Rapid clearance of fetal DNA from maternal plasma

Prospective study of fetal DNA in serum and disease activity during pregnancy in women with inflammatory arthritis

OBJECTIVE

Rheumatoid arthritis (RA) usually improves during pregnancy and recurs postpartum. Fetal cells and cell-free DNA reach the maternal circulation during normal pregnancy. The present study investigated dynamic changes in levels of fetal DNA in serum from women with RA and inflammatory arthritis during and after pregnancy to test the hypothesis that the levels of circulating fetal DNA correlate with arthritis improvement.

METHODS

Twenty-five pregnant patients were prospectively studied. A real-time quantitative polymerase chain reaction panel targeting unshared, paternally transmitted HLA sequences, a Y chromosome-specific sequence, or an insertion sequence within the glutathione S-transferase M1 gene was used to measure cell-free fetal DNA. Results were expressed as fetal genomic equivalents per milliliter (gE/ml) of maternal serum. Physical examinations were conducted during and after pregnancy.

RESULTS

Levels of fetal DNA in women with improvement in or remission of arthritis were higher than those in women with active disease, especially in the third trimester. Overall, an inverse relationship between serum fetal DNA levels and disease activity was observed (P < 0.001). Serum fetal DNA increased with advancing gestation, reaching median levels of 24 gE/ml (range 0-334), 61 gE/ml (range 0-689), and 199 gE/ml (range 0-2,576) in the first, second, and third trimesters, respectively, with fetal DNA clearance observed postpartum. Arthritis improvement was initially noted in the first trimester for most patients, increased further or was sustained with advancing gestation, and was active postpartum.

CONCLUSION

Changes in serum fetal DNA levels correlated with arthritis improvement during pregnancy and recurrence postpartum. Immunologic mechanisms by which pregnancy might modulate RA activity are described.

Non-invasive diagnosis of fetal sex; utilisation of free fetal DNA in maternal plasma and ultrasound

Non-invasive prenatal diagnosis is now a clinical reality, using both early ultrasound and molecular DNA methods. Technical advances in the sensitivity of the polymerase chain reaction (PCR), coupled with the finding that significant levels of fetal DNA (ffDNA) are found in maternal plasma and serum, has enabled the ready detection of paternally inherited genes or polymorphisms. Routine maternal plasma-based genotyping is now available for the determination of fetal sex and RHD blood group status (Van der Schoot et al., 2003). This review touches briefly on the ultrasound diagnoses and then focuses on the application of free ffDNA for fetal sex determination, indicating the Y-chromosome targets exploited in this strategy and the merits of their utilisation.

Genetic screening and diagnosis

PURPOSE OF REVIEW

To review the latest developments in screening and diagnosis of non-chromosomal genetic diseases.

RECENT FINDINGS

Major recent advances include the completion of the Human Genome Project, the use of microarray and related technologies for mass screening and diagnosis of thousands of genetic abnormalities, and non-invasive prenatal diagnosis using fetal DNA in maternal plasma.

SUMMARY

The rapid development in molecular biological technologies makes it possible to screen and to diagnosis thousands of genetic conditions, mutations and also predispositions to chronic diseases or traits, either prenatally or after birth. Clinical application of non-invasive prenatal diagnosis using fetal DNA in maternal plasma has become a reality. The arrival of the molecular genetic era also leads to many new ethical, social and medico-legal problems and dilemmas that obstetricians will have to face in the near future. There is an urgent need for the development of a new model for provision of genetic screening and diagnosis.

Noninvasive prenatal RHD genotyping by real-time polymerase chain reaction using plasma from D-negative pregnant women

OBJECTIVE

Prenatal noninvasive determination of fetal Rh status is an important aid to the management of hemolytic disease of the fetus and newborn. We performed real-time polymerase chain reaction on fetal DNA derived from maternal plasma to determine fetal Rh status.

STUDY DESIGN

Cell-free plasma DNA from 98 D-negative pregnant women was tested for the presence of exons 4, 5, and 10 of RHD. The presence of fetal DNA was confirmed by detection of SRY or biallelic insertion/deletion polymorphisms in the maternal plasma and buffy coat.

RESULTS

Seventy-two D-positive infants and 26 D-negative infants were determined by serologic studies. All 3 RHD exon sequences were detected in 68 of 72 mothers of D-positive infants. The presence of fetal DNA in mothers of D-negative infants was confirmed in all 10 boys and in 14 of 16 girls.

CONCLUSION

Fetal RHD genotyping in this study correctly predicted fetal Rh status in 92 of 98 (94%) cases.

Detection and quantification of mutations in the plasma of patients with colorectal tumors

The early detection of cancers through analysis of circulating DNA could have a substantial impact on morbidity and mortality. To achieve this goal, it is essential to determine the number of mutant molecules present in the circulation of cancer patients and to develop methods that are sufficiently sensitive to detect these mutations. Using a modified version of a recently developed assay for this purpose, we found that patients with advanced colorectal cancers consistently contained mutant adenomatous polyposis coli (APC) DNA molecules in their plasma. The median number of APC DNA fragments in such patients was 47,800 per ml of plasma, of which 8% were mutant. Mutant APC molecules were also detected in >60% of patients with early, presumably curable colorectal cancers, at levels ranging from 0.01% to 1.7% of the total APC molecules. These results have implications for the mechanisms through which tumor DNA is released into the circulation and for diagnostic tests based on this phenomenon.

Quantitative analysis of plasma HBV DNA for early evaluation of the response to transcatheter arterial embolization for HBV-related hepatocellular carcinoma

AIM: To assesse changes in plasma HBV DNA after TAE in HBV-related HCC and correlate the levels with the pattern of lipiodol accumulation on CT.

