Biological variability in concentrations of serum lipids: sources of variation among results from published studies and composite predicted values

To obtain the best estimates of the average intraindividual biological variability (CVb) in the concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDLC), high-density lipoprotein cholesterol (HDLC), and triglyceride serum lipids in a person's blood, we evaluated results from 30 studies published from 1970 to 1992. The usually more applicable random-effects model estimated an average CVb of 6.1% for TC, 7.4% for HDLC, 9.5% for LDLC, and 22.6% for triglyceride. Composite estimates of the average CVb from all evaluated published studies by different models of estimation ranged from 6.0% to 6.4% for TC, from 6.2% to 7.5% for HDLC, from 7.0% to 9.6% for LDLC, and from 22.4% to 22.9% for triglyceride. Two important factors influenced the reported biological variation of the study subjects: (a) the magnitude of the variability of the analytical method used and (b) the design characteristics of the study--primarily the number of subjects, the sampling interval, and the number of measurements per subject. For TC, we found a statistically significant positive correlation between the reported mean CVb and both the number of study subjects and the analytical variation. For TC and LDLC we estimate CVb as a function of the study design features. The number of patient specimens required to obtain reliable estimates for serum lipid concentrations are determined from the CVb and the current analytical variation.

Biological variability in concentrations of serum lipids: sources of variation among results from published studies and composite predicted values

To obtain the best estimates of the average intraindividual biological variability (CVb) in the concentrations of total cholesterol (TC), low-density lipoprotein cholesterol (LDLC), high-density lipoprotein cholesterol (HDLC), and triglyceride serum lipids in a person's blood, we evaluated results from 30 studies published from 1970 to 1992. The usually more applicable random-effects model estimated an average CVb of 6.1% for TC, 7.4% for HDLC, 9.5% for LDLC, and 22.6% for triglyceride. Composite estimates of the average CVb from all evaluated published studies by different models of estimation ranged from 6.0% to 6.4% for TC, from 6.2% to 7.5% for HDLC, from 7.0% to 9.6% for LDLC, and from 22.4% to 22.9% for triglyceride. Two important factors influenced the reported biological variation of the study subjects: (a) the magnitude of the variability of the analytical method used and (b) the design characteristics of the study--primarily the number of subjects, the sampling interval, and the number of measurements per subject. For TC, we found a statistically significant positive correlation between the reported mean CVb and both the number of study subjects and the analytical variation. For TC and LDLC we estimate CVb as a function of the study design features. The number of patient specimens required to obtain reliable estimates for serum lipid concentrations are determined from the CVb and the current analytical variation.

Abnormal cerebral hemodynamics in pregnancy-related hypertensive encephalopathy

A patient with an imminent pregnancy-related hypertensive encephalopathy is presented in whom transcranial Doppler ultrasound studies revealed increased middle cerebral artery blood flow velocities before and up to 7 days after cesarean section. These increased velocities are normally caused by cerebral vasospasm and subsequent hypoperfusion in pregnancy-related hypertensive encephalopathy. Additional duplex volume flow studies of the common carotid artery were in favor of cerebral hyperperfusion as a cause of the increased blood flow velocities. The clinical implications of these findings are discussed.

The individualised birthweight ratio: a more logical outcome measure of pregnancy than birthweight alone

OBJECTIVE

To provide a new outcome measure for pregnancy specifically related to the individual.

DESIGN

Computer analysis of physiological factors affecting birthweight.

SETTING

Two provincial teaching hospitals (University and City Hospitals, Nottingham) and an associated district general hospital (Derby City Hospital) serving a defined catchment area in the East Midlands.

SUBJECTS

All women delivering in the above hospitals since the start of computerised obstetric records: 31,561 women with gestational age verified by early pregnancy ultrasound scan data.

MAIN OUTCOME MEASURES

Calculation of the predicted birthweight taking into account maternal and fetal physiological factors. Derivation of the individualised birthweight ratio (actual birthweight divided by predicted birthweight expressed as a percentage) for each individual baby.

