Epigenome-wide association study of systemic effects of obesity susceptibility in human twins.

The current study was designed to use an epigenome-wide association approach (EWAS) to identify potential systemic DNA methylation alterations that are associated with obesity using 22 discordant twin pairs. Buccal cells (from a cheek swab) were used as a non-obesity relevant purified marker cell for the epigenetic analysis. Analysis of differential DNA methylation regions (DMRs) was used to identify epigenetic associations with metabolic and dietary measures related to obesity with discordant twins. An edgeR analysis provided a DMR signature with p < 1e-04, but statistical significance was reduced due to low sample size and known multiple origins of obesity. A weighted gene coexpression network analysis (WGCNA) was performed and identified modules (p < 0.005) of epigenetic sites that correlated with different metabolic and dietary measures. The DMR and WGCNA epigenetic sites were near genes (e.g., CIDEC, SPP1, ZFPG9, and POMC) with previously identified obesity associated pathways (e.g., metabolism, cholesterol, and fat digestion). Observations demonstrate the feasibility of identifying systemic epigenetic biomarkers for obesity, which can be further investigated for clinical relevance in future research with larger sample sizes. The availability of a systemic epigenetic biomarker for obesity susceptibility may facilitate preventative medicine and clinical management of the disease early in life.

Analysis of differential DNA methylation regions (DMRs) was used to identify epigenetic associations with metabolic and dietary measures related to obesity with discordant twins.A weighted genome coexpression network analysis (WGCNA) was performed and identified modules of epigenetic sites that correlated with different metabolic and dietary measures.Observations demonstrate the feasibility of identifying systemic epigenetic biomarkers for obesity, which can be further investigated for clinical relevance in future research with larger sample sizes.The availability of a systemic epigenetic biomarker for obesity susceptibility may facilitate preventative medicine and clinical management of the disease early in life.

Cross-Sectional Study of Location-Based Built Environments, Physical Activity, Dietary Intake, and Body Mass Index in Adult Twins.

We examined relationships between walkability and health behaviors between and within identical twin pairs, considering both home (neighborhood) walkability and each twin's measured activity space. Continuous activity and location data (via accelerometry and GPS) were obtained in 79 pairs over 2 weeks. Walkability was estimated using Walk Score® (WS); home WS refers to neighborhood walkability, and GPS WS refers to the mean of individual WSs matched to every GPS point collected by each participant. GPS WS was assessed within (WHN) and out of the neighborhood (OHN), using 1-mile Euclidean (air1mi) and network (net1mi) buffers. Outcomes included walking and moderate-to-vigorous physical activity (MVPA) bouts, dietary energy density (DED), and BMI. Home WS was associated with WHN GPS WS (b = 0.71, SE = 0.03, p < 0.001 for air1mi; b = 0.79, SE = 0.03, p < 0.001 for net1mi), and OHN GPS WS (b = 0.18, SE = 0.04, p < 0.001 for air1mi; b = 0.22, SE = 0.04, p < 0.001 for net1mi). Quasi-causal relationships (within-twin) were observed for home and GPS WS with walking (ps < 0.01), but not MVPA, DED, or BMI. Results support previous literature that neighborhood walkability has a positive influence on walking.

Quasi-causal associations between chronotype and post-traumatic stress disorder symptoms: A twin study.

