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PubMed2006

AKT1 provides an essential survival signal required for differentiation and stratification of primary human keratinocytes.

Keratinocyte differentiation and stratification are complex processes involving multiple signaling pathways, which convert a basal proliferative cell into an inviable rigid squame. Loss of attachment to the basement membrane triggers keratinocyte differentiation, while in other epithelial cells, detachment from the extracellular matrix leads to rapid programmed cell death or anoikis. The potential role of AKT in providing a survival signal necessary for stratification and differentiation of primary human keratinocytes was investigated. AKT activity increased during keratinocyte differentiation and was attributed to the specific activation of AKT1 and AKT2. Targeted reduction of AKT1 expression, but not AKT2, by RNA interference resulted in an abnormal epidermis in organotypic skin cultures with a thin parabasal region and a pronounced but disorganized cornified layer. This abnormal stratification was due to significant cell death in the suprabasal layers and was alleviated by caspase inhibition. Normal expression patterns of both early and late markers of keratinocyte differentiation were also disrupted, producing a poorly developed stratum corneum.

Apoptosis↗
PubMed2003

Social interaction distance and stratification.

There have been calls from several sources recently for a renewal of class analysis that would encompass social and cultural, as well as economic elements. This paper explores a tradition in stratification that is founded on this idea: relational or social distance approaches to mapping hierarchy and inequality which theorize stratification as a social space. The idea of 'social space' is not treated as a metaphor of hierarchy nor is the nature of the structure determined a priori. Rather, the space is identified by mapping social interactions. Exploring the nature of social space involves mapping the network of social interaction--patterns of friendship, partnership and cultural similarity--which gives rise to relations of social closeness and distance. Differential association has long been seen as the basis of hierarchy, but the usual approach is first to define a structure composed of a set of groups and then to investigate social interaction between them. Social distance approaches reverse this, using patterns of interaction to determine the nature of the structure. Differential association can be seen as a way of defining proximity within a social space, from the distances between social groups, or between social groups and social objects (such as lifestyle items). The paper demonstrates how the very different starting point of social distance approaches also leads to strikingly different theoretical conclusions about the nature of stratification and inequality.

Hierarchy, Social↗
PubMed1988

Molecular characterization and expression of the stratification-related cytokeratins 4 and 15.

A number of human cytokeratins are expressed during the development of stratified epithelia from one-layered polar epithelia and continue to be expressed in several adult epithelial tissues. For studies of the regulation of the synthesis of stratification-related cytokeratins in internal tissues, we have prepared cDNA and genomic clones encoding cytokeratin 4, as a representative of the basic (type II) cytokeratin subfamily and cytokeratin 15, as representative of the acidic (type I) subfamily, and determined their nucleotide sequences. The specific expression of mRNAs encoding these two polypeptides in certain stratified tissues and cultured cell lines is demonstrated by Northern blot hybridization. Hybridization in situ with antisense riboprobes and/or synthetic oligonucleotides shows the presence of cytokeratin 15 mRNA in all layers of esophagus, whereas cytokeratin 4 mRNA tends to be suprabasally enriched, although to degrees varying in different regions. We conclude that the expression of the genes encoding these stratification-related cytokeratins starts already in the basal cell layer and does not depend on vertical differentiation and detachment from the basal lamina. Our results also show that simple epithelial and stratification-related cytokeratins can be coexpressed in basal cell layers of certain stratified epithelia such as esophagus. Implications of these findings for epithelial differentiation and the formation of squamous cell carcinomas are discussed.

Amino Acid Sequence↗
PubMed1999

Use of unlinked genetic markers to detect population stratification in association studies.

We examine the issue of population stratification in association-mapping studies. In case-control studies of association, population subdivision or recent admixture of populations can lead to spurious associations between a phenotype and unlinked candidate loci. Using a model of sampling from a structured population, we show that if population stratification exists, it can be detected by use of unlinked marker loci. We show that the case-control-study design, using unrelated control individuals, is a valid approach for association mapping, provided that marker loci unlinked to the candidate locus are included in the study, to test for stratification. We suggest guidelines as to the number of unlinked marker loci to use.

Alleles↗
PubMed2006

Predicting hospitalization and mortality in end-stage renal disease (ESRD) patients using an Index of Coexisting Disease (ICED)-based risk stratification model.