RESULTS

The individualised birthweight ratio redefines as normally grown 41% of babies below the 10th centile of crude birthweight for gestation. Other babies previously regarded as normal are redefined as growth retarded. At the upper end of the distribution 46% of those above the 90th centile of birthweight for gestation are redefined as normally grown.

CONCLUSIONS

The predicted birthweight can be calculated for an individual pregnancy at a given gestation. The standardised comparison between this predicted birthweight and the actual birthweight is a more logical reflection of the normality of intrauterine growth and therefore more logical as an outcome measure for pregnancy than crude birthweight for gestation.

Surgical treatment of children with medically intractable frontal or temporal lobe epilepsy: results and highlights of 40 years' experience

Etiologic, pathologic, and clinical features of possible prognostic significance were studied in 118 children who underwent frontal or temporal lobe epilepsy surgery at the Montreal Neurological Institute (MNI) between 1940 and 1980 (excluding tumor cases). Mean age of seizure onset was 5.1 years (range 0-12 years), mean age at operation was 11.7 years (range 0.6-15 years), and median duration of follow-up was 15 years (range 2-31 years). Thirteen of 45 frontal surgery patients and 43 of 73 temporal surgery patients had an excellent outcome. In the frontal surgery group, this was restricted almost entirely to patients with an established etiology, particularly if this included a circumscribed resectable structural abnormality. In the temporal surgery group, a history of early, prolonged febrile seizures was usually associated with good outcome, unless there was additional evidence of extratemporal epilepsy. In the entire series, the presence of a nonresectable structural lesion or secondarily generalized seizures was associated with a poor outcome.

Spatial and temporal dissection of immediate and early events following cadherin-mediated epithelial cell adhesion

Cell-cell adhesion is at the top of a molecular cascade of protein interactions that leads to the remodeling of epithelial cell structure and function. The earliest events that initiate this cascade are poorly understood. Using high resolution differential interference contrast microscopy and retrospective immunohistochemistry, we observed that cell-cell contact in MDCK epithelial cells consists of distinct stages that correlate with specific changes in the interaction of E-cadherin with the cytoskeleton. We show that formation of a stable contact is preceded by numerous, transient contacts. During this time and immediately following formation of a stable contact, there are no detectable changes in the distribution, relative amount, or Triton X-100 insolubility of E-cadherin at the contact. After a lag period of approximately 10 min, there is a rapid acquisition of Triton X-100 insolubility of E-cadherin localized to the stable contact. Significantly, the total amount of E-cadherin at the contact remains unchanged during this time. The increase in the Triton X-100 insoluble pool of E-cadherin does not correlate with changes in the distribution of actin or fodrin, suggesting that the acquisition of the Triton X-100 insolubility is due to changes in E-cadherin itself, or closely associated proteins such as the catenins. The 10 minute lag period, and subsequent prompt and localized nature of E-cadherin reorganization indicate a form of signaling is occurring.

Bleeding varices due to portal hypertension in sarcoidosis. Favorable effect of propranolol and prednisone

A 58-year-old white man had bleeding varices in the gastric fundus due to portal hypertension attributable to histologically proven hepatic sarcoid involvement with a giant splenomegaly and with an angiographically demonstrated significant flow toward the liver. Treatment with corticosteroids and beta-blockade (30 mg propranolol daily) resulted in no rebleeding for over one year follow-up.

A rapid bioassay for the determination of non-nucleoside HIV-1 reverse transcriptase inhibitor plasma levels

A rapid method for measuring pyridinone HIV-1 reverse transcriptase inhibitor plasma levels was necessary for identifying potential clinical candidates and for choosing a clinical formulation. Due to its sensitivity to the pyridinones, ability to tolerate extraneous material, and its capability for rapid, high through-put screening, the HIV-1 RT assay was developed into a bioassay for determining plasma levels of the pyridinones in Rhesus monkey plasma. With this assay, dose proportionality of L-697, 639 was established. Formulation studies using L-697, 639 indicated that the plasma levels achieved in Rhesus monkeys with the clinical formulation (peak levels = 3.9 microM at 30 min) fall between the levels achieved with polyethylene glycol 300 and hydroxypropyl methyl cellulose formulations (peak levels = 8.9 microM and 0.4 microM respectively, at 60 min). Two other pyridinones, L-696, 229 and L-697, 661, administered as the clinical formulation, had peak plasma levels of 1.6 microM (30 min) and 0.3 microM (60 min), respectively. In Rhesus monkeys, the bioavailabilities of these compounds (administered as the clinical formulation) ranged from 11 to 24% and their half-life values ranged from 24 to 120 min. The results of oral studies in Rhesus monkeys with these compounds were very similar to initial results of studies in humans.

