Sex differences in the genetic and environmental influences on childhood conduct disorder and adult antisocial behavior

Sex differences in the genetic and environmental influences on childhood conduct disorder and adult antisocial behavior were examined in a large community sample of 6,383 adult male, female, and opposite-sex twins. Retrospective reports of childhood conduct disorder (prior to 18 years of age) were obtained when participants were approximately 30 years old, and lifetime reports of adult antisocial behavior (antisocial behavior after 17 years of age) were obtained 8 years later. Results revealed that either the genetic or the shared environmental factors influencing childhood conduct disorder differed for males and females (i.e., a qualitative sex difference), but by adulthood, these sex-specific influences on antisocial behavior were no longer apparent. Further, genetic and environmental influences accounted for proportionally the same amount of variance in antisocial behavior for males and females in childhood and adulthood (i.e., there were no quantitative sex differences). Additionally, the stability of antisocial behavior from childhood to adulthood was slightly greater for males than females. Though familial factors accounted for more of the stability of antisocial behavior for males than females, genetic factors accounted for the majority of the covariation between childhood conduct disorder and adult antisocial behavior for both sexes. The genetic influences on adult antisocial behavior overlapped completely with the genetic influences on childhood conduct disorder for both males and females. Implications for future twin and molecular genetic studies are discussed.     

Etiological Distinctions between Aggressive and Non-aggressive Antisocial Behavior: Results from a Nuclear Twin Family Model

A recent meta-analysis of 103 studies Burt (Clinical Psychology Review, 29:163-178, 2009a) highlighted the presence of etiological distinctions between aggressive (AGG) and non-aggressive rule-breaking (RB) dimensions of antisocial behavior, such that AGG was more heritable than was RB, whereas RB was more influenced by the shared environment. Unfortunately, behavioral genetic research on antisocial behavior to date (and thus, the research upon which the meta-analysis was based) has relied almost exclusively on the classical twin model. This reliance is problematic, as the strict assumptions that undergird this model (e.g., shared environmental and dominant genetic influences are not present simultaneously; there is no assortative mating) can have significant consequences on heritability estimates when they are violated. The nuclear twin family model, by contrast, allows researchers to relax and statistically evaluate many of the assumptions of the classical twin design by incorporating parental self-report data along with the more standard twin data. The goal of the current study was thus to evaluate whether prior findings of etiological distinctions between AGG and RB persisted when using the nuclear twin family model. We examined a sample of 312 child twin families from the Michigan State University Twin Registry. Results strongly supported prior findings of etiological distinctions between AGG and RB, such that broad genetic influences were observed to be particularly important to AGG whereas shared environmental influences contributed only to RB. Nevertheless, the current findings also implied that additive genetic influences on antisocial behavior may be overestimated when using the classical twin design.     

The heritability of antisocial behavior: A meta-analysis of twin and adoption studies

In this paper, we describe a quantitative summary of 12 twin (n=3795 twin pairs and 3 adoption studies=338 adoptees) published since 1975 which provided 21 estimates of the heritability of antisocial behavior. Medium to large effect sizes were found for genetic influences across studies, with approximately 50% of the variance in measures of antisocial behavior attributable to genetic effects. Although effect sizes did not vary across different definitions of antisocial behavior (criminality, aggression, or antisocial personality), significantly larger estimates of genetic effect were found for severe manifestations of antisocial behavior. The importance of severity was further underscored by the significantly larger effects obtained in studies using clinic-referred samples compared to the effects obtained in studies using volunteer samples. Demographic characteristics of the samples did not influence effect sizes, although studies using more stringent methodology tended to find larger effects. These results must be interpreted in light of the small literature that was suitable for the meta-analysis due to numerous methodological limitations in existing studies.     

