The genetic and environmental etiology of antisocial behavior from childhood to emerging adulthood

Continuity and Change in the Genetic and Environmental Etiology of Youth Antisocial Behavior

Trajectories of youth antisocial behavior (ASB) are characterized by both continuity and change. Twin studies have further indicated that genetic factors underlie continuity, while environmental exposures unique to each child in a given family underlie change. However, most behavioral genetic studies have examined continuity and change during relatively brief windows of development (e.g., during childhood but not into adolescence). It is unclear whether these findings would persist when ASB trajectories are examined across multiple stages of early development (i.e., from early childhood into emerging adulthood). Our study sought to fill this gap by examining participants assessed up to five times between the ages of 3 and 22 years using an accelerated longitudinal design in the Michigan State University Twin Registry (MSUTR). We specifically examined the etiologies of stability and change via growth curve modeling and a series of univariate and bivariate twin analyses. While participants exhibited moderate-to-high rank-order stability, mean levels of ASB decreased linearly with age. Genetic and nonshared environmental influences that were present in early childhood also contributed to both stability and change across development, while shared environmental contributions were negligible. In addition, genetic and nonshared environmental influences that were not yet present at the initial assessment contributed to change over time. Although ASB tended to decrease in frequency with age, participants who engaged in high levels of ASB during childhood generally continued to do so throughout development. Moreover, the genetic and nonshared environmental contributions to ASB early in development also shaped the magnitude of the decrease with age.

The neurobiology of human aggressive behavior: Neuroimaging, genetic, and neurochemical aspects

In modern societies, there is a strive to improve the quality of life related to risk of crimes which inevitably requires a better understanding of brain determinants and mediators of aggression. Neurobiology provides powerful tools to achieve this end. Pre-clinical and clinical studies show that changes in regional volumes, metabolism-function and connectivity within specific neural networks are related to aggression. Subregions of prefrontal cortex, insula, amygdala, basal ganglia and hippocampus play a major role within these circuits and have been consistently implicated in biology of aggression. Genetic variations in proteins regulating the synthesis, degradation, and transport of serotonin and dopamine as well as their signal transduction have been found to mediate behavioral variability observed in aggression. Gene-gene and gene-environment interactions represent additional important risk factors for aggressiveness. Considering the social burden of pathological forms of aggression, more basic and translational studies should be conducted to accelerate applications to clinical practice, justice courts, and policy making.

Associations between adolescent social phobia, sickness absence and unemployment: a prospective study of twins in Sweden

BACKGROUND

Little is known about adolescent mental health problems, including social phobia, as risk factors for future work incapacity. The aim of this study was to investigate the association between social phobia in adolescence and unemployment and sickness absence (SA) in early adulthood, also evaluating the role of familial factors (genetics and shared environment).

METHODS

A sample of 2845 Swedish twins born in 1985-86 in Sweden was followed longitudinally in the population-based and prospective Twin study of CHild and Adolescent Development. Information on twins' social phobia was collected at ages 13-4, 16-7 and 19-20 years. Logistic regression providing odds ratios (OR) with 95% confidence intervals (95% CI) was used to analyze the associations between social phobia, unemployment and SA during the follow-up 2006-12. The influence of familial factors was evaluated by conditional logistic regression.

RESULTS

Presence of social phobia during adolescence was associated with increased odds for unemployment and SA in young adulthood. For unemployment, the highest OR was at the age of 13-4 years (1.58 [95% CI: 1.22-2.06]), and the associations became null after adjusting for familial factors. For SA, the highest OR was at the age of 19-20 years (1.73 [95% CI: 1.13-2.65]), and the estimates changed slightly after adjusting for familial factors.

CONCLUSIONS

: Results suggest that social phobia experienced in adolescence contribute to early adulthood unemployment and SA. Familial factors seemed to explain the association between social phobia and unemployment.

Polymorphism of serotonin transporter gene in male subjects with antisocial behavior and MMA fighters

In our study, the frequencies of serotonin transporter gene (5-HTT) polymorphisms and their combinations are compared in the healthy male subjects with antisocial behavior, in general, and in those with its particular forms, as well as in the reference group of MMA fighters. Subjects convicted of unlawful actions were classified into those convicted of violent crimes or non-violent ones. The group of subjects convicted of violent crimes was further subdivided into those convicted of murder, or robbery, or of inflicting grave body injuries. The group of MMA fighters was selected from the subjects without a prior history of antisocial behavior or criminal record in the subjects or their relatives. The frequency of D allele in the groups of convicted subjects and MMA fighters was higher, than in the population sample. Furthermore, the frequencies of D/D and 12/12 genotype combinations were shown to be higher in the group of convicted subjects, especially, in habitual criminals and those convicted of grave crimes or murder. The predisposition of MMA fighters to violent behavior and physical aggressive suppression of an opponent is successfully implemented in their professional career; however, this behavioral pattern appears to represent the controlled aggression.

