High sensitivity of fetal DNA in plasma compared to serum and nucleated cells using unnested PCR in maternal blood

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.

Y-chromosome DNA is present in the blood of female dogs suggesting the presence of fetal microchimerism

Fetal microchimerism has been suggested to play contradictory roles in women’s health, with factors including age of the recipient, time elapsed since microchimerism occurred, and microchimeric cell type modulating disease. Both beneficial and harmful effects have been identified in wound healing and tissue regeneration, immune mediated disease, and cancer. This area of research is relatively new, and hindered by the time course from occurrence of fetal microchimerism to the multi-factorial development of disease. Dogs represent an excellent model for study of fetal microchimerism, as they share our environment, have a naturally condensed lifespan, and spontaneously develop immune-mediated diseases and cancers similar to their human counterparts. However, fetal microchimerism has not been described in dogs. These experiments sought preliminary evidence that dogs develop fetal microchimerism following pregnancy. We hypothesized that Y chromosomal DNA would be detected in the peripheral blood mononuclear cells of female dogs collected within two months of parturition. We further hypothesized that Y chromosomal DNA would be detected in banked whole blood DNA samples from parous female Golden Retrievers with at least one male puppy in a prior litter. Amplification of DNA extracted from five female Golden Retrievers that had whelped within the two months prior to collection revealed strong positive bands for the Y chromosome. Of banked, parous samples, 36% yielded positive bands for the Y chromosome. This is the first report of persistent Y chromosomal DNA in post-partum female dogs and these results suggest that fetal microchimerism occurs in the canine species. Evaluation of the contributions of fetal microchimeric cells to disease processes in dogs as a model for human disease is warranted.

Circulating nucleic acids in plasma and serum: applications in diagnostic techniques for noninvasive prenatal diagnosis

The analysis of fetal nucleic acids in maternal blood 13 years ago has led to the initiation of noninvasive methods for the early determination of fetal gender, rhesus D status, and a number of aneuploid disorders and hemoglobinopathies. Subsequently, a comparatively large quantity of fetal DNA and RNA has been demonstrated in amniotic fluid as well as small amounts in premature infant saliva. The DNA and RNA in amniotic fluid has permitted an analysis of core transcriptomes, whilst the DNA and RNA in saliva allows the early detection and treatment monitoring of fetal developmental problems. These aspects are discussed together with the methodology and limits of analysis for noninvasive prenatal diagnosis in predictive, preventive, and personalized medicine.

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.

Non-invasive prenatal diagnostic test accuracy for fetal sex using cell-free DNA a review and meta-analysis

Background

Cell-free fetal DNA (cffDNA) can be detected in maternal blood during pregnancy, opening the possibility of early non-invasive prenatal diagnosis for a variety of genetic conditions. Since 1997, many studies have examined the accuracy of prenatal fetal sex determination using cffDNA, particularly for pregnancies at risk of an X-linked condition. Here we report a review and meta-analysis of the published literature to evaluate the use of cffDNA for prenatal determination (diagnosis) of fetal sex. We applied a sensitive search of multiple bibliographic databases including PubMed (MEDLINE), EMBASE, the Cochrane library and Web of Science.

Results

Ninety studies, incorporating 9,965 pregnancies and 10,587 fetal sex results met our inclusion criteria. Overall mean sensitivity was 96.6% (95% credible interval 95.2% to 97.7%) and mean specificity was 98.9% (95% CI = 98.1% to 99.4%). These results vary very little with trimester or week of testing, indicating that the performance of the test is reliably high.

Conclusions

Based on this review and meta-analysis we conclude that fetal sex can be determined with a high level of accuracy by analyzing cffDNA. Using cffDNA in prenatal diagnosis to replace or complement existing invasive methods can remove or reduce the risk of miscarriage. Future work should concentrate on the economic and ethical considerations of implementing an early non-invasive test for fetal sex.

