The Association Between Peer and own Aggression is Moderated by the BDNF Val-met Polymorphism

Age Effects Aggressive Behavior: RNA-Seq Analysis in Cattle with Implications for Studying Neoteny Under Domestication

The reactive type of aggression is regulated mostly by the brain's prefrontal cortex; however, the molecular changes underlying aggressiveness in adults have not been fully characterized. We used an RNA-seq approach to investigate differential gene expression in the prefrontal cortex of bovines from the aggressive Lidia breed at different ages: young three-year old and adult four-year-old bulls. A total of 50 up and 193 down-regulated genes in the adult group were identified. Furthermore, a cross-species comparative analysis retrieved 29 genes in common with previous studies on aggressive behaviors, representing an above-chance overlap with the differentially expressed genes in adult bulls. We detected changes in the regulation of networks such as synaptogenesis, involved in maintenance and refinement of synapses, and the glutamate receptor pathway, which acts as excitatory driver in aggressive responses. The reduced reactive aggression typical of domestication has been proposed to form part of a retention of juvenile traits as adults (neoteny).

MicroRNA-206 Regulates Stress-Provoked Aggressive Behaviors in Post-weaning Social Isolation Mice

When facing stressful conditions, some people tend to be impulsively aggressive whereas others are not. However, the causes and underlying mechanisms remain elusive. It has been reported that acute stress induces outbursts of aggression in post-weaning social isolation (SI) mice but not in group housing (GH) mice. Here we report epigenetic regulation of impulsive aggression in SI mice. At post-natal day 21, mice were randomly assigned to GH or SI groups. We found that SI mice exhibited a higher level of microRNA 206 (miR-206) compared with GH mice. Intra-hippocampal injection of AM206, an antagomir of miR-206, decreased stress-induced attack behavior in SI mice and increased BDNF expression. Moreover, BDNF expression was required for AM206 effects on the reduction of aggression. On the other hand, miR-206 overexpression in GH mice induced attack behavior. Intranasal administration of AM206 rather than a scramble control significantly reduced attack behavior and depression-like behavior in SI mice. Our results suggest that miR-206 mediates development of maladaptive impulsive aggression in early life adversity and that its antagomir could potentially be a therapeutic target against stress-exacerbated aggressive behavior.

Are Owls and Larks Different When it Comes to Aggression? Genetics, Neurobiology, and Behavior

This review focuses on the contribution of circadian rhythms to aggression with a multifaceted approach incorporating genetics, neural networks, and behavior. We explore the hypothesis that chronic circadian misalignment is contributing to increased aggression. Genes involved in both circadian rhythms and aggression are discussed as a possible mechanism for increased aggression that might be elicited by circadian misalignment. We then discuss the neural networks underlying aggression and how dysregulation in the interaction of these networks evoked by circadian rhythm misalignment could contribute to aggression. The last section of this review will present recent human correlational data demonstrating the association between chronotype and/or circadian misalignment with aggression. With circadian rhythms and aggression being a burgeoning area of study, we hope that this review initiates more interest in this promising and topical area.

Predicting risk of suicidal ideation in youth using a multigene panel for impulsive aggression

Childhood traumatic experiences and impulsive aggression are strong predictors of suicide ideation in youth.  This study examines whether a gene panel previously associated with impulsive aggression, together with a measure of traumatic experience, will predict suicidal ideation in youth. The sample consisted of 158 youth (ages 9-17 years) of European ancestry that participated in a case-control study for childhood aggression.  The Massachusetts Youth Screening Instrument (MAYSI-2) was used to examine suicide ideation and traumatic experiences. The impulsive aggression gene panel consists of 5 markers across 5 susceptibility genes (CRH, CRHR2, MC2R, OXTR, BDNF). A multi-gene risk score (MRS) for each individual was calculated by taking the total number of risk genotypes for that person. The covariates for the multiple regression model included sex, age, symptoms of anxiety/depression, MRS, traumatic experiences, and MRS x traumatic experience interaction. Results show the MRS x traumatic experience interaction term and the anxious/depressed symptoms to be significant predictors of suicide ideation in the full model. Importantly, genetic susceptibility to impulsive aggression and traumatic experiences remained a significant predictor for suicide ideation over and above the youth's level of anxiety and depression. This finding may have important implications for early intervention for youth suicide-related behaviors.

