Fluctuation of maternal and fetal free extracellular circulatory DNA in maternal plasma

A Reliable Method for Quantifying Plasma Cell-Free DNA Using an Internal Standard Strategy: Evaluation in a Cohort of Non-Pregnant and Pregnant Women

The use of plasma cell-free DNA (cfDNA) as a useful biomarker in obstetric clinical practice has been delayed due to the lack of reliable quantification protocols. We developed a protocol to quantify plasma cfDNA using an internal standard strategy to overcome difficulties posed by low levels and high fragmentation of cfDNA. cfDNA was isolated from plasma samples of non-pregnant (NP, n = 26) and pregnant (P, n = 26) women using a commercial kit and several elution volumes were evaluated. qPCR parameters were optimized for cfDNA quantification, and several quantities of a recombinant standard were evaluated as internal standard. Absolute quantification was performed using a standard curve and the quality of the complete method was evaluated. cfDNA was eluted in a 50-μl volume, actin-β (ACTB) was selected as the target gene, and qPCR parameters were optimized. The ACTB standard was constructed and 1000 copies were selected as internal standard. The standard curve showed R2 = 0.993 and E = 109.7%, and the linear dynamic range was defined between 102 and 106 ACTB copies/tube. Repeatability and reproducibility in terms of CV were 19% and up to 49.5% for ACTB copies per milliliter of plasma, respectively. The range of cfDNA levels was 428-18,851 copies/mL in NP women and 4031-2,019,363 copies/mL in P women, showing significant differences between the groups. We recommend the application of internal standard strategy for a reliable plasma cfDNA quantification. This methodology holds great potential for a future application in the obstetric field.

Extracellular DNA Correlates with Intestinal Inflammation in Chemically Induced Colitis in Mice

Circulating extracellular DNA (ecDNA) is known to worsen the outcome of many diseases. ecDNA released from neutrophils during infection or inflammation is present in the form of neutrophil extracellular traps (NETs). It has been shown that higher ecDNA concentration occurs in a number of inflammatory diseases including inflammatory bowel disease (IBD). Enzymes such as peptidyl arginine deiminases (PADs) are crucial for NET formation. We sought to describe the dynamics of ecDNA concentrations and fragmentation, along with NETosis during a mouse model of chemically induced colitis. Plasma ecDNA concentration was highest on day seven of dextran sulfate sodium (DSS) intake and the increase was time-dependent. This increase correlated with the percentage of cells undergoing NETosis and other markers of disease activity. Relative proportion of nuclear ecDNA increased towards more severe colitis; however, absolute amount decreased. In colon explant medium, the highest concentration of ecDNA was on day three of DSS consumption. Early administration of PAD4 inhibitors did not alleviate disease activity, but lowered the ecDNA concentration. These results uncover the biological characteristics of ecDNA in IBD and support the role of ecDNA in intestinal inflammation. The therapeutic intervention aimed at NETs and/or nuclear ecDNA has yet to be fully investigated.

Diurnal stability of cell-free DNA and cell-free RNA in human plasma samples

Many emerging technologies are reliant on circulating cell-free DNA (cfDNA) and cell-free RNA (cfRNA) applications in the clinic. However, the impact of diurnal cycles or daily meals on circulating analytes are poorly understood and may be confounding factors when developing diagnostic platforms. To begin addressing this knowledge gap, we obtained plasma from four healthy donors serially sampled five times during 12 h in a single day. For all samples, we measured concentrations of cfDNA and cfRNA using both bulk measurements and gene-specific digital droplet PCR. We found no significant variation attributed to blood draw number for the cfDNA or cfRNA. This indicated that natural diurnal cycles and meal consumption do not appear to significantly affect abundance of total cfDNA, total cfRNA, or our two selected cfRNA transcripts. Conversely, we observed significant variation between individual donors for cfDNA and one of the cfRNA transcripts. The results of this work suggest that it will be important to consider patient-specific baselines when designing reliable circulating cfDNA or cfRNA clinical assays.

