Parental mosaic trisomy 21 detected following maternal cell contamination of an amniotic fluid specimen from a normal male pregnancy

We report a case of maternal mosaic trisomy 21 ascertained at prenatal diagnosis as a result of maternal cell contamination of an amniotic fluid sample. A 34 year old female was referred for karyotyping because of a previous trisomy 21 pregnancy. Chromosome analysis of primary in situ cultures showed a karyotype of 47,XX, + 21[6]/46,XY[32]/46,XX[2]. Molecular testing demonstrated maternal cell contamination of the amniotic fluid sample and G-banded karyotyping of maternal blood showed that 3/200 cells had trisomy 21, consistent with the mother being a Down syndrome mosaic. A normal male baby with a 46,XY chromosome complement was delivered at 30 weeks. This case emphasises the need for close collaboration between cytogenetic and molecular genetics laboratories in resolving unusual cases of mosaicism. Copyright © 2007 John Wiley & Sons, Ltd.     

Time discounting and the decision to protect areas that are near and threatened or remote and cheap to acquire

Should conservation organizations focus on protecting habitats that are at imminent risk of being converted but are expensive or more remote areas that are less immediately threatened but where a large amount of land can be set aside? Variants of this trade‐off commonly arise in spatial planning. I used models of land‐use change near a deforestation frontier to examine this trade‐off. The optimal choice of where to protect was determined by how decisions taken today accounted for ecological benefits and economic costs of conservation actions that would occur sometime in the future. I used an ecological and economic discount rate to weight these benefits and costs. A large economic discount rate favored protecting more remote areas, whereas a large, positive ecological discount rate favored protecting habitat near the current deforestation frontier. The decision over where to protect was also affected by the influence economic factors had on landowners' decisions, the rate of technological change, and ecological heterogeneity of the landscape. How benefits and costs through time are accounted for warrants careful consideration when specifying conservation objectives. It may provide a niche axis along which conservation organizations differentiate themselves when competing for donor funding or other support.     

Detection and false-positive rates of maternal serum markers for Down syndrome screening according to maternal age in women over 35 years of age. A study of the agreement of eight dedicated software packages

Maternal serum markers for trisomy 21 screening (MSS) can be assayed in women ≥35 years in an attempt to reduce the need for invasive procedures and thereby avoid their side effects. Our objective was to compare, in women ≥35, eight different software packages dedicated to second trimester MSS, thus providing reliable data for patient counselling. A simulation study was carried out on 189 sera from women with Down syndrome fetuses and 11 962 sera from mothers of unaffected babies. The first step was to estimate the joint distribution of alpha-fetoprotein (AFP) and free beta-human chorionic gonadotrophin (β-hCG). The second step was to calculate trisomy 21 detection and false-positive rates for each software according to maternal age (35–45 years), using the usual 1:250 risk threshold. Agreement between software packages was measured using 2×2 kappa coefficients. Detection rates and false-positive rates increased with maternal age. Depending on the software, 57–71% detection rates were achieved at 35 years with 12–18% false-positive rates. At 45 years, 61–100% detection rates were achieved with 66–95% false-positive rates. Up to 39 years, all softwares were concordant (kappa coefficients >0.75). In the range 35–45 years, false-positive and detection rates increased substantially with maternal age and differences between software packages are observed. Copyright © 2002 John Wiley & Sons, Ltd.     

Minor sonographic signs of trisomy 21 at 15–20 weeks' gestation in fetuses born without malformations: a prospective study

A prospective study was performed on 2119 pregnancies that underwent genetic amniocentesis. Indications for amniocentesis were either maternal age (⩾35) or triple-test results (risk⩾1/380). The study covered a 36-month period and assessed the prevalence of minor ultrasound markers both in fetuses with Down syndrome and normal control fetuses at 15–19 week' gestation. Only fetuses with normal karyotype or trisomy 21 were considered. Six minor sonographic markers were considered: nuchal thickness, pyelectasia, femur observed/expected and humerus observed/expected ratios, bowel echogenicity, and choroid plexus cysts. One or more ultrasound soft markers were present in 23 out of 33 fetuses with Down syndrome (70%) and in 572 out of 2069 normal fetuses (28%). Copyright © 2001 John Wiley & Sons, Ltd.     

编研“中国西部开发综合安全减灾规划战略”的建议

中国西部大开发作为历史性的壮举 ,重在要有创新思路及观念的大转变。安全减灾作为一种国策及保障手段 ,必须是西部开发的先决条件 ,如果忽略了安全减灾规划战略的布署和开发行动 ,必然迟早要招致悲惨的后果。笔者提出此建议 ,旨在为中国西部开发探索一条生态、安全、减灾和谐发展之路 ,意在促进西部开发健康而有序的可持续发展。