Latent variables and structural equation models for longitudinal relationships: an illustration in nutritional epidemiology

The relationship between obsessive-compulsive symptoms and real-life functioning in schizophrenia: New insights from the multicenter study of the Italian Network for Research on Psychoses

BACKGROUND

Although obsessive-compulsive disorder (OCD) is highly prevalent in schizophrenia, its relationship with patients' real-life functioning is still controversial.

METHODS

The present study aims at investigating the prevalence of OCD in a large cohort of non-preselected schizophrenia patients living in the community and verifying the relationship of OCD, as well as of other psychopathological symptoms, with real-life functioning along a continuum of OCD severity and after controlling for demographic variables.

RESULTS

A sample of 327 outpatients with schizophrenia was enrolled in the study and collapsed into three subgroups according to OCD severity (subclinical, mild-moderate, severe). A series of structural equation modeling (SEM) was performed to analyze in each subgroup the association of obsessive-compulsive symptoms with real-life functioning, assessed through the Specific Levels of Functioning Scale and the UCSD Performance-Based Skills Assessment. Moreover, latent profile analysis (LPA) was performed to infer latent subpopulations. In the subclinical OCD group, obsessive-compulsive symptoms (OCS) were not associated with functioning, whereas in the mild-moderate OCD group, they showed a positive relationship, particularly in the domains of work and everyday life skills. The paucity of patients with severe OCD did not allow performing SEM analysis in this group. Finally, LPA confirmed a subgroup with mild-moderate OCS and more preserved levels of functioning.

CONCLUSIONS

These findings hint at a positive association between mild-moderate OCD and real-life functioning in individuals with schizophrenia and encourage a careful assessment of OCD in personalized programs to sustain daily life activities.

Cognitive function is mediated by deficit accumulation in older, long-term breast cancer survivors

PURPOSE

This study aims to examine whether cognitive function in older, long-term breast cancer survivors is both a direct effect of cancer and cancer treatments and an indirect effect mediated by deficit accumulation.

PATIENTS AND METHODS

Female breast cancer survivors who had been diagnosed and treated at age 60 or older and were 5-15-year survivors (N = 220) and age- and education-matched non-cancer controls (N = 123) were assessed at enrollment and at 8-, 16-, and 24-month follow-ups with standard neuropsychological tests and the comprehensive geriatric assessment which was used to calculate the deficit accumulation frailty index (DAFI). Blood or saliva samples for APOE genotyping were collected at enrollment. Participants were purposely recruited so that approximately 50% had a history of treatment with chemotherapy or and 50% were not exposed to chemotherapy.

RESULTS

Latent variable mediation analysis revealed that cognitive performance was mediated by deficit accumulation for all three domains. The direct effect of cancer diagnosis and treatment history was significant for the Language domain (p = 0.04), a trend for the learning and memory domain (p = 0.054), and non-significant for the attention, processing speed, executive function (APE) domain. Carrying the APOE ε4 allele had a significant negative direct effect on the APE domain (p = 0.05) but no indirect effect through deficit accumulation.

CONCLUSION

Cognitive function in older, long-term breast cancer survivors appears to be primarily mediated through deficit accumulation.

IMPLICATIONS FOR CANCER SURVIVORS

These findings have important clinical implications suggesting that the most effective intervention to prevent or slow cognitive aging in older cancer survivors may be through prevention or management of comorbidities and interventions that maintain functional capacity (exercise, physical therapy) and social and mental health.

The moderating role of eating behaviour traits in the association between exposure to hot food takeaway outlets and body fatness

BACKGROUND

Previous studies demonstrated a relation between takeaway outlet exposure and health outcomes. Individual characteristics, such as eating behaviour traits, could make some people more susceptible to the influence of the food environment. Few studies have investigated this topic. We aimed to investigate the moderating role of eating behaviour traits (cognitive restraint, uncontrolled eating and emotional eating) in the association between neighbourhood exposure to hot food takeaway outlets (hereafter referred to as takeaway outlets), and takeaway food consumption and adiposity.