We evaluated the use of an additive Index of Coexisting Diseases (ICED)-based stratification schema to determine subsequent hospitalization and mortality in a hemodialysis population. Patients from five commercial health plans were stratified into low-, medium-, and high-risk groups and followed for up to 1 year. Patients were reassessed and restratified at 90-day intervals and censored when disease management ceased. Outcome measures collected through selfreports and health plan records were captured in an active database. Survival to first hospitalization/ mortality was compared by Kaplan Meier curves, survivor function differences by the Wilcoxon test, and group comparisons by ANOVA and chi square. Population characteristics included mean age of 63.0, 57.7% male, and 58.8% diabetic. Mortality was 13.0% per patient year (standardized mortality ratio 0.43) and the hospitalization rate was 0.59 per patient year (standardized hospitalization ratio 0.24). Survival curves demonstrated differences in mortality and hospitalization between the patients in different initial risk categories (p < 0.01). Mean hospitalizations were 0.81 +/- 1.53 per patient year (high risk), 0.45 +/- 0.99 (medium risk), and 0.15 +/- 0.51 for the low-risk group (p < 0.001). Stratification was dynamic; 47.3% decreased and 4.7% increased risk level between the first and second assessment. These changes were associated with survival differences for initial low (p = 0.06) or medium patients (p < 0.01), and hospital-free survival for initial medium (p = 0.08) or high patients (p < 0.05). In conclusion, this ICED-based stratification schema predicted mortality and hospitalization for hemodialysis patients participating in our disease management program.

Analysis of Variance↗
PubMed1988

Asymmetric stratification. An outline for an efficient method for controlling confounding in cohort studies.

Confounding is usually controlled by either cross-stratification or multivariate modeling. The first approach is simple and intuitive, but it is not practical for controlling many factors. The second approach, although less intuitive, may provide a more efficient means for controlling many confounders, but its ability to control confounding depends on the appropriateness of the chosen model. Hybrid methods based on a multivariate confounder score or a propensity score combine the favorable characteristics of both methods and may be better suited for controlling many confounders. However, the resulting strata are defined by subranges of a multivariate model, and, therefore, may possess little intrinsic meaning. The authors propose the principle of asymmetric stratification to control efficiently a number of confounders in cohort studies while retaining the intuitive appeal and general framework of cross-stratification. The proposed method resembles a propensity score analysis but does not use a multivariate model to define the strata. Instead, strata are defined by the categories of only a subset of the original potential confounders. The authors also demonstrate how our proposed method can be implemented by an application of classification and regression trees (CART) (recursive partitioning), as outlined by Breiman et al. (Classification and Regression Trees. Belmont, CA: Wadsworth, 1984). Computer simulations and an actual example suggest that the proposed method is a potentially simpler alternative to the standard propensity score analysis. Specific recommendations on how the proposed method can be improved are also presented.

Aged↗
PubMed1997

Risk stratification after myocardial infarction. A reappraisal in the era of thrombolysis. The Groupe d'Etude du Pronostic de l'Infarctus du Myocarde (GREPI)

OBJECTIVES: The present study was performed to evaluate whether the modalities of risk stratification after myocardial infarction were still operative in the thrombolytic era. BACKGROUND: Prediction of fatal events in the aftermath of myocardial infarction relies on tests which aim to assess myocardial function, residual ischaemia and propensity for ventricular arrhythmias. Recent data on improved myocardial infarction prognosis have led to the view that risk stratification needs to be updated. METHODS: In this multicentre, prospective study, 471 acute myocardial infarction patients, 45% of whom were given thrombolytic therapy, were enrolled from the 10th day and underwent all or part of the following tests exercise test, radionuclide ventriculography (resting and exertional ejection fraction). Holter monitoring, signal-averaged electrocardiography and programmed electrical stimulation. Univariate and multivariate analyses were performed to identify predictors of mortality. RESULTS: One year and long-term (mean follow-up 31.4 months) mortality rates were 5.5% and 8.4%, respectively. Prediction of mortality was assessed and the role of the following variables was thus determined: age over 56 years (P = 0.01), previous coronary attacks (P < 0.001), history of heart failure (P < 0.001), early heart failure after myocardial infarction (P = 0.017), maximum workload of lest than 120 W at exercise test (P = 0.014), ineligibility to perform exercise (P = 0.002), depressed left ventricular ejection fraction (P = 0.013), late potentials as identified using 50 Hz high pass filtering (P = 0.012), mean night-time cycle length of less than 750 ms (P < 0.001), standard deviation of day time RR intervals of less than 100 ms (P = 0.04), the last two measures reflecting heart rate variability. In this population, neither ventricular ectopic activity nor inducibility of sustained monomorphic ventricular tachycardia at electrophysiological study carried any prognostic significance. Multivariate analyses showed that decreased heart rate variability, presence of late potentials and low ejection fraction (< 30%) made an independent contribution to the survival models. CONCLUSION: In the current context of management of acute coronary patients, the basis for risk stratification after myocardial infarction remain roughly unchanged.

