关于新时期师德建设的探索

本文笔者通过回顾历史上优秀的师德观,明确加强新时期师德建设的意义;分析现阶段师德面临的新问题,探讨应如何正视和解决这些问题,以加强新时期师德建设。     

Screening for fetal Down syndrome with maternal serum hCG and oestriol: A prospective study

We report the preliminary results of a prospective study aimed at evaluating the effectiveness of Down syndrome (DS) screening using second-trimester measurement of maternal serum human chorionic gonadotrophin (hCG) and unconjugated oestriol (uE3) together with maternal age. Reference values for hCG, uE3, and the hCG/uE3 ratio in normal pregnancies were established from more than 3000 normal gestations and found to follow a log-normal statistical distribution. Risk evaluation was made using reference values for affected pregnancies from retrospective studies. Screening of 10 000 women under 38 years resulted in 412 amniocenteses and the prenatal diagosis of six cases of DS, whereas four cases remained undetected until term. In a parallel study, diagnostic amniocentesis was performed in women over 38 years and in women with a previous affected child, and an evaluation of the risk of fetal DS based on serum hCG and uE3 levels was made in all cases. Fourteen cases of DS were detected. Median values for hCG and uE3 in the 24 affected pregnancies were close to the 90th and tenth centiles of the normal reference values, respectively, and thus are in good agreement with the values reported by others in retrospective studies.     

Heteroduplex formation: A potential source of genotyping error from PCR products

The formation of heteroduplexes from polymerase chain reaction (PCR) products has recently become a diagnostic tool that is routinely used for the prenatal detection of small deletions or insertions in a number of disease-causing alleles. We present evidence illustrating that heterozygous PCR products can manifest ‘invisible’ heteroduplexes that can ultimately lead to genotyping errors. Justifications for these ‘invisible’ heteroduplexes and requisite parameters to optimize their detection are presented.     

Droplet digital PCR is a cost-effective method for analyzing long cell-free DNA in maternal plasma: Application in preeclampsia

Objective

Long cell-free DNA (cfDNA) can be found in the plasma of pregnant women and cancer patients. We investigated if droplet digital PCR (ddPCR) can analyze such molecules for diagnostic purposes using preeclampsia as a model.

Method

Plasma samples from ten preeclamptic and sixteen normal pregnancies were analyzed. Two ddPCR assays targeting a single-copy gene, VCP, and one ddPCR assay targeting LINE-1 repetitive regions were used to measure the percentages of long cfDNA >533, 1001, and 170 bp, respectively. The LINE-1 assay was developed as guided by in silico PCR analyses to better differentiate preeclamptic and normal pregnancies.

Results

Preeclamptic patients had a significantly lower median percentage of long cfDNA than healthy pregnant controls, as determined by the LINE-1 170 bp assay (28.9% vs. 35.1%, p < 0.0001) and the VCP 533 bp assay (6.6% vs. 8.7%, p = 0.014). The LINE-1 assay provided a better differentiation than the VCP 533 bp assay (area under ROC curves, 0.94 vs. 0.79).

Conclusion

ddPCR is a cost-effective approach for unlocking diagnostic information carried by long cfDNA in plasma and may have applications for the detection of preeclampsia. Further longitudinal studies with larger cohorts are required to assess the clinical utility of this test.     

Population screening for gestational hypertensive disorders using maternal,fetal and placental characteristics: A population-based prospective cohort study

Objective

To determine screening performance of maternal, fetal and placental characteristics for selecting pregnancies at risk of gestational hypertension and preeclampsia in a low-risk multi-ethnic population.

Method

In a prospective population-based cohort among 7124 pregnant women, we collected maternal characteristics including body mass index, ethnicity, parity, smoking and blood pressure in early-pregnancy. Fetal characteristics included second and third trimester estimated fetal weight and sex determined by ultrasound. Placental characteristics included first and second trimester placental growth factor concentrations and second and third trimester uterine artery resistance indices.

Results

Maternal characteristics provided the best screening result for gestational hypertension (area-under-the-curve [AUC] 0.79 [95% Confidence interval {CI} 0.76-0.81]) with 40% sensitivity at 90% specificity. For preeclampsia, the maternal characteristics model led to a screening performance of AUC 0.74 (95% CI 0.70-0.78) with 33% sensitivity at 90% specificity. Addition of second and third trimester placental ultrasound characteristics only improved screening performance for preeclampsia (AUC 0.78 [95% CI 0.75-0.82], with 48% sensitivity at 90% specificity).