Day-to-day and within-day biological variation of cell-free DNA

BACKGROUND

Numerous studies have shown that cell-free DNA (cfDNA) levels may serve as a non-invasive biomarker of a broad spectrum of acute and chronic pathologies. However, in order to make clinical decisions based on cfDNA measurements, it is essential to understand the magnitude of biological variation so this variation is not confused with a variation that actually represent a clinically relevant change. The present study was designed to evaluate the biological variation of cfDNA in healthy subjects and lung cancer patients.

METHODS

Plasma samples were collected from 33 healthy subjects and ten lung cancer patients over three days, as well as during the same day. CfDNA was quantified using droplet digital PCR. Biological variation data was estimated using mixed models.

FINDINGS

The within-subject variation was 25% and the between-subject variation was 30%. The reference change value for the healthy subjects was 70%. There was no systematic difference in cfDNA levels from day-to-day (p = 0⋅61), but there was a significant decline during the day (p<0⋅01). The within-subject variation in cancer patients was comparable to healthy subjects, whereas the between-subject variation was much larger (139%). No systematic differences from day-to-day were observed for the cancer patients (p>0⋅3).

INTERPRETATION

Our findings show that cfDNA levels fluctuate significantly during the day and exhibit considerable within-subject variation. Thus, the data presented offer a substantial contribution to the interpretation of the clinical significance of cfDNA.

FUNDING

Læge Sofus Carl Emil Friis og hustru Olga Doris Friis' Legat, Harboefonden, and Dagmar Marshalls Fond.

Sex, Age, and Bodyweight as Determinants of Extracellular DNA in the Plasma of Mice: A Cross-Sectional Study

Extracellular DNA (ecDNA) is studied as a possible biomarker, but also as a trigger of the immune responses important for the pathogenesis of several diseases. Extracellular deoxyribonuclease (DNase) activity cleaves ecDNA. The aim of our study was to describe the interindividual variability of ecDNA and DNase activity in the plasma of healthy mice, and to analyze the potential determinants of the variability, including sex, age, and bodyweight. In this experiment, 58 adult CD1 mice (41 females and 31 males) of a variable age (3 to 16 months old) and bodyweight (females 25.7 to 52.1 g, males 24.6 to 49.6 g) were used. The plasma ecDNA was measured using a fluorometric method. The nuclear ecDNA and mitochondrial ecDNA were quantified using real-time PCR. The deoxyribonuclease activity was assessed using the single radial enzyme diffusion method. The coefficient of variance for plasma ecDNA was 139%, and for DNase 48%. Sex differences were not found in the plasma ecDNA (52.7 ± 73.0 ηg/mL), but in the DNase activity (74.5 ± 33.5 K.u./mL for males, and 47.0 ± 15.4 K.u./mL for females). There were no associations between plasma ecDNA and bodyweight or the age of mice. Our study shows that the variability of plasma ecDNA and DNase in adult healthy mice is very high. Sex, age, and bodyweight seem not to be major determinants of ecDNA variability in healthy mice. As ecDNA gains importance in the research of several diseases, it is of importance to understand its production and cleavage. Further studies should, thus, test other potential determinants, taking into account cleavage mechanisms other than DNase.

The cell-free fetal DNA fraction in maternal blood decreases after physical activity

OBJECTIVE

If noninvasive prenatal testing using next generation sequencing is to be effective for pregnant women, a cell-free fetal DNA (cffDNA) fraction above 4% is essential unless the depth of sequencing is increased. This study's objective is to determine whether physical activity has an effect on the proportion of cell-free DNA (cfDNA) arising from the fetus (fetal fraction).