Predictors of adult outcomes in clinically- and legally-ascertained youth with externalizing problems

Externalizing problems (EP), including rule-breaking, aggression, and criminal involvement, are highly prevalent during adolescence, but the adult outcomes of adolescents exhibiting EP are characterized by heterogeneity. Although many youths' EP subside after adolescence, others' persists into adulthood. Characterizing the development of severe EP is essential to prevention and intervention efforts. Multiple predictors of adult antisocial personality disorder (ASPD) and legal outcomes of a large sample (N = 1205) of clinically- or legally-ascertained adolescents (ages 12-19 years) with severe EP were examined. Many psychosocial predictors hypothesized to predict persistence of EP demonstrated zero-order associations with adult outcomes, but accounted for little unique variation after accounting for baseline conduct disorder symptoms (CD) and demographic factors. Baseline measures of intelligence, which explained independent variation in legal outcomes, provided the only consistent exception to this pattern, though future work is needed to parse these effects from those of socioeconomic factors. CD severity during adolescence is a parsimonious index of liability for persistence of EP into adulthood that explains outcome variance above and beyond all other demographic and psychosocial predictors in this sample.

Heart rate and hurtful behavior from teens to adults: Paths to adult health

A low resting heart rate across development from infancy to young adulthood relates to greater aggression/hostility. Adult aggression and a high heart rate relate to health risk. Do some aggressive individuals retain low heart rate and less health risk across development while others show high heart rate and more risk? A longitudinal sample of 203 men assessed as teens (age 16.1) and adults (mean age 32.0) permitted us to assess (a) stability of heart rate levels and reactivity, (b) stability of aggression/hostility, and (c) whether change or stability related to health risk. Adults were assessed with Buss-Perry measures of aggression/hostility; teens with the Zuckerman aggression/hostility measure. Mean resting heart rate, heart rate reactivity to speech preparation, and aggression/hostility were moderately stable across development. Within age periods, mean heart rate level, but not reactivity, was negatively related to hostility/aggression. Maintaining low heart rate into adulthood was related to better health among aggressive individuals relative to those with increasing heart rate into adulthood. Analyses controlled for weight gain, socioeconomic status, race, health habits, and medication. Low heart rate as a characteristic of hostile/aggressive individuals may continue to relate to better health indices in adulthood, despite possible reversal of this relationship with aging.

Oxytocin Receptor Gene (OXTR) and Deviant Peer Affiliation: A Gene-Environment Interaction in Adolescent Antisocial Behavior

Although the oxytocin receptor gene (OXTR) is involved in aggression and social affiliation, it has not been examined in gene-environment interaction studies. This longitudinal study examined the effect of genetic variants in OXTR and its gene-environment interaction with perceived deviant peer affiliation in the trajectories of antisocial behavior in 323 adolescents (182 males) from 13 to 18 years. Annual assessments of reactive and proactive aggression, delinquency, and friends' delinquency, as well as DNA at age 17 were collected. Gene-based tests yielded no main effect of OXTR, but revealed a significant gene-environment interaction in proactive aggression and delinquency. Variation in the OXTR might affect the influence of deviant peer affiliation on antisocial behavior, contributing to a better understanding of individual differences in antisocial behavior.

Recent advances in genetics of aggressive behavior

One of the most important problems of modern neurobiology and medicine is an understanding of the mechanisms of normal and pathological behavior of a person. Aggressive behavior is an integral part of the human psyche. However, environmental risk factors, mental illness and somatic diseases can lead to increased aggression to be the biological basis of antisocial behavior in a human society. An important role in development of aggressive behavior belongs to the hereditary factors that may be linked to abnormal functioning of neurotransmitter systems in the brain yet the underlying genetic mechanisms remain unclear, which is due to a large number of single nucleotide polymorphisms, insertions and deletions in the structure of genes that encode the components of the neurotransmitter systems. The most studied candidate genes for aggressive behavior are serotonergic (TPH1, TPH2, HTR2A, SLC6A4) and dopaminergic (DRD4, SLC6A3) system genes, as well as the serotonin or catecholamine metabolizing enzyme genes (COMT, MAOA). In addition, there is evidence that the hypothalamic-pituitary system genes (OXT, OXTR, AVPR1A, AVPR1B), the sex hormone receptors genes (ER1, AR), neurotrophin (BDNF) and neuronal apoptosis genes (CASP3, BAX) may also be involved in development of aggressive behavior. The results of Genome-Wide Association Studies (GWAS) have demonstrated that FYN, LRRTM4, NTM, CDH13, DYRK1A and other genes are involved in regulation of aggressive behavior. These and other evidence suggest that genetic predisposition to aggressive behavior may be a very complex process.

