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.     

Effects of Chorion Type on Neonatal Temperament Differences in Monozygotic Twin Pairs

Monozygotic (MZ) twins with a known chorion type were assessed in the neonatal period to determine if placentation was related to twin similarity in early temperament development. The sample included 48 pairs with monochorionic placentas and 29 pairs with dichorionic placentas. The assessment focused on irritability, resistance to soothing, activity while awake, activity during sleep, reactivity, and reinforcement value. There were no differences between the monochorionic and the dichorionic twins in any of the temperament ratings. Chorion type was not related to cotwin similarity on any of the temperament ratings. It was concluded that differences in prenatal environment reflected in placentation type did not affect early temperament for MZ twins.     

Genetic and Environmental Influences on Verbal Fluency in Middle Age: A Longitudinal Twin Study

Mounting evidence suggests that measures of phonemic fluency and semantic fluency are differentially associated with other cognitive and health phenotypes, but few studies have examined their shared and unique variance, especially using genetically-informative designs. In this study, 1464 middle-aged twins completed six fluency subtests at up to two time-points (mean age 56 and 62 years). Confirmatory factor analyses supported a two-factor solution: a General Fluency latent factor explained variation in all six subtests and a Semantic-Specific factor accounted for additional variance in semantic subtests. Both factors were explained primarily by genetic influences at both waves (a²?=?0.57–0.76). There was considerable stability of individual differences over 6 years (r?=?.90 for General Fluency, r?=?.81 for Semantic-Specific), especially for genetic influences (r_g?=?.94 and 1.0, respectively). These results suggest that semantic fluency can be viewed as a combination of general and semantic-specific variance, but phonemic fluency is captured entirely by the general factor.     

Shared Environmental Influences on Personality: A Combined Twin and Adoption Approach

In the past, shared environmental influences on personality traits have been found to be negligible in behavior genetic studies (e.g., Bouchard and McGue, J Neurobiol 54:4–45, 2003). However, most studies have been based on biometrical modeling of twins only. Failure to meet key assumptions of the classical twin design could lead to biased estimates of shared environmental effects. Alternative approaches to the etiology of personality are needed. In the current study we estimated the impact of shared environmental factors on adolescent personality by simultaneously modeling both twin and adoption data. We found evidence for significant shared environmental influences on Multidimensional Personality Questionnaire Absorption (15 % variance explained), Alienation (10 %), Harm Avoidance (14 %), and Traditionalism (26 %) scales. Additionally, we found that in most cases biometrical models constraining parameter estimates to be equal across study type (twins vs. adoptees) fit no worse than models allowing these parameters to vary; this suggests that results converge across study design despite the potential (sometimes opposite) biases of twin and adoption studies. Thus, we can be more confident that our findings represent the true contribution of shared environmental variance to personality development.     

Genetic and Environmental Influences on the Stability of Withdrawn Behavior in Children: A Longitudinal,Multi-informant Twin Study

We examined the contribution of genetic and environmental influences on the stability of withdrawn behavior (WB) in childhood using a longitudinal multiple rater twin design. Maternal and paternal ratings on the withdrawn subscale of the Child Behavior Checklist (CBCL) were obtained from 14,889 families when the twins were 3, 7, 10 and 12 years old. A longitudinal psychometric model was fitted to the data and the fit of transmission and common factor models were evaluated for each variance component. WB showed considerable stability throughout childhood, with correlation coefficients ranging from about .30 for the 9-year time interval to .65 for shorter time intervals. Individual differences in WB as observed by the mother and the father were found to be largely influenced by genetic effects at all four time points, in both boys (50–66%) and girls (38–64%). Shared environmental influences explained a small to modest proportion (0–24%) of the variance at all ages and were slightly more pronounced in girls. Non-shared environmental influences were of moderate importance to the variance and slightly increased with age, from 22–28% at age 3 to 35–41% at age 12 years. The stability of WB was largely explained by genetic effects, accounting for 74% of stability in boys and 65% in girls. Shared environmental effects explained 7% (boys) and 17% (girls) of the behavioral stability. Most shared environmental effects were common to both raters, suggesting little influence of rater bias in the assessment of WB. The shared environmental effects common to both raters were best described by a common factor model, indicating that these effects are stable and persistent throughout childhood. Non-shared environmental effects accounted for the remaining covariance over time. Edited by Hermine Maes.     

