孕妇血浆中胎儿游离DNA的生化特征及其应用研究新进展

孕妇血浆中胎儿游离DNA,源于胎儿细胞和(或)胎盘的凋亡,经核酸内切酶选择性地剪切为313bp以下的短片段分子,在孕早期和孕晚期分别平均占血浆DNA总量的3.4%和6.2%,因相对含量丰富,已成为当前无创伤性产前分子遗传诊断中胎儿DNA的重要来源,现开展了胎儿性别鉴定、RhD阴性孕妇的Rh(D)基因检测、胎儿非整倍体病的诊断、STR遗传标记检测等应用研究。该文对母体血浆中胎儿游离DNA的来源、胎儿游离DNA的浓度、纯度、分子片段大小和分布、产后清除等基础性研究以及业已开展的临床应用,进行了总结和分析。根据胎儿游离DNA的生化特征和检测的靶基因,采用相应的分子基因诊断策略和实验设计,限制扩增产物的片段长度和优化PCR反应条件,有助于提高无创伤性产前胎儿分子遗传诊断的成功率。     

Isolating fetal cells in the maternal circulation

Fetal cells exist in maternal blood and can be utilized forprenatal genetic diagnosis. The use of polymerase chain reaction(PCR) technology on maternal blood has enabled the detectionof fetal sex, Mendelian disorders (e.g. (rß-globinmutations), HLA polymorphisms and fetal Rhesus (D) blood type.Enrichment for erythro-blasts and trophoblasts by various densitygradient and flow sorting techniques followed by fluorescencein-situ hybridization (FISH) with chromosome-specific DNA probeshas allowed detection of trisomy 21, trisomy 18, Klinefeltersyndrome (47,XXY) and 47,XYY. The fetal cell type that has generatedthe most success is the nucleated erythrocyte; however, trophoblasts,lymphocytes and granulocytes are also considered to be presentin maternal blood. Fetal cells circulate in maternal blood duringthe first and second trimesters, with frequency increasing asgestation advances. Emphasis is thus now directed toward determiningthe most practical and efficacious manner for this techniqueto be applied to prenatal genetic diagnosis. A large scale collaborationof clinical evaluations is underway in the USA, upon completionof which assessment can be made of whether this technology canserve as an alternative to conventional invasive and non-invasivemethods of prenatal cytogenetic diagnosis.     

Culture of fetal cells from maternal blood for prenatal diagnosis

The isolation and analysis of fetal cells from maternal blood would allow non-invasive prenatal genetic screening and diagnosis. Over the past decade, progress has been made towards this goal using various enrichment strategies and analysis by fluorescence in-situ hybridization with chromosome-specific probes and PCR. One method that is currently being explored involves culturing fetal cells. Developing conditions which allow the number of fetal-derived cells to expand in culture and the number of maternally derived cells to be suppressed in culture may lead to a new selection process for obtaining fetal cells. Culturing of fetal cells from maternal blood could make possible conventional metaphase analysis of fetal cells for diagnosis of chromosomal abnormalities.     

Fetal cells and cell-free fetal DNA in maternal blood: new insights into pre-eclampsia

The examination of fetal cells, specifically erythroblasts, and cell-free fetal DNA from the blood of pregnant women is currently the subject of intense research with the aim of developing new risk-free methods for prenatal diagnosis. An unexpected finding made during these studies was that the traffic of fetal erythroblasts into the maternal peripheral circulation was enhanced in pre-eclampsia. Independent prospective studies examining samples collected in the second trimester indicated that this perturbation in fetal cell trafficking occurs early in pregnancy, well before the onset of pre-eclampsia symptoms. The quantitative analysis of cell-free fetal and maternal DNA levels indicated that these concentrations were elevated in a co-ordinate manner in manifest pre-eclampsia, and that these elevations corresponded to disease severity. On the other hand, analysis of prospectively collected samples indicated that only cell-free fetal but not maternal DNA levels were elevated before onset of symptoms in pregnancies which subsequently developed pre-eclampsia. These data support hypotheses suggesting that pre-eclampsia is a multi-step disorder, initiated by a placental lesion that occurs early in pregnancy and which subsequently leads to a systemic maternal inflammatory response and associated endothelial cell damage.     