METHODS

Nine pregnant women carrying male fetuses at gestational age 12(+0)  weeks to 14(+6)  weeks were included. Plasma from nine pregnant women was drawn prior to, immediately after, and 30 min after 30 min of cycling with a pulse-rate of 150 beats per minute. The concentrations of cffDNA (DYS14) and cfDNA (RASSF1A) were assessed using quantitative real-time polymerase chain reaction.

RESULTS

The fetal fraction decreased significantly in all participants after physical activity (p < 0.01), a decrease varying from 1-17 percentage points. This was due to a significant increase in the concentration of cfDNA (p < 0.01), whereas the concentration of cffDNA remained the same. This alteration of the fetal fraction was not present 30 min after physical activity.

CONCLUSION

When planning the timing of noninvasive prenatal diagnosis based on the fetal fraction, physical activity prior to sampling should be avoided.

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.

Noninvasive fetal sex determination using cell-free fetal DNA: a systematic review and meta-analysis

CONTEXT

Noninvasive prenatal determination of fetal sex using cell-free fetal DNA provides an alternative to invasive techniques for some heritable disorders. In some countries this testing has transitioned to clinical care, despite the absence of a formal assessment of performance.

OBJECTIVE

To document overall test performance of noninvasive fetal sex determination using cell-free fetal DNA and to identify variables that affect performance.

DATA SOURCES

Systematic review and meta-analysis with search of PubMed (January 1, 1997-April 17, 2011) to identify English-language human studies reporting primary data. References from review articles were also searched.

STUDY SELECTION AND DATA EXTRACTION

Abstracts were read independently to identify studies reporting primary data suitable for analysis. Covariates included publication year, sample type, DNA amplification methodology, Y chromosome sequence, and gestational age. Data were independently extracted by 2 reviewers.

RESULTS

From 57 selected studies, 80 data sets (representing 3524 male-bearing pregnancies and 3017 female-bearing pregnancies) were analyzed. Overall performance of the test to detect Y chromosome sequences had the following characteristics: sensitivity, 95.4% (95% confidence interval [CI], 94.7%-96.1%) and specificity, 98.6% (95% CI, 98.1%-99.0%); diagnostic odds ratio (OR), 885; positive predictive value, 98.8%; negative predictive value, 94.8%; area under curve (AUC), 0.993 (95% CI, 0.989-0.995), with significant interstudy heterogeneity. DNA methodology and gestational age had the largest effects on test performance. Methodology test characteristics were AUC, 0.988 (95% CI, 0.979-0.993) for polymerase chain reaction (PCR) and AUC, 0.996 (95% CI, 0.993-0.998) for real-time quantitative PCR (RTQ-PCR) (P = .02). Gestational age test characteristics were AUC, 0.989 (95% CI, 0.965-0.998) (<7 weeks); AUC, 0.994 (95% CI, 0.987-0.997) (7-12 weeks); AUC, 0.992 (95% CI, 0.983-0.996) (13-20 weeks); and AUC, 0.998 (95% CI, 0.990-0.999) (>20 weeks) (P = .02 for comparison of diagnostic ORs across age ranges). RTQ-PCR (sensitivity, 96.0%; specificity, 99.0%) outperformed conventional PCR (sensitivity, 94.0%; specificity, 97.3%). Testing after 20 weeks (sensitivity, 99.0%; specificity, 99.6%) outperformed testing prior to 7 weeks (sensitivity, 74.5%; specificity, 99.1%), testing at 7 through 12 weeks (sensitivity, 94.8%; specificity, 98.9%), and 13 through 20 weeks (sensitivity, 95.5%; specificity, 99.1%).

CONCLUSIONS

Despite interstudy variability, performance was high using maternal blood. Sensitivity and specificity for detection of Y chromosome sequences was greatest using RTQ-PCR after 20 weeks' gestation. Tests using urine and tests performed before 7 weeks' gestation were unreliable.

