The relationship between weight-related indicators and depressive symptoms during adolescence and adulthood: results from two twin studies

BACKGROUND

The association between weight and depressive symptoms is well established, but the direction of effects remains unclear. Most studies rely on body mass index (BMI) as the sole weight indicator, with few examining the aetiology of the association between weight indicators and depressive symptoms.

METHODS

We analysed data from the Twins Early Development Study (TEDS) and UK Adult Twin Registry (TwinsUK) (7658 and 2775 twin pairs, respectively). A phenotypic cross-lagged panel model assessed the directionality between BMI and depressive symptoms at ages 12, 16, and 21 years in TEDS. Bivariate correlations tested the phenotypic association between a range of weight indicators and depressive symptoms in TwinsUK. In both samples, structural equation modelling of twin data investigated genetic and environmental influences between weight indicators and depression. Sensitivity analyses included two-wave phenotypic cross-lagged panel models and the exclusion of those with a BMI <18.5.

RESULTS

Within TEDS, the relationship between BMI and depression was bidirectional between ages 12 and 16 with a stronger influence of earlier BMI on later depression. The associations were unidirectional thereafter with depression at 16 influencing BMI at 21. Small genetic correlations were found between BMI and depression at ages 16 and 21, but not at 12. Within TwinsUK, depression was weakly correlated with weight indicators; therefore, it was not possible to generate precise estimates of genetic or environmental correlations.

CONCLUSIONS

The directionality of the relationship between BMI and depression appears to be developmentally sensitive. Further research with larger genetically informative samples is needed to estimate the aetiological influence on these associations.

Socioeconomic status and risk for child psychopathology: exploring gene-environment interaction in the presence of gene-environment correlation using extended families in the Norwegian Mother, Father and Child Birth Cohort Study

BACKGROUND

Low socioeconomic status (SES) is associated with increased risk for emotional and behavioural problems among children. Evidence from twin studies has shown that family SES moderates genetic and environmental influences on child mental health. However, it is also known that SES is itself under genetic influence and previous gene-environment interaction (G×E) studies have not incorporated the potential genetic overlap between child mental health and family SES into G×E analyses. We applied a novel approach using extended family data to investigate the moderation of aetiological influences on child emotional and behavioural problems by parental socioeconomic status in the presence of modelled gene-environment correlation.

METHODS

The sample comprised >28,100 children in extended-family units drawn from the Norwegian Mother, Father and Child Cohort Study (MoBa). Mothers reported children's emotional and behavioural symptoms. Parents' income and educational attainment were obtained through linkage to administrative register data. Bivariate moderation Multiple-Children-of-Twins-and-Siblings (MCoTS) models were used to analyse relationships between offspring outcomes (emotional and behavioural symptom scores) and parental socioeconomic moderators (income rank and educational attainment).

RESULTS

The aetiology of child emotional symptoms was moderated by maternal and paternal educational attainment. Shared environmental influences on child emotional symptoms were greater at lower levels of parents' education. The aetiology of child behavioural symptoms was moderated by maternal, but not paternal, socioeconomic factors. Genetic factors shared between maternal income and child behavioural symptoms were greater in families with lower levels maternal income. Nonshared environmental influences on child behavioural symptoms were greater in families with higher maternal income and education.

CONCLUSIONS

Parental socioeconomic indicators moderated familial influences and nonshared environmental influences on child emotional and behavioural outcomes. Maternal SES and child mental health share aetiological overlap such that shared genetic influence was greater at the lower end of the socioeconomic distribution. Our findings collectively highlight the role that family socioeconomic factors play in shaping the origins of child emotional and behavioural problems.

The Colombo Twin and Singleton Study (COTASS): Piloting the Feasibility of Collecting Nutritional Data and Extension of the Sample to Include Children of Twins

Nutrition and diet are key modifiable risk factors for the rising burden of non-communicable diseases like cardio-vascular diseases and diabetes in low- and middle- income countries (LMICs). The nutritional transition in dietary behaviours in LMICs has most likely contributed to this problem. Although traditionally assumed to be environmental, dietary choices are also genetically influenced. Twin study designs can be used to investigate the relative influence of genes and environment on nutrition intake, eating behaviours and associated psychological health. The overall aim of this project is to: provide proof-of-concept for the feasibility of using dietary (biomarker) data within the Children-of-Twin design in nutrition studies, develop laboratory skills and statistical genetic skills and establish a Sri Lankan-specific food composition database. Currently, a pilot study is being conducted with 304 individuals (38 Monozygotic twin pairs, 38 Dizygotic twin pairs and their male or female adult offspring). Questionnaire data on nutritional intake, eating behaviours, psychological well-being, physical health, and bio-specimens are being collected. A Sri Lankan-specific food composition database was developed, training sessions on macro and micro element analysis in biological samples and statistical genetics skills development were conducted and Community Engagement and Involvement programs were carried out in two districts of Sri Lanka.

Frequency of Consumption of Food Groups and Cardio-Metabolic Risk Factors: A Genetically Informative Twin Study in Sri Lanka

Low- and middle-income countries (LMICs) globally have undergone rapid urbanisation, and changes in demography and health behaviours. In Sri Lanka, cardio-vascular disease and diabetes are now leading causes of mortality. High prevalence of their risk factors, including hypertension, dysglycaemia and obesity have also been observed. Diet is a key modifiable risk factor for both cardio-vascular disease and diabetes as well as their risk factors. Although typically thought of as an environmental risk factor, dietary choice has been shown to be genetically influenced, and genes associated with this behaviour correlate with metabolic risk indicators. We used Structural Equation Model fitting to investigate the aetiology of dietary choices and cardio-metabolic phenotypes in COTASS, a population-based twin and singleton sample in Colombo, Sri Lanka. Participants completed a Food Frequency Questionnaire (N = 3934) which assessed frequency of intake of 14 food groups including meat, vegetables and dessert or sweet snacks. Anthropometric (N = 3675) and cardio-metabolic (N = 3477) phenotypes were also collected including weight, blood pressure, cholesterol, fasting plasma glucose and triglycerides. Frequency of consumption of most food items was found to be largely environmental in origin with both the shared and non-shared environmental influences indicated. Modest genetic influences were observed for some food groups (e.g. fruits and leafy greens). Cardio-metabolic phenotypes showed moderate genetic influences with some shared environmental influence for Body Mass Index, blood pressure and triglycerides. Overall, it seemed that shared environmental effects were more important for both dietary choices and cardio-metabolic phenotypes compared to populations in the Global North.