Heterogeneity in the development of proactive and reactive aggression in childhood: Common and specific genetic - environmental factors

BACKGROUND

Few studies are grounded in a developmental framework to study proactive and reactive aggression. Furthermore, although distinctive correlates, predictors and outcomes have been highlighted, proactive and reactive aggression are substantially correlated. To our knowledge, no empirical study has examined the communality of genetic and environmental underpinning of the development of both subtypes of aggression. The current study investigated the communality and specificity of genetic-environmental factors related to heterogeneity in proactive and reactive aggression's development throughout childhood.

METHODS

Participants were 223 monozygotic and 332 dizygotic pairs. Teacher reports of aggression were obtained at 6, 7, 9, 10 and 12 years of age. Joint development of both phenotypes were analyzed through a multivariate latent growth curve model. Set point, differentiation, and genetic maturation/environmental modulation hypotheses were tested using a biometric decomposition of intercepts and slopes.

RESULTS

Common genetic factors accounted for 64% of the total variation of proactive and reactive aggression's intercepts. Two other sets of uncorrelated genetic factors accounted for reactive aggression's intercept (17%) on the one hand, and for proactive (43%) and reactive (13%) aggression's slopes on the other. Common shared environmental factors were associated with proactive aggression's intercept (21%) and slope (26%) and uncorrelated shared environmental factors were also associated with reactive aggression's slope (14%). Common nonshared environmental factors explained most of the remaining variability of proactive and reactive aggression slopes.

CONCLUSIONS

A genetic differentiation hypothesis common to both phenotypes was supported by common genetic factors associated with the developmental heterogeneity of proactive and reactive aggression in childhood. A genetic maturation hypothesis common to both phenotypes, albeit stronger for proactive aggression, was supported by common genetic factors associated with proactive and reactive aggression slopes. A shared environment set point hypothesis for proactive aggression was supported by shared environmental factors associated with proactive aggression baseline and slope. Although there are many common features to proactive and reactive aggression, the current research underscores the advantages of differentiating them when studying aggression.

Antisocial behavior and polymorphisms in the oxytocin receptor gene: findings in two independent samples

The quantitative genetic contribution to antisocial behavior is well established, but few, if any, genetic variants are established as risk factors. Emerging evidence suggests that the neuropeptide oxytocin (OXT) may modulate interpersonal aggression. We here investigated whether single-nucleotide polymorphisms (SNPs) in the OXT receptor gene (OXTR) are associated with the expression of antisocial behavior. A discovery sample, including both sexes, was drawn from the Child and Adolescent Twin Study in Sweden (CATSS; n=2372), and a sample from the Twin Study of Child and Adolescent Development (TCHAD; n=1232) was used for replication. Eight SNPs in OXTR, selected on previous associations with social and antisocial behavior, were genotyped in the participants of CATSS. Significant polymorphisms were subsequently genotyped in TCHAD for replication. Participants completed self-assessment questionnaires-Life History of Aggression (LHA; available only in CATSS), and Self-Reported Delinquency (SRD; available in both samples)-designed to capture antisocial behavior as continuous traits. In the discovery sample, the rs7632287 AA genotype was associated with higher frequency of antisocial behavior in boys, and this was then replicated in the second sample. In particular, overt aggression (directly targeting another individual) was strongly associated with this genotype in boys (P=6.2 × 10(-7) in the discovery sample). Meta-analysis of the results for antisocial behavior from both samples yielded P=2.5 × 10(-5). Furthermore, an association between rs4564970 and LHA (P=0.00013) survived correction in the discovery sample, but there was no association with the SRD in the replication sample. We conclude that the rs7632287 and rs4564970 polymorphisms in OXTR may independently influence antisocial behavior in adolescent boys. Further replication of our results will be crucial to understanding how aberrant social behavior arises, and would support the OXT receptor as one potential target in the treatment of aggressive antisocial behavior.

Aetiological influences on stability and change in emotional and behavioural problems across development: a systematic review

Emotional and behavioural problems in childhood and adolescence can be chronic and are predictive of future psychiatric problems. Understanding what factors drive the development and maintenance of these problems is therefore crucial. Longitudinal behavioural genetic studies using twin, sibling or adoption data can be used to explore the developmental aetiology of stability and change in childhood and adolescent psychopathology. We present a systematic review of longitudinal, behavioural genetic analyses of emotional and behavioural problems between ages 0 to 18 years. We identified 58 studies, of which 19 examined emotional problems, 30 examined behavioural problems, and 9 examined both. In the majority of studies, stability in emotional and behavioural problems was primarily genetically influenced. Stable environmental factors were also widely found, although these typically played a smaller role. Both genetic and environmental factors were involved in change across development. We discuss the findings in the context of the wider developmental literature and make recommendations for future research.