Prenatal diagnosis: update on invasive versus noninvasive fetal diagnostic testing from maternal blood

The modern obstetrics care includes noninvasive prenatal diagnosis testing such as first trimester screening performed between 11 and 14 weeks' gestation and second trimester screening performed between 15 and 20 weeks. In these screening tests, biochemical markers are measured in the maternal blood with or without ultrasound for fetal nuchal translucency with reported accuracy of up to 90%. Invasive procedures, including amniocentesis or chorionic villi sampling, are used to achieve over 99% accuracy. During these procedures direct fetal material is examined and, therefore, these tests are highly accurate with the caveat of a small risk for pregnancy loss. Much research now focuses on other noninvasive highly accurate and risk-free tests that will identify fetal material in the maternal blood. Fetal cells and fetal DNA/RNA provide fetal information but are hard to find in an overwhelming background of maternal cells and in the absence of specific fetal cell markers. The most experience has been accumulated with fetal rhesus and fetal sex determination from maternal blood, with an accuracy of up to 100% by using gene sequences that are absent from maternal blood. Although not clinically applicable yet, fetal cells, fetal DNA/RNA and fetal proteomics in combination with cutting edge technology are described to prenatally diagnose aneuploidies and single-gene disorders.

Non-invasive prenatal diagnosis of single gene disorders: how close are we?

Analysis of cell free fetal DNA (cffDNA) in maternal plasma provides the opportunity for reliable, timely, safe and cost-effective diagnosis of single gene disorders. The detection of certain fetal loci using cffDNA and conventional molecular analytic approaches is possible from 4 weeks gestation. To date, non-invasive first-trimester analysis for single gene disorders has been limited by assay sensitivity and specificity, due to the background maternal DNA. The anticipated ability to enrich the fetal component of cell free DNA will increase the robustness of tests and permit semi-quantitative analysis, broadening the scope of testing to include recessive disorders such as cystic fibrosis. Testing for large-scale mutations might remain limited by the fragmented nature of cffDNA and, when testing very early in gestation, careful ultrasound examination will be needed to determine the number of gestational sacs, because of the risk of discordant twin pregnancies.

Detection of Y STR markers of male fetal dna in maternal circulation

BACKGROUND:

Circulating fetal cells and cell free DNA in the maternal blood has been shown to help in prenatal diagnosis of genetic disorders without relying on invasive procedures leading to significant risk of pregnancy loss.

AIM:

The current study was undertaken to detect the male fetal population using Y STR markers DYS 19, DYS 385 and DYS 392 and also to study the extent of persistence of fetal DNA in the mother following delivery.

MATERIALS AND METHODS:

Blinded study was conducted on 50 mothers delivering male and female babies. Cellular and cell free DNA was extracted from maternal and fetal cord blood and amplified for Y STR markers by PCR.

RESULTS:

The amplification sensitivity of Y specific STR, DYS19 was 100% (22/22) in the male fetal DNA samples. The incidence of other STRs, i.e., DYS385 and DYS392 were 91% (20/22) each. Analysis of results revealed that thirteen of the twenty six women had detectable male fetal DNA at the time of delivery. However fetal DNA was not detectable twenty four hours after delivery.

CONCLUSION:

Preliminary results show that the separation of fetal cell-free DNA in the maternal circulation is a good low-cost approach for the future development of novel strategies to provide non-invasive techniques for early prenatal diagnosis.

Non-Invasive Prenatal Detection of Paternal Origin Hb Lepore in a Male Fetus at the 7th Week of Gestation

OBJECTIVE

To perform a reliable non-invasive prenatal detection of the Hb Lepore paternal mutation and determine the fetal gender in the first trimester of pregnancy.

METHODS

DNA was extracted from a serum sample obtained from a pregnant woman at the mid first trimester of gestation. Hb Lepore-specific, mutant and normal, primers as well as Y-chromosome-specific STSs were used to carry out the analysis.

RESULTS

Paternal Hb Lepore and the DYS14 and DYZ1 gene-specific sequences were detected in the serum sample obtained at the 7th week of pregnancy. None of the above sequences was detectable in the maternal peripheral blood cell DNA.

CONCLUSION

Conventional polymerase chain reaction analysis of cell-free fetal DNA can be used to determine fetal gender and paternal Hb Lepore as early as the 7th week of pregnancy.

Évaluation de la détermination du statut Rhésus-D fœtal sur plasma maternel par la technique d’hemi-nested PCR

AIMS

The aim of our study was to evaluate the possibility of identifying the fetal RhD status in maternal plasma using conventional hemi nested PCR analysis.

SUBJECTS AND METHODS

After informed written consent, 20 mL of peripheral blood were collected in 99 D-negative pregnant women either at an amniocentesis for prenatal diagnosis or at a prenatal checkup. Fetal DNA extracted from 400 microL of maternal plasma was analyzed by two different operators with a hemi-nested PCR extending an area of the RhD gene exon 10. The results were compared to the fetal RhD status obtained by PCR amniotic fluid analysis or blood analysis of newborns after delivery. The influence of mother's and baby's phenotype were also studied.