Genetic influences on the overlap between low IQ and antisocial behavior in young children

The well-documented relation between the phenotypes of low IQ and childhood antisocial behavior could be explained by either common genetic influences or environmental influences. These competing explanations were examined through use of the Environmental Risk Longitudinal Twin Study 1994-1995 cohort (Moffitt & the E-Risk Study Team, 2002) of 1,116 twin pairs and their families. Children's IQ was assessed via individual testing at age 5 years. Mothers and teachers reported on children's antisocial behavior at ages 5 and 7 years. Low IQ was related to antisocial behavior at age 5 years and predicted relatively higher antisocial behavior scores at age 7 years when antisocial behavior at age 5 years was controlled. This association was significantly stronger among boys than among girls. Genetic influences common to both phenotypes explained 100% of the low IQ-antisocial behavior relation in boys. Findings suggest that specific candidate genes and neurobiological processes should be tested in relation to both phenotypes.     

Genetic effects on male sexual coercion

The genetic and environmental influences on sexual coercion, and to what extent its associations with alcohol use and psychopathy depend on shared genetic and environmental effects, were explored in a Finnish population-based sample of 938 men, aged 33-43 years, using the classical twin study design. All three phenotypes were associated positively and affected by genes (sexual coercion 28%, alcohol use 60%, psychopathy 54%), with 46% of the correlation between sexual coercion and psychopathy, 89% of the correlation between alcohol use and psychopathy and 100% of the correlation between sexual coercion and alcohol use being explained by shared genetic effects. Further, the results showed that a proportion of the variance in sexual coercion was derived from a highly genetic source that was common with alcohol use and psychopathy. This latent factor was hypothesized to reflect a general tendency for antisocial behavior that is pervasive across different situations. Relevant theories on sexual coercion were discussed in light of the results.     

Religiousness, antisocial behavior, and altruism: genetic and environmental mediation

Although religiousness is considered a protective factor against antisocial behaviors and a positive influence on prosocial behaviors, it remains unclear whether these associations are primarily genetically or environmentally mediated. In order to investigate this question, religiousness, antisocial behavior, and altruistic behavior were assessed by self-report in a sample of adult male twins (165 MZ and 100 DZ full pairs, mean age of 33 years). Religiousness, both retrospective and current, was shown to be modestly negatively correlated with antisocial behavior and modestly positively correlated with altruistic behavior. Joint biometric analyses of religiousness and antisocial behavior or altruistic behavior were completed. The relationship between religiousness and antisocial behavior was due to both genetic and shared environmental effects. Altruistic behavior also shared most all of its genetic influence, but only half of its shared environmental influence, with religiousness.     

Influences of Biological and Adoptive Mothers’ Depression and Antisocial Behavior on Adoptees’ Early Behavior Trajectories

Research clearly demonstrates that parents pass risk for depression and antisocial behavior on to their children. However, most research confounds genetic and environmental mechanisms by studying genetically related individuals. Furthermore, most studies focus on either depression or antisocial behavior in parents or children, despite evidence of co-occurrence and shared etiology, and few consider the early origins of these problems in childhood. We estimated the influence of biological and adoptive mothers’ depression and antisocial behavior on growth in child externalizing and internalizing behaviors across early childhood using data from a prospective adoption study. Participants were 346 matched triads of physically healthy children (196 boys; 150 girls), biological mothers (BM), and adoptive mothers (AM). Latent growth curve models were estimated using AM reports of child internalizing and externalizing behaviors at ages 18, 27, and 54 months. Predictors of intercept (18 months) but not slope were identified. BM lifetime histories of major depressive disorder predicted child externalizing behaviors and BM antisocial behavior predicted child internalizing behavior. AM depressive symptoms and antisocial behavior were associated with both child outcomes. AM paths, but not BM paths were partially replicated using adopted fathers’ reports of child outcomes. BM obstetric complications, prenatal depressive symptoms, and postnatal adoptive family contact with BM did not account for BM paths. This adoption study distinguished risks conferred by biological mothers’ depression and antisocial behavior to children’s behaviors from those associated with adoptive mothers’ related symptoms. Future studies should examine gene-environment interplay to explain the emergence of serious problem trajectories in later childhood.     