The association between the MAOA 2R genotype and delinquency over time among men: the interactive role of parental closeness and parental incarceration

Using a panel of 6,001 males from the National Longitudinal Study of Adolescent and Adult Health, we examine potential moderation by paternal incarceration and parent-child closeness altering the relationship between the rare 2R MAOA genotype and delinquency. By jointly examining moderation patterns for both the mother and father with the transmission of the MAOA genotype from mother to son, we are able to make inferences about the specific genetic model that best explains these outcomes. In line with prior research, we find a direct relationship between the MAOA 2R genotype and delinquency, independent of parental incarceration and closeness. Examining moderation patterns, we find that delinquency risk for the 2R allele is buffered for males close to their biological or social father, but not their biological mother. We conclude that the 2R delinquency association is not due to passive gene-environment correlation but is best characterized as a social control gene-environment interaction.

Genetics of aggressive behavior: An overview

The Research Domain Criteria (RDoC) address three types of aggression: frustrative non-reward, defensive aggression and offensive/proactive aggression. This review sought to present the evidence for genetic underpinnings of aggression and to determine to what degree prior studies have examined phenotypes that fit into the RDoC framework. Although the constructs of defensive and offensive aggression have been widely used in the animal genetics literature, the human literature is mostly agnostic with regard to all the RDoC constructs. We know from twin studies that about half the variance in behavior may be explained by genetic risk factors. This is true for both dimensional, trait-like, measures of aggression and categorical definitions of psychopathology. The non-shared environment seems to have a moderate influence with the effects of shared environment being unclear. Human molecular genetic studies of aggression are in an early stage. The most promising candidates are in the dopaminergic and serotonergic systems along with hormonal regulators. Genome-wide association studies have not yet achieved genome-wide significance, but current samples are too small to detect variants having the small effects one would expect for a complex disorder. The strongest molecular evidence for a genetic basis for aggression comes from animal models comparing aggressive and non-aggressive strains or documenting the effects of gene knockouts. Although we have learned much from these prior studies, future studies should improve the measurement of aggression by using a systematic method of measurement such as that proposed by the RDoC initiative.

Differential genetic and environmental influences on developmental trajectories of antisocial behavior from adolescence to young adulthood

Little research has investigated differential genetic and environmental influences on different developmental trajectories of antisocial behavior. This study examined genetic and environmental influences on liabilities of being in life-course-persistent (LCP) and adolescent-limited (AL) type delinquent groups from adolescence to young adulthood while considering nonviolent and violent delinquency subtypes and gender differences. A genetically informative sample (n = 356, 15-16 years) from the first three waves of In-Home Interview of the National Longitudinal Study of Adolescent to Adult Health was used, with 94 monozygotic and 84 dizygotic pairs of same-sex twins (50% male). Biometric liability threshold models were fit and found that the male-specific LCP type class, chronic, showed more genetic influences, while the AL type classes, decliner and desister, showed more environmental influences. Genetic liability and shared environment both influence the persistence of antisocial behavior. The development of female antisocial behavior appears to be influenced more by shared environment.

Relationships between problematic alcohol consumption and delinquent behaviour from adolescence to young adulthood

BACKGROUND

Heavy episodic drinking (HED) has been associated with increased risk for short- and long-term injury and harms, such as violence and delinquent behaviour; however, the temporal relationship between the two remains unclear, particularly on transition to young adulthood. This study investigates transactional pathways between HED and delinquent behaviour from adolescence to emerging adulthood.

METHODS

Data were drawn from the Australian Temperament Project; a population-based longitudinal study that has followed the health and development of participants (and parents) across 30 years from birth in 1982. The analytic sample was 1650 participants and included five measurement waves spanning adolescence (3 waves: 13-18 years) and young adulthood (2 waves; 19-24 years).

RESULTS

There was strong continuity across waves of both HED and delinquency, as well as across-time associations between them. Delinquent behaviour in adolescence was associated with up to twofold increases in the odds of HED at each subsequent adolescent wave. HED in the late teens was associated with over fourfold increases in the odds of persistent (two waves) HED in young adulthood. HED in the late teens was associated with increases in the odds of delinquent behaviour in young adulthood (over twofold for male and one and a half-fold for female participants).

CONCLUSIONS

While delinquent behaviour predicts both future HED and future delinquent behaviour in adolescence, once young people reach the legal drinking age of 18 years, HED becomes a predictor of current and future delinquent behaviour and future HED, suggesting that increased access to alcohol increases the likelihood of young people engaging in delinquent behaviour. [Miller PG, Butler E, Richardson B, Staiger PK, Youssef GJ, Macdonald JA, Sanson A, Edwards B, Olsson CA. Relationships between problematic alcohol consumption and delinquent behaviour from adolescence to young adulthood. Drug Alcohol Rev 2016;35:317-325].

Heritable influences on behavioural problems from early childhood to mid-adolescence: evidence for genetic stability and innovation

BACKGROUND

Although behavioural problems (e.g., anxiety, conduct, hyperactivity, peer problems) are known to be heritable both in early childhood and in adolescence, limited work has examined prediction across these ages, and none using a genetically informative sample.