METHODS

We used cross-sectional data from a cohort in Cambridgeshire, UK (The Fenland study). Takeaway outlet exposure was derived using participants' residential address and data from local authorities and divided into quarters. The Three Factor Eating questionnaire (TFEQ-R18) was used to measure eating behaviour traits. Primary outcomes were consumption of takeaway-like foods (derived from food frequency questionnaire), and body fat percentage (measured using dual-energy X-ray absorptiometry).

RESULTS

Mean age of participants (n = 4791) was 51.0 (SD = 7.2) and 53.9% were female. Higher exposure to takeaway outlets in the neighbourhood and higher eating behaviour trait scores were independently associated with greater takeaway consumption and body fat percentage. Uncontrolled eating did not moderate the associations between takeaway outlet exposure and takeaway consumption or body fat percentage. The association between takeaway outlet exposure and takeaway consumption was slightly stronger in those with higher cognitive restraint scores, and the association between takeaway outlet exposure and body fat percentage was slightly stronger in those with lower emotional eating scores.

CONCLUSION

Eating behaviour traits and exposure to takeaway outlets were associated with greater takeaway consumption and body fat, but evidence that individuals with certain traits are more susceptible to takeaway outlets was weak. The findings indicate that interventions at both the individual and environmental levels are needed to comprehensively address unhealthy diets.

TRIAL REGISTRY

ISRCTN72077169.

Associations of audiometric hearing and speech-in-noise performance with cognitive decline among older adults: The Baltimore Longitudinal Study of Aging (BLSA)

Background

Established associations between hearing loss and cognitive decline were primarily defined by pure-tone audiometry, which reflects peripheral hearing ability. Speech-in-noise performance, which reflects central hearing ability, is more limited in prior literature. We examined the longitudinal associations of audiometric hearing and speech-in-noise performance with cognitive decline.

Methods

We studied 702 participants aged ≥60 years in the Baltimore Longitudinal Study of Aging 2012-2019. Global and domain-specific (language, memory, attention, executive function, visuospatial ability) cognitive performance were assessed by the cognitive assessment battery. Hearing thresholds at 0.5, 1, 2, and 4 kilohertz obtained from pure-tone audiometry were averaged to calculate better-ear pure-tone average (PTA) and participants were categorized as having hearing loss (>25 decibels hearing level [dB HL]) or normal hearing (≤25 dB HL). Speech-in-noise performance was assessed by the Quick Speech-in-Noise (QuickSIN) test, and participants were categorized as having below-median (worse) or above-median performance. Linear mixed effects models with random intercepts and slopes were used to assess baseline cognitive performance and cognitive decline by hearing status. Models adjusted for demographic, lifestyle and disease factors.

Results

Participants with audiometric hearing loss showed similar baseline cognitive performance but faster decline in global cognitive function, language, executive function, and attention. Participants with below-median QuickSIN score showed worse baseline cognitive performance in all domains and faster decline in global cognitive function, language, memory, executive function and attention.

Conclusions

Audiometric hearing might be targeted to delay cognitive decline. Speech-in-noise performance might be a novel marker and might be more sensitive to memory decline.

Pentachlorophenol exposure in early pregnancy and gestational diabetes mellitus: A nested case-control study

Pentachlorophenol (PCP) is an endocrine-disrupting chemical that is ubiquitously found in the environment. Few studies have reported PCP exposure in pregnant women and its association with gestational diabetes mellitus (GDM). This nested case-control study aimed to determine the concentration of urinary PCP in early pregnancy and explore the association between PCP exposure and GDM risk. This study included 293 GDM cases and 586 non-GDM controls matched by fetal sex and maternal age from a birth cohort in Wuhan, China. PCP concentrations in spot urine samples collected between 8 and 16 weeks of gestation were measured by ultra-performance liquid chromatography-tandem mass spectrometry. Conditional logistic regression was used to assess the association between PCP exposure and the odds ratio of GDM. The median concentrations of specific gravity-adjusted PCP in controls and cases were 0.70 and 0.80 ng/mL, respectively, with no significant differences (P > 0.05). The multivariate-adjusted odds ratios (ORs) (95% confidence intervals) for GDM across quartiles of urinary PCP were 1 (reference), 1.63 (1.06-2.50), 1.70 (1.11-2.61), and 1.35 (0.87-2.08), respectively, showing a potential "inverted-U" shaped association. In addition, PCP levels and maternal age or fetal sex had significant interactions with GDM risk (both P for interaction < 0.05). Among older women and those carrying female fetuses, the ORs of GDM risk were higher. This study suggests that pregnant women in central China are widely exposed to PCP, and this is the first time to report that PCP exposure may increase the risk of GDM (with potential effect modifications by maternal age and fetal sex). The association observed is in agreement with PCP's "inverted-U" anti-estrogenic effect in vivo; thus, such an effect in humans at environmentally relevant doses should be studied further.

