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Genetic factors explain a major proportion of human height variation, but differences in mean stature have also been found between socio-economic categories suggesting a possible effect of environment. By utilizing a classical twin design which allows decomposing the variation of height into genetic and environmental components, we tested the hypothesis that environmental variation in height is greater in offspring of lower educated parents. Twin data from 29 cohorts including 65,978 complete twin pairs with information on height at ages 1 to 69 years and on parental education were pooled allowing the analyses at different ages and in three geographic-cultural regions (Europe, North America and Australia, and East Asia). Parental education mostly showed a positive association with offspring height, with significant associations in mid-childhood and from adolescence onwards. In variance decomposition modeling, the genetic and environmental variance components of height did not show a consistent relation to parental education. A random-effects meta-regression analysis of the aggregate-level data showed a trend towards greater shared environmental variation of height in low parental education families. In conclusion, in our very large dataset from twin cohorts around the globe, these results provide only weak evidence for the study hypothesis.

Objective: The objective of this study was to analyze how parental education modifies the genetic and environmental variances of BMI from infancy to old age in three geographic-cultural regions., Methods: A pooled sample of 29 cohorts including 143,499 twin individuals with information on parental education and BMI from age 1 to 79 years (299,201 BMI measures) was analyzed by genetic twin modeling., Results: Until 4 years of age, parental education was not consistently associated with BMI. Thereafter, higher parental education level was associated with lower BMI in males and females. Total and additive genetic variances of BMI were smaller in the offspring of highly educated parents than in those whose parents had low education levels. Especially in North American and Australian children, environmental factors shared by co-twins also contributed to the higher BMI variation in the low education level category. In Europe and East Asia, the associations of parental education with mean BMI and BMI variance were weaker than in North America and Australia., Conclusions: Lower parental education level is associated with higher mean BMI and larger genetic variance of BMI after early childhood, especially in the obesogenic macro-environment. The interplay among genetic predisposition, childhood social environment, and macro-social context is important for socioeconomic differences in BMI., (© 2019 The Obesity Society.)

Objective: Social relationships, such as committed partnerships, limit risky behaviors like heavy drinking, in part, because of increased social control. The current analyses examine whether involvement in committed relationships or social support extend beyond a main effect to limit genetic liability in heavy drinking (gene-environment interaction) during young adulthood., Method: Using data from the young adult wave of the Finnish Twin Study, FinnTwin12 (n = 3,269), we tested whether involvement in romantic partnerships or social support moderated genetic influences on heavy drinking using biometric twin modeling for gene-environment interaction., Results: Involvement in a romantic partnership was associated with a decline in genetic variance in both males and females, although the overall magnitude of genetic influence was greater in males. Sex differences emerged for social support: increased social support was associated with increased genetic influence for females and reduced genetic influence for males., Conclusions: These findings demonstrate that social relationships are important moderators of genetic influences on young adult alcohol use. Mechanisms of social control that are important in limiting genetic liability during adolescence extend into young adulthood. In addition, although some relationships limit genetic liability equally, others, such as extensive social networks, may operate differently across sex.

Background: Genes and the environment contribute to variation in adult body mass index [BMI (in kg/m 2 )], but factors modifying these variance components are poorly understood. Objective: We analyzed genetic and environmental variation in BMI between men and women from young adulthood to old age from the 1940s to the 2000s and between cultural-geographic regions representing high (North America and Australia), moderate (Europe), and low (East Asia) prevalence of obesity. Design: We used genetic structural equation modeling to analyze BMI in twins ≥20 y of age from 40 cohorts representing 20 countries (140,379 complete twin pairs). Results: The heritability of BMI decreased from 0.77 (95% CI: 0.77, 0.78) and 0.75 (95% CI: 0.74, 0.75) in men and women 20-29 y of age to 0.57 (95% CI: 0.54, 0.60) and 0.59 (95% CI: 0.53, 0.65) in men 70-79 y of age and women 80 y of age, respectively. The relative influence of unique environmental factors correspondingly increased. Differences in the sets of genes affecting BMI in men and women increased from 20-29 to 60-69 y of age. Mean BMI and variances in BMI increased from the 1940s to the 2000s and were greatest in North America and Australia, followed by Europe and East Asia. However, heritability estimates were largely similar over measurement years and between regions. There was no evidence of environmental factors shared by co-twins affecting BMI. Conclusions: The heritability of BMI decreased and differences in the sets of genes affecting BMI in men and women increased from young adulthood to old age. The heritability of BMI was largely similar between cultural-geographic regions and measurement years, despite large differences in mean BMI and variances in BMI. Our results show a strong influence of genetic factors on BMI, especially in early adulthood, regardless of the obesity level in the population., (© 2017 American Society for Nutrition.)