Sex differences in genetic and environmental influences on DSM-III-R attention-deficit/hyperactivity disorder

Approximately 5% of children are affected by attention-deficit/hyperactivity disorder (ADHD), and more boys are affected than girls. This study examined the magnitude of genetic and environmental influences on ADHD and several questions regarding sex differences in its prevalence and liability. The participants were 2,391 twin and sibling pairs from Australia, ages 3-18. ADHD symptoms in the general population were highly heritable (h2 = .85-.90), as were deviant ADHD scores in the selected population. The magnitude of familial influences was similar for boys and girls, although there were shared environmental influences on ADHD in girls but not boys and dominance genetic influences on ADHD in boys but not girls. Specific genetic and environmental influences were highly similar for boys and girls. Evidence supported the polygenic multiple threshold model rather than the constitutional variability model of sex differences in ADHD.     

Maternal expressed emotion predicts children's antisocial behavior problems: using monozygotic-twin differences to identify environmental effects on behavioral development

If maternal expressed emotion is an environmental risk factor for children's antisocial behavior problems, it should account for behavioral differences between siblings growing up in the same family even after genetic influences on children's behavior problems are taken into account. This hypothesis was tested in the Environmental Risk Longitudinal Twin Study with a nationally representative 1994-1995 birth cohort of twins. The authors interviewed the mothers of 565 five-year-old monozygotic (MZ) twin pairs and established which twin in each family received more negative emotional expression and which twin received more warmth. Within MZ pairs, the twin receiving more maternal negativity and less warmth had more antisocial behavior problems. Qualitative interviews were used to generate hypotheses about why mothers treat their children differently. The results suggest that maternal emotional attitudes toward children may play a causal role in the development of antisocial behavior and illustrate how genetically informative research can inform tests of socialization hypotheses.     

The etiology of behavioral problems and competencies in very young twins

Although genetic and environmental influences on behavior problems in middle childhood and adolescence have been well-studied, little is known about the etiology of behavior problems in very early childhood. The present study explores genetic and environmental contributions to individual differences in behavior problems and competences in an infant-toddler sample of twins. There were 1,950 twin pairs (mean age=23.8 months) who were rated by parents on the Infant-Toddler Social and Emotional Assessment. All four domains (Externalizing, Internalizing, Dysregulation, Competence) and 20 subscales-indices on the Infant-Toddler Social and Emotional Assessment displayed significant heritability. There were also substantial shared environmental influences operating on most of the domains and subscales. Compared with behavior problems, behavioral competencies were less heritable and more influenced by shared environments.     

Beyond Heritability: Twin Studies in Behavioral Research

ABSTRACT— The heritability of human behavioral traits is now well established, due in large measure to classical twin studies. We see little need for further studies of the heritability of individual traits in behavioral science, but the twin study is far from having outlived its usefulness. The existence of pervasive familial influences on behavior means that selection bias is always a concern in any study of the causal effects of environmental circumstances. Twin samples continue to provide new opportunities to identify causal effects with appropriate genetic and shared environmental controls. We discuss environmental studies of discordant twin pairs and twin studies of genetic and environmental transactions in this context.     

Parent-Offspring and Sibling Adoption Analyses of Parental Ratings of Temperament in Infancy and Childhood

A first step toward understanding the etiology of personality is to investigate the relative impact of genetic and environmental factors using twin and adoption designs. Twin studies of infants and young children indicate substantial genetic influence for parental ratings of temperament in the preschool years. Adoption studies, however, have not previously been reported during the early years of life. We present parent-offspring comparisons for temperament (emotionality, activity, sociability, and impulsivity) for adopted and nonadopted children yearly from 1 to 7 years of age and their biological, adoptive, and nonadoptive parents. Also presented are correlations for adoptive and nonadoptive siblings when each child was 1, 2, 3, and 4 years of age. In contrast with twin results, little evidence is found for genetic influence. The average correlation between biological parents and their adopted-away children for data averaged over the 7 years is only .03. Similarly, the average parent-offspring correlation in nonadoptive families (.08) is no greater than in adoptive families (.12). Results for nonadoptive and adoptive siblings also indicate little genetic influence. The difference between the twin and adoption results may be due to environmental effects or to nonadditive genetic variance.     

