Effects of Social Attitude Change on Smoking Heritability

Societal attitudes and norms to female smoking changed in Spain in the mid-twentieth century from a restrictive to a tolerant, and an even pro-smoking, posture, while social attitudes remained stable for males. We explored whether this difference in gender-related social norms influenced the heritability of two tobacco use measures: lifetime smoking and number of years smoking. We used a population-based sample of 2285 twins (mean age?=?55.78; SD?=?7.45; 58% females) whose adolescence began between the mid-1950s and the early 1980s. After modeling the effect of sex and year of birth on the variance components, we observed that the impact of the genetic and shared environmental factors varied differently by birth cohort between males and females. For females, shared environment explained a higher proportion of variance than the genetic factors in older cohorts. However, this situation was inverted in the younger female cohorts. In contrast, no birth cohort effect was observed for males, where the impact of the genetic and environmental factors remained constant throughout the study period. These results suggest that heritability is larger in a permissive social environment, whereas shared-environmental factors are more relevant in a society that is less tolerant to smoking.     

Genetic and Environmental Influences on Individual Differences in Attitudes Toward Homosexuality: An Australian Twin Study

Previous research has shown that many heterosexuals hold negative attitudes toward homosexuals and homosexuality (homophobia). Although a great deal of research has focused on the profile of homophobic individuals, this research provides little theoretical insight into the aetiology of homophobia. To examine genetic and environmental influences on variation in attitudes toward homophobia, we analysed data from 4,688 twins who completed a questionnaire concerning sexual behaviour and attitudes, including attitudes toward homosexuality. Results show that, in accordance with literature, males have significantly more negative attitudes toward homosexuality than females and non-heterosexuals are less homophobic than heterosexuals. In contrast with some earlier findings, age had no significant effect on the homophobia scores in this study. Genetic modelling showed that variation in homophobia scores could be explained by additive genetic (36%), shared environmental (18%) and unique environmental factors (46%). However, corrections based on previous findings show that the shared environmental estimate may be almost entirely accounted for as extra additive genetic variance arising from assortative mating for homophobic attitudes. The results suggest that variation in attitudes toward homosexuality is substantially inherited, and that social environmental influences are relatively minor.     

The Implications of Simultaneous Smoking Initiation for Inferences about the Genetics of Smoking Behavior from Twin Data

We examined early social influences across stages of smoking within the context of a twin study using an environmental exposure specific to smoking: whether twins started smoking at the same time (“simultaneous smoking initiation”: SSI). We expected that SSI would be a good index of shared social influences on smoking initiation. Rates of SSI were indeed significantly higher in MZ twins and in twins who shared peers and classes, as well as in male twins. With the exception of regular smoking in females, we found no significant difference in estimates of genetic and environmental parameters between SSI and non-SSI pairs for any of the smoking measures that we examined (DSM-IV and Fagerstrom HSI measures of nicotine dependence; DSM-IV nicotine withdrawal; heavy smoking; and in males, regular smoking). For regular smoking in females, allowing for additional shared environmental influences associated with SSI only modestly reduced our estimates of additive genetic variance (56% vs. 68%). These results indicate the important social influences that may occur for smoking initiation do not appear to seriously bias estimates of genetic effects on later stages of smoking.     

Modeling the direction of causation between cross‐sectional measures of disrupted sleep,anxiety and depression in a sample of male and female Australian twins

The direction of causation between measures of disrupted sleep, anxiety and depression is not well understood. Under certain conditions, cross‐sectional analysis based on genetically informative data can provide important information about the direction of causation between variables. Two community‐based samples of 7235 Australian twins aged 18–87 years were mailed an extensive questionnaire that covered a wide range of personality and behavioral measures. Included were self‐report measures of disrupted sleep, as well as symptoms of anxiety and depression. Among all females, modeling the direction of causation did not support the hypothesis of sleep having a direct causal impact on risk of anxiety or depression. Among older females, we found evidence that both anxiety and depression interact reciprocally with disrupted sleep, whereas among younger women both anxiety and depression appear to have a causal impact on sleep. Results for males were equivocal. The nosological implications of our findings are discussed.     

Shared Environmental Contributions to Substance Use

The current study examined the association between substance use in the household during childhood, parental attitudes towards substance use and lifetime substance use in males. Subjects included 1081 monozygotic and 707 dizygotic twins from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. Retrospective reports of substance use and features of the family environment (adult household substance use and parental attitudes towards substance use) were obtained using a life history interview. A trivariate Cholesky decomposition was conducted using the program Mx to decompose common shared environmental variance. Findings suggest that family environmental factors accounted for a large proportion of the shared environmental effects for illicit drug use. Results illustrate an important way of extending behavior genetic research to reveal specific etiological environmental mechanisms.     

