Testing different types of genotype-environment correlation: an extended children-of-twins model

Annual Research Review: Towards a deeper understanding of nature and nurture: combining family-based quasi-experimental methods with genomic data

Distinguishing between the effects of nature and nurture constitutes a major research goal for those interested in understanding human development. It is known, for example, that many parent traits predict mental health outcomes in children, but the causal processes underlying such associations are often unclear. Family-based quasi-experimental designs such as sibling comparison, adoption and extended family studies have been used for decades to distinguish the genetic transmission of risk from the environmental effects family members potentially have on one another. Recently, these designs have been combined with genomic data, and this combination is fuelling a range of exciting methodological advances. In this review we explore these advances - highlighting the ways in which they have been applied to date and considering what they are likely to teach us in the coming years about the aetiology and intergenerational transmission of psychopathology.

Using genetic designs to identify likely causal environmental contributions to psychopathology

The multifactorial nature of psychopathology, whereby both genetic and environmental factors contribute risk, has long been established. In this paper, we provide an update on genetically informative designs that are utilized to disentangle genetic and environmental contributions to psychopathology. We provide a brief reminder of quantitative behavioral genetic research designs that have been used to identify potentially causal environmental processes, accounting for genetic contributions. We also provide an overview of recent molecular genetic approaches that utilize genome-wide association study data which are increasingly being applied to questions relevant to psychopathology research. While genetically informative designs typically have been applied to investigate the origins of psychopathology, we highlight how these approaches can also be used to elucidate potential causal environmental processes that contribute to developmental course and outcomes. We highlight the need to use genetically sensitive designs that align with intervention and prevention science efforts, by considering strengths-based environments to investigate how positive environments can mitigate risk and promote children's strengths.

Intergenerational transmission of psychopathology: An examination of symptom severity and directionality

The present study examined the intergenerational transmission of internalizing and externalizing symptom severity, which indexes comorbidity, and symptom directionality, which indicates differentiation toward externalizing versus internalizing problems. Data are from 854 male and female, same-sex adult twin pairs born between 1926 and 1971 (32-60 years old, M = 44.9 years, SD = 4.9 years) from the Twin and Offspring Study in Sweden and their adolescent offspring (11-22 years old, M = 15.7 years, SD = 2.4 years, 52% female). Children-of-twins models revealed additive (9%) and dominant (45%) genetic and nonshared environmental (47%) influences on twins' symptom severity, and additive genetic (39%) and nonshared environmental (61%) influences on twins' symptom directionality. Both comorbid problems and preponderance of symptoms of a particular - internalizing versus externalizing - spectrum were correlated across parent and child generations, although associations were modest especially for directionality (i.e., transmission of specific symptom type). By interpreting findings alongside a recent study of adolescent twins, we demonstrate that the intergenerational transmission of symptom severity and symptom directionality are both unlikely to be attributable to genetic transmission, are both likely to be influenced by direct phenotypic transmission and/or nonpassive rGE, and the intergenerational transmission of symptom severity is also likely to be influenced by passive rGE.

Illuminating the origins of the intergenerational transmission of psychopathology with a novel genetically informed design

Although it is well known that parental depression is transmitted within families across generations, the etiology of this transmission remains unclear. Our goal was to develop a novel study design capable of explicitly examining the etiologic sources of intergenerational transmission. We specifically leveraged naturally-occurring variations in genetic relatedness between parents and their adolescent children in the 720 families participating in the Nonshared Environment in Adolescent Development (NEAD) study, 58.5% of which included a rearing stepparent (nearly always a stepfather). Results pointed squarely to the environmental transmission of psychopathology between fathers and children. Paternal depression was associated with adolescent depression and adolescent behavior problems (i.e., antisocial behavior, headstrong behavior, and attention problems) regardless of whether or not fathers and their children were genetically related. Moreover, these associations persisted to a subset of "blended" families in which the father was biologically related to one participating child but not to the other, and appeared to be mediated via father-child conflict. Such findings are not only fully consistent with the environmental transmission of psychopathology across generations, but also add to extant evidence that parent-child conflict is a robust and at least partially environmental predictor of adolescent psychopathology.

Parental criticism and adolescent internalising symptoms: using a Children-of-Twins design with power calculations to account for genetic influence

BACKGROUND

Parental criticism is correlated with internalising symptoms in adolescent offspring. This correlation could in part reflect their genetic relatedness, if the same genes influence behaviours in both parents and offspring. We use a Children-of-Twins design to assess whether parent-reported criticism and offspring internalising symptoms remain associated after controlling for shared genes. To aid interpretation of our results and those of previous Children-of-Twins studies, we examine statistical power for the detection of genetic effects and explore the direction of possible causal effects between generations.

METHODS

Data were drawn from two Swedish twin samples, comprising 876 adult twin pairs with adolescent offspring and 1,030 adolescent twin pairs with parents. Parent reports of criticism towards their offspring were collected concurrently with parent and offspring reports of adolescent internalising symptoms. Children-of-Twins structural equation models were used to control for genetic influence on the intergenerational association between parental criticism and adolescent internalising.

RESULTS

Parental criticism was associated with adolescent internalising symptoms after controlling for genetic influence. No significant role was found for shared genes influencing phenotypes in both generations, although power analyses suggested that some genetic effects may have gone undetected. Models could not distinguish directionality for nongenetic, causal effects between generations.

CONCLUSIONS

Parental criticism may be involved in psychosocial family processes in the context of adolescent internalising. Future studies should seek to identify these processes and provide clarity on the direction of potential causal effects.

Parenting in the Context of the Child: Genetic and Social Processes

The focus on the role of parenting in child development has a long-standing history. When measures of parenting precede changes in child development, researchers typically infer a causal role of parenting practices and attitudes on child development. However, this research is usually conducted with parents raising their own biological offspring. Such research designs cannot account for the effects of genes that are common to parents and children, nor for genetically influenced traits in children that influence how they are parented and how parenting affects them. The aim of this monograph is to provide a clearer view of parenting by synthesizing findings from the Early Growth and Development Study (EGDS). EGDS is a longitudinal study of adopted children, their birth parents, and their rearing parents studied across infancy and childhood. Families (N = 561) were recruited in the United States through adoption agencies between 2000 and 2010. Data collection began when adoptees were 9 months old (males = 57.2%; White 54.5%, Black 13.2%, Hispanic/Latinx 13.4%, Multiracial 17.8%, other 1.1%). The median child age at adoption placement was 2 days (M = 5.58, SD = 11.32). Adoptive parents were predominantly in their 30s, White, and coming from upper-middle- or upper-class backgrounds with high educational attainment (a mode at 4-year college or graduate degree). Most adoptive parents were heterosexual couples, and were married at the beginning of the project. The birth parent sample was more racially and ethnically diverse, but the majority (70%) were White. At the beginning of the study, most birth mothers and fathers were in their 20s, with a mode of educational attainment at high school degree, and few of them were married. We have been following these family members over time, assessing their genetic influences, prenatal environment, rearing environment, and child development. Controlling for effects of genes common to parents and children, we confirmed some previously reported associations between parenting, parent psychopathology, and marital adjustment in relation to child problematic and prosocial behavior. We also observed effects of children's heritable characteristics, characteristics thought to be transmitted from parent to child by genetic means, on their parents and how those effects contributed to subsequent child development. For example, we found that genetically influenced child impulsivity and social withdrawal both elicited harsh parenting, whereas a genetically influenced sunny disposition elicited parental warmth. We found numerous instances of children's genetically influenced characteristics that enhanced positive parental influences on child development or that protected them from harsh parenting. Integrating our findings, we propose a new, genetically informed process model of parenting. We posit that parents implicitly or explicitly detect genetically influenced liabilities and assets in their children. We also suggest future research into factors such as marital adjustment, that favor parents responding with appropriate protection or enhancement. Our findings illustrate a productive use of genetic information in prevention research: helping parents respond effectively to a profile of child strengths and challenges rather than using genetic information simply to identify some children unresponsive to current preventive interventions.

