Rapid prenatal diagnosis of Down syndrome using quantitative fluorescence in situ hybridization on interphase nuclei

OBJECTIVES: Presently, conventional cytogenetic analysis of metaphase chromosomes remains the reference approach in prenatal diagnosis. However, this method is labor-intensive and time-consuming. The first step toward the rapid identification of aneuploidies is achieved by interphase fluorescence in situ hybridization (FISH) with centromeric or locus-specific probes. Spot counting using this type of probes is a reliable approach, but is very time-consuming with some technical and biological limitations. In this study, we present a new FISH method using image cytometry for the detection of trisomy 21 within interphase nuclei. METHODS: The method is based on a comparative quantitation of the fluorescence signals emitted by whole chromosome 21 and 22 painting probes cohybridized on interphase nuclei. The chromosomal imbalance was determined with an automated image cytometer by detecting an abnormal ratio of both fluorescence emissions when compared with the ratio obtained in normal cells. RESULTS: Ten blood samples and twenty amniotic fluids were analyzed. Results from FISH and standard cytogenetics were compared and 100% correlation was achieved. CONCLUSIONS: This method, which enables an easy detection of chromosomal imbalances without a need for metaphase preparations, can be applied to the diagnosis of trisomy 21 and extended to other disorders with chromosomal imbalances. Compared to other interphase FISH techniques, it avoids spot-scoring difficulties.     

Sequential and contingent prenatal screening for Down syndrome

OBJECTIVE: To compare the Integrated test in three policies for prenatal Down syndrome screening: Integrated screening for all women, sequential screening (first-trimester tests allowing early completion of screening for high-risk pregnancies), and Contingent screening (early completion of screening for high- and low-risk pregnancies). DESIGN AND METHODS: Estimation of detection rates (DRs) and false-positive rates (FPRs) using Monte Carlo simulation and cost effectiveness for each method. SETTING AND POPULATION: Down syndrome affected and unaffected pregnancies studied in the Serum Urine and Ultrasound Screening Study (SURUSS). RESULTS AND MAIN OUTCOMES: Integrated screening has the best screening performance. The performance of the other two policies approached that of Integrated screening as the first-trimester test FPR decreased. If the first-trimester FPR is set to 0.5% (risk >or= 1 in 30) with an overall DR of 90%, sequential and contingent screening yield overall FPRs of 2.25% and 2.42%, respectively, and 66% of the affected pregnancies are detected by the first-trimester test. The Integrated test on all women yields an FPR of 2.15%. With sequential screening, 99.5% of women would proceed to an Integrated test, or 30% with contingent screening if those with first-trimester test risks of 相似文献   

Prospective prenatal serum screening for Down syndrome in Venezuela

OBJECTIVE: To assess the usefulness of triple-marker screening for Down syndrome in Venezuela. METHOD: Maternal serum concentrations of alpha fetoprotein (AFP), beta human chorionic gonadotropin (beta-hCG), and unconjugated estriol (uE3) were measured weekly in 3895 women from the 15th to the 20th week of pregnancy. Population-specific likelihood ratios were determined and used to calculate the risk of fetal Down syndrome for each pregnancy. RESULTS: The median multiple of the median values for AFP, beta-hCG, and uE3 concentrations were 0.69, 2.10, and 0.67 for the affected pregnancies. The likelihood ratio for a positive result was 1:19. The detection and false-positive rates were 69.23% and 5.8%. CONCLUSION: These findings were consistent with reported data and therefore confirmed triple-marker serum screening as effective and suitable for prenatal care in Venezuela. Latin American governments and Health Agencies should recommend offering this screening method to all pregnant women.     