Using twin-pairs to assess potential bias in polygenic prediction of externalising behaviours across development

Prediction from polygenic scores may be confounded sources of passive gene-environment correlation (rGE; e.g. population stratification, assortative mating, and environmentally mediated effects of parental genotype on child phenotype). Using genomic data from 10,000 twin pairs, we asked whether polygenic scores from the recent externalising genome-wide association study predicted conduct problems, ADHD symptomology and callous-unemotional traits, and whether these predictions are biased by rGE. We ran regression models including within-family and between-family polygenic scores, to separate the direct genetic influence on a trait from environmental influences that correlate with genes (indirect genetic effects). Findings suggested that this externalising polygenic score is a good index of direct genetic influence on conduct and ADHD-related symptoms across development, with minimal bias from rGE, although the polygenic score predicted less variance in CU traits. Post-hoc analyses showed some indirect genetic effects acting on a common factor indexing stability of conduct problems across time and contexts.

Associations between socioeconomic factors and depression in Sri Lanka: The role of gene-environment interplay

BACKGROUND

Low socioeconomic status is a risk factor for depression. The nature and magnitude of associations can differ cross-culturally and is influenced by a range of contextual factors. We examined the aetiology of socioeconomic indicators and depression symptoms and investigated whether socioeconomic indicators moderate genetic and environmental influences on depression symptoms in a Sri Lankan population.

METHODS

Data were from a population-based sample of twins (N = 2934) and singletons (N = 1035) in Colombo, Sri Lanka. Standard of living, educational attainment, and financial strain were used to index socioeconomic status. Depression symptoms were assessed using the Revised Beck Depression Inventory. Structural equation modelling explored genetic and environmental influences on socioeconomic indicators and depression symptoms and moderation of aetiological influences on depression symptoms by socioeconomic status.

RESULTS

Depression symptoms were associated with lower standard of living, lower educational attainment, and financial strain. Sex differences were evident in the aetiology of standard of living, with a small contribution of genetic influences in females. Educational attainment was moderately heritable in both males and females. Total variance in depression was greater among less socioeconomically advantaged individuals. Modest evidence of moderation of the aetiology of depression by standard of living and education was observed.

LIMITATIONS

While the sample is representative of individuals living in Colombo District, it may not be representative of different regions of Sri Lanka.

CONCLUSIONS

The aetiology of depression varies across socioeconomic contexts, suggesting a potential mechanism through which socioeconomic disadvantage increases the risk for depression in Sri Lanka. Findings have implications for cross-cultural investigations of the role of socioeconomic factors in depression and for identifying targets for social interventions.

Sub-types of insomnia in adolescents: Insights from a quantitative/molecular twin study

Background

Insomnia with short sleep duration has been postulated as more severe than that accompanied by normal/long sleep length. While the short duration subtype is considered to have greater genetic influence than the other subtype, no studies have addressed this question. This study aimed to compare these subtypes in terms of: (1) the heritability of insomnia symptoms; (2) polygenic scores (PGS) for insomnia symptoms and sleep duration; (3) the associations between insomnia symptoms and a wide variety of traits/disorders.

Methods

The sample comprised 4000 pairs of twins aged 16 from the Twins Early Development Study. Twin models were fitted to estimate the heritability of insomnia in both groups. PGS were calculated for self-reported insomnia and sleep duration and compared among participants with short and normal/long sleep duration.

Results

Heritability was not significantly different in the short sleep duration group (A = 0.13 [95%CI = 0.01, 0.32]) and the normal/long sleep duration group (A = 0.35 [95%CI = 0.29, 0.40]). Shared environmental factors accounted for a substantial proportion of the variance in the short sleep duration group (C = 0.19 [95%CI = 0.05, 0.32]) but not in the normal/long sleep duration group (C = 0.00 [95%CI = 0.00, 0.04]). PGS did not differ significantly between groups although results were in the direction expected by the theory. Our results also showed that insomnia with short (as compared to normal/long) sleep duration had a stronger association with anxiety and depression (p < .05)-although not once adjusting for multiple testing.

Conclusions

We found mixed results in relation to the expected differences between the insomnia subtypes in adolescents. Future research needs to further establish cut-offs for 'short' sleep at different developmental stages and employ objective measures of sleep.

Cardiometabolic risk profiles in a Sri Lankan twin and singleton sample

Introduction

Prevention of cardiovascular disease and diabetes is a priority in low- and middle-income countries, especially in South Asia where these are leading causes of morbidity and mortality. The metabolic syndrome is a tool to identify cardiometabolic risk, but the validity of the metabolic syndrome as a clinical construct is debated. This study tested the existence of the metabolic syndrome, explored alternative cardiometabolic risk characterisations, and examined genetic and environmental factors in a South Asian population sample.

Methods

Data came from the Colombo Twin and Singleton follow-up Study, which recruited twins and singletons in Colombo, Sri Lanka, in 2012–2015 (n = 3476). Latent class analysis tested the clustering of metabolic syndrome indicators (waist circumference, high-density lipoprotein cholesterol, triglycerides, blood pressure, fasting plasma glucose, medications, and diabetes). Regression analyses tested cross-sectional associations between the identified latent cardiometabolic classes and sociodemographic covariates and health behaviours. Structural equation modelling estimated genetic and environmental contributions to cardiometabolic risk profiles. All analyses were stratified by sex (n = 1509 men, n = 1967 women).

