Genetic and environmental architecture of human aggression

Associations between Omega-3 Index, Dopaminergic Genetic Variants and Aggressive and Metacognitive Traits: A Study in Adult Male Prisoners

Omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) are critical for cell membrane structure and function. Human beings have a limited ability to synthesise docosahexaenoic acid (DHA), the main n-3 LCPUFA required for neurological development. Inadequate levels of n-3 LCPUFA can affect the dopaminergic system in the brain and, when combined with genetic and other factors, increase the risk of developing aggression, inattention and impulse-control disorders. In this study, male prisoners were administered questionnaires assessing aggressive behaviour and executive functions. Participants also produced blood sampling for the measurement of the Omega-3 Index and the genotyping of dopaminergic genetic variants. Significant associations were found between functional genetic polymorphism in DBH rs1611115 and verbal aggression and between DRD2 rs4274224 and executive functions. However, the Omega-3 Index was not significantly associated with the tested dopaminergic polymorphisms. Although previous interactions between specific genotypes and n-3 LCPUFA were previously reported, they remain limited and poorly understood. We did not find any association between n-3 LCPUFA and dopaminergic polymorphisms in adult male prisoners; however, we confirmed the importance of genetic predisposition for dopaminergic genes (DBH and DRD2) in aggressive behaviour, memory dysfunction and attention-deficit disorder.

Association of serotonin system-related genes with homicidal behavior and criminal aggression in a prison population of Pakistani Origin

The serotonin transporter (SLC6A4), 5-HT_2A (HTR2A) and 5-HT_2B (HTR2B) recepter genes, express proteins that are important regulators of serotonin reuptake and signaling, and thereby may contribute to the pathogenesis of aggressive criminal behavior. 370 sentenced murderers in Pakistani prisons and 359 men without any history of violence or criminal delinquency were genotyped for six candidate polymorphisms in SLC6A4, HTR2A and HTR2B genes. An association of higher expressing L/L and L_A/L_A variants of the 5-HTTLPR polymorphism was observed with homicidal behavior (bi-allelic: OR = 1.29, p = 0.016, tri-allelic: OR = 1.32, p = 0.015) and in the murderer group only with response to verbal abuse (OR = 2.11, p = 0.015), but not with other measures of self-reported aggression. L/L and L_A/L_A genotypes of the 5-HTTLPR polymorphism were associated with higher aggression scores on STAX1 scale of aggression compared to lower expressing genotypes (S/S, S/L_G, L_G/L_G) in prison inmates. No associations were apparent for other serotonergic gene polymorphisms analyzed. Using the Braineac and GTEx databases, we demonstrated significant eQTL based functional effects for rs25531 in HTTLPR and other serotonergic polymorphisms analyzed in different brain regions and peripheral tissues. In conclusion, these findings implicate SLC6A4* HTTLPR as a major genetic determinant associated with criminal aggression. Future studies are needed to replicate this finding and establish the biologic intermediate phenotypes mediating this relationship.

Genetic and Environmental Influences on Different Forms of Bullying Perpetration, Bullying Victimization, and Their Co-occurrence

Bullying comes in different forms, yet most previous genetically-sensitive studies have not distinguished between them. Given the serious consequences and the high prevalence of bullying, it is remarkable that the aetiology of bullying and its different forms has been under-researched. We present the first study to investigate the genetic architecture of bullying perpetration, bullying victimization, and their co-occurrence for verbal, physical and relational bullying. Primary-school teachers rated 8215 twin children on bullying perpetration and bullying victimization. For each form of bullying, we investigated, through genetic structural equation modelling, the genetic and environmental influences on being a bully, a victim or both. 34% of the children were involved as bully, victim, or both. The correlation between being a bully and being a victim varied from 0.59 (relational) to 0.85 (physical). Heritability was ~ 70% for perpetration and ~ 65% for victimization, similar in girls and boys, yet both were somewhat lower for the relational form. Shared environmental influences were modest and more pronounced among girls. The correlation between being a bully and being a victim was explained mostly by genetic factors for verbal (~ 71%) and especially physical (~ 77%) and mostly by environmental factors for relational perpetration and victimization (~ 60%). Genes play a large role in explaining which children are at high risk of being a victim, bully, or both. For victimization this suggests an evocative gene-environment correlation: some children are at risk of being exposed to bullying, partly due to genetically influenced traits. So, genetic influences make some children more vulnerable to become a bully, victim or both.