Cross-trimester marker ratios in prenatal screening for Down syndrome

OBJECTIVE: To examine the performance of Integrated Down syndrome screening (first- and second-trimester measurements integrated into a single screening test) when ratios of the levels of the same serum markers measured in both these trimesters (cross-trimester ratios) are added as new screening markers. METHODS: Using data from Serum Urine and Ultrasound Screening Study (SURUSS), second-trimester concentrations (in multiples of the median, or MoM) of pregnancy associated plasma protein A (PAPP-A), alphafetoprotein (AFP), unconjugated oestriol (uE(3)), human chorionic gonadotrophin (hCG) (free beta and total), and inhibin-A were divided by the first-trimester concentration to obtain a cross-trimester (CT) ratio for each analyte in 74 Down syndrome and 492 unaffected pregnancies. We identified CT ratios that improved screening performance and then, using Monte Carlo simulations, estimated the efficacy and cost effectiveness of adding them to the Integrated and serum Integrated tests. RESULTS: All the median CT ratios differed significantly between Down syndrome and unaffected pregnancies. Setting the Integrated test to achieve a 90% detection rate, the false-positive rate (FPR) was 0.7% with CT ratios for PAPP-A, uE(3), inhibin-A, and total hCG compared with 2.2% without CT ratios, a reduction of about two-thirds. Using the serum Integrated test to achieve the same 90% detection rate and the first-trimester measurements made at 11 completed weeks of pregnancy, the corresponding FPRs were 2.4 and 8.1%, a similar proportional reduction. The AFP CT ratio had little effect on screening performance. Using CT ratios did not increase the cost per Down syndrome pregnancy detected. CONCLUSION: The addition of CT ratios to an Integrated test substantially improves the efficacy and safety of prenatal screening for Down syndrome. It is cost effective and could be usefully introduced into screening programmes. Copyright (c) 2006 John Wiley & Sons, Ltd.     

Identifying Smith-Lemli-Opitz syndrome in conjunction with prenatal screening for Down syndrome

BACKGROUND: Smith-Lemli-Opitz syndrome (SLOS) is a rare hereditary disorder of cholesterol metabolism. We examine the feasibility of identifying SLOS as a part of a routine prenatal screening and evaluate diagnostic testing in maternal urine (or serum), in addition to amniotic fluid. METHODS: Our SLOS risk algorithm utilized three Down syndrome screening markers (estimated 62% detection rate; 0.3% screen-positive rate). Fifteen North American prenatal screening programs implemented this algorithm. RESULTS: SLOS risk was assigned to 1 079 301 pregnancies; 3083 were screen-positive (0.29%). Explanations were found for 1174, including 914 existing fetal deaths. Among the remaining pregnancies, 739 were screen-positive only for SLOS; 1170 were also screen-positive for other fetal disorders. Five of six SLOS pregnancies (83%) were screen-positive. All six had sonographic findings, were biochemically confirmed, and were terminated. Maternal urine steroid measurements were confirmatory in four cases tested. Second-trimester prevalence among Caucasians was 1 in 101 000 (1 in 130 000 overall; no cases in other racial groups). Among 739 pregnancies screen-positive only for SLOS, two cases were identified; another 69 had major fetal abnormalities. CONCLUSIONS: Although SLOS occurred less often than previously reported, many other major abnormalities were detected. Implementing the algorithm as an adjunct to Down syndrome screening may be feasible.     

Combined screening for Down syndrome in Marseille multidisciplinary prenatal centers

Combined screening for trisomy 21 (CS) is established since January 2010 in multidisciplinary centers for prenatal screening in Marseille. Our work investigates its implementation. To date, the false positive rate is 3.5% and the coverage of the SC after six months is 5.7% in our low-risk population.     

A cost-effectiveness analysis of prenatal screening strategies for Down syndrome

OBJECTIVE: To evaluate which Down syndrome screening strategy is the most cost-effective. METHODS: Using decision-analysis modeling, we compared the cost-effectiveness of 9 screening strategies for Down syndrome: 1) no screening, 2) first-trimester nuchal translucency (NT) only, 3) first-trimester combined NT and serum screen, 4) first-trimester serum only, 5) quadruple screen, 6) integrated screening, 7) sequential screening, 8) integrated serum only, or 9) maternal age. Costs included cost of tests and resources used for raising a child with Down syndrome. One-way and multiway sensitivity analyses were performed for all model variables. The main outcome measures were cost per Down syndrome case detected, rate of delivering a liveborn neonate with Down syndrome, and rate of diagnostic procedure-related pregnancy loss for each strategy. RESULTS: Sequential screening detected more Down syndrome cases compared with the other strategies, but it had a higher procedure-related loss rate. Integrated serum screening was the most cost-effective strategy. Sensitivity analyses revealed the model to be robust over a wide range of values for the variables. The addition of the cost of genetic sonogram to the second-trimester strategies resulted in first-trimester combined screening becoming the most cost-effective strategy. CONCLUSION: Within our baseline assumptions, integrated serum screening was the most cost-effective screening strategy for Down syndrome. If the cost of nuchal translucency is less than dollars 57 or when genetic sonogram is included in the second-trimester strategies, first-trimester combined screening became the most cost-effective strategy. LEVEL OF EVIDENCE: III.     