Results

Three classes were identified in men: 1) “Healthy” (52.3%), 2) “Central obesity, high triglycerides, high fasting plasma glucose” (40.2%), and 3) “Central obesity, high triglycerides, diabetes” (7.6%). Four classes were identified in women: 1) “Healthy” (53.2%), 2) “Very high central obesity, low high-density lipoprotein cholesterol, raised fasting plasma glucose” (32.8%), 3) “Very high central obesity, diabetes” (7.2%) and 4) “Central obesity, hypertension, raised fasting plasma glucose” (6.8%). Older age in men and women, and high socioeconomic status in men, was associated with cardiometabolic risk classes, compared to the “Healthy” classes. In men, individual differences in cardiometabolic class membership were due to environmental effects. In women, genetic differences predicted class membership.

Conclusion

The findings did not support the metabolic syndrome construct. Instead, distinct clinical profiles were identified for men and women, suggesting different aetiological pathways.

The aetiological relationship between depressive symptoms and health-related quality of life: A population-based twin study in Sri Lanka

Objective

Depression often co-occurs with poor health-related quality of life (HRQL). Twin studies report genetic and individual-level environmental underpinnings in the aetiology of both depression and HRQL, but there is limited twin research exploring this association further. There is also little evidence on sex differences and non-Western populations are underrepresented. In this paper we explored the phenotypic and aetiological relationship between depressive symptoms and HRQL and possible sex differences in a low-middle-income Sri Lankan population.

Method

Data for 3,948 participants came from the Colombo Twin and Singleton Follow-up Study (CoTaSS-2). Using self-report measures of depressive symptoms and HRQL, we conducted univariate and bivariate sex-limitation twin analyses.

Results

Depressive symptoms showed moderate genetic (33%) and strong nonshared environmental influences (67%). Nonshared environment accounted for the majority of variance in all the subscales of HRQL (ranging from 68 to 93%), alongside small genetic influences (ranging from 0 to 23%) and shared environmental influences (ranging from 0 to 28%). Genetic influences were significant for emotional wellbeing (23%). Shared environmental influences were significant for four out of the eight HRQL variables (ranging from 22–28%), and they were more prominent in females than males. Depressive symptoms were significantly associated with lower HRQL scores. These correlations were mostly explained by overlapping nonshared environmental effects. For traits related to emotional functioning, we also detected substantial overlapping genetic influences with depressive symptoms.

Conclusions

Our study confirmed previous findings of a negative association between depressive symptoms and HRQL. However, some of the aetiological factors of HRQL differed from Western studies, particularly regarding the effects of shared environment. Our findings highlight the importance of cross-cultural research in understanding associations between psychological wellbeing and HRQL.

The association between bullying-victimisation and sleep disturbances in adolescence: Evidence from a twin study

Bullying-victimisation has been associated with sleep disturbances. This study investigated the degree to which subtypes of bullying-victimisation in adolescence are linked with sleep disturbances. Genetic and environmental contributions underlying bullying-victimisation and sleep disturbances were investigated. Participants (3,242-5,076 pairs) from a longitudinal community twin study reported on their bullying-victimisation at the age of 14 years, and sleep quality and insomnia symptoms at age 16. Regression analyses were used, accounting for the role of individual and family factors. Structural equation twin model fitting was conducted. Bullying-victimisation was modestly associated with sleep quality and insomnia symptoms (r = 0.22-0.23) and a similar strength of associations was found across bullying-victimisation subtypes (r = 0.11-0.22). Bullying-victimisation, sleep quality and insomnia symptoms were predominantly influenced by genes (25-59%) and non-shared environments (40-62%). The association between bullying-victimisation and sleep quality was explained by genetic and non-shared environmental influences. For insomnia symptoms and sleep quality, the association with bullying-victimisation was in part explained by a genetic overlap. Associations between bullying-victimisation and sleep disturbances are not limited to specific aspects of bullying-victimisation but appear to exist for all subtypes. These findings stimulate research questions regarding the mechanisms underlying these links. For example, could certain heritable traits, such as temperament, increase vulnerability to experiencing sleep disturbances and being bullied? Research on bullying and sleep should aim to take the role of genetic predisposition into account, while also noting that it is not the only causal influence. Understanding more about these pathways could strengthen the development of techniques to prevent these difficulties from occurring.

Twins and Causal Inference: Leveraging Nature's Experiment

In this review, we discuss how samples comprising monozygotic and dizygotic twin pairs can be used for the purpose of strengthening causal inference by controlling for shared influences on exposure and outcome. We begin by briefly introducing how twin data can be used to inform the biometric decomposition of population variance into genetic, shared environmental, and nonshared environmental influences. We then discuss how extensions to this model can be used to explore whether associations between exposure and outcome survive correction for shared etiology (common causes). We review several analytical approaches that can be applied to twin data for this purpose. These include multivariate structural equation models, cotwin control methods, direction of causation models (cross-sectional and longitudinal), and extended family designs used to assess intergenerational associations. We conclude by highlighting some of the limitations and considerations that researchers should be aware of when using twin data for the purposes of interrogating causal hypotheses.

Associations Between Anxiety Symptoms and Health-Related Quality of Life: A Population-Based Twin Study in Sri Lanka

Anxiety not only concerns mental wellbeing but also negatively impacts other areas of health. Yet, there is limited research on (a) the genetic and environmental aetiology of such relationships; (b) sex differences in aetiology and (c) non-European samples. In this study, we investigated the genetic and environmental variation and covariation of anxiety symptoms and eight components of health-related quality of life (QoL), as measured by the short form health survey (SF-36), using genetic twin model fitting analysis. Data was drawn from the Colombo Twin and Singleton Study (COTASS), a population-based sample in Sri Lanka with data on twins (N = 2921) and singletons (N = 1027). Individual differences in anxiety and QoL traits showed more shared environmental (family) effects in women. Men did not show familial effects. Anxiety negatively correlated with all eight components of QoL, mostly driven by overlapping unique (individual-specific) environmental effects in both sexes and overlapping shared environmental effects in women. This is the first study in a South Asian population supporting the association between poor mental health and reduced QoL, highlighting the value of integrated healthcare services. Associations were largely environmental, on both individual and family levels, which could be informative for therapy and intervention.