The detection of autoantibodies to IgE in plasma of individuals infected with hookworm (Necator americanus) and the demonstration of a predominant IgG1 anti-IgE autoantibody response

In this study we have demonstrated significantly elevated levels of circulating IgG autoanti-IgE antibody in hookworm infected individuals from Kebasob village on Karkar Island, Papua New Guinea. Although anti-IgE activity was demonstrable in IgG1, IgG3 and IgG4, IgG1 was by far the most important subclass of IgG anti-IgE in terms of frequency of detection (34/39; 87.2%) and magnitude of increase (P = 0.0000); with IgG3 (16/39; 41.0%) and IgG4 (15/39; 38.5%) antibodies being considerably less prevalent. Plasma levels of IgG1 anti-IgE (P = 0.0019) and IgG3 anti-IgE (P = 0.0034) showed significant correlations with total IgE concentrations, but not with IgE specific to excretory-secretory worm products; thus suggesting that anti-IgE synthesis is more related to polyclonal hyper IgE production than to antigen-specific IgE stimulation. No correlation was seen between IgG subclass anti-IgE levels and faecal egg counts or worm burden. Given that our data failed to show a negative or a positive correlation between anti-IgE and the degree of infection with hookworm, it is tempting to speculate that the main role of autoanti-IgE is to provide the host with protection against immune complex- and IgE-mediated hypersensitivity reactions to parasitic antigens.

A study of the interrelationship between circulating IgG subclass anti-IgE autoantibodies, IgE and soluble CD23 in asthma

In this paper we hypothesise that circulating autoanti-IgE antibodies, which are found in allergic asthma patients, could potentially enhance IgE synthesis by blocking its binding to CD23 on B lymphocytes, thereby potentiating the release of soluble fragments of CD23 which have B cell growth-promoting activity. We have investigated this possibility indirectly by measuring soluble (s) CD23 and IgG subclass anti-IgE antibody levels in asthmatic patients' sera, to find out if the two parameters are related. However, we were unable to show any significant correlations between serum IgG subclass anti-IgE activities and sCD23 levels. This may have been due, at least in part, to the heterogeneous epitope specificity of the autoanti-IgE being detected. Interestingly, there was a significant inverse correlation (p = 0.0178) between serum IgE and sCD23 levels in asthma; an observation which underlines the notion that binding of IgE to membrane CD23 abrogates the release of sCD23. The present study confirms and extends previous reports of significantly raised circulating levels of IgG anti-IgE in asthma patients (p = 0.0004), by further demonstrating that IgG anti-IgE is mostly restricted to IgG1. Given that IgG1 binds very efficiently to C1q and Fc gamma Rs, our observation lends further support to the notion that IgG anti-IgE may facilitate the removal of IgE-allergen complexes by triggering IgG effector function pathways.

A case-control study of congenital hip dislocation

In this study we have investigated various epidemiological factors which may be related to congenital dislocation of the hip (CDH). Eighty-one cases born during the period 1st January 1988 to 31st August 1990, with four matched controls per case, were identified from consultants' records held at the Queen's Medical Centre and City Hospital, Nottingham. One hundred and twenty-four subjects who were referred to a new Hip Instability Clinic with suspected CDH, but not diagnosed or treated for CDH, were also included as a third group. Information about the mother's pregnancy, previous medical history and family history was collected from obstetric records kept at the two hospitals. Multigravidae and similarly multiparous women had a statistically significantly reduced risk of having a baby with CDH. The relative risks were 0.55 (95% confidence interval 0.33, 0.93) and 0.53 (95% confidence interval 0.31, 0.91) respectively. The method of delivery was also of importance. Babies born by Caesarean section or in breech position had an increased risk of CDH which was statistically significant. Using addition clinical information obtained from subjects attending the Hip Instability Clinic we also found that cases were more likely to have a family history of CDH than subjects who were screened for CDH but found to be normal.