RESULTS

Among the 99 D-negative pregnant women, all Caucasian, 47 were in their second trimester and 52 in their third trimester (mean: 27.20 weeks of gestation +/-8.25). Sixty-nine fetuses were D-positive and thirty D-negative. The sensitivity and specificity of our technique were respectively 100% and 86.7% and 15% of discordant results were observed between the two operators. Four false positives were observed. According to maternal phenotype, a fetal unexpressed RHD gene was suspected in only one case because of a particular fetal phenotype (ddCcEe).

CONCLUSION

A conventional hemi nested PCR analysis of maternal plasma could be used for accurate fetal RhD status. However this procedure is difficult to apply for routine analysis because of the importance of anti-contamination measures required to obtain good results. Real time quantitative PCR analysis on fetal DNA is more suitable. Whatever the operating procedure used, polymorphism of RhD gene may follow in either false negative from presence of rearranged gene or false positive from occasional presence of a non functional RHD gene.

Rapid prenatal diagnosis of trisomy 21 by real-time quantitative polymerase chain reaction with amplification of small tandem repeats and S100B in chromosome 21

Trisomy 21 (Down syndrome) is the most common congenital anomaly, and it occurs in one out of 700-1000 births. Current techniques such as amniocentesis and chorionic villi sampling (CVS) require lengthy laboratory culture procedures and high costs. This study was undertaken to establish a rapid prenatal diagnosis of trisomy 21 using real-time quantitative polymerase chain reaction (PCR) of fetal DNA from amniotic fluid. Real-time quantitative PCR was performed with DNA templates obtained from 14 normal blood samples, 10 normal amniotic fluid samples, 14 Down syndrome blood samples, and 7 Down syndrome amniotic fluid samples. Primers for D21S167 and S100B of chromosome 21 were used. Primers that direct the amplification of the 165-bp fragment of the insulin-like growth factor (IGF)-1 gene on chromosome 12 using a PCR primer were included to generate an internal standard for quantitation. The relative levels of D21S167 and S100B were 2.6 and 2.4 times higher in the blood of Down syndrome patients than those in the control group. The differences between these two groups were statistically significant (p-values were 0.0012 and 0.0016, respectively). The relative levels of D21S167 and S100B were 2.1 and 2.7 times higher in the amniotic fluid of Down syndrome fetuses than those in the control group. The difference between these two groups was statistically significant (p-values were 0.0379 and 0.0379, respectively). Prenatal diagnosis of trisomy 21 by real-time quantitative PCR using STR (small tandem repeats) amplification of D21S167 and S100B is a useful, accurate and rapid diagnostic method. Furthermore, it may also be useful for prenatal diagnosis with fetal DNA from maternal blood, and for preimplantation genetic diagnosis and prenatal counseling.

Cell-free fetal DNA in maternal blood: kinetics, source and structure

The kinetics and structure of cell-free fetal DNA in maternal plasma is currently under investigation. Plasma fetal DNA seems quite stable albeit cleared rapidly following birth, suggesting continuous fetal DNA release into the maternal circulation during pregnancy. However, to understand better the kinetics of circulating DNA, studies to determine the biological (structural) form in which fetal and maternal DNA exist and the mechanisms underlying variation in plasma are warranted to ensure quantitative diagnostic reliability. It is likely that circulating fetal DNA is released from fetal and/or placental cells undergoing apoptosis. Thus, the majority of fetal DNA is proposed to circulate in membrane-bound vesicles (apoptotic bodies). This review summarizes the latest reports in this field.

Size Separation of Circulatory DNA in Maternal Plasma Permits Ready Detection of Fetal DNA Polymorphisms

Background: Analysis of fetal DNA in maternal plasma has recently been introduced as a new method for noninvasive prenatal diagnosis, particularly for the analysis of fetal genetic traits, which are absent from the maternal genome, e.g., RHD or Y-chromosome-specific sequences. To date, the analysis of other fetal genetic traits has been more problematic because of the overwhelming presence of maternal DNA sequences in the circulation. We examined whether different biochemical properties can be discerned between fetal and maternal circulatory DNA.