Twins and Causal Inference: Leveraging Nature's Experiment

In this review, we discuss how samples comprising monozygotic and dizygotic twin pairs can be used for the purpose of strengthening causal inference by controlling for shared influences on exposure and outcome. We begin by briefly introducing how twin data can be used to inform the biometric decomposition of population variance into genetic, shared environmental, and nonshared environmental influences. We then discuss how extensions to this model can be used to explore whether associations between exposure and outcome survive correction for shared etiology (common causes). We review several analytical approaches that can be applied to twin data for this purpose. These include multivariate structural equation models, cotwin control methods, direction of causation models (cross-sectional and longitudinal), and extended family designs used to assess intergenerational associations. We conclude by highlighting some of the limitations and considerations that researchers should be aware of when using twin data for the purposes of interrogating causal hypotheses.

Incorporating Polygenic Risk Scores in the ACE Twin Model to Estimate A-C Covariance

The assumption in the twin model that genotypic and environmental variables are uncorrelated is primarily made to ensure parameter identification, not because researchers necessarily think that these variables are uncorrelated. Although the biasing effects of such correlations are well understood, a method to estimate these parameters in the twin model would be useful. Here we explore the possibility of relaxing this assumption by adding polygenic scores to the (univariate) twin model. We demonstrate that this extension renders the additive genetic (A)—common environmental (C) covariance (σ_AC) identified. We study the statistical power to reject σ_AC = 0 in the ACE model and present the results of simulations.

How important are parents in the development of child anxiety and depression? A genomic analysis of parent-offspring trios in the Norwegian Mother Father and Child Cohort Study (MoBa)

BACKGROUND

Many studies detect associations between parent behaviour and child symptoms of anxiety and depression. Despite knowledge that anxiety and depression are influenced by a complex interplay of genetic and environmental risk factors, most studies do not account for shared familial genetic risk. Quantitative genetic designs provide a means of controlling for shared genetics, but rely on observed putative exposure variables, and require data from highly specific family structures.

METHODS

The intergenerational genomic method, Relatedness Disequilibrium Regression (RDR), indexes environmental effects of parents on child traits using measured genotypes. RDR estimates how much the parent genome influences the child indirectly via the environment, over and above effects of genetic factors acting directly in the child. This 'genetic nurture' effect is agnostic to parent phenotype and captures unmeasured heritable parent behaviours. We applied RDR in a sample of 11,598 parent-offspring trios from the Norwegian Mother, Father and Child Cohort Study (MoBa) to estimate parental genetic nurture separately from direct child genetic effects on anxiety and depression symptoms at age 8. We tested for mediation of genetic nurture via maternal anxiety and depression symptoms. Results were compared to a complementary non-genomic pedigree model.

RESULTS

Parental genetic nurture explained 14% of the variance in depression symptoms at age 8. Subsequent analyses suggested that maternal anxiety and depression partially mediated this effect. The genetic nurture effect was mirrored by the finding of family environmental influence in our pedigree model. In contrast, variance in anxiety symptoms was not significantly influenced by common genetic variation in children or parents, despite a moderate pedigree heritability.

CONCLUSIONS

Genomic methods like RDR represent new opportunities for genetically sensitive family research on complex human traits, which until now has been largely confined to adoption, twin and other pedigree designs. Our results are relevant to debates about the role of parents in the development of anxiety and depression in children, and possibly where to intervene to reduce problems.

Maternal and paternal effects on offspring internalizing problems: Results from genetic and family-based analyses

It is unclear to what extent parental influences on the development of internalizing problems in offspring are explained by indirect genetic effects, reflected in the environment provided by the parent, in addition to the genes transmitted from parent to child. In this study, these effects were investigated using two innovative methods in a large birth cohort. Using maternal-effects genome complex trait analysis (M-GCTA), the effects of offspring genotype, maternal or paternal genotypes, and their covariance on offspring internalizing problems were estimated in 3,801 mother-father-child genotyped trios. Next, estimated genetic correlations within pedigree data, including 10,688 children, were used to estimate additive genetic effects, maternal and paternal genetic effects, and a shared family effect using linear mixed effects modeling. There were no significant maternal or paternal genetic effects on offspring anxiety or depressive symptoms at age 8, beyond the effects transmitted via the genetic pathway between parents and children. However, indirect maternal genetic effects explained a small, but nonsignificant, proportion of variance in childhood depressive symptoms in both the M-GCTA (~4%) and pedigree (~8%) analyses. Our results suggest that parental effects on offspring internalizing problems are predominantly due to transmitted genetic variants, rather than the indirect effect of parental genes via the environment.

Longitudinal examination of pathways to peer problems in middle childhood: A siblings-reared-apart design

To advance research from Dishion and others on associations between parenting and peer problems across childhood, we used a sample of 177 sibling pairs reared apart since birth (because of adoption of one of the siblings) to examine associations between parental hostility and children's peer problems when children were ages 7 and 9.5 years (n = 329 children). We extended conventional cross-lagged parent-peer models by incorporating child inhibitory control as an additional predictor and examining genetic contributions via birth mother psychopathology. Path models indicated a cross-lagged association from parental hostility to later peer problems. When child inhibitory control was included, birth mother internalizing symptoms were associated with poorer child inhibitory control, which was associated with more parental hostility and peer problems. The cross-lagged paths from parental hostility to peer problems were no longer significant in the full model. Multigroup analyses revealed that the path from birth mother internalizing symptoms to child inhibitory control was significantly higher for birth parent-reared children, indicating the possible contribution of passive gene-environment correlation to this association. Exploratory analyses suggested that each child's unique rearing context contributed to his or her inhibitory control and peer behavior. Implications for the development of evidence-based interventions are discussed.