Environmental Contributions to the Stability of Antisocial Behavior over Time: Are They Shared or Non-shared?

It has recently been argued that shared environmental influences are moderate, identifiable, and persistent sources of individual differences in most forms of child and adolescent psychopathology, including antisocial behavior. Unfortunately, prior studies examining the stability of shared environmental influences over time were limited by possible passive gene-environment correlations, shared informants effects, and/or common experiences of trauma. The current study sought to address each of these limitations. We examined adolescent self-reported antisocial behavior in a 3.5 year longitudinal sample of 610 biological and adoptive sibling pairs from the Sibling Interaction and Behavior Study (SIBS). Results revealed that 74–81% of shared environmental influences present at time 1 were also present at time 2, whereas most non-shared environmental influences (88–89%) were specific to a particular assessment period. Such results provide an important constructive replication of prior research, strongly suggesting that shared environmental contributions to antisocial behavior are systematic in nature.     

Genetic and environmental stability differs in reactive and proactive aggression

The aim of this study was to examine stability and change in genetic and environmental influences on reactive (impulsive and affective) and proactive (planned and instrumental) aggression from childhood to early adolescence. The sample was drawn from an ongoing longitudinal twin study of risk factors for antisocial behavior at the University of Southern California (USC). The twins were measured on two occasions: ages 9–10 years (N=1,241) and 11–14 years (N=874). Reactive and proactive aggressive behaviors were rated by parents. The stability in reactive aggression was due to genetic and nonshared environmental influences, whereas the continuity in proactive aggression was primarily genetically mediated. Change in both reactive and proactive aggression between the two occasions was mainly explained by nonshared environmental influences, although some evidence for new genetic variance at the second occasion was found for both forms of aggression. These results suggest that proactive and reactive aggression differ in their genetic and environmental stability, and provide further evidence for some distinction between reactive and proactive forms of aggression. Aggr. Behav. 35:437–452, 2009. © 2009 Wiley‐Liss, Inc.     

Disordered gambling as defined by the Diagnostic and Statistical Manual of Mental Disorders and the South Oaks Gambling Screen: evidence for a common etiologic structure

In a previous article, we demonstrated in a large twin study that disordered gambling (DG), as defined by the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV), ran in families, that about half of the variation in liability for DG was due to familial factors, and that all of this was explained by shared genetic rather than shared environmental influences (Slutske, Zhu, Meier, & Martin, 2010). The purpose of the present study is to extend this work to include an alternative conceptualization of DG that is provided by the South Oaks Gambling Screen (SOGS) item set in order to (a) compare the magnitude of the familial resemblance obtained when using the two definitions of DG (based on the DSM-IV and the SOGS), (b) examine the extent to which the 2 definitions tap the same underlying sources of genetic and environmental variation, and (c) examine whether the same results will be obtained among men and women. The results of bivariate twin model-fitting analyses suggested that DG, as defined by the DSM-IV and the SOGS, substantially overlapped at the etiologic level among both men and women, which supports the construct validity of both the DSM and the SOGS conceptualizations of DG. This study highlights the utility of twin studies for appraising the validity of the diagnostic nomenclature.     