Non-invasive aneuploidy detection using free fetal DNA and RNA in maternal plasma: recent progress and future possibilities

BACKGROUND

Cell-free fetal DNA (cff DNA) and RNA can be detected in maternal plasma and used for non-invasive prenatal diagnostics. Recent technical advances have led to a drastic change in the clinical applicability and potential uses of free fetal DNA and RNA. This review summarizes the latest clinical developments in non-invasive prenatal diagnosis in the context of the latest technical developments.

METHODS

We searched PubMed with the search terms 'prenatal', 'non-invasive', 'fetal DNA', 'mRNA' and cross-referenced them with 'diagnostics', 'microRNA', 'aneuploidy', 'trisomy' and 'placenta'. We also searched the reference list of the articles identified by this search strategy.

RESULTS

Genome-wide methods have been, or can be, successfully applied on total DNA (DNA-seq), methylated DNA immunoprecipitation (with tiling array), microRNA (Megaplex) and total RNA (RNA-seq). Chromosome- or gene-specific assays have been successively applied on placenta RNA (allele ratio) or DNA multiplex ligation-dependent probe amplification (MLPA). These methods are reviewed for their merits and pitfalls with consideration of the placental biology. For the purpose of clarity, the technical and clinical characteristics are limited to non-invasive prenatal detection of chromosomal aneuploidies, with emphasis on trisomy 21.

CONCLUSIONS

The technical advances for non-invasive aneuploidy tests based on cff DNA and placental mRNA in maternal plasma have been enormous. Multimarker assays including genome-wide approaches with the option of qualitative information on variation (polymorphism or mutation) besides quantitative information are the preferred methods of choice. The time for population-based, double blind, large-scale clinical cohort trials has come.

Cell-free DNA in the plasma of patients with systemic sclerosis

The aim of the present study was to evaluate the concentration of cell-free DNA (cf-DNA) in the plasma of patients with systemic sclerosis (SSc) and to examine the correlation of cf-DNA with clinical variables of the disease. The study population consisted of 122 SSc patients and 16 healthy controls. Epidemiological and clinical data were collected by direct assessment. The beta-globin gene was used to determine the total amount of DNA in the plasma by real-time quantitative PCR analysis. cf-DNA was found in all patients (mean concentration 1,420.7 copies/ml) and controls (mean concentration 1,462.5), with no significant difference. In SSc patients, no correlation was found between cf-DNA and the type of organ involvement, but patients with active disease presented significantly higher cf-DNA concentrations than those with inactive disease (p < 0.05). Our data suggest that cf-DNA could provide a useful biomarker for the assessment of disease activity in SSc patients.

Assessment of the female fetal DNA concentration in the plasma of the pregnant women as preeclampsia indicator--preliminary report

OBJECTIVES

This research was designed to analyze the presence of fetal female DNA, expressed in copy number, in the plasma of the pregnant woman with preeclampsia-complicated pregnancy.

STUDY DESIGN

Twenty-four pregnant women with female fetuses identified by means of ultrasound scanning were enrolled in this pilot study. The study group consisted of 12 pregnant women with symptoms of preeclampsia, with 12 healthy women, matched for gestational age, as controls.

RESULTS

Mean DNA number of genomic equivalents per reaction in the group was 201 geq/PCR (from 44.9 to 375) and increased over time after onset of PE, which was the reason for pregnancy termination. In the group of women with preeclampsia, a notably higher DNA copy number in comparison to the control group was noted (p=0.0003 U Mann-Whitney test).

CONCLUSIONS

The pilot study presented in this work confirms that also in the case of preeclampsia-complicated pregnancy with female fetuses it is possible to implement the method of fetal DNA quantification. Use of the presented methods confirms that in severe preeclampsia-complicated pregnancies an increase of the number of DNA genomic equivalents per reaction in comparison to the control group is observed. Due to the small study group further research on the described issue is vital, but this study proves that it is also feasible among women carrying female fetuses.

