Genetic and Environmental Influences on the Stability of Withdrawn Behavior in Children: A Longitudinal,Multi-informant Twin Study

We examined the contribution of genetic and environmental influences on the stability of withdrawn behavior (WB) in childhood using a longitudinal multiple rater twin design. Maternal and paternal ratings on the withdrawn subscale of the Child Behavior Checklist (CBCL) were obtained from 14,889 families when the twins were 3, 7, 10 and 12 years old.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.     

Are there meaningful etiological differences within antisocial behavior? Results of a meta-analysis

There is mounting evidence of etiologically driven distinctions between aggressive (AGG) and non-aggressive rule-breaking (RB) forms of antisocial behavior. To date, however, these differences remain somewhat speculative. The current meta-analysis of twin and adoption studies sought to clarify these distinctions by comparing meta-analytic estimates of genetic, shared environmental, and non-shared environmental influences across AGG and RB to more clearly ascertain whether they evidence differential patterns of genetic and environmental influence. A comprehensive literature search resulted in the collection of 103 twin and adoption studies, of which 15 RB samples and 19 AGG samples were ultimately included in the analyses. Results reveal clear evidence of etiological distinctions between AGG and RB. Namely, AGG appears to be a highly heritable condition (genetic factors account for 65% of the variance), with little role for the shared or common environment, particularly after childhood. By contrast, while genetic influences also contribute to RB (48% of the variance), there is an important role for shared environmental effects as well (18% of the variance). Such findings are indicative of meaningful etiologic distinctions between aggressive and rule-breaking forms of antisocial behavior, and underscore the advantage of differentiating between these behavioral subtypes when studying the causal processes that underlie antisocial behavior.     

Individual Differences in Aggression: Genetic Analyses by Age, Gender, and Informant in 3-, 7-, and 10-Year-Old Dutch Twins

Aggression in humans is associated with substantial morbidity and mortality. In this study we report on the aggressive behavior syndrome (AGG) in young children as defined by the Child Behavior Checklist (CBCL) and the Teacher Report Form (TRF). We assessed aggression in a large sample of Dutch twins at ages 3, 7, and 10 years. The purpose of this study was three-fold. First, we determined the number of children who are clinically deviant on the AGG scale. Second, we assessed the genetic and environmental contributions to AGG for the maternal, paternal, and teacher ratings at each age, for boys and girls. Third, we explored issues of rater bias by analyzing parental and teacher data simultaneously. CBCL data were available from mothers on 6436 three-year-old, 5451 seven-year-old, and 2972 ten-year-old twin pairs and CBCL data from fathers on 4207 three-year-old, 4269 seven-year-old, and 2295 ten-year-old twin pairs. Teacher report data from the TRF were collected for 1036 seven-year-old and 903 ten-year-old twin pairs from the Netherlands Twin Registry. Structural equation modeling was employed to obtain genetic and environmental estimates at each age. Analyses were conducted separately by age and informant, as well as simultaneously, for all informants. Differences in raw scores across gender were found, with boys being rated as more aggressive than girls by all informants. Mothers reported more symptoms than fathers, who reported more symptoms than teachers. Evidence for moderate to high genetic influence (51%–72%) was seen for AGG by all three informants at all ages with only small sex differences in heritability estimates. Best fitting models for AGG by parent reports also included a small contribution of common environment. The largest sex differences in heritabilities were seen at age 10. Contributions of common (13%–27%) and unique (16%–31%) environment were small to moderate. There was some evidence of genetic dominance by teacher report for 10-year-old girls.     

Sex differences in the genetic and environmental influences on the development of antisocial behavior

The present study uses a population-based sample of 6.806 adult twins from same-sex and opposite-sex twin pairs to examine sex differences in the underlying genetic and environmental architecture of the development of antisocial behavior (AB). Retrospective reports of AB during three different developmental periods were obtained: prior to age 15 years (childhood), age 15-17 years (adolescent), and age 18 years and older (adult). Structural equation modeling analyses revealed that there was no evidence for sex-specific genetic or sex-specific shared family environmental influences on the development of AB; that is, the types of genetic and environmental influence were similar for males and females. For both sexes, a model that allowed for genetic influences on adolescent and adult AB that were not shared with childhood AB fit better than a model with a single genetic factor. In contrast, shared environmental influences on adolescent and adult AB overlapped entirely with shared environmental influences on childhood AB. Genetic factors played a larger role in variation in childhood AB among females, whereas shared environmental factors played a larger role among males. However, heritability of AB increased from childhood to adolescence and adulthood for both sexes, and the magnitude of genetic and environmental influences on adolescent and adult AB was approximately equal across sex. We speculate that sex differences in timing of puberty may account for the earlier presence of genetic effects among females.     