The Longitudinal Israeli Study of Twins (LIST) Reaches Adolescence: Genetic and Environmental Pathways to Social, Personality and Moral Development

The Longitudinal Israeli Study of Twins (LIST) focuses on the developmental, genetic and environmental contributions to individual differences in children's and adolescents' social behavior. Key variables have been empathy, prosocial behavior, temperament and values. Another major goal of LIST has been to study gene-environment correlations, mainly concerning parenting. LIST includes 1657 families of Hebrew-speaking Israeli twins who have participated at least once in the study. Children's environment and their development are assessed in a multivariate, multimethod fashion, including observed, parent-reported and self-reported data. The current article summarizes and updates recent findings from LIST. For example, LIST provided evidence for the heritability of human values with the youngest sample to date, and the first genetic investigation of adolescents' identity formation. Finally, future aims of LIST are discussed.

Immunomodulatory Effects of Flavonoids: Possible Induction of T CD4+ Regulatory Cells Through Suppression of mTOR Pathway Signaling Activity

The increasing rate of autoimmune disorders and cancer in recent years has been a controversial issue in all aspects of prevention, diagnosis, prognosis and treatment. Among dietary factors, flavonoids have specific immunomodulatory effects that might be of importance to several cancers. Over different types of immune cells, T lymphocytes play a critical role in protecting the immune system as well as in the pathogenesis of specific autoimmune diseases. One of the important mediators of metabolism and immune system is mTOR, especially in T lymphocytes. In the current review, we assessed the effects of flavonoids on the immune system and then their impact on the mTOR pathway. Flavonoids can suppress mTOR activity and are consequently able to induce the T regulatory subset.

Revisiting the Children-of-Twins Design: Improving Existing Models for the Exploration of Intergenerational Associations

Datasets comprising twins and their children can be a useful tool for understanding the nature of intergenerational associations between parent and offspring phenotypes. In the present article we explore structural equation models previously used to analyse Children-of-Twins data, highlighting some limitations and considerations. We then present new variants of these models, showing that extending the models to include multiple offspring per parent addresses several of the limitations discussed. Accompanying the updated models, we provide power calculations and demonstrate with application to simulated data. We then apply to intergenerational analyses of height and weight, using a sub-study of the Norwegian Mother and Child Cohort (MoBa); the Intergenerational Transmission of Risk (IToR) project, wherein all kinships in the MoBa data have been identified (a children-of-twins-and-siblings study). Finally, we consider how to interpret the findings of these models and discuss future directions.

Rigor and reproducibility in genetic research on eating disorders

OBJECTIVE

We explored both within-method and between-method rigor and reproducibility in the field of eating disorders genetics.

METHOD

We present critical evaluation and commentary on component methods of genetic research (family studies, twin studies, molecular genetic studies) and discuss both successful and unsuccessful efforts in the field.

RESULTS

Eating disorders genetics has had a number of robust results that converge across component methodologies. Familial aggregation of eating disorders, twin-based heritability estimates of eating disorders, and genome-wide association studies (GWAS) all point toward a substantial role for genetics in eating disorders etiology and support the premise that genes do not act alone. Candidate gene and linkage studies have been less informative historically.

DISCUSSION

The eating disorders field has entered the GWAS era with studies of anorexia nervosa. Continued growth of sample sizes is essential for rigorous discovery of actionable variation. Molecular genetic studies of bulimia nervosa, binge-eating disorder, and other eating disorders are virtually nonexistent and lag seriously behind other major psychiatric disorders. Expanded efforts are necessary to reveal the fundamental biology of eating disorders, inform clinical practice, and deliver new therapeutic targets.

Shared genetic influences do not explain the association between parent-offspring relationship quality and offspring internalizing problems: results from a Children-of-Twins study

BACKGROUND

Associations between parenting and child outcomes are often interpreted as reflecting causal, social influences. However, such associations may be confounded by genes common to children and their biological parents. To the extent that these shared genes influence behaviours in both generations, a passive genetic mechanism may explain links between them. Here we aim to quantify the relative importance of passive genetic v. social mechanisms in the intergenerational association between parent-offspring relationship quality and offspring internalizing problems in adolescence.

METHODS

We used a Children-of-Twins (CoT) design with data from the parent-based Twin and Offspring Study of Sweden (TOSS) sample [909 adult twin pairs and their offspring; offspring mean age 15.75 (2.42) years], and the child-based Swedish Twin Study of CHild and Adolescent Development (TCHAD) sample [1120 adolescent twin pairs; mean age 13.67 (0.47) years]. A composite of parent-report measures (closeness, conflict, disagreements, expressions of affection) indexed parent-offspring relationship quality in TOSS, and offspring self-reported internalizing symptoms were assessed using the Child Behavior Checklist (CBCL) in both samples.

RESULTS

A social transmission mechanism explained the intergenerational association [r = 0.21 (0.16-0.25)] in our best-fitting model. A passive genetic transmission pathway was not found to be significant, indicating that parental genetic influences on parent-offspring relationship quality and offspring genetic influences on their internalizing problems were non-overlapping.

CONCLUSION

These results indicate that this intergenerational association is a product of social interactions between children and parents, within which bidirectional effects are highly plausible. Results from genetically informative studies of parenting-related effects should be used to help refine early parenting interventions aimed at reducing risk for psychopathology.

Widespread covariation of early environmental exposures and trait-associated polygenic variation

Although gene-environment correlation is recognized and investigated by family studies and recently by SNP-heritability studies, the possibility that genetic effects on traits capture environmental risk factors or protective factors has been neglected by polygenic prediction models. We investigated covariation between trait-associated polygenic variation identified by genome-wide association studies (GWASs) and specific environmental exposures, controlling for overall genetic relatedness using a genomic relatedness matrix restricted maximum-likelihood model. In a UK-representative sample (n = 6,710), we find widespread covariation between offspring trait-associated polygenic variation and parental behavior and characteristics relevant to children's developmental outcomes-independently of population stratification. For instance, offspring genetic risk for schizophrenia was associated with paternal age (R² = 0.002; P = 1e-04), and offspring education-associated variation was associated with variance in breastfeeding (R² = 0.021; P = 7e-30), maternal smoking during pregnancy (R² = 0.008; P = 5e-13), parental smacking (R² = 0.01; P = 4e-15), household income (R² = 0.032; P = 1e-22), watching television (R² = 0.034; P = 5e-47), and maternal education (R² = 0.065; P = 3e-96). Education-associated polygenic variation also captured covariation between environmental exposures and children's inattention/hyperactivity, conduct problems, and educational achievement. The finding that genetic variation identified by trait GWASs partially captures environmental risk factors or protective factors has direct implications for risk prediction models and the interpretation of GWAS findings.

Adverse Pregnancy Outcomes in Asthmatic Women: A Population-Based Family Design Study

BACKGROUND

Asthma is associated with several adverse pregnancy and perinatal outcomes. Familial factors may confound these associations.