Prevalence of overweight among Dutch primary school children living in JOGG and non-JOGG areas

Background

One of the most influential integrated approaches towards reducing childhood obesity is EPODE, a program that has been translated to over 20 different countries worldwide.

Aim

The goal of this study was to explore how JOGG–the Dutch EPODE adaptation–might reduce overweight prevalence among children.

Methods

To compare whether overweight prevalence was different in JOGG areas vs. non-JOGG areas, in long-term JOGG areas vs. short-term JOGG areas, and in low SES JOGG areas vs. middle/high SES JOGG areas, secondary anthropometric and personal data of 209,565 Dutch children were mapped onto publicly available JOGG data.

Results

Findings showed that overweight prevalence decreased from 25.17% to 16.08% in JOGG-areas, and from 32.31% to 18.43% in long-term JOGG areas. However, when taking into account SES, the decrease in prevalence was mainly visible in low SES long-term JOGG areas.

Conclusion

JOGG appeared to be successful in targeting areas where overweight was most prevalent. Low SES areas that had implemented JOGG for a longer period of time, i.e., six years, appeared to be successful in decreasing overweight prevalence.

Understanding the dynamics of asthma symptoms between childhood and adolescence using latent transition analysis

OBJECTIVES

Asthma patterns in childhood are important predictors of unwanted outcomes in adolescence. We aimed to define asthma phenotypes in childhood and adolescence and evaluate the transitions between these phenotypes and factors potentially associated with the transitions.

METHODS

Baseline (1445 children), first round (1363 children/early adolescents) and second round (1206 adolescents) data from the SCAALA Project in Salvador, Brazil, were used. Phenotypes were defined by latent class analysis at three time points. Transitions between phenotypes were described and the effects of factors associated with transition probabilities estimated using latent transition analysis.

RESULTS

The "asymptomatic" and "symptomatic" phenotypes were identified. Approximately 5-6% of asymptomatic children in childhood/later childhood and early adolescence became symptomatic later in time. Maternal common mental disorders were identified as important risk factor for unhealthy states.

CONCLUSIONS

Asthma manifestations are characterized by frequent movements, especially between childhood and adolescence. Our study, by simultaneously defining disease subtypes, and examining the transitions and their potential predictors, highlights the importance of longitudinal studies to advance the understanding of the effects of social, environmental and biological mechanisms underlying asthma trajectories over time.

The cognitive, affective motivational and clinical longitudinal determinants of apathy in schizophrenia

Apathy is a frequent and debilitating condition with few treatment options available in schizophrenia patients. Despite evidence of its multidimensional structure, most of past studies have explored apathy through a categorical approach. The main objective of this study was to identify the cognitive, emotional, motivational, and clinical factors at baseline that best predicted the three subtypes of apathy dimensions at follow-up. In a longitudinal study, 137 participants diagnosed with schizophrenia underwent different assessments including clinical, motivational, affective and cognitive measurements, at 1-month (referred to as baseline) and 12-month follow-ups. Data were analyzed using partial least squares variance-based structural equation modeling. Three latent variables representing the three previously described domains of apathy reaching consensus in the literature were extracted from the Lille Apathy Rating Scale. Results showed that in addition to baseline apathy, positive symptoms, anticipatory pleasure and sensibility to punishment at baseline predicted cognitive apathy at follow-up. Likewise, both baseline apathy and sensibility to punishment predicted emotional apathy at follow-up. Finally, baseline anhedonia and episodic memory were the main variables the predicted behavioral apathy at follow-up. This is the first study to show specific associations between apathy subtypes and clinical and cognitive motivational dysfunction in individual with schizophrenia, indicating possible distinct underlying mechanisms to these demotivational symptoms. Treatment for apathy should address both types of processes. Importantly, our results demonstrate the interest of multidimensional approaches in the understanding of apathy in schizophrenia.

