Differential DNA methylation as a tool for noninvasive prenatal diagnosis (NIPD) of X chromosome aneuploidies.

Institute of Genetics and Biophysics A. Buzzati Traverso, Naples, Italy.
The Journal of molecular diagnostics: JMD (Impact Factor: 3.96). 11/2010; 12(6):797-807. DOI: 10.2353/jmoldx.2010.090199
Source: PubMed

ABSTRACT The demographic tendency in industrial countries to delay childbearing, coupled with the maternal age effect in common chromosomal aneuploidies and the risk to the fetus of invasive prenatal diagnosis, are potent drivers for the development of strategies for noninvasive prenatal diagnosis. One breakthrough has been the discovery of differentially methylated cell-free fetal DNA in the maternal circulation. We describe novel bisulfite conversion- and methylation-sensitive enzyme digestion DNA methylation-related approaches that we used to diagnose Turner syndrome from first trimester samples. We used an X-linked marker, EF3, and an autosomal marker, RASSF1A, to discriminate between placental and maternal blood cell DNA using real-time methylation-specific PCR after bisulfite conversion and real-time PCR after methylation-sensitive restriction digestion. By normalizing EF3 amplifications versus RASSF1A outputs, we were able to calculate sex chromosome/autosome ratios in chorionic villus samples, thus permitting us to correctly diagnose Turner syndrome. The identification of this new marker coupled with the strategy outlined here may be instrumental in the development of an efficient, noninvasive method of diagnosis of sex chromosome aneuploidies in plasma samples.

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    ABSTRACT: Quantitative polymerase chain reaction (qPCR) is widely used in quantitation of plasma DNA for non‑invasive prenatal diagnosis (NIPD). Control genes are indispensable as standard normalizers in qPCR analysis, and there is increasing evidence indicating that the content levels of commonly used control genes vary significantly in different independent experiments. The commonly used control genes for DNA quantitation using qPCR in plasma DNA analysis are frequently chosen without any preliminary evaluation of their suitability. The present study aimed to examine a panel of six common control genes (HBB, TERT, GAPDH, ALB, ACTB and TRG) in order to evaluate and validate the most reliable control genes for qPCR studies in the quantitation of plasma DNA from pregnant and non‑pregnant females for NIPD. Plasma DNA was extracted from the peripheral blood of 18 pregnant females and 18 non‑pregnant females by the QIAamp DNA mini kit. qPCR followed by geNorm, NormFinder and BestKeeper based analysis was conducted to evaluate the DNA content stabilities of the six candidate control genes. DSCR3 was used to validate the result. The study recommended TERT and the combination of ACTB and TERT as the optimal control genes for qPCR studies on pregnant/non‑pregnant plasma DNA quantitation. Thus, the study reveals that the DNA content stability of widely used control genes varies significantly in pregnant and non‑pregnant plasma DNA.
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    ABSTRACT: RASSF1A has been described to be differentially methylated between fetal and maternal DNA and can therefore be used as a universal sex-independent marker to confirm the presence of fetal sequences in maternal plasma. However, this requires highly sensitive methods. We have previously shown that Pyrophosphorolysis-activated Polymerization (PAP) is a highly sensitive technique that can be used in noninvasive prenatal diagnosis. In this study, we have used PAP in combination with bisulfite conversion to develop a new universal methylation-based assay for the detection of fetal methylated RASSF1A sequences in maternal plasma. Bisulfite sequencing was performed on maternal genomic (g)DNA and fetal gDNA from chorionic villi to determine differentially methylated regions in the RASSF1A gene using bisulfite specific PCR primers. Methylation specific primers for PAP were designed for the detection of fetal methylated RASSF1A sequences after bisulfite conversion and validated. Serial dilutions of fetal gDNA in a background of maternal gDNA show a relative percentage of ∼3% can be detected using this assay. Furthermore, fetal methylated RASSF1A sequences were detected both retrospectively as well as prospectively in all maternal plasma samples tested (n = 71). No methylated RASSF1A specific bands were observed in corresponding maternal gDNA. Specificity was further determined by testing anonymized plasma from non-pregnant females (n = 24) and males (n = 21). Also, no methylated RASSF1A sequences were detected here, showing this assay is very specific for methylated fetal DNA. Combining all samples and controls, we obtain an overall sensitivity and specificity of 100% (95% CI 98.4%-100%). Our data demonstrate that using a combination of bisulfite conversion and PAP fetal methylated RASSF1A sequences can be detected with extreme sensitivity in a universal and sex-independent manner. Therefore, this assay could be of great value as an addition to current techniques used in noninvasive prenatal diagnostics.
    PLoS ONE 01/2013; 8(12):e84051. DOI:10.1371/journal.pone.0084051 · 3.53 Impact Factor
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    ABSTRACT: DNA methylation is the most studied form of epigenetic regulation, a process by which chromatin composition and transcription factor binding is altered to influence tissue specific gene expression and differentiation. Such tissue specific methylation patterns are investigated as biomarkers for cancer and cell-free fetal DNA using various methodologies. We have utilized methylation DNA immunoprecipitation (MeDIP) and real-time quantitative PCR to investigate the inter-individual methylation variability of differentially methylated regions (DMRs) on chromosomes 18 and 21. We have characterized 15 newly selected and seven previously validated DMRs in 50, 1(st) trimester Chorionic villus samplings (CVS) and 50 female non-pregnant peripheral blood (WBF) samples. qPCR results from MeDIP and genomic DNA (Input) assays were used to calculate fold enrichment values for each DMR. For all regions tested, enrichment was higher in CVS than in WBF samples with mean enrichments ranging from 0.22 to 6.4 and 0.017 to 1 respectively. Despite inter-individual variability, mean enrichment values for CVS were significantly different than those for WBF in all DMRs tested (p < 0.01). This observation is reinforced by the absence of overlap in CVS and WBF enrichment value distributions for 15 of 22 DMRs. Our work provides an expansion in the biomarker panel available for non-invasive prenatal diagnosis (NIPD) using the MeDIP-qPCR methology for Down syndrome and can eventually provide the starting point towards the development for assays towards the detection of Edwards syndrome. Furthermore, our data indicate that inter-experimental and inter-individual variation in methylation is apparent, yet the difference in methylation status across tissues is large enough to allow for robust tissue specific methylation identification.
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