Adult↗
PubMed2001

Cardiovascular risk stratification in hypertensive patients: impact of echocardiography and carotid ultrasonography.

BACKGROUND: Decision about the management of hypertensive patients should not be based on the level of blood pressure alone, but also on the presence of other risk factors, target organ damage (TOD) and cardiovascular and renal disease. OBJECTIVE: To evaluate the impact of echocardiography and carotid ultrasonography in a more precise stratification of absolute cardiovascular risk. METHODS: Never-treated essential hypertensives (n = 141; 73 men, 68 women, mean age 46 +/- 11 years) referred for the first time to our out-patient clinic were included in the study. They underwent the following procedures: (1) family and personal medical history, (2) clinical blood pressure (BP) measurement, (3) routine blood chemistry and urine analysis, (4) electrocardiogram, (5) echocardiogram, (6) carotid ultrasonogram. Risk was stratified according to the criteria suggested by the 1999 WHO/ISH guidelines. TOD was initially evaluated by routine procedures only, and subsequently reassessed by using data on cardiac and vascular structure obtained by ultrasound examinations (left ventricular hypertrophy (LVH) as left ventricular mass index (LVMI) > 134 g/m2 in men and > 110 g/m2 in women; carotid plaque as focal thickening > 1.3 mm). RESULTS: According to the first classification 20% were low-risk patients, 50% medium-risk, 22% high-risk and 8% very-high-risk patients. A marked change in risk stratification was obtained when TOD was assessed by adding ultrasound examinations: low-risk patients 18%, medium-risk 28%, high-risk 45%, very-high-risk patients 9%. CONCLUSIONS: The detection of TOD by ultrasound techniques allowed a much more accurate identification of high-risk patients, who represented a very large fraction (45%) of the patient population seen at our hypertension clinic. In particular, a large proportion of patients classified as at moderate risk by routine investigations were instead found to be at high risk when ultrasound examinations were added. The results of this study suggest that cardiovascular risk stratification only based on simple routine work-up can often underestimate overall risk, thus leading to a potentially inadequate therapeutic management especially of low-medium risk patients.

Adult↗
PubMedDate not supplied

A new model for risk stratification and delivery of cardiovascular rehabilitation services in the long-term clinical management of patients with coronary artery disease.

This model for risk stratification includes variables that classify patients for Risk of Event similar to current models of risk stratification, as well as variables that stratify patients for Risk of Progression of Atherosclerosis by established risk factors. Categories of risk are established using accepted data from the literature for each risk factor that targets regression or plaque stabilization as the goal for Low Risk. A case-rate charging system and the proposed removal of time restrictions for length of cardiovascular rehabilitation fit neatly into the present climate for health care. Health maintenance organizations will be seeking programs that use similar models to address cost issues inherent in cardiovascular rehabilitation programs under current fee-for-service models. Improved outcomes will also be targets for these programs and case-management lends itself to disease management, thus, improved outcomes. Tracking outcomes becomes even more important to both the provider and the insurer because results drive referrals. Likewise, removal of the time restriction for cardiovascular rehabilitation allows programs to individualize care and to target risk factors that are not only most deleterious, but also where patients show readiness for change. The changing environment of health care virtually mandates change in cardiovascular rehabilitation. It is imperative that programs manage the disease process, are effective in achieving outcomes that affect both patient function and the disease process, and are cost effective. This model for risk stratification and delivery of services addresses these requirements and provides a beginning for implementing these changes in cardiovascular rehabilitation.

Coronary Artery Disease↗
PubMedDate not supplied

Optimizing risk stratification in cardiac rehabilitation with inclusion of a comorbidity index.