A twin study of sex differences in social support

BACKGROUND: Social support may reduce the risk of psychiatric illness. Though perceived as an environmental measure, genetic factors may influence levels of social support. A relationship between social roles and personality with social support suggests possible sex effects on the sources of individual differences in social support. METHOD: We used the responses of MZ and DZ same and opposite sex twins to 16 questions regarding their social life. Six factors--friend support, relative support, friend problem, relative problem, confidants and social integration were used for structural equation modelling. Factor derived scales were analysed for genetic, shared and unique environmental influences. Quantitative and qualitative gender differences were analysed using the software package Mx. RESULTS: Except for relative support and confidants, no qualitative sex differences were seen. Genetic and individual specific environmental influences accounted for the variance for friend support, friend problems, relative problems and social integration and no quantitative gender differences were seen. For relative support genetic factors were detected in females but not males, while for confidants, the shared environment was important in females but not males. CONCLUSIONS: Except for relative support in males, genetic factors influence variation in all dimensions of social support. Shared environmental factors influence relative support and relative problems in both sexes. Sex differences were detected for confidants and relative support.     

Genetic and Environmental Transmission of Body Mass Index Fluctuation

This study sought to determine the relationship between body mass index (BMI) fluctuation and cardiovascular disease phenotypes, diabetes, and depression and the role of genetic and environmental factors in individual differences in BMI fluctuation using the extended twin-family model (ETFM). This study included 14,763 twins and their relatives. Health and Lifestyle Questionnaires were obtained from 28,492 individuals from the Virginia 30,000 dataset including twins, parents, siblings, spouses, and children of twins. Self-report cardiovascular disease, diabetes, and depression data were available. From self-reported height and weight, BMI fluctuation was calculated as the difference between highest and lowest BMI after age 18, for individuals 18–80 years. Logistic regression analyses were used to determine the relationship between BMI fluctuation and disease status. The ETFM was used to estimate the significance and contribution of genetic and environmental factors, cultural transmission, and assortative mating components to BMI fluctuation, while controlling for age. We tested sex differences in additive and dominant genetic effects, parental, non-parental, twin, and unique environmental effects. BMI fluctuation was highly associated with disease status, independent of BMI. Genetic effects accounted for ~34 % of variance in BMI fluctuation in males and ~43 % of variance in females. The majority of the variance was accounted for by environmental factors, about a third of which were shared among twins. Assortative mating, and cultural transmission accounted for only a small proportion of variance in this phenotype. Since there are substantial health risks associated with BMI fluctuation and environmental components of BMI fluctuation account for over 60 % of variance in males and over 50 % of variance in females, environmental risk factors may be appropriate targets to reduce BMI fluctuation.     

Exploring the inter-relationship of smoking age-at-onset, cigarette consumption and smoking persistence: genes or environment?

BACKGROUND: We investigated the genetic and environmental contributions to covariation between smoking age-at-onset, cigarette consumption and smoking persistence. METHOD: Multivariate biometrical modelling methods were applied to questionnaire data from Australian twins and their siblings (14 472 individuals from 6247 families). The contributions of genetic and environmental factors to covariation between the three traits were estimated, allowing for sex differences in both trait prevalence and the magnitude of genetic and environmental effects. RESULTS: All traits were moderately heritable in males and females (estimates between 0.40 and 0.62), but there were sex differences in the extent to which additive genetic influences were shared across traits. Twin-specific environmental factors accounted for a substantial proportion of the variance in smoking age-at-onset in females (0.19) and males (0.12), but had little influence (<0.08) on other traits. Unique environmental factors were estimated to have a moderate influence on smoking age-at-onset (0.17 for females, 0.19 for males), but a stronger influence on other traits (between 0.39 and 0.49). CONCLUSIONS: These results provide some insight into observed sex differences in smoking behaviour, and suggest that searching for pleiotropic genes may prove fruitful. However, further work on phenotypic definitions of smoking behaviour, particularly persistence, is warranted.     