METHOD

We examined, first, whether parental ratings of behavioural problems (indexed by the Strengths and Difficulties questionnaire) at ages 4, 7, 9, 12, and 16 years were stable across these ages. Second, we examined the extent to which stability reflected genetic or environmental effects through multivariate quantitative genetic analysis on data from a large (n > 3000) population (UK) sample of monozygotic and dizygotic twins.

RESULTS

Behavioural problems in early childhood (age 4 years) showed significant associations with the corresponding behavioural problem at all subsequent ages. Moreover, stable genetic influences were observed across ages, indicating that biological bases underlying behavioural problems in adolescence are underpinned by genetic influences expressed as early as age 4 years. However, genetic and environmental innovations were also observed at each age.

CONCLUSION

These observations indicate that genetic factors are important for understanding stable individual differences in behavioural problems across childhood and adolescence, although novel genetic influences also facilitate change in such behaviours.

Effects of Behavioral Genetic Evidence on Perceptions of Criminal Responsibility and Appropriate Punishment

Demonstrations of a link between genetic variants and criminal behavior have stimulated increasing use of genetic evidence to reduce perceptions of defendants' responsibility for criminal behavior and to mitigate punishment. However, because only limited data exist regarding the impact of such evidence on decision makers and the public at large, we recruited a representative sample of the U.S. adult population (n=960) for a web-based survey. Participants were presented with descriptions of three legal cases and were asked to: determine the length of incarceration for a convicted murderer; adjudicate an insanity defense; and decide whether a defendant should receive the death penalty. A fully crossed, between-participants, factorial design was used, varying the type of evidence (none, genetic, neuroimaging, both), heinousness of the crime, and past criminal record, with sentence or verdict as the primary outcome. Also assessed were participants' apprehension of the defendant, belief in free will, political ideology, and genetic knowledge. Across all three cases, genetic evidence had no significant effects on outcomes. Neuroimaging data showed an inconsistent effect in one of the two cases in which it was introduced. In contrast, heinousness of the offense and past criminal record were strongly related to participants' decisions. Moreover, participants' beliefs about the controllability of criminal behavior and political orientations were significantly associated with their choices. Our findings suggest that neither hopes that genetic evidence will modify judgments of culpability and punishment nor fears about the impact of genetic evidence on decision makers are likely to come to fruition.

"Bad genes" & criminal responsibility

The genetics of the accused is trying to break into the courts. To date several candidate genes have been put forward and their links to antisocial behavior have been examined and documented with some consistency. In this paper, we focus on the so called "warrior gene", or the low-activity allele of the MAOA gene, which has been most consistently related to human behavior and specifically to violence and antisocial behavior. In preparing this paper we had two objectives. First, to summarize and analyze the current scientific evidence, in order to gain an in depth understanding of the state of the issue and determine whether a dominant line of generally accepted scientific knowledge in this field can be asserted. Second, to derive conclusions and put forward recommendations related to the use of genetic information, specifically the presence of the low-activity genotype of the MAOA gene, in modulation of criminal responsibility in European and US courts.

A longitudinal twin study of physical aggression during early childhood: evidence for a developmentally dynamic genome

BACKGROUND

Physical aggression (PA) tends to have its onset in infancy and to increase rapidly in frequency. Very little is known about the genetic and environmental etiology of PA development during early childhood. We investigated the temporal pattern of genetic and environmental etiology of PA during this crucial developmental period.

METHOD

Participants were 667 twin pairs, including 254 monozygotic and 413 dizygotic pairs, from the ongoing longitudinal Quebec Newborn Twin Study. Maternal reports of PA were obtained from three waves of data at 20, 32 and 50 months. These reports were analysed using a biometric Cholesky decomposition and linear latent growth curve model.

RESULTS

The best-fitting Cholesky model revealed developmentally dynamic effects, mostly genetic attenuation and innovation. The contribution of genetic factors at 20 months substantially decreased over time, while new genetic effects appeared later on. The linear latent growth curve model revealed a significant moderate increase in PA from 20 to 50 months. Two separate sets of uncorrelated genetic factors accounted for the variation in initial level and growth rate. Non-shared and shared environments had no effect on the stability, initial status and growth rate in PA.

CONCLUSIONS

Genetic factors underlie PA frequency and stability during early childhood; they are also responsible for initial status and growth rate in PA. The contribution of shared environment is modest, and perhaps limited, as it appears only at 50 months. Future research should investigate the complex nature of these dynamic genetic factors through genetic-environment correlation (r GE) and interaction (G×E) analyses.

The double helix takes the witness stand: behavioral and neuropsychiatric genetics in court

Data on neuropsychiatric and behavioral genetics have attracted legal interest, as attorneys explore their use in criminal and civil cases. These developments may assist judges and juries in making difficult judgments-but they bring substantial risk of misinterpretation and misuse.