Investigation of maternal blood enriched for fetal cells: Role in screening and diagnosis of fetal trisomies

Prenatal diagnosis of chromosomal abnormalities relies on assessment of risk followed by invasive testing in the group with highest risk. Assessment of risk by a combination of maternal age and fetal nuchal translucency and invasive testing in the 5% of the population with the highest risk would identify about 80% of trisomy 21 pregnancies. Preliminary reports suggest that chromosomal abnormalities can also be diagnosed by fluorescent in situ hybridization (FISH) in maternal blood enriched for fetal cells. This study examines the potential role of this method on the prenatal diagnosis of fetal trisomies. Maternal blood was obtained before invasive testing in 230 pregnancies at 10–14 weeks of gestation. After enrichment for fetal cells, by triple density centrifugation and anti-CD71 magnetic cell sorting, FISH was performed and the proportion of cells with positive signals in the chromosomally normal and abnormal groups was determined. Fetal karyotype was normal in 150 cases and abnormal in 80 cases, including 36 with trisomy 21. Using a 21 chromosome-specific probe, three-signal nuclei were present in at least 5% of the enriched cells from 61% of the trisomy 21 pregnancies and in none of the normal pregnancies. For a cut-off of 3% of three-signal nuclei the sensitivity for trisomy 21 was 97% for a false positive rate of 13%. Similar values were obtained in trisomies 18 and 13 using the appropriate chromosome-specific probe. Examination of fetal cells from maternal blood may provide a noninvasive prenatal diagnostic test for trisomy 21 with the potential of identifying about 60% of affected pregnancies. Alternatively, this technique can be combined with maternal age and fetal nuchal translucency as a method of selecting the high-risk group for invasive testing. Potentially, 80% of trisomy 21 pregnancies could be identified after invasive testing in less than 1% of the pregnant population. Am. J. Med. Genet. 85:66–75, 1999. © 1999 Wiley-Liss, Inc.     

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.     

孕妇血中胎儿微小RNA等核酸在唐氏综合征无创产前诊断中的应用

唐氏综合征是最常见的染色体非整倍体遗传病,出生干预是预防该病的有效措施.传统的产前诊断具有创伤等缺陷,无创产前诊断是未来发展的需求.孕妇血胎儿细胞、胎儿游离DNA、胎儿游离RNA及胎儿游离microRNA的分析是新近发展的4种唐氏综合征无创产前诊断技术.母血胎儿游离miRNA有足够的稳定性、特异性和准确性,是最具临床应...     

Intact fetal cell isolation from maternal blood: improved isolation using a simple whole blood progenitor cell enrichment approach (RosetteSep)

Isolation and analysis of intact fetal cells in maternal blood is an attractive method of non-invasive prenatal diagnosis; however, detection levels are not optimal. The poor sensitivity and inconsistent recovery of fetal cells is compounded by small numbers of circulating fetal cells and loss of fetal cells during enrichment procedures. Optimizing selection criteria by utilizing less complicated methods for target cell enrichment is essential. We report here salutary results using a simple density-based depletion method that requires neither MACS (magnetic-activated cell sorting) nor flow cytometric separation for enrichment of progenitor cells. Maternal blood samples (n = 81) were obtained from women prior to invasive prenatal genetic diagnostic procedures and processed randomly within 24 h using one of two density-based enrichment methods. For progenitor cell enrichment, samples (n = 49) were labeled with a RosetteSep progenitor antibody cocktail to remove unwanted mature T-cells, B-cells, granulocytes, natural killer cells, neutrophils and myelomonocytic cells. For CD45-negative cell enrichment, samples (n = 14) were labeled with RosetteSep CD45 antibody to remove unwanted maternal white cells. The desired cellular fraction was collected and analyzed by either fluorescent in situ hybridization (FISH) or real-time PCR for the presence of intact fetal cells and to quantify Y-chromosome-specific DYS1 sequences, respectively. Overall, FISH and real-time PCR correct detection rates for the progenitor cell enrichment approach were 53% and 89% with 3% (1 out of 30 cases) and 0% false-positive detection, respectively. Fetal sequences were detected in the range from 0.067 to 1.167 genome equivalents per milliliter of blood. No fetal cells were detected using the CD45-negative enrichment method. Flow cytometric analysis of cord blood showed that a unique myeloid population of cells was recovered using RosetteSep trade mark progenitor enrichment compared with the CD45-negative enrichment method. Sensitivity of the RosetteSep progenitor enrichment approach for detection of fetal cells in this pilot study shows great promise with recovery of cells that are suitable for FISH and automated microscope scanning. This simple and rapid method may also allow expansion in culture and characterization of the fetal cell type(s) that circulate in maternal blood, hence, greatly improving reliability of non-invasive prenatal diagnosis.     

