Multiplex and real-time quantitative PCR on fetal DNA in maternal plasma. A comparison with fetal cells isolated from maternal blood

Biochemical parameters, dynamic tensiometry and circulating nucleic acids for cattle blood analysis: a review

The animal’s blood is the most complicated and important biological liquid for veterinary medicine. In addition to standard methods that are always in use, recent technologies such as dynamic tensiometry (DT) of blood serum and PCR analysis of particular markers are in progress. The standard and modern biochemical tests are commonly used for general screening and, finally, complete diagnosis of animal health. Interpretation of major biochemical parameters is similar across animal species, but there are a few peculiarities in each case, especially well-known for cattle. The following directions are discussed here: hematological indicators; “total protein” and its fractions; some enzymes; major low-molecular metabolites (glucose, lipids, bilirubin, etc.); cations and anions. As example, the numerous correlations between DT data and biochemical parameters of cattle serum have been obtained and discussed. Changes in the cell-free nucleic acids (cfDNA) circulating in the blood have been studied and analyzed in a variety of conditions; for example, pregnancy, infectious and chronic diseases, and cancer. CfDNA can easily be detected using standard molecular biological techniques like DNA amplification and next-generation sequencing. The application of digital PCR even allows exact quantification of copy number variations which are for example important in prenatal diagnosis of chromosomal aberrations.

Cell-free fetal nucleic acid testing: a review of the technology and its applications

Cell-free fetal nucleic acids circulating in the blood of pregnant women afford the opportunity for early, noninvasive prenatal genetic testing. The predominance of admixed maternal genetic material in circulation demands innovative means for identification and analysis of cell-free fetal DNA and RNA. Techniques using polymerase chain reaction, mass spectrometry, and sequencing have been developed for the purposes of detecting fetal-specific sequences, such as paternally inherited or de novo mutations, or determining allelic balance or chromosome dosage. Clinical applications of these methods include fetal sex determination and blood group typing, which are currently available commercially although not offered routinely in the United States. Other uses of cell-free fetal DNA and RNA being explored are the detection of single-gene disorders, chromosomal abnormalities, and inheritance of parental polymorphisms across the whole fetal genome. The concentration of cell-free fetal DNA may also provide predictive capabilities for pregnancy-associated complications. The roles that cell-free fetal nucleic acid testing assume in the existing framework of prenatal screening and invasive diagnostic testing will depend on factors such as costs, clinical validity and utility, and perceived benefit-risk ratios for different applications. As cell-free fetal DNA and RNA testing continues to be developed and translated, significant ethical, legal, and social questions will arise that will need to be addressed by those with a stake in the use of this technology.

TARGET AUDIENCE

Obstetricians & Gynecologists and Family Physicians Learning Objectives: After participating in this activity, physicians should be better able to evaluate techniques and tools for analyzing cell-free fetal nucleic acids, assess clinical applications of prenatal testing, using cell-free fetal nucleic acids and barriers to implementation, and distinguish between relevant clinical features of cell-free fetal nucleic acid testing and existing prenatal genetic screening and diagnostic procedures.

Real-time quantitative polymerase chain reaction measurement of male fetal DNA in maternal plasma

Cell-free fetal DNA can be detected in the blood plasma of pregnant women as early as 5 wk into pregnancy. At present noninvasive prenatal diagnosis has already begun to impact clinical practice. The established applications are for the determination of fetal sex and rhesus D blood group when the mother is rhesus D negative. Both methods are currently evaluated and standardized by a large laboratory network (the Special Non-Invasive Advances in Fetal and Neonatal Evaluation Network, or SAFE) that aims to implement widespread noninvasive prenatal diagnosis throughout the European Union. This chapter presents the basic methodology used in this noninvasive analysis.

