Συμβολή στη μοριακή προγεννητική διάγνωση ανευπλοειδιών και φύλου με χρήση μεθόδων αλυσιδωτής αντίδρασης πολυμεράσης

To clarify the origin of cell-free fetal DNA in maternal plasma, we analyzed bidirectional transfer of plasma DNA between fetus and mother. We analyzed maternal and fetal plasma DNA obtained from 15 pregnant women at the time of Cesarean section. The subjects were five patients with preeclampsia and 10 gestational-age-matched normal controls. DNA was extracted from 1.5-ml plasma samples and the cellular fraction of maternal and umbilical blood. Seven polymorphic marker genes were analyzed. The relative concentration of fetal DNA in maternal plasma and maternal DNA in cord blood were evaluated. The relative concentration of maternal DNA in fetal circulation (median, 0.9%; range, 0.2-8.4%) was significantly lower than that of fetal DNA in maternal blood (14.3%, 2.3-64%), with P=0.007. The relative concentration of maternal DNA in fetal blood was not affected by preeclampsia. These findings indicate that cell-free DNA is unequally transferred through the placenta. The structural characteristics of the placenta suggest that the majority of cell-free fetal DNA in maternal plasma is derived from villous trophoblasts.

Objective To assess the clinical value of fetal chromosomal aneuploidy diagnosed by free fetal DNA in maternal plasma in 11-13+6 gestational weeks.Methods A total of 2 650 pregnant women who had prenatal care in Tianjin Center Hospital of Obstetrics and Gynecology from January 1,2010 to December 31,2010 were included.Each of them had an ultrasound scan to measure fetal nuchal translucency thickness.Maternal serum free β-human chorionic gonadotropin and pregnancy-associated plasma protein A test was performed as part of screening for chromosomal abnormalities.Results of ultrasound and maternal plasma biochemical analysis were entered into the database,and converted into multiple of median (MoM) by factors such as maternal age,weight,ethnicity,smoking history and mode of conception.The cutoff value was 1 ∶ 270.Meanwhile,20 cases had cell free fetal DNA (cffDNA) test and the ratio of the single nucleotide polymorphism on two alleles of plancenta-specific 4 (PLAC4) were measured in 16 cases.T-test,rank sum test,MannWhitney U test and Chi-square test were used as statistical methods.Results (1) A total of 74 cases were judged as high-risk,among which 35 cases underwent transabdominal chorionic villus sampling (18 cases had cffDNA test),37 cases underwent amniocentesis at the week of 20,and two cases of Rh negative did not receive the invasive examination.Totally 20 cases,including two Rh negative cases,had the cell-free fetal DNA test.(2) By cffDNA test of maternal plasma,two cases of 21 trisomy,one case of 18 trisomy,two cases of 45,XO and one case of balanced translocation were diagnosed.(3) In the two cases of 21 trisomy,maternal plasma G/A ratio ofPL4C4 RNA-single nucleotide polymorphism alleles was 1.00 (0.98,1.02) ; in 14 pregnancies with normal chromosome,the ratio was 1.055 (1.02,1.13,Z=3.5).There was no significant difference (P=0.066).Conclusion Diagnosing of fetal chromosomal aneuploidy by cffDNA in maternal plasma is feasible and noninvasive with high negative predictive value,and can be used in Rh-negative pregnant women for prenatal screening and diagnosis. Key words: Aneuploidy; Prenatal diagnosis; DNA; Pregnancy trimester, first

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. 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). 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%). 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.

In Brief Objective To examine whether concentrations of free extra-cellular fetal circulatory DNA in maternal plasma are stable or fluctuate. Methods Consecutive blood samples were drawn from 13 healthy nonpregnant volunteers and from 16 healthy pregnant women over 3 days. DNA was isolated from the plasma fraction and quantified by real-time polymerase chain reaction (PCR). Results In nonpregnant controls the total amount of cell free DNA fluctuated by an average of 13.5-fold. In samples obtained from pregnant women the amount of maternal cell free DNA varied by an average of 21.5-fold. Because ten of those women were pregnant with male fetuses, the concentration of free fetal DNA in these cases was determined by a real-time PCR assay for the Y chromosome. The mean variation in free fetal DNA levels in male fetuses was 2.2-fold. Conclusion The degree of variation in free fetal DNA concentrations observed in this study was similar to published values, so these results imply that care should be exercised when considering quantitation of this fetal material for potential diagnostic or screening purposes. Quantitative polymerase chain reaction analysis showed that levels of fetal and maternal circulating extracellular DNA in plasma vary over time.