METHODS: Between April and June 2001, 14 patients with HBV-associated HCC who underwent TAE for inoperable or recurrent tumor were studied. Levels of plasma HBV DNA were measured by real-time quantitative PCR daily for five consecutive days after TAE. More than twofold elevation of circulating HBV DNA was considered as a definite elevation. Abdominal CT was performed 1-2 mo after TAE for the measurement of lipiodol retention.

RESULTS: Circulating HBV DNA in 10 out of 13 patients was elevated after TAE, except for one patient whose plasma HBV DNA was undetectable before and after TAE. In group I patients (n = 6), the HBV DNA elevation persisted for more than 2 d, while in group II (n = 7), the HBV DNA elevation only appeared for 1 d or did not reach a definite elevation. There were no significant differences in age or tumor size between the two groups. Patients in group I had significantly better lipiodol retention (79.31±28.79%) on subsequent abdominal CT than group II (18.43±10.61%) (P = 0.02).

CONCLUSION: Patients with durable HBV DNA elevation for more than 2 d correlated with good lipiodol retention measured 1 mo later, while others associated with poor lipiodol retention. Thus, circulating HBV DNA may be an early indicator of the success or failure of TAE.

Cell-free foetal DNA in maternal plasma does not appear to be derived from the rich pool of cell-free foetal DNA in amniotic fluid

BACKGROUND

Large quantities of cell-free foetal DNA have been detected in amniotic fluid, and it has been proposed that this material may contribute to the pool of cell-free foetal DNA in maternal plasma.

METHODS

Twelve maternal blood samples were obtained from pregnant women about to undergo an amniocentesis. Cell-free DNA was extracted from the maternal plasma samples and the matched amniotic fluid samples. The amount of cell-free foetal DNA was quantified by real-time PCR assays for the SRY and RHD genes.

RESULTS

Amniotic fluid was found to contain vast quantities of cell-free DNA (median concentration = 3,978 copies/ml amniotic fluid). The concentration of cell-free foetal DNA in maternal plasma was much lower (median concentration = 96.6 copies/ml maternal plasma). No significant correlation could, however, be determined between these two pools of cell-free foetal DNA.

CONCLUSIONS

Our data confirm that amniotic fluid contains prodigious quantities of cell-free foetal DNA, but as no relationship exists between this material and that in the maternal circulation, it is unlikely that the amnion contributes to the presence of cell-free foetal DNA in maternal plasma.

Preoperative serum DNA GSTP1 CpG island hypermethylation and the risk of early prostate-specific antigen recurrence following radical prostatectomy

PURPOSE

Hypermethylation of the CpG island at the promoter region of the pi-class glutathione S-transferase gene (GSTP1) is the most common somatic genome abnormality in human prostate cancer. We evaluated circulating cell-free DNA GSTP1 CpG island hypermethylation as a prognostic biomarker in the serum of men with prostate cancer.

EXPERIMENTAL DESIGN

Prostate cancer DNA GSTP1 CpG island hypermethylation was detected using a restriction endonuclease quantitative PCR technique. We analyzed preoperative serum from 85 men with clinically localized prostate cancer treated with radical prostatectomy and from 35 men with a negative prostate biopsy. We then assayed preoperative serum from a data set of 55 pairs of men with clinically localized prostate cancer treated with radical prostatectomy, matched for Gleason score, comprising 55 men suffering prostate-specific antigen (PSA) recurrence (median, 2 years) and 55 men who were free of disease at last follow-up (median, 3 years). The association of serum GSTP1 CpG island hypermethylation and PSA recurrence was determined.

RESULTS

Circulating cell-free DNA with GSTP1 CpG island hypermethylation was not detected in the serum of men with a negative prostate biopsy but was detected in 12% of men with clinically localized disease and 28% of men with metastatic cancer (P = 0.003). In the matched data set, eight men (15%) who developed PSA recurrence were positive for DNA with GSTP1 CpG hypermethylation, whereas no patient who was free of disease was positive for GSTP1 CpG island hypermethylation (McNemar test, chi(2) = 6.1, P = 0.01). In a multivariable analysis that accounted for recognized prognostic factors, the presence of serum DNA with GTSP1 CpG island hypermethylation was the most significant predictor of PSA recurrence (hazard ratio, 4.4; 95% confidence interval, 2.2, 8.8; P < 0.001).

CONCLUSION

Our study suggests that GSTP1 CpG island hypermethylation may be an important DNA-based prognostic serum biomarker for prostate cancer.

Diagnostic developments involving cell-free (circulating) nucleic acids

BACKGROUND

The detection of circulating nucleic acids has long been explored for the non-invasive diagnosis of a variety of clinical conditions. In earlier studies, detection of circulating DNA has been investigated for the detection of various forms of cancer. Metastasis and recurrence in certain cancer types have been associated with the presence of high levels of tumor-derived DNA in the circulation. In the case of pregnancies, detection of fetal DNA in maternal plasma is a useful tool for detecting and monitoring certain fetal diseases and pregnancy-associated complications. Similarly, levels of circulating DNA have been reported to be elevated in acute medical emergencies, including trauma and stroke, and have been explored as indicators of clinical severity. Apart from circulating DNA, much attention and effort have been put into the study of circulating RNA over the last few years. This area started from the detection of tumor-derived RNA in the plasma of cancer patients. Soon after that, detection of circulating fetal RNA in maternal plasma was described. Plasma RNA detection appears to be a promising approach for the development of gender- and polymorphism-independent fetal markers for prenatal diagnosis and monitoring. This development also opens up the possibility of non-invasive prenatal gene expression profiling by maternal blood analysis. Besides circulating DNA and RNA in plasma and serum, cell-free DNA in other body fluids, such as urine, has been detected in patients with different clinical conditions. Regardless of the sources of cell-free DNA for clinical use, the amount is frequently scarce.