OBJECTIVE

To examine the role of measured and unmeasured confounding by conducting a study that compared differentially exposed cousins and siblings from the same families.

METHODS

We retrieved data on adverse pregnancy outcomes, prescribed drugs, and physician-diagnosed asthma from nationwide registers for all women in Sweden with singleton births between 2001 and 2013. Logistic and linear regression estimated the association between maternal asthma and several outcomes in the whole population and within differently exposed pregnant relatives.

RESULTS

In total, 1,075,153 eligible pregnancies were included and 10.1% of the study population had asthma. We identified 475,200 cousin and 341,205 sister pregnancies. Women with asthma had increased risks for preeclampsia (adjusted odds ratio [aOR], 1.17; 95% CI, 1.13-1.21), emergency cesarean section (aOR, 1.24; 95% CI, 1.22-1.27), and having a child small for gestational age (aOR, 1.18; 95% CI, 1.12-1.23). In the conditional regression analyses, after adjustment for familial factors, the associations remained: preeclampsia in cousins (aOR, 1.16; 95% CI, 1.07-1.25) and siblings (aOR, 1.23; 95% CI, 1.08-1.38), emergency cesarean section in cousins (aOR, 1.28) and siblings (aOR, 1.21), and small for gestational age in cousins (aOR, 1.17) and siblings (aOR, 1.13).

CONCLUSIONS

Factors shared by siblings and cousins do not seem to explain the observed association between maternal asthma and adverse pregnancy outcomes. This implies that targeting the asthma disease will continue to be important in reducing risks for adverse outcomes in pregnancy.

Cultivating Conformists or Raising Rebels? Connecting Parental Control and Autonomy Support to Adolescent Delinquency

This study investigates short-term and long-term associations between parenting in early adolescence and delinquency throughout adolescence using data from the National Longitudinal Surveys. Multilevel longitudinal Poisson regressions show that behavioral control, psychological control, and decision-making autonomy in early adolescence (ages 10-11) are associated with delinquency trajectories throughout adolescence (ages 10-17). Path analyses reveal support for three mediation hypotheses. Parental monitoring (behavioral control) is negatively associated with delinquency in the short term and operates partly through changes in self-control. Parental pressure (psychological control) shows immediate and long-lasting associations with delinquency through changes in self-control and delinquent peer pressures. Decision-making autonomy is negatively associated with delinquency in the long term, yet may exacerbate delinquency in early adolescence by increasing exposure to delinquent peers.

Maltreatment-associated neurodevelopmental disorders: a co-twin control analysis

BACKGROUND

Childhood maltreatment (CM) is strongly associated with psychiatric disorders in childhood and adulthood. Previous findings suggest that the association between CM and psychiatric disorders is partly causal and partly due to familial confounding, but few studies have investigated the mechanisms behind the association between CM and neurodevelopmental disorders (NDDs). Our objective was to determine whether maltreated children have an elevated number of NDDs and whether CM is a risk factor for an increased NDD 'load' and increased NDD symptoms when controlling for familial effects.

METHODS

We used a cross-sectional sample from a population-representative Swedish twin study, comprising 8,192 nine-year-old twins born in Sweden between 1997 and 2005. CM was defined as parent-reported exposure to emotional abuse/neglect, physical neglect, physical abuse, and/or sexual abuse. Four NDDs were measured with the Autism-Tics, AD/HD, and other comorbidities inventory.

RESULTS

Maltreated children had a greater mean number of NDDs than nonmaltreated children. In a co-twin control design, CM-discordant monozygotic twins did not differ significantly for their number of NDDs, suggesting that CM is not associated with an increased load of NDDs when genetic and shared environmental factors are taken into account. However, CM was associated with a small increase in symptoms of attention-deficit/hyperactivity disorder and autism spectrum disorder in CM-discordant MZ twins, although most of the covariance of CM with NDD symptoms was explained by common genetic effects.

CONCLUSIONS

Maltreated children are at higher risk of having multiple NDDs. Our findings are, however, not consistent with the notion that CM causes the increased NDD load in maltreated children. Maltreated children should receive a full neurodevelopmental assessment, and clinicians should be aware that children with multiple NDDs are at higher risk of maltreatment.

The Maternal Emotional Climate Predicts Twin Sibling Relationship Quality

We investigated the association between maternal expressed emotion and twin relationship quality, after controlling for a maternal questionnaire measure of the mother-child relationship. This was explored within a community sample of 156 mothers and their two young twin children (M child age = 3.69 years; SD child age = 0.37). Mothers reported on the twin-twin relationship and the mother-child relationship via questionnaire. They were also interviewed about each child using the innovative Preschool Five Minute Speech Sample (Daley et al., 2003), which yields information about relative positive:negative maternal expressed emotion. Mothers who expressed more family-wide positive emotion and less family-wide negative emotion also reported more positivity, but not negativity, within the twin relationship - even when controlling for questionnaire reports of the mother-child relationship. Counter to expectations, discrepancies in mothers' expressed emotion between their twins also predicted more positive sibling relationships. Our findings corroborate the well established spill-over effect, whereby families are viewed as emotional units of interdependent individuals, none of whom can be understood in isolation from one another. Most importantly, the Preschool Five Minute Speech Sample provides information about mothering that questionnaire reports may not, and thus it is a useful tool in better understanding the twin family system.

Associations between the parent-child relationship and adolescent self-worth: a genetically informed study of twin parents and their adolescent children

BACKGROUND

Low self-worth during adolescence predicts a range of emotional and behavioural problems. As such, identifying potential sources of influence on self-worth is important. Aspects of the parent-child relationship are often associated with adolescent self-worth but to date it is unclear whether such associations may be attributable to familial confounding (e.g. genetic relatedness). We set out to clarify the nature of relationships between parental expressed affection and adolescent self-worth, and parent-child closeness and adolescent self-worth.

METHODS

We used data from the Twin and Offspring Study in Sweden, a children-of-twins sample comprising 909 adult twin pairs with adolescent children. Using these data we were able to apply structural equation models with which we could examine whether associations remained after accounting for genetic transmission.

RESULTS

Results demonstrated that parent-child closeness and parental-expressed affection were both phenotypically associated with adolescent self-worth. Associations could not be attributed to genetic relatedness between parent and child.

CONCLUSIONS

Parent-child closeness and parental affection are associated with adolescent self-worth above and beyond effects attributable to genetic relatedness. Data were cross-sectional, so the direction of effects cannot be confirmed but findings support the notion that positive parent-child relationships increase adolescent self-worth.