The Modulatory Effect of Gender and Cytomegalovirus-Seropositivity on Circulating Inflammatory Factors and Cognitive Performance in Elderly Individuals

Aging is characterized by a chronic increase in the systemic levels of inflammatory cytokines even in ostensibly healthy individuals. The drivers of age-related increase in systemic inflammation are unclear but one potential contributor may be a persistent infection with Cytomegalovirus (CMV). In this study, we characterized the inflammatory status of 161 older participants recruited to undergo a six-month training intervention. We investigated the influence of gender and CMV-seropositivity on the main inflammatory and anti-inflammatory circulating biomarkers, such as cytokines, receptor antagonist, soluble receptor, immune cells, and relevant metabolic markers. We found that both gender and CMV-seropositivity modulate circulating peripheral biomarkers, and that CMV-infection modifies associations among the latter. Moreover, we observed an interaction between CMV-serostatus and gender associations with cognitive abilities: gender differences in fluid intelligence (Gf) and working memory (WM) were noted only in CMV-negative individuals. Finally, we found that in the CMV-seronegative participants Gf, episodic memory (EM), and WM correlated negatively with pro-inflammatory tumor necrosis factor (TNF); and EM correlated positively with anti-inflammatory interleukin (IL)-10. In CMV-seropositive individuals EM and Gf correlated negatively with pro-inflammatory IL-6, while EM, Gf, and WM correlated negatively with anti-inflammatory IL-1RA. We conclude that both CMV-serostatus and gender may modulate neuroimmune factors, cognitive performance and the relationship between the two domains and should therefore be considered in comparative and interventional studies with elderly people.

Modeling of the Weight Status and Risk of Nonalcoholic Fatty Liver Disease in Elderly Individuals: The Potential Impact of the Disulfide Bond-Forming Oxidoreductase A-Like Protein (DsbA-L) Polymorphism on the Weight Status

Nonalcoholic fatty liver disease (NAFLD) is closely associated with obesity. Disulfide bond‐forming oxidoreductase A‐like protein (DsbA‐L) is known to be a key molecule in protection against obesity and obesity‐induced inflammation. In the present study, we used a modeling and simulation approach in an attempt to develop body mass index (BMI) and BMI‐based NAFLD prediction models incorporating the DsbA‐L polymorphism to predict the BMI and NAFLD in 341 elderly subjects. A nonlinear mixed‐effect model best represented the sigmoidal relationship between the BMI and the logit function of the probability of NAFLD prevalence. The final models for BMI and NAFLD showed that DsbA‐L rs1917760 polymorphism, age, and gender were associated with the BMI, whereas gender, patatin‐like phospholipase 3 rs738409 polymorphism, HbA1c, and high‐density and low‐density lipoprotein cholesterol levels were associated with the risk of NAFLD. This information may aid in the genetic‐based prevention of obesity and NAFLD in the general elderly population.

Mediation and modification of genetic susceptibility to obesity by eating behaviors