The Influence of Religion on Alcohol Use Initiation: Evidence for Genotype X Environment Interaction

We examined the possible role of religious upbringing as a mediator of the shared environmental influences and as a moderator of the genetic influences on the risk of alcohol use initiation in a large population-based sample of Dutch adolescent and young adult twins (1967 twin pairs). There was not a significant association between religious participation and alcohol use initiation among Dutch adolescents and young adults. We also hypothesized that the relative magnitude of the genetic influences on the risk of alcohol use initiation would be greater for those adolescents and young adults who were raised in a less religious environment compared to those adolescents and young adults who were raised in a more religious environment. We indeed found higher heritabilities for females without a religious upbringing compared to females with a religious upbringing. Genetic influences accounted for 40% of the variance in alcohol use initiation in nonreligious females, compared to 0% in religiously raised females. Shared environmental influences accounted for 54% of the variance for nonreligious females and 88% of the variance in religious females. For males, the genetic variance was also higher in the nonreligious group compared to the religious group, but this difference was not statistically significant. Whether or not they were raised religiously, the liability to alcohol use initiation in males was moderately influenced by genetic factors (30%) and substantially influenced by shared environmental factors (60%).     

The genetic epidemiology of body attitudes, the attitudinal component of body image in women

BACKGROUND: There were four purposes of the current study, including the investigation of the: (i) adequacy of a multidimensional measure of body image; (ii) genetic and environmental epidemiology of this measure; (iii) shared variance between genetic and environmental risk factors for body mass index (BMI) and body image; and (iv) Equal Environment Assumption (EEA) as it related to body attitudes. METHOD: Six types of body attitudes, as measured by the Body Attitudes Questionnaire (BAQ) and reported by 894 complete female-female twin pairs (mean age 32.35 years, S.D. = 41.8) from the Australian Twin Registry, were analysed. RESULTS: Confirmatory factor analysis of the BAQ supported the adequacy of the measure. Additive genetic and unique environmental influences best accounted for the variance of all six of the BAQ subscales. The relationship between BMI and body attitudes was primarily due to shared genes rather than environment but the majority of genetic and environmental effects on body attitudes were independent of BMI, with the exception of the Feeling Fat subscale, which shared 53% of its genetic risk factors with BMI. One violation of the EEA was suggested, namely similarity of childhood treatment influenced similarity on Lower Body Fatness subscale. CONCLUSIONS: Findings support the notion that: (i) body image is a multidimensional concept; (ii) it is relatively independent of BMI; and (iii) both genetic and non-shared environment are influential determinants of body attitudes.     

Genetic and Environmental Factors in Relative Body Weight and Human Adiposity

We review the literature on the familial resemblance of body mass index (BMI) and other adiposity measures and find strikingly convergent results for a variety of relationships. Results from twin studies suggest that genetic factors explain 50 to 90% of the variance in BMI. Family studies generally report estimates of parent–offspring and sibling correlations in agreement with heritabilities of 20 to 80%. Data from adoption studies are consistent with genetic factors accounting for 20 to 60% of the variation in BMI. Based on data from more than 25,000 twin pairs and 50,000 biological and adoptive family members, the weighted mean correlations are .74 for MZ twins, .32 for DZ twins, .25 for siblings, .19 for parent–offspring pairs, .06 for adoptive relatives, and .12 for spouses. Advantages and disadvantages of twin, family, and adoption studies are reviewed. Data from the Virginia 30,000, including twins and their parents, siblings, spouses, and children, were analyzed using a structural equation model (Stealth) which estimates additive and dominance genetic variance, cultural transmission, assortative mating, nonparental shared environment, and special twin and MZ twin environmental variance. Genetic factors explained 67% of the variance in males and females, of which half is due to dominance. A small proportion of the genetic variance was attributed to the consequences of assortative mating. The remainder of the variance is accounted for by unique environmental factors, of which 7% is correlated across twins. No evidence was found for a special MZ twin environment, thereby supporting the equal environment assumption. These results are consistent with other studies in suggesting that genetic factors play a significant role in the causes of individual differences in relative body weight and human adiposity.     