Chimerism in the immunohematology laboratory in the molecular biology era

Dual or multiple cell populations, induced by chimeras, have been the subject of many studies. This long-standing fascination with chimeras has revealed a good deal of knowledge about human inheritance. Although historically most chimeras were caused by natural events, certain current medical intervention therapies are increasing the number of situations that can lead to a mixed cell population, that is, the chimeric condition, in humans. Medical therapies such as transfusion, stem cell transplantation, kidney transplantation, and artificial insemination induce temporary and sometimes permanent chimeras. Such natural or therapeutically induced presentations of chimerism can present challenging issues to the clinical immunohematology laboratory with regard to interpretation of results and subsequent patient management. The purpose of this review was to highlight some of these chimeric states and hypothesize how testing DNA from various tissues can cause apparent discrepancies between phenotype and genotype results.

Quantification of fetal and total circulatory DNA in maternal plasma samples before and after size fractionation by agarose gel electrophoresis

Fetal extracellular DNA is mainly derived from apoptotic bodies of trophoblast. Recent studies have shown size differences between fetal and maternal extracellular DNA. We have examined the quantification of fetal (SRY gene) and total (GLO gene) extracellular DNA in maternal plasma in different fractions (100-300, 300-500, 500-700, 700-900, and >900 bp) after size fractionation by agarose gel electrophoresis. DNA was extracted from maternal plasma samples from 11 pregnant women carrying male foetuses at the 16th week of gestation. Fetal circulatory DNA was mainly detected in the 100-300 bp fraction with the median concentration being 14.4 GE/ml. A lower median amount of 4.9 GE/ml was also found in the 300-500 bp fraction. Circulatory DNA extracted from the 100-300 bp fraction contained 4.2 times enriched fetal DNA when compared with unseparated DNA sample. Fetal DNA within the 300-500 bp fraction was 2.5 times enriched. Circulatory fetal DNA is predominantly present in a fraction with molecular size <500 bp, which can be used for the detection of paternally inherited alleles. However, the usage of size-separated DNA is not suitable for routine clinical applications because of risk of contamination.

Rapid and/or high-throughput genotyping for human red blood cell, platelet and leukocyte antigens, and forensic applications

BACKGROUND

Traditionally, transfusion medicine, platelet and human leukocyte antigen (HLA) typing, and forensic medicine relied on serologic studies.

METHODS

In recent years, molecular testing on nucleic acids has been increasingly applied to these areas. Although conventional molecular diagnostic methods such as PCR-sequence-specific priming, PCR-restriction fragment-length polymorphism, PCR-single-strand conformation polymorphism, sequence-based typing, and DNA fingerprinting have been shown to perform well, their use is limited by long turnaround times, high cost, labor-intensiveness, the need for special technical skills, and/or the high risk of amplicon contamination. With advance of fast and/or high-throughput methods and platforms that often combine amplification and detection, a new era of molecular genotyping is emerging in these fields dominated by serology for a century. As new targets, short tandem repeats, mitochondrial DNA and Y-chromosome sequences were introduced for forensic applications. This article reviews the current status of the application of rapid and/or high-throughput genotyping methods to these areas.

RESULTS

The results are already promising with real-time PCR, pyrosequencing, microarrays, and mass spectrometry and show high concordance rates with classic serologic and earlier manual molecular diagnostic methods. Exploration of other emerging methodologies will likely further enhance the diagnostic utility of molecular testing in these areas.

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.

Non-invasive fetal RHD and RHCE genotyping from maternal plasma in alloimmunized pregnancies

BACKGROUND

In this prospective study, we assessed the feasibility of fetal RH genotyping by analysis of DNA extracted from maternal plasma samples of alloimmunized pregnant women using real-time PCR and primers and probes targeted toward RHD (exon 7 and exon 10) and RHCE (intron 2 and exon 5) genes.

METHODS

We analysed 23 alloimmunized pregnant women (16 anti-D, 5 anti-D + C, 2 anti-E) at risk of haemolytic disease of the newborn (HDN) within 11th and 37th week of pregnancy and correlated the results with serological analysis of cord blood.