Background: Many genetic variants show highly robust associations with body mass index (BMI). However, the mechanisms through which genetic susceptibility to obesity operates are not well understood. Potentially modifiable mechanisms, including eating behaviors, are of particular interest to public health.Objective: Here we explore whether eating behaviors mediate or modify genetic susceptibility to obesity.Design: Genetic risk scores for BMI (BMI-GRSs) were calculated for 3515 and 2154 adults in the Fenland and EDEN (Etude des déterminants pré et postnatals de la santé et du développement de l'enfant) population-based cohort studies, respectively. The eating behaviors-emotional eating, uncontrolled eating, and cognitive restraint-were measured through the use of a validated questionnaire. The mediating effect of each eating behavior on the association between the BMI-GRS and measured BMI was assessed by using the Sobel test. In addition, we tested for interactions between each eating behavior and the BMI-GRS on BMI.Results: The association between the BMI-GRS and BMI was mediated by both emotional eating (EDEN: P-Sobel = 0.01; Fenland: P-Sobel = 0.02) and uncontrolled eating (EDEN: P-Sobel = 0.04; Fenland: P-Sobel = 0.0006) in both sexes combined. Cognitive restraint did not mediate this association (P-Sobel > 0.10), except among EDEN women (P-Sobel = 0.0009). Cognitive restraint modified the relation between the BMI-GRS and BMI among men (EDEN: P-interaction = 0.0001; Fenland: P-interaction = 0.04) and Fenland women (P-interaction = 0.0004). By tertiles of cognitive restraint, the association between the BMI-GRS and BMI was strongest in the lowest tertile of cognitive restraint, and weakest in the highest tertile.Conclusions: Genetic susceptibility to obesity was partially mediated by the "appetitive" eating behavior traits (uncontrolled and emotional eating) and, in 3 of the 4 population groups studied, was modified by cognitive restraint. High levels of cognitive control over eating appear to attenuate the genetic susceptibility to obesity. Future research into interventions designed to support restraint may help to protect genetically susceptible individuals from weight gain.

Estimators for longitudinal latent exposure models: examining measurement model assumptions

Latent variable (LV) models are increasingly being used in environmental epidemiology as a way to summarize multiple environmental exposures and thus minimize statistical concerns that arise in multiple regression. LV models may be especially useful when multivariate exposures are collected repeatedly over time. LV models can accommodate a variety of assumptions but, at the same time, present the user with many choices for model specification particularly in the case of exposure data collected repeatedly over time. For instance, the user could assume conditional independence of observed exposure biomarkers given the latent exposure and, in the case of longitudinal latent exposure variables, time invariance of the measurement model. Choosing which assumptions to relax is not always straightforward. We were motivated by a study of prenatal lead exposure and mental development, where assumptions of the measurement model for the time-changing longitudinal exposure have appreciable impact on (maximum-likelihood) inferences about the health effects of lead exposure. Although we were not particularly interested in characterizing the change of the LV itself, imposing a longitudinal LV structure on the repeated multivariate exposure measures could result in high efficiency gains for the exposure-disease association. We examine the biases of maximum likelihood estimators when assumptions about the measurement model for the longitudinal latent exposure variable are violated. We adapt existing instrumental variable estimators to the case of longitudinal exposures and propose them as an alternative to estimate the health effects of a time-changing latent predictor. We show that instrumental variable estimators remain unbiased for a wide range of data generating models and have advantages in terms of mean squared error. Copyright © 2017 John Wiley & Sons, Ltd.

Examining the relationship between socio-economic status, WASH practices and wasting

Childhood wasting is a global problem and is significantly more pronounced in low and middle income countries like Bangladesh. Socio Economic Status (SES) and Water, Sanitation and Hygiene (WASH) practices may be significantly associated with wasting. Most previous research is consistent about the role of SES, but the significance of WASH in the context of wasting remains ambiguous. The effect of SES and WASH on weight for length (WHZ) is examined using a Structural Equation Model (SEM) to explicitly describe the direct and indirect role of WASH in the context of SES.A nationally representative survey of 10,478 Bangladeshi children under 5 were examined. An expert defined SEM was used to construct latent variables for SES and WASH. The SEM included a direct pathway from SES to WHZ and an indirect pathway from SES to WHZ via WASH along with regression of relevant covariates on the outcome WHZ and the latent variables. Both SES (p<0.01) and WASH (p<0.05) significantly affect WHZ. SES (p<0.01) also significantly affects WASH. Other structural components showed that child's age (p<0.01) affects WHZ and types of residence (p<0.01) affects SES. WASH practices at least partially mediate the association between SES and wasting status. WASH and SES are both significantly associated with WHZ.