Sex steroids at birth: genetic and environmental variation and covariation.

Three sex-steroids (estradiol, progesterone, & testosterone) were assayed from the umbilical cord blood of 58 same-sex twin pairs in an investigation of the effects of sex, as well as genetic and environmental factors, on neonatal hormone levels. Although significant mean differences were found between boys and girls for both testosterone and progesterone, sex appeared to account for very little of the total variation for any of the hormones. Results showed that genetic influences significantly affected within-sex variation in both estradiol and progesterone levels, while variations in the intrauterine (shared twin) environment accounted primarily for differences in levels of testosterone. Moderate correlations were also found among the three hormones. Multivariate biometrical analyses revealed these relationships to be explained by an underlying general factor of nonshared environmental influences affecting all three hormones. Genetic factors appeared to be specific to each hormone rather than correlated across hormones. These results suggest not only that genes are operating at this early age, but also that maternal and other prenatal factors (e.g., placental effects, uterine position) have a significant role in variations of sex-steroids and possibly on later behaviors.     

Using Shared and Unique Parental Views to Study the Etiology of 7-Year-Old Twins' Internalizing and Externalizing Problems

In a sample of 1,940 Dutch 7-year-old twin pairs we studied the etiology of individual differences in Internalizing and Externalizing behavioral problems. For the majority of twins in the sample, both maternal and paternal ratings of behavioral problems were obtained from the Child Behavior Checklist. This made it possible to take into account processes underlying agreement and disagreement between maternal and paternal ratings. For both problem behaviors, a Psychometric model fitted the data better than a Rater Bias model, implying that parents, in addition to the behaviors they similarly observed, also assessed unique aspects of their children's behaviors. Relatively large genetic influences were found for Externalizing problems, explaining over 50% of the variance in both boys and girls. For internalizing problems, the heritability was over 30% in both sexes. Shared environmental factors were nearly as important as genetic influences in explaining the variation in behavioral problems. For both Externalizing and Internalizing problems, around 30% of the variance was accounted for by the shared environmental factors.     

A longitudinal behavioral genetic analysis of the etiology of aggressive and nonaggressive antisocial behavior

Developmental studies of antisocial behavior (ASB) have found two subgroups of behaviors, roughly described as aggressive and nonaggressive ASB. Theoretical accounts predict that aggressive ASB, which shows greater stability, should have high heritability. In contrast, nonaggressive ASB is very common in adolescence, shows less continuity, and should be influenced both by genes and shared environment. This study explored the genetic and environmental influences on aggressive and nonaggressive ASB in over 1,000 twin pairs aged 8-9 years and again at 13-14 years. Threshold models were fit to the data to incorporate the skew. In childhood, aggressive ASB was highly heritable and showed little influence of shared environment, whereas nonaggressive ASB was significantly influenced both by genes and shared environment. In adolescence, both variables were influenced both by genes and shared envirnmment. The continuity in aggressive antisocial behavior symptoms from childhood to adolescence was largely mediated by genetic influences, whereas continuity in nonaggressive antisocial behavior was mediated both by the shared environment and genetic influences. These data are in agreement with the hypothesis that aggressive ASB is a stable heritable trait as compared to nonaggressive behavior, which is more strongly influenced by the environment and shows less genetic stability over time.     

Genetic and environmental influences on growth from late childhood to adulthood: a longitudinal study of two Finnish twin cohorts

Objectives: Human growth is a complex process that remains insufficiently understood. We aimed to analyze genetic and environmental influences on growth from late childhood to early adulthood. Methods: Two cohorts of monozygotic and dizygotic (same sex and opposite sex) Finnish twin pairs were studied longitudinally using self‐reported height at 11–12, 14, and 17 years and adult age (FinnTwin12) and at 16, 17, and 18years and adult age (FinnTwin16). Univariate and multivariate variance component models for twin data were used. Results: From childhood to adulthood, genetic differences explained 72–81% of the variation of height in boys and 65–86% in girls. Environmental factors common to co‐twins explained 5–23% of the variation of height, with the residual variation explained by environmental factors unique to each twin individual. Common environmental factors affecting height were highly correlated between the analyzed ages (0.72–0.99 and 0.91–1.00 for boys and girls, respectively). Genetic (0.58–0.99 and 0.70–0.99, respectively) and unique environmental factors (0.32–0.78 and 0.54–0.82, respectively) affecting height at different ages were more weakly, but still substantially, correlated. Conclusions: The genetic contribution to height is strong during adolescence. The high genetic correlations detected across the ages encourage further efforts to identify genes affecting growth. Common and unique environmental factors affecting height during adolescence are also important, and further studies are necessary to identify their nature and test whether they interact with genetic factors. Am. J. Hum. Biol., 2011. © 2011Wiley‐Liss, Inc.     