Methods: Plasma DNA was examined by agarose gel electrophoresis. The fractions of fetal and maternal DNA in size-fractionated fragments were assayed by real-time PCR. The determination of paternally and maternally inherited fetal genetic traits was examined by use of highly polymorphic chromosome-21-specific microsatellite markers.

Results: Size fractionation of circulatory DNA indicated that the major portion of cell-free fetal DNA had an approximate molecular size of <0.3 kb, whereas maternally derived sequences were, on average, considerably larger than 1 kb. Analysis of size-fractionated DNA (≤0.3 kb) from maternal plasma samples facilitated the ready detection of paternally and maternally inherited microsatellite markers.

Conclusions: Circulatory fetal DNA can be enriched by size selection of fragment sizes less than ∼0.3kb. Such selection permits easier analysis of both paternally and maternally inherited DNA polymorphisms.

Clinical applications of cell-free fetal DNA from maternal plasma

OBJECTIVE

To describe our clinical experience with detection and analysis of cell-free fetal DNA derived from maternal plasma for prenatal sexing and fetal rhesus-D typing.

METHODS

Real-time quantitative polymerase chain reactions (PCRs) of rhesus-D sequences and the SRY gene were validated and offered to patients with an enhanced risk for sex-linked fetal pathology and patients with rhesus-D antibodies.

RESULTS

In the validation group, 72 samples were analyzed. Sensitivity of the rhesus-D real-time quantitative PCR in maternal plasma was 100% (95% confidence interval [CI]91.8%, 100%) and specificity was 96.6% (95% CI 82.2%, 99.9%). Sensitivity of the SRY real-time quantitative PCR was 97.2% (95% CI 85.5%, 99.9%), and specificity was 100% (95% CI 88.1%, 100%). The technique was used successfully in a clinical setting in 24 women. Overall, invasive tests were avoided in 41.7% of these patients.

CONCLUSION

Detection of cell-free fetal DNA from maternal plasma is a reliable technique that can substantially reduce invasive prenatal tests.

[Follow-up of the feto-maternal allo-immunization]

Immunohaematological tests used in antenatal patients have come a long way. However, despite a great deal of progress, we should not loose sight of the fact that these tests give only an indirect measurement and will only help the obstetrician, in conjunction with other fetal parameters, to assess the severity of the haemolytic disease (HD) of the fetus and newborn. The best method to assess the severity is the direct determination of foetal blood group hemoglobin after foetal blood sampling but this procedure is not without risk. Since 10 years ago, it is possible to determine the RHD genotype of the fetus using amniocytes and, today, maternal plasma directly. All pregnant women should be grouped for ABO-RH-KEL1 and the sera tested for clinically irregular antibodies (anti-RH are still the most frequent). The trend in anti-RH levels is more important than the level itself. The perfect technique for anti-RH quantitation has not been developed. Manual titration is simple but only provides rough, semiquantitatives estimates of anti-RH concentration. Quantitative haemagglutination methods, using auto-analyzers and appropriate anti-RH1 standards, measure in microg/ml, are sensitive, rapid and have acceptable intra-laboratory reproductibility.

Evaluation of the clinical usefulness of isolation of fetal DNA from the maternal circulation

OBJECTIVE

To assess the reliability of isolating free fetal DNA from maternal usefulness.

DESIGN

Fetal DNA was isolated from plasma or serum that was either collected prospectively or from archived samples collected for the purposes of second trimester screening.

METHODS

Prospective samples were collected from patients undergoing prenatal diagnostic procedures (n = 24). A second group of samples from Rhesus negative women (n = 28) were assayed in which blood had originally been collected for maternal triple serum screening. DNA was extracted from all samples and assayed for the presence of the beta-globin gene, sex-determing region Y (SRY) gene and Rh gene. All DNA sample handling and extraction was carried out by a single operator, and polymerase chain reaction (PCR) was carried out using previously published PCR primers and appropriate controls. The accuracy of results was assessed relative to the karyotype in the case of the SRY gene or cord blood phenotype in the case of the Rh gene.

RESULTS

The SRY PCR results were compared to fetal cell karyotypes obtained from invasive diagnostic testing, 21 out of the 24 samples were correctly 'sexed'. The RhD PCR results were compared to fetal cord blood samples at the time of delivery, and showed both false positive and false negative results. Two RhD negative babies were genotyped as RhD positive, despite repeat analysis.

