Y chromosome marker DYS14 in maternal plasma. The test was evaluated on 60 samples of known fetal genotype obtained from RhD-negative pregnant women before being applied prospectively on 158 consecutive clinical cases. Results were compared with newborn phenotypes.

RESULTS

Automated DNA extraction allowed successful analysis of all samples. DYS14 was detected in 118 cases (male fetuses) and both RHD exon 5 and 7 were detected in 148 samples. In 70 samples neither RHD exon 5 nor RHD exon 7 were detected (RhD-negative fetuses). Absence of all three sequences (female RhD-negative fetuses) was assessed in 33 samples. All prenatal results were in concordance with postnatal RhD status and fetal sex without false- positive or -negative results.

CONCLUSION

The automated DNA extraction procedure coupled with a novel multiplex rt-PCR assay proved accurate, efficient and reliable allowing rapid and high throughput noninvasive determination of fetal sex and RhD status in clinical samples.

Reliable Determination of Fetal RhD Status by RHD Genotyping from Maternal Plasma

BACKGROUND

Immunoprophylaxis with IgG anti-D is a standard prevention of hemolytic disease of the fetus and newborn. Fetal Rhesus D (RhD) blood group genotyping from maternal plasma of RhD-negative pregnant women allows targeted prophylaxis with IgG anti-D in RhD-positive pregnancies only. We set up a reliable protocol for prenatal RHD genotyping.

METHODS

153 pregnant Caucasian RhD-negative women were tested in the 27th week (range 7-38th week) of pregnancy. 18 of them were alloimmunized to the RhD antigen. The fetal RHD genotype was determined based on an automated DNA extraction and real-time polymerase chain reaction method. Intron 4 and exons 5, 7 and 10 of the RHD gene and the SRY gene were targeted.

RESULTS

The fetal RhD status and gender was 100% correctly predicted in all 153 pregnancies (55 RhD-positive males, 45 RhD-positive females; 23 RhD-negative males, 30 RhD-negative females).

CONCLUSION

The accuracy and applicability of our protocol for non-invasive fetal RhD determination allows the correct management of RhD-incompatible pregnancies. Our protocol could prevent unnecessary immunoprophylaxis in 53 of 153 cases. We therefore recommend that non-invasive fetal RHD genotyping is introduced as an obligatory part of prenatal screening.

Fetal Laboratory Medicine: On the Frontier of Maternal–Fetal Medicine

BACKGROUND

Emerging antenatal interventions and care delivery to the fetus require diagnostic support, including laboratory technologies, appropriate methodologies, establishment of special algorithms, and interpretative guidelines for clinical decision-making.

CONTENT

Fetal diagnostic and therapeutic interventions vary in invasiveness and are associated with a spectrum of risks and benefits. Fetal laboratory assessments are well served by miniaturized diagnostic methods for blood analysis. Expedited turnaround times are mandatory to support invasive interventions such as cordocentesis and intrauterine transfusions. Health-associated reference intervals are required for fetal test interpretation. Fetal blood sampling by cordocentesis carries substantial risk and is therefore performed only when fetal health is impaired, or at risk. When the suspected pathology is not confirmed, however, normative fetal data can be collected. Strategies for assurance of sample integrity from cordocenteses and confirmation of fetal origin are described. After birth, definitive assessment of prenatal environmental and/or drug exposures to the fetus can be retrospectively assessed by analysis of meconium, hair, and other alternative matrices. A rapidly advancing technology for fetal assessment is the use of fetal laboratory diagnostic techniques that use cell-free fetal DNA collected from maternal plasma, and genetic analysis based on molecular counting techniques.

SUMMARY

Developmental changes in fetal biochemical and hematologic parameters in health and disease are continually delineated by analysis of our collective outcome-based experience. Noninvasive technologies for fetal evaluation are realizing the promise of lower risk yet robust diagnostics; examples include sampling and analysis of free fetal DNA from maternal blood, and analysis of fetal products accessible at maternal sites. Application of diagnostic technologies for nonmedical purposes (e.g., sex selection) underscores the importance of ethical guidelines for new technology implementation.