MAOA variants differ in oscillatory EEG & ECG activities in response to aggression-inducing stimuli

Among the genetic variations in the monoamine oxidase A (MAOA) gene, upstream variable number tandem repeats (uVNTRs) of the promoter have been associated with individual differences in human physiology and aggressive behaviour. However, the evidence for a molecular or neural link between MAOA uVNTRs and aggression remains ambiguous. Additionally, the use of inconsistent promoter constructs in previous studies has added to the confusion. Therefore, it is necessary to demonstrate the genetic function of MAOA uVNTR and its effects on multiple aspects of aggression. Here, we identified three MAOA alleles in Koreans: the predominant 3.5R and 4.5R alleles, as well as the rare 2.5R allele. There was a minor difference in transcriptional efficiency between the 3.5R and 4.5R alleles, with the greatest value for the 2.5R allele, in contrast to existing research. Psychological indices of aggression did not differ among MAOA genotypes. However, our electroencephalogram and electrocardiogram results obtained under aggression-related stimulation revealed oscillatory changes as novel phenotypes that vary with the MAOA genotype. In particular, we observed prominent changes in frontal γ power and heart rate in 4.5R carriers of men. Our findings provide genetic insights into MAOA function and offer a neurobiological basis for various socio-emotional mechanisms in healthy individuals.

Non-invasive genotyping with a massively parallel sequencing panel for the detection of SNPs in HPA-axis genes

We designed a genotyping panel for the investigation of the genetic underpinnings of inter-individual differences in aggression and the physiological stress response. The panel builds on single nucleotide polymorphisms (SNPs) in genes involved in the three subsystems of the hypothalamic-pituitary-adrenal (HPA)-axis: the catecholamine, serotonin and corticoid metabolism. To promote the pipeline for use with wild animal populations, we used non-invasively collected faecal samples from a wild population of Assamese macaques (Macaca assamensis). We targeted loci of 46 previously reported SNPs in 21 candidate genes coding for elements of the HPA-axis and amplified and sequenced them using next-generation Illumina sequencing technology. We compared multiple bioinformatics pipelines for variant calling and variant effect prediction. Based on this strategy and the application of different quality thresholds, we identified up to 159 SNPs with different types of predicted functional effects among our natural study population. This study provides a massively parallel sequencing panel that will facilitate integrating large-scale SNP data into behavioural and physiological studies. Such a multi-faceted approach will promote understanding of flexibility and constraints of animal behaviour and hormone physiology.

Appetitive and reactive aggression are differentially associated with the STin2 genetic variant in the serotonin transporter gene

Appetitive aggression is a sub-category of instrumental aggression, characterised by the primary intrinsic enjoyment of aggressive activity. Aggression is heritable, and serotonergic and monoaminergic neurotransmitter systems have been found to contribute to the underlying molecular mechanisms. The aim of this study was to investigate the role that genetic variants in the serotonin transporter (SLC6A4) and monoamine oxidase A (MAOA) genes play in the aetiology of appetitive aggression in South African Xhosa males (n = 290). SLC6A4 5-HTTLPR, rs25531, and STin2 variants, as well as MAOA-uVNTR were investigated for their association with levels of appetitive aggression using Poisson regression analysis. The STin2 VNTR12 allele was found to be associated with increased levels of appetitive aggression (p = 0.003), but with decreased levels of reactive aggression (p = 7 × 10^-5). This study is the first to investigate genetic underpinnings of appetitive aggression in a South African population, with preliminary evidence suggesting that SCL6A4 STin2 variants play a role in its aetiology, and may also be important in differentiating between appetitive and reactive aggression. Although the results require replication, they shed some preliminary light on the molecular dichotomy that may underlie the two forms of aggression.

Polymorphisms in dopaminergic system genes; association with criminal behavior and self-reported aggression in violent prison inmates from Pakistan

Genetic factors contribute to antisocial and criminal behavior. Dopamine transporter DAT-1 (SLC6A3) and DRD2 gene for the dopamine-2 receptor are dopaminergic system genes that regulate dopamine reuptake and signaling, and may be part of the pathogenesis of psychiatric disorders including antisocial behaviors and traits. No previous studies have analyzed DAT-1 and DRD2 polymorphisms in convicted murderers, particularly from Indian subcontinent. In this study we investigated the association of 40 bp VNTR polymorphism of DAT-1 and Taq1 variant of DRD2 gene (rs1800479) with criminal behavior and self-reported aggression in 729 subjects, including 370 men in Pakistani prisons convicted of first degree murder(s) and 359 control men without any history of violence or criminal tendency. The 9R allele of DAT-1 VNTR polymorphism was more prevalent in convicted murderers compared with control samples, for either one or two risk alleles (OR = 1.49 and 3.99 respectively, P = 0.003). This potential association of DAT-1 9R allele polymorphism with murderer phenotype was confirmed assuming different genetic models of inheritance. However, no genetic association was found for DRD2 Taq1 polymorphism. In addition, a combined haplotype (9R-A2) of DAT-1 and DRD2 genes was associated with this murderer phenotype. Further, 9R allele of DAT-1 was also associated with response to verbal abuse and parental marital complications, but not with other measures pertinent to self-reported aggression. These results suggest that 9R allele, which may influence levels of intra-synaptic dopamine in the brain, may contribute to criminal tendency in this sample of violent murderers of Pakistani origin. Future studies are needed to replicate this finding in other populations of murderers and see if this finding extends to other forms of violence and lesser degrees of aggression.