CONCLUSION

It is possible to isolate fetal DNA from maternal serum. It is a potentially clinically useful technique in our laboratory and can be used to detect male fetuses, and Rh negative fetuses. To be useful in clinical practice, it is necessary to safeguard against contamination at the time of sample handling, and to use the optimal range of primers available to cover the polymorphisms present within the RhD gene. Although not robust enough yet to be used with diagnostic certainty in our hands, immense improvements in technique, probes and real-time PCR equipment make this type of diagnosis a reality in the near future.

[First trimester fetal sex determination in maternal serum using real-time PCR]

OBJECTIVE

Fetal sex prediction can be achieved using PCR targeted at the SRY gene by analyzing cell-free fetal DNA in maternal serum. Unfortunately, the results reported to date, show lack of sensitivity, especially in the first trimester of pregnancy. Therefore, determination of fetal sex by maternal serum analysis can not replace caryotype analysis following chorionic villus sampling.

PATIENTS AND METHODS

A new highly sensitive real-time PCR was developed to detect a SRY gene sequence in maternal serum. Analysis was performed on 121 pregnant women during their first trimester of pregnancy (mean gestational age: 11.8 weeks). Among them, 61 had at least one previous male-bearing pregnancy. Results were compared to fetal sex.

RESULTS

SRY PCR analysis of maternal serum was in complete concordance with fetal sex. Among the 121 pregnant women, 61 were bearing a male fetus and 60 a female fetus No false negative results were observed. Furthermore, no false positive results results occurred although 27 women carried female fetus during the current pregnancy, had at least one previous male-bearing pregnancy.

DISCUSSION AND CONCLUSION

This study demonstrates that a reliable, non-invasive sex determination can be achieved by PCR analysis of maternal serum during the first trimester of pregnancy. This non-invasive approach for fetal sex prediction should have great implications in the management of pregnant women carriers of an X-linked genetic disorder. Prenatal diagnosis is thus performed for male fetuses only, avoiding invasive procedures and the risk of fetal loss for female fetuses.

[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.

First-trimester fetal sex determination in maternal serum using real-time PCR

Fetal sex prediction can be achieved using PCR targeted at the SRY gene by analysing cell-free fetal DNA in maternal serum. Unfortunately, the results reported to date show a lack of sensitivity, especially during the first trimester of pregnancy. Therefore, determination of fetal sex by maternal serum analysis could not replace karyotype analysis following chorionic villus sampling. A new highly sensitive real-time PCR was developed to detect an SRY gene sequence in maternal serum. Analysis was performed on 121 pregnant women during the first trimester of pregnancy (mean gestational age: 11.8 weeks). Among them, 51 had at least one previous male-bearing pregnancy. Results were compared with fetal sex. SRY PCR analysis of maternal serum was in complete concordance with fetal sex. Among the 121 pregnant women, 61 were bearing a male fetus and 60 a female fetus. No false-negative results were observed. Furthermore, no false-positive results occurred, even though 27 women carrying a female fetus during the current pregnancy had at least one previous male-bearing pregnancy. This study demonstrates that a reliable, non-invasive sex determination can be achieved by PCR analysis of maternal serum during the first trimester of pregnancy. This non-invasive approach for fetal sex prediction should have great implications in the management of pregnant women who are carriers of an X-linked genetic disorder. Prenatal diagnosis might thus be performed for male fetuses only, avoiding invasive procedures and the risk of the loss of female fetuses.

Circulating fetal DNA in maternal plasma

BACKGROUND

The existence of high concentrations of circulating fetal DNA in maternal plasma may enable non-invasive prenatal diagnosis. There are many applications of fetal DNA in maternal plasma for clinical diagnosis.

CONCLUSIONS

We expect fetal DNA in material plasma will be incorporated into past of the prenatal investigation of pregnant women in the near future.

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.