OBJECTIVE: The evening ("night owl") chronotype is associated with greater severity and lifetime prevalence of post-traumatic stress disorder (PTSD) symptoms compared to morning or intermediate chronotypes. This twin study investigated the gene-environment relationships between chronotype, recent PTSD symptoms, and lifetime intrusive symptoms. METHODS: We used the reduced Horne-Östberg Morningness-Eveningness Questionnaire (rMEQ) to assess chronotype in a sample of 3777 same-sex adult twin pairs raised together (70.4% monozygotic, 29.6% dizygotic) in the community-based Washington State Twin Registry. PTSD symptoms were reported on the Impact of Events Scale (IES) and a single item for lifetime experience of intrusive symptoms after a stressful or traumatic event. RESULTS: Genetic influences accounted for 50% of chronotype variance, 30% of IES score variance, and 14% of lifetime intrusive symptom variance. Bivariate twin models showed a phenotypic association (bp) between evening chronotype and more severe PTSD symptoms (bp = -0.16, SE = 0.02, p < .001) that remained significant even after adjusting for shared genetic and environmental influences (bp = -0.10, SE = 0.04, p = .009), as well as age, sex, and self-reported sleep duration (bp = -0.11, SE = 0.04, p = .004). An association was found between evening chronotype and lifetime intrusive symptoms (bp = -0.11, SE = 0.03, p < .001) that was no longer significant after adjusting for shared genetic and environmental influences (bp = 0.04, SE = 0.06, p = .558). CONCLUSIONS: Our results suggest a "quasi-causal" relationship between evening chronotype and PTSD symptoms that is not purely attributable to genetic or shared environmental factors. Evening chronotype may increase vulnerability to pathologic stress responses in the setting of circadian misalignment, providing potential avenues of prevention and treatment using chronobiological strategies.

Do married and/or cohabiting individuals fare better during the COVID-19 pandemic? Satisfaction with life and depression among adult twins in the United States.

Due to social distancing measures implemented to mitigate the COVID-19 pandemic, individuals are spending more time isolated at home with limited physical social interactions. The current study investigated whether marriage and/or cohabitation is associated with satisfaction with life and depression among 732 adult same-sex twin pairs (monozygotic and dizygotic) in the US using online survey data. Twin analysis showed that married and/or cohabiting individuals were more satisfied with life and less depressed than those not married and/or cohabiting. The association between marriage and/or cohabiting and satisfaction with life was not confounded by between-family factors, whereas that between depression was mediated by familial factors. These findings suggest that being in a close relationship may mitigate some of the adverse consequences of the COVID-19 pandemic. Close relationships may be an essential source of support as individuals rely on their intimate partners when faced with the uncertainty and stress of the pandemic.

Epigenome-wide association study of physical activity and physiological parameters in discordant monozygotic twins.

An epigenome-wide association study (EWAS) was performed on buccal cells from monozygotic-twins (MZ) reared together as children, but who live apart as adults. Cohorts of twin pairs were used to investigate associations between neighborhood walkability and objectively measured physical activity (PA) levels. Due to dramatic cellular epigenetic sex differences, male and female MZ twin pairs were analyzed separately to identify differential DNA methylation regions (DMRs). A priori comparisons were made on MZ twin pairs discordant on body mass index (BMI), PA levels, and neighborhood walkability. In addition to direct comparative analysis to identify specific DMRs, a weighted genome coexpression network analysis (WGCNA) was performed to identify DNA methylation sites associated with the physiological traits of interest. The pairs discordant in PA levels had epigenetic alterations that correlated with reduced metabolic parameters (i.e., BMI and waist circumference). The DNA methylation sites are associated with over fifty genes previously found to be specific to vigorous PA, metabolic risk factors, and sex. Combined observations demonstrate that behavioral factors, such as physical activity, appear to promote systemic epigenetic alterations that impact metabolic risk factors. The epigenetic DNA methylation sites and associated genes identified provide insight into PA impacts on metabolic parameters and the etiology of obesity.

Cross-sectional associations between neighbourhood walkability and objective physical activity levels in identical twins.

OBJECTIVES: Physical activity is a cornerstone of chronic disease prevention and treatment, yet most US adults do not perform levels recommended for health. The neighborhood-built environment (BE) may support or hinder physical activity levels. This study investigated whether identical twins who reside in more walkable BEs have greater activity levels than twins who reside in less walkable BEs (between-twin analysis), and whether associations remain significant when controlling for genetic and shared environmental factors (within-twin analysis). DESIGN: A cross-sectional study. SETTING: The Puget Sound region around Seattle, Washington, USA. PARTICIPANTS: The sample consisted of 112 identical twin pairs who completed an in-person assessment and 2-week at-home measurement protocol using a global positioning system (GPS)monitor and accelerometer. EXPOSURE: The walkability of each participants' place of residence was calculated using three BE dimensions (intersection density, population density and destination accessibility). For each variable, z scores were calculated and summed to produce the final walkability score. OUTCOMES: Objectively measured bouts of walking and moderate-to-vigorous physical activity (MVPA), expressed as minutes per week. RESULTS: Walkability was associated with walking bouts (but not MVPA) within the neighbourhood, both between (b=0.58, SE=0.13, p<0.001) and within pairs (b=0.61, SE=0.18, p=0.001). For a pair with a 2-unit difference in walkability, the twin in a more walkable neighbourhood is likely to walk approximately 16 min per week more than the co-twin who lives in a less walkable neighbourhood. CONCLUSIONS: This study provides robust evidence of an association between walkability and objective walking bouts. Improvements to the neighbourhood BE could potentially lead to increased activity levels in communities throughout the USA.