Genetic and Environmental Influences on Separation Anxiety Disorder Symptoms and Their Moderation by Age and Sex

We estimated genetic and environmental influences on mother-rated DSM-III-R separation anxiety disorder (SAD) symptoms in 2043 3 to 18-year-old male and female twin pairs and their siblings (348 pairs) recruited from the Australian NH&MRC Twin Registry. Using DeFries and Fulker's (1985) multiple regression analysis, we found that genetic and shared environmental influences both contributed appreciably to variation in SAD symptoms (h ² = .47, SE = .07; c ² = .21, SE = .05) and were significantly moderated by both sex and age. Genetic influences were greater for girls than boys (h ² = .50 and .14, respectively), whereas shared environmental influences were greater for boys than girls (c ² = .51 and .21, respectively). Genetic influences increased with age, whereas shared environmental influences decreased with age. Shared environmental influences were greater in magnitude for twins than for nontwin siblings (c ² = .28 versus .13, respectively). Implications of these findings for theories of the cause of separation anxiety are discussed.     

Genetic and environmental factors affecting self-esteem from age 14 to 17: a longitudinal study of Finnish twins

BACKGROUND: We analysed genetic and environmental influences on self-esteem and its stability in adolescence. METHOD: Finnish twins born in 1983-1987 were assessed by questionnaire at ages 14 (n = 4132 twin individuals) and 17 years (n = 3841 twin individuals). Self-esteem was measured using the Rosenberg global self-esteem scale and analyzed using quantitative genetic methods for twin data in the Mx statistical package. RESULTS: The heritability of self-esteem was 0.62 [95% confidence interval (CI) 0.56-0.68] in 14-year-old boys and 0.40 (95% CI 0.26-0.54) in 14-year-old girls, while the corresponding estimates at age 17 were 0.48 (95% CI 0.39-0.56) and 0.29 (95% CI 0.11-0.45). Rosenberg self-esteem scores at ages 14 and 17 were modestly correlated (r = 0.44 in boys, r = 0.46 in girls). In boys, the correlation was mainly (82%) due to genetic factors, with residual co-variation due to unique environment. In girls, genetic (31%) and common environmental (61%) factors largely explained the correlation. CONCLUSIONS: In adolescence, self-esteem seems to be differently regulated in boys versus girls. A key challenge for future research is to identify environmental influences contributing to self-esteem during adolescence and determine how these factors interact with genetic influences.     

Contributions of Genes and Environments to Stability and Change in Externalizing and Internalizing Problems During Elementary and Middle School

We examined longitudinally collected behavioral reports by teachers on a unique twin sample at the ages of 7, 8, 9, 10, 11, and 12 years. As twin and adoption studies implicate the role of genetic influence on behavioral problems found to be stable in epidemiological samples, the current study employs a developmental behavior genetic model to examine the extent to which genetic and environmental contributions to problem behaviors are stable and/or change during development. In this sample of 410 monozygotic (MZ) and 354 dizygotic (DZ) twins, MZ twins were rated as more similar than DZ twins on average. In general, boys were more frequently rated as displaying externalizing behaviors than were girls across each of the six observations, while girls’ internalizing problems were found not to be significantly different from boys’. For both sexes, stability in externalizing problem behaviors was due to a single common genetic factor whose effects acted pleiotropically at each age in the presence of unique environmental influences that were transmitted from age-to-age. Change was largely due to uncorrelated age-specific non-shared environmental and additive genetic effects. Contributions to stability for internalizing problems were due to age-to-age transmission of earlier expressed genetic effects. Change for girls and boys internalizing problems were largely due to environmental experiences unique to siblings along with uncorrelated age-specific genetic effects. These results further inform the notion that individual environments are important factors in the etiology of problem behaviors, but suggest that heritable contributions to phenotypic stability are largely the same across middle childhood and early adolescence. Clinical implications of these findings are discussed.     

Genetics of pre-pubertal growth: A longitudinal study of Japanese twins

Background: Genetic factors explain a major part of the variation of adult stature, but little is still known on the genetics of growth, especially in non-Caucasian populations.

Aim: To analyse the quantitative genetics of pre-pubertal growth in Japanese children.