Catechol-O-Methyltransferase Val158Met and brain-derived neurotrophic factor Val66Met gene polymorphisms in paraphilic sexual offenders

BACKGROUND

Child sexual abuse (CSA) is an important problem worldwide. The reason of sex abuse is considered as multifactorial. Genetic contribution reported by recent studies is a significant evidence for this pathologic behavior. Catechol-O-Methyltransferase (COMT) is an enzyme in the metabolic inactivation of catecholamine and substances containing catecholamines such as dopamine, epinephrine, and norepinephrine. COMT polymorphism causes functional changes in COMT enzyme activity. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor usually synthesized from central nervous system neurons. With the effect of BDNF, dopamine and serotonin play important roles on neurogenesis, survival, and synaptic plasticity.

AIM

This study aims to examine COMT Val158Met (rs4680) and BDNF Val66Met (rs6265) polymorphisms in CSA.

SETTINGS AND DESIGN

This was a case-control study.

MATERIALS AND METHODS

Seventy paraphilic child sexual abuser patients and seventy age- and gender-matched healthy controls participated in this study. COMT Val158Met and BDNF Val66Met polymorphisms were genotyped by real-time polymerase chain reaction assay.

RESULTS

COMT Val158Met genotype frequencies were determined as GG 31.4%, GA 45.7%, and AA 22.9% in patients; GG 24.3%, GA 45.7%, and AA 8.6% in controls; and exhibited a positive relationship between the groups (P = 0.018). BDNF Val66Met genotype frequencies were determined as GG 77.1%, GA 21.4%, and AA 1.4% in patients; GG 65.7%, GA 31.4%, AA 2.9% in controls; and no significant relationship was observed between the groups (P = 0.317).

CONCLUSIONS

This research investigated COMT (Val158Met) and BDNF (Val66Met) in paraphilic child sexual offenders. A positive relationship was found for COMT gene; however, no significant relation was observed for BDNF gene between paraphilic sexual offenders and controls.

The interplay of polygenic plasticity and adrenocortical activity as sources of variability in pathways among family adversity, youth emotional reactivity, and psychological problems

This study examined the interplay between a polygenic composite and cortisol activity as moderators of the mediational pathway among family adversity, youth negative emotional reactivity to family conflict, and their psychological problems. The longitudinal design contained three annual measurement occasions with 279 adolescents (Mean age = 13.0 years) and their parents. Latent difference score analyses indicated that observational ratings of adversity in interparental and parent-child interactions at Wave 1 predicted increases in a multimethod, multi-informant assessment of youth negative emotional reactivity to family conflict from Waves 1 to 2. Changes in youth negative emotional reactivity, in turn, predicted increases in a multi-informant (i.e., parents, adolescent, and teacher) assessment of psychological problems from Waves 1 to 3. Consistent with differential susceptibility theory, the association between family adversity and negative emotional reactivity was stronger for adolescents who carried more sensitivity alleles in a polygenic composite consisting of 5-HTTLPR, DRD4 VNTR, and BDNF polymorphisms. Analyses of adolescent cortisol in the period surrounding a family disagreement task at Wave 1 revealed that overall cortisol output, rather than cortisol reactivity, served as an endophenotype of the polygenic composite. Overall cortisol output was specifically associated with polygenic plasticity and moderated the association between family adversity and youth negative emotional reactivity in the same for better or for worse manner as the genetic composite. Finally, moderator-mediated-moderation analyses indicated that the moderating role of the polygenic plasticity composite was mediated by the moderating role of adolescent cortisol output in the association between family adversity and their emotional reactivity.

Postnatal TrkB ablation in corticolimbic interneurons induces social dominance in male mice

The tight balance between synaptic excitation and inhibition (E/I) within neocortical circuits in the mammalian brain is important for complex behavior. Many loss-of-function studies have demonstrated that brain-derived neurotrophic factor (BDNF) and its cognate receptor tropomyosin receptor kinase B (TrkB) are essential for the development of inhibitory GABAergic neurons. However, behavioral consequences of impaired BDNF/TrkB signaling in GABAergic neurons remain unclear, largely due to confounding motor function deficits observed in previous animal models. In this study, we generated conditional knockout mice (TrkB cKO) in which TrkB was ablated from a majority of corticolimbic GABAergic interneurons postnatally. These mice showed intact motor coordination and movement, but exhibited enhanced dominance over other mice in a group-housed setting. In addition, immature fast-spiking GABAergic neurons of TrkB cKO mice resulted in an E/I imbalance in layer 5 microcircuits within the medial prefrontal cortex (mPFC), a key region regulating social dominance. Restoring the E/I imbalance via optogenetic modulation in the mPFC of TrkB cKO mice normalized their social dominance behavior. Taken together, our results provide strong evidence for a role of BDNF/TrkB signaling in inhibitory synaptic modulation and social dominance behavior in mice.