What Drives the Development of Social Inequality Over the Life Course? The German TwinLife Study

The German twin family study ‘TwinLife’ was designed to enhance our understanding of the development of social inequalities over the life course. The interdisciplinary project investigates mechanisms of social inequalities across the lifespan by taking into account psychological as well as social mechanisms, and their genetic origin as well as the interaction and covariation between these factors. Main characteristics of the study are: (1) a multidimensional perspective on social inequalities, (2) the assessment of developmental trajectories in childhood, adolescence, and young adulthood in a longitudinal design by using (3) a combination of a multi-cohort cross-sequential and an extended twin family design, while (4) capturing a large variation of behavioral and environmental factors in a representative sample of about 4,000 German twin families. In the present article, we first introduce the theoretical and empirical background of the TwinLife study, and second, describe the design, content, and implementation of TwinLife. Since the data will be made available as scientific use file, we also illustrate research possibilities provided by this project to the scientific community.

Passive rGE or Developmental Gene-Environment Cascade? An Investigation of the Role of Xenobiotic Metabolism Genes in the Association Between Smoke Exposure During Pregnancy and Child Birth Weight

There is considerable evidence that smoke exposure during pregnancy (SDP) environmentally influences birth weight after controlling for genetic influences and maternal characteristics. However, maternal smoking during pregnancy-the behavior that leads to smoke exposure during pregnancy-is also genetically-influenced, indicating the potential role of passive gene-environment correlation. An alternative to passive gene-SDP correlation is a cascading effect whereby maternal and child genetic influences are causally linked to prenatal exposures, which then have an 'environmental' effect on the development of the child's biology and behavior. We describe and demonstrate a conceptual framework for disentangling passive rGE from this cascading GE effect using a systems-based polygenic scoring approach comprised of genes shown to be important in the xenobiotic (substances foreign to the body) metabolism pathway. Data were drawn from 5044 families from the Avon Longitudinal Study of Parents and Children with information on maternal SDP, birth weight, and genetic polymorphisms in the xenobiotic pathway. Within a k-fold cross-validation approach (k = 5), we created weighted maternal and child polygenic scores using 18 polymorphisms from 10 genes that have been implicated in the xenobiotic metabolism pathway. Mothers and children shared variation in xenobiotic metabolism genes. Amongst mothers who smoked during pregnancy, neither maternal nor child xenobiotic metabolism polygenic scores were associated with a higher likelihood of smoke exposure during pregnancy, or the severity of smoke exposure during pregnancy (and therefore, neither proposed mechanism was supported), or with child birth weight. SDP was consistently associated with lower child birth weight controlling for the polygenic scores, maternal educational attainment, social class, psychiatric problems, and age. Limitations of the study design and the potential of the framework using other designs are discussed.

Adolescent age moderates genetic and environmental influences on parent-adolescent positivity and negativity: Implications for genotype-environment correlation

We examined how genotype-environment correlation processes differ as a function of adolescent age. We tested whether adolescent age moderates genetic and environmental influences on positivity and negativity in mother-adolescent and father-adolescent relationships using parallel samples of twin parents from the Twin and Offspring Study in Sweden and twin/sibling adolescents from the Nonshared Environment in Adolescent Development Study. We inferred differences in the role of passive and nonpassive genotype-environment correlation based on biometric moderation findings. The findings indicated that nonpassive gene-environment correlation played a stronger role for positivity in mother- and father-adolescent relationships in families with older adolescents than in families with younger adolescents, and that passive gene-environment correlation played a stronger role for positivity in the mother-adolescent relationship in families with younger adolescents than in families with older adolescents. Implications of these findings for the timing and targeting of interventions on family relationships are discussed.

Top 10 Replicated Findings From Behavioral Genetics

In the context of current concerns about replication in psychological science, we describe 10 findings from behavioral genetic research that have replicated robustly. These are "big" findings, both in terms of effect size and potential impact on psychological science, such as linearly increasing heritability of intelligence from infancy (20%) through adulthood (60%). Four of our top 10 findings involve the environment, discoveries that could have been found only with genetically sensitive research designs. We also consider reasons specific to behavioral genetics that might explain why these findings replicate.

The Gender Gap in Second Language Acquisition: Gender Differences in the Acquisition of Dutch among Immigrants from 88 Countries with 49 Mother Tongues

Gender differences were analyzed across countries of origin and continents, and across mother tongues and language families, using a large-scale database, containing information on 27,119 adult learners of Dutch as a second language. Female learners consistently outperformed male learners in speaking and writing proficiency in Dutch as a second language. This gender gap remained remarkably robust and constant when other learner characteristics were taken into account, such as education, age of arrival, length of residence and hours studying Dutch. For reading and listening skills in Dutch, no gender gap was found. In addition, we found a general gender by education effect for all four language skills in Dutch for speaking, writing, reading, and listening. Female language learners turned out to profit more from higher educational training than male learners do in adult second language acquisition. These findings do not seem to match nurture-oriented explanatory frameworks based for instance on a human capital approach or gender-specific acculturation processes. Rather, they seem to corroborate a nature-based, gene-environment correlational framework in which language proficiency being a genetically-influenced ability interacting with environmental factors such as motivation, orientation, education, and learner strategies that still mediate between endowment and acquiring language proficiency at an adult stage.

The Intergenerational Transmission of Anxiety: A Children-of-Twins Study

OBJECTIVE

The transmission of anxiety within families is well recognized, but the underlying processes are poorly understood. Twin studies of adolescent anxiety demonstrate both genetic and environmental influence, and multiple aspects of parenting are associated with offspring anxiety. To date, the children-of-twins design has not been used to evaluate the relative contributions of genetic transmission compared with direct transmission of anxiety from parents to their offspring.

METHOD

Anxiety and neuroticism measures were completed by 385 monozygotic and 486 dizygotic same-sex twin families (37% male twin pair families) from the Twin and Offspring Study in Sweden. Structural equation models tested for the presence of both genetic and environmental transmission from one generation to the next.

RESULTS

For both anxiety and neuroticism, the models provide support for significant direct environmental transmission from parents to their adolescent offspring. In contrast, there was no evidence of significant genetic transmission.

CONCLUSIONS

The association between parental and offspring anxiety largely arises because of a direct association between parents and their children independent of genetic confounds. The lack of genetic transmission may reflect there being different genetic effects on these traits in adolescence and adulthood. Direct environmental transmission is in line with developmental theories of anxiety suggesting that children and adolescents learn anxious behaviors from their parents through a number of pathways such as modeling. Future analyses should combine children-of-twins data with child twin data in order to examine whether this direct effect solely represents parental influences on the offspring or whether it also includes child/adolescent anxiety evoking parental anxiety.

The etiology of the association between child antisocial behavior and maternal negativity varies across aggressive and non-aggressive rule-breaking forms of antisocial behavior

There is a robust association between negative parenting and child antisocial behavior problems. However, the etiology of this association remains unclear. Extant literature has reported strikingly different conclusions across studies, with some highlighting genetic mediation and others highlighting environmental mediation. One possible reason for these discrepancies across studies may be the failure to differentiate between aggressive and non-aggressive (rule-breaking) dimensions of childhood antisocial behavior, given their notably different etiologies and developmental trajectories (Burt 2012). The current study sought to examine the phenotypic and etiologic associations of maternal negativity with aggressive and rule-breaking antisocial behavior, respectively. Participants included 824 mothers and their twin children between the ages of 6 and 10. Our results highlighted clear etiologic distinctions in the associations of aggression and rule-breaking with maternal negativity. Aggression was associated with maternal negativity via both genetic and environmental factors, whereas the association between non-aggressive rule-breaking and maternal negativity was entirely environmental in origin. These findings provide additional support for the presence of meaningful distinctions between aggressive and non-aggressive forms of antisocial behavior, and highlight the complex relationship between parenting and child outcome.

