Second-trimester diurnal variation of maternal serum alpha-fetoprotein,human chorionic gonadotropin,and unconjugated oestriol: Is it present and does it affect the prediction of a patient's risk for fetal down syndrome?

Both a cross-sectional and a longitudinal study were performed to investigate whether or not the collection time should be taken into consideration when generating a patient's risk for fetal Down syndrome with multiple marker screening. Diurnal variations of third-trimester alpha-fetoprotein (AFP) levels and first-trimester human chorionic gonadotropin (hCG) levels have been previously reported. In addition, large episodic fluctuations of conjugated and unconjugated oestriol (uE3) as well as a diurnal variation have also been reported in the third trimester. If the levels of these analytes routinely fluctuate during the day, they could affect a patient's risk calculation for fetal Down syndrome. The longitudinal study evaluated ten non-diabetic women who underwent sequential sampling for AFP, hCG, and uE3. The cross-sectional study evaluated 1953 patients for these three markers whose time of sampling was recorded between 8·00 a.m. and 5·59 p.m. Using either study design, no significant effect was seen in the median MOM levels of the screening analytes as a function of the time of day.     

Changes in element composition along the spinning duct in a Nephila spider

The silk gland of the golden orb spider Nephila edulis connects to the exit spigot through a long S-shaped duct that assists in the formation of the thread. Previous evidence suggests that the epithelium of the distal (last) part of the duct is specialized for ion transport and that a proton pump is involved in this process. Here, we present evidence from SEM (scanning electron microscope)-EDAX (energy dispersive X-ray) microanalysis of rapidly frozen material maintained at approximately -150°C and from the use of pH indicators that the element composition and pH change progressively as the dragline silk dope (spinning solution) passes down the duct to form the thread. Na⁺ and Cl^- composition decreased while K⁺ and P and S increased. Indicators suggested that the pH dropped from 6.9ǂ.1 to 6.3ǂ.1. These novel findings suggest that the absorption of Na⁺ and secretion of the more chaotropic K⁺ may help the silk protein molecules to refold while the secretion of H⁺ may assist in this process and reduce the repulsive charges on them. This in turn may allow the molecules to approach one another more closely to crystallize. Thus precise control of the ionic environment within the spider's spinning duct may be important in forming a tough insoluble thread and when devising mimetic processes to spin silk proteins industrially.     

Amniotic alpha-fetoprotein in the prenatal diagnosis of congenital nephrotic syndrome of the finnish type

Congenital nephrosis of the Finnish type (CNF) is rare outside Finland, where the incidence may be as high as 1 in 2000 live births. Neonates with the disorder develop renal failure within the first months of life and without renal transplantation, the prognosis is extremely poor. This case report describes a woman's three pregnancies, two of which were affected with CNF.     

Amniotic fluid acetylcholinesterase measurements: Comparing immunochemical and polyacrylamide gel techniques

In the present study, a recently reported immunochemical technique for measuring acetylcholinesterase (AChE) in amniotic fluid utilizing the 4F19 antibody was compared with the widely utilized polyacrylamide gel technique to determine whether the immunochemical assay provided an advantage in separating unaffected pregnancies from those associated with open spina bifida (OSB) and open ventral wall defects (OVWD). The study included (1) 73 amniotic fluid samples from unaffected pregnancies [alpha-fetoprotein (AFP) < 2 MoM] with no visible gel AChE band, (2) nine bloodstained samples from unaffected pregnancies (AFP 2·2–4·0 MoM) with visible gel AChE bands, (3) 18 samples associated with OSB (AFP 2·2–7·0 MoM) with visible gel AChE bands, and (4) 20 samples associated with OVWD (AFP 3·2–53·5 MoM) with visible gel AChE bands. The immunochemical assay produced ranges of measurements in the four respective categories as follows: (1) 2–60 arbitrary units (AU): (2) 14–69 AU, (3) 61–593 AU, and (4)22–476 AU. Eight of the nine unaffected pregnancies with visible gel AChE bands had immunochemical measurements below the highest measurement for the samples with no visible AChE band (60 AU), as did five out of 20 OVWD pregnancies. Two of the OSB cases had values of 61 and 62 AU. These data indicate that the 4F19 specific monoclonal antibody to AChE is capable of distinguishing unaffected from affected pregnancies with reasonable reliability but that more work needs to be done to establish the extent of overlap between the unaffected and affected populations.     

Amniotic fluid alpha-fetoprotein and acetylcholinesterase measurements in pregnancies associated with gastroschisis

In this study we define for the first time the distribution of alpha-fetoprotein levels and acetylcholinesterase ratios in amniotic fluid samples associated with fetal gastroschisis. Elevated alpha-fetoprotein levels and positive acetylcholinesterase measurements are found in virtually all cases, indicating that these combined measurements are highly reliable in detecting this lesion.     

Prenatal diagnosis of 45,X/46,XX mosaicism: True mosaicism in only one of four primary cultures

45,X/46,XX mosaicism was found in only one of four primary amniotic fluid cultures. Repeat amniocentesis revealed 45,X/46,XX mosaicism in all four primary cultures. Mosaicism was confirmed in tissues from the abortus.     