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.

Learning to blast a way into crime, or just good clean fun? Examining aggressive play with toy weapons and its relation with crime

BACKGROUND

Researchers, such as Bandura, have proposed that children's mere exposure to the use of play weapons encourages deviant displays of aggression, but there is very little research to support this hypothesis of 20 years.

AIM

To examine the relationship between amount of weapon play and concurrent aggression as well as later violent juvenile crime, while controlling for other variables possibly influencing criminal pathways.

METHOD

Using longitudinal survey data collected from mothers and children (n = 2019) from age 5, with follow-up at age 15, correlations between children's play with toy weapons and juvenile criminality were examined. Multivariate regression analyses were employed to determine to what extent early childhood aggression, symptoms of attention deficit hyperactivity disorder, and symptoms of depression were antecedents of juvenile crime.

RESULTS

For bivariate analysis between toy weapon play and juvenile criminality, the effect size was small and not significant. The relationship remained not significant once control variables were introduced into the model.

CONCLUSIONS AND IMPLICATIONS

The act of pretending to be aggressive in childhood thus plays little role in predicting later criminality after other factors, such as gender, attention deficit hyperactivity disorder or depression, have been taken into account. Involvement in imaginative play with toy gun use in early childhood is unlikely to be useful as a risk marker for later criminal behaviour. Play fighting and war toy games may even be considered necessary components within the frame of normal development. Copyright © 2018 John Wiley & Sons, Ltd.

Genetically defined fear-induced aggression: Focus on BDNF and its receptors

Brain-derived neurotrophic factor (BDNF), its precursor proBDNF, BDNF pro-peptide, BDNF mRNA levels, as well as TrkB and p75^NTR receptors mRNA and protein levels, were studied in the brain of rats, selectively bred for more than 85 generations for either the high level or the lack of fear-induced aggressive behavior. Furthermore, we have found that rats of aggressive strain demonstrated both high level of aggression toward humans and increased amplitude of acoustic startle response compared to rats selectively bred for the lack of fear-induced aggression. Significant increase in the BDNF mRNA, mature BDNF and proBDNF protein levels in the raphe nuclei (RN), hippocampus (Hc), nucleus accumbens (NAcc), amygdala, striatum and hypothalamus (Ht) of aggressive rats was revealed. The BDNF/proBDNF ratio was significantly reduced in the Hc and NAcc of highly aggressive rats suggesting prevalence of the proBDNF in these structures. In the Hc and frontal cortex (FC) of aggressive rats, the level of the full-length TrkB (TrkB-FL) receptor form was decreased, whereas the truncated TrkB (TrkB-T) protein level was increased in the RN, FC, substantia nigra and Ht. The TrkB-FL/TrkB-T ratio was significantly decreased in highly aggressive rats suggesting TrkB-T is predominant in highly aggressive rats. The p75^NTR expression was slightly changed in majority of studied brain structures of aggressive rats. The data indicate the BDNF system in the brain of aggressive and nonaggressive animals is extremely different at all levels, from transcription to reception, suggesting significant role of BDNF system in the development of highly aggressive phenotype.

SLC6A3 Is Associated With Relational Aggression in Children

Abstract. Understanding the genetic influence on aggressive behavior in children is one way to understand pathways to the development of aggression in adults. While aggression is likely under some environmental influence, it is also likely under some genetic influence. Overt aggression associates with a variety of genes including dopaminergic and serotonergic genes. Dopaminergic and serotonergic genes are known to be associated with overt aggression. However, little is known regarding the genetic pathways associated with relational aggression. Detecting genetic associates of relational aggression is important to eventually understand pathways to socially aggressive behaviors in children. Therefore, we attempted to determine if relational aggression was also associated with dopaminergic and serotonergic genes. We invited the parents of 327 children to complete a modified version of the MacArthur Health and Behavior Questionnaire (HBQ-P), which has a subscale for relational aggression. We used logistic regression models that predicted relational aggression after controlling for covariates. One genetic predictor was added at a time until there was no model improvement. The covariates were overt aggression scores obtained from the HBQ-P and age. The final (best) model included as a significant predictor of relational aggression one single nucleotide polymorphisms (SNP) on SLC6A3 (rs2617605) and the covariates.