Psychotic experiences as a predictor of the natural course of suicidal ideation: a Swedish cohort study

Psychotic experiences are far more prevalent in the population than psychotic disorders and are associated with a wide range of depressive, anxiety and behavioral disorders, as well as increased risk for psychotic disorder. Recently, psychotic experiences have been highlighted as a potentially valuable clinical marker of risk for suicidal behavior. There have been few studies to date, however, to assess psychotic experiences as a predictor of suicidality over time. We wished to assess whether young persons with suicidal ideation at baseline assessment who reported psychotic experiences were at higher risk for persistence of suicidal ideation at follow-up than young persons who also reported suicidal ideation at baseline but who did not report co-occurring psychotic experiences. A total of 2,263 adolescents were assessed at age 13 to 14 years for psychotic experiences, suicidal ideation and internalizing and externalizing psychopathology. Participants were re-assessed at ages 16 to 17 years and 19 to 20 years. Among 13- to 14-year olds with suicidal ideation, co-occurring psychotic experiences did not predict an increased odds of persistence of suicidal ideation to age 16 to 17 years (OR=0.94, 95% CI: 0.19-4.78). Among 16- to 17-year olds with suicidal ideation, however, co-occurring psychotic experiences predicted a 6-fold increased odds of persistence of suicidal ideation to age 19 to 20 years (OR=5.53, 95% CI: 1.33-23.00). Psychotic experiences are an important but under-recognized marker of risk for persistence of suicidal ideation, in particular from mid-adolescence. An increased emphasis on the clinical assessment of psychotic experiences in mental health services should be a priority.

Alcohol consumption in men is influenced by qualitatively different genetic factors in adolescence and adulthood

BACKGROUND

Alcohol consumption is influenced by genetic factors. Previous studies have examined the heritability of alcohol consumption, or related phenotypes, from adolescence into adulthood, frequently finding that total heritability changes over time. However, it remains unclear whether the same genes underlie liability to alcohol consumption across development versus whether novel risk genes become important over time. Method A population-based study of adult male twins (n=1790) born in Virginia, USA, retrospectively reported on their average monthly alcohol consumption from early adolescence through adulthood. We used twin modeling methods to explore genetic and environmental influences on alcohol consumption over time.

RESULTS

One latent genetic factor accounted for the majority of the heritability in alcohol consumption during mid- to late adolescence, but its influence declined thereafter; from young adulthood forward, heritability was largely attributable to a second genetic factor. The total heritability of alcohol consumption increased from 0 at ages 12-14 years to 0.40 by ages 18-21 years. Shared environmental factors declined in influence over time.

CONCLUSIONS

The heritability of alcohol consumption over time is dynamic both quantitatively and qualitatively. These results have important implications for gene identification endeavors. Furthermore, these findings could inform efforts to elucidate developmentally dynamic behaviors, such as antisocial behavior.

Do etiological influences on aggression overlap with those on rule breaking? A meta-analysis

BACKGROUND

Although aggressive (AGG) and non-aggressive rule-breaking (RB) dimensions of antisocial behavior have been shown to be differentially heritable, available studies have disagreed on the extent to which the genetic and environmental factors influencing AGG also influence RB. The current meta-analysis sought to clarify the extent of etiological overlap between AGG and RB. Method Thirteen twin/sibling studies examining the covariation between AGG and RB were collected, of which 11 (with 12 independent samples) were ultimately included in the analyses (n=12923 twin/sibling pairs). Genetic and environmental correlations between AGG and RB served as study effect sizes. When squared, these correlations directly index the proportion of genetic and environmental overlap. Data were analyzed using mixed effect models.

RESULTS

Analyses revealed that genetic influences on AGG were largely, but not entirely, distinct from those on RB: only 38.4% of the genetic influences on AGG overlapped with those on RB. Similarly, only 10.2% of the non-shared environmental influences on AGG overlapped with those on RB. Although the conclusion that etiological influences on AGG are partially distinct from those on RB persisted across several potential moderators, the age of the sample and the informant used were found to moderate the extent of overlap.

CONCLUSIONS

The findings underscore the presence of meaningful etiological distinctions between AGG and RB, and imply that future conceptualizations of antisocial behavior should be organized (at least in part) around the dimensions of AGG and RB.

Maternal smoking during pregnancy and offspring conduct problems: evidence from 3 independent genetically sensitive research designs

IMPORTANCE

Several studies report an association between maternal smoking during pregnancy and offspring conduct disorder. However, past research evidences difficulty in disaggregating prenatal environmental influences from genetic and postnatal environmental influences.

OBJECTIVE

To examine the relationship between maternal smoking during pregnancy and offspring conduct problems among children reared by genetically related mothers and genetically unrelated mothers.