Looking for reward in all the wrong places: dopamine receptor gene polymorphisms indirectly affect aggression through sensation-seeking

Individuals with genotypes that code for reduced dopaminergic brain activity often exhibit a predisposition toward aggression. However, it remains largely unknown how dopaminergic genotypes may increase aggression. Lower-functioning dopamine systems motivate individuals to seek reward from external sources such as illicit drugs and other risky experiences. Based on emerging evidence that aggression is a rewarding experience, we predicted that the effect of lower-functioning dopaminergic functioning on aggression would be mediated by tendencies to seek the environment for rewards. Caucasian female and male undergraduates (N = 277) were genotyped for five polymorphisms of the dopamine D2 receptor (DRD2) gene; they reported their previous history of aggression and their dispositional reward-seeking. Lower-functioning DRD2 profiles were associated with greater sensation-seeking, which then predicted greater aggression. Our findings suggest that lower-functioning dopaminergic activity puts individuals at risk for violence because it motivates them to experience aggression's hedonically rewarding qualities.

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.

Motivation for aggressive religious radicalization: goal regulation theory and a personality × threat × affordance hypothesis

A new set of hypotheses is presented regarding the cause of aggressive religious radicalization (ARR). It is grounded in classic and contemporary theory of human motivation and goal regulation, together with recent empirical advances in personality, social, and neurophysiological psychology. We specify personality traits, threats, and group affordances that combine to divert normal motivational processes toward ARR. Conducive personality traits are oppositional, anxiety-prone, and identity-weak (i.e., morally bewildered). Conducive threats are those that arise from seemingly insurmountable external forces and frustrate effective goal regulation. Conducive affordances include opportunity for immediate and concrete engagement in active groups that are powered by conspiracy narratives, infused with cosmic significance, encouraging of moral violence, and sealed with religious unfalsifiability. We propose that ARR is rewarding because it can spur approach motivated states that mask vulnerability for people whose dispositions and circumstances would otherwise leave them mired in anxious distress.

Genetic associations with intimate partner violence in a sample of hazardous drinking men in batterer intervention programs

The etiology of intimate partner violence (IPV) is multifactorial. However, etiological theories of IPV have rarely included potential genetic factors. The purpose of the present study was to examine whether a cumulative genetic score (CGS) containing the monoamine oxidase A (MAOA) and the human serotonin transporter gene linked polymorphism (5-HTTLPR) was associated with IPV perpetration after accounting for the effects of alcohol problems, drug problems, age, and length of relationship. We obtained DNA from 97 men in batterer intervention programs in the state of Rhode Island. In the full sample, the CGS was significantly associated with physical and psychological aggression and injuries caused to one's partner, even after controlling for the effects of alcohol problems, drug problems, age, and length of relationship. Two of the men in the sample likely had Klinefelter's syndrome, and analyses were repeated excluding these two individuals, leading to similar results. The implications of the genetic findings for the etiology and treatment of IPV among men in batterer intervention programs are briefly discussed.

Aggression and polymorphisms in AR, DAT1, DRD2, and COMT genes in Datoga pastoralists of Tanzania

The aim of this study was to analyse the relationships between polymorphisms in four candidate genes (AR, DAT1, DRD2, and COMT) and aggression in men from a traditional society of East African pastoralists, the Datoga. Buss and Perry's Aggression Questionnaire was used to measure aggression. The number of CAG repeats in the AR gene was negatively correlated with physical aggression, anger, and hostility. Among the genes of the dopaminergic system, a significant single-gene effect was detected only for DRD2 with regard to anger. At the level of a two-gene model, a significant effect for DRD2 and a tendency for DAT1 were observed for the DAT1-DRD2 gene pair regarding hostility, and two tendencies were observed for the interaction effect of the DAT1-COMT pair regarding anger and hostility. These data suggest a probable link between physical aggression and direct fitness caused by strong sexual selection in Datoga men.