Bring Your Own Location Data: Use of Google Smartphone Location History Data for Environmental Health Research.

BACKGROUND: Environmental exposures are commonly estimated using spatial methods, with most epidemiological studies relying on home addresses. Passively collected smartphone location data, like Google Location History (GLH) data, may present an opportunity to integrate existing long-term time-activity data. OBJECTIVES: We aimed to evaluate the potential use of GLH data for capturing long-term retrospective time-activity data for environmental health research. METHODS: We included 378 individuals who participated in previous Global Positioning System (GPS) studies within the Washington State Twin Registry. GLH data consists of location information that has been routinely collected since 2010 when location sharing was enabled within android operating systems or Google apps. We created instructions for participants to download their GLH data and provide it through secure data transfer. We summarized the GLH data provided, compared it to available GPS data, and conducted an exposure assessment for nitrogen dioxide (NO2) air pollution. RESULTS: Of 378 individuals contacted, we received GLH data from 61 individuals (16.1%) and 53 (14.0%) indicated interest but did not have historical GLH data available. The provided GLH data spanned 2010-2021 and included 34 million locations, capturing 66,677 participant days. The median number of days with GLH data per participant was 752, capturing 442 unique locations. When we compared GLH data to 2-wk GPS data (∼1.8 million points), 95% of GPS time-activity points were within 100m of GLH locations. We observed important differences between NO2 exposures assigned at home locations compared with GLH locations, highlighting the importance of GLH data to environmental exposure assessment. DISCUSSION: We believe collecting GLH data is a feasible and cost-effective method for capturing retrospective time-activity patterns for large populations that presents new opportunities for environmental epidemiology. Cohort studies should consider adding GLH data collection to capture historical time-activity patterns of participants, employing a "bring-your-own-location-data" citizen science approach. Privacy remains a concern that needs to be carefully managed when using GLH data. https://doi.org/10.1289/EHP10829.

Measuring and modelling perceptions of the built environment for epidemiological research using crowd-sourcing and image-based deep learning models.

BACKGROUND: Perceptions of the built environment, such as nature quality, beauty, relaxation, and safety, may be key factors linking the built environment to human health. However, few studies have examined these types of perceptions due to the difficulty in quantifying them objectively in large populations. OBJECTIVE: To measure and predict perceptions of the built environment from street-view images using crowd-sourced methods and deep learning models for application in epidemiologic studies. METHODS: We used the Amazon Mechanical-Turk crowdsourcing platform where participants compared two street-view images and quantified perceptions of nature quality, beauty, relaxation, and safety. We optimized street-view image sampling methods to improve the quality and resulting perception data specific to participants enrolled in the Washington State Twin Registry (WSTR) health study. We used a transfer learning approach to train deep learning models by leveraging existing image perception data from the PlacePulse 2.0 dataset, which includes 1.1 million image comparisons, and refining based on new WSTR perception data. Resulting models were applied to WSTR addresses to estimate exposures and evaluate associations with traditional built environment measures. RESULTS: We collected over 36,000 image comparisons and calculated perception measures for each image. Our final deep learning models explained 77.6% of nature quality, 68.1% of beauty, 72.0% of relaxation, and 64.7% of safety in pairwise image comparisons. Applying transfer learning with the new perception labels specific to the WSTR yielded an average improvement of 3.8% for model performance. Perception measures were weakly to moderately correlated with traditional built environment exposures for WSTR participant addresses; for example, nature quality and NDVI (r = 0.55), neighborhood area deprivation (r = -0.16), and walkability (r = -0.20), respectively. SIGNIFICANCE: We were able to measure and model perceptions of the built environment optimized for a specific health study. Future applications will examine associations between these exposure measures and mental health in the WSTR. IMPACT STATEMENT: Built environments influence health through complex pathways. Perceptions of nature quality, beauty, relaxation and safety may be particularly import for understanding these linkages, but few studies to-date have examined these perceptions objectively for large populations. For quantitative research, an exposure measure must be reproducible, accurate, and precise--here we work to develop such measures for perceptions of the urban environment. We created crowd-sourced and image-based deep learning methods that were able to measure and model these perceptions. Future applications will apply these models to examine associations with mental health in the Washington State Twin Registry.