Genetic and Environmental Influences on the Wisconsin Card Sorting Test Performance in Healthy Adolescents: A Twin/Sibling Study

This study aimed to estimate the relative contributions from genetic and environmental factors to the Wisconsin Card Sorting Test (WCST) performance, a widely used measurement for assessing frontal lobe function. Participants included 350 pairs of twins (257 MZ and 93 DZ) and 47 same-sex sib-pairs, aged 12–16 years, systematically recruited from junior high schools in Taipei. A computerized version of the WCST was administered for each participant and its nine indexes were used for subsequent analysis. Univariate analysis in structural equation modeling was performed for each WCST index using Mx program. The ACE model for each WCST index indicated no significant genetic influence, whereas the shared environmental influence ranged from 30 to 38% for four indexes (Perseverative Errors, Perseverative Responses, Categories Achieved, and Conceptual Level Responses). We concluded that WCST performance might be an indicator more for environmental insult than for genetic influences on frontal lobe function.     

Genetic Influences on Human Conditionability: A Twin Study of the Conditioned Eyeblink Response

Acquisition of the classically conditioned eyeblink response is generally regarded as one of the most basic forms of associative learning. A great deal is known about how the brain encodes this simple form of learning, so that performance of this task may be an indirect indicator of brain functioning. Individual differences in response acquisition have been revealed, but largely ignored, in the research literature. We tested the temporal stability and familial origins of these individual differences using a classic twin study design. Results reveal substantial individual differences in acquisition of the conditioned eyeblink response. These differences are stable across brief retest, and differences in response acquisition exhibit familial aggregation, apparently due, in part, to genetic resemblance.     

Genetic and Environmental Influences on Schizotypy among Adolescents in Taiwan: A Multivariate Twin/sibling Analysis

This study aimed to examine the relative contribution of genes and environment to psychometrically measured schizotypy and the causes for the covariation between different dimensions of schizotypy in a total of 330 pairs of twins and 36 same-sex sib-pairs aged 12–16 and systematically recruited from junior high schools in Taipei. Twins’ zygosity was determined by a combination of DNA typing and physical similarity. Schizotypy was measured using the Perceptual Aberration Scale (PAS) as well as the Schizotypal Personality Questionnaire (SPQ) and its three factors (Cognitive-perceptual Dysfunction, Disorganization, and Interpersonal Dysfunction). Univariate analyses of structural equation modeling using Mx program showed that scores on these schizotypal measures were substantially heritable (h ² ranging from 41 to 49%), with some genetic effects being non-additive. Multivariate analyses revealed common genetic factors linking between various traits of schizotypy, with bivariate heritability ranging from 50 to 65%. The proportion of the genetic contributions not shared with the other measures of schizotypy ranged from 24% for the Disorganization to 49% for the PAS scores. We concluded that there exist both common and specific genetic factors between the various dimensions of schizotypy, and at least half of their correlations were genetic in nature. Edited by Peter McGuffin     

Genetic and Environmental Influences on Child Reports of Manifest Anxiety and Symptoms of Separation Anxiety and Overanxious Disorders: A Community-Based Twin Study

Genetic and environmental influences in the determination of individual differences in self-reported symptoms of separation anxiety (SAD), overanxious disorder (OAD), and manifest anxiety (MANX) were evaluated in children and adolescents for three age groups (8–10, 11–13, and 14–16). Symptom counts for SAD and OAD were assessed for 1412 twin pairs using the children's version of the Child and Adolescent Psychiatric Assessment, and MANX scores were based on child report from the Revised Children's Manifest Anxiety Scales. Despite significant age and gender differences in thresholds of liability for child reports of symptoms of SAD and OAD, additive genetic and environmental effects could be set equal across age and gender for these variables. For MANX, however, the best-fitting model was a common effects sex-limitation model with estimates of heritabiliry varying dependent upon age and gender. Parameter estimates from the ACE models of OAD and SAD showed that additive genetic variation was a necessary component in the explanation of individual differences in child-reported symptoms of OAD (h ² = .37) across gender, but does not appear to be a major contributor to the explanation of individual differences in symptoms of SAD reported by children. Shared environmental effects (c ² = .40) were found to play a moderate role for SAD but could be dropped from the model for OAD and from all of the age groups for MANX, although the parameter approached significance among 11 yr to 13-year-old males.     

The Impact of Variation in Twin Relatedness on Estimates of Heritability and Environmental Influences

By taking advantage of the natural variation in genetic relatedness among identical (monozygotic: MZ) and fraternal (dizygotic: DZ) twins, twin studies are able to estimate genetic and environmental contributions to complex human behaviors. Recently concerns have been raised about the accuracy of twin studies in light of findings of genetic and epigenetic changes in twins. One of the concerns raised is that MZ twins are not 100% genetically and epigenetically similar because they show variations in their genomes and epigenomes leading to inaccurate estimates of heritability. This article presents findings from a simulation study that examined the degree of bias in estimates of heritability and environmentality when the genetic and epigenetic similarity of MZ twins differs from 1.00 and when the genetic and epigenetic similarity of DZ twins differs from 0.50. The findings suggest that in the standard biometric model when MZ or DZ twin similarity differs from 1.00 or 0.50, respectively, the variance that should be attributed to genetic influences is instead attributed to nonshared environmental influences, thus deflating the estimates of genetic influences and inflating the estimates of nonshared environmental influences. Although estimates of genetic and nonshared environmental influences from the standard biometric model were found to deviate from “true” values, the bias was usually smaller than 10% points indicating that the interpretations of findings from previous twin studies are mostly correct.     