Understanding aggressive behaviour across the lifespan

Aggressive behaviour is the observable manifestation of aggression and is often associated with developmental transitions and a range of medical and psychiatric diagnoses across the lifespan. As healthcare professionals involved in the medical and psychosocial care of patients from birth through death, nurses frequently encounter - and may serve as - both victims and perpetrators of aggressive behaviour in the workplace. While the nursing literature has continually reported research on prevention and treatment approaches, less emphasis has been given to understanding the aetiology, including contextual precipitants of aggressive behaviour. This paper provides a brief review of the biological, social and environmental risk factors that purportedly give rise to aggressive behaviour. Further, many researchers have focused specifically on aggressive behaviour in adolescence and adulthood. Less attention has been given to understanding the aetiology of such behaviour in young children and older adults. This paper emphasizes the unique risk factors for aggressive behaviour across the developmental spectrum, including childhood, adolescence, adulthood and late life. Appreciation of the risk factors of aggressive behaviour, and, in particular, how they relate to age-specific manifestations, can aid nurses in better design and implementation of prevention and treatment programmes.

Externalizing problems, attention regulation, and household chaos: a longitudinal behavioral genetic study

Previous research documented a robust link between difficulties in self-regulation and development of externalizing problems (i.e., aggression and delinquency). In this study, we examined the longitudinal additive and interactive genetic and environmental covariation underlying this well-established link using a twin design. The sample included 131 pairs of monozygotic twins and 173 pairs of same-sex dizygotic twins who participated in three waves of annual assessment. Mothers and fathers provided reports of externalizing problems. Teacher report and observer rating were used to assess twin's attention regulation. The etiology underlying the link between externalizing problems and attention regulation shifted from a common genetic mechanism to a common environmental mechanism in the transition across middle childhood. Household chaos moderated the genetic variance of and covariance between externalizing problems and attention regulation. The genetic influence on individual differences in both externalizing problems and attention regulation was stronger in more chaotic households. However, higher levels of household chaos attenuated the genetic link between externalizing problems and attention regulation.

Serotonin receptor 1B genotype and hostility, anger and aggressive behavior through the lifespan: the Young Finns study

The serotonin system has been shown to be involved in the regulation of hostility, anger, and aggressive behavior. Previous molecular genetic studies suggest that the serotonin receptor 1B (HTR1B) rs6296 genotype might have a particular role in these types of behaviors. We examined whether HTR1B is related to hostility, anger, and aggressive behavior phenotypes over a lifespan and whether it modifies the connection between childhood aggressive behavior and adulthood hostility and anger. The participants were 967 women and men from a large population based sample (The Young Finns Study) with a 27-year follow-up. Childhood aggressive behavior was reported by the mother twice when the participants were 3 to 12 years of age. Adulthood hostility and anger were self-reported by the participants between ages 24 and 36. Childhood aggressive behavior predicted adulthood hostility over 27 years. HTR1B SNP rs6296 was associated with childhood aggressive behavior but not with adulthood anger or hostility. The HTR1B SNP rs6296 modified the association between childhood aggressive behavior and adulthood hostility. Aggressive behavior and hostility might form a life course pattern, and the HTR1B might contribute to a development of this pattern.

Genetic and environmental influences underlying externalizing behaviors, cigarette smoking and illicit drug use across adolescence

We investigated genetic and environmental influences common to adolescent externalizing behavior (at age 12), smoking (at age 14) and initiation of drug use (at age 17) using the FinnTwin12 cohort data. Multivariate Cholesky models were fit to data from 737 monozygotic and 722 dizygotic twin pairs. Heritability of externalizing behavior was 56%, that of smoking initiation/amount 20/32%, and initiation of drug use 27%. In the best-fitting model common environmental influences explained most of the covariance between externalizing behavior and smoking initiation (69%) and amount (77%). Covariance between smoking initiation/amount and drug use was due to additive genetic (42/22%) and common environmental (58/78%) influences. Half of the covariance between externalizing behavior and drug use was due to shared genetic and half due to the environments shared by co-twins. Using a longitudinal, prospective design, our results indicate that early observed externalizing behavior provides significant underlying genetic and environmental influences common to later substance use, here manifested as initiation of drug use in late adolescence.

Gene-environment interplay in the association between pubertal timing and delinquency in adolescent girls

Early pubertal timing places girls at elevated risk for a breadth of negative outcomes, including involvement in delinquent behavior. While previous developmental research has emphasized the unique social challenges faced by early maturing girls, this relation is complicated by genetic influences for both delinquent behavior and pubertal timing, which are seldom controlled for in existing research. The current study uses genetically informed data on 924 female-female twin and sibling pairs drawn from the National Longitudinal Study of Adolescent Health to (1) disentangle biological versus environmental mechanisms for the effects of early pubertal timing and (2) test for gene-environment interactions. Results indicate that early pubertal timing influences girls' delinquency through a complex interplay between biological risk and environmental experiences. Genes related to earlier age at menarche and higher perceived development significantly predict increased involvement in both nonviolent and violent delinquency. Moreover, after accounting for this genetic association between pubertal timing and delinquency, the impact of nonshared environmental influences on delinquency are significantly moderated by pubertal timing, such that the nonshared environment is most important among early maturing girls. This interaction effect is particularly evident for nonviolent delinquency. Overall, results suggest early maturing girls are vulnerable to an interaction between genetic and environmental risks for delinquent behavior.