DESIGN, SETTING, AND PARTICIPANTS

The following 3 studies using distinct but complementary research designs were used: The Christchurch Health and Development Study (a longitudinal cohort study that includes biological and adopted children), the Early Growth and Development Study (a longitudinal adoption-at-birth study), and the Cardiff IVF (In Vitro Fertilization) Study (an adoption-at-conception study among genetically related families and genetically unrelated families). Maternal smoking during pregnancy was measured as the mean number of cigarettes per day (0, 1-9, or 10) smoked during pregnancy. Possible covariates were controlled for in the analyses, including child sex, birth weight, race/ethnicity, placement age, and breastfeeding, as well as maternal education and maternal age at birth and family breakdown, parenting practices, and family socioeconomic status.

MAIN OUTCOMES AND MEASURE

Offspring conduct problems (age range, 4-10 years) reported by parents or teachers using the behavior rating scales by Rutter and Conners, the Child Behavior Checklist and the Children's Behavior Questionnaire Short Form, and the Strengths and Difficulties Questionnaire.

RESULTS

A significant association between maternal smoking during pregnancy and offspring conduct problems was observed among children reared by genetically related mothers and genetically unrelated mothers. Results from a meta-analysis affirmed this pattern of findings across pooled study samples.

CONCLUSIONS AND RELEVANCE

Findings across 3 studies using a complement of genetically sensitive research designs suggest that smoking during pregnancy is a prenatal risk factor for offspring conduct problems when controlling for specific perinatal and postnatal confounding factors.

Genetic associations between the ADHD symptom dimensions and Cloninger's temperament dimensions in adult twins

Previous studies have identified phenotypic associations between Cloninger's temperament dimensions and the symptoms of attention deficit hyperactivity disorder (ADHD) in adults. However the underlying aetiology of these associations remains unclear. We investigate the extent to which genetic and environmental influences contribute to the relationship between temperament and ADHD, examining the ADHD symptoms of inattention (IA) and hyperactivity/impulsivity (HI) separately. Participants were 886 adult twin pairs aged 19-20 years. ADHD symptoms of IA and HI were measured using a DSM-IV based rating scale. Temperament was measured using Cloninger's Temperament and Character Inventory (TCI), across four dimensions: novelty seeking (NS), harm avoidance (HA), reward dependence (RD) and persistence (PS). The twin method was used to decompose phenotypic variance/covariance among these variables into genetic and environmental components. We found that NS was genetically associated with both ADHD symptom dimensions (IA and HI), but that HA was genetically associated with IA only. There was also some evidence of genetic association between PS, IA and HI. These findings suggest that unique profiles of temperament are genetically related to the two ADHD symptom dimensions in adults. Further work is now needed to elucidate the mechanisms that underlie both the combined and separate symptom factor domains of ADHD.

The intergenerational transmission of conduct problems

PURPOSE

Drawing on prospective longitudinal data, this paper examines the intergenerational transmission of childhood conduct problems in a sample of 209 parents and their 331 biological offspring studied as part of the Christchurch Health and Developmental Study. The aims were to estimate the association between parental and offspring conduct problems and to examine the extent to which this association could be explained by (a) confounding social/family factors from the parent's childhood and (b) intervening factors reflecting parental behaviours and family functioning.

METHODS

The same item set was used to assess childhood conduct problems in parents and offspring. Two approaches to data analysis (generalised estimating equation regression methods and latent variable structural equation modelling) were used to examine possible explanations of the intergenerational continuity in behaviour.

RESULTS

Regression analysis suggested that there was moderate intergenerational continuity (r = 0.23, p < 0.001) between parental and offspring conduct problems. This continuity was not explained by confounding factors but was partially mediated by parenting behaviours, particularly parental over-reactivity. Latent variable modelling designed to take account of non-observed common genetic and environmental factors underlying the continuities in problem behaviours across generations also suggested that parenting behaviour played a role in mediating the intergenerational transmission of conduct problems.

CONCLUSIONS

There is clear evidence of intergenerational continuity in conduct problems. In part this association reflects a causal chain process in which parental conduct problems are associated (directly or indirectly) with impaired parenting behaviours that in turn influence risks of conduct problems in offspring.

Genetic innovation and stability in externalizing problem behavior across development: a multi-informant twin study

The use of cross-informant ratings in previous longitudinal studies on externalizing behavior may have obscured the presence of continuity of genetic risk. The current study included latent factors representing the latent estimates of externalizing behavior based on both parent and self-report which eliminated rater-specific effects from these latent estimates. Symptoms of externalizing behavior of 1,480 Swedish twin pairs were obtained at ages 8-9, 13-14, 16-17 and 19-20 both by parent and self-report. Mx modeling was used to estimate additive genetic, shared and specific environmental influences. Genetic continuity was found over the entire developmental period as well as additional sources of genetic influence emerging around early and late adolescence. New unique environmental effects (E) on externalizing behavior arose early in adolescence. The results support both the presence of genetic continuity and change in externalizing behavior during adolescence due to newly emerging genetic and environmental risk factors.