孕妇血浆中的游离胎儿DNA及其意义

孕妇血浆中已证实存在着胎儿来源的游离DNA。作为一种胎儿新的检测材料,游离胎儿DNA的发现为非侵入性产前基因诊断提供了可能。有关游离胎儿DNA的临床应用以及其生物学包括来源、动力学和性质等,近年来引起人们很大关注。实时定量PCR技术是目前检测孕妇血浆中游离胎儿DNA的主要方法。实验室的一些技术因素会影响游离胎儿DNA的检测。尽管有些问题还不很清楚,但母体血浆中游离胎儿DNA的检测对于胎儿遗传病和妊娠相关性疾病的非侵入性产前诊断仍具有重要临床意义。讨论孕妇血浆中游离胎儿DNA的最新研究状况。     

Elevated levels of total (maternal and fetal) beta-globin DNA in maternal blood from first trimester pregnancies with trisomy 21

BACKGROUND: Elevated levels of circulating fetal DNA have been observed in maternal plasma when a trisomy 21 fetus is confirmed. However, these studies have been limited to pregnancies carrying a male fetus. We sought to quantify total (fetal and maternal) DNA from dried blood spots (DBS) for use as an additional factor in multi-parameter prenatal screening for aneuploidy. METHODS: Maternal DBS were obtained from the NICHD-sponsored multi-center cohort (BUN) study. Seventeen confirmed trisomy 21 (mean gestational age 12.23 +/- 0.77 weeks) cases were each matched by gestational age to euploid controls (n = 30). DNA was extracted and quantitative PCR was performed to measure four non-chromosome 21 loci, including glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (12p13), beta-globin (11p15.5), beta-actin (7p15-12) and p53 (17p13.1). RESULTS: Beta-globin DNA levels were significantly elevated (P = 0.003) in 13 of 17 trisomy 21 cases (4.08 +/- 1.78 Geq/ml x 10(5)) compared with matched controls (2.35 +/- 1.84 Geq/ml x 10(5)). Following conversion of beta-globin concentrations into multiples of the median (MoM), MoM for trisomy 21 cases was 2.8 compared with 1.0 in euploid cases. No significant differences in levels of circulating GAPDH, beta-actin and p53 sequences were detected. CONCLUSIONS: This work demonstrates differential levels of circulating beta-globin DNA in maternal blood of euploid and trisomy 21 cases. Sequence-specific quantification could provide an additional measure to improve non-invasive methods of prenatal screening to detect trisomy 21 using dried blood. Beta-globin in particular is an attractive biomarker that could contribute to enhance multiple serum parameter testing in the first trimester.     

Performance of prenatal screening by non-invasive cell-free fetal DNA testing for women with various indicationsCSCD

Objective: To assess the performance of non-invasive prenatal testing (NIPT) based on massive parallel sequencing. Methods: A total of 10 275 maternal blood samples were collected. Fetal chromosomal aneuploides were subjected to low coverage whole genome sequencing. Patients with high risks received further prenatal diagnosis. The outcome of all patients were followed up. Results: High-throughput sequencing detected 72 pregnancies with fetal autosomal chromosomal aneuploidy, including 57 cases of trisomy 21, 14 cases of trisomy 18, and 1 case of trisomy 13. The positive predictive value for trisomies 21 and 18 were 98.25% and 91.67%, respectively. Comparing its performance in intermediate or high risk pregnancies, advanced maternal age pregnancies and volunteering to test pregnancies, the positive predictive value were 100%, 95%, 90% and 50%, respectively. The follow up result was only 1 case of 21 trisomy false negative with high risk. For the 56 cases of trisomy 21, the high risk group accounted for 55%, advanced maternal age accounted for 29%, the intermediate risk referred to 14%, the volunteering to test group accounted for 2%. Conclusion: The performance of NIPT for trisomies 21, 18 and 13 was satisfactory. The method can be used for women with advanced gestational age. NIPT has offered an ideal secondary screening method for those with an intermediate or high risk, and can reduce the rate of birth defects. © 2018 West China University of Medical Sciences. All rights reserved.     