Genetic and Environmental Influences on the Junior Temperament and Character Inventory in a Preadolescent Twin Sample

This study evaluated the genetic and environmental structure of personality variables from the Junior Temperament and Character Inventory (JTCI), in 605 pairs of 9- and 10-year old twins. There is a paucity of information on the biometric structure of temperament and character traits in preadolescent children. Latent factor models were fit to the subscales/items of each trait as a method of estimating genetic and environmental effects on true score variance, especially since internal consistency and reliability were moderate or low for some scales (particularly Reward Dependence and Persistence). Shared environmental influences on Cooperativeness were substantial. Significant heritability estimates were obtained for Self-directedness and Harm Avoidance, but not Novelty Seeking, Reward Dependence or Persistence. With the exception of Harm Avoidance, each of the scales failed to show measurement invariance with respect to sex, suggesting these scales may differ in meaning for boys and girls at this age. Edited by Danielle Posthuma.     

Environmental Effects Exceed Genetic Effects on Perceived Intensity and Pleasantness of Several Odors: A Three-Population Twin Study

Human genes encoding odorant receptors have been identified, but the contribution of genetic effects to total variation in specific odor perceptions is largely unknown. We estimated the relative contributions of genetic and environmental effects to variation in the perceived intensity and pleasantness of cinnamon, chocolate, turpentine, and isovaleric acid (sweaty) odors by quantitative genetic modeling of odor rating data from 856 twin individuals (including 83 complete monozygotic and 275 dizygotic twin pairs) aged 10–60 years (44% males and 56% females) from Australia, Denmark, and Finland. Results from fitting univariate models including components for additive genetic (A), shared environmental (C), and non-shared environmental (E) effects to the data implied that non-shared environmental effects account for the most variation in ratings of individual odors while genetic effects play only a minor role. Multivariate independent pathway model revealed a modest but significant common additive genetic component for intensity ratings, explaining 18% of the total variation. The results promote the importance of inter-individual variation in odor exposures and olfactory plasticity to odor perception. Edited by Deborah Finkel.     

Workaholism and Sleep Quality Among Japanese Employees: A Prospective Cohort Study

Background

This study focused on workaholism as a personal attitude toward work and examined its effects on sleep quality among Japanese employees from various occupations.

Purpose

The present study aimed to demonstrate the prospective association of workaholism (i.e., working excessively hard in a compulsive fashion) with sleep quality among Japanese employees.

Methods

A Web-based prospective survey was conducted in October 2010 and May 2011 among registered monitors of a survey company. The questionnaire included workaholism, sleep quality, job characteristics, and demographics. Overall, 13,564 monitors were randomly invited to complete the first wave of the survey. The first 2,520 respondents were included in this study. The respondents who completed the first wave were invited to complete the second wave of the survey; 2,061 answered. A total of 364 respondents who changed their working conditions during the follow-up period were excluded. In addition, due to missing values, data from 14 respondents were excluded. Thus, the responses from 1,683 respondents were included in the analysis (859 males and 824 females). An analysis of covariance (ANCOVA) was conducted to compare adjusted sleep quality at follow-up among workaholism groups (low, middle, and high). To conduct the ANCOVA, we adjusted for demographics, sleep quality at baseline, and job characteristics.

Results

The high-workaholic group had significantly longer sleep latency at follow-up compared with the low- and middle-workaholic groups after adjusting for demographics, sleep latency at baseline, and job characteristics. In addition, the high-workaholic group demonstrated significantly higher levels of daytime dysfunction compared with the low-workaholic group. However, no significant differences were found among workaholic groups in terms of overall sleep quality, sleep duration, habitual sleep efficiency, sleep disturbance, and use of sleep medication.

Conclusion

Workaholism was associated with poor sleep quality at the 7-month follow-up in terms of sleep latency and daytime dysfunction.     