The pillars of health: influence of multiple lifestyle behaviors on body mass index and depressive symptoms in adult twins.

BACKGROUND: Guidelines promoting healthy lifestyles are cornerstones of chronic disease prevention and treatment. The purpose of this study is to investigate independent and joint associations of five key health behaviors with health outcomes (body mass index (BMI kg/m2) and depressive symptoms) in adult twins. METHODS: We included 6,048 twin pairs from a community-based registry. Five key health behaviors were: (1) ≥ 8 h of sleep per night, (2) ≥ 5 servings of fruits and vegetables daily, (3) ≤ 2 h sedentary time per day, (4) ≥ 150 min of moderate-to-vigorous physical activity (MVPA) per week, and (5) no smoking. We analyzed phenotypic associations between behaviors and outcomes; whether phenotypic associations were confounded by additive genetic and shared environmental factors within twin pairs ("quasi-causal" associations); and which behaviors, considered simultaneously, had the largest associations with outcomes. RESULTS: We found negative phenotypic associations between number of behaviors achieved with BMI and depressive symptoms score (ps < 0.05). Associations remained significant, though attenuated, when controlling for genetic and shared environmental factors, and demographics, for depressive symptoms score but not BMI (p < 0.05). Quantitative variable importance measures derived from regression tree models showed sedentary time and MVPA were the most important variables in partitioning twins with different BMI, and smoking and sedentary time for partitioning twins with different depressive symptoms score. CONCLUSIONS: Achievement of commonly endorsed health behaviors is associated with lower BMI (especially sedentary and MVPA targets) and depressive symptoms score (especially sedentary and smoking targets). This provides further support of health behavior promotion to improve health outcomes.

Changes in physical activity levels and mental health during COVID-19: Prospective findings among adult twin pairs.

BACKGROUND: Physical distancing and other COVID-19 pandemic mitigation strategies have negatively impacted physical activity (PA) levels and mental health in cross-sectional studies. The purpose of this study was to investigate associations between changes in PA and mental health outcomes during the COVID-19 pandemic, following implementation of mitigation strategies, in a sample of adult twins. METHODS: This was a prospective study of 3,057 adult twins from the Washington State Twin Registry. Study participants completed online surveys in 2020, at baseline (March 26 -April 5), and three follow-up waves (W1: April 20 -May 3; W2: Jul 16 -Aug 2; W3: Sept 16 -Oct 1). Physical activity was operationalized as self-reported moderate-to-vigorous PA (MVPA) and neighborhood walking (minutes/week), and mental health outcomes, operationalized as self-reported anxiety and perceived stress were assessed in the three waves of follow-up. Latent growth curve models (LGCMs) were used to assess changes in PA and mental health outcomes over time. Parallel LGCMs were used to estimate the cross-sectional, parallel, and prospective associations between PA and mental health over time. All models took into within-pair correlations and adjusted for age, sex, and race. RESULTS: Individuals' amount of MVPA and walking decreased over time, whereas levels of anxiety remained stable, and stress increased slightly. Cross-sectional associations observed between both PA predictors and mental health outcomes were weak. After taking into account cross-sectional associations between PA and mental health outcomes, changes in PA over time were not associated with changes in mental health outcomes over time. CONCLUSIONS: Over a time period aligned with COVID-19 mitigation strategies and social restrictions, changes in physical activity was not associated with changes in anxiety or stress levels in the current sample. Nonetheless, the average decline in PA over time is worrisome. Public health resources should continue to promote PA as a means to improve physical health during the pandemic.