Diverse migratory pathways in the developing cerebral cortex

During early development of the mammalian cerebral cortex, young neurons migrate outward from the site of their final mitosis in the ventricular zone into the cortical plate, where they form the adult cortex. Time-lapse confocal microscopy was used to observe directly the dynamic behaviors of migrating cells in living slices of developing cortex. The majority of cells migrated along a radial pathway, consistent with the view that cortical neurons migrate along radial glial fibers. A fraction of cells, however, turned within the intermediate zone and migrated orthogonal to the radial fibers. This orthogonal migration may contribute to the tangential dispersion of clonally related cortical neurons.

A real-time analysis of growth cone-target cell interactions during the formation of stable contacts between hippocampal neurons in culture

Mechanisms of cell-cell recognition and structural changes of growth cones (g.c.) and target membranes during contact formation are poorly understood. To examine these issues, we obtained a high magnification, real-time record of stable contact formation in cultured cells from the hippocampal CA1 area in the newborn rat. We used differential interference contrast (DIC) optics coupled to a video microscope for periods of over 24 h of continuous time-lapse recording. Our goal was to observe the sequential changes exhibited by afferent and target cells as they form a stable contact. Understanding the process of how stable contacts are made is important because such contacts are the first step in synapse formation. Four principal observations emerged from our study: (1) The target cell was receptive to a contact on a specific patch on its surface defined by the presence of lamellae and filopodia. This specific patch (named target site) was invariably present on the target cell surface before the time the growth cone arrived. (2) Stable adhesion between filopodia on the two cells initiated events leading to cell-cell contact formation. Specifically, the remaining filopodia on the growth cone and target cell were redirected toward the adhering filopodia, and the growth cone size decreased dramatically. (3) The axonal process then grew at a significantly accelerated rate (up to 50 times its baseline growth rate). (4) In addition, a number of observations were obtained on axonal turns towards the target cell, induction of target sites, and architectural remodelling of cells after the formation of a new contact. Our findings indicate that in this neuronal system, filopodia are the means used by cells to interact at stages prior to and during contact formation. We speculate that the molecules involved in cell recognition and the machinery that initiates contact formation are embedded in the fine structure of filopodia. Finally, our results provide possible clues as to some of the stages that may be involved in synapse formation in the mammalian central nervous system.

Neurally evoked calcium transients in terminal Schwann cells at the neuromuscular junction

We examined the effects of motor-nerve stimulation on the intracellular Ca2+ levels of Schwann cells, the glial cells at the frog neuromuscular junction. Schwann cells, which were loaded with the fluorescent Ca2+ indicator fluo-3 and examined by confocal microscopy, showed a transient increase in free Ca2+ within a few seconds of the onset of tetanic stimulation of the motor nerve. The Ca2+ response was specific to the synapse in that it was found in the terminal Schwann cells at the junction but not in the myelinating Schwann cells along the axon. The Ca2+ transients occurred in the presence of d-tubocurare, indicating that they were not mediated by nicotinic acetylcholine receptors and recurred when the stimulus was repeated. The Ca2+ response persisted after degeneration of the postsynaptic muscle fiber, demonstrating that the terminal Schwann cell was stimulated directly by presynaptic activity. The finding that terminal Schwann cells at the neuromuscular junction respond to presynaptic activity suggests that glial-cell function is modulated by synaptic transmission.

12 alpha-hydroxytestosterone. A hitherto unidentified testosterone metabolite produced by cytochrome P-450 2A2

Several cytochrome P-450 enzymes are able to hydroxylate testosterone to many different metabolites, some of which remain to be identified. One hitherto unidentified metabolite represents a major metabolite of P-450 2A2, present in the liver of adult male rats, and a minor metabolite of several other cytochrome P-450 enzymes. Using the techniques of HPLC and GC/MS, we have obtained unequivocal evidence that this metabolite is 12 alpha-hydroxytestosterone.