Integrative Analysis of Immunological Data to Explore Chronic Immune T-Cell Activation in Successfully Treated HIV Patients

OBJECTIVES

To unravel the complex relationships between cytomegalovirus-induced-, autoimmune-induced responses, microbial translocation and chronic immune activation (CIA) in successfully treated HIV-infected patients and to explore the mediating role of alpha-interferon in these processes.

DESIGN

Cross-sectional study nested in the ANRS CO3 Aquitaine Cohort, a prospective hospital-based cohort of HIV-1-infected patients in South-Western France.

METHODS

Patients initiated antiretroviral therapy between 2005 and 2008 and were treated with sustained virological suppression for at least two years. CIA was defined by the percentage of HLA-DR+/CD38+ among CD8+T-cells. Integrative analyses were performed using structural equation modelling (SEM).

RESULTS

The main analysis was performed in 57 HLA-A*0201 positive patients, due to availability of percentages of actin-, vimentin-, lamin-specific CD8+T-cells (HLA-A2-restricted tests) to further characterize autoimmune response. Cytomegalovirus-induced response was assessed by Quantiferon and pp-65 ELISPOT. SEM revealed a direct effect of cytomegalovirus-induced response on CIA (standardized estimate βstd = 0.56, p-value = 0.0004). The effect of autoimmune-induced response on CIA was indirect through alpha-interferon pathway, assessed by expression levels of 5 alpha-interferon-stimulated genes ADAR, ISG15, IFIT1, Mx1 and OAS1 (effect of autoimmune response on alpha-interferon: βstd = 0.36, p-value = 0.0401; effect of alpha-interferon on CIA: βstd = 0.39, p-value = 0.0044). There was no direct effect of autoimmune-induced response on CIA (p-value = 0.3169). Microbial translocation as measured by 16SrDNA and sCD14 in plasma was not associated with CIA. Results were consistent in 142 patients in whom cytomegalovirus and auto-immunity responses were measured by Quantiferon and anti-nuclear antibodies, respectively. All analyses performed in HLA-A*0201 positive patients and in the overall population revealed a significant effect of IFN-α latent variable on CIA.

CONCLUSION

The role of cytomegalovirus-induced response on CIA was confirmed as well as the involvement of alpha-interferon on CIA. The indirect effect of auto-immunity response on CIA revealed through the alpha-interferon pathway requires further investigation to confirm the potential role of auto-immunity for CIA in HIV-infected patients.

Structural equation modeling with latent variables for longitudinal blood pressure traits using general pedigrees

Structural equation modeling (SEM) has been used in a wide range of applied sciences including genetic analysis. The recently developed R package, strum, implements a framework for SEM for general pedigree data. We explored different SEM techniques using strum to analyze the multivariate longitudinal data and to ultimately test the association of genotypes on blood pressure traits. The quantitative blood pressure (BP) traits, systolic BP (SBP) and diastolic BP (DBP) were analyzed as the main traits of interest with age, sex, and smoking status as covariates. The single nucleotide polymorphism (SNP) genotype information from genome-wide association studies (GWAS) data was used for the test of association. The adjustment for hypertension treatment effect was done by the censored regression approach. Two different longitudinal data models, autoregressive model and latent growth curve model, were used to fit the longitudinal BP traits. The test of association for SNP was done using a novel score test within the SEM framework of strum. We found the 10 SNPs within the GWAS suggestive P value level, and among those 10, the most significant top 3 SNPs agreed in rank in both analysis models. The general SEM framework in strum is very useful to model and test for the association with massive genotype data and complex systems of multiple phenotypes with general pedigree data.

Closing the gap on causal processes of infection risk from cross-sectional data: structural equation models to understand infection and co-infection

Background

Epidemiological studies of disease exposure risk are frequently based on observational, cross-sectional data, and use statistical approaches as crucial tools for formalising causal processes and making predictions of exposure risks. However, an acknowledged limitation of traditional models is that the inferred relationships are correlational, cannot easily distinguish direct from indirect determinants of disease risk, and are often considerable simplifications of complex interrelationships. This may be particularly important when attempting to infer causality in patterns of co-infection through pathogen-facilitation.