Introduction: There has been rapid growth in research exploring gene-environment interaction (G×E) contributing to smoking behaviors. Yet, no systematic review exists to date., Methods: This article aims to review evidence on the contribution of G×E to the risk of smoking. Through a search of electronic databases (ie, Google Scholar, PubMed, ScienceDirect, and Elsevier) up until May 2014, 16 studies of G×E focused on smoking behaviors were identified. These studies were compared in terms of: research design and sample studied, measure of smoking behavior and environments used, genes explored, and G×E in relation to these factors., Results: Thirteen of 16 studies (81.2%) found at least one significant G×E association. Wide variation in analytic methods was found across studies, especially with respect to the phenotypes of interest, environmental measures used, and tests conducted to estimate G×E. Heterogeneity across studies made it difficult to compare findings and evaluate the strength of evidence for G×E., Conclusions: G×E research on smoking contains studies that are methodologically different, making it difficult to assess the current state of the evidence. To decrease heterogeneity, we offer recommendations related to: (1) choice of measurement for environmental variables, (2) testing and reporting of main and interaction effects, (3) treatment of covariates, (4) reporting gene-environment correlation, and (5) conducting sensitivity analyses and checking for scaling artifacts. Continued study is needed to identify mechanisms by which genes and environmental factors combine to influence smoking behaviors., Implications: No comprehensive review of G×E studies of smoking behavior has previously been published. The present article seeks to fill this gap by providing a comprehensive review of: how G×E has been defined, how twin and molecular genetic methodologies have been used to test for G×E, and which genes and environmental factors are associated with smoking behaviors. Variations in methodological approaches make it difficult to interpret and summarize findings, so recommendations for future research are provided as a means to more easily compare and replicate findings across studies., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Research on Nicotine and Tobacco. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Shared experiences within families play an important role in the initiation of cigarette use among adolescents. Behavioral genetic studies using various samples have implicated that the shared environment that twins experience is an important source of influence on whether adolescents initiate cigarette use. Whether the special twin environment, in addition to the shared environment, contributes significantly to making twin siblings more similar in cigarette initiation, and whether the influence of the special twin environment persists into adulthood, is less clear., Methods: Data for this study came from the National Longitudinal Survey of Adolescent Health. Twin, full-, and half-sibling pairs between the ages of 12 and 33 were separated into three age groups, with about 3,000 individuals in each age group. The proportion of variance in cigarette use initiation explained by genetic, shared, special twin, and unique environmental factors were examined., Results: The results of separate age-moderated univariate variance decomposition models indicate that the special twin environment does not significantly contribute to the variance in cigarette use initiation in adolescence or young adulthood., Conclusion: Factors shared by individuals in a family, but that are not specific to being a twin, are important in determining whether adolescents will initiate the use of cigarettes.