Why do depression, conduct, and hyperactivity symptoms co-occur across adolescence? The role of stable and dynamic genetic and environmental influences

Depression, conduct, and hyperactivity symptoms are chronic and frequently co-occur in adolescence. Common genetic and environmental vulnerability to these conditions have previously been demonstrated, however, the manner in which common versus disorder-specific etiological influences operate across development and maintain symptom co-occurrence is unclear. Thus, the current study investigated the role of common genetic and environmental influences in the comorbidity of depression, conduct, and hyperactivity across adolescence. Over 10,000 twins and their parents reported adolescents' symptoms at mean ages 11 and 16 years. Biometric independent pathway models were fitted to estimate genetic and environmental contributions to the continuity of symptom co-occurrence over time, as well as time- and symptom-specific influences. Results found that a common stable genetic factor accounted for the concurrent and longitudinal co-occurrence of depression, conduct, and hyperactivity symptoms. New genetic influences common to these three symptom scales emerged at 16 years, and further contributed to symptom co-occurrence. Conversely, environmental influences largely contributed to the time-specific associations. The findings were generally consistent for self- and parent-reported symptoms. Overall, the results suggest that stable, overlapping genetic influences contribute to the co-occurrence of depression, conduct, and hyperactivity symptoms across adolescence. The results are in line with hierarchical causal models of psychopathology, which posit that much of the developmental co-occurrence between different symptoms is due to common liability. Specifically, current findings indicate that only genetic influences constitute common liability over time. Future studies should identify genetically influenced transdiagnostic risk and maintenance factors to inform prevention and treatment of comorbid internalizing and externalizing symptoms in adolescence.

The relationship between independent and dependent life events and depression symptoms in Sri Lanka: a twin and singleton study

PURPOSE

Life events have been associated with a variety of mental health conditions including depression. There is a scarcity of research in South Asia exploring the aetiology of independent and dependent life events and their relationship with depression symptoms. This study aimed, in a Sri Lankan population, to identify the socio-demographic correlates and genetic and environmental influences on independent and dependent life events and their relationship with depression.

METHODS

Questionnaire data came from the Colombo Twin and Singleton Follow-up Study, CoTaSS-2 (N = 3969), a population study of Sri Lankan twins and singletons. Lifetime-ever independent and dependent life events were measured using a questionnaire and depressive symptoms using the Revised Beck's Depression Inventory. Structural Equation Model-fitting analyses explored the genetic and environmental influences on life events and depression.

RESULTS

Living in a rural environment and financial hardship were associated with greater reporting of independent and dependent life events. Sex differences were evident in the aetiology of life events and depression symptoms. Independent and dependent life events, but not depression symptoms, were heritable in males. Independent life events and depression symptoms, but not dependent life events, were heritable in females. Non-shared environmental influences explained phenotypic associations between independent life events and depression symptoms in both males and females. Genetic and non-shared environmental influences explained the phenotypic associations between dependent life events and depression symptoms in males. Only non-shared environment explained the covariation between dependent life events and depression symptoms in females.

CONCLUSIONS

Socio-demographic correlates of independent and dependent life events were similar to those reported in Western populations. Life events were associated with increased depression symptoms. Contrary to research in Western populations, we found that non-shared environmental, rather than genetic, influences explained much of the covariation between life events and depression symptoms. This suggests that whilst independent LEs may be heritable, the relationship is unlikely to be confounded by genetic influences and has significant implications for possible interventions for depression.

Protocol for establishing a child and adolescent twin register for mental health research and capacity building in Sri Lanka and other low and middle-income countries in South Asia

INTRODUCTION

Worldwide, 10%-20% of children and adolescents experience mental health conditions. However, most such disorders remain undiagnosed until adolescence or adulthood. Little is known about the factors that influence mental health in children and adolescents, especially in low and middle-income countries (LMIC), where environmental threats, such as poverty and war, may affect optimal neurodevelopment. Cohort studies provide important information on risks and resilience across the life course by enabling tracking of the effects of early life environment on health during childhood and beyond. Large birth cohort studies, including twin cohorts that can be aetiologically informative, have been conducted within high-income countries but are not generalisable to LMIC. There are limited longitudinal birth cohort studies in LMIC.

METHODS

We sought to enhance the volume of impactful research in Sri Lanka by establishing a Centre of Excellence for cohort studies. The aim is to establish a register of infant, child and adolescent twins, including mothers pregnant with twins, starting in the districts of Colombo (Western Province) and Vavuniya (Northern Province). We will gain consent from twins or parents for future research projects. This register will provide the platform to investigate the aetiology of mental illness and the impact of challenges to early brain development on future mental health. Using this register, we will be able to conduct research that will (1) expand existing research capacity on child and adolescent mental health and twin methods; (2) further consolidate existing partnerships and (3) establish new collaborations. The initiative is underpinned by three pillars: high-quality research, ethics, and patient and public involvement and engagement (PPIE).

ETHICS AND DISSEMINATION

Ethical approval for this study was obtained from the Ethics Review Committee of Sri Lanka Medical Association and Keele University's Ethical Review Panel. In addition to journal publications, a range of PPIE activities have been conducted.

Mindfulness and associations with symptoms of insomnia, anxiety and depression in early adulthood: A twin and sibling study

This study investigated associations between mindfulness and symptoms of insomnia, depression and anxiety. Mindfulness was disaggregated into five subscales: 'nonreactivity to inner experience', 'observing', 'acting with awareness', 'describing' and 'nonjudging of inner experience'. Twin models were used to examine genetic and environmental influences on mindfulness, symptoms of insomnia, depression and anxiety and on their associations. Data came from a longitudinal twin/sibling study (G1219) comprising 862 individuals (age range 22-32 years, 66% females). Less mindfulness was associated with greater symptoms of insomnia, depression and anxiety (r = .22-.48). Of the mindfulness subscales, 'nonjudging of inner experience' was most strongly associated with the other traits. Overall mindfulness was largely influenced by non-shared environmental factors (E = .72) although familial influences played a role for overall mindfulness, as well as for the 'acting with awareness' and 'describing' subscales. The genetic correlations between overall mindfulness and symptoms of insomnia, depression and anxiety ranged from .32 to .75 (but were non-significant), while the shared environmental correlations ranged from -.78 to .79 (also non-significant). The non-shared environmental influences between these three variables were moderately, significantly correlated (rE = .21-.55).