Prenatal RhD Testing: A Review of Studies Published from 2006 to 2008

The availability of noninvasive prenatal diagnosis for the fetal RhD status (NIPD RhD) is an obvious benefit for alloimmunized pregnant women. This review gives information about the performance characteristics of current diagnostic technologies and recent promising proof-of-principle studies. Notably, during the past 3 years almost twice as much samples have been investigated with NIPD RhD compared with the studies from 1998 to 2005. Thus we have now a lot more information compared with the knowledge before 2006. There is no doubt that funding of the SAFE Network of Excellence (2004-2009) from the European Commission within the framework 6 program has massively increased the worldwide experience in NIPD RhD. In 2009 European funding has been stopped. Because of this large investment from public funding sources, it is now the duty of policy makers (scientific boards, patient groups, physician organizations, and health assurances) to discuss if targeted antenatal Rh prophylaxis should be introduced in German-speaking countries or which additional data are required to make a decision and how these additional studies should be funded.

The effect of labour and placental separation on the shedding of syncytiotrophoblast microparticles, cell-free DNA and mRNA in normal pregnancy and pre-eclampsia

The clinical features of the maternal syndrome of pre-eclampsia can be explained by generalised maternal endothelial cell dysfunction, which is a part of a more global maternal systemic inflammatory response. There is growing evidence that these effects are associated with the shedding of cellular debris, including syncytiotrophoblast microparticles (STBM), cell-free DNA and mRNA, from the surface of the placenta (syncytiotrophoblast) into the maternal circulation. The increased shedding of this debris seen in pre-eclampsia is believed to be caused by placental ischaemia, reperfusion and oxidative stress. This study was carried out to determine whether uterine contractions during labour and subsequent placental separation lead to an acute increase in the release of placental debris into the maternal circulation. To assess the effects of labour, samples were taken from 10 normal pregnant (NP) and 10 pre-eclamptic (PE) women at varied time points. Similarly to assess the effects of placental delivery, plasma samples were taken from 10 NP and 10 PE women undergoing elective caesarean section. There was a significant increase in the shedding of STBM in pre-eclampsia which was not seen in normal pregnancy and there was a small rise in STBM levels at placental separation in both normal pregnant and pre-eclamptic women undergoing caesarean section, but the differences were not significant. However, levels of placental cell-free corticotrophin releasing hormone mRNA were significantly increased in labour in both normal pregnancy and pre-eclampsia and were still high 24 h after delivery in the pre-eclamptic women. There was no significant increase in fetal or total DNA in labour, but the overall levels of total DNA (maternal and fetal) was increased in labour in pre-eclampsia compared to normal labour. The enhanced shedding of STBM and CRH mRNA in pre-eclampsia labour may have a role in cases of postpartum worsening of pre-eclampsia.

Circulating nucleic acids (CNAs) and cancer--a survey

It has been known for decades that it is possible to detect small amounts of extracellular nucleic acids in plasma and serum of healthy and diseased human beings. The unequivocal proof that part of these circulating nucleic acids (CNAs) is of tumor origin, initiated a surge of studies which confirmed and extended the original observations. In the past few years many experiments showed that tumor-associated alterations can be detected at the DNA and RNA level. At the DNA level the detection of point mutations, microsatellite alterations, chromosomal alterations, i.e. inversion and deletion, and hypermethylation of promoter sequences were demonstrated. At the RNA level the overexpression of tumor-associated genes was shown. These observations laid the foundation for the development of assays for an early detection of cancer as well as for other clinical means.

The struggle to detect circulating DNA

In various diseases, such as cancer, autoimmune disease, sepsis or myocardial infarction, elevated levels of circulating DNA can be measured. However, its predictive value is under debate. Circulating DNA in plasma is protein-bound (nucleosomal) DNA. Quantification of circulating DNA can be performed by real-time quantitative PCR or immunological methods such as ELISA. The diagnostic value of both methods can be impaired by inappropriate handling of the samples. Assessment of circulating DNA in patients admitted to the intensive care unit offers a tool for predicting morbidity and mortality.