Introduction: Although epidemiologic studies suggest low levels of cigarette use among African American adolescents relative to White U.S. adolescents, it is not known whether this may be due to racial differences in the relative contribution of genes and environment to cigarette use initiation and progression to regular use., Methods: Using data from White (n=2665) and African American (n=809) twins and full siblings sampled in the National Longitudinal Study of Adolescents, we fitted age-, sex- and race-specific variance decomposition models to estimate the magnitude of genetic and environmental effects on cigarette use initiation and cigarette use quantity in Whites and African Americans across adolescence and adulthood. We employ a causal-contingent-common pathway model to estimate the amount of variance explained in quantity of cigarettes smoked contingent on cigarette use initiation., Results: African Americans had lower cigarette use prevalence from adolescence through adulthood, and used cigarettes less heavily than Whites. Race-specific causal-contingent-common pathway models indicate that racial differences in genetic and environmental contributions to cigarette use initiation and cigarette use quantities are not present in adolescence but appear in young adulthood. Additive genetic factors were an important risk factor for cigarette use initiation for White but not African American young adults and adults., Conclusions: Genetic and environmental contributions for cigarette use are similar by race in adolescence. In adulthood, genes have a stronger influence for cigarette use among White adolescents while the influence of the environment is minimal. For African Americans, both genetic and environmental influences are important in young adulthood and adulthood., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Background: Both genetic and environmental factors are known to affect body mass index (BMI), but detailed understanding of how their effects differ during childhood and adolescence is lacking., Objectives: We analyzed the genetic and environmental contributions to BMI variation from infancy to early adulthood and the ways they differ by sex and geographic regions representing high (North America and Australia), moderate (Europe), and low levels (East Asia) of obesogenic environments., Design: Data were available for 87,782 complete twin pairs from 0.5 to 19.5 y of age from 45 cohorts. Analyses were based on 383,092 BMI measurements. Variation in BMI was decomposed into genetic and environmental components through genetic structural equation modeling., Results: The variance of BMI increased from 5 y of age along with increasing mean BMI. The proportion of BMI variation explained by additive genetic factors was lowest at 4 y of age in boys (a(2) = 0.42) and girls (a(2) = 0.41) and then generally increased to 0.75 in both sexes at 19 y of age. This was because of a stronger influence of environmental factors shared by co-twins in midchildhood. After 15 y of age, the effect of shared environment was not observed. The sex-specific expression of genetic factors was seen in infancy but was most prominent at 13 y of age and older. The variance of BMI was highest in North America and Australia and lowest in East Asia, but the relative proportion of genetic variation to total variation remained roughly similar across different regions., Conclusions: Environmental factors shared by co-twins affect BMI in childhood, but little evidence for their contribution was found in late adolescence. Our results suggest that genetic factors play a major role in the variation of BMI in adolescence among populations of different ethnicities exposed to different environmental factors related to obesity., (© 2016 American Society for Nutrition.)

Background: Few studies examining the genetic architecture of cigarette smoking have focused on adolescents or examined developmental changes in additive genetic, shared environment, and unique environmental influences on liability to initiate cigarette smoking and quantity of cigarettes smoked. The aim of this study was to add to the literature on liability to initiate and use cigarettes during adolescence using a nationally representative sample., Method: Data for this study came from adolescent and young adult twin pairs (aged 14-33 years) from the National Longitudinal Study of Adolescent to Adult Health. We ran a series of developmental causal-contingent-common pathway models to examine whether additive genetic, shared, and unique environmental influences on liability to the initiation of cigarette use are shared with those on smoking quantity, and whether their contributions change across development., Results: We found evidence for a developmental shift in genetic and shared environmental contributions to cigarette use. Early in adolescence, genetic and environmental influences work independently on liability to cigarette smoking initiation and quantity of cigarettes smoked, but liability to these behaviors becomes correlated as individuals age into young adulthood., Conclusions: These findings provide insight into the causal processes underlying the liability to smoke cigarettes. With age, there is greater overlap in the genetic and environmental factors that influence the initiation of cigarette smoking and quantity of cigarettes smoked.

For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m2) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.

Background: Prior twin and adoption studies have demonstrated the importance of both genetic and shared environmental factors in the etiology of criminal behavior (CB). However, despite substantial interest in life-course theories of CB, few genetically informative studies have examined CB in a developmental context., Method: In 69,767 male-male twin pairs and full-sibling pairs with ≤ 2 years' difference in age, born 1958-1976 and ascertained from the Swedish Twin and Population Registries, we obtained information on all criminal convictions from 1973 to 2011 from the Swedish Crime Register. We fitted a Cholesky structural model, using the OpenMx package, to CB in these pairs over three age periods: 15-19, 20-24, and 25-29., Results: The Cholesky model had two main genetic factors. The first began at ages 15-19 and declined in importance over development. The second started at ages 20-24 and was stable over time. Only one major shared environmental factor was seen, beginning at ages 15-19. Heritability for CB declined from ages 15-29, as did shared environmental effects, although at a slower rate., Conclusions: Genetic risk factors for CB in males are developmentally dynamic, demonstrating both innovation and attenuation. These results are consistent with theories of adolescent-limited and life-course persistent CB subtypes. Heritability for CB did not increase over time as might be predicted from active gene-environmental correlation. However, consistent with expectation, the proportion of variability explained by shared environmental effects declined slightly as individuals aged and moved away from their original homes and neighborhoods.