Comparison of the adolescent and adult mouse prefrontal cortex proteome

Adolescence is a developmental period characterized by unique behavioral phenotypes (increased novelty seeking, risk taking, sociability and impulsivity) and increased risk for destructive behaviors, impaired decision making and psychiatric illness. Adaptive and maladaptive adolescent traits have been associated with development of the medial prefrontal cortex (mPFC), a brain region that mediates regulatory control of behavior. However, the molecular changes that underlie brain development and behavioral vulnerability have not been fully characterized. Using high-throughput 2D DIGE spot profiling with identification by MALDI-TOF mass spectrometry, we identified 62 spots in the PFC that exhibited age-dependent differences in expression. Identified proteins were associated with diverse cellular functions, including intracellular signaling, synaptic plasticity, cellular organization and metabolism. Separate Western blot analyses confirmed age-related changes in DPYSL2, DNM1, STXBP1 and CFL1 in the mPFC and expanded these findings to the dorsal striatum, nucleus accumbens, motor cortex, amygdala and ventral tegmental area. Ingenuity Pathway Analysis (IPA) identified functional interaction networks enriched with proteins identified in the proteomics screen, linking age-related alterations in protein expression to cellular assembly and development, cell signaling and behavior, and psychiatric illness. These results provide insight into potential molecular components of adolescent cortical development, implicating structural processes that begin during embryonic development as well as plastic adaptations in signaling that may work in concert to bring the cortex, and other brain regions, into maturity.

Parental brain-derived neurotrophic factor genotype, child prosociality, and their interaction as predictors of parents' warmth

BACKGROUND

Parental warmth has been associated with various child behaviors, from effortful control to callous-unemotional traits. Factors that have been shown to affect parental warmth include heritability and child behavior. However, there is limited knowledge about which specific genes are involved, how they interact with child behavior, how they affect differential parenting, and how they affect fathers. We examined what affects paternal and maternal warmth by focusing on the child's prosocial behavior and parents' genotype, specifically a Valine to Methionine substitution at codon 66 in the brain-derived neurotrophic factor (BDNF) gene.

METHODS

Data was available from a sample of 6.5 year-old twins, consisting of 369 mothers and 663 children and 255 fathers and 458 children. Self-reports were used to assess mothers' and fathers' warmth. Child prosociality was assessed with the other-parent report and experimental assessments.

RESULTS

Mothers' warmth was not affected by their BDNF genotype, neither as a main effect nor in an interaction with child prosociality. Fathers with the Met allele scored higher on warmth. Additionally, there was a significant interaction between fathers' BDNF genotype and child prosociality. For fathers with the Met allele there was a positive association between warmth and child prosociality. Conversely, for fathers with the Val/Val genotype there was no association between warmth and child prosociality. Results were repeated longitudinally in a subsample with data on age 8-9 years. A direct within family analysis showed that fathers with the Met allele were more likely than Val/Val carriers to exhibit differential parenting toward twins who differed in their prosocial behavior. The same pattern of findings was found with mother-rated and experimentally assessed prosociality.

CONCLUSIONS

These results shed light on the genetic and environmental underpinnings of paternal behavior and differential parenting.

Sensation seeking, peer deviance, and genetic influences on adolescent delinquency: Evidence for person-environment correlation and interaction

Both sensation seeking and affiliation with deviant peer groups are risk factors for delinquency in adolescence. In this study, we use a sample of adolescent twins (n = 549), 13 to 20 years old (M age = 15.8 years), in order to test the interactive effects of peer deviance and sensation seeking on delinquency in a genetically informative design. Consistent with a socialization effect, affiliation with deviant peers was associated with higher delinquency even after controlling for selection effects using a co-twin-control comparison. At the same time, there was evidence for person-environment correlation; adolescents with genetic dispositions toward higher sensation seeking were more likely to report having deviant peer groups. Genetic influences on sensation seeking substantially overlapped with genetic influences on adolescent delinquency. Finally, the environmentally mediated effect of peer deviance on adolescent delinquency was moderated by individual differences in sensation seeking. Adolescents reporting high levels of sensation seeking were more susceptible to deviant peers, a Person × Environment interaction. These results are consistent with both selection and socialization processes in adolescent peer relationships, and they highlight the role of sensation seeking as an intermediary phenotype for genetic risk for delinquency. (PsycINFO Database Record