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.

Noninvasive determination of fetal RHD status by examination of cell-free DNA in maternal plasma

BACKGROUND

Cell-free fetal DNA in maternal plasma opens the way for routine risk-free diagnosis of fetal D status of D- mothers. The focus was on accuracy of RHD typing and confirmation of fetal DNA in maternal plasma while RHD was not detected.

STUDY DESIGN AND METHODS

Plasma DNA was extracted (by manual and/or automatic method) from 255 D- pregnant women and amplified in exons 7 and 10 and intron 4 of RHD gene with real-time polymerase chain reaction. The presence of fetal DNA was confirmed by testing SRY and, when negative, by one of 11 different polymorphisms found in the father but not in the mother. The results were compared with the D status of the newborns.

RESULTS

After exclusion of 25 cases (10%) because of material shortage, in 230 cases (90%) available for complete study, the predictive value of the procedure of fetal RHD testing (RHD genotyping plus confirmation of fetal DNA) was 99.6 percent. SRY detection confirmed fetal DNA presence in maternal plasma in all boys, whereas the detection of various polymorphisms in all girls but one.

CONCLUSIONS

Fetal RHD genotyping from maternal plasma may be used with confidence, although additional polymorphisms for confirmation of fetal DNA should be included for 100 percent predictive value (instead of 99.6%).

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.

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.

Prenatal genotyping of RHD and SRY using maternal blood

BACKGROUND AND OBJECTIVES

The aim of the study was to perform fetal RHD genotyping in maternal plasma using a fluorescent polymerase chain reaction (PCR) technique. Duplex PCR, amplifying RHD and SRY in the same tube, was undertaken. The effect of varying storage temperatures on the concentration of fetal DNA was investigated in a separate study involving 10 RhD-negative pregnant women.

MATERIALS AND METHODS

Primers and probes for the RHD gene's exon 7 and the sex-determining region, Y, were designed, and monoplex and duplex PCR were performed. Blood samples from 10 RhD-negative women were split into four and treated in four different ways before measuring the concentration of fetal DNA by quantitative PCR.

RESULTS

DNA extracted from the plasma of 114 RhD-negative pregnant women was tested for the presence of fetal RHD. The discrepancy between genotyping and serological RhD typing of the babies postpartum was 8% when counting one positive replicate as a positive result. Duplex PCR, amplifying RHD and SRY in the same tube, showed a reduced sensitivity for amplification of the SRY gene segment. There was a statistically significant reduction of fetal DNA in blood samples stored at room temperature for 48 h compared with the same sample stored at a temperature of <10 degrees C for the same length of time.

CONCLUSIONS

This method is not suitable for routine analysis because of the lack of a positive control for RHD-negative female fetuses and a decrease in PCR sensitivity when performing duplex PCR. Fetal DNA in maternal plasma is better preserved when the blood sample is kept cool.

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.

Circulating DNA in plasma and serum: biology, preanalytical issues and diagnostic applications

The recent studies in circulating nucleic acids have brought about a new dimension to medical diagnostics. In oncology, various tumor-associated molecular alterations have been detected in the plasma/serum of cancer patients. These findings have important implications for the diagnosis, prognostication and monitoring of many types of malignancies. In pregnancy, the discovery of fetal DNA in maternal circulation has opened up a new source of fetal genetic material for noninvasive analysis for numerous fetal conditions and detection of certain pregnancy-associated disorders. The measurement of circulating DNA has also found potential application in the post-treatment monitoring of transplant patients and the assessment and prognostication of trauma patients. Although much attention has focused on circulating DNA, the knowledge of its biology is still at an early stage. For example, the origin and mechanisms of release of circulating DNA remain to be elucidated. The eventual clinical application of circulating DNA technology would also require the thorough elucidation of preanalytical factors that may affect its measurement in clinical laboratories.

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.

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.