Parental criticism is an environmental influence on adolescent somatic symptoms

Previous studies have suggested that parental criticism leads to more somatic symptoms in adolescent children. However, this research has not assessed the direction of causation or whether genetic and/or environmental influences explain the association between parental criticism and adolescent somatic symptoms. As such, it is impossible to understand the mechanisms that underlie this association. The current study uses the Extended Children of Twins design to examine whether parents' genes, adolescents' genes, and/or environmental factors explain the relationship between parental criticism and adolescent somatic symptoms. Participants came from 2 twin samples, including the Twin and Offspring Study in Sweden (N = 868 pairs of adult twins and each twin's adolescent child) and from the Twin Study of Child and Adolescent Development (N = 690 pairs of twin children and their parents). Findings showed that environmental influences account for the association between parental criticism and adolescent somatic symptoms. This suggests that parents' critical behaviors exert a direct environmental effect on somatic symptoms in adolescent children. Results support the use of intervention programs focused on parental criticism to help reduce adolescents' somatic symptoms.

Angry responses to infant challenges: parent, marital, and child genetic factors associated with harsh parenting

This study examined genetic and environmental influences on harsh parenting of adopted 9-month-olds (N = 503), with an emphasis on positive child-, parent-, and family-level characteristics. Evocative gene-environment correlation (rGE) was examined by testing the effect of both positive and negative indices of birth parent temperament on adoptive parents' harsh parenting. Adoptive fathers' harsh parenting was inversely related to birth mother positive temperament, indicating evocative rGE, as well as to marital quality. Adoptive parents' negative temperamental characteristics were related to hostile parenting for both fathers and mothers. Findings support the importance of enhancing positive family characteristics in addition to mitigating negative characteristics, as well as engaging multiple levels of the family system to prevent harsh parenting.

Parental knowledge is an environmental influence on adolescent externalizing

BACKGROUND

There is evidence both that parental monitoring is an environmental influence serving to diminish adolescent externalizing problems and that this association may be driven by adolescents' characteristics via genetic and/or environmental mechanisms, such that adolescents with fewer problems tell their parents more, and therefore appear to be better monitored. Without information on how parents' and children's genes and environments influence correlated parent and child behaviors, it is impossible to clarify the mechanisms underlying this association.

METHOD

The present study used the Extended Children of Twins model to distinguish types of gene-environment correlation and direct environmental effects underlying associations between parental knowledge and adolescent (age 11-22 years) externalizing behavior with a Swedish sample of 909 twin parents and their adolescent offspring and a US-based sample of 405 White adolescent siblings and their parents.

RESULTS

Results suggest that more parental knowledge is associated with less adolescent externalizing via a direct environmental influence independent of any genetic influences. There was no evidence of a child-driven explanation of the association between parental knowledge and adolescent externalizing problems.

CONCLUSIONS

In this sample of adolescents, parental knowledge exerted an environmental influence on adolescent externalizing after accounting for genetic influences of parents and adolescents. Because the association between parenting and child development originates in the parent, treatment for adolescent externalizing must not only include parents but should also focus on altering their parental style. Thus, findings suggest that teaching parents better knowledge-related monitoring strategies is likely to help reduce externalizing problems in adolescents.

Child-evoked maternal negativity from 9 to 27 months: Evidence of gene-environment correlation and its moderation by marital distress

Past research has documented pervasive genetic influences on emotional and behavioral disturbance across the life span and on liability to adult psychiatric disorder. Increasingly, interest is turning to mechanisms of gene-environment interplay in attempting to understand the earliest manifestations of genetic risk. We report findings from a prospective adoption study, which aimed to test the role of evocative gene-environment correlation in early development. Included in the study were 561 infants adopted at birth and studied between 9 and 27 months, along with their adoptive parents and birth mothers. Birth mother psychiatric diagnoses and symptoms scales were used as indicators of genetic influence, and multiple self-report measures were used to index adoptive mother parental negativity. We hypothesized that birth mother psychopathology would be associated with greater adoptive parent negativity and that such evocative effects would be amplified under conditions of high adoptive family adversity. The findings suggested that genetic factors associated with birth mother externalizing psychopathology may evoke negative reactions in adoptive mothers in the first year of life, but only when the adoptive family environment is characterized by marital problems. Maternal negativity mediated the effects of genetic risk on child adjustment at 27 months. The results underscore the importance of genetically influenced evocative processes in early development.

Genotype-environment correlation in the era of DNA

One of John Loehlin’s many contributions to the field of behavioral genetics involves gene-environment (GE) correlation. The empirical base for GE correlation was research showing that environmental measures are nearly as heritable as behavioral measures and that genetic factors mediate correlations between environment and behavior. Attempts to identify genes responsible for these phenomena will come up against the ‘missing heritability’ problem that plagues DNA research on complex traits throughout the life sciences. However, DNA can also be used for quantitative genetic analyses of unrelated individuals (Genome-wide Complex Trait Analysis, GCTA) to investigate genetic influence on environmental measures and their behavioral correlates. A novel feature of GCTA is that it enables genetic analysis of family-level environments (e.g., parental socioeconomic status) and school-level environments (e.g., teaching quality) that cannot be investigated using within-family designs such as the twin method. An important implication of GE correlation is its shift from a passive model of the environment imposed on individuals to an active model in which individuals actively create their own experiences in part on the basis of their genetic propensities.

The intergenerational multiple deficit model and the case of dyslexia

Which children go on to develop dyslexia? Since dyslexia has a multifactorial etiology, this question can be restated as: what are the factors that put children at high risk for developing dyslexia? It is argued that a useful theoretical framework to address this question is Pennington’s (2006) multiple deficit model (MDM). This model replaces models that attribute dyslexia to a single underlying cause. Subsequently, the generalist genes hypothesis for learning (dis)abilities (Plomin and Kovas, 2005) is described and integrated with the MDM. Next, findings are presented from a longitudinal study with children at family risk for dyslexia. Such studies can contribute to testing and specifying the MDM. In this study, risk factors at both the child and family level were investigated. This led to the proposed intergenerational MDM, in which both parents confer liability via intertwined genetic and environmental pathways. Future scientific directions are discussed to investigate parent-offspring resemblance and transmission patterns, which will shed new light on disorder etiology.