The mechanism of nitrate transport across the tonoplast of barley root cells

Nitrate-selective microelectrodes were used to measure not only nitrate activity in the cytoplasm and vacuole of barley (Hordeum vulgare L.) root cells, but also the tonoplast electrical membrane potential. For epidermal cells, the mean cytoplasmic and vacuolar pNO3 (-log10 [NO3]) values were 2.3±0.04 (n=19) and 1.41±0.03 (n=35), respectively, while for cortical cells, the mean cytoplasmic and vacuolar nitrate values were 2.58±0.18 (n=4) and 1.17±0.06 (n=13), respectively. These results indicate that the accumulation of nitrate in the vacuole must be an active process. Proton-selective microelectrodes were used to measure the proton gradient across the tonoplast to assess the possibility that nitrate transport into the vacuole is mediated by an H(+)/NO 3 (-) antiport mechanism. For epidermal cells, the mean cytoplasmic and vacuolar pH values were 7.12±0.06 (n=10) and 4.93±0.11 (n=22), respectively, while for cortical cells, the mean cytoplasmic and vacuolar pH values were 7.24±0.07 (n=3) and 5.09±0.17 (n=7), respectively. Calculations of the energetics for this mechanism indicate that the observed gradient of nitrate across the tonoplast of both epidermal and cortical cells could be achieved by an H(+)/NO 3 (-) antiport with a 1∶1 stoichiometry.

Performance characteristics of a composite multivariate quality control system

We present the results of an evaluation of the performance characteristics of a composite multivariate quality control (CMQC) system that incorporates quality control rules for univariate, multivariate, and correlation conditions. The CMQC system evaluated is designed to help analysts detect unacceptable trends and systematic error in one or more variables, unacceptable random error in one or more variables, and unacceptable changes in the correlation structure of any pair of variables. It is also designed to be tolerant of missing data, to allow analysts to reject as few as one or as many as all variables in a run, and to provide analysts with control statistics and graphics that logically relate to sources of analytical error. We show that the various components of the CMQC system have adequate statistical power to detect systematic errors, random errors, and correlation changes under the conditions likely to be encountered with multivariate analytical measurement systems: (1) a single variable with increased systematic or random error; (2) all variables or a subgroup of variables affected by a common problem that increases systematic or random error; and (3) missing data for one or more variables in a run. We also show that the power of the multivariate component of the CMQC system to detect systematic and random errors is higher than the power of an alternative multivariate test criterion.

Open stereotactic selective amygdalo-hippocampectomy for drug resistant epilepsy

Selective removal of the medio-basal temporal structures has been introduced as an alternative to standard temporal lobectomy in the treatment of intractable temporal lobe epilepsy not related to gross structural lesions. Various approaches have been described for the surgical excision of the amygdalo-hippocampal complex, each of them presenting advantages and limitations. The recently introduced computer-assisted technique of volumetric stereotactic excision of deep-seated intracerebral lesions combines precision of targeting with elimination of unnecessary cortical trauma and may potentially provide an alternative method in the treatment of temporal lobe epilepsy. We present our experience of stereotactic volumetric selective amygdalo-hippocampectomy in six patients with medically intractable temporal lobe epilepsy. The criteria for selection, the pre-operative evaluation and the operative technique are discussed. All patients had a cessation or considerable reduction in seizure frequency while the morbidity was minimal.

Neuronal activity triggers calcium waves in hippocampal astrocyte networks

The recent discovery that the neurotransmitter glutamate can trigger actively propagating Ca2+ waves in the cytoplasm of cultured astrocytes suggests the possibility that synaptically released glutamate may trigger similar Ca2+ waves in brain astrocytes in situ. To explore this possibility, we used confocal microscopy and the Ca2+ indicator fluo-3 to study organotypically cultured slices of rat hippocampus, where astrocytic and neuronal networks are intermingled in their normal tissue relationships. We find that astrocytic Ca2+ waves are present under these circumstances and that these waves can be triggered by the firing of glutamatergic neuronal afferents with latencies as short as 2 s. The Ca2+ waves closely resemble those previously observed in cultured astrocytes: they propagate both within and between astrocytes at velocities of 7-27 microns/s at 21 degrees C. The ability of tissue astrocyte networks to respond to neuronal network activity suggests that astrocytes may have a much more dynamic and active role in brain function than has been generally recognized.