The neurobiological basis of human aggression: A review on genetic and epigenetic mechanisms

Aggression is an evolutionary conserved behavior present in most species including humans. Inadequate aggression can lead to long-term detrimental personal and societal effects. Here, we differentiate between proactive and reactive forms of aggression and review the genetic determinants of it. Heritability estimates of aggression in general vary between studies due to differing assessment instruments for aggressive behavior (AB) as well as age and gender of study participants. In addition, especially non-shared environmental factors shape AB. Current hypotheses suggest that environmental effects such as early life stress or chronic psychosocial risk factors (e.g., maltreatment) and variation in genes related to neuroendocrine, dopaminergic as well as serotonergic systems increase the risk to develop AB. In this review, we summarize the current knowledge of the genetics of human aggression based on twin studies, genetic association studies, animal models, and epigenetic analyses with the aim to differentiate between mechanisms associated with proactive or reactive aggression. We hypothesize that from a genetic perspective, the aminergic systems are likely to regulate both reactive and proactive aggression, whereas the endocrine pathways seem to be more involved in regulation of reactive aggression through modulation of impulsivity. Epigenetic studies on aggression have associated non-genetic risk factors with modifications of the stress response and the immune system. Finally, we point to the urgent need for further genome-wide analyses and the integration of genetic and epigenetic information to understand individual differences in reactive and proactive AB. © 2015 Wiley Periodicals, Inc.

Aggressive behavior in humans: Genes and pathways identified through association studies

Aggressive behavior has both genetic and environmental components. Many association studies have been performed to identify genetic factors underlying aggressive behaviors in humans. In this review we summarize the previous work performed in this field, considering both candidate gene (CGAS) and genome-wide association studies (GWAS), excluding those performed in samples where the primary diagnosis is a psychiatric or neurological disorder other than an aggression-related phenotype. Subsequently, we have studied the enrichment of pathways and functions in GWAS data. The results of our searches show that most CGAS have identified associations with genes involved in dopaminergic and serotonergic neurotransmission and in hormone regulation. On the other hand, GWAS have not yet identified genome-wide significant associations, but top nominal findings are related to several signaling pathways, such as axon guidance or estrogen receptor signaling, and also to neurodevelopmental processes and synaptic plasticity. Future studies should use larger samples, homogeneous phenotypes and standardized measurements to identify genes that underlie aggressive behaviors in humans. © 2016 Wiley Periodicals, Inc.

Beyond risk: Prospective effects of GABA Receptor Subunit Alpha-2 (GABRA2) × Positive Peer Involvement on adolescent behavior

Research on Gene × Environment interactions typically focuses on maladaptive contexts and outcomes. However, the same genetic factors may also impact susceptibility to positive social contexts, leading to adaptive behavior. This paper examines whether the GABA receptor subunit alpha-2 (GABRA2) single nucleotide polymorphism rs279858 moderates the influence of positive peer affiliation on externalizing behavior and various forms of competence. Regions of significance were calculated to determine whether the form of the interaction supported differential susceptibility (increased sensitivity to both low and high positive peer affiliation) or vantage sensitivity (increased sensitivity to high positive peer affiliation). It was hypothesized that those carrying the homozygous minor allele (GG) would be more susceptible to peer effects. A sample (n = 300) of primarily male (69.7%) and White (93.0%) adolescents from the Michigan Longitudinal Study was assessed from ages 12 to 17. There was evidence for prospective Gene × Environment interactions in three of the four models. At low levels of positive peer involvement, those with the GG genotype were rated as having fewer adaptive outcomes, while at high levels they were rated as having greater adaptive outcomes. This supports differential susceptibility. Conceptualizing GABRA2 variants as purely risk factors may be inaccurate. Genetic differences in susceptibility to adaptive environmental exposures warrants further investigation.

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.

