Approach For Noninvasive Prenatal Diagnosis Research Articles

Non-Invasive Screening Tools for Down's Syndrome: A Review.

Down’s syndrome (DS) is the most common genetic cause of developmental delay with an incidence of 1 in 800 live births, and is the predominant reason why women choose to undergo invasive prenatal diagnosis. However, as invasive tests are associated with around a 1% risk of miscarriage new non-invasive tests have been long sought after. Recently, the most promising approach for non-invasive prenatal diagnosis (NIPD) has been provided by the introduction of next generation sequencing (NGS) technologies. The clinical application of NIPD for DS detection is not yet applicable, as large scale validation studies in low-risk pregnancies need to be completed. Currently, prenatal screening is still the first line test for the detection of fetal aneuploidy. Screening cannot diagnose DS, but developing a more advanced screening program can help to improve detection rates, and therefore reduce the number of women offered invasive tests. This article describes how the prenatal screening program has developed since the introduction of maternal age as the original “screening” test, and subsequently discusses recent advances in detecting new screening markers with reference to both proteomic and bioinformatic techniques.

Fetal Nucleic Acids in Maternal Circulation: A Genetic Resource for Noninvasive Prenatal Diagnosis

Invasive prenatal diagnosis (PND) holds a multitude of psychological considerations for women, their partners, family and community as a whole. Earlier, the non-invasive screening methods for certain disorders were serum analytes or ultrasound with low sensitivity and high false positivity. The discovery of fetal DNA in maternal plasma has opened up an approach for noninvasive PND (NIPD). Presence of fetal cells and cell-free fetal DNA (cffDNA) in the blood of pregnant women has been accepted universally and constant efforts are being made to enrich fetal DNA from maternal blood/plasma. Real-time quantitative polymerase chain reaction (qrt-PCR) has enabled fetal DNA to serve as a marker for chromosomal abnormalities, for example, trisomy 21, preterm labor, and preeclampsia. In India, PND is provided in few centers since invasive methods require trained gynecologists, this limits investigation and therefore NIPD with cffDNA from mother's blood will revolutionize fetal medicine. The present paper deals with the latest developments in procurement of cffDNA, the probable source and enrichment of fetal DNA in maternal plasma, and the current status of its detection methodologies, applications, and its potential to be used as a powerful diagnostic tool.

Noninvasive Prenatal Detection of Fetal Trisomy 18 by Epigenetic Allelic Ratio Analysis in Maternal Plasma: Theoretical and Empirical Considerations

The discovery of cell-free fetal DNA in maternal plasma has opened up new possibilities for noninvasive prenatal diagnosis. However, the use of maternal plasma fetal DNA for the direct detection of fetal chromosomal aneuploidies has not been reported. We postulate that the aneuploidy status of a fetus could be revealed by an epigenetic allelic ratio approach, i.e., by analyzing the allelic ratio of a single-base variation present within DNA molecules exhibiting a placental-specific epigenetic signature in maternal plasma. Placental-derived fetal-specific unmethylated maspin (SERPINB5) promoter sequences on human chromosome 18 were detectable in placental-maternal DNA mixtures and in maternal plasma by bisulfite modification followed by methylation-specific PCR (MSP) and primer extension. The ratios between the extension products of the 2 alleles were calculated for heterozygous placentas, placental-maternal blood cell DNA mixtures, and maternal plasma samples. The allelic ratios were compared between pregnancies carrying trisomy 18 and euploid fetuses. The epigenetic allelic ratios of all tested trisomy 18 samples deviated from the reference range obtained from euploid samples (placental DNA, 1.135 to 2.052; placental-maternal DNA mixtures, 1.170 to 1.985; maternal plasma, 0.330 to 3.044; without skew correction on the raw mass spectrometric data). A theoretical model was established and validated that predicted that a minimum of 200 copies of genomic DNA after bisulfite conversion were required for distinguishing euploid and aneuploid fetuses with confidence. Epigenetic allelic ratio analysis of maternal plasma DNA represents a promising approach for noninvasive prenatal diagnosis of fetal chromosomal aneuploidies.

Identification of fetal gender in maternal blood is a helpful tool in the prenatal diagnosis of haemophilia

Fetal DNA identification in maternal circulation has provided a new approach for non-invasive prenatal diagnosis. However, fetal DNA can persist in maternal blood long after the delivery, severely hampering this possibility. We addressed the issue of fetal DNA persistence in maternal blood. Thus, we investigated cell-free fetal DNA as a reliable approach in prenatal diagnosis of haemophilia. Forty non-pregnant women, who had had at least a male fetus, 29 control pregnant women, and 14 pregnant women, carriers of hemophilia A or B. The assessment of Y-chromosomal sequences was performed by analysing SRY and amelogenin genes using PCR-based techniques. A protocol consisting of double centrifugation at full speed followed by plasma filtration hampered the detection of Y chromosome-specific sequence in non-pregnant women. In 29 control pregnant women, blinded determination of fetal sex confirmed the specificity and sensitivity of the method applied. In 14 pregnant carriers of hemophilia, the investigation revealed a male fetus in nine pregnancies. Excluding the three cases in which a spontaneous miscarriage occurred, the sensitivity and specificity of fetal sex prediction by SRY and amelogenin gene analyses were both 100% as compared with the invasive approach and the fetal sex outcome at birth (six males and five females). Because of its high accuracy in prediction, fetal gender determination with cell-free fetal DNA in maternal plasma may be a useful tool in prenatal diagnosis of haemophilia allowing for the avoidance of invasive procedures for female fetuses.