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

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

Observed externalizing behavior: a developmental comparison of genetic and environmental influences across three samples

Estimates of genetic and environmental influences on externalizing behavior are markedly inconsistent. In an attempt to refine and extend our knowledge of externalizing behavior, the current study examined the etiology of externalizing behavior using observational data in middle childhood and adolescence from three twin and sibling samples. Observational ratings offer a unique perspective on externalizing behavior rarely examined within behavioral genetic designs. Shared environmental influences were significant and moderate to large in magnitude across all three samples (i.e., 44, 77, and 38%), while genetic influences (31%) were significant only for the adolescent sample. All three samples showed greater shared environmental influences and less genetic influence than is typically found when examining self-, parent-, and teacher-reports of externalizing behavior. These findings are consistent with other reports that have found evidence for shared environmental influences on measures of child externalizing behavior-in direct contrast to a commonly held perception that shared environmental factors do not have significant influences on behavior beyond early childhood.

Repeatability and heritability of behavioural types in a social cichlid

Aim. The quantitative genetics underlying correlated behavioural traits (''animal personality") have hitherto been studied mainly in domesticated animals. Here we report the repeatability (R) and heritability (h(2)) of behavioural types in the highly social cichlid fish Neolamprologus pulcher. Methods. We tested 1779 individuals repeatedly and calculated the h(2) of behavioural types by variance components estimation (GLMM REML), using 1327 offspring from 162 broods from 74 pairs. Results. Repeatability of behavioural types was significant and considerable (0.546), but declined from 0.83 between tests conducted on the same day, to 0.19 on tests conducted up to 1201 days apart. All h(2) estimates were significant but low (e.g., pair identity h(2) = 0.15 ± 0.03 SE). Additionally, we found significant variation between broods nested within the parent(s), but these were not related to several environmental factors tested. Conclusions. We conclude that despite a considerable R, h(2) in this cichlid species is low, and variability in behavioural type appears to be strongly affected by other (non)genetic effects.

Adolescent sexual activity and the development of delinquent behavior: the role of relationship context

Despite the well-established association between adolescent sexual activity and delinquent behavior, little research has examined the potential importance of relationship contexts in moderating this association. The current study used longitudinal, behavioral genetic data on 519 same-sex twin pairs (48.6% female) divided into two age cohorts (13-15 and 16-18 years olds) drawn from the National Longitudinal Study of Adolescent Health. Analyses tested whether adolescent sexual activity that occurred in romantic versus non-romantic relationships was associated with delinquency from adolescence to early adulthood, after controlling for genetic influences. Results indicated that, for both younger and older adolescents, common underlying genes influence both sexual behavior and delinquency. After controlling for these genetic influences, there was no within-twin pair association between sexual activity and delinquency in younger adolescents. In older adolescents, sexual activity that occurred in romantic relationships predicted lower levels of delinquency, both cross-sectionally and longitudinally, whereas sexual activity in non-romantic relationships predicted higher levels of delinquency. These results are consistent with emerging research that suggests that the psychological correlates of adolescent sexual activity may be moderated by the social context in which this activity occurs.

Multivariate behavior genetic analyses of aggressive behavior subtypes

This study examined the genetic and environmental architecture underlying aggressive behavior measured by the Life History of Aggression Questionnaire (LHA; Coccaro et al. 1997a). Following preliminary phenotypic factor analysis procedures, multivariate behavioral genetics models were fit to responses from 2,925 adult twins from the PennTwins cohort on five LHA items assessing lifetime frequency of temper tantrums, indirect aggression, verbal aggression, fighting, and physical assault. The best-fitting model was a 2-factor common pathway model, indicating that these five aggressive behaviors are underpinned by two distinct etiological factors with different genetic and nonshared environmental influences. Although there was evidence of significant sex differences, the structure of the two factors appeared to be quite similar in males and females, where General Aggression and Physical Aggression factors emerged. Heritability of these factors ranged from .37 to .57, and nonshared environmental effects ranged from .43 to .63. The results of this study highlight the heterogeneous nature of the aggression construct and the need to consider differences in genetic and environmental influences on individual aggressive behaviors in a multivariate context.