Methods

We describe analyses of cross-sectional data using structural equation models (SEMs), a contemporary advancement on traditional regression approaches, based on our study system of feline gammaherpesvirus (FcaGHV1) in domestic cats.

Results

SEMs strongly supported a latent (host phenotype) variable associated with FcaGHV1 exposure and co-infection risk, suggesting these individuals are simply more likely to become infected with multiple pathogens. However, indications of pathogen-covariance (potential facilitation) were also variably detected: potentially among FcaGHV1, Bartonella spp and Mycoplasma spp.

Conclusions

Our models suggest multiple exposures are primarily driven by host phenotypic traits, such as aggressive male phenotypes, and secondarily by pathogen-pathogen interactions. The results of this study demonstrate the application of SEMs to understanding epidemiological processes using observational data, and could be used more widely as a complementary tool to understand complex cross-sectional information in a wide variety of disciplines.

Unraveling the relationship between obesity, schizophrenia and cognition

INTRODUCTION

Previous studies investigating the relationship between obesity and cognition as well as gender differences in these relationships reported equivocal results. Here, we examined age, years of education, schizophrenia, and gender differences which might affect the relationship between obesity and cognition.

METHODS

1012 healthy controls and 707 participants with schizophrenia were recruited. Information on body mass index (BMI) was obtained and a neurocognitive battery was administered. Structural equation modeling (SEM) was performed to examine the relationship between BMI, schizophrenia, cognition and its covariates.

RESULTS

No significant direct effect of BMI on cognition was found when cognition was regressed on age, years of education, diagnosis of schizophrenia and BMI. Instead, two SEM models indicated that indirect effects between BMI and cognition exist. The indirect effect of BMI on cognition through schizophrenia was present in both genders, while the indirect effect of cognition on BMI through schizophrenia was only found in females. BMI affecting cognition through age, years of education and schizophrenia appears to be the most plausible model that explains the data. This indirect effect was larger in females and was masked by diagnosis of schizophrenia.

CONCLUSION

With increased rates of obesity in schizophrenia, it is important to highlight the potentially deleterious effect of obesity on cognition. BMI could be used as a candidate risk marker to identify people at higher risk of cognitive deficits, and as an intervention target for modifications of cognitive outcomes.

Expanding conceptual frameworks: life course risk modelling for mental disorders

Psychiatric epidemiology has made significant contributions to the identification of risk factors for mental disorders. Available evidence underscores the complexity of the interactions between risk and disease and highlights conceptual and methodological challenges particularly in examining risk and disease relations beyond the level of simple associations. We propose that a life course approach in the study of risk factors for mental disorders, combined with fast developing analytical statistical tools, is the most promising avenue towards shifting the focus of the field from associations to generating and testing aetiological hypotheses. This review presents the basic tenants of life course risk modelling, highlighting key examples in the available literature that demonstrate the potential of this approach to advance our understanding of the trajectories from risk to disease and discusses priorities for future research.

Quantitatively analyze composition principle of Ma Huang Tang by structural equation modeling

ETHNOPHARMACOLOGICAL RELEVANCE

In Chinese classic formulas, Ma Huang Tang (MHT), composed of Ephedra, Cassia twig, Bitter apricot kernel and Prepared licorice, has been widely used to treat cold, influenza, acute bronchitis, bronchial asthma and other pulmonary diseases. However, there is no quantitative interpretation about composition principle of MHT as well as other Chinese compound prescriptions. This study was aimed using structural equation modeling (SEM) to decipher 'monarch, minister, assistant and guide' which is the unique and integrated composition principle of Chinese compound recipes, by taking MHT for instance.

MATERIALS AND METHODS

Sixteen prescriptions of different dose ratios were combined orthogonally from four herbal drugs of MHT, then their diaphoretic, antispasmodic and analgesic effects were assessed by the indicators of the rat sweating point number, the spasmolysis percentage of guinea pig trachea and the murine writhing number, respectively. Basing on SME, the systematology analysis method to complex causality, path diagrams for herbal drugs were drawn with the Amos software and the relationships of the four herbal ingredients and therapeutic effects were measured.