Detection of chromosomal aneuploidies in fetal cells isolated from maternal blood using single-chromosome dual-probe FISH analysis

Detection of chromosomal aneuploidies using fetal cells isolated from maternal blood, for prenatal non-invasive genetic investigation, has been a long-sought goal of clinical genetics to replace amniocentesis and chorionic villous sampling to avoid any risk to the fetus. The purpose of this study was to develop a sensitive and specific new assay for diagnosing aneuploidy with circulating fetal cells isolated from maternal blood as previously reported using two novel approaches: (i) simultaneous immunocytochemistry (ICC) evaluation using a monoclonal antibody for i-antigen, followed by fluorescence in situ hybridization (FISH); (ii) dual-probe FISH analysis of interphase nuclei using two differently labeled probes, specific for different loci of chromosomes 21 and 18; in addition, short tandem repeats (STR) analysis on single cells isolated by micromanipulation was applied to confirm the presence of fetal cells in the cell sample enriched from maternal blood. Blood samples were obtained from women carrying trisomic fetuses, and from non-pregnant women and men as controls. Using ICC-FISH approach, a large heterogeneity in immunostaining pattern was observed, which is a source of very subjective signal interpretation. Differently, dual-probe FISH analysis provided for a correct diagnosis of all pregnancies: the mean percentage of trisomic cells was 0.5% (range, 0.36-0.76%), while the mean percentage of trisomic cells in the control group (normal pregnancies or non-pregnant women) was ≤0.20%. The application of the dual-probe FISH protocol on fetal cells isolated from maternal blood enables accurate molecular detection of fetal aneuploidy, thus providing a foundation for development of non-invasive prenatal diagnostic testing.     

孕妇血浆中游离胎儿DNA的检测与分析

目的 建立不依赖于胎儿性别和父本DNA、可适用于染色体数目异常和单基因遗传病的无创性产前诊断方法.方法 应用降落PCR和二次PCR扩增技术,联合检测41例正常孕妇(其中孕龄7 w 1例,14～20 w 39例,32 w 1例)血浆中游离胎儿DNA的SRY基因和D17S1293、D21S11、DXS8377等3个短串联重复序列(short tandem repeat,STR)位点.SRY基因扩增产物进行琼脂糖凝胶电泳,STR位点扩增产物进行变性聚丙烯酰胺凝胶电泳并银染显色.结果 41例孕妇血浆DNA中均检出非母源性等位基因条带;联合SRY基因和X-STR位点鉴定胎儿性别,38例判断明确,3例不能明确判断性别.结论 检测孕妇血浆中的游离胎儿DNA,可快捷地获得男性胎儿和女性胎儿的父源性DNA信息,不仅适用于性连锁遗传疾病,而且适用于常染色体遗传疾病等的产前基因诊断.     

The use of cell-free fetal nucleic acids in maternal blood for non-invasive prenatal diagnosis