对妊娠中晚期孕妇行超声检测胎儿鼻骨发育状况以筛查唐氏综合征

目的 探讨超声检测胎儿鼻骨发育状况对产前筛查唐氏综合征的临床应用价值.方法 2004年10月至2007年3月,应用二维超声对中山大学附属第一医院1863例中晚期孕妇(正常组)和25例妊娠唐氏综合征胎儿的孕妇(研究组)检测其胎儿鼻骨,观察两组中正常胎儿和唐氏综合征胎儿的鼻骨缺失、鼻骨短小的发生率.鼻骨缺失为胎儿面部矢状切面、横切面和冠状切面均未能显示鼻骨声像;鼻骨短小为鼻骨超声测值小于同孕周正常值的第2.5百分位数.计算鼻骨发育异常值筛查唐氏综合征的诊断试验结果.结果 (1)正常组孕妇中成功检测胎儿鼻骨1761例,102例受胎位等因素影响未能得到清晰图像,检测成功率为94.5%(1761/1863);(2)正常组中1761例胎儿鼻骨长度与孕周呈正相关关系(r=0.605,P＜0.05),其中鼻骨缺失3例(0.2%,3/1761),鼻骨短小44例(2.5%,44/1761);(3)研究组唐氏综合征胎儿中,鼻骨缺失7例(28.0%,7/25),鼻骨短小15例(60.0%,15/25);(4)以鼻骨缺失为截断值筛查唐氏综合征的敏感度为28.O%,特异度为99.8%,阳性似然比164.45(95%可信区间为45.11～599.60),阴性似然比0.72(95%可信区间为0.57～0.92);以鼻骨短小为截断值筛查唐氏综合征的敏感度为60.0%,特异度为97.5%,阳性似然比24.03(95%可信区间为7.15～80.71),阴性似然比0.41(95%可信区间为0.29～0.59).结论 胎儿鼻骨发育异常尤其是鼻骨缺失,与唐氏综合征关系密切,可作为产前超声筛查唐氏综合征的指标应用于临床.     

Quality assurance of nuchal translucency for prenatal fetal Down syndrome screening

Objective: To assess the quality of nuchal translucency, (NT) measurements were performed at four public institutions performing routine first trimester combined prenatal screening for Down syndrome. Methods: The median of the NT-MoM distribution and standard deviation (SD) of the log₁₀ NT-MoM were determined. Sonographers and screening centres distributions were assessed for measures of central tendency (median) and dispersion (log₁₀ SD). Cumulative Sum (CUSUM) charts were created to assess whether screening centres and individual sonographers who had performed at least 30 NT measurements exhibited any systematic bias by checking whether their CUSUM scores exceeded predefined upper and lower control limits. Results: Of the 36 sonographers, only 67% (n?=?24) had performed 30 or more scans. The median NT-MOM at each screening centre ranged from 1.02 to 1.09. Screening centre standard deviations ranged from 0.073 to 0.099. CUSUM charts indicated that only one screening centre remained within the predefined control limits throughout the assessment period. Analysis of variance indicated that a statistically significant difference existed between the log NT-MoM distributions of the individual sonographers (F?=?10.7; p <0.0001). Inspection of the individual sonographer CUSUM charts indicated that 11 (45%) of the 24, with more than 30 NT measurements were either under or over measuring the NT. Conclusion: Prospective monitoring and feedback of quality assurance assessment results of sonographers and screening centres should be routinely reported as both are responsible, if equity of screening performance is to be maintained.     