RESULTS AND CONCLUSION

Detection of the presence of the RHD gene, the C and/or E alleles of the RHCE gene in maternal plasma samples is highly accurate and enables implementation in a clinical diagnostic algorithm for following pregnancies at risk for HDN. The absence of RHD gene, the C and/or E alleles of RHCE gene in the current pregnancy excludes the risk of HDN caused by anti-D, anti-C and/or anti-E alloantibodies and the performance of invasive fetal-blood sampling.

Quantification of fetal microchimeric cells in clinically affected and unaffected skin of patients with systemic sclerosis

OBJECTIVE

Fetal microchimerism has been hypothesized as a potential pathogenic mechanism for systemic sclerosis (SSc). This hypothesis was based on the clinical similarities between SSc and graft-vs-host disease and the identification of microchimeric cells in affected SSc tissues. The aim of this study was to compare the quantity of microchimeric cells in clinically affected and non-affected skin of female patients with SSc.

METHODS

Fluorescence in situ hybridization (FISH) and real-time PCR were employed in paired skin biopsies obtained from clinically affected and unaffected areas from five female SSc patients with diffuse cutaneous SSc (dcSSC) and 10 healthy women. All women in the study had delivered a male fetus.

RESULTS

FISH analysis revealed the presence of male fetal cells in 1/5 SSc patients (20.0%) compared with 0/10 healthy women (P = 0.0037), whereas quantification by real-time PCR revealed that all SSc samples were positive for male DNA compared with none of the controls. In the five patients with dcSSc, there were similar numbers of microchimeric cells in both affected and unaffected skin (P = 0.4)

CONCLUSION

The presence of higher numbers of microchimeric cells in clinically unaffected SSc skin, before any clinically detectable evidence of sclerotic changes, suggests that an influx of microchimeric cells may precede the development of tissue fibrosis. This provides additional support to the hypothesis that fetal microchimerism may play a role in the pathogenesis of SSc.

HLA-DQA1 is not an apparent risk factor for microchimerism in patients with various autoimmune diseases and in healthy individuals

OBJECTIVE

Microchimeric cells have been identified in lesions and peripheral blood of patients with systemic sclerosis (SSc) and idiopathic inflammatory myopathies (IIM), and HLA-DQA1*0501 is a risk factor for these diseases in some populations. Furthermore, DQA1*0501 has been associated with T lymphocyte microchimerism in SSc. To better define the strength of this association, we assessed the relationship among DQA1 alleles and microchimerism.

METHODS

DNA from whole peripheral blood or magnetically sorted T cells was tested for microchimeric cells by polymerase chain reaction of the Y chromosome or of HLA-Cw in 87 SSc patients, 28 juvenile IIM patients, and 88 healthy controls. Thirty-seven mother-son pairs were also analyzed for microchimerism and DQA1*0501.

RESULTS

We were unable to demonstrate that DQA1*0501 is associated with microchimerism in T lymphocytes or in whole peripheral blood DNA in patients with SSc or juvenile IIM or in healthy individuals. In the 37 mother-son pairs, we were unable to demonstrate an association of DQA1*0501 with microchimerism in peripheral blood DNA or T lymphocytes, and compatibility between the donor's and recipient's HLA alleles did not influence microchimerism in the recipient.

CONCLUSION

These data suggest that HLA-DQA1 alleles do not appear to play a role in the persistence of microchimerism in the peripheral blood or T lymphocytes of patients with selected autoimmune diseases or in healthy individuals.

Methodology for Detecting Trace Amounts of Microchimeric DNA from Peripheral Murine White Blood Cells by Real-Time PCR

Real-time PCR methodology can successfully quantitate microchimeric cell populations at a concentration of 100 microchimeric cells/100,000 host cells; however, it has not been successful in quantitating DNA from trace numbers of microchimeric white blood cells which we reported are present in murine peripheral blood at a concentration as low as 2/100,000 host cells. We report methodology using primers for a portion of the H2-k(b) murine histocompatibility sequence, specific for the C57BL/6J mouse. When these primers were used in the presence of 11,000 microM primer, a 20-fold increase in the median manufacturer's recommended concentration, the assay could be optimized to detect 34 pg of C57BL/6J DNA in a background of 2.5 microg of carrier BALB/cJ DNA (1/100,000). These conditions resulted in a detection limit half as sensitive as that found when no carrier DNA was present.