Behavioral Genetic Approaches and Family Theory

Family theories have been founded on research that cannot discriminate genetic and environmental influences and, consequently, most theories do not have highly developed models of gene-environment interplay in families. Behavioral genetic approaches, which can identify gene-environment interplay, have typically not been driven by family theories and have lacked adequate measurement of family processes. In this article, the authors describe behavioral genetic mechanisms and methods using representative examples of research on family processes, highlighting the advantages of an integrated approach. New directions in research and theory driven by an integrated approach are discussed.

Pediatric anxiety disorders: from neuroscience to evidence-based clinical practice

The objective of this narrative review of the literature is to describe the epidemiology, etiology, pathophysiology, diagnosis, and treatment of pediatric anxiety disorders. We aim to guide clinicians in understanding the biology of anxiety disorders and to provide general guidelines for the proper diagnoses and treatment of these conditions early in life. Anxiety disorders are prevalent, associated with a number of negative life outcomes, and currently under-recognized and under-treated. The etiology involves both genes and environmental influences modifying the neural substrate in a complex interplay. Research on pathophysiology is still in its infancy, but some brain regions, such as the amygdala and the prefrontal cortex, have been implicated in fear and anxiety. Current practice is to establish diagnosis based purely on clinical features, derived from clinical interviews with the child, parents, and teachers. Treatment is effective using medication, cognitive behavioral therapy, or a combination of both. An introduction to the neuroscience behind anxiety disorders combined with an evidence-based approach may help clinicians to understand these disorders and treat them properly in childhood.

The Impact of Child Behaviour Problems on Maternal Employment: A Longitudinal Cohort Study

This prospective population-based study examined associations between children's behaviour problems and maternal employment. Information on children's behaviour problems at 3 years from 22,115 mothers employed before pregnancy and participating in the Norwegian Mother and Child Cohort Study were linked to national register data on employment and relevant social background factors, mothers' self-reported susceptibility to anxiety/depression and mother-reports of day-care attendance and fathers' income. Mothers reporting their child to have severe (>2 SD) internalizing or severe combined behaviour problems (5 %) had excess risk of leaving paid employment irrespective of other important characteristics generally associated with maternal employment (RR 1.24-1.31). The attributable risk percent ranged from 30.3 % (internalizing problems) to 32.4 % (combined problems). Externalizing behaviour problems were not uniquely associated with mothers leaving employment.

Gene-environment correlation underlying the association between parental negativity and adolescent externalizing problems

Studies of adolescent or parent-based twins suggest that gene-environment correlation (rGE) is an important mechanism underlying parent-adolescent relationships. However, information on how parents' and children's genes and environments influence correlated parent and child behaviors is needed to distinguish types of rGE. The present study used the novel Extended Children of Twins model to distinguish types of rGE underlying associations between negative parenting and adolescent (age 11-22 years) externalizing problems with a Swedish sample of 909 twin parents and their adolescent offspring and a U.S.-based sample of 405 adolescent siblings and their parents. Results suggest that evocative rGE, not passive rGE or direct environmental effects of parenting on adolescent externalizing, explains associations between maternal and paternal negativity and adolescent externalizing problems.

Biological and rearing mother influences on child ADHD symptoms: revisiting the developmental interface between nature and nurture

BACKGROUND

Families of children with attention deficit hyperactivity disorder (ADHD) report more negative family relationships than families of children without ADHD. Questions remain as to the role of genetic factors underlying associations between family relationships and children's ADHD symptoms, and the role of children's ADHD symptoms as an evocative influence on the quality of relationships experienced within such families. Utilizing the attributes of two genetically sensitive research designs, the present study examined associations between biologically related and nonbiologically related maternal ADHD symptoms, parenting practices, child impulsivity/activation, and child ADHD symptoms. The combined attributes of the study designs permit assessment of associations while controlling for passive genotype-environment correlation and directly examining evocative genotype-environment correlation (rGE); two relatively under examined confounds of past research in this area.

METHODS

A cross-sectional adoption-at-conception design (Cardiff IVF Study; C-IVF) and a longitudinal adoption-at-birth design (Early Growth and Development Study; EGDS) were used. The C-IVF sample included 160 mothers and children (age 5-8 years). The EGDS sample included 320 linked sets of adopted children (age 6 years), adoptive-, and biologically related mothers. Questionnaires were used to assess maternal ADHD symptoms, parenting practices, child impulsivity/activation, and child ADHD symptoms. A cross-rater approach was used across measures of maternal behavior (mother reports) and child ADHD symptoms (father reports).

RESULTS

Significant associations were revealed between rearing mother ADHD symptoms, hostile parenting behavior, and child ADHD symptoms in both samples. Because both samples consisted of genetically unrelated mothers and children, passive rGE was removed as a possible explanatory factor underlying these associations. Further, path analysis revealed evidence for evocative rGE processes in the longitudinal adoption-at-birth study (EGDS) from biologically related maternal ADHD symptoms to biologically unrelated maternal hostile parenting through early disrupted child behavior (impulsivity/activation), with maternal hostile parenting and disrupted child behavior associated with later child ADHD symptoms, controlling for concurrent adoptive mother ADHD symptoms.

CONCLUSIONS

Results highlight the importance of genetically influenced child ADHD-related temperamental attributes on genetically unrelated maternal hostility that in turn links to later child ADHD symptoms. Implications for intervention programs focusing on early family processes and the precursors of child ADHD symptoms are discussed.

Observed positive parenting behaviors and youth genotype: evidence for gene-environment correlations and moderation by parent personality traits

Gene-environment correlations (rGE) have been demonstrated in behavioral genetic studies, but rGE have proven elusive in molecular genetic research. Significant gene-environment correlations may be difficult to detect because potential moderators could reduce correlations between measured genetic variants and the environment. Molecular genetic studies investigating moderated rGE are lacking. This study examined associations between child catechol-O-methyltransferase genotype and aspects of positive parenting (responsiveness and warmth), and whether these associations were moderated by parental personality traits (neuroticism and extraversion) among a general community sample of third, sixth, and ninth graders (N = 263) and their parents. Results showed that parent personality traits moderated the rGE association between youths' genotype and coded observations of positive parenting. Parents with low levels of neuroticism and high levels of extraversion exhibited greater sensitive responsiveness and warmth, respectively, to youth with the valine/valine genotype. Moreover, youth with this genotype exhibited lower levels of observed anger. There was no association between the catechol-O-methyltransferase genotype and parenting behaviors for parents high on neuroticism and low on extraversion. Findings highlight the importance of considering moderating variables that may influence child genetic effects on the rearing environment. Implications for developmental models of maladaptive and adaptive child outcomes, and interventions for psychopathology, are discussed within a developmental psychopathology framework.

Annual Research Review: Resilience--clinical implications

BACKGROUND

It is a universal finding that there is huge heterogeneity in people's responses to all kinds of stress and adversity. Resilience is an interactive phenomenon that is inferred from findings indicating that some individuals have a relatively good outcome despite having experienced serious adversities.