The Colombo Twin and Singleton Follow-up Study: a population based twin study of psychiatric disorders and metabolic syndrome in Sri Lanka

BACKGROUND

The disease burden related to mental disorders and metabolic syndrome is growing in low-and middle-income countries (LMIC). The Colombo Twin and Singleton Study (COTASS) is a population-based sample of twins and singletons in Colombo, Sri Lanka. Here we present prevalence estimates for metabolic syndrome (metS) and mental disorders from a follow-up (COTASS-2) of the original study (COTASS-1), which was a mental health survey.

METHODS

In COTASS-2, participants completed structured interviews, anthropometric measures and provided fasting blood and urine samples. Depressive disorder, depressive symptoms, anxiety symptoms, post-traumatic stress disorder (PTSD) and hazardous alcohol use were ascertained with structured psychiatric screens (Composite International Diagnostic Interview (CIDI), Beck Depression Inventory (BDI-II), Generalised Anxiety Disorder Questionnaire (GAD-7), PTSD Checklist - Civilian Version (PCL-C), and Alcohol Use Disorders Identification Test (AUDIT)). We defined metS according to the International Diabetes Federation (IDF) criteria and the revised National Cholesterol Education Programme Adult Treatment Panel (NCEP ATP III) criteria. We estimated the prevalence of psychiatric disorders and metS and metS components, and associations with gender, education and age.

RESULTS

Two thousand nine hundred thirty-four twins and 1035 singletons were followed up from COTASS-1 (83.4 and 61.8% participation rate, respectively). Prevalence estimates for depressive disorder (CIDI), depressive symptoms (BDI ≥ 16), anxiety symptoms (GAD-7 ≥ 10) and PTSD (PCL-C DSM criteria) were 3.8, 5.9, 3.6, and 4.5% respectively for twins and 3.9, 9.8, 5.1 and 5.4% for singletons. 28.1 and 30.9% of male twins and singletons respectively reported hazardous alcohol use. Approximately one third met the metS criteria (IDF: 27.4% twins, 44.6% singletons; NCEP ATP III: 30.6% twins, 48.6% singletons). The most prevalent components were central obesity (59.2% twins, 71.2% singletons) and raised fasting blood glucose or diabetes (38.2% twins, 56.7% singletons).

CONCLUSION

MetS was highly prevalent in twins, and especially high in singletons, whereas the prevalence of mental disorders was low, but consistent with local estimates. The high levels of raised fasting plasma glucose and central obesity were particularly concerning, and warrant national diabetes prevention programmes.

Sleep Treatment Outcome Predictors (STOP) Pilot Study: a protocol for a randomised controlled trial examining predictors of change of insomnia symptoms and associated traits following cognitive-behavioural therapy for insomnia in an unselected sample

INTRODUCTION

Cognitive-behavioural therapy for insomnia (CBT-I) leads to insomnia symptom improvements in a substantial proportion of patients. However, not everyone responds well to this treatment, and it is unclear what determines individual differences in response. The broader aim of this work is to examine to what extent response to CBT-I is due to genetic and environmental factors. The purpose of this pilot study is to examine feasibility of a design to test hypotheses focusing on an unselected sample, that is, without selection on insomnia complaints, in order to plan a larger behavioural genetics study where most participants will likely not have an insomnia disorder.

METHODS AND ANALYSIS

A two parallel-group randomised controlled trial is being conducted across three London universities. Female students (minimum age 18 years) enrolled on a psychology programme at one of the three sites were invited to participate. The target number of participants to be recruited is 240. Following baseline assessments, participants were randomly allocated to either the treatment group, where they received weekly sessions of digital CBT-I for 6 weeks, or the control group, where they completed an online puzzle each week for 6 weeks. Follow-up assessments have taken place mid-intervention (3 weeks) and end of intervention (6 weeks). A 6-month follow-up assessment will also occur. Primary outcomes will be assessed using descriptive statistics and effect size estimates for intervention effects. Secondary outcomes will be analysed using multivariate generalised estimating equation models.

ETHICS AND DISSEMINATION

The study received ethical approval from the Research Ethics and Integrity subcommittee, Goldsmiths, University of London (application reference: EA 1305). DNA sample collection for the BioResource received ethical approval from the NRES Committee South Central-Oxford (reference number: 15/SC/0388). The results of this work shall be published in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT03062891; Results.

Shared Etiology of Psychotic Experiences and Depressive Symptoms in Adolescence: A Longitudinal Twin Study

Psychotic disorders and major depression, both typically adult-onset conditions, often co-occur. At younger ages psychotic experiences and depressive symptoms are often reported in the community. We used a genetically sensitive longitudinal design to investigate the relationship between psychotic experiences and depressive symptoms in adolescence. A representative community sample of twins from England and Wales was employed. Self-rated depressive symptoms, paranoia, hallucinations, cognitive disorganization, grandiosity, anhedonia, and parent-rated negative symptoms were collected when the twins were age 16 (N = 9618) and again on a representative subsample 9 months later (N = 2873). Direction and aetiology of associations were assessed using genetically informative cross-lagged models. Depressive symptoms were moderately correlated with paranoia, hallucinations, and cognitive disorganization. Lower correlations were observed between depression and anhedonia, and depression and parent-rated negative symptoms. Nonsignificant correlations were observed between depression and grandiosity. Largely the same genetic effects influenced depression and paranoia, depression and hallucinations, and depression and cognitive disorganization. Modest overlap in environmental influences also played a role in the associations. Significant bi-directional longitudinal associations were observed between depression and paranoia. Hallucinations and cognitive disorganization during adolescence were found to impact later depression, even after controlling for earlier levels of depression. Our study shows that psychotic experiences and depression, as traits in the community, have a high genetic overlap in mid-adolescence. Future research should test the prediction stemming from our longitudinal results, namely that reducing or ameliorating positive and cognitive psychotic experiences in adolescence would decrease later depressive symptoms.

Association between stressful life events and psychotic experiences in adolescence: evidence for gene-environment correlations

BACKGROUND

Stressful life events (SLEs) are associated with psychotic experiences. SLEs might act as an environmental risk factor, but may also share a genetic propensity with psychotic experiences.