The Genetic and Environmental Etiology of Sympathetic and Parasympathetic Activity in Children

The present study examines the genetic and environmental etiology of the associations among respiratory sinus arrhythmia (RSA), heart rate (HR), skin conductance level (SCL), and non-specific skin conductance responses (NS-SCR)—measures that purportedly index the parasympathetic and sympathetic branches of the autonomic nervous system. The sample was drawn from a cohort of 1,219 preadolescent twins (aged 9–10). Multivariate analyses of the data were conducted using structural equation modeling. Almost all genetic and environmental influences on the measures acted through two latent factors. The first latent factor was largely responsible for the variance in heart rate, SCL and NS-SCR, reflecting sympathetic activity, and its proportions of variance due to genetic and shared environmental influences were 27 and 28% in males, and 31 and 41% in females, respectively. The second latent factor accounted for the variance in RSA and heart rate, reflecting parasympathetic activity; genetic and shared environmental factors explained 27 and 23% of the variance in males, respectively, and 35 and 18% of the variance in females. Measurement-specific genetic effects accounted for 14–27% of the total variance in RSA and SCL, and measurement-specific shared environmental effects accounted for 10–12% in SCL. In general, the validity of separate sympathetic and parasympathetic constructs was supported.     

The Genetic Relationship Between Social Cognition and Conduct Problems

Studies of children and adolescents with conduct problems suggest both genetic and environmental influences on population variance. Any genetic influence is likely to be complex and to act via mediating attributes of personality or cognitive style. One potential mediating attribute is social cognitive ability, as conduct problems have been shown to be associated with deficient social cognitive skills. The current investigation has examined the correlation between conduct problems and social cognition and has investigated the genetic and environmental influences on these measures and their covariation using a twin design. A population-based sample of twins aged 5-17 was used to examine the genetic relationship between conduct problems and social cognition using parent-report questionnaires. Conduct problems and social cognition were found to be highly correlated and to share common genetic influences that accounted for about half the covariation in scores. Each phenotype was subject to its own environmental influences that were not shared.     

Genetic and environmental influences on birthweight in a sample of Korean twins

This study is the first report of genetic and environmental influences on birthweight using Korean twins. The sample consisted of 255 monozygotic (MZ) and 178 dizygotic (DZ) twin pairs drawn from the Seoul Twin Family Study. Intraclass twin correlations were computed for the twins' birthweights obtained from parents (typically mothers) of the twins. To estimate genetic and shared and nonshared environmental influences on birthweight, standard univariate model-fitting analyses were performed using a software, Mx. For each gender, MZ twin correlations were higher than DZ twin correlations, suggesting existence of genetic influences on birthweight; however, DZ twin correlations were higher than half the MZ twin correlations, indicating that shared environmental factors are also important. For each zygosity, twin correlations were not significantly different between males and females, implicating that genes and environments that cause individual differences in birthweight may not vary between males and females. Model-fitting analyses based on the data pooled across gender yielded estimates of 17% for genetic, 60% for shared environmental, and 23% for nonshared environmental influences on birthweight.     

The Genetic Architecture of Liver Enzyme Levels: GGT, ALT and AST

High levels of liver enzymes GGT, ALT and AST are predictive of disease and all-cause mortality and can reflect liver injury, fatty liver and/or oxidative stress. Variation in GGT, ALT and AST levels is heritable. Moderation of the heritability of these liver enzymes by age and sex has not often been explored, and it is not clear to what extent non-additive genetic and shared environmental factors may play a role. To examine the genetic architecture of GGT, ALT and AST, plasma levels were assessed in a large sample of twins, their siblings, parents and spouses (N = 8,371; age range 18–90). For GGT and ALT, but not for AST, genetic structural equation modeling showed evidence for quantitative sex differences in the genetic architecture. There was no evidence for qualitative sex differences, i.e. the same genes were expressed in males and females. Both additive and non-additive genetic factors were important for GGT in females (total heritability h² 60 %) and AST in both sexes (total h² 43 %). The heritability of GGT in males and ALT for both sexes was due to additive effects only (GGT males 30 %; ALT males 40 %, females 22 %). Evidence emerged for shared environmental factors influencing GGT in the male offspring generation (variance explained 28 %). Thus, the same genes influence liver enzyme levels across sex and age, but their relative contribution to the variation in GGT and ALT differs in males and females and for GGT across age. Given adequate sample sizes these results suggest that genome-wide association studies may result in the detection of new susceptibility loci for liver enzyme levels when pooling results over sex and age.     