Genetic diagnosis of Gaucher's disease

The inherited disorder Gaucher's disease can be caused by various mutations in the glucocerebrosidase gene. Some mutations may be associated with greater severity, and there is a need for methods of gene analysis that would facilitate screening and diagnosis. We have studied the molecular basis of Gaucher's disease in twelve unrelated patients of diverse ethnic origin by means of the amplification refractory mutation system (ARMS). Primers for the polymerase chain reaction were designed to discriminate between mutant and wild-type alleles of glucocerebrosidase and to allow separation from products of the related pseudogene. The nucleotide 1226 mutation (asparagine 370----serine) and 84GG (an insertional frameshift mutation) were found exclusively in five patients of Ashkenazi Jewish descent (7 and 2 of the 10 disease alleles, respectively). Two point mutations, at nucleotides 1448 (leucine 444----proline) and 1504 (arginine 463----cysteine), were found in 4 and 3 alleles, respectively; they were associated with rapidly progressive disease and neurological involvement in non-Jewish patients. The ARMS procedure for direct detection of common mutations in glucocerebrosidase will facilitate genetic counselling and screening programmes for individuals at risk of Gaucher's disease.

Auditory function in patients infected with the human immunodeficiency virus

A prospective study of auditory function in 18 HIV positive male patients at different CDC (Centres for Disease Control) stages was undertaken. One-third had abnormalities on either auditory evoked response testing or pure tone audiometry. No correlation was found between interwave latencies I-V, I-III, III-V and stage of disease determined either clinically or by T-cell subset. There was a weak correlation between pure tone averages at 1,2,4 kHz and 2,4,8 kHz and T-cell subset ratio in CDC Group IV disease (Rs = 0.56 and 0.57 respectively; P less than 0.05). Abnormalities of BSER were similar to those previously reported in HIV infection, and suggest isolated changes within the brain-stem.

Blood lipid measurements. Variations and practical utility

OBJECTIVE

To describe the magnitude and impact of the major biological and analytical sources of variation in serum lipid and lipoprotein levels on risk of coronary heart disease; to present a way to qualitatively estimate the total intraindividual variation; and to demonstrate how to determine the number of specimens required to estimate, with 95% confidence, the "true" underlying total cholesterol value in the serum of a patient.

DATA SOURCES

Representative references on each source of variation were selected from more than 300 reviewed publications, most published within the past 5 years, to document current findings and concepts. Most articles reviewed were in English.

STUDY SELECTIONS

Studies on biological sources of variation were selected using the following criteria: representative of published findings, clear statement of either significant or insignificant results, and acquisition of clinical and laboratory data under standardized conditions. Representative results for special populations such as women and children are reported when results differ from those of adult men.

DATA EXTRACTION

References were selected based on acceptable experimental design and use of standardized laboratory lipid measurements.

DATA SYNTHESIS

The lipid levels considered representative for a selected source of variation arose from quantitative measurements by a suitably standardized laboratory. Statistical analysis of data was examined to assure reliability. The proposed method of estimating the biological coefficient of variation must be considered to give qualitative results, because only two or three serial specimens are collected in most cases for the estimation.

CONCLUSIONS

Concern has arisen about the magnitude, impact, and interpretation of preanalytical as well as analytical sources of variation on reported results of lipid measurements of an individual. Preanalytical sources of variation from behavioral, clinical, and sampling sources constitute about 60% of the total variation in a reported lipid measurement of an individual. A technique is presented to allow physicians to qualitatively estimate the intraindividual biological variation of a patient from the results of two or more specimens reported from a standardized laboratory and to determine whether additional specimens are needed to meet the National Cholesterol Education Program recommendation that the intraindividual serum total cholesterol coefficient of variation not exceed 5.0. A National Reference Method Network has been established to help solve analytical problems.