Unraveling the genetic etiology of adult antisocial behavior: a genome-wide association study

Crime poses a major burden for society. The heterogeneous nature of criminal behavior makes it difficult to unravel its causes. Relatively little research has been conducted on the genetic influences of criminal behavior. The few twin and adoption studies that have been undertaken suggest that about half of the variance in antisocial behavior can be explained by genetic factors. In order to identify the specific common genetic variants underlying this behavior, we conduct the first genome-wide association study (GWAS) on adult antisocial behavior. Our sample comprised a community sample of 4816 individuals who had completed a self-report questionnaire. No genetic polymorphisms reached genome-wide significance for association with adult antisocial behavior. In addition, none of the traditional candidate genes can be confirmed in our study. While not genome-wide significant, the gene with the strongest association (p-value = 8.7×10(-5)) was DYRK1A, a gene previously related to abnormal brain development and mental retardation. Future studies should use larger, more homogeneous samples to disentangle the etiology of antisocial behavior. Biosocial criminological research allows a more empirically grounded understanding of criminal behavior, which could ultimately inform and improve current treatment strategies.

Additional evidence against shared environmental contributions to attention-deficit/hyperactivity problems

A recent meta-analysis "Burt (Psychol Bull 135:608-637, 2009)" indicated that shared environmental influences (C) do not contribute to Attention-Deficit/Hyperactivity Disorder (ADHD). Unfortunately, the meta-analysis relied almost exclusively on classical twin studies. Although useful in many ways, some of the assumptions of the classical twin model (e.g., dominant genetic and shared environmental influences do not simultaneously influence the phenotype) can artifactually decrease estimates of C. There is thus a need to confirm that dominant genetic influences are not suppressing estimates of C on ADHD. The current study sought to do just this via the use of a nuclear twin family model, which allows researchers to simultaneously model and estimate dominant genetic and shared environmental influences. We examined two independent samples of child twins: 312 pairs from the Michigan State University Twin Registry and 854 pairs from the PrE School Twin Study in Sweden. Shared environmental influences were found to be statistically indistinguishable from zero and to account for less than 5 % of the variance. We conclude that the presence of dominant genetic influences does not account for the absence of C on ADHD.

The role of oxytocin and oxytocin receptor gene variants in childhood-onset aggression

Aggressive antisocial behaviours are the most common reasons why adolescents are referred to mental health clinics. Antisocial behaviours are costly in social and financial terms. The aetiology of aggressive behaviours is unknown but growing evidence suggests it is heritable, and certain genetic variants have been implicated as contributing factors. The purpose of this study was to determine whether genes regulating the hormone oxytocin (OXT) were associated with aggressive antisocial behaviour. The case-control study sample consisted of 160 cases of children displaying extreme, persistent and pervasive aggressive behaviour. This case sample was compared with 160 adult controls. We used polymerase chain reaction (PCR) to determine the genotype for three oxytocin gene (OXT) single nucleotide polymorphisms (SNPs): rs3761248, rs4813625 and rs877172; and five oxytocin receptor gene (OXTR) SNPs: rs6770632, rs11476, rs1042778, rs237902 and rs53576. Genotypic analyses were performed using stata, while differences in haplotypic and allelic frequencies were analysed using Unphased. We also performed within-case analyses (n = 236 aggressive cases) examining genotypic and allelic associations with callous-unemotional (CU) scores (as measured by the psychopathic screening device). OXTR SNPs rs6770632 and rs1042778 may be associated with extreme, persistent and pervasive aggressive behaviours in females and males, respectively. These and haplotype results suggest gender-specific effects of SNPs. No significant differences were detected with respect to CU behaviours. These results may help to elucidate the biochemical pathways associated with aggressive behaviours, which may aid in the development of novel medications.

Human aggression across the lifespan: genetic propensities and environmental moderators

This chapter reviews the recent evidence of genetic and environmental influences on human aggression. Findings from a large selection of the twin and adoption studies that have investigated the genetic and environmental architecture of aggressive behavior are summarized. These studies together show that about half (50%) of the variance in aggressive behavior is explained by genetic influences in both males and females, with the remaining 50% of the variance being explained by environmental factors not shared by family members. Form of aggression (reactive, proactive, direct/physical, indirect/relational), method of assessment (laboratory observation, self-report, ratings by parents and teachers), and age of the subjects-all seem to be significant moderators of the magnitude of genetic and environmental influences on aggressive behavior. Neither study design (twin vs. sibling adoption design) nor sex (male vs. female) seems to impact the magnitude of the genetic and environmental influences on aggression. There is also some evidence of gene-environment interaction (G × E) from both twin/adoption studies and molecular genetic studies. Various measures of family adversity and social disadvantage have been found to moderate genetic influences on aggressive behavior. Findings from these G × E studies suggest that not all individuals will be affected to the same degree by experiences and exposures, and that genetic predispositions may have different effects depending on the environment.