METHODS

Technical advancements in detecting free DNA have been made over the years.

CONCLUSIONS

It is likely that further developments in the field of circulating nucleic acids will provide us with new diagnostic and monitoring possibilities over the next few years.

Cell-free fetal DNA in the maternal circulation and its future uses in obstetrics

OBJECTIVE

To provide an introduction to new technologies involving maternal plasma cell-free fetal DNA for non-invasive prenatal diagnosis and screening in obstetrics.

OPTIONS

Limited to introductory discussion of maternal plasma cell-free fetal DNA.

EVIDENCE

MEDLINE was searched to identify publications related to the topic after 1996. This document represents an abstraction of the information.

VALUES

This update is a consensus of the Genetics Committee of the Society of Obstetricians and Gynaecologists of Canada (SOGC).

BENEFITS, HARMS, AND COSTS

This update educates about new technology and its future use in obstetrics. At present, there is no harm or cost (research with limited clinical application) identified.

CONCLUSIONS

1. Significant and measurable amounts of cell-free fetal DNA are present in the maternal circulation and increase throughout pregnancy. 2. Different fetal (trisomy 21, trisomy 13) and placental abnormalities can affect the levels of cell-free fetal DNA within the maternal plasma. 3. Diagnostic and screening techniques may be able to utilize this cell-free fetal DNA in the future to provide non-invasive screening and diagnosis opportunities. This DNA technique is already well established for fetal sexing in pregnancies at risk of an X-linked disorder and fetal rhesus-D evaluation. Other conditions with well-identified unique paternal mutations can also reliably apply this cell-free fetal DNA technology for prenatal diagnosis. 4. The overall use of this molecular technology is still limited and requires the identification of sex-independent DNA markers so that female fetal DNA can be distinguished from maternal DNA, allowing its use in the screening or diagnosis of fetal and placental disease in pregnancies of either fetal sex.

Red Blood Cell Alloimmunization in Pregnancy

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

Fetal DNA detection in maternal plasma throughout gestation

The presence of fetal DNA in maternal plasma may represent a source of genetic material which can be obtained noninvasively. We wanted to assess whether fetal DNA is detectable in all pregnant women, to define the range and distribution of fetal DNA concentration at different gestational ages, to identify the optimal period to obtain a maternal blood sample yielding an adequate amount of fetal DNA for prenatal diagnosis, and to evaluate accuracy and predictive values of this approach. This information is crucial to develop safe and reliable non-invasive genetic testing in early pregnancy and monitoring of pregnancy complications in late gestation. Fetal DNA quantification in maternal plasma was carried out by real-time PCR on the SRY gene in male-bearing pregnancies to distinguish between maternal and fetal DNA. A cohort of 1,837 pregnant women was investigated. Fetal DNA could be detected from the sixth week and could be retrieved at any gestational week. No false-positive results were obtained in 163 women with previous embryo loss or previous male babies. Fetal DNA analysis performed blindly on a subset of 464 women displayed 99.4, 97.8 and 100% accuracy in fetal gender determination during the first, second, and third trimester of pregnancy, respectively. No SRY amplification was obtained in seven out of the 246 (2.8%) male-bearing pregnancies. Fetal DNA from maternal plasma seems to be an adequate and reliable source of genetic material for a noninvasive prenatal diagnostic approach.

Influence of Maternal-Fetal Histocompatibility and MHC Zygosity on Maternal Microchimerism

To investigate the relationship between maternal-fetal histocompatibility and maternal microchimerism, we developed a sensitive quantitative PCR assay for the neomycin resistance gene (neoR), and, in a mouse model system, used neoR as a noninherited maternal allele marker of maternal cells to detect and quantitate maternal microchimerism in tissues of neoR(-/-) N2 backcross progeny of (neoR(+/-))F(1) females mated with neoR(-/-) males. Using this approach, we obtained evidence for the presence of chimeric maternal cells in the brain, spleen, and thymus of all weanling and adult mice so tested. The numbers of chimeric maternal cells present in the spleen did not differ significantly from those in the thymus regardless of age or maternal-fetal histocompatibility. At all ages, brain tissue had higher level of maternal microchimerism than lymphoid tissue in mice MHC identical with their mothers, but the levels were similar in mice MHC disparate with their mothers. The levels of chimeric maternal cells in both brain and lymphoid tissue of mice with homozygous syngenicity and maternal allogenicity were similar, and tended to be higher than tissue-specific levels in mice with either combined maternal-fetal allogenicity or heterozygous syngenicity. Thus, MHC homozygous progeny had higher levels of maternal microchimerism than MHC heterozygous progeny. We conclude that normal mice possess small numbers of maternal cells in spleen, thymus, brain, and probably most other tissues, and that maternal-fetal histocompatibility influences the levels of these cells by mechanisms related to MHC zygosity of the progeny.

Recent advances in fetal nucleic acids in maternal plasma

The discovery of cell-free fetal DNA in maternal plasma in 1997 has opened up new possibilities for noninvasive prenatal diagnosis. Circulating fetal DNA molecules have been detected in maternal plasma from the first trimester onwards and can be robustly detected using a variety of molecular methods. This approach has been used for the prenatal investigation of sex-linked diseases, fetal RhD status, and prenatal exclusion of beta-thalassemia major. Recently, fetal RNA has also been found in maternal plasma. Such fetal RNA has been shown to originate from the placenta and to be remarkably stable. The use of microarray-based approaches has made it feasible to rapidly generate new circulating RNA markers. It is hoped that further developments in this field will make the routine and widespread practice of noninvasive nucleic acid-based prenatal diagnosis for common pregnancy-associated disorders feasible in the near future.