Little is known regarding the underlying relationship between smoking initiation and current quantity smoked during adolescence into young adulthood. It is possible that the influences of genetic and environmental factors on this relationship vary across sex and age. To investigate this further, the current study applied a common causal contingency model to data from a Virginia-based twin study to determine: (1) if the same genetic and environmental factors are contributing to smoking initiation and current quantity smoked; (2) whether the magnitude of genetic and environmental factor contributions are the same across adolescence and young adulthood; and (3) if qualitative and quantitative differences in the sources of variance between males and females exist. Study results found no qualitative or quantitative sex differences in the relationship between smoking initiation and current quantity smoked, though relative contributions of genetic and environmental factors changed across adolescence and young adulthood. More specifically, smoking initiation and current quantity smoked remain separate constructs until young adulthood, when liabilities are correlated. Smoking initiation is explained by genetic, shared, and unique environmental factors in early adolescence and by genetic and unique environmental factors in young adulthood; while current quantity smoked is explained by shared environmental and unique environmental factors until young adulthood, when genetic and unique environmental factors play a larger role.

Background: Alcohol consumption is typically correlated with the alcohol use behaviors of one's peers. Previous research has suggested that this positive relationship could be due to social selection, social influence, or a combination of both processes. However, few studies have considered the role of shared genetic and environmental influences in conjunction with causal processes., Methods: This study uses data from a sample of male twins (N = 1,790) who provided retrospective reports of their own alcohol consumption and their peers' alcohol-related behaviors, from adolescence into young adulthood (ages 12 to 25). Structural equation modeling was employed to compare 3 plausible models of genetic and environmental influences on the relationship between phenotypes over time., Results: Model fitting indicated that one's own alcohol consumption and the alcohol use of one's peers are related through both genetic and shared environmental factors and through unique environmental causal influences. The relative magnitude of these factors, and their contribution to covariation, changed over time, with genetic factors becoming more meaningful later in development., Conclusions: Peers' alcohol use behaviors and one's own alcohol consumption are related through a complex combination of genetic and environmental factors that act via correlated factors and the complementary causal mechanisms of social selection and influence. Understanding these processes can inform risk assessment as well as improve our ability to model the development of alcohol use., (Copyright © 2015 by the Research Society on Alcoholism.)

The authors sought to decompose the covariance between seven dimensions of religiosity and two internalizing psychiatric disorders (major depression and phobia) and two externalizing substance use disorders (alcohol dependence and nicotine dependence). Significant negative correlations, accounted for by shared additive genetic effects, were found between alcohol dependence and six of the seven religiosity factors. Additive genetic effects accounted for significant negative correlations between nicotine dependence and one religiosity factor, social religiosity, and between phobia and unvengefulness. Common environmental effects accounted for a significant positive correlation between phobia and the factor God as judge. No statistically significant covariance due to genetic or environmental effects was found for major depression and any of the seven religiosity factors. Overall, although several statistically significant bivariate relationships were found, the estimates of covariance due to additive genetic effects were modest.

The importance of including developmental and environmental measures in genetic studies of human pathology is widely acknowledged, but few empirical studies have been published. Barriers include the need for longitudinal studies that cover relevant developmental stages and for samples large enough to deal with the challenge of testing gene-environment-development interaction. A solution to some of these problems is to bring together existing data sets that have the necessary characteristics. As part of the National Institute on Drug Abuse-funded Gene-Environment-Development Initiative, our goal is to identify exactly which genes, which environments, and which developmental transitions together predict the development of drug use and misuse. Four data sets were used of which common characteristics include (1) general population samples, including males and females; (2) repeated measures across adolescence and young adulthood; (3) assessment of nicotine, alcohol, and cannabis use and addiction; (4) measures of family and environmental risk; and (5) consent for genotyping DNA from blood or saliva. After quality controls, 2,962 individuals provided over 15,000 total observations. In the first gene-environment analyses, of alcohol misuse and stressful life events, some significant gene-environment and gene-development effects were identified. We conclude that in some circumstances, already collected data sets can be combined for gene-environment and gene-development analyses. This greatly reduces the cost and time needed for this type of research. However, care must be taken to ensure careful matching across studies and variables.