Subjects and methods: Data from birth until 11 years of age were collected on 349 complete twin pairs based on previously recorded height measures. The data were analysed using two different multivariate models by the Mx statistical package.

Results: No major sex differences were found and thus boys and girls were analysed together. Since 1 year of age, genetic factors explained from 42–71% and environmental factors shared by co-twins from 14–33% of the variation of height. Genetic continuity of height was high and 75% of the genetic variance was shared since 1 year of age. Environmental factors affecting height showed weaker correlations between early and late childhood than genetic factors.

Conclusion: Growth from early to late childhood is largely regulated by the same set of genes. However, also environmental factors shared by co-twins are important for growth. Identifying specific environmental factors affecting growth has potentially important public health implications, even in an affluent society such as Japan.     

Parent- and Observer-Rated Positive Affect in Early Childhood: Genetic Overlap and Environmental Specificity

The sources of individual differences in both observed and parent-rated positive affect (PA) were examined in a sample of 304 3-year-old twin pairs (140 MZ, 164 DZ). Based on model-fitting analyses, individual differences in observed PA were attributed to moderate genetic and high nonshared environmental factors, but not shared environmental factors. In contrast, shared environmental effects accounted for over half of the variance in parent-rated PA and genetic and nonshared environmental effects were more modest. The genetic correlation across the two measures was high, indicating substantial overlap between genetic factors influencing the two. It was these overlapping genetic effects that fully explained the phenotypic correlation between both measures. There was no significant covariance between the environmental influences on parent rated and observed PA. Thus, the two measures of PA in early childhood have common genetic underpinnings, whereas environmental influences are measure-specific. Measurement implications are discussed.     

Genetic and Environmental Etiology of Disregard for Rules

Disregard for rules, a key component of oppositional defiant and conduct disorders, is stable during early childhood. This study investigates for the first time the relative importance of genetic and environmental factors underlying this early developmental stability. Maternal reports of child disregard for rules were obtained at four time points from 20 to 64 months of age in a population-based twin sample (N = 597 twin pairs, including 238 monozygotic and 359 dizygotic pairs). Structural equation modeling was conducted using both variance–covariance and latent growth curve approaches. Genetic factors accounted for most of the stability in disregard for rules throughout early childhood. In contrast, most environmental effects were age specific. Developmental stability in early symptoms of disregard for rules is best explained by the stable action of genetic factors, suggesting that preventive interventions should take an intergenerational approach, targeting at-risk families as early as possible.     

Co-occurrence of Aggressive Behavior and Rule-Breaking Behavior at Age 12: Multi-Rater Analyses

Aggressive Behavior (AGG) and Rule-Breaking Behavior (RB) are two of the eight CBCL syndromes. The phenotypic correlation between AGG and RB ranges from .48 to .76, and varies depending on the rater and the sex of the child. Prevalence of AGG and RB (i.e., T 67) is in the range of 6%–7% in both boys and girls. Fifty percent to 60% of the children who are deviant on AGG are also deviant on RB and vice versa. Why so many children show problem behavior in the clinical range for both syndromes is unclear. This co-occurrence could be due to genetic factors influencing both traits, to environmental factors influencing both traits, or to both. The purpose of this study is to use a genetically informative sample to estimate genetic and environmental influences on AGG and RB and to investigate the etiology of the co-occurrence of both behaviors. We do this using multiple informants to take into account underlying sources of parental agreement and disagreement in ratings of their offspring. To this end, mother and father ratings of AGG and RB were collected by using the Child Behavior Checklist in a large sample of 12-year-old twins. Parental agreement is represented by an interparent correlation in the range of .53–.76, depending on phenotype (AGG or RB) and sex of the child. Genetic influences account for 79% and 69% of the individual differences in RB and AGG behavior (defined as AGG and RB on which both parents do agree) in boys. In girls 56% and 72% of the variance in RB and AGG are accounted for by genetic factors. Shared environmental influences are significant for RB in girls only, explaining 23% of the total variance. Eighty percent of the covariance between AGG and RB, similarly assessed by both parents, can be explained by genetic influences. So, co-occurrence in AGG and RB is mainly caused by a common set of genes. Parental disagreement seems to be a combination of so-called rater bias and of parental specific views.     

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.     