Fetal Rhesus D mRNA Is Not Detectable in Maternal Plasma

Detection of fetal-derived DNA and RNA molecules in maternal plasma is a promising approach for noninvasive prenatal diagnosis (1). Analysis of circulating fetal RNA, unlike analysis of fetal Y-chromosomal DNA, can be used in pregnancies with fetuses of either gender(2). Placenta-derived mRNA species are readily detectable in maternal plasma(2). The fetal hematopoietic compartment may be another source of nucleic acids in maternal plasma(3). Wataganara et al.(4) reported detection of γ-globin mRNA in maternal plasma. However, expression of γ-globin is not a fetus-specific phenomenon and is shared by maternal erythroid cells(5), and γ-globin mRNA is readily detectable in nonpregnant individuals(4). In this study, we assessed whether rhesus D ( RHD gene) mRNA derived from fetal erythroid cells is detectable in the plasma of rhesus D-negative pregnant women. Fifteen rhesus D-negative women at 11–40 weeks of gestation (Table 1⇓ ), attending the University Women’s Hospital, Basel, were recruited with informed consent and institutional ethics approval. Trisomy 21 was subsequently …

Feasibility study for a microchip-based approach for noninvasive prenatal diagnosis of genetic diseases.

Fetal DNA in maternal plasma may represent a source of genetic material for prenatal noninvasive diagnosis of genetic diseases. We evaluated a cohort of physiological pregnancies to determine if fetal DNA can be retrieved at any gestational week in sufficient quantity to be analyzed with advanced mutation detection technologies. We performed fetal DNA quantification by real-time polymerase chain reaction (PCR) on the SRY gene in 356 women sampled from 6 to 40 gestational weeks. Fetal DNA was retrieved at any week. All female fetuses were correctly identified. In 5 of 188 (2.6%) male-bearing pregnancies, no amplification was obtained. For noninvasive testing, complete clearance of fetal DNA after delivery is mandatory. Long-term persistence was not detected in women with previous sons or abortions. These findings confirm that maternal plasma may represent the optimal source of fetal genetic material. For noninvasive diagnosis of genetic diseases, we evaluated microchip technology. The detection limit for a minority allele determined by diluting a mutated DNA into a wild-type plasma sample was 5 genome equivalents, indicating that the test might be applied to the identification of paternally inherited fetal alleles in maternal plasma. The addition of peptide nucleic acids (PNAs) to either the PCR reaction or the chip hybridization mixture allowed approximately 50% inhibition of wild-type allele signals.

Size distributions of maternal and fetal DNA in maternal plasma.

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.

Prenatal exclusion of β thalassaemia major by examination of maternal plasma

The discovery of the presence of fetal DNA in maternal plasma has provided a new approach for non-invasive prenatal diagnosis. At present, the prenatal diagnosis of beta thalassaemia relies on invasive methods. We designed allele-specific primers and a fluorescent probe for detection of the codon 41/42 (-CTTT) mutation in the beta globin gene from maternal plasma by real-time PCR. The specificity and sensitivity of the allele-specific assay was confirmed by subjecting plasma, buffy coat, and amniotic fluid samples from 100 pregnancies to screening for the mutation. Subsequently, the assay was applied to the prenatal testing of eight fetuses at risk of beta thalassaemia major, the aim being to exclude fetal inheritance of paternally transmitted codon 41/42 mutation. The fetal genotype was completely concordant with conventional analysis and beta thalassaemia major was excluded in two of the pregnancies non-invasively.

Detection of fetal trisomies 21 and 18 from maternal blood using triple gradient and magnetic cell sorting.

The need for an inexpensive and reproducible technique for noninvasive prenatal diagnosis by fetal cell isolation from maternal blood. For enrichment of fetal cells we used a combination of triple density gradient and magnetic sorting (MACS) of (anti-CD71) transferrin receptor antibody labeled cells followed by fluorescence in situ hybridization (FISH) with chromosome-specific DNA probes for detection of fetal aneuploidies. We identified 15 cases of fetal trisomy (five cases with a trisomy 18 and ten cases with a trisomy 21) with subsequent chromosome-specific FISH. We found in all of the aneuploid pregnancies that the percentage of cells with three hybridization signals did not overlap with those of normal controls independent from gestational ages and previous invasive procedures. Our new approach for noninvasive prenatal diagnosis has proven to be reliable in this first series.