Genetic Influences on Change in BMI from Middle to Old Age: A 29-Year Follow-up Study of Twin Sisters

Weight gain through middle age is a common phenomenon that increases the risk for different types of metabolic diseases and functional limitations later in life. This study examined genetic and environmental influences on the evolution of body mass index (BMI) in women from middle to old age. BMI was evaluated in 102 monozygotic and 114 dizygotic pairs of twin sisters from the year 1975, when they were 42.6 ± 3.4 years-old, and thereafter in 1981, 1990, 2001 and 2004, in a total 29-year follow-up period. We examined genetic and environmental influences explaining BMI overall level and its rate of change using a latent growth modeling approach. The results showed that mean (±SD) BMI increased from 24.1 ± 3.1 to 28.2 ± 5.1 kg/m² during the 29-year period. The heritability of BMI showed a consistent increment across occasions, from 54% in 1975, to 72% in 2004. Genetic influences accounted for both overall BMI level (60%) and BMI rate of change (64%). Genetic and environmental correlations between BMI level and rate of change were: r_g = 0.40 and r_e = −0.24, respectively. We conclude that in relatively healthy women, genes affecting level of BMI may differ from those affecting change in BMI with age. These results provide a basis for identifying genetic variants for change in BMI. Edited by Danielle Posthuma.     

Sex Differences in Subjective and Actigraphic Sleep Measures: A Population-Based Study of Elderly Persons

Study Objectives:

To investigate and explain sex differences in subjective and actigraphic sleep parameters in community-dwelling elderly persons.

Design:

Cross-sectional study.

Setting:

The study was embedded in the Rotterdam Study, a population-based study.

Participants:

Nine hundred fifty-six participants aged 59 to 97 years.

Interventions:

N/A.

Measurements and Results:

Participants wore an actigraph and kept a sleep diary for an average of 6 consecutive nights. Subjective sleep quality was assessed with the Pittsburgh Sleep Quality Index. Unadjusted sex differences in sleep parameters were assessed with t tests. Women reported shorter total sleep time, a less favorable sleep-onset latency, lower sleep efficiency, and worse global sleep quality, as compared with men. When assessed with actigraphy, however, women were found to have longer and less-fragmented sleep than men. Sex differences in diary-reported sleep duration and other subjective sleep parameters were attenuated by adjustment for marital status, the use of sleep medication, and other covariates, but all sex differences remained significant in a multivariate-adjusted model. Sex differences in actigraphic sleep parameters were barely attenuated by multivariate adjustment, although the shorter actigraphically measured sleep duration in men was partly explained by their higher alcohol consumption. Some covariates (eg, sleep medication) had a different relationship with diary-reported or actigraphic total sleep time in men and women.

Conclusions:

If assessed by diary or interview, elderly women consistently reported shorter and poorer sleep than elderly men. In contrast, actigraphic sleep measures showed poorer sleep in men. These discrepancies are partly explained by determinants of sleep duration, such as sleep medication use and alcohol consumption.

Citation:

van den Berg JF; Miedema HME; Tulen JHM; Hofman A; Knuistingh Neven A; Tiemeier H. Sex differences in subjective and actigraphic sleep measures: a population-based study of elderly persons. SLEEP 2009;32(10):1367-1375.     

遗传与家庭环境对儿童个性影响的双生子研究

目的:探索遗传和家庭环境对儿童个性的影响.方法:采用横断面设计,以学籍登记为线索募集6-16岁的双生子56对,采集颊黏膜标本提取DNA,进行卵型鉴定.用儿童版艾森克个性测验(EPQ)作为儿童个性测缝工具,用一般健康问卷(GHQ-12)、父母的养育方式和维度问卷(PSDQ)、家庭活动计划一般功能量表(FAD-GFS)、应激生活事件问卷等向其父母收集家庭环境信息.结果:(1)50对双生子成功提取DNA,卵型鉴定结果显示:同卵双生子24对,异卵双生予26对;(2)同卵双生(MZ)组的EPQ内外向、稳定性、掩饰度三个因子分每对双生子个体之间均正相关(r=0.75,0.73,0.56;P＜0.05),而异卵双生(DZ)组仅有稳定性因子分在每对双生子个体之间有相关性,且相关系数小于MZ组(r=0.47,P＜0.05;MZ组:Z值呵信区间为(0.94±0.44);DZ组:Z=0.51);(3)110位双生子个体的EPQ内外倾向性(E分)与FAD-GFS分值呈负相关(r=-0.20,P＜0.05),精神质(P分)与母亲GHQ-12分值呈正相关(r=0.22,P＜0.05),稳定性(N分)与父亲的专制养育分呈正相关(r=0.24,P＜0.05).结论:本研究提示儿童个性主要受遗传因素决定,但家庭环境中母亲的心理健康状况、父亲的养育方式、健康的家庭功能等对儿童个性的形成也可能有不可忽视的作用.