Maternal cigarette smoking during pregnancy and offspring externalizing behavioral problems: a propensity score matching analysis

A body of empirical research has revealed that prenatal exposure to tobacco smoke is related to a host of negative outcomes, including reduced cognitive abilities, later-life health problems, and childhood behavioral problems. While these findings are often interpreted as evidence of the causal role that prenatal exposure to tobacco smoke has on human phenotypes, emerging evidence has suggested that the association between prenatal exposure to tobacco smoke and behavioral phenotypes may be spurious. The current analysis of data from the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B) revealed that the association between prenatal exposure to cigarette smoke and externalizing behavioral problems was fully accounted for by confounding factors. The implications that these findings have for policy and research are discussed.

The heterogeneity of disruptive behavior disorders - implications for neurobiological research and treatment

Disruptive behavior disorders (DBDs) are reflected by a great variety of symptoms ranging from impulsive-hot-tempered quarrels to purposeful and goal-directed acts of cruelty. A growing body of data indicates that there are neurobiological factors that increase the risk for developing DBDs. In this review, we give a broad overview of recent studies investigating physiological, neural, genetic factors, and specific neurotransmitter systems. We also discuss the impact of psychosocial risk and consider the effects of gene-environment interactions. Due to the heterogeneity of DBDs, it is concluded that specific subtypes of disruptive behavior should be considered both in terms their biological basis and in regard to specific treatment needs.

Infant pathways to externalizing behavior: evidence of Genotype x Environment interaction

To further the understanding of the effects of early experiences, 9-month-old infants were observed during a frustration task. The analytical sample was composed of 348 linked triads of participants (adoptive parents, adopted child, and birth parent[s]) from a prospective adoption study. It was hypothesized that genetic risk for externalizing problems and affect dysregulation in the adoptive parents would independently and interactively predict a known precursor to externalizing problems: heightened infant attention to frustrating events. Results supported the moderation hypotheses involving adoptive mother affect dysregulation: Infants at genetic risk showed heightened attention to frustrating events only when the adoptive mother had higher levels of anxious and depressive symptoms. The Genotype x Environment interaction pattern held when substance use during pregnancy was considered.

School performance and genetic and environmental variance in antisocial behavior at the transition from adolescence to adulthood

Antisocial behavior increases in adolescence, particularly among those who perform poorly in school. As adolescents move into adulthood, both educational attainment and the extent to which antisocial behavior continues have implications for adolescents' abilities to take on constructive social roles. The authors used a population-representative longitudinal twin study to explore how links among genetic and environmental influences at ages 17 and 24 may be implicated in the developmental processes involved. At age 17, expression of both genetic and nonshared environmental vulnerabilities unique to antisocial behavior was greater among those with low GPA than among those with higher GPA. This suggested that maintenance of high GPA buffered the impact of both genetic and environmental influences encouraging antisocial behavior. When GPA was high, both genetic and environmental influences involved in both traits encouraged good school performance and restrained antisocial behavior. At age 24, however, correlated family environmental influences drove the association between educational attainment and antisocial behavior. Antisocial characteristics involving school performance and educational attainment that transcend generations may slot individuals into social categories that restrict opportunities and reinforce antisocial characteristics.

Differential genetic and environmental influences on reactive and proactive aggression in children

While significant heritability for childhood aggression has been claimed, it is not known whether there are differential genetic and environmental contributions to proactive and reactive forms of aggression in children. This study quantifies genetic and environmental contributions to these two forms of aggression in an ethnically diverse urban sample of 9-10 year old twins (N = 1219), and compares results across different informants (child self-report, mother, and teacher ratings) using the Reactive-Proactive Aggression Questionnaire (RPQ). Confirmatory factor analysis of RPQ items indicated a significant and strong fit for a two-factor proactive-reactive model which was significantly superior to a one-factor model and which replicated across gender as well as the three informant sources. Males scored significantly higher than females on both self-report reactive and proactive aggression, findings that replicated on mother and teacher versions of the RPQ. Asian-Americans scored lower than most ethnic groups on reactive aggression yet were equivalent to Caucasians on proactive aggression. African-Americans scored higher than other ethnic groups on all measures of aggression except caregiver reports. Heritable influences were found for both forms of aggression across informants, but while boys' self-reports revealed genetic influences on proactive (50%) and reactive (38%) aggression, shared and non-shared environmental influences almost entirely accounted for girls' self-report reactive and proactive aggression. Although genetic correlations between reactive and proactive aggression were significant across informants, there was evidence that the genetic correlation was less than unity in boys self reported aggression, indicating that genetic factors differ for proactive and reactive aggression. These findings provide the first evidence for varying genetic and environmental etiologies for reactive and proactive aggression across gender, and provide additional support for distinction between these two forms of aggression.