Risk-based prenatal screening for trisomy 18 using alpha-fetoprotein,unconjugated oestriol and human chorionic gonadotropin

Nine centres collaborated to examine the feasibility of a screening method for trisomy 18 that was based on assigning individual risk, using a combination of maternal age and measurements of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and human chorionic gonadotropin (hCG). Second-trimester measurements of these analytes were obtained from 94 trisomy 18 pregnancies. In the 89 pregnancies without an associated open defect, the median levels for AFP, uE3, and hCG were 0.65, 0.43 and 0.36 multiples of the unaffected population median, respectively. The strongest individual predictor of risk for trisomy 18 was uE3, followed by hCG, AFP, and maternal age, in that order. Using a method of individual risk estimation that is based on the three markers and maternal age, 60 per cent of pregnancies associated with trisomy 18 would be detected at a risk cut-off level of 1:100, with a false-positive rate of about 0.2 per cent. One in nine pregnancies identified as being at increased risk for trisomy 18 would be expected to have an affected pregnancy. This risk-based screening method is more efficient than an existing method that is based on fixed analyte cut-off levels. Even though the birth prevalence of trisomy 18 is low, prenatal screening can be justified when performed in conjunction with Down syndrome screening and when a high proportion of women offered amniocentesis have an affected fetus.     

Human chorionic gonadotropin and unconjugated oestriol measurements in insulin-dependent diabetic pregnant women being screened for fetal down syndrome

This prospective study investigates the relationship between insulin-dependent diabetes and maternal serum levels of alpha-fetoprotein (AFP), unconjugated oestriol (uE3), and human chorionic gonadotropin (hCG). It also examines the potential impact on screening for Down syndrome. The population-based cohort included 20 321 pregnant women in Maine who underwent routine serum screening for Down syndrome in the second trimester. The cohort included 52 women with insulin-dependent diabetes. Maternal serum AFP levels are now routinely adjusted for insulin-dependent diabetes. These adjustments, therefore, were made routinely in the diabetic women, but no equivalent adjustments were made for uE3 and hCG values. The initial false-positive rate (using all three markers) among the women with diabetes was not significantly different from that in the non-diabetic population (7·7 and 5·4 per cent, respectively). Prior to adjustment for insulin-dependent diabetes, the median AFP level in the 52 women was 0·73 multiples of the median (MOM); the median levels of uE3 and hCG were 0·93 and 0·98 MOM, respectively. When the uE3 and hCG levels were adjusted, the initial false-positive rate was unchanged. Median serum levels of uE3 were significantly higher in the 33 women whose onset of diabetes was prior to 19 years of age (0·99 MOM) than in the 19 women whose onset of diabetes was at age 19 or older (0·84 MOM). This is the first population-based study to investigate the relationship between diabetes and serum levels of AFP, uE3, and hCG, and confirms earlier observations from a case—control study that found only slightly lower uE3 and hCG levels.     

Effects of channel incision on base flow stream habitats and fishes

Channel incision is a widespread phenomenon that results in stream and riparian habitat degradation. Fishes and physical habitat variables were sampled at base flow from three incised stream channels and one reference stream in northwest Mississippi, USA, to quantify incision effects on fish habitat and provide a basis for habitat rehabilitation planning and design. Incised channels were sampled in spring and autumn; the reference channel was sampled only in the autumn. Incised channel habitat quality was inferior to the reference channel despite the presence of structures designed to restore channel stability. Incised channels had physical habitat diversity levels similar to a nonincised reference channel, but contained fewer types of habitat. At base flow, incised channels were dominated by shallow, sandy habitats, moderate to high mean local Froude numbers, and had relatively little organic debris in their beds. In contrast, the reference stream had greater mean water depth, contained more woody debris, and provided more deep pool habitat. Fish assemblages in incised channels were composed of smaller fishes representing fewer species relative to the reference site. Fish species richness was directly proportional to the mean local Froude number, an indicator of the availability of pool habitat.     

The case of the disappearing firms: empirical evidence and implications

Organizational survival represents a vital objective for firms, managers, and owners. Most organizational theories regard survival as the ‘correct’ outcome for firms whose managers successfully navigate across a hostile competitive landscape. On the other hand, when a firm ‘disappears,’ scholars, managers, and owners ask, What went wrong?' Failure, exit, bankruptcy, liquidation, hostile takeovers, are largely viewed as results of managerial ‘bungling.’ Many theories about performance, competitive advantage, legitimacy, and leadership rest upon a core assumption that firms, at least some of them, have long, perhaps limitless, life‐spans. Long‐term survival is not seen as merely a random outcome or an unattainable goal. This paper surveys a broad set of empirical findings about firms' life‐spans. It is consistently revealed in the empirical literature that the VAST majority of firms, even large firms, survive relatively short periods. Some themes and their implications are discussed. Copyright © 2006 John Wiley & Sons, Ltd.