AIMS

To estimate the extent to which genetic and environmental factors influence the relationship between SLEs and psychotic experiences.

METHOD

Self- and parent reports from a community-based twin sample (4830 16-year-old pairs) were analysed using structural equation model fitting.

RESULTS

SLEs correlated with positive psychotic experiences (r = 0.12-0.14, all P<0.001). Modest heritability was shown for psychotic experiences (25-57%) and dependent SLEs (32%). Genetic influences explained the majority of the modest covariation between dependent SLEs and paranoia and cognitive disorganisation (bivariate heritabilities 74-86%). The relationship between SLEs and hallucinations and grandiosity was explained by both genetic and common environmental effects.

CONCLUSIONS

Further to dependent SLEs being an environmental risk factor, individuals may have an underlying genetic propensity increasing their risk of dependent SLEs and positive psychotic experiences.

Etiology of Pervasive Versus Situational Antisocial Behaviors: A Multi-Informant Longitudinal Cohort Study

The aim of this study was to disentangle pervasive from situational antisocial behaviors using multiple informants, and to investigate their genetic and environmental etiologies in preadolescence and across time. Antisocial behaviors were assessed in 2,232 twins from the Environmental Risk (E‐Risk) Longitudinal Twin Study at ages 5 and 12. Pervasive antisocial behaviors were defined as behaviors that mothers, teachers, interviewers, and twins themselves agreed on. Results from a psychometric model indicated that the variation in children's pervasive antisocial behaviors was mostly accounted for by familial influences that originated in childhood, whereas situational behaviors were explained by newly emerging nonshared environmental and genetic influences. This study shows that children's pervasive and situational antisocial behaviors have distinct etiologies that could guide research and treatment.

A twin and molecular genetics study of sleep paralysis and associated factors

Sleep paralysis is a relatively common but under-researched phenomenon. In this paper we examine prevalence in a UK sample and associations with candidate risk factors. This is the first study to investigate the heritability of sleep paralysis in a twin sample and to explore genetic associations between sleep paralysis and a number of circadian expressed single nucleotide polymorphisms. Analyses are based on data from the Genesis1219 twin/sibling study, a community sample of twins/siblings from England and Wales. In total, data from 862 participants aged 22-32 years (34% male) were used in the study. This sample consisted of monozygotic and dizygotic twins and siblings. It was found that self-reports of general sleep quality, anxiety symptoms and exposure to threatening events were all associated independently with sleep paralysis. There was moderate genetic influence on sleep paralysis (53%). Polymorphisms in the PER2 gene were associated with sleep paralysis in additive and dominant models of inheritance-although significance was not reached once a Bonferroni correction was applied. It is concluded that factors associated with disrupted sleep cycles appear to be associated with sleep paralysis. In this sample of young adults, sleep paralysis was moderately heritable. Future work should examine specific polymorphisms associated with differences in circadian rhythms and sleep homeostasis further in association with sleep paralysis.

A multivariate twin study of trait mindfulness, depressive symptoms, and anxiety sensitivity

BACKGROUND

Mindfulness-based therapies have been shown to be effective in treating depression and reducing cognitive biases. Anxiety sensitivity is one cognitive bias that may play a role in the association between mindfulness and depressive symptoms. It refers to an enhanced sensitivity toward symptoms of anxiety, with a belief that these are harmful. Currently, little is known about the mechanisms underpinning the association between mindfulness, depression, and anxiety sensitivity. The aim of this study was to examine the role of genetic and environmental factors in trait mindfulness, and its genetic and environmental overlap with depressive symptoms and anxiety sensitivity.

METHODS

Over 2,100 16-year-old twins from a population-based study rated their mindfulness, depressive symptoms, and anxiety sensitivity.

RESULTS

Twin modeling analyses revealed that mindfulness is 32% heritable and 66% due to nonshared environmental factors, with no significant influence of shared environment. Genetic influences explained over half of the moderate phenotypic associations between low mindfulness, depressive symptoms, and anxiety sensitivity. About two-thirds of genetic influences and almost all nonshared environmental influences on mindfulness were independent of depression and anxiety sensitivity.

CONCLUSIONS

This is the first study to show that both genes and environment play an important role in the etiology of mindfulness in adolescence. Future research should identify the specific environmental factors that influence trait mindfulness during development to inform targeted treatment and resilience interventions. Shared genetic liability underpinning the co-occurrence of low mindfulness, depression, and anxiety sensitivity suggests that the biological pathways shared between these traits should also be examined.

Cognitive content specificity in anxiety and depressive disorder symptoms: a twin study of cross-sectional associations with anxiety sensitivity dimensions across development

BACKGROUND

The classification of anxiety and depressive disorders has long been debated and has important clinical implications. The present study combined a genetically sensitive design and multiple time points to investigate cognitive content specificity in anxiety and depressive disorder symptoms across anxiety sensitivity dimensions, a cognitive distortion implicated in both disorders.

METHOD

Phenotypic and genetic correlations between anxiety sensitivity dimensions, anxiety and depressive disorder symptoms were examined at five waves of data collection within childhood, adolescence and early adulthood in two representative twin studies (n pairs = 300 and 1372).

RESULTS

The physical concerns dimension of anxiety sensitivity (fear of bodily symptoms) was significantly associated with anxiety but not depression at all waves. Genetic influences on physical concerns overlapped substantially more with anxiety than depression. Conversely, mental concerns (worry regarding cognitive control) were phenotypically more strongly associated with depression than anxiety. Social concerns (fear of publicly observable symptoms of anxiety) were associated with both anxiety and depression in adolescence. Genetic influences on mental and social concerns were shared to a similar extent with both anxiety and depression.

CONCLUSIONS

Phenotypic patterns of cognitive specificity and broader genetic associations between anxiety sensitivity dimensions, anxiety and depressive disorder symptoms were similar at all waves. Both disorder-specific and shared cognitive concerns were identified, suggesting it is appropriate to classify anxiety and depression as distinct but related disorders and confirming the clinical perspective that cognitive therapy is most likely to benefit by targeting cognitive concerns relating specifically to the individual's presenting symptoms across development.