Differences in Stress and Anxiety Among Women With and Without Children in the Household During the Early Months of the COVID-19 Pandemic.

The COVID-19 pandemic and resulting lockdowns have had a disproportionate impact on parents of children under 18, particularly women. Mandatory school closures and loss of childcare resulted in parents balancing work, teaching, and childcare needs. A number of studies have examined changes in mental health of parents, but to date no studies have compared the differences in stress and anxiety levels between women with and without children in the United States. Adult women from the Washington State Twin Registry (WSTR) (N = 1,014, pair N = 529) and mothers of twin children enrolled in the WSTR (N = 147) completed an online survey examining several health-related behaviors and outcomes and their self-reported changes due to COVID-19. We conducted two studies to examine the impact of children on stress and anxiety levels among women. In study 1, we assessed whether women living in households with children under the age of 18 have higher levels of stress and anxiety than those without children in their household. We found that perceived stress levels did not differ between women with and without children in the household, but anxiety levels were higher among women living with children than those without. In study 2, we assessed whether the correlation between children in the household and stress/anxiety is accounted for by non-random genetic and environmental selection effects, causal processes, or both using a sample of adult female twins. We found that the presence of children in the household was associated with higher levels of stress and anxiety. However, this association is confounded by genetic and shared environmental factors. Our findings highlight the need to provide supporting resources to women living with children in the household during and after the COVID-19 pandemic.

Measurement of neighborhood-based physical activity bouts.

This study examined how buffer type (shape), size, and the allocation of activity bouts inside buffers that delineate the neighborhood spatially produce different estimates of neighborhood-based physical activity. A sample of 375 adults wore a global positioning system (GPS) data logger and accelerometer over 2 weeks under free-living conditions. Analytically, the amount of neighborhood physical activity measured objectively varies substantially, not only due to buffer shape and size, but by how GPS-based activity bouts are identified with respect to containment within neighborhood buffers. To move the "neighborhood-effects" literature forward, it is critical to delineate the spatial extent of the neighborhood, given how different ways of measuring GPS-based activity containment will result in different levels of physical activity across different buffer types and sizes.

Is COVID-19 Keeping us Up at Night? Stress, Anxiety, and Sleep Among Adult Twins.

In response to the COVID-19 pandemic, a variety of social distancing measures to mitigate the virus outbreak have been implemented. These measures may have unintended consequences on individuals' well-being, such as increased stress, anxiety, and sleep disruptions. We investigated the extent to which individuals' mental health status is associated with perceived changes in sleep amount and sleep quality among a sample of adult twin pairs (N = 909 pairs; 77% MZ, 23% DZ), less than a month after the outbreak was declared a pandemic by the World Health Organization. About half of participants reported no change in sleep amount (50.1%) or sleep quality (55.6%). Approximately one-third of the participants had increased amount of sleep (29.8%), and 32.9% reported a decrease in sleep quality. We found that stress and anxiety levels were associated with sleep reduction (ORs = 2.36 and 3.12 for stress and anxiety, respectively) and poorer sleep quality (ORs = 2.45 and 3.73 for stress and anxiety, respectively), even after taking into account between-family confounds. A much smaller association was observed between levels of stress and anxiety and increased sleep amount (ORs = 1.42 and 1.60 for stress and anxiety, respectively) and sleep quality (OR = 1.21 and 1.29 for stress and anxiety, respectively), which was no longer significant after controlling for between-family confounds. Our results demonstrate that stress and anxiety associated with the COVID-19 pandemic and social distancing measures may be linked to reduced sleep amount and quality.

Fear and depression linked to COVID-19 exposure A study of adult twins during the COVID-19 pandemic.

Millions of people have been impacted by the novel coronavirus (COVID-19) pandemic worldwide. High infection rates and death tolls, combined with social distancing measures, may have unintended psychological consequences on individuals. The goal of this study was to examine the interrelations between COVID-19 exposure, fear of COVID-19, and depression among a community-based sample of adult twins. We further explored whether fear of COVID-19 mediated the association between COVID-19 exposure and depression. 732 same-sex adult twin pairs (78.1% MZ, 21.9% DZ) completed an online survey examining their feelings in May 2020. About one-fifth of the participants reported having any COVID-19 exposure. Most participants (>80%) were somewhat concerned about themselves or their household members being infected by COVID-19. The average depression level was relatively low (M = 0.9 out of 6). We found that COVID-19 exposure was related to increased fears of COVID-19 and depression, and that depressive feelings increased with fear of COVID-19. The correlation between COVID-19 exposure and depression was partially mediated by fear of COVID-19. However, these associations were confounded by familial influences. As society navigates through the pandemic, it is essential to implement public health strategies to help individuals cope with the concerns and fears about COVID-19.