Replicate real-time PCR testing of DNA in maternal plasma increases the sensitivity of non-invasive fetal sex determination

BACKGROUND

We determined fetal sex in pregnancies referred for invasive prenatal diagnosis procedures by analysis of DNA in maternal plasma.

METHODS

Twelve pregnancies at risk of X-linked haemophilia and 32 pregnancies at risk of chromosomal aneuploidies at a gestational age ranging from 10 to 18 weeks recruited before chorionic villus sampling or amniocentesis were involved in the study. Male fetal DNA in maternal plasma was detected by using real-time polymerase chain reaction with the SRY gene as a marker.

RESULTS

The specificity of the system reached 100% (no Y signal was detected in 17 women pregnant with a female fetus) and the sensitivity reached 100% (SRY amplification in 27 examined samples).

CONCLUSIONS

Amplification of free fetal DNA in maternal plasma is a valid and rapid technique for predicting fetal sex in first- and second-trimester pregnancies and could allow the restriction of invasive sampling procedures to male fetuses at risk of X-linked disorders.

Quantitative analysis of male fetal DNA in maternal serum of gravid rhesus monkeys (Macaca mulatta)

The isolation of human fetal DNA from the maternal circulation has provided a source of fetal material for prenatal diagnosis. The objective of this study was to investigate whether a similar pattern could be observed in the maternal circulation of male-bearing gravid rhesus monkeys. A real-time PCR TaqMan system for the rhesus Y-chromosome sex determining region was used to determine fetal sex and to quantify fetal DNA concentrations. Results in 14 healthy pregnancies indicated that fetal male DNA could be routinely detected in maternal serum by 50 d of gestation (late first trimester; term 165 +/- 10 d). Fetal DNA concentrations increased with advancing gestation, reaching a mean of 341 genome equivalents/mL of serum (range 11-1570 copies/mL) in the last trimester of gestation, similar to findings in humans. The fetal DNA concentration corresponded to 2.7% of the total maternal serum DNA in the third trimester. Similar to findings in humans, male fetal DNA sequences were not detected postpartum (through 4 wk postpartum) or in animals with a previous history of delivering male offspring. These data indicate that fetal male DNA is present in the maternal circulation of gravid rhesus monkeys comparable to findings in humans and further support the use of this nonhuman primate species as a model to investigate fetomaternal cell trafficking and microchimerism.

Increased microchimeric CD4+ T lymphocytes in peripheral blood from women with systemic sclerosis

Recent studies have demonstrated the presence of microchimeric cells in peripheral blood and skin lesions from patients with systemic sclerosis (SSc). In a previous study we found that some peripheral blood CD3+ cells from female patients with SSc contained male DNA. Here, peripheral blood samples from 47 patients with SSc (30 with diffuse cutaneous SSc and 17 with limited cutaneous SSc) and 22 healthy controls were sorted for CD4+ and CD8+ T cells. Both positively and negatively selected populations were analyzed for male DNA by quantitative PCR. Analysis of Y chromosome sequences in the sorted cells demonstrated the presence of microchimerism in 82.9% of SSc patients compared to 63.6% of controls. The numbers of CD4+ and CD8+ T cells were found to be significantly higher in the SSc patients than in controls. Furthermore, patients with dcSSc were observed to have significantly more CD4+ microchimeric T cells than the controls. In the CD8+ T-cell population, there was a trend toward more microchimeric cells in the patients but this did not reach significance. These results support the hypothesis that microchimeric CD4+ T cells may be involved in the pathogenesis of SSc.