Persistent elevation of cell-free fetal DNA levels in maternal plasma after selective laser coagulation of chorionic plate anastomoses in severe midgestational twin-twin transfusion syndrome

OBJECTIVE

This study was undertaken to determine whether laser thermocoagulation for twin-twin transfusion syndrome (TTTS) causes increased cell-free fetal DNA levels in maternal plasma, potentially as a result of placental injury.

STUDY DESIGN

We enrolled 34 patients with twin pregnancies complicated by severe TTTS who underwent fetoscopic selective laser ablation of placental vascular anastomoses. Blood samples were drawn before and sequentially after the procedure. Fetal DNA in maternal plasma was quantified by polymerase chain reaction amplification of a Y-chromosome sequence.

RESULTS

Compared with baseline, median elevations of fetal DNA levels were 0.8% at 30 minutes ( P = .32), 15.8% at 60 minutes ( P = .1), 179.5% at 24 hours ( P = .003), and 172.9% at 48 hours ( P = .003). Factors associated with increased fetal DNA levels at 24 hours after procedure included longer operation time, higher number of vessels ablated, and subsequent in utero fetal death ( P = .01, .04, and .04, respectively).

CONCLUSIONS

Persistent elevation of fetal DNA levels in maternal plasma after laser ablation suggests that circulating fetal DNA could derive from placental injury. Plasma fetal DNA analysis may be an additional prognostic marker for fetal outcome after laser therapy.

Fragmentation of cell-free fetal DNA in plasma and urine of pregnant women

OBJECTIVES

We assessed the effect of freezing on fragmentation of fetal DNA in maternal plasma and differences in DNA fragmentation between plasma and urine from pregnant women.

METHODS

1. We prepared seven kinds of real-time PCR assays to amplify different-sized amplicons targeting the SRY gene. Fragmentation of fetal DNA in maternal plasma was compared between new (n=10) and 4-year-old samples (n=10). 2. To investigate differences in fragmentation of fetal DNA between plasma and urine from pregnant women, we amplified three different-sized amplicons and compared DNA fragmentation between plasma and urine (n=7).

RESULTS

1. Relative concentrations of fetal DNA compared to a 63-bp amplicon in new samples were 53.1, 42.0, 9.2 and 2.0% (median) for PCR amplicons of 107, 137, 193 and 313 bp, respectively. Concentrations in 4-year-old samples were 70.4, 40.9, 11.9 and 2.3%, respectively. 2. Although fetal DNA in urine was not detected for 107- and 137-bp amplicons of the SRY sequence, fetal DNA using a 63-bp amplicon was detectable in five of seven cases (71.4%).

CONCLUSION

Cell-free fetal DNA in maternal plasma is stable under cryopreservation at -20 degrees C for at least 4 years. Approximately, 60% of fetal DNA in maternal plasma was fragmented to <100-bp long, and fetal DNA in urine was further fragmented. Maternal urine may be usable for detection of fetal DNA, although smaller target size is more important for PCR amplification of fetal DNA in urine than in the analysis of plasma from pregnant women.

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.

Fetal cell-free DNA circulates in the plasma of pregnant mice: relevance for animal models of fetomaternal trafficking

BACKGROUND

Cell-free fetal DNA (fDNA) can be detected in maternal plasma throughout human pregnancy and is rapidly cleared after delivery. fDNA measurement has clinical application in many complications of pregnancy. Our aim was to determine if fDNA could be detected in maternal plasma during pregnancy in a mouse model system. We then compared the levels of fDNA during pregnancies in which the mother and fetus were either congenic or allogenic.

METHODS

C57BL/6J (H-2b) or DBA/2J (H-2d) wild-type female mice were mated to C57BL/6J mice transgenic for the enhanced green fluorescent protein (gfp) and sacrificed while pregnant. C57BL/6J female mice that had previously given birth to three to six litters after mating with transgenic males were sacrificed after delivery. We used real-time quantitative PCR amplification to detect and measure gfp sequences in maternal plasma.

RESULTS

fDNA was consistently detected in maternal plasma during pregnancy and was always absent after delivery [median 211 genome equivalents (GE)/ml vs 0 GE/ml, respectively, P=0.0001]. The level of fDNA was higher in allogenic matings compared to congenic matings (median 167 GE/ml/GFP + fetus vs 81 GE/ml/GFP + fetus, respectively).

CONCLUSIONS

fDNA sequences can be reliably detected in maternal plasma during murine pregnancy. Our data lends further support to the use of nonhuman species to investigate the mechanisms involved in fetomaternal trafficking.

Fetal blood group genotyping from DNA from maternal plasma: an important advance in the management and prevention of haemolytic disease of the fetus and newborn

The cloning of blood group genes and subsequent identification of the molecular bases of blood group polymorphisms has made it possible to predict blood group phenotypes from DNA with a reasonable degree of accuracy. The major application of this technology, which has now become the standard of care, is the determination of a fetal RHD genotype in women with anti-D, to assess whether the fetus is at risk of haemolytic disease of the fetus and newborn (HDFN). Initially, the procurement of fetal DNA required the invasive procedures of amniocentesis or chorionic villus sampling. Since the discovery of fetal DNA in maternal plasma in 1997, the technology of detecting an RHD gene in this very small quantity of fetal DNA has developed rapidly, so that non-invasive fetal D typing can now be provided as a diagnostic service for D-negative pregnant women with anti-D. Within a few years, it is probable that fetuses of all D-negative pregnant women will be tested for RHD, to establish whether the mother requires antenatal anti-D immunoglobulin prophylaxis.