Stress, Anxiety, and Change in Alcohol Use During the COVID-19 Pandemic: Findings Among Adult Twin Pairs.

The novel coronavirus (COVID-19) has impacted the lives of people worldwide since being declared a pandemic on March 11, 2020. Social restrictions aimed at flattening the curve may be associated with an increase in stress and anxiety, which may increase the use of alcohol as a coping mechanism. The objective of this study was to examine if stress and anxiety were associated with changes in alcohol use in a sample of adult twins. Twins allowed us to control for genetic and shared environmental factors that would confound the alcohol - mental health relationship. Twins (N = 3,971; 909 same-sex pairs) from the Washington State Twin Registry (WSTR) completed an online survey examining several health-related behaviors and outcomes and their self-reported changes due to COVID-19. About 14% of the respondents reported an increase in alcohol use. We found an association between both stress and anxiety and increased alcohol use, where twins with higher levels of stress and anxiety were more likely to report an increase in alcohol consumption. The associations were small and confounded by between-family factors and demographic characteristics. However, there was no significant difference in stress or anxiety levels between non-drinkers and those who reported no change in alcohol use. Our findings suggest that individuals' mental health may be associated with changes in alcohol use during the COVID-19 pandemic.

Perceived change in physical activity levels and mental health during COVID-19: Findings among adult twin pairs.

BACKGROUND: Physical distancing and other COVID-19 pandemic mitigation strategies may have unintended consequences on a number of health behaviors and health outcomes. The purpose of this study was to investigate the association between perceived change in physical activity or exercise and mental health outcomes over the short-term in response to COVID-19 mitigation strategies in a sample of adult twins. METHODS: This was a cross-sectional study of 3,971 identical and same-sex fraternal adult twins (909 pairs, 77% identical) from the community-based Washington State Twin Registry. Participants in this study completed an online survey examining the impact of COVID-19 mitigation on a number of health-related behaviors and outcomes, administered between March 26 and April 5, 2020. In the present study, the exposure was perceived change in physical activity or exercise. The outcomes were levels of perceived anxiety and stress. RESULTS: More twin pairs reported a decrease in physical activity levels (42%) than those reporting no change (31%) or increased physical activity levels (27%). A perceived decrease in physical activity or exercise was associated with higher stress and anxiety levels. However, the physical activity-stress relationship was confounded by genetic and shared environmental factors. On the other hand, the physical activity-anxiety relationship held after controlling for genetic and shared environmental factors, although it was no longer significant after further controlling for age and sex, with older twins more likely to report lower levels of anxiety and females more likely to report higher levels of anxiety. CONCLUSIONS: Strategies to mitigate the COVID-19 pandemic may be impacting physical activity and mental health, with those experiencing a decrease in physical activity also having higher levels of stress and anxiety. These relationships are confounded by genetic and shared environmental factors, in the case of stress, and age and sex, in the case of anxiety.

Psychometric and Classification Properties of the Peas in a Pod Questionnaire.

We examined the item properties of the Two Peas Questionnaire (TPQ) among a sample of same-sex twin pairs from the Washington State Twin Registry. With the exception of the 'two peas' item, three of the mistakenness items showed differential item functioning. Results showed that the monozygotic (MZ) and dizygotic (DZ) pairs may differ in their responses on these items, even among those with similar latent traits of similarity and confusability. Upon comparing three classification methods to determine the zygosity of same-sex twins, the overall classification accuracy rate was over 90% using the unit-weighted pair zygosity sum score, providing an efficient and sufficiently accurate zygosity classification. Given the inherent nature of twin-pair similarity, the TPQ is more accurate in the identification of MZ than DZ pairs. We conclude that the TPQ is a generally accurate, but by no means infallible, method of determining zygosity in twins who have not been genotyped.