Assessment of the value of reporting partial screening results in prenatal screening for Down syndrome

Prenatal screening for Down syndrome can be performed using the first trimester Combined Test [nuchal translucency (NT), pregnancy-associated plasma protein A (PAPP-A), free beta-human chorionic gonadotrophin (hCG) and maternal age] or the Integrated Test (for example, NT and PAPP-A in the first trimester and two or more serum markers in the second trimester, all with maternal age). We investigated the value of providing partial results when using the Combined Test or Integrated Test to identify women with a high enough risk of having an affected pregnancy based on NT and maternal age alone such that there would be little advantage in combining this information with data on the serum markers. We also assessed whether in programmes using the Integrated Test it is worthwhile reporting partial results based on risk using first trimester markers and not obtaining a second trimester blood sample. Published data based on 480 affected and 96 839 unaffected pregnancies were used for the present study. Using NT and age alone, about 0.14% of all women screened would have such a high risk that they would always remain screen-positive after the Combined Test and only 0.06% would remain screen-positive after the Integrated Test. Similarly, about 0.07% of all women screened who have a high risk based on NT, PAPP-A and age would remain screen-positive after the Integrated Test. These percentages are too small to justify reporting two risk estimates for all women, given the confusion this would generate. It is therefore not worthwhile reporting partial risk estimates in screening programmes using the Combined Test or Integrated Test.     

Prenatal screening for Down syndrome with maternal serum human chorionic gonadotropin levels

Human chorionic gonadotropin levels in midtrimester pregnancies may be predictive of Down syndrome. A commercially available enzyme immunoassay kit was used to measure the beta-subunit of human chorionic gonadotropin in maternal sera from 38 Down syndrome pregnancies and 114 gestational age matched controls. The human chorionic gonadotropin levels were also assayed in 236 normal sera and plasma samples to determine normative values and appropriate individual corrections. Serum and plasma human chorionic gonadotropin levels are closely correlated and are stable at room temperature, during refrigeration, and throughout freeze-thaw cycles. There is no correlation between the human chorionic gonadotropin level and maternal age, weight, or race. However, the human chorionic gonadotropin level decreases with each week of gestation from 15 to 19 weeks. Medians for each week of gestation were established to account for this variable. Up to 63% of the Down syndrome pregnancies were detected with a cutoff of 2.0 multiples of the normal median. A computational combination of human chorionic gonadotropin and maternal serum alpha-fetoprotein testing will detect additional Down syndrome pregnancies and decrease the false-positive rate. The measurement of human chorionic gonadotropin appears to be a valuable addition to maternal serum alpha-fetoprotein screening programs that can significantly increase the proportion of Down syndrome cases diagnosed.     

Residual risk for cytogenetic abnormalities after prenatal diagnosis by interphase fluorescence in situ hybridization (FISH)

Results from conventional cytogenetic studies on 21 609 amniotic fluid specimens were analyzed retrospectively to determine the residual risk for a cytogenetic abnormality if interphase FISH, capable of only detecting aneuploidy for chromosomes 13, 18, 21, X and Y, was performed and did not reveal an abnormality. Detection rates (the probability of detecting a cytogenetic abnormality when an abnormality is present) and residual risks (the likelihood of a cytogenetic abnormality, in view of normal interphase FISH results) were calculated for the four major clinical indications for prenatal diagnosis (advanced maternal age, abnormal maternal serum screen indicating increased risk for trisomy 18 or trisomy 21, abnormal maternal serum screen indicating increased risk for neural tube defects and ultrasound abnormality). Differences in detection rates were observed to depend on clinical indication and presence or absence of ultrasound abnormalities. The detection rate ranged from 18.2 to 82.6% depending on the clinical indication. The detection rates of abnormalities significant to the pregnancy being evaluated (i.e. abnormalities excluding familial balanced rearrangements and familial markers) were between 28.6 and 86.4%. The presence of ultrasound abnormalities increased the detection rate from 72.2 to 92.5% for advanced maternal age and from 78.6 to 91.3% for abnormal maternal serum screen, indicating increased risk for trisomy 18 or trisomy 21. With regard to residual risk, the risk for a clinically significant abnormality decreased from 0.9-10.1%, prior to the interphase FISH assay, to a residual risk of 0.6-1.5% following a normal interphase FISH result in the 4 groups studied. Providing patients with detection rates and residual risks, most relevant to their situation (clinical indication and presence or absence of ultrasound abnormality) during counseling, could help them better understand the advantages and limitations of interphase FISH in their prenatal diagnostic evaluation.     

Current methods of prenatal screening for Down syndrome and other fetal abnormalities

Prenatal diagnosis of Down syndrome is widely available, but the determination of which patients should undergo prenatal diagnosis is changing. With the recent acceptance of first-trimester and integrated screening as a part of routine clinical practice, there are now a variety of accepted screening protocols for Down syndrome and other aneuploidies. These choices can be confusing both to both patients and providers. The following discussion is meant to outline the various options in prenatal screening, and their individual advantages and disadvantages.     