The primary aim of this study was to quantify genetic and environmental influences on the frequency of spontaneously occurring micronuclei in children and adults. To meet this aim, a total of 63 male and female twin pairs and 19 singletons (145 individuals) were evaluated, ranging in age from 7 to 85 years. Micronuclei frequencies significantly increased with age for both genders (r = 0.49, P < 0.001), with the lowest and highest rates being seen in the 7- to 9 (mean = 0.56%, SD = .28) and 60- to 69-year-olds (mean = 2.12%, SD = 1.0), respectively. This age effect was significantly more pronounced in females than males (P = 0.017). In addition to the main effect of age, the completion of puberty in either gender (P = 0.036) and menopause in females (P = 0.024) was associated with a significant increase in micronuclei frequencies. Genetic model fitting indicated that influences from both additive genetic (65.2% of variance) and unique environmental (34.8% of variance) sources best explained the observed micronuclei frequencies in monozygotic and dizygotic twin pairs. Self-reported health conditions associated with an increased frequency of micronuclei included a history of allergies (P < 0.007) and migraines (P = 0.026). Multivitamin use was also associated with increased micronuclei frequencies (P = 0.004). In contrast, significantly lower micronuclei frequencies were associated with arthritis (P = 0.002), as well as consuming fruit (P = 0.014), green, leafy vegetables (P < 0.001) and/or folate-enriched bread (P = 0.035). A sex-specific effect, resulting in a significantly increased frequency of micronuclei with tobacco usage, was observed for females (but not males). Gender differences also moderated the impact of vitamin D and calcium consumption. In conclusion, the frequency of spontaneously arising micronuclei in humans is a complex trait, being influenced by both heritable genetic and environmental components. Recognition of factors contributing to baseline levels of micronuclei should provide guidance to researchers in designing studies to evaluate agents hypothesised to influence chromosomal instability.

To determine the relationship between the genetic and environmental risk factors for common internalizing psychopathology (IP) and mental well-being (MWB), we examined detailed measures of emotional, social and psychological well-being, and a history of major depression (MD), generalized anxiety disorder (GAD) and panic attacks in the last year, in 1,386 twins from same-sex pairs from the MIDUS national USA sample assessed in 1995 and then again in 2005. Statistical analyses were performed with the Mx program. In the 1995 data, the best fit model contained one substantially heritable common factor for MD, GAD and panic attacks, and one strongly heritable common factor for the three well-being measures. Genetic and environmental risk factors for IP accounted for, respectively, 50 and 5%, of the genetic and environmental influences on MWB. We then constructed, using 1995 and 2005 data, two common factors that reflected temporally stable influences on (i) MD and GAD, and (ii) on emotional and psychological well-being. Genetic and environmental risk factors for the stable liability to IP accounted for 41 and 29% of the stable genetic and environmental influences, respectively, on MWB. This study suggests that genetic risk factors for IP make up 41-50% of the genetic influences on MWB. The overlap of environmental risk factors is more modest. Although low levels of IP on average reflect a high genetic propensity for MWB, other independent genetic influences play an important role in producing good mental health.

Childhood socioeconomic status (SES) is an important aspect of early life environment associated with later life health/health behaviors, including alcohol misuse. However, alcohol misuse is modestly heritable and involves differing etiological pathways. Externalizing disorders show significant genetic overlap with substance use, suggesting an impulsivity pathway to alcohol misuse. Alcohol misuse also overlaps with internalizing disorders, suggesting alcohol is used to cope. These differing pathways could lead to different patterns over time and/or differential susceptibility to environmental conditions, such as childhood SES. We examine whether: 1) genetic risk for externalizing and internalizing disorders influence trajectories of alcohol problems across adolescence to adulthood, 2) childhood SES alters genetic risk these disorders on trajectories of alcohol problems, and 3) these patterns are consistent across sex. We find modest evidence of gene-environment interaction. Higher childhood SES increases the risk of alcohol problems in late adolescence/early adulthood, while lower childhood SES increases the risk of alcohol problems in later adulthood, but only among males at greater genetic risk of externalizing disorders. Females from lower SES families with higher genetic risk of internalizing or externalizing disorders have greater risk of developing alcohol problems. [ABSTRACT FROM AUTHOR]