Isolation of fetal cells from the maternal circulation: prospects for the non-invasive prenatal diagnosis

The research into non-invasive and invasive prenatal diagnostic techniques developed almost in parallel. On the one hand the need was arising to ensure the birth of normal progeny in all cases, while on the other, it was not possible to eliminate the abortion risks connected with the invasiveness of amniocentesis (risk of abortion 1/200), chorion villi sampling, (risk of abortion 2%) and funicolocentesis (risk of abortion 3-4%). One of the first researchers in the non-invasive field was Adinolfi who published the earliest data in 1974 on the possibility of detecting three types of fetal cells in the maternal circulation using flow cytometry. Adinolfi suggested the possibility of using fetal cells present in the maternal circulation for prenatal diagnosis of chromosome or biochemical anomalies. Our review takes into consideration the latest methodological and technical progress in relation to the study of fetal cells in maternal circulation, without considering cells present in the endocervical canal where from the 8th week of pregnancy it is only possible to obtain trophoblast cells. This technique has since been abandoned due to the scarcity of cellular material available, the greater risk of contamination by cells of maternal origin, and also because the recovery of the cells is unpredictable, despite their potential use for the early non-invasive diagnosis of sex. The following issues are addressed in this review: the characterization of the fetal cell types present in the maternal circulation, the methods of their separation and enrichment, and the methods of genetic diagnostics applied.

Genotyping fetal DNA by non-invasive means: extraction from maternal plasma

BACKGROUND AND OBJECTIVES

Identification of fetal DNA in maternal plasma may allow genetic analysis without the use of invasive techniques. The aim of this study was to extract DNA from maternal plasma, identify fetal material through the presence of SRY or RHD gene sequences and assess the reliability of these results.

MATERIALS AND METHODS

A polymerase chain reaction (PCR) method of a commercial kit was used with primers for SRY or exon 10 of the RHD gene sequence.

RESULTS

Multiple plasma samples were collected from 60 women who were evaluable for either SRY or RHD, or both, fetally derived DNA sequences. Fetal DNA was present in the plasma throughout the pregnancies and for some hours or days after delivery.

CONCLUSION

Fetal DNA can be reliably detected in maternal plasma from early in pregnancy and normally is cleared within days of delivery.

Successful Diagnosis of Fetal Gender Using Conventional PCR Analysis of Maternal Serum

Background: Fetal DNA has been found in maternal plasma and serum. Diagnosis of fetal gender using maternal plasma and serum has been attempted in an effort to develop a new noninvasive method of prenatal diagnosis.

Methods: Peripheral blood samples were obtained from 61 pregnant women at 10–17 weeks of gestation before amniocentesis. DNA was extracted from 800 μL of each plasma or serum sample. To detect the Y-chromosome-specific sequences DYS14 and DYZ3 in the maternal plasma and serum, 40 cycles of PCR were carried out for each DNA extract. The PCR products were analyzed by 2.5% agarose gel electrophoresis and ethidium bromide staining, and the results were compared with the results of the cytogenetic analyses of amniocentesis.

Results: Cytogenetic analysis of amniocentesis revealed that 31 pregnant women had a male fetus and the remaining 30 pregnant women had a female fetus. Both DYS14 and DYZ3 were detected in 27 of the 31 plasma samples obtained from pregnant women carrying a male fetus and in all of 31 serum samples obtained from the same women. Neither DYS14 nor DYZ3 was detected in either the plasma or serum samples obtained from any of the 30 pregnant women carrying a female fetus.

Conclusion: PCR analysis of maternal serum can be used to diagnose fetal gender.

Fetal DNA in Maternal Plasma: Biology and Diagnostic Applications

Background: Molecular analysis of plasma DNA during human pregnancy has led to the discovery that maternal plasma contains both fetal and maternal DNA. This valuable source of fetal DNA opens up new possibilities for noninvasive prenatal diagnosis.

Approach: Published data from the last 3 years demonstrating the feasibility and utility of analyzing fetal DNA in maternal plasma are reviewed.

Content: The detection of fetal DNA in maternal plasma is much simpler and more robust than detecting fetal nucleated cells in maternal blood, and does not require prior enrichment. This approach has been shown to have application in the prenatal diagnosis of fetal rhesus D status, sex-linked disorders, and other paternally inherited genetic disorders. Abnormal fetal DNA concentrations in maternal plasma and serum have been found in common pregnancy-associated disorders, including preterm labor and preeclampsia, as well as in pregnancies complicated by fetal trisomy 21. After delivery, fetal DNA is cleared rapidly from maternal plasma, with a half-life in the order of minutes. These clearance kinetics exhibit an important difference from fetal cell clearance, where long-term persistence has been demonstrated.

Summary: It has been only 3 years since fetal DNA was first detected in maternal plasma, and much remains to be learned about the biology of this phenomenon. In addition, additional diagnostic applications beyond those discussed here can be expected in the near future.