Genetic and environmental mechanisms underlying stability and change in problem behaviors at ages 3, 7, 10, and 12

Maternal ratings on internalizing (INT) and externalizing (EXT) behaviors were collected in a large, population-based longitudinal sample. The numbers of participating twin pairs at ages 3, 7, 10, and 12 were 5,602, 5,115, 2,956, and 1,481, respectively. Stability in both behaviors was accounted for by genetic and shared environmental influences. The genetic contribution to stability (INT: 43%; EXT: 60%) resulted from the fact that a subset of genes expressed at an earlier age was still active at the next time point. A common set of shared environmental factors operated at all ages (INT: 47%; EXT: 34%). The modest contribution of nonshared environmental factors (INT: 10%; EXT: 6%) could not be captured by a simple model. Significant age-specific influences were found for all components, indicating that genetic and environmental factors also contributed to changes in problem behavior.     

Genetic and environmental influences on girls' and boys' gender-typed and gender-neutral values

In this first investigation of genetic and environmental influences on children's values, 271 German twin pairs (50.2% boys) reported their values at ages 7-11 years using the Portrait Values Questionnaire (Schwartz & Rubel, 2005). We distinguished between gender-neutral (conservation vs. openness to change) and gender-typed (self-transcendence vs. self-enhancement) values. Boys differed from girls in the importance given to gender-typed benevolence, achievement, and power values. Gender-neutral values showed moderate (.34) and gender-typed values showed higher (.49) heritability, with nonshared environment and error accounting for the remaining variance. For both sexes, substantial genetic effects accounted for the importance children gave to their respective gender-stereotypical end of the self-transcendence versus self-enhancement dimension. However, dramatic sex differences emerged in the gender-atypical end of the distribution. For girls, low self-transcendence (high gender-atypical values) showed a large (.76) group heritability. For boys, gender-atypical values (high self-transcendence) showed no heritability and a modest (.10) shared environment effect.     

The Association Between Internalizing and Externalizing Behavior in Childhood and Early Adolescence: Genetic or Environmental Common Influences?

This study analyzed the genetic and environmental influences on internalizing and externalizing behavior problems and the nature of their cooccurrence in a national Norwegian twin sample. The sample comprised 526 identical and 389 fraternal same-sexed twin pairs from five birth cohorts, aged 5-6, 8-9, 12-13, 13-14, and 14-15 years. Behavior problems were assessed by parental ratings on the Child Behavior Checklist. A model of additive genetic, shared, and nonshared environmental influences was fitted to both internalizing and externalizing behavior in four sex and age groups. The considerable covariance,r = .51 to .58, between these traits is accounted for mainly by common environmental components; this effect was most marked in the 5 to 9-year olds. Concordance rates for children scoring above 1 standard deviation from the total sample mean on the internalizing scale only, externalizing scale only, or both indicated stronger genetic influences for internalizing or externalizing problems only than for combined problems.     

Intergenerational transmission of antisocial behavior: How do kids become antisocial adults?

Exposure to many potential environmental risk factors for child antisocial behavior is associated with one of the strongest predictors of antisocial behavior, a family history of antisociality. Because most studies of putative environmental factors do not take into account genetic propensities for antisocial behavior shared between parent and child, the possibility of genetic contributions to these “environmental” markers is typically not evaluated. In this paper, we review research on the environmental correlates of antisociality, their association with parental antisociality, and highlight findings from studies that have controlled for either genetic propensities or parental antisociality.     

Implications of the restricted range of family environments for estimates of heritability and nonshared environment in behavior-genetic adoption studies.

Group and individual-difference adoption designs lead to opposite conclusions concerning the importance of shared environment (SE) for the child outcomes of IQ and antisocial behavior. This paradox could be due to the range restriction (RR) of family environments (FE) that goes with adoption studies. Measures of FE from 2 of the most recent adoption studies indicate that RR is substantial, about 67%, which corresponds to the top half of a normal FE distribution. RR of 67% cuts effect sizes and R2 statistics by factors of 3 and 2-2.5, respectively. Because selection into an adoption study in inherently a between-family process and assuming that comparable restriction of genetic (G) influences are absent, estimates of SE, G, and nonshared influences will be substantially biased, respectively, down, up, and up by RR. Corrections for RR applied to adoption studies indicate that SE could account for as much as 50% of the variance in IQ.