RESULTS

Sixteen recipes induced SD rats sweating, remitted spasm of guinea pig trachea smooth muscle, and relieved ICR mouse pain due to acetic acid in comparison with animal model group or normal control groups. Three different SME models were specified and the relevant relationship was analyzed. According to the results of measured standardized path coefficients, Ephedra exerts the greatest contribution to the integral potency, so it acts as the monarch drug in MHT; Cassia twig is slightly weakly effective than Ephedra, and has the most significant interaction with Ephedra, which shows that it is the minister drug; the direct effects of Bitter apricot kernel and Prepared licorice on the integral potency are non-significant, while these two drugs have very significant synergetic effect with Ephedra or Cassia twig, thus they can be interpreted as subordinate drugs to strengthen the therapeutical effects of the monarch and minister drugs; the higher interaction values of Bitter apricot kernel suggest that it is the assistant drug, and Prepared licorice is the guide drug with lower values.

CONCLUSION

SME can be used to quantitatively analyze the composition principle of Chinese compound prescriptions like MHT, which demystifies the ancient and classical system theory of traditional Chinese medicine from a totally new viewpoint.

Structural equation modeling in epidemiology

Structural equation modeling (SEM) is an important statistical tool for evaluating complex relations in several research areas. In epidemiology, the use and discussion of SEM have been limited thus far. This article presents basic principles and concepts in SEM, including an application using epidemiological data analysis from a study on the determinants of cognitive development in young children, considering constructs related to organization of the child's home environment, parenting style, and the child's health status. The relations between the constructs and cognitive development were measured. The results showed a positive association between psychosocial stimulus at home and cognitive development in young children. The article presents the contributions by SEM to epidemiology, highlighting the need for an a priori theoretical model for improving the study of epidemiological questions from a new perspective.

Overeating styles and adiposity among multiethnic youth

Reasons for inconsistent associations between overeating styles and adiposity among youth may include differences in effects by age, gender, or ethnicity; failure to control for social desirability of response; or adiposity measurement limitations. This study examined the relationship between overeating styles and multiple measures of adiposity, after controlling for social desirability and testing for moderation by ethnicity, age, and gender. Data from 304 9-10 year old children and 264 17-18 year old adolescents equally representing African American, Hispanic, and White ethnic groups were extracted from a larger cross-sectional study. Measures included the Dutch Eating Behavior Questionnaire (restrained, external, and emotional overeating subscales), the "Lie Scale" from the Revised Children's Manifest Anxiety Scale, and measured weight, height, waist circumference, and triceps skinfold. BMI z-score and a global adiposity index were calculated. Mixed model linear regression showed restraint was positively and external eating was negatively related to measures of adiposity. African American youth had a stronger inverse association between emotional eating and adiposity than White or Hispanic youth. Relationships were not influenced by social desirability nor moderated by age or gender. Overeating styles are related to adiposity in nearly all youth but the nature of these associations are moderated by ethnicity.

Dipyrimidine amines: a novel class of chemokine receptor type 4 antagonists with high specificity

The C-X-C chemokine receptor type 4 (CXCR4)/stromal cell derived factor-1 (SDF-1 or CXCL12) interaction and the resulting cell signaling cascade play a key role in metastasis and inflammation. On the basis of the previously published CXCR4 antagonist 5 (WZ811), a series of novel nonpeptidic anti-CXCR4 small molecules have been designed and synthesized to improve potency. Following a structure-activity profile around 5, more advanced compounds in the N,N'-(1, 4-phenylenebis(methylene)) dipyrimidin-2-amines series were discovered and shown to possess higher CXCR4 binding potential and specificity than 5. Compound 26 (508MCl) is the lead compound and exhibits subnanomolar potency in three in vitro assays including competitive binding, Matrigel invasion and Gα(i) cyclic adenosine monophosphate (cAMP) modulation signaling. Furthermore, compound 26 displays promising effects by interfering with CXCR4 function in three mouse models: paw inflammation, Matrigel plug angiogenesis, and uveal melanoma micrometastasis. These data demonstrate that dipyrimidine amines are unique CXCR4 antagonists with high potency and specificity.