Detection of fetal DNA in maternal plasma by microarray coupled with emulsions PCR

Multiplex fluorescent PCR for noninvasive prenatal detection of fetal-derived paternally inherited diseases using circulatory fetal DNA in maternal plasma

BackgroundMolecular size determination of circulating free fetal DNA in maternal plasma is an important detection method for noninvasive prenatal testing (NIPT). The fetal DNA molecule is the primary factor determining the overall performance of NIPT and its clinical interpretation. The proportion of cell-free fetal DNA molecules is expressed as the fetal DNA fraction in the plasma of pregnant women.MethodsWe proposed an effective method to deduce fetal chromosomal aneuploidy based on the proportion of a certain range of DNA fragment lengths from maternal plasma. We gradually narrowed the range of the upper and lower boundary via a traversing algorithm.ResultsWe explored the optimal range of the upper and lower boundary by using size-based DNA fragment length. Using this range, the accuracy of the sensitivity and specificity could be improved by up to 100% for detecting the three most common autosomal aneuploidies, namely trisomy 13, trisomy 18, trisomy 21 in the sample set.ConclusionsNumerical experiments demonstrate that our method is effective and efficient. The program is available upon request.

One potential noninvasive approach for antenatal diagnosis is the use of fetal cells in maternal circulation as a source of fetal DNA (1). To date, fetal DNA has been extracted from maternal nucleated blood cells and amplified by nested PCR of Y-chromosome sequences from male fetuses (2)(3). A recent study (4) demonstrated the presence of fetal DNA in maternal plasma. After a single PCR with a high number of cycles, detection of fetal DNA was possible in 24 (80%) of the 30 maternal plasma samples, using 10 μL of boiled plasma (4). When DNA extracted from a similar volume of whole blood was used, only 17% of the samples gave a Y-positive signal, suggesting an enrichment of fetal DNA in plasma compared with whole blood cells (4). The mechanism responsible for fetal DNA release in maternal circulation is unclear. It has been postulated that fetal cell lysis after physical and immunological damage, as well as developmentally regulated apoptosis of certain fetal tissues, may be responsible for this phenomenon (5). Furthermore, the release and clearance of fetal DNA from maternal plasma may be influenced by pathophysiological factors that are still to be determined. The efficacy of the single PCR protocol on maternal plasma DNA has not yet been compared to established methodologies of nested amplification of DNA prepared from intact cells. The present work compares single PCR on plasma DNA with nested PCR on DNA extracted from plasma or nucleated blood cells. We collected 27 maternal blood samples at gestational ages ranging from the 7th to the 32nd weeks (16 male- and 11 female-bearing pregnancies). Nine, 14, and 4 samples were from the first (7–12 weeks), second (14–20 weeks), and third (27–32 weeks) trimesters. Fetal gender was unknown at the time of sampling and analysis and was verified …

Early detection of cell-free fetal DNA in maternal plasma

To evaluate whether cell-free fetal (cff) DNA in maternal plasma during the second trimester is a marker for developing pregnancy-associated complications. Two PCR techniques for the detection and quantitation of fetal DNA were compared. Plasma samples were prospectively collected from 84 pregnant women carrying male fetuses before amniocentesis (14-29 weeks). We later recorded 26 pregnancies with complicated outcomes, including five cases of fetal chromosomal abnormalities. For statistical analysis, two overlapping subgroups A and B were made. Each group was separately compared for total and fetal DNA with a corresponding group considered normal using Wilcoxon rank sum test. Male fetal DNA concentration in maternal plasma was quantified using real-time quantitative polymerase chain reaction (PCR) of SRY sequences. The samples were also analyzed by quantitative fluorescent PCR (QF-PCR) using highly polymorphic short tandem repeat DNA sequences (STRs), and the percentage of relative fetal allele concentration in maternal alleles was calculated and compared to the fetal/total DNA ratio obtained by real-time PCR. Quantities of total and fetal circulating DNA were significantly correlated (r(2) = 0.44, P < 0.0001) with a median total DNA concentration of 522 GE/mL (range 51-3047) and a median fetal DNA concentration of 8 GE/mL (range 0-879). Neither level was correlated with gestational age in pregnancies with normal (r(2) = -0.05; P = 0.66, and r(2) = 0.02; P = 0.88, respectively) and abnormal (r(2) = 0.45; P = 0.17, and r(2) = 0.11; P = 0.76, respectively) outcomes. Although both total and fetal DNA levels were always higher in women carrying pregnancies with chromosomal aberrations or having other pregnancy complications (P-values range from 0.028 to 0.267), these differences reached statistical significance only for total DNA levels between the group A and corresponding normal pregnancies (P = 0.028). The correlation between the fetal/total DNA ratio obtained by real-time PCR and the percentage of relative fetal allele concentration in maternal alleles obtained by QF-PCR was not found to be statistically significant (r(2) = 0.04; P = 0.76). Our results confirm the clinical value of fetal DNA measurement in maternal plasma during the second trimester as a supplement for the diagnosis of aneuploidies. Its use as a screening instrument for complications that develop later in pregnancy seems to be limited but needs further investigation. Although the QF-PCR assay has the advantage of being applicable to both female and male fetuses, this approach cannot be used for quantitation of cff DNA in maternal plasma samples.