Quantitative analysis of DNA levels in maternal plasma in normal and Down syndrome pregnancies

BACKGROUND: We investigated fetal and total DNA levels in maternal plasma in patients bearing fetuses affected with Down syndrome in comparison to controls carrying fetuses with normal karyotype. METHODS: DNA levels in maternal plasma were measured using real-time quantitative PCR using SRY and beta-globin genes as markers. Twenty-one pregnant women with a singleton fetus at a gestational age ranging from 15 to 19 weeks recruited before amniocentesis (carried out for reasons including material serum screening and advanced material age), and 16 pregnant women bearing fetuses affected with Down syndrome between 17 to 22 weeks of gestation were involved in the study. RESULTS: The specificity of the system reaches 100% (no Y signal was detected in 14 women pregnant with female fetuses) and the sensitivity 91.7% (SRY amplification in 22 of 24 examined samples). The median fetal DNA levels in women carrying Down syndrome (n=11) and the controls (n=13) were 23.3 (range 0-58.5) genome-equivalents/ml and 24.5 (range 0-47.5) genome-equivalents/ml of maternal plasma, respectively (P = 0.62). The total median DNA levels in pregnancies with Down syndrome and the controls were 10165 (range 615-65000) genome-equivalents/ml and 7330 (range 1300-36750) genome-equivalents/ml, respectively (P = 0.32). The fetal DNA proportion in maternal plasma was 0%-6 % (mean 0.8%) in women carrying Down syndrome and 0%-2.6 % (mean 0.7 %) in the controls, respectively (P=0.86). CONCLUSIONS: Our study revealed no difference in fetal DNA levels and fetal DNA: maternal DNA ratio between the patients carrying Down syndrome fetuses and the controls.

Molecular approaches to blood group identification

Allogeneic barriers to transfusion are caused by differences between those portions of the donor and recipient genomes that define the antigenicity and immune response to the transfused cells. Historically, a blood group antigen was identified when an immune response (alloantibody) was detected by hemagglutination in the serum of a transfused patient. There has been an astounding pace of growth over the past two decades in the field of molecular biology techniques and even more recently in the understanding of the basis of many blood group antigens and phenotypes. Identification of blood group antigens can now be performed in genetic terms, and identification of blood group antibodies can be performed using molecular approaches. This knowledge is being applied to help resolve some long-standing clinical problems that cannot be resolved by classical hemagglutination. This article reviews knowledge of molecular approaches for identifying blood group antigens and antibodies as applied to transfusion medicine practice.

[What's new in fetal medicine?]

One of the major progress in fetal medicine in recent years is the increased sensitivity of sonographic screening for foetal malformations, due to technical improvement but also to a better training of professionals. Screening for chromosomal abnormalities is no longer based on maternal age alone. Second trimester maternal serum screening (MSS) is increasingly used: thus in 1997, 376,798 MSS tests were performed in France, yielding to the prenatal diagnosis of 391 cases of Down's syndrome. First trimester sonographic nuchal translucency measurement (NTM) is an effective screening method when performed under stringent conditions. Quality control however, is more difficult to implement on a large scale for NTM than for MSS. Performing screening tests sequentially carries a danger of generating an unnecessarily high number of amniocentesis, which may be obviated by a rational calculation of an individual's risk to carry an aneuploid baby. First trimester MSS is expected to become standard practice in the next years, probably in combination with NTM. Cytogenetics underwent substantial innovations recently, due to the ever-increasing use of molecular cytogenetics. FISH techniques allow: 1) precise analysis of unexpected structural chromosomal abnormalities diagnosed by routine amniocentesis, 2) rapid screening of the most common aneuploidies by amniocentesis when a fetal structural anomaly is detected by 3rd trimester ultrasound, 3) diagnosis of micro-deletions suspected by fetal ultrasound or post-mortem. Prenatal diagnosis by maternal blood sampling and fetal cells or DNA analysis is now part of routine clinical practice in selected cases, such as fetal sexing in families affected by an X linked disease. Thus one can select those pregnancies eligible to invasive prenatal diagnosis. Pre implantation diagnosis, which has not been legal in France until 1999 is now increasingly used as an alternative to first trimester diagnosis. As for fetal therapy, a major recent breakthrough is the prenatal management of twin to twin transfusion syndrome by either amnioreduction or laser coagulation of inter-twin vascular shunts. In addition, new pathophysiologic concepts involving the renin angiotestin system could lead to further therapeutic innovations. A European randomised trial is now being completed to establish the respective indications of drainage and Laser. All this underscores that fetal medicine is no longer solely a succession of dramatic technical breakthroughs, but is entered an era of large-scale diffusion that requires evidence based evaluation.