Does percutaneous liver biopsy of hepatocellular carcinoma cause hematogenous dissemination? An in vivo study with quantitative assay of circulating tumor DNA using methylation-specific real-time polymerase chain reaction

OBJECTIVE

Our purpose was to find out whether percutaneous biopsy of hepatocellular carcinoma will cause significant dissemination of tumor into the circulation by quantitative analysis of circulating tumor DNA.

SUBJECTS AND METHODS

In this prospective study of 32 patients with suspected hepatocellular carcinoma who underwent sonographically guided liver biopsy, a peripheral venous blood sample was obtained before and 5 min after the procedure. Biopsy was performed using an 18-gauge biopsy gun. DNA was extracted from the plasma of the blood samples for methylation-specific polymerase chain reaction. Quantitative measures of the plasma tumor DNA were determined with real-time quantitative polymerase chain reaction, and the amount was expressed as a methylation index (%) in plasma.

RESULTS

Nineteen (59.4%) of 32 patients did not have detectable p16 tumor suppressor gene marker (p16M) in plasma before biopsy, and they showed no detectable plasma p16M after biopsy. Thirteen (65%) of 20 patients had p16M identified in the plasma before liver biopsy. Quantitative analysis of the plasma tumor DNA in these 13 patients showed no statistically significant difference in the methylation index before and after biopsy (p = 0.345, Wilcoxon's signed rank test).

CONCLUSION

No evidence exists that percutaneous liver biopsy results in hematogenous dissemination of hepatocellular carcinoma as shown by quantitative analysis of circulating tumor DNA (p16M) using methylation-specific real-time polymerase chain reaction.

Rapid clearance of fetal cells from maternal circulation after delivery

We previously reported increased apoptosis in the maternal circulation during pregnancy, partly accounting for the presence of cell-free fetal DNA in maternal plasma. In the current study, apoptosis was quantitated in 60 peripheral blood samples obtained from 15 women sequentially tested postpartum using the binding of annexin V. FISH with X/Y probes was performed on annexin V-positive cells isolated by MACS in patients with male fetuses to estimate the proportion of fetal cells among the apoptotic cell population. Twenty-four women at the thirty-seventh to thirty-eighth week of gestation and 35 nonpregnant females were used as controls. Apoptosis rate in the thirty-seventh to thirty-eighth week was 12.5% (9.2-14.7%). At 30 minutes, 12 hours, 24 hours, and 48 hours postpartum, it was 25.1% (16.8-28.5%), 12.5% (10.9-14.1%), 6.1% (4.8-7.1%), and 2.3% (1.3-3.0%), respectively. Male apoptotic cells were identified in all cases with male fetuses at 37 to 38 weeks of gestation, and the mean proportion was 9.9% (5.9-13.2%). The proportion of fetal cells 30 minutes after delivery was 14.8% (12.5-25.5%) and 12 hours postpartum 2.1% (0.8-4.1%). Male fetal apoptotic cells were detected in three of eight samples collected 24 hours after delivery from women who delivered males, at frequencies of 0.10%, 0.15%, and 0.25% (mean 0.16%). There were no fetal apoptotic cells 48 hours after delivery. Apoptosis partly accounts for the clearance of fetal cells from the maternal circulation. Because it is a rapid reaction, completed within 2-3 hours, persistence of fetal cells is possibly due to apoptosis-resistant progenitors or to defective regulation of apoptosis, leading to fetal cell microchimerism associated with autoimmune diseases.

Circulating nucleic acids and proteomics of plasma/serum: clinical utility

Circulating tumor-specific nucleic acids have been identified in plasma, serum, and other body fluids from cancer patients with tumors originating in almost any organ site. Polymerase chain reaction provides a highly sensitive and specific technique for the detection of these genetic changes in a limited amount of tissue/fluid. The presence of elevated levels of free DNA/RNA in many medical conditions, malignancy, and infectious processes is being investigated for screening, diagnosis, prognosis, surveillance for occult disease progression, identifying potential therapeutic targets, and monitoring treatment response. Additionally, elevated fetal DNA/RNA in maternal blood is being used to determine gender identity, assess chromosomal abnormalities, and monitor pregnancy-associated complications. Questions remain on the etiology, characteristics, stability, and potential pathologic consequences of cell-free DNA/RNA in the circulation. Nevertheless, nucleic acid-based assays that monitor plasma, serum, and body fluids provide a noninvasive, facile, and practical method for assessing patients. Proteomic profiling may prove complementary to a total functionality approach in providing a comprehensive evaluation of the patient's disease.

Recent developments in fetal DNA in maternal plasma

It has been several years since the presence of fetal DNA in maternal plasma was first discovered. Numerous potential applications have been reported to date. However, the study of maternal plasma for the prenatal diagnosis of fetal genetic traits has largely centered on paternally inherited autosomal dominant traits. Recently, a number of approaches have been developed that allow the prenatal assessment of autosomal recessive conditions through fetal DNA analysis in maternal plasma. On the other hand, aberrations in fetal DNA concentrations in maternal plasma have been reported in a number of pregnancy-associated conditions. Recent studies have begun to address the possible underlying mechanisms causing such quantitative aberrations. Current studies on circulating fetal DNA have focused on the detection of the paternally inherited fetal-specific alleles in maternal plasma. However, it has been demonstrated that the development of fetal epigenetic markers has great potential to expand the field.

