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排序方式: 共有246条查询结果,搜索用时 15 毫秒
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Kevin Spencer 《黑龙江环境通报》2002,22(3):244-246
Over the past three years approximately 12 000 women have been screened in the first trimester through our OSCAR programme, which utilizes fetal NT and maternal serum free β-hCG and PAPP-A. During this time 30 cases of Down syndrome were identified either prenatally or postnatally. Using an established procedure the accuracy of predicted risk for Down syndrome was assessed in a population of 30 cases of Down syndrome and 11 758 unaffected pregnancies. The correlation between predicted risk and prevalence of Down syndrome was very high (r=0.9995). It is concluded that risks produced by the Fetal Medicine Foundation combined risk algorithm agree very closely with Down syndrome prevalence and can be used with confidence when counselling women of their risk. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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The great majority of genetic defects underlying steroid 21-hydroxylase deficiency appear to result from intergenic recombinations between the homologous CYP21 and CYP21P genes. For a minority, novel sporadic point mutations have been detected. De novo mutations in CYP21 have also been reported, but only a few studies have systematically screened their occurrence. We here describe a population-based patient sample in order to estimate the rate of single-family (i.e. sporadic) and de novo germline mutations in the human CYP21 locus. Among 76 Finnish families were observed three single-family mutations and two de novo mutations in CYP21. The rates obtained, ∼5% and ∼2% for novel and de novo mutations, respectively, indicate that they are not rare and that their occurrence should not be ignored in genetic diagnostics of this disorder. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Kevin Spencer Adolfo W. Liao Charas Y. T. Ong Lut Geerts Kypros H. Nicolaides 《黑龙江环境通报》2001,21(6):441-444
Dimeric inhibin A was measured in maternal serum samples from 45 pregnancies affected by trisomy 21 and 493 samples from unaffected pregnancies at 10–14 weeks of gestation. Inhibin A levels in affected pregnancies were compared with levels of free β-hCG and PAPP-A in the same series. In the trisomy 21 group, the median multiple of the median (MoM) inhibin A was not significantly elevated (1.28 vs 1.00) with only 15.5% being above the 95th centile. In contrast, the median MoM free β-hCG was significantly increased (2.05 vs 1.00) with 36% above the 95th centile and PAPP-A was significantly reduced (0.49 vs 1.00) with 42% below the 5th centile. Inhibin A levels in the trisomy 21 group were significantly correlated with gestational age such that median levels rose from 1.04 at 11 weeks to 1.30 at 12 weeks and 1.67 at 13 weeks. These findings suggest that first trimester biochemical screening for trisomy 21, which is currently optimised using maternal serum free β-hCG and PAPP-A and fetal nuchal translucency, will not benefit from the inclusion of inhibin A. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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7Be、210Pb等放射性核素已被广泛应用于区域及全球物质传输途径示踪的研究中。2009年8月到2010年10月在上海市普陀区华东师范大学校园设采样点采集了51场大气降水样品,分析了单次降水事件中7Be和210Pb的含量以及湿沉降通量的变化特征,并对比不同季节的变化特征。结果表明:1)单次降水事件中7Be的浓度变化范围为0.21~5.99 Bq/L,210Pb浓度的变化范围为0.01~0.90 Bq/L。7Be和210Pb的月均浓度具有明显的季节变化特征:7Be的浓度高值出现在冬季,夏季浓度最低;210Pb浓度高值出现在秋、冬季节,夏季浓度最低;7Be/210Pb高值主要出现在春、秋季节。2)7Be、210Pb沉降通量与降水量有一定相关性,但单次降水事件7Be和210Pb浓度与降水量并没有很好的相关性。7Be和210Pb沉降通量存在着较好的相关性,指示7Be、210Pb沉降路径有着较好的一致性。 相似文献
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This paper analyzes whether energy performance certificates (EPCs) serve as means to reduce the information asymmetry among market participants during the sale of homes. Using a sample of 876,000 single-family homes in the Netherlands, we examine the impact of EPC adoption on the speed of sale. Our results indicate that energy-rated homes sell faster than non-energy-rated homes, an effect that varies by 7–12 percent depending on model specifications and increases when positive (green) ratings are granted. The information conveyed by these certificates reduces the information asymmetry between buyers and sellers, which helps to reduce the uncertainty of quality. 相似文献
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Assessments of risk to biodiversity often rely on spatial distributions of species and ecosystems. Range‐size metrics used extensively in these assessments, such as area of occupancy (AOO), are sensitive to measurement scale, prompting proposals to measure them at finer scales or at different scales based on the shape of the distribution or ecological characteristics of the biota. Despite its dominant role in red‐list assessments for decades, appropriate spatial scales of AOO for predicting risks of species’ extinction or ecosystem collapse remain untested and contentious. There are no quantitative evaluations of the scale‐sensitivity of AOO as a predictor of risks, the relationship between optimal AOO scale and threat scale, or the effect of grid uncertainty. We used stochastic simulation models to explore risks to ecosystems and species with clustered, dispersed, and linear distribution patterns subject to regimes of threat events with different frequency and spatial extent. Area of occupancy was an accurate predictor of risk (0.81<|r|<0.98) and performed optimally when measured with grid cells 0.1–1.0 times the largest plausible area threatened by an event. Contrary to previous assertions, estimates of AOO at these relatively coarse scales were better predictors of risk than finer‐scale estimates of AOO (e.g., when measurement cells are <1% of the area of the largest threat). The optimal scale depended on the spatial scales of threats more than the shape or size of biotic distributions. Although we found appreciable potential for grid‐measurement errors, current IUCN guidelines for estimating AOO neutralize geometric uncertainty and incorporate effective scaling procedures for assessing risks posed by landscape‐scale threats to species and ecosystems. 相似文献