Cell-free DNA in urine: a marker for kidney graft rejection, but not for prenatal diagnosis?

Intrigued by the rapid clearance of free fetal DNA from the maternal circulation, we have investigated whether this fetal genetic material could be cleared via the kidney. For this purpose, we examined for the presence of Y chromosome-specific DNA sequences in urine samples obtained from 8 women pregnant with male fetuses. No male-specific sequences could be detected, despite the use of a very sensitive nested PCR assay nor a highly reproducible real-time PCR assay. We did, however, detect maternal DNA sequences. To determine if this cell-free DNA was derived from the kidney or another source, we next examined urine from female kidney transplant patients who had received male kidneys. Y chromosome-specific sequences were indeed detectable by both nested and real-time PCR in these samples, thereby confirming a recent report describing urinary DNA microchimerism. Quantitative analysis of serially obtained samples furthermore suggests that transplant-derived sequences are elevated during periods of graft rejection. These results imply that the measurement of graft-derived urinary DNA may serve as a new marker for kidney graft tolerance.

Circulating nucleic acids and apoptosis

It is well documented that plasma contains DNA from tissues throughout the body, including developing fetuses, and tumors. A portion of this DNA crosses the kidney barrier and appears in urine (i.e., transrenal DNA). However, molecular, cellular, and physiological mechanisms of the circulating DNA phenomenon and renal clearance are in an early phase of investigation. Here, we discuss possible forms of circulating DNA, factors affecting representation of different tissues and genomic sequences in plasma DNA, possible mechanisms of renal DNA clearance, and technical problems encountered in DNA isolation from urine. We suggest that apoptotic cells are an important source of DNA in both plasma and urine. Further analysis of the data has led us to propose that a significant portion of circulating DNA can be represented in apoptotic bodies.

Prenatal diagnosis using fetal cells and free fetal DNA in maternal blood

The presence of fetal cells and free fetal DNA in maternal blood offers an exciting opportunity for the development of safe noninvasive forms of prenatal diagnosis. Research in this field has, however, also indicated that their levels in the maternal circulation are increased in certain pregnancy-related disorders, such as preeclampsia. Their closer examination may shed new light on the underlying etiology of this enigmatic disorder.

Elevation of both maternal and fetal extracellular circulating deoxyribonucleic acid concentrations in the plasma of pregnant women with preeclampsia

OBJECTIVE

Elevated amounts of circulating fetal deoxyribonucleic acid in maternal plasma have recently been detected in pregnancies complicated by preeclampsia. We attempted to confirm this finding and simultaneously examined the quantity of maternal circulating deoxyribonucleic acid.

STUDY DESIGN

Circulating deoxyribonucleic acid was measured by realtime quantitative polymerase chain reaction in plasma samples obtained from 44 women with preeclampsia and a matched cohort of 53 normotensive pregnant women.

RESULTS

We confirmed that circulating fetal deoxyribonucleic acid levels were significantly elevated in pregnancies complicated by preeclampsia (3194.6 vs 332.8 copies/mL; P < .001). We also showed for the first time that circulating maternal deoxyribonucleic acid levels are also elevated (219,023.9 vs 20,235.8 copies/mL; P < .001). The increases in these deoxyribonucleic acid levels corresponded to the severity of the disorder, and values were correlated with each other in pregnancies complicated by preeclampsia (r = 0.556; P < .001) but not normotensive pregnancies (r = 0.046; P = .747).

CONCLUSION

The releases of both free fetal and maternal deoxyribonucleic acid were found to be affected in preeclampsia.