Intense‐personal celebrity worship and body image: Evidence of a link among female adolescents

Objectives. The aim of the present study was to examine the relationship between celebrity worship and body image within the theoretical perspective of intense para‐social relationships with celebrities. Design. Correlation and multiple regression analyses were used to examine the relationships between celebrity worship and body image. Method. Three samples, 229 (102 males and 127 females) adolescents, 183 (88 males and 95 females) full‐time university undergraduate students, and 289 (126 males and 163 females) adults were administered an amended version of the Celebrity Attitude Scale, the Attention to Body Shape Scale, and the Body Shape Questionnaire –Revised. Results. Significant relationships were found between attitudes toward celebrities and body image only among female adolescents. Multiple regression analyses suggested that Intense‐personal celebrity worship accounted for unique variance in scores in body image. Conclusions. Findings suggest that in female adolescents, there is an interaction between Intense‐personal celebrity worship and body image between the ages of 14 and 16 years, and some tentative evidence has been found to suggest that this relationship disappears at the onset of adulthood, 17 to 20 years. Results are consistent with those authors who stress the importance of the formation of para‐social relationships with media figures, and suggest that para‐social relationships with celebrities perceived as having a good body shape may lead to a poor body image in female adolescents.     

Causes of variation in birth weight: A study of offspring of twins

In an effort to explain the causes of variation in birth weight within and between families, birth weights of 13,970 sons and daughters of monozygotic (MZ) and dizygotic (DZ) twins were analysed. The sample included birth weights of halfsibs and cousins related either through females or males, permitting the distinction between maternal and fetal genetic effects. Models of genetic and environmental variances were fitted to mean squares from analysis of variance. The results indicate that more than 50% of the total variation in birth weight is caused by variation in fetal genes, and that less than 20% is caused by variation in maternal genes. The remaining variance (20–30%) could be explained by random environmental effects. No certain effects were found of family-specific environment or of interactions between fetal and maternal genes.     

Do aggressive and non-aggressive antisocial behaviors in adolescents result from the same genetic and environmental effects?

Antisocial behavior (ASB) in adolescents can broadly be separated into two forms; aggressive and non-aggressive. Both are heritable and it has been suggested that aggressive ASB is more heritable. The extent to which genes contribute to the correlation between the two is unknown. Structural equation modeling was applied to a population-based twin sample of 258 twins pairs aged 11-18 to estimate the heritability of each form of ASB and to estimate the extent to which the phenotypic correlation was the consequence of shared genes and environmental factors. Non-shared environment and genetic factors substantially influenced both forms of ASB. The heritability of aggressive (but not non-aggressive) ASB was significantly higher in girls than in boys. Combining both sexes, a model in which the genetic effects on aggressive and non-aggressive ASB were identical could be rejected. Our results suggest a partial genetic overlap with a specific genetic effect contributing to the variance of aggressive ASB and a stronger genetic effect on aggression in females than in males.     

Transmission of Attitudes Toward Abortion and Gay Rights: Effects of Genes,Social Learning and Mate Selection

The biological and social transmission of attitudes toward abortion and gay rights are analyzed in a large sample of adult twins, siblings, and their parents. We present a linear model for family resemblance allowing for both genetic and cultural transmission of attitudes from parents to offspring, as well as phenotypic assortative mating (the tendency to marry like) and other environmental sources of twin and sibling resemblance that do not depend on the attitudes of their parents. The model gives a close fit to the patterns of similarity between relatives for the two items. Results are consistent with a substantial role of genetic liability in the transmission of both attitudes. Contrary to the dominant paradigm of the social and political sciences, the kinship data are consistent with a relatively minor non-genetic impact of parental attitudes on the development of adult attitudes in their children. By contrast, the choice of mate is a social action that has a marked impact on the polarization of social attitudes and on the long-term influence that parents exert upon the next generation. Edited by John K Hewitt.     

Cancer prevention behaviors among African-American adults: a survey of wards 7 and 8 in Washington, DC.

A telephone survey of knowledge, attitude, and health practices regarding cancer was undertaken in wards 7 and 8, Washington, DC in 1988. These wards have the highest cancer rates in the city and are predominantly African American. Of the 670 randomly selected persons over 18 years of age, 243 were males and 427 were females. Among females, 84% believed cigarette smoking causes cancer, and 48% thought alcohol causes cancer; 31% smoked cigarettes and 38% consumed alcoholic beverages. Among males, 91% and 52% thought cigarettes and alcohol causes cancer respectively; 41% smoked and 54% consumed alcoholic beverages. Only 6% of the males over age 40 practiced all eight recommended cancer prevention behaviors, while 2% of the females over age 40 practiced all preventive health behaviors. Cancer preventive behavior was examined in relation to socioeconomic status. This study indicates that preventive health behaviors were not associated with socioeconomic status. Data suggest that cancer prevention and control programs and services targeted to this Washington, DC population should be increased and intensified.