Weight adjustment of serum markers in early first-trimester prenatal screening for Down syndrome

OBJECTIVE: To assess whether existing weight correction formulas for PAPP-A and free-beta-hCG developed for weeks 11 to 14 can be applied to pregnancies in weeks 8 to 10. METHODS: Development of formulas based on limited data sets of 8- to 10-week pregnancies and comparison with existing formulas. Calculation of median MoMs adjusted with different formulas for weight correction. RESULTS: Weight correction formulas for the gestational age of 11 to 14 weeks were not appropriate in the 8- to 10-week gestational age interval for PAPP-A, whereas existing weight correction formulas could be applied to free-beta-hCG, independent of gestational age interval. CONCLUSION: If PAPP-A is used in different gestational age intervals, weight corrections should be developed for the interval.     

Chinese weight-correction model for maternal serum markers in Down syndrome prenatal screening.

OBJECTIVE: To determine the best weight-correction model by means of analyzing the relationship between maternal weight and maternal serum markers when screening for Down syndrome in China. METHODS: Serum levels of alpha-fetoprotein (AFP) and free beta-human chorionic gonadotropin (hCG) were measured in 35,917 Chinese women during the second semester of a normal singleton pregnancy and converted to multiple of median (MoM) values. Using 2 methods of statistical analysis, the all-point method and the median regression method, 4 weight-correction models were then tried, the simple linear, reciprocal, quadratic, and log-linear regression models. RESULTS: The median regression method performed better than the all-point method, and the quadratic regression model showed the best fit for both AFP and hCG in the median regression method, with adjusted R(2)s of 0.987 and 0.988, respectively. CONCLUSION: The quadratic regression model was found to be the most suitable for Chinese pregnant women.     

Second-trimester prenatal screening markers for Down syndrome in women with insulin-dependent diabetes mellitus

Published studies have shown that some serum markers used in screening for Down syndrome tend to be lower among women with insulin-dependent diabetes mellitus (IDDM). On this basis, many screening programmes adjust the marker levels to take account of this difference. Recent studies suggested that the marker levels were not different, and so adjustment may no longer be needed, possibly because of better diabetic control. Data from a prenatal screening programme for Down syndrome were examined to see whether the median values of second-trimester screening markers were still reduced in pregnant women with IDDM. A total of 366 women with IDDM singleton pregnancies without Down syndrome were identified from the screening programme at Barts from 1989 to 2002. After allowing for maternal weight, the median multiples of the median (MoM) for IDDM-unaffected singleton pregnancies were as follows: 0.88 (95% confidence interval 0.84-0.93) for alphafetoprotein (AFP), 0.95 (0.91-0.99) for unconjugated oestriol (uE3), 0.90 (0.80-1.01) for total human chorionic gonadotrophin (total hCG), 0.98 (0.88-1.08) for free beta-hCG, and 0.99 (0.89-1.10) for inhibin-A. The median levels for AFP and uE3 were statistically significantly lower in pregnant women with IDDM. The other markers were not significantly different in women with and without IDDM. There remains a case for adjusting AFP and uE3 levels in women with IDDM in prenatal screening programmes for Down syndrome.     

双色共变性荧光原位杂交产前诊断胎儿唐氏综合征

目的 探讨双色共变性荧光原位杂交用于非侵入性产前诊断胎儿唐氏综合征的可行性。方法 对11例孕妇外周血中的胎儿有核红细胞进行抗血型糖蛋白磁珠直接标记,再经磁激活细胞分选法富集,以Y和21号染色体专一探针对分离的胎儿有核红细胞行双色共变性荧光原位杂交,预测胎儿21号染色体倍性和性别,并用羊水染色体核型分析结果,验证预测准确性。结果 11例胎儿21号染色体倍性均正常,与羊水染色体核型分析结果相符。其中5例为男性胎儿,男性胎儿有核红细胞数量为9－65个,平均为25个,男性胎儿有核红细胞纯度为1．4％－18．8％;6例为女性胎儿,孕妇外周血中未见男性胎儿有核红细胞;性别预测结果与羊水染色体型分析结果一致。结论 双色共变性荧光原位杂交用于分析胎儿21号染色体倍性及性别,诊断胎儿唐氏综合征准确、可靠。