Standardization non-invasive fetal RHD and SRY determination into clinical routine using a new multiplex RT-PCR assay for fetal cell-free DNA in pregnant women plasma: results in clinical benefits and cost saving

INTRODUCTION

Among negative RhD mothers it is essential to know the fetal RhD status in order to avoid the possibility of hemolytic disease of the newborn. In this regard, the detection of fetal DNA in maternal plasma might become a new diagnostic tool. In the current study, we have evaluated the standardization of a Multiplex-PCR targeted towards two exons of the RHD and one SRY gene to monitor RhD negative women. The current study addresses questions concerning feasibility and applicability of this approach into the clinical practice.

MATERIALS AND METHODS

Both single and multiplex real-time PCRs targeting RHD exons 5 and 7 and SRY were applied for the detection of fetal-specific RHD sequences and sex in maternal plasma. A large cohort of 2127 women was studied between 10 and 28 weeks of pregnancy. 134 of them were used for single TaqMan PCR studies and 1993 were evaluated using Multiplex TaqMan PCR studies. All of them were serologically typed as RhD negative according to Spanish guidelines. Single and multiplex real-time PCR results were compared with postnatal serology and sex identification.

RESULTS

There was a 100% concordance between results obtained with single and multiplex real-time PCR assays. At present, 1012 of the 1993 pregnant women studied gave birth and the results of RHD status obtained with the multiplex TaqMan PCR assay were confirmed postpartum by serological methods showing that sensitivity, specificity, and accuracy of the multiplex assay were 100, 98.6, and 99.3%, respectively. This procedure improved the speed of the assay, avoided over-treatment among RhD negative pregnant women bearing RhD negative fetus, and reduced the requirements for clinical and biological monitoring, resulting in a clinical benefit and cost saving.

CONCLUSIONS

The routine determination of fetal RHD status and SRY in maternal plasma, using multiplex real-time PCR, is feasible. The use of multiplex real-time PCR allows improving the response of the laboratory, saving time and reagent costs, opening the door to a complete automatization of the process.

Diagnostic laboratory technologies for the fetus and neonate with isoimmunization

Maternal-fetal blood group incompatibility is common but less commonly results in hemolytic disease of the fetus and newborn (HDFN). HDFN is associated with greater peak bilirubin, at an earlier age, and for longer duration than other causes of hyperbilirubinemia. It poses a substantial risk for kernicterus and accounts for the majority of exchange transfusions for hyperbilirubinemia. Advances in diagnosis and management are described, from identification of the alloimmunized pregnancy by maternal ABO and Rh typing, antibody screen (indirect Coombs test), identification and titration; laboratory evaluation of the maternal-fetal unit with a critical maternal antibody titer to prompt fetal antigen status determination; assessment of fetomaternal hemorrhage by conventional Kleihauer-Betke testing or by flow cytometric methodology; to antenatal management of isoimmunization and fetal status assessments using the systems of Liley, Queenan, and serial Doppler fetal middle cerebral artery peak velocity measurements. The utility of laboratory diagnostics in the approach to hemolysis in the neonate, including hematology, chemistry, and peripheral blood smear review, is reviewed. The goal of management, to deliver a healthy infant at or near term, is attained for the majority of cases using current modalities; future directions include noninvasive genotyping of fetal blood from maternal serum to fully eliminate RhD alloimmunization and HDFN; and development of prophylaxis and intervention strategies for non-RhD alloimmunizations for which immune globulin is currently unavailable.