PURPOSE: The risk stratification criteria of the American Association of Cardiovascular and Pulmonary Rehabilitation include guidelines to be used in stratifying cardiac rehabilitation (CR) patients for risk of disease progression (long term) and clinical events (short term). Noncardiac comorbidities are not included as indicators in these criteria. This study was designed to ascertain the prevalence of noncardiac comorbidities among CR patients, and to assess their relation to the current risk stratification algorithm for clinical events. METHODS: Patients were stratified into high-, intermediate-, and low-risk groups according to the American Association of Cardiovascular and Pulmonary Rehabilitation risk stratification criteria for clinical events (ARSE) at program entry. Within each risk group, age, gender, race, and noncardiac comorbidities were ascertained. Comorbidities were summarized in a comorbidity index (CMI). The relation between clinical events and risk status by ARSE and CMI was evaluated by logistic regression. RESULTS: Among 490 patients (age, 60 +/- 12 years; 35% women; 30% nonwhite) enrolled in CR with ischemic heart disease, the number of comorbidities ranged from 0 to 7 (median, 2; 75th percentile, 3). The patients categorized in the three ARSE groups differed significantly in age and comorbidities. Although ARSE tended to identify patients with a greater comorbidity burden, 38% of the patients with a comorbidity index exceeding the 75th percentile were not classified in the highest ARSE group. Clinical events increased across ARSE and CMI risk strata. Both ARSE and CMI were independent predictors of events in an age-, gender-, and race-adjusted logistic regression analysis (ARSE odds ratio [OR], 1.56; 95% confidence interval [CI], 1.14-2.12; CMI OR, 1.23, 95% CI, 1.03a-1.47). Events were predicted best when both classifications were combined. Exploratory gender-specific analyses suggested that ARSE performed better among men than among women, whereas CMI was a more important predictor among women. CONCLUSIONS: To appreciate more fully the overall complexity of disease among CR patients, ARSE should be supplemented not only with the inclusion of cardiac risk factors, as suggested in the current guidelines, but also with an assessment of noncardiac comorbidities.

Age Factors↗
PubMed2003

Simple staging criteria for esophageal carcinoma: classification with a strict prognostic stratification.

Some staging criteria for carcinoma of the esophagus have been proposed. However, none of them satisfied all the appropriateness providing an excellent prognostic stratification and simplicity to use. The aim of the current study was to establish simple and appropriate criteria to determine the clinical stage with a strict prognostic stratification for carcinoma of the esophagus. Two hundred sixty patients with esophageal carcinoma, who had undergone esophagectomy and reconstruction, were included. These patients were classified according to our newly established staging criteria (SN classification), and the clinicopathologic features and survival rates were investigated. The 1-, 3, and 5-year survival rates in patients classified as SN stage A were 100%, 94.7%, and 88.8%, respectively. In patients with stage B, the survival rates were 94.4%, 71.7%, and 62.2%. In patients in stage C were 72.3%, 33.5%, and 31.3%. In patients with stage D, survival rates were 32.4%, 8.9%, and 8.9%. All the comparative analyses between stages were significantly different (p = 0.002 for stage A vs. stage B, p < 0.0001 for stage B vs. stage C, and p < 0.0001 for stage C vs. stage D). Devised staging criteria for esophageal carcinoma providing an excellent stratification of disease has been established. The criteria are quite simple and convenient for physicians to apply clinically in determining the stage of esophageal carcinoma.

Esophageal Neoplasms↗
PubMed2002

Principal stratification in causal inference.

Many scientific problems require that treatment comparisons be adjusted for posttreatment variables, but the estimands underlying standard methods are not causal effects. To address this deficiency, we propose a general framework for comparing treatments adjusting for posttreatment variables that yields principal effects based on principal stratification. Principal stratification with respect to a posttreatment variable is a cross-classification of subjects defined by the joint potential values of that posttreatment variable tinder each of the treatments being compared. Principal effects are causal effects within a principal stratum. The key property of principal strata is that they are not affected by treatment assignment and therefore can be used just as any pretreatment covariate. such as age category. As a result, the central property of our principal effects is that they are always causal effects and do not suffer from the complications of standard posttreatment-adjusted estimands. We discuss briefly that such principal causal effects are the link between three recent applications with adjustment for posttreatment variables: (i) treatment noncompliance, (ii) missing outcomes (dropout) following treatment noncompliance. and (iii) censoring by death. We then attack the problem of surrogate or biomarker endpoints, where we show, using principal causal effects, that all current definitions of surrogacy, even when perfectly true, do not generally have the desired interpretation as causal effects of treatment on outcome. We go on to forrmulate estimands based on principal stratification and principal causal effects and show their superiority.