Conclusion

Routinely measured maternal characteristics, known at the start of pregnancy, can be used in screening for pregnancies at risk of gestational hypertension or preeclampsia within a low-risk multi-ethnic population. Addition of combined second and third trimester placental ultrasound characteristics only improved screening for preeclampsia.

     

Detection of fetal HLA-DQα sequences in maternal blood: A gender-independent technique of fetal cell identification

The objective of this study was to detect fetal HLA-DQα gene sequences in maternal blood. HLA-DQα genotypes of 70 pregnant women and their partners were determined for type A1. We specifically sought couples where the father, but not the mother, had genotype A1. In 12 women, maternal blood samples were flow-sorted. Candidate fetal cells were isolated and amplified by using PCR primers specific for a paternal HLA-DQα A1 allele. Fetal HLA-DQα A1 genotype was predicted from sorted cells; amniocytes or cheek swabs were used for confirmation. Six of twelve sorted samples had amplification products indicating the presence of the HLA-DQα A1 allele; 6/12 did not. Prediction of the fetal genotype was 100 per cent correct, as determined by subsequent amplification of amniocytes or cheek swabs. We conclude that paternally inherited uniquely fetal HLA-DQα gene sequences can be identified in maternal blood. This system permits the identification of fetal cells independent of fetal gender, and has the potential for non-invasive prenatal diagnosis of paternally inherited conditions.     

Raised maternal serum alpha-fetoprotein in the absence of fetal abnormality-placental findings. A quantitative morphometric study

Ten placentae from pregnancies proceeding to term from mothers who on routine screening at 16–18 weeks gestation were found to have a raised serum AFP but no increase in amniotic fluid AFP and no fetal abnormality, were studied using morphometric techniques. The results were compared with 20 placentae from normal term pregnancies where the maternal serum AFP level was not elevated. The mean total placental volume, volume of parenchyma and villous surface area were increased in the placentae associated with a raised maternal serum AFP. More of these placentae were infarcted and the fetal-placental weight ratio was significantly lower. The hypothesis that elevation of maternal serum AFP level is related to the increase in placental size is addressed.     

Duplication of chromosome 11 centromere in fetal and maternal karyotypes: A new variant?

Fetal chromosome analysis in a 39-year-old mother revealed a chromosome 11 aberration interj ireted as a duplication of the centromere. This was also found in the mother's karyotype, raising the possibility that the abnormality was a new variant of no clinical consequence.     

Real-time PCR with molecular beacons provides a highly accurate assay for detection of Tay-Sachs alleles in single cells

The results presented here provide the first single-cell genetic assay for Tay-Sachs disease based on real-time PCR. Individual lymphoblasts were lysed with an optimized lysis buffer and assayed using one pair of primers that amplifies both the wild type and 1278 + TATC Tay-Sachs alleles. The resulting amplicons were detected in real time with two molecular beacons each with a different colored fluorochrome. The kinetics of amplicon accumulation generate objective criteria by which to evaluate the validity of each reaction. The assay had an overall utility of 95%, based on the detection of at least one signal in 235 of the 248 attempted tests and an efficiency of 97%, as 7 of the 235 samples were excluded from further analysis for objective quantitative reasons. The accuracy of the assay was 99.1%, because 228 of 230 samples gave signals consistent with the genotype of the cells. Only two of the 135 heterozygous samples were allele drop-outs, a rate far lower than previously reported for single-cell Tay-Sachs assays using conventional methods of PCR. Copyright © 2002 John Wiley & Sons, Ltd.     

Trophoblast-like cells sorted from peripheral maternal blood using flow cytometry: A multiparametric study involving transmission electron microscopy and fetal dna amplification

Three monoclonal antibodies (MAbs) against trophoblast (GB17, GB21, and GB25) and flow cytometry were used to sort trophoblast-like cells (TLCs) from peripheral blood of pregnant women. Sorted TLCs were processed for electron microscopy and fetal DNA amplification of the Y-specific sequences from mothers carrying male fetuses. At the ultra-structural level, most of the nucleated cells had the morphology of leucocytes, suggesting maternal contaminants, and we did not find the characteristic features of the free inter-villous trophoblast cells. Nevertheless, polymerase chain reaction (PCR) analysis showed an amplification of Y-specific sequences in two out of three samples of sorted TLCs. These results suggest that besides the maternal leucocytes, sufficient trophoblast nucleated fetal cells can be obtained using cell enrichment by sorting. This sensitive method holds promise for non-invasive prenatal diagnosis of fetal sex and if sufficient Y(positive) nuclei are found, for the diagnosis of selected numerical chromosome abnormalities.