Depression and internally directed aggression: genetic and environmental contributions

This study uses behavior genetic (BG) methodology to investigate Freud's theory of depression as aggression directed toward the self (1930) and the extent to which genetically and environmentally influenced aggressive tendencies contribute to depressive symptoms. Data from the Twin and Offspring Study in Sweden (TOSS) is used to demonstrate how, in estimating shared and unique environmental influences, BG methods can inform psychoanalytic theory and practice, particularly because of their shared emphasis on the importance of individual experience in development. The TOSS sample consists of 909 pairs of adult twins, their partners, and one adolescent child per couple. The Center for Epidemiologic Studies Depression Scale (Radloff 1977) was used to measure depressive symptoms and the Karolinska Scales of Personality (Schalling and Edman 1993) to measure internally directed aggression. Genetic analyses indicated that for both men and women, their unique experiences as well as genetic factors contributed equally to the association between internally directed aggression and depressive symptoms. These findings support Freud's theory that constitutionally based differences in aggression, along with individual experiences, contribute to a person's depressive symptoms. Establishing that an individual's unique, not shared, experiences and perceptions contribute to depressive symptoms and internally directed aggression reinforces the use of patient-specific treatment approaches implemented in psychoanalytic psychotherapy or psychoanalysis.

Linkages between children's and their friends' social and physical aggression: evidence for a gene-environment interaction?

Based on a sample of 406 seven-year-old twins, this study examined whether exposure to friends' social or physical aggression, respectively, moderates the effect of heritability on children's own social and physical aggression. Univariate analyses showed that children's own social and physical aggression were significantly explained by genetic factors, whereas friends' social and physical aggression represented "true" environmental factors that were unrelated to children's genetic dispositions. Multivariate analyses further suggested a possible gene-environment interaction in the link between friends' and children's physical aggression but not in the link between friends' and children's social aggression. Instead, friends' social aggression was directly related to children's social aggression, in addition to genetic effects on this behavior. Theoretical and practical implications of these results are discussed.

Rethinking Timing of First Sex and Delinquency

The relation between timing of first sex and later delinquency was examined using a genetically informed sample of 534 same-sex twin pairs from the National Longitudinal Study of Adolescent Health, who were assessed at three time points over a 7-year interval. Genetic and environmental differences between families were found to account for the association between earlier age at first sex and increases in delinquency. After controlling for these genetic and environmental confounds using a quasi-experimental design, earlier age at first sex predicted lower levels of delinquency in early adulthood. The current study is contrasted with previous research with non-genetically informative samples, including Armour and Haynie. Results suggest a more nuanced perspective on the meaning and consequences of adolescent sexuality than is commonly put forth in the literature.

Serotonin transporter polymorphism and borderline or antisocial traits among low-income young adults

OBJECTIVES

The short allele of the serotonin transporter linked polymorphic region, 5HTTLPR has been associated with anxiety, major depressive disorder and suicidality. The impulsive self- and other-damaging behaviors seen in borderline personality disorder and antisocial personality disorder also have substantial comorbidity with depression but are associated with more severe environmental stressors. This study tested the hypothesis of an association between the short allele of the 5HTTLPR and borderline or antisocial traits in young adulthood.

METHODS

The 5HTTLPR was genotyped among 96 young adults from low to moderate income families (62 adults without and 34 adults with borderline personality disorder or antisocial personality disorder traits). Traits of borderline and antisocial personality disorders were assessed with the Structured Clinical Interview for Diagnosis-Axis II.

RESULTS

The number of short 5HTTLPR alleles were significantly related to incidence of borderline personality disorder or antisocial personality disorder traits and also to each set of traits independently. Male sex and quality of care in infancy were also associated with incidence of borderline personality disorder and antisocial personality disorder traits but did not account for the association with the short allele. Depressive disorders were not associated with the short allele in this sample.

CONCLUSIONS

Young adults of lower socioeconomic status who carry the short 5HTTLPR allele may be especially vulnerable to developing antisocial or borderline traits by young adulthood.

Alcohol use in adolescent twins and affiliation with substance using peers

Affiliation with substance using peers is one of the strongest predictors of adolescent alcohol use. This association is typically interpreted causally: peers who drink incite their friends to drink. This association may be complicated by uncontrolled genetic and environmental confounds because teens with familial predispositions for adolescent substance use may be more likely to select into social networks where drinking is common. We test this alternative hypothesis using a sample of 1,820 twin and sibling pairs, and their same-sex best friends, from three waves of the National Longitudinal Study of Adolescent Health. Across all three waves, peer report of substance use did not influence adolescent alcohol use when genetic and shared environmental predispositions for drinking were considered. The association between alcohol use and peer behavior may be a spurious association attributable to a shared genetic liability to drink alcohol and associate with peers who drink alcohol.