The discovery of fetal DNA in maternal plasma has opened up an approach for noninvasive prenatal diagnosis. Despite the rapid expansion in clinical applications, the molecular characteristics of plasma DNA in pregnant women remain unclear. We investigated the size distribution of plasma DNA in 34 nonpregnant women and 31 pregnant women, using a panel of quantitative PCR assays with different amplicon sizes targeting the leptin gene. We also determined the size distribution of fetal DNA in maternal plasma by targeting the SRY gene. The median percentages of plasma DNA with size >201 bp were 57% and 14% for pregnant and nonpregnant women, respectively (P <0.001, Mann-Whitney test). The median percentages of fetal-derived DNA with sizes >193 bp and >313 bp were 20% and 0%, respectively, in maternal plasma. Plasma DNA molecules are mainly short DNA fragments. The DNA fragments in the plasma of pregnant women are significantly longer than those in the plasma of nonpregnant women, and the maternal-derived DNA molecules are longer than the fetal-derived ones.

84: First trimester free fetal DNA in the maternal circulation as a predictor of preeclampsia

Detection of circulating fetal nucleic acids in maternal plasma is a promising approach to noninvasive prenatal assessment and fetal monitoring. Cell-free fetal/placental (cff) DNA concentrations in maternal plasma undergo transient increases after amniocentesis, suggesting that cff DNA in maternal plasma is a sensitive marker for fetal-maternal hemorrhage (1). However, cff DNA measurement is a sex-dependent marker used only in pregnancies with male fetuses, whereas cell-free placental (cff) mRNA in maternal plasma, recently quantified with real-time reverse-transcription PCR, is considered a sex-independent marker for monitoring placental conditions (2). Evidence suggests that cff mRNA release into the maternal circulation is comparable to cff DNA release, but it is not known which molecular marker is more sensitive for detection of fetal-maternal hemorrhage. To investigate this question, we performed a quantitative analysis of cff DNA and cff mRNA in maternal plasma collected before and 10-min after amniocentesis and evaluated which molecular marker was more sensitive for detection of fetal-maternal hemorrhage. Study participants were 32 pregnant women, at 15–17 weeks of gestation, who underwent amniocentesis at …

Objective: This study aims to assess whether the fraction of cell-free fetal DNA (cffDNA) is different at 24 h or 7 days after chorionic villus sampling (CVS), compared to subjects that do not undergo CVS.Methods: Pregnant women undergoing CVS for genetic testing and matched subjects undergoing first trimester combined screening alone were enrolled between 110/7 and 136/7 weeks gestation. The fractions of cffDNA were compared before the procedure, 24 h after and 7 days after between CVS patients and ultrasound-only patients.Results: Forty-five women underwent CVS and 45 had ultrasound alone. The women undergoing CVS were, on average, older (36.8 years versus 28.5 years, p=0.001) and had a higher baseline fraction of cffDNA than women in the comparison group (11.4% versus 9.8%, p=0.033). Both groups had a decrease in the mean fraction of cffDNA after 24 h. After 7 days, the trend of the mean fraction of cffDNA continued to decline in the CVS group but began to trend toward an increase in the ultrasound only group.Conclusions: CVS does not significantly increase the fraction of cell free fetal (placental) DNA in the maternal plasma. A downward trend in cffDNA in maternal plasma is seen at 24 h and 7 days following CVS compared to baseline.

Cell free fetal DNA (cffDNA) circulates in low concentration in maternal plasma and is a source of genetic material for safe non-invasive prenatal testing (NIPT). It is in routine use...