Child↗
PubMed2004

Tailored medicine: whom will it fit? The ethics of patient and disease stratification.

A key selling point of pharmacogenetics is the genetic stratification of either patients or diseases in order to target the prescribing of medicine. The hope is that genetically 'tailored' medicines will replace the current 'one-size-fits-all' paradigm of drug development and usage. This paper is concerned with the relationship between difference and justice in the use of pharmacogenetics. This new technology, which facilitates the identification and use of difference, has, we shall argue, the potential to lead to injustice either by the inappropriate use of difference or through the inappropriate failure to use difference. We build on empirical data from a detailed study of the range of options for the development of pharmacogenetics to present a consideration of the ethical issues that surround patient and disease stratification. In it we explore the ways in which the use of pharmacogenetics may lead to the creation of new, genetically stratified, forms of difference and new forms of injustice based on these divisions. We also examine the ways in which existing forms of difference and social stratification may interact with the use of pharmacogenetics. In conclusion, we suggest how an understanding of these ethical issues could usefully inform future policy discussions.

Clinical Trials as Topic↗
PubMed2005

Allocation of patients to conditions in headache clinical trials: randomization, stratification, and treatment matching.

Assuming control over the allocation of patients to treatment conditions is a fundamental element of any comparative clinical trial. There are three critical considerations investigators must balance in choosing an allocation scheme: reducing bias in patient allocation, producing balanced patient groups across treatment arms, and reducing the likelihood of errors attributable to chance variation. The authors review the principles of three key approaches to the allocation of patients to conditions within clinical trials, and their respective advantages with regard to these critical considerations. These allocation methods include randomization, stratification, and patient-treatment matching. Randomization is fundamental to most clinical trials. Stratification is an advanced step in a systematic program of research investigating the efficacy and effectiveness of an intervention. If the trial has less than 100 per arm and there is a known prognostic factor, stratification is the best choice to ensure equal allocation across groups. Treatment matching (tailoring) attempts to match the most appropriate treatment to a specific patient based on a priori hypotheses. Two techniques used for exploring treatment matching are: patient typologies (patient profiling), and aptitude-treatment interactions. Additional details pertaining to the rationale for selecting among these various approaches to patient allocation is provided, and their methodology is summarized with specific consideration for their application within clinical trials of headache treatment.

Analysis of Variance↗
PubMed2006

Case-control association tests correcting for population stratification.

In case-control association studies unobserved population stratification may act as a confounder, leading to an increased number of false positive results. Methods accounting for population structure by using additional genetic markers broadly follow one of two concepts: Genomic Control (GC) and Structured Association (SA). While extending existing methods of Structured Association we show that it is necessary to incorporate phenotypic information when inferring population structure, otherwise a systematic bias is introduced. Moreover, for moderate population stratification a Wald test statistic should be preferred as a Structured Association test statistic in comparison to a likelihood ratio test. The introduced extensions are compared to existing methods of Structured Association, as well as to Genomic Control, in a simulation study which is based on realistic situations of large case-control studies with moderate population stratification. A disadvantage of Genomic Control turns out to be the large variation in estimating the variance inflation factor, as well as the power loss if population structure increases. We come to the overall conclusion that Structured Association, if applied correctly, is superior to Genomic Control, at least in the case of simple population structure as simulated here.

Case-Control Studies↗
PubMed2005

Linear parameter haplotype models with stratification.