Allelic imbalance on 12q22-23 in serum circulating DNA of melanoma patients predicts disease outcome

Allelic imbalance (AI) encompassing the apoptotic protease-activating factor 1 (APAF-1) locus (12q22-23) is found frequently in metastatic melanoma. Circulating DNA with AI on 12q22-23 in serum was evaluated as a surrogate marker to predict biochemotherapy (BC) treatment response in melanoma patients. Sera were collected from 49 American Joint Committee on Cancer stage IV melanoma patients treated with BC. Serum AI of the 12q22-23 region was demonstrated to be present before and/or after BC. BC responders showed a significantly lower frequency of AI (5 of 24, 21%) compared with nonresponders (11 of 20, 55%; Fisher's exact test, P < 0.029). Serum AI on 12q22-23 was associated with worse prognosis (log-rank test, P < 0.046). These findings indicate that serial serum genetic analysis of tumor-related AI on 12q22-23 may have clinical use in predicting tumor response to therapy.

Sex-determining region Y levels in maternal plasma: Evaluation in abnormal pregnancy

AIM

A number of studies for the measurement of cell-free fetal DNA in maternal blood have been reported; however, their clinical significance has remained unclear. We proposed to clarify the relationship between fetal DNA levels and obstetrical disorders.

METHODS

One hundred and eighty-five cases of normal pregnancy, ranging from 8 to 40 weeks' gestation, and 70 cases of abnormal pregnancy were included. SRY levels in maternal plasma were quantified with a real-time quantitative polymerase chain reaction.

RESULTS

Sex-determining region Y (SRY) levels and the number of patients with positive levels peaked at 33-36 weeks in normal pregnancy. The SRY levels in threatened abortion (11.6 +/- 4.8 copies/mL to 0 +/- 0, P < 0.05) and threatened preterm labor (44.6 +/- 16.1 copies/mL to 15.9 +/- 6.2, P < 0.01) were significantly higher than those of the normal group. In pre-eclamptic patients, SRY levels were markedly higher than those of the normal group (173.2 +/- 94.8 copies/mL to 22.4 +/- 8.9, P < 0.05). Patients with premature separation of the placenta (266.8 +/- 137.1 copies/mL to 4.9 +/- 3.7, P < 0.05) and placenta previa (167.7 +/- 32.4 copies/mL to 37.0 +/- 17.3, p <0.01) also showed elevated SRY levels.

CONCLUSION

Sex-determining region Y levels in maternal plasma were elevated in patients with an abnormal pregnancy, particularly those with placental injury of damage. These results suggested that increased SRY levels are consistently caused by the leak of fetal components, and thus the measurement of SRY levels in maternal plasma is useful for the evaluation of placental injuries.

Self-recognition and the role of fetal microchimerism

The course and severity of the autoimmune thyroid diseases (AITD) is known to be influenced by pregnancy as evidenced by disease suppression during pregnancy and initiation, or exacerbation, of disease postpartum. AITD is also known to affect both fertility and pregnancy outcome as evidenced by increased fetal loss. However, the precise mechanisms of this influence have not been fully understood. Here we have reviewed the mechanisms of self-recognition thought to be active in AITD and we have included recent information on the potential role of fetal microchimerism (exposure of paternal antigen to the mother during and after pregnancy).

Fetal Cell-Free Nucleic Acids in the Maternal Circulation: New Clinical Applications

Six years after the demonstration of the presence of cell-free fetal nucleic acids in maternal plasma, perinatal clinical applications continue to expand. The focus of this article is on advances that have occurred since the CNAPS II conference held in Hong Kong in 2001. Circulating fetal DNA levels (fDNA) are elevated in pregnancies complicated by fetal trisomies 13 and 21 but not 18. Measurement of fDNA levels improves the performance of the current standard maternal serum screen, by increasing the detection of Down syndrome cases by 5% with no increase in the false-positive rate. fDNA levels are elevated in women who have developed clinical symptoms of preeclampsia, but they are also elevated by the early second trimester in women who will eventually develop preeclampsia. fDNA and mRNA gamma globin measurement may have clinical utility as markers for fetomaternal hemorrhage in the late first trimester. Cell-free fetal DNA levels are quite high in the amniotic fluid, permitting fetal genomic isolation and analysis using comparative genomic hybridization techniques. Fetal DNA crosses the blood-brain barrier and is detectable in maternal cerebrospinal fluid in a subset of pregnant women. The biological implications of this are currently unknown. Review of the literature suggests that the placenta is the predominant source of the circulating fetal nucleic acids. However, detection of gamma globin mRNA sequences in the plasma of pregnant women suggests that fetal blood cells also contribute to the pool of nucleic acids. Widespread incorporation of fetal nucleic acid measurement into routine prenatal care depends on the identification of a readily accessible gender-independent fetal marker.

Free fetal DNA concentration in maternal plasma during normal labour at term

OBJECTIVE

Our aim was to investigate the effect of uterine contractions on free fetal DNA concentration in maternal plasma at term.

STUDY DESIGN

Nine pregnant women were admitted for elective induction of labour between 38 and 40 weeks of gestation. All patients carrying male fetuses and without history of pre-term labour and membrane rupture were selected. Maternal venous blood samples were serially collected every hour during labour, one hour after delivery and 24 h after delivery. In order to amplify fetal and total free DNA, primers for SRY and GAPDH genes were respectively chosen. Real- time PCR analysis was performed with an GeneAmp 5700 Sequence Detection System (Applied Biosystems Foster City, USA). Statistical significance was determined using the Wilcoxon test.