The phenotypic and genetic structure of depression and anxiety disorder symptoms in childhood, adolescence, and young adulthood

IMPORTANCE

The DSM-5 classifies mood and anxiety disorders as separate conditions. However, some studies in adults find a unidimensional internalizing factor that underpins anxiety and depression, while others support a bidimensional model where symptoms segregate into distress (depression and generalized anxiety) and fear factors (phobia subscales). However, little is known about the phenotypic and genetic structure of internalizing psychopathology in children and adolescents.

OBJECTIVE

To investigate the phenotypic associations between depression and anxiety disorder symptom subscales and to test the genetic structures underlying these symptoms (DSM-5-related, unidimensional and bidimensional) across 3 developmental stages: childhood, adolescence, and early adulthood.

DESIGN, SETTING, AND PARTICIPANTS

Two population-based prospective longitudinal twin/sibling studies conducted in the United Kingdom. The child sample included 578 twins (mean age, approximately 8 and 10 years at waves 1 and 2, respectively). The adolescent and early adulthood sample included 2619 twins/siblings at 3 waves (mean age, 15, 17, and 20 years at each wave).

MAIN OUTCOMES AND MEASURES

Self-report symptoms of depression and anxiety disorders.

RESULTS

Phenotypically, when controlling for other anxiety subscales, depression symptoms were only associated with generalized anxiety disorder symptoms in childhood (r = 0.20-0.21); this association broadened to panic and social phobia symptoms in adolescence (r = 0.17-0.24 and r = 0.14-0.16, respectively) and all anxiety subscales in young adulthood (r = 0.06-0.19). The genetic associations were in line with phenotypic results. In childhood, anxiety subscales were influenced by a single genetic factor that did not contribute to genetic variance in depression symptoms, suggesting largely independent genetic influences on anxiety and depression. In adolescence, genetic influences were significantly shared between depression and all anxiety subscales in agreement with DSM-5 conceptualization. In young adulthood, a genetic internalizing factor influencing depression and all anxiety subscales emerged, alongside a small significant genetic fear factor.

CONCLUSIONS AND RELEVANCE

These results provide preliminary evidence for different phenotypic and genetic structures of internalizing disorder symptoms in childhood, adolescence, and young adulthood, with depression and anxiety becoming more associated from adolescence. The results inform molecular genetics research and transdiagnostic treatment approaches. The findings affirm the need to continue examining the classification of mood and anxiety disorders in diagnostic systems.

Shared genetic factors underlie chronic pain syndromes

Chronic pain syndromes (CPS) are highly prevalent in the general population, and increasingly the evidence points to a common etiological pathway. Using a large cohort of twins (n=8564) characterized for chronic widespread musculoskeletal pain (CWP), chronic pelvic pain (PP), migraine (MIG), dry eye disease, and irritable bowel syndrome (IBS), we explored the underlying genetic and environmental factors contributing to CPS and the correlation between them. The sample was predominantly female (87.3%), with a mean age of 54.7 (±14.7) years. Prevalence of the different CPS ranged from 7.4% (PP) to 15.7% (MIG). For all CPS the within-twin correlation in monozygotic twin pairs was higher than in dizygotic pairs, suggesting a heritable component. Estimated heritability ranged from 19% (IBS) to 46% (PP). Except for MIG, we found significant pairwise phenotypic correlations between the CPS. The phenotypic correlation was highest between CWP and IBS (0.40; 95% confidence interval: 0.27 to 0.46). Excluding MIG from further analyses, cross-twin cross-trait correlations were higher in monozygotic compared with dizygotic twin pairs, suggestive of shared genetic factors between CWP, PP, IBS, and dry eye disease. Twin modeling analysis revealed the common pathway model as the model best explaining the observed pattern of correlation between the traits, with an estimated heritability of 66% of the underlying latent variable. These results are evidence of shared genetic factors in conditions manifesting chronic pain and justify the search for underlying genetic variants.

Genetic and environmental contributions to separation anxiety: a meta-analytic approach to twin data

BACKGROUND

Separation anxiety disorder (SAD) and separation anxiety symptoms (SA) have been studied both epidemiologically and genetically; however, large between-studies discrepancies emerge relative to the role of genetic, shared-, and nonshared environmental influences on these conditions.

METHODS

Based upon available literature, 18 cohorts and 31,859 subjects belonging to twin samples in Europe, the United States, and Australia were included in three meta-analytic estimations of: the standardized variance components of etiological influences on SAD/SA, and on the effect of sex and rater.

RESULTS

Meta-analytic estimations carried out on all cohorts showed that within-family (genetic 43% and shared environmental 17%) factors explain most of individual differences for SAD/SA. Meta-heritability estimates were higher among females (.52) than males (.26), whereas nonshared environmental effects were stronger for the latter (.74) than for the former (.41). When SAD/SA was rated by parents, the shared environmental influences were higher than those obtained with self-assessment instruments (.23 versus .05), but this may reflect an age difference between subsamples.

CONCLUSIONS

A shared environmental effect is present and important in SAD/SA. Our results support at an etiological level the involvement of parents in treating SAD/SA in children, and the provision of specific strategies to parents to manage their own anxiety.

Genetic and environmental etiology of nicotine use in Sri Lankan male twins

Little is known about the prevalence and etiology of tobacco use in Asian populations. This study aims to test whether the finding of substantial heritability for tobacco-related phenotypes in Western populations is generalizable to developing countries. The twin method was used to estimate the relative contribution of genetic and environmental influences on nicotine-related phenotypes. Participants were selected from the population based Sri Lankan Twin Registry. The Composite International Diagnostic Interview was administered to 1,804 male individuals to assess five phenotypes: nicotine use; desire and unsuccessful attempts to quit smoking; subjective feeling of being tobacco dependent; and two DSM-IV diagnoses; nicotine dependence and nicotine withdrawal. Almost one-third of the male twins were life-time smokers. The genetic results were consistent with the previously reported findings from Western and Chinese populations, in that the nicotine use traits were significantly heritable, with environmental influences being of the non-shared nature. The results derived from the Causal Contingent Common pathway model (CCC) supported previous findings that show that liabilities to regular smoking and subsequent problem smoking have both shared and specific genetic influences.