Multivariate Cholesky models of human female fertility patterns in the NLSY

Substantial evidence now exists that variables measuring or correlated with human fertility outcomes have a heritable component. In this study, we define a series of age-sequenced fertility variables, and fit multivariate models to account for underlying shared genetic and environmental sources of variance. We make predictions based on a theory developed by Udry [(1996) Biosocial models of low-fertility societies. In: Casterline, JB, Lee RD, Foote KA (eds) Fertility in the United States: new patterns, new theories. The Population Council, New York] suggesting that biological/genetic motivations can be more easily realized and measured in settings in which fertility choices are available. Udry's theory, along with principles from molecular genetics and certain tenets of life history theory, allow us to make specific predictions about biometrical patterns across age. Consistent with predictions, our results suggest that there are different sources of genetic influence on fertility variance at early compared to later ages, but that there is only one source of shared environmental influence that occurs at early ages. These patterns are suggestive of the types of gene-gene and gene-environment interactions for which we must account to better understand individual differences in fertility outcomes.

Proximal peer-level effects of a small-group selected prevention on aggression in elementary school children: an investigation of the peer contagion hypothesis

Examined peer contagion in small group, selected prevention programming over one school year. Participants were boys and girls in grades 3 (46 groups, 285 students) and 6 (36 groups, 219 students) attending school in low-resource, inner city communities or moderate resource urban communities. Three-level hierarchical linear modeling (observations within individuals within groups) indicated that individual change in aggression over time related to the average aggression of others in the intervention group. The individual child was "pulled" toward peers' mean level of aggression; so the intervention appeared to reduce aggression for those high on aggression, and to make those low on aggression more aggressive. Effects appeared to be magnified in either direction when the child was more discrepant from his or her peers. From these results we derive a principle of "discrepancy-proportional peer-influence" for small group intervention, and discuss the implications of this for aggregating aggressive children in small group programs.

Examining Genetic and Environmental Effects on Social Aggression: A Study of 6-Year-Old Twins

Using a genetic design of 234 six-year-old twins, this study examined (a) the contribution of genes and environment to social versus physical aggression, and (b) whether the correlation between social and physical aggression can be explained by similar genetic or environmental factors or by a directional link between the phenotypes. For social aggression, substantial (shared and unique) environmental effects but only weak genetic effects were found. For physical aggression, significant effects of genes and unique environment were found. Bivariate modeling suggests that social and physical aggression share most of their underlying genes but only very few overlapping environmental factors. The correlation between the two phenotypes can also be explained by a directional effect from physical to social aggression.

Genetic and environmental (inter)actions in male mouse lines selected for aggressive and nonaggressive behavior

The purpose of this study was to investigate the effects of genetic and environmental factors, as well as their interaction, in the etiology of aggressive behavior in two mouse lines bidirectionally selected for offensive aggression. To this end, we raised the Finnish TA (aggressive) and TNA (nonagressive) selection lines either in isolation or in cohabitation with a female after weaning. At the age of 3 months we determined their aggressive behavior in three paradigms (intruder resident, neutral cage, resident intruder) against a male standard opponent. We also determined the animals' aggressive behavior against a female mouse. The results show genetic and environmental effects, as well as gene-environment interaction. We see prominent genotype effects under all conditions but each test is sensitive to a specific combination of environmental effects. A particularly noteworthy result is that variation in the unusual behavior of aggression towards a female is largely explained by the interaction of genotype with isolation. We also examined whether test experience influenced the outcome of an encounter between an experimental animal and an opponent, and found that this factor should not be underestimated, its effect size and direction depending on the type of paradigm and way of housing. These data suggest that the identification of genes underlying aggressive behavior in mice is by no means straightforward and that the result of this search will depend on the environmental design of the study (type of paradigm, housing conditions). These data also suggest that the use of 'test battery' mice might produce different results than the use of test-naïve animals.

A biopsychosocial model of the development of chronic conduct problems in adolescence

A biopsychosocial model of the development of adolescent chronic conduct problems is presented and supported through a review of empirical findings. This model posits that biological dispositions and sociocultural contexts place certain children at risk in early life but that life experiences with parents, peers. and social institutions increment and mediate this risk. A transactional developmental model is best equipped to describe the emergence of chronic antisocial behavior across time. Reciprocal influences among dispositions, contexts, and life experiences lead to recursive iterations across time that exacerbate or diminish antisocial development. Cognitive and emotional processes within the child, including the acquisition of knowledge and social-information-processing patterns, mediate the relation between life experiences and conduct problem outcomes. Implications for prevention research and public policy are noted.