RESULT

Median concentration of fetal DNA in plasma before labour was 3081 copies/mL (Range 812-15 864 copies/mL). No significant difference between the number of copies per millilitre before any contractions and during labour was demonstrated. One hour after delivery, significant decrease in the fetal DNA rate was observed with a median concentration of 293 copies/mL (Range 0-2037 copies/mL) (p-value: 0.04). This drop was more significant 24 h after delivery with a median concentration of 0 copies/mL (Range 0-95 copies/mL) (p-value: 0.02).

CONCLUSIONS

During labour, no changes in free fetal DNA in maternal plasma were demonstrated. This suggests that labour does not have effect on free fetal DNA release in maternal circulation at term.

Cell-free fetal DNA in the cerebrospinal fluid of women during the peripartum period

OBJECTIVE

The purpose of this study was to determine whether cell-free fetal DNA is detectable in the cerebrospinal fluid of women during pregnancy and after delivery.

STUDY DESIGN

Cerebrospinal fluid was collected from 39 women who underwent an indicated spinal anesthesia procedure. Twenty-six samples were from women who carried at least 1 male fetus, and 13 samples were from women with only a female fetus. DNA was analyzed with the use of real-time polymerase chain reaction for DYS-1 (which represented male fetal DNA) and beta-globin (which represented maternal and fetal DNA).

RESULTS

beta-Globin DNA was detected in all cerebrospinal samples. DYS-1 gene sequences were detected in 4 cerebrospinal fluid samples from women who had male fetuses (2 samples were from women who underwent cesarean delivery of singleton pregnancies, 1 sample was from a triplet pregnancy, and 1 sample was from a woman after delivery). No male DNA was detected in the cerebrospinal fluid of women who carried female fetuses.

CONCLUSION

Male fetal cells and/or cell-free fetal DNA is detectable in the cerebrospinal fluid of some pregnant women or some women after delivery.

Circulating Fetal DNA: Its Origin and Diagnostic Potential—A Review

OBJECTIVE

In contrast to the traditional teaching that the placenta forms an impermeable barrier, multiple studies show that both intact fetal cells and cell-free nucleic acids circulate freely in maternal blood. Complications of pregnancy, such as pre-eclampsia, or fetal cytogenetic abnormalities, such as trisomy 21, increase transfusion of both intact fetal cells and cell-free fetal nucleic acids into the maternal circulation. The objective of our research is to show that abnormal feto-maternal trafficking of nucleic acids is associated with fetal and placental pathology, and that these observations may lead to novel non-invasive diagnostic and screening tests.

METHODS

Real-time quantitative PCR amplification of DYS1 is used to measure the levels of male fetal DNA in case-control sets of serum or plasma taken from pregnant women. In our laboratory, we use DYS1, a Y-chromosome specific gene, as a uniquely fetal DNA marker for the development of gestation-specific normal values and theoretical models.

RESULTS

Women carrying fetuses with trisomies 21 or 13 (but not 18) have increased levels of fetal DNA in their fresh or archived serum and/or plasma samples. Women destined to develop pre-eclampsia have a characteristic bi-phasic elevation of cell-free fetal DNA that precedes clinical symptoms. Data obtained from a variety of clinical scenarios suggest that the placenta is the predominant source of the circulating fetal nucleic acids, although apoptotic haematopoietic cells may contribute to the pool as well.

CONCLUSIONS

Fetal cell-free DNA is elevated in a number of conditions associated with placental pathology. Widespread clinical implementation of fetal DNA as a screening tool awaits discovery of a reliable gender-independent marker, which may be DNA polymorphisms, epigenetic markers, or mRNA. Fetal cell-free nucleic acids have potential for non-invasive monitoring of placental pathology.

Quantification of circulating Epstein-Barr virus (EBV) DNA in the diagnosis and monitoring of natural killer cell and EBV-positive lymphomas in immunocompetent patients

In Epstein-Barr-virus (EBV)-positive lymphomas in immunocompetent patients, release of EBV DNA from tumor cells into the plasma might be useful for disease monitoring and prognostication. To test this hypothesis, we quantified serially plasma EBV DNA by quantitative polymerase chain reaction in 39 cases of EBV-positive (natural killer [NK] cell, n = 23; T cell, n = 8; B cell, n = 4; Hodgkin, n = 4) lymphomas. As control, EBV DNA was undetectable in 34 cases of EBV-negative lymphomas at diagnosis and during chemotherapy. In all cases of EBV-positive lymphomas, EBV DNA was detectable (10(5)-10(10) copies/mL) at diagnosis. It paralleled the clinical course, with EBV DNA becoming undetectable at remission and remaining elevated in refractory disease. On multivariate analysis, high-presentation EBV DNA (> 7.3 x 10(7) copies/mL) was significantly associated with an inferior overall survival (OS). Subgroup analysis of NK cell lymphomas, the largest cohort in this study, showed that presentation EBV DNA was correlated with disease stage and lactate dehydrogenase. On multivariate analysis, high-presentation EBV DNA (> 6.1 x 10(7) copies/mL) was significantly associated with an inferior disease-free survival. During treatment, patients with EBV DNA that showed further increases or failed to become undetectable had significantly inferior OS. In EBV-positive lymphomas, plasma EBV DNA is valuable as a tumor biomarker and for prognostication.

Cell-free fetal DNA levels in maternal plasma after elective first-trimester termination of pregnancy

OBJECTIVE

To determine if first-trimester elective termination of pregnancy affects cell-free fetal DNA (fDNA) levels in maternal plasma.