BACKGROUND: Cell-free fetal nucleic acids (cffNA) can be detected in thematernal circulation during pregnancy, potentially offeringan excellent method for early non-invasive prenatal diagnosis(NIPD) of the genetic status of a fetus. Using molecular techniques,fetal DNA and RNA can be detected from 5 weeks gestation andare rapidly cleared from the circulation following birth. METHODS: We searched PubMed systematically using keywords free fetalDNA and NIPD. Reference lists from relevant papers were alsosearched to ensure comprehensive coverage of the area. RESULTS: Cell-free fetal DNA comprises only 3–6% of the total circulatingcell-free DNA, therefore diagnoses are primarily limited tothose caused by paternally inherited sequences as well as conditionsthat can be inferred by the unique gene expression patternsin the fetus and placenta. Broadly, the potential applicationsof this technology fall into two categories: first, high geneticrisk families with inheritable monogenic diseases, includingsex determination in cases at risk of X-linked diseases anddetection of specific paternally inherited single gene disorders;and second, routine antenatal care offered to all pregnant women,including prenatal screening/diagnosis for aneuploidy, particularlyDown syndrome (DS), and diagnosis of Rhesus factor status inRhD negative women. Already sex determination and Rhesus factordiagnosis are nearing translation into clinical practice forhigh-risk individuals. CONCLUSIONS: The analysis of cffNA may allow NIPD for a variety of geneticconditions and may in future form part of national antenatalscreening programmes for DS and other common genetic disorders.     

Rh阴性孕妇外周血基因鉴定胎儿RhD血型的方法

目的建立可靠有效的检测孕妇外周血中胎儿游离DNA的方法,探讨其在非创伤性产前诊断中的价值。结论采用PCR技术对5例RhD阴性孕妇外周血血浆DNA进行分析,然后对出生后婴儿脐带血进行Rh血清学表型分析,回顾性评价无创性预测胎儿RhD基因分析的准确性。结果 5例RhD阴性血浆标本扩增出180bp与156bp两条特异性片段,产后新生儿脐血血清学检测结果为RhD阳性,与PCR检测结果完全吻合。结论孕妇外周血浆中胎儿游离DNA的测定能实现对胎儿RhD基因型的预测判定。孕妇外周血检测胎儿DNA可应用于非创伤性产前诊断。     

Circulating cell-free fetal DNA in maternal serum appears to originate from cyto- and syncytio-trophoblastic cells. Case report

Circulating cell-free fetal DNA in maternal serum offers an early and non-invasive method for prenatal diagnosis, but the origin of this DNA is still unknown. We report the absence of the SRY gene in maternal serum of a pregnant woman despite male genitalia at ultrasound. The karyotype was 45,X after direct trophoblast analysis and 45,X/46,Xidic(Yp) after culture and in all fetal tissues studied. Due to the absence of the SRY sequence in maternal blood and in the cytotrophoblast, we presume that free fetal DNA in this case originates from trophoblastic cells. As the case presented here is exceptional, it only has a minor impact on the accuracy of fetal sex determination by maternal serum analysis, but highlights the importance of and the necessity for the complementary ultrasonographic control.     

Investigation of maternal blood enriched for fetal cells: role in screening and diagnosis of fetal trisomies.

Prenatal diagnosis of chromosomal abnormalities relies on assessment of risk followed by invasive testing in the group with highest risk. Assessment of risk by a combination of maternal age and fetal nuchal translucency and invasive testing in the 5% of the population with the highest risk would identify about 80% of trisomy 21 pregnancies. Preliminary reports suggest that chromosomal abnormalities can also be diagnosed by fluorescent in situ hybridization (FISH) in maternal blood enriched for fetal cells. This study examines the potential role of this method on the prenatal diagnosis of fetal trisomies. Maternal blood was obtained before invasive testing in 230 pregnancies at 10-14 weeks of gestation. After enrichment for fetal cells, by triple density centrifugation and anti-CD71 magnetic cell sorting, FISH was performed and the proportion of cells with positive signals in the chromosomally normal and abnormal groups was determined. Fetal karyotype was normal in 150 cases and abnormal in 80 cases, including 36 with trisomy 21. Using a 21 chromosome-specific probe, three-signal nuclei were present in at least 5% of the enriched cells from 61% of the trisomy 21 pregnancies and in none of the normal pregnancies. For a cut-off of 3% of three-signal nuclei the sensitivity for trisomy 21 was 97% for a false positive rate of 13%. Similar values were obtained in trisomies 18 and 13 using the appropriate chromosome-specific probe. Examination of fetal cells from maternal blood may provide a noninvasive prenatal diagnostic test for trisomy 21 with the potential of identifying about 60% of affected pregnancies. Alternatively, this technique can be combined with maternal age and fetal nuchal translucency as a method of selecting the high-risk group for invasive testing. Potentially, 80% of trisomy 21 pregnancies could be identified after invasive testing in less than 1% of the pregnant population.     