Anxiety sensitivity in adolescence and young adulthood: the role of stressful life events, 5HTTLPR and their interaction

BACKGROUND

Cognitive biases have long been hypothesized to influence the development and maintenance of symptoms of internalizing problems. Anxiety sensitivity represents one such bias and refers to sensitivity to the physical and emotional symptoms of anxiety and the belief that these are harmful. Twin studies indicate a role for both environmental and genetic influences on anxiety sensitivity. However, little work has been done specifying environments or genes involved in this phenotype. In light of this, we looked at the association between stressful life events, the serotonin transporter gene polymorphism (5HTTLPR), and anxiety sensitivity in a longitudinal sample of adolescents.

METHODS

Stressful life events and anxiety sensitivity were measured in over 1,500 individuals at three time points (mean ages 15, 17, and 20 years). 5HTTLPR was genotyped in 1,109 participants.

RESULTS

There was consistent evidence for an association between stressful life events and both anxiety sensitivity and change in anxiety sensitivity over time. Although the effect of independent stressful life events was relatively short lived, dependent stressful life events were associated with anxiety sensitivity over time. There was no evidence for a main effect of 5HTTLPR on anxiety sensitivity. 5HTTLPR genotype did not moderate the effect of stressful life events on anxiety sensitivity.

CONCLUSIONS

The current study extends previous work by showing that stressful life events, independent of the individual, explained change in cognitions associated with anxiety and depression. This effect does not, however, appear to be moderated by genotype.

Stable genetic influence on anxiety-related behaviours across middle childhood

We examined the aetiology of anxiety symptoms in an unselected population at ages 7 and 9, a period during which anxiety disorders first begin to develop (mean age at onset is 11 years). Specifically, the aim of the study was to investigate genetic and environmental continuity and change in components of anxiety in middle childhood. Parents of over 3,500 twin pairs completed the Anxiety-Related Behaviours Questionnaire (ARBQ) when twins were 7 and 9 years old. Multivariate-longitudinal analyses were conducted to examine genetic and environmental influences on stability and change in four anxiety scales: Negative Cognition, Negative Affect, Fear and Social Anxiety. We found moderate temporal stability in all four scales from 7 to 9 years (correlations ranging from 0.45 to 0.54) and moderate heritability (average 54%). Both shared and non-shared environmental influences were modest (average 18%–28% respectively). Genetic factors (68%) explained most of the homotypic continuity in anxiety. We show that homotypic continuity of Anxiety-Related Behaviours (i.e. the continuation of one specific type of anxiety over time) was largely driven by genetic factors. In contrast, though more varied, heterotypic continuity between some traits (i.e. the change from one type of anxiety-related behaviour into another over time) was mainly due to shared-environmental factors.

Sleep quality and diurnal preference in a sample of young adults: associations with 5HTTLPR, PER3, and CLOCK 3111

Research investigating associations between specific genes and individual differences with regards to the quality and timing of sleep has primarily focussed on serotonin-related and clock genes. However, there are only a few studies of this type and most of those to date have not considered the possibility of gene-environment interaction. Here, we describe associations between sleep quality and diurnal preference and three functional polymorphisms: 5HTTLPR, PERIOD3, and CLOCK 3111. Furthermore, we assessed whether associations between genotypes and sleep phenotypes were moderated by negative life events-a test of gene-environment interaction. DNA from buccal swabs was collected from 947 individuals [mean age = 20.3 years (SD = 1.77), age range = 18-27 years; 61.8% female] and genotyped for the three polymorphisms. Participants completed the Pittsburgh Sleep Quality Index and the Morningness-Eveningness Questionnaire. There was a significant main effect of 5HTTLPR on sleep quality, indicating that "long-long" homozygotes experienced significantly poorer sleep quality (mean = 6.35, SD = 3.36) than carriers of at least one "short" allele (mean = 5.67, SD = 2.96; β = -0.34, P = 0.005). There were no main effects of 5HTTLPR on diurnal preference; no main effects of PERIOD3 or CLOCK on sleep quality or diurnal preference; and no significant interactions with negative life events. The main effect of the "long" 5HTTLPR allele contradicts previous research, suggesting that perhaps the effects of this gene are heterogeneous in different populations. Failure to replicate previous research in relation to PERIOD3 and CLOCK concurs with previous research suggesting that the effects of these genes are small and may be related to population composition.

Genetic influences on the cognitive biases associated with anxiety and depression symptoms in adolescents

BACKGROUND

There is a substantial overlap between genes affecting anxiety and depression. Both anxiety and depression are associated with cognitive biases such as anxiety sensitivity and attributional style. Little, however, is known about the relationship between these variables and whether these too are genetically correlated.

METHODS

Self-reports of anxiety sensitivity, anxiety symptoms, attributional style and depression symptoms were obtained for over 1300 adolescent twin and sibling pairs at two time points. The magnitude of genetic and environmental influences on the measures was examined.

RESULTS

Strongest associations were found between anxiety sensitivity and anxiety ratings at both measurement times (r=.70, .72) and between anxiety and depression (r=.62 at both time points). Correlations between the cognitive biases were modest at time 1 (r=-.12) and slightly larger at time 2 (r=-.31). All measures showed moderate genetic influence. Generally genetic correlations reflected phenotypic correlations. Thus the highest genetic correlations were between anxiety sensitivity and anxiety ratings (.86, .87) and between anxiety and depression ratings (.77, .71). Interestingly, depression ratings also showed a high genetic correlation with anxiety sensitivity (.70, .76). Genetic correlations between the cognitive bias measures were moderate (-.31, -.46).

LIMITATIONS

The sample consists primarily of twins, there are limitations associated with the twin design.

CONCLUSIONS

Cognitive biases associated with depression and anxiety are not as genetically correlated as anxiety and depression ratings themselves. Further research into the cognitive processes related to anxiety and depression will facilitate understanding of the relationship between bias and symptoms.