DESIGN

Prospective cohort study.

SETTING

Clinical and academic research centers.

PATIENT(S)

One hundred thirty-four women who underwent first-trimester elective termination procedures.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Real-time polymerase chain reaction (PCR) amplification and measurement of DYS1, a Y-chromosome sequence, was used as a marker of fDNA.

RESULT(S)

We detected fDNA in pretermination samples from 27 out of 71 patients in the surgical arm, and 29 out of 63 patients in the medical arm. Based on confirmation of male gender in placental tissue, the sensitivity of fDNA detection is 92.6%. We detected fDNA as early as 32 days of gestation, which increased 4.2 genome equivalents/mL/week. In the surgical arm, the mean level of posttermination fDNA, adjusted for the clearance of fDNA in maternal blood, was higher than projected based on an expected increase with gestational age. In the medical arm, six patients had increased fDNA levels up to 11 days following termination.

CONCLUSION(S)

We found that fDNA can be reliably quantified in the early first trimester; fDNA elevation that occurs shortly after surgical termination may reflect fetomaternal hemorrhage or destruction of trophoblastic villi. Continued elevation of fDNA for several days may occur following medical termination.

[Contribution of genotyping for fetal sex determination in maternal serum for preimplantation genetic diagnosis of X-linked diseases]

OBJECTIVE

Couples with a risk of transmitting X-linked diseases included in a preimplantation genetic diagnosis (PGD) center need early and rapid fetal sex determination during pregnancy in two situations. The first situation corresponds to control of embryo sexing after PGD, the second one being that of couples in PGD program having a spontaneous pregnancy. Determination of fetal sex can be achieved by karyotyping using invasive procedures such as chorionic villus sampling (CVS), amniocentesis or cordocentesis and by non-invasive procedures such as ultrasound (US) examination. CVS is the earliest invasive procedure for fetal sex determination and molecular analysis of X-linked genetic disorders during the first trimester but it is associated with a risk of fetal loss. US allows reliable fetal sex determination only during the second trimester. Recently, reliable non-invasive fetal sex determination was realized by using SRY gene amplification in maternal serum.

PATIENTS AND METHODS

We report the prospective use of fetal sex determination in maternal serum in our PGD center. Management of pregnancies was performed using this non-invasive procedure in four cases of embryo sexing control and nine cases of spontaneous pregnancies in couples included in PGD program for X-linked diseases.

RESULTS

Fetal sex results using SRY gene amplification on maternal serum were in complete concordance with fetal sex observed by cytogenetic analysis or US examination, as well as at birth.

DISCUSSION AND CONCLUSION

This new strategy allowed rapid sex determination during the first trimester and permitted to avoid performing invasive procedures in nine pregnancies.

Fetal DNA quantitation in peripheral blood is not useful as a marker of disease severity in women with preeclampsia

OBJECTIVE

Trophoblast migration into the maternal circulation is increased in preeclampsia and can trigger the endothelial dysfunction that characterizes the clinical disease. We hypothesised that 'fetal trafficking' is increased in women with severe preeclampsia and that the quantity of trafficking is greater in women with more severe disease.

STUDY DESIGN

To test the hypothesis, we used a technique that quantifies a genetic marker specific for the fetomaternal unit, that is, the SRY gene in a pregnant woman carrying a male fetus. Thirty two women with pre-eclampsia and 32 control women (women without preeclampsia) were recruited. Preeclampsia was defined according to the International Society for the Study of Hypertension in Pregnancy (ISSHP). All subjects with preeclampsia had evidence of the multisystemic nature of the disease. DNA was extracted from maternal peripheral blood and RTQ PCR analysis was performed to quantify the fetal DNA (SRY) and the total DNA (beta-actin) in each sample. The ratio of fetal to total DNA was calculated and compared between women with preeclampsia and controls.

RESULTS

The women with preeclampsia and the control women did not differ in parity, blood pressure at booking, and gestational age at sampling. The groups differed significantly in age (29 +/- 5.7 vs 25 +/- 5.1 years; P =.007), diastolic blood pressure (DBP) at sampling (101 +/- 9.5 vs 70 +/- 5.5 mm Hg; P <.0001), gestational age at delivery (33 +/- 4.3 vs 39 +/- 1.8 weeks; P <.001), and fetal weight (1.98 +/- 1 vs 3.35 +/- 0.5 kgs; P <.0001). SRY was detected in 31 out of 32 women with preeclampsia and in 24 out of 32 control women (P <.001). The median SRY copy number per micro L was greater in women with preeclampsia (10.6, interquartile range 12.89) than in the control women (8.6, interquartile range 20.1) but these differences were not statistically significant at P =.75. The median ratio of fetal to total DNA was almost identical in both groups (0.06, interquartile range 0.13) in PET compared to (0.06, interquartile range 0.17) the control women. No correlation was found between the quantity of fetal DNA and disease severity.

CONCLUSION

Fetal trafficking is more likely to be detected in women with preeclampsia compared to control women but the quantity does not appear to correlate with disease severity.

Fetal cells and DNA in maternal blood

Although fetal cells have been known to escape to the maternal circulation for a number of years, research attempts to use them for prenatal diagnosis have not had any consistent success. This review attempts to trace the history of such attempts and to document their progress and reasons for success or failure. The opinions of recent conferences including that of the US National Institute of Child Health and Human Development, a sponsor of major US research in the field, are reported and discussed. It is concluded that although basic work has demonstrated the biologic availability of both fetal cells and their free DNA representatives in the maternal circulation at gestational ages relevant to prenatal diagnosis, much work remains to develop practical technology for their consistent recovery and assay.