METHODS

Resilience can only be inferred if there has been testing of environmental mediation of risks and quantification of the degree of risk. The use of 'natural experiments' to test environmental mediation is briefly discussed. The literature is then reviewed on features associated with resilience in terms of (a) those that are neutral or risky in the absence of the risk experience (such as adoption); (b) brief exposure to risks and inoculation effects; (c) mental features (such as planning, self-regulation or a sense of personal agency); (d) features that foster those mental features; (e) turning point effects; (f) gene-environment interactions; (g) social relationships and promotive effects; and (h) the biology of resilience.

RESULTS

Clinical implications are considered with respect to (a) conceptual implications; (b) prevention; and (c) treatment.

CONCLUSION

Resilience findings do not translate into a clear programme of prevention and treatment, but they do provide numerous leads that focus on the dynamic view of what may be involved in overcoming seriously adverse experiences.

Genes of experience: explaining the heritability of putative environmental variables through their association with behavioural and emotional traits

An increasing body of evidence shows that many ‘environmental’ measures are heritable, indicating genetic involvement in environmental exposure (or gene–environment correlation). In the present study we attempt to clarify why three such ‘environmental’ measures (maternal negativity, paternal negativity and negative life events) are consistently found to be heritable. Through multivariate genetic analysis of a sample of adolescent twins from the UK we show that the heritability of these putative environmental measures can be explained via their association with five behavioural phenotypes: oppositionality, delinquency, physical aggression, depression and anxiety. This is consistent with the notion that being genetically susceptible to certain behavioural difficulties could lead to exposure to certain life events, and this may account for the reported heritability of ‘environmental’ measures. Results are discussed in the context of possible active, evocative and passive gene–environment correlations.

Infant development in family context: call for a genetically informed approach

We call for a genetically informed approach in the examination of infant social and emotional development in family context. We recommend that scholars conceptualize family functioning as occurring on three unique levels: the parent-child dyad, the inter-parental dyad, and whole family functioning. Although advances in the area of understanding genetic variation in infants as a potential moderator of the influence of parent-child dyadic functioning have been made over the past decade, it is time to widen this inquiry to consider genetic variation in infants as a potential moderator of the influence of inter-parental dyadic and whole family functioning as well. A critical review of the literature also calls for additional examination of genetic variation in infants as a moderator of positive contextual influences, the integration of unique temperament variables with studies of infant genotype, consideration of the role of the gene-environment correlation, and epigenetic effects. Furthermore, we call for the application of genetically-informed research methods to these questions. Expanding knowledge in this area has the potential to refine treatment and prevention efforts aimed at promoting infant social and emotional development.

Current parental depression and offspring perceived self-competence: a quasi-experimental examination

A genetically-informed, quasi-experimental design was used to examine the genetic and environmental processes underlying associations between current parental depressive symptoms and offspring perceived self-competence. Participants, drawn from a population-based Swedish sample, were 852 twin pairs and their male (52 %) and female offspring aged 15.7 ± 2.4 years. Parental depressive symptoms were measured using the Center for Epidemiological Studies Depression scale. Offspring perceived self-competence was measured using a modified Harter Perceived Competence Scale. Cousin comparisons and Children of Twins designs suggested that associations between maternal depressive symptoms and offspring perceived self-competence were due to shared genetic/environmental liability. The mechanism responsible for father-offspring associations, however, was independent of genetic factors and of extended family environmental factors, supporting a causal inference. Thus, mothers and fathers may impact offspring perceived self-competence via different mechanisms and unmeasured genetic and environmental selection factors must be considered when studying the intergenerational transmission of cognitive vulnerabilities for depression.

Unraveling the effect of genes and environment in the transmission of parental antisocial behavior to children's conduct disturbance, depression and hyperactivity

BACKGROUND

  A critical issue in devising effective interventions for the treatment of children's behavioral and emotional problems identifying genuine family environmental factors that place children at risk. In most twin and family studies, environmental factors are confounded with both direct genetic risk from parents and the indirect effect of genes influencing parents' ability to provide an optimal rearing environment. The present study was undertaken to determine whether parental psychopathology, specifically parental antisocial behavior (ASP), is a genuine environmental risk factor for juvenile conduct disturbance, depression and hyperactivity, or whether the association between parental ASP and children's behavioral and emotional problems can be explained as a secondary consequence of the intergenerational transmission of genetic factors.

METHODS

  An extended children of twins design comprised of data collected on 2,674 adult female and male twins, their spouses, and 2,454 of their children was used to test whether genetic and/or family environmental factors best accounted for the association between parental antisocial behavior and children's behavioral problems. An age-matched sample of 2,826 juvenile twin pairs from the Virginia Twin Study of Adolescent Behavioral Development was also included to examine developmental differences in gene expression by partitioning child-specific transmissible effects from those effects that persist into adulthood. The fit of alternative models was evaluated using the statistical program Mx.

RESULTS

  We found distinct patterns of transmission between parental antisocial behavior and juvenile conduct, depression and hyperactivity. Genetic and family environmental factors accounted for the resemblance between parents' ASP and children's conduct disturbance. Family environmental factors alone explained the association between child depression and parental ASP, and the impact of parental ASP on hyperactivity was entirely genetic.

CONCLUSIONS

  These findings underscore differences in the contribution of genetic and environmental factors on the patterns of association between parental antisocial behavior and juvenile psychopathology, having important clinical implications for the prevention and amelioration of child behavioral and emotional problems.

From correlates to causes: can quasi-experimental studies and statistical innovations bring us closer to identifying the causes of antisocial behavior?

Longitudinal, epidemiological studies have identified robust risk factors for youth antisocial behavior, including harsh and coercive discipline, maltreatment, smoking during pregnancy, divorce, teen parenthood, peer deviance, parental psychopathology, and social disadvantage. Nevertheless, because this literature is largely based on observational studies, it remains unclear whether these risk factors have truly causal effects. Identifying causal risk factors for antisocial behavior would be informative for intervention efforts and for studies that test whether individuals are differentially susceptible to risk exposures. In this article, we identify the challenges to causal inference posed by observational studies and describe quasi-experimental methods and statistical innovations that may move researchers beyond discussions of risk factors to allow for stronger causal inference. We then review studies that used these methods, and we evaluate whether robust risk factors identified from observational studies are likely to play a causal role in the emergence and development of youth antisocial behavior. There is evidence of causal effects for most of the risk factors we review. However, these effects are typically smaller than those reported in observational studies, suggesting that familial confounding, social selection, and misidentification might also explain some of the association between risk exposures and antisocial behavior. For some risk factors (e.g., smoking during pregnancy, parent alcohol problems), the evidence is weak that they have environmentally mediated effects on youth antisocial behavior. We discuss the implications of these findings for intervention efforts to reduce antisocial behavior and for basic research on the etiology and course of antisocial behavior.