母血浆及血清中胎儿游离DNA的研究进展

1997年胎儿游离DNA的发现为无创性产前诊断开辟了新的途径。母血循环中的胎儿游离DNA含量相对较高,获取方法比较简单,在早孕阶段就可以检测到,这些优点成为极具潜力的无创伤性产前诊断方法。目前,胎儿游离DNA已经应用于某些性连锁疾病、妊娠相关疾病、染色体病、胎儿RhD血型检测等很多疾病的产前诊断中。我们希望此技术的进一步发展和完善可以使这种无创性的产前诊断方法在临床得到更广泛的应用。     

The introduction of QF-PCR in prenatal diagnosis of fetal aneuploidies: time for reconsideration

Quantitative fluorescent polymerase chain reaction (QF-PCR) has recently entered the field of prenatal diagnosis to overcome the need to culture fetal cells, hence to allow rapid diagnosis of some selected chromosomal anomalies. We reviewed the studies on the accuracy of QF-PCR in detecting chromosomal anomalies at prenatal diagnosis. Overall, 22 504 samples have been analysed. The detection rate of aneuploidies of the selected chromosomes (13, 18 and 21, and X and Y) was 98.6% (95% confidence interval 97.8-99.3). QF-PCR might play a major role and be considered a valid alternative to the full karyotype. Being less expensive, and almost entirely automated, more women could undergo invasive prenatal diagnosis without significant increase in health expenditure. By using QF-PCR as a stand-alone test, the chances of non diagnosing the commonest, and the only chromosome anomalies which do increase in frequency with maternal age, are approximately one in 150 abnormal karyotypes, or one in 10-30 000 samples, based on the age distribution. These error rates might be deemed acceptable, although most structural chromosomal anomalies will be missed. At present, women are rarely informed about the full spectrum of the conditions which might be diagnosed via amniocentesis or chorionic villous sampling. Some of these anomalies might be acceptable, in view of their limited or uncertain clinical relevance, and decision analysis might, in the majority of cases, confine the full karyotype to selected women who have specific indications.     

2433例孕妇血浆胎儿游离DNA无创性产前非整倍性检测结果分析

目的探讨应用高通量测序技术对孕妇血浆胎儿游离DNA进行无创性胎儿染色体非整倍性检测的准确性。方法选择2011年10月至2013年9月于佛山市妇幼保健院行无创性非整倍性产前基因检测的2433例名孕妇,孕周12-24w,均为单胎,年龄21-41岁。对无创性非整倍性筛查高风险的孕妇行羊膜腔穿刺或脐静脉血穿刺,行常规染色体核型分析。对筛查结果低风险者行电话随访其胎儿出生后情况,统计分析无创性产前非整倍性检测的准确性。结果2433例孕妇中,母体血浆胎儿游离DNA高通量测序技术检测出42例胎儿染色体非整倍性高风险。其中33例通过羊膜腔穿刺或脐静脉血穿刺对比分析,27例21三体高风险者行有创性产前诊断,26例为47,XN,＋21,l例为46,XN。2例18三体高风险者行进一步确诊,其中1例为47,XN,＋18,1例为46,XN。2例i3三体高风险孕妇结果均与穿刺结果为46,XN。1例XO高风险孕妇与穿刺结果为45X[25]／46,XX[25]。1例XXY高风险孕妇结果为47,XXY。孕妇血浆中游离胎儿DNA检测结果阴性者2391例,经电话随访有效者2145例,截止至2014年4月30日,已出生的新生儿均未发现唐氏综合征患儿。无创性非整倍体检测对常见染色体非整倍体的检出率100％,灵敏废100％,特异度99.8,假阳性率0.33％,假阴性率为0,阳性预测值87.9％。结论应用高通量测序技术在染色体非整倍性无创性检测具有很高的灵敏性,假阳性率很低,在胎儿染色体非整倍性疾病的产前检测中具有广泛的应用前景。