OBJECTIVES: The question of interest is estimating the relationship between haplotypes and an outcome measure, based upon unphased genotypes. The outcome of interest might be predicting the presence of disease in a logistic model, predicting a numeric drug response in a linear model, or predicting survival time in a parametric survival model with censoring. Explanatory variables may include phased haplotype design variables, environmental variables, or interactions between them. METHODS: We extend existing generalized linear haplotype models to parametric survival outcomes. To improve the stability of model variance estimates, a profile likelihood solution is proposed. An adjustment for population stratification is also considered. Here we investigate data sampled from known 'strata' (e.g., gender or ethnicity) that influence haplotype prior probabilities and thus the regression model weights. Differing linear model variance estimates, and the effect of stratification and departures from Hardy-Weinberg Equilibrium (HWE) on parameter estimates, are compared and contrasted via simulation. RESULTS: From simulations, we observed an improvement in statistical power when using a solution to profile likelihood equations. We also saw that stratification had little impact on estimates. Haplotypes that are not in HWE had a negative impact on power to test hypotheses. Finally, profile likelihood solutions for haplotypes deviating from HWE had improved power and confidence interval coverage of regression model coefficients.

Carcinoma, Squamous Cell↗
PubMed2003

Noninvasive arrhythmia risk stratification in idiopathic dilated cardiomyopathy: results of the Marburg Cardiomyopathy Study.

BACKGROUND: Arrhythmia risk stratification with regard to prophylactic implantable cardioverter-defibrillator therapy is a completely unsolved issue in idiopathic dilated cardiomyopathy (IDC). METHODS AND RESULTS: Arrhythmia risk stratification was performed prospectively in 343 patients with IDC, including analysis of left ventricular (LV) ejection fraction and size by echocardiography, signal-averaged ECG, arrhythmias on Holter ECG, QTc dispersion, heart rate variability, baroreflex sensitivity, and microvolt T-wave alternans. During 52+/-21 months of follow-up, major arrhythmic events, defined as sustained ventricular tachycardia, ventricular fibrillation, or sudden death, occurred in 46 patients (13%). On multivariate analysis, LV ejection fraction was the only significant arrhythmia risk predictor in patients with sinus rhythm, with a relative risk of 2.3 per 10% decrease of ejection fraction (95% CI, 1.5 to 3.3; P=0.0001). Nonsustained ventricular tachycardia on Holter was associated with a trend toward higher arrhythmia risk (RR, 1.7; 95% CI, 0.9 to 3.3; P=0.11), whereas beta-blocker therapy was associated with a trend toward lower arrhythmia risk (RR, 0.6; 95% CI, 0.3 to 1.2; P=0.13). In patients with atrial fibrillation, multivariate Cox analysis also identified LV ejection fraction and absence of beta-blocker therapy as the only significant arrhythmia risk predictors. CONCLUSIONS: Reduced LV ejection fraction and lack of beta-blocker use are important arrhythmia risk predictors in IDC, whereas signal-averaged ECG, baroreflex sensitivity, heart rate variability, and T-wave alternans do not seem to be helpful for arrhythmia risk stratification. These findings have important implications for the design of future studies evaluating prophylactic implantable cardioverter-defibrillator therapy in IDC.

Adolescent↗
PubMed1997

Preoperative renal risk stratification.

BACKGROUND: After cardiac surgery, acute renal failure (ARF) requiring dialysis develops in 1% to 5% of patients and is strongly associated with perioperative morbidity and mortality. Prior studies have attempted to identify predictors of ARF but have had insufficient power to perform multivariable analyses or to develop risk stratification algorithms. METHODS AND RESULTS: We conducted a prospective cohort study of 43 642 patients who underwent coronary artery bypass or valvular heart surgery in 43 Department of Veterans Affairs medical centers between April 1987 and March 1994. Logistic regression analysis was used to identify independent predictors of ARF requiring dialysis. A risk stratification algorithm derived from recursive partitioning was constructed and was validated on an independent sample of 3795 patients operated on between April and December 1994. The overall risk of ARF requiring dialysis was 1.1%. Thirty-day mortality in patients with ARF was 63.7%, compared with 4.3% in patients without ARF. Ten clinical variables related to baseline cardiovascular disease and renal function were independently associated with the risk of ARF. A risk stratification algorithm partitioned patients into low-risk (0.4%), medium-risk (0.9% to 2.8%), and high-risk (> or = 5.0%) groups on the basis of several of these factors and their interactions. CONCLUSIONS: The risk of ARF after cardiac surgery can be accurately quantified on the basis of readily available preoperative data. These findings may be used by physicians and surgeons to provide patients with improved risk estimates and to target high-risk subgroups for interventions aimed at reducing the risk and ameliorating the consequences of this serious complication.

Acute Kidney Injury↗