Genetic and Environmental Correlations Between Body Mass Index and Waist Circumference in China: The Qingdao Adolescent Twin Study

We aimed to analyze how genetic and environmental factors account for variations in body mass index (BMI), waist circumference (WC) and their mutual correlation in Chinese children. We measured BMI and WC in 588 pairs of twins (53 % monozygotic twins) aged 8–17 years and applied structural equation modeling to the data. For the younger children (8–12 years of age), heritability estimates of BMI were 0.56 for boys and 0.69 for girls; for the older children (13–17 years of age), the corresponding figures were 0.64 and 0.71, respectively. We observed moderate heritability estimates in WC: the corresponding figures were 0.24 and 0.56 for the younger children, and 0.27 and 0.33 for the older children, respectively. The heterogeneity test for genetic variance of BMI and WC was statistically significant between the two age groups for both sexes (p < 0.001). The proportions of BMI and WC variations due to shared and non-shared environmental factors remained stable during childhood in both sexes. Bivariate genetic analyses showed that genetic correlations between BMI and WC were strong for the younger children (r_g = 0.75 for boys, r_g = 0.98 for girls) and the older children (r_g = 1.0 for both boys and girls). Both sexes showed moderate non-shared environmental correlations in the two age groups, whereas shared environmental correlations––except among male younger children––were not statistically significant. Genetic factors play an important role in variations in BMI and WC during childhood. Common genetic and non-shared environmental factors explained most of the association between BMI and WC for both boys and girls.     

Genetic and environmental determinants of the cardio-respiratory response to submaximal exercise--a six-year follow-up study of twins

The fat-free mass and the ventilatory and cardiac frequency responses to submaximal exercise have been assessed longitudinally over six years in a total of 65 identical and non-identical boy and girl twin pairs. Exercise ventilation at rates of work below the anaerobic threshold was independent of the genetic and environmental factors which were investigated. The anaerobic threshold increased with age. The fat-free mass and the exercise cardiac frequency were subject to both genetic and environmental control with the genetic component predominating initially. The subsequent environmental component was larger for non-identical than for identical twin pairs and for boys than for girls. It is concluded that in identical twin boys by the time they reach adolescence the performance during submaximal exercise has a material environmental component. There appears to be interaction between the genetic and environmental components.     

The genetic and environmental structure of fear and anxiety in juvenile twins

Fear and anxiety are conceptualized as responses to acute or potential threat, respectively. Adult twin studies found substantial interplay between genetic and environmental factors influencing fear disorders (phobias) and anxiety disorders. Research in children, however, has largely examined these factors independently. Thus, there exists a substantial knowledge gap regarding the underlying etiologic structure of these closely‐related constructs during development. Symptom counts for five fear (criticism, the unknown, death, animal, medical) and four anxiety (generalized, panic, separation, social) dimensions were obtained for 373 twin pairs ages 9–14. Multivariate twin modeling was performed to elucidate the genetic and environmental influences distributed amongst these dimensions. The best fitting model contained one genetic, two familial environmental, and two unique environmental factors shared between fear and anxiety symptoms plus dimension‐specific genetic and unique environmental factors. Although several environmental factors were shared between fear and anxiety dimensions, one latent factor accounted for genetic influences across both domains. While adult studies find somewhat distinct etiological differences between anxiety and phobic disorders, the current results suggest that their relative genetic and environmental influences are not as clearly demarcated in children. These etiological distinctions are more nuanced, likely contributing to the highly diffuse symptom patterns seen during development.     

Genetic and Environmental Vulnerabilities Underlying Adolescent Substance Use and Problem Use: General or Specific?

Are genetic and environmental risks for adolescent substance use specific to individual substances or general across substance classes? We examined this question in 645 monozygotic twin pairs, 702 dizygotic twin pairs, 429 biological sibling pairs, and 96 adoptive (biologically unrelated) sibling pairs ascertained from community-based samples, and ranging in age from 12 to 18 years. Substance use patterns and symptoms were assessed using structured psychiatric interviews. Biometrical model fitting was carried out using age- and sex-specific thresholds for (a) repeated use and (b) problem use, defined as one or more DSM-IV symptoms of abuse or dependence. We hypothesized that problem use would be more heritable than use in adolescence, and that both genetic and environmental risks underlying tobacco, alcohol, and marijuana use and problem use would be significantly correlated. Results of univariate analyses suggested significant heritable factors for use and problem use for all substances with the exception of alcohol use. Shared environmental factors were important in all cases and special twin environmental factors were significant for tobacco use, tobacco problem use, and alcohol use. Multivariate analyses yielded significant genetic correlations between each of the substances (for both levels studied), and significant shared environmental correlations among use variables only. Our results suggest that tobacco, alcohol, and marijuana problem use are mediated by common genetic influences, but shared environmental influences may be more substance-specific for problem use.