Sleep duration and post-traumatic stress disorder symptoms: a twin study.

STUDY OBJECTIVES: Long and short sleep duration are associated with greater risk of developing post-traumatic stress disorder (PTSD); however, it is unknown how genetic and environmental influences affect this relationship. Thus, we investigated the association between sleep duration and PTSD symptoms using twin models. METHODS: Data were obtained from 1865 monozygotic and 758 dizygotic twin pairs enrolled in the community-based Washington State Twin Registry. PTSD symptoms were assessed using the Impact of Events Scale (IES). A classical twin model decomposed the variances of sleep duration and IES score into additive genetic, shared environmental, and unique environmental components. We used correlated factor models to examine the moderation of variance components of sleep duration and IES. RESULTS: Shorter and longer sleep duration were associated with higher IES scores with a quadratic association (p < 0.001). The heritability of sleep duration was 36%, and IES 31%. Variance in sleep duration attributable to shared (b1C1 = 2.91, 95% CI = 1.40 to 4.43; p < 0.001) and unique (b1E1 = 0.18, 95% CI = 0.10 to 0.27; p < 0.001) environment was moderated by IES score. Similarly, but to a lesser extent, variance in IES attributable to additive genetics (b1A2 = -0.23, 95% CI = -0.45 to 0.00; p = 0.048) was moderated by sleep duration. CONCLUSIONS: Greater PTSD symptom severity was associated with short and long sleep duration. Increasing PTSD symptoms increased variability in sleep duration primarily via shared environmental factors, whereas decreasing sleep duration increased variability in PTSD symptoms primarily via additive genetic factors. This suggests childhood experiences affect variability of sleep duration and genetic factors affect the variability of PTSD symptoms in trauma-exposed individuals.

The Washington State Twin Registry: 2019 Update.

It has been over 5 years since the last special issue of Twin Research and Human Genetics on 'Twin Registries Worldwide: An Important Resource for Scientific Research' was published. Much progress has been made in the broad field of twin research since that time, and the current special issue is a follow-up to update the scientific community about twin registries around the globe. The present article builds upon our 2013 Registry description by summarizing current information on the Washington State Twin Registry (WSTR), including history and construction methods, member characteristics, available data, and major research goals. We also provide a section with brief summaries of recently completed studies and discuss the future research directions of the WSTR. The Registry has grown in terms of size and scope since 2013; highlights include recruitment of youth pairs under 18 years of age, extensive geocoding work to develop environmental exposures that can be linked to survey and administrative health data such as death records, and expansion of a biobank with specimens collected for genotyping, DNA methylation, and microbiome based-studies.

Heritability of Type 2 Diabetes in the Washington State Twin Registry.

Approximately 12% of U.S. adults have type 2 diabetes (T2D). Diagnosed T2D is caused by a combination of genetic and environmental factors including age and lifestyle. In adults 45 years and older, the Discordant Twin (DISCOTWIN) consortium of twin registries from Europe and Australia showed a moderate-to-high contribution of genetic factors of T2D with a pooled heritability of 72%. The purpose of this study was to investigate the contributions of genetic and environmental factors of T2D in twins 45 years and older in a U.S. twin cohort (Washington State Twin Registry, WSTR) and compare the estimates to the DISCOTWIN consortium. We also compared these estimates with twins under the age of 45. Data were obtained from 2692 monozygotic (MZ) and same-sex dizygotic (DZ) twin pairs over 45 and 4217 twin pairs under 45 who responded to the question 'Has a doctor ever diagnosed you with (type 2) diabetes?' Twin similarity was analyzed using both tetrachoric correlations and structural equation modeling. Overall, 9.4% of MZ and 14.7% of DZ twins over the age of 45 were discordant for T2D in the WSTR, compared to 5.1% of MZ and 8% of DZ twins in the DISCOTWIN consortium. Unlike the DISCOTWIN consortium in which heritability was 72%, heritability was only 52% in the WSTR. In twins under the age of 45, heritability did not contribute to the variance in T2D. In a U.S. sample of adult twins, environmental factors appear to be increasingly important in the development of T2D.