Noninvasive approach for the management of hemolytic disease of the fetus

Hemolytic disease of the fetus and newborn (HDFN) is due to maternal alloantibodies directed against paternally inherited antigens on fetal red cells, and it is still a problem in affected pregnancies despite the routine use of anti-D immunoglobulin during pregnancy and shortly after delivery. The current noninvasive management of HDFN starts with the determination of fetal RhD genotype by use of cell-free fetal DNA in maternal plasma. When the fetus is antigen positive, the follow-up is performed by Doppler ultrasonography for the detection of moderate or severe anemia on the basis of an increase peak velocity of systolic blood in the middle cerebral artery. Finally, if anemia is suspected, an invasive approach is required in order to perform an intrauterine blood transfusion, which should only be attempted when the fetus needs transfusion. This approach reduces the iatrogenic conversion of mild-to-severe disease, which occurred as a result of the previous invasive management, and prevents unnecessary administration of human-derived blood products. These changes represent one of the genuine successes of fetal therapy.

Progress in heritable skin diseases: translational implications of mutation analysis and prospects of molecular therapies*

Epidermolysis bullosa, a group of blistering disorders, serves as the paradigm of the tremendous progress made in understanding the molecular genetics of heritable skin diseases. Mutations in 10 distinct genes have been disclosed in the classic forms of epidermolysis bullosa, and the level of expression of the mutated genes within the cutaneous basement membrane zone, the types and combinations of mutations and their consequences at the mRNA and protein levels, when placed in the context of the individual's genetic background and exposure to environmental trauma, all determine the subtype and the phenotypic severity in each case. The translational implications of mutation analysis include improved diagnosis and subclassification, refined genetic counseling of families at risk, and development of DNA-based pre natal and preimplantation genetic diagnosis. The prospects of molecular therapies for epidermolysis bullosa include further development of strategies for gene therapy, protein replacement therapy and cell-based therapies, including stem cell therapy and bone marrow transfer. Collectively, advances in the molecular genetics of heritable skin diseases clearly emphasize the value of basic research for improved diagnostics and patient care for genetic skin diseases.

MALDI-TOF MS in Prenatal Genomics

Prenatal diagnosis aims either to provide the reassurance to the couples at risk of having an affected child by timely appropriate therapy or to give the parents a chance to decide the fate of the unborn babies with health problems. Invasive prenatal diagnosis (IPD) is accurate, however, carrying a risk of miscarriage. Non-invasive prenatal diagnosis (NIPD) has been developed based on the existing of fetal genetic materials in maternal circulation; however, a minority fetal DNA in majority maternal background DNA hinders the detections of fetal traits. Different protocols and assays, such as homogenous MassEXTEND (hME), single allele base extension reaction (SABER), precise measuring copy number variation of each allele, and quantitative methylation and expression analysis using the high-throughput sensitive matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS), allow NIPD for single gene disorders, fetal blood group genotyping and fetal aneuploidies as well as the development of fetal gender-independent biomarkers in maternal circulation for management of pathological pregnancies. In this review, we summarise the use of MALDI-TOF MS in prenatal genomics.

High throughput non-invasive determination of foetal Rhesus D status using automated extraction of cell-free foetal DNA in maternal plasma and mass spectrometry

PURPOSE

To examine the potential high throughput capability and efficiency of an automated DNA extraction system in combination with mass spectrometry for the non-invasive determination of the foetal Rhesus D status.

METHODS

A total of 178 maternal plasma samples from RHD-negative pregnant women were examined, from which DNA was extracted using the automated Roche MagNA Pure system. Presence of the foetal RHD gene was detected by PCR for RHD exon 7 and subsequent analysis using the Sequenom MassArray mass spectrometric system.

RESULTS

We determined that as little as 15 pg of RHD-positive genomic DNA could be detected in a background of 585 pg of RHD-negative genomic DNA. The analysis of the clinical samples yielded a sensitivity and specificity of 96.1 and 96.1%, respectively.

CONCLUSION

Our study indicated that automated DNA extraction in combination with mass spectrometry permits the determination of foetal Rhesus D genotype with an accuracy comparable to the current approaches using real-time PCR.