Biological Risk for the Development of Problem Behavior in Adolescence: Integrating Insights from Behavioral Genetics and Neuroscience

Adolescence is a time of increasing engagement in a variety of problem behaviors, including substance use and delinquency. Genetic risk for problem behavior increases over adolescence, is mediated partially by individual differences in sensation seeking, and is exacerbated by involvement with deviant peers. In this article, we describe how findings from behavioral genetic research on problem behavior intersect with research from developmental neuroscience. In particular, the incentive-processing system, including the ventral striatum, responds increasingly to rewards in adolescence, particularly in peer contexts. This developmental shift may be influenced by hormonal changes at puberty. Individual differences in the structure and function of reward-responsive brain regions may be intermediary phenotypes that mediate adolescents' genetic risk for problem behavior. The study of problem behavior can be enriched by interdisciplinary research that integrates measures of brain structure and function into genetically informed studies.

The neurobiology of psychopathy: recent developments and new directions in research and treatment

Psychopathic individuals account for substantial predatory and impulsive violence. To the present, the principal intervention used to decrease the harm inflicted by psychopaths has been confinement. Nevertheless, most confined psychopathic persons return to the community. Recent advances in the understanding of the neurobiology of psychopathy hold promise for new research directions and more effective treatments. In this article, we will explore recent advances in genetics, electrophysiology, brain imaging, and psychopharmacology, as well as, in brief, their implications for new directions in research and treatment.

Genetic Influences on Peer and Family Relationships Across Adolescent Development: Introduction to the Special Issue

Nearly all aspects of human development are influenced by genetic and environmental factors, which conjointly shape development through several gene-environment interplay mechanisms. More recently, researchers have begun to examine the influence of genetic factors on peer and family relationships across the pre-adolescent and adolescent time periods. This article introduces the special issue by providing a critical overview of behavior genetic methodology and existing research demonstrating gene-environment processes operating on the link between peer and family relationships and adolescent adjustment. The overview is followed by a summary of new research studies, which use genetically informed samples to examine how peer and family environment work together with genetic factors to influence behavioral outcomes across adolescence. The studies in this special issue provide further evidence of gene-environment interplay through innovative behavior genetic methodological approaches across international samples. Results from the quantitative models indicate environmental moderation of genetic risk for coercive adolescent-parent relationships and deviant peer affiliation. The molecular genetics studies provide support for a gene-environment interaction differential susceptibility model for dopamine regulation genes across positive and negative peer and family environments. Overall, the findings from the studies in this special issue demonstrate the importance of considering how genes and environments work in concert to shape developmental outcomes during adolescence.

Genotypes do not confer risk for delinquency but rather alter susceptibility to positive and negative environmental factors: gene-environmentinteractions of BDNF Val66Met, 5-HTTLPR, and MAOA-uVNTR [corrected]

BACKGROUND

Previous evidence of gene-by-environment interactions associated with emotional and behavioral disorders is contradictory. Differences in findings may result from variation in valence and dose of the environmental factor, and/or failure to take account of gene-by-gene interactions. The present study investigated interactions between the brain-derived neurotrophic factor gene (BDNF Val66Met), the serotonin transporter gene-linked polymorphic region (5-HTTLPR), the monoamine oxidase A (MAOA-uVNTR) polymorphisms, family conflict, sexual abuse, the quality of the child-parent relationship, and teenage delinquency.

METHODS

In 2006, as part of the Survey of Adolescent Life in Västmanland, Sweden, 1 337 high-school students, aged 17-18 years, anonymously completed questionnaires and provided saliva samples for DNA analyses.

RESULTS

Teenage delinquency was associated with two-, three-, and four-way interactions of each of the genotypes and the three environmental factors. Significant four-way interactions were found for BDNF Val66Met × 5-HTTLPR×MAOA-uVNTR × family conflicts and for BDNF Val66Met × 5-HTTLPR×MAOA-uVNTR × sexual abuse. Further, the two genotype combinations that differed the most in expression levels (BDNF Val66Met Val, 5-HTTLPR LL, MAOA-uVNTR LL [girls] and L [boys] vs BDNF Val66Met Val/Met, 5-HTTLPR S/LS, MAOA-uVNTR S/SS/LS) in interaction with family conflict and sexual abuse were associated with the highest delinquency scores. The genetic variants previously shown to confer vulnerability for delinquency (BDNF Val66Met Val/Met × 5-HTTLPR S × MAOA-uVNTR S) were associated with the lowest delinquency scores in interaction with a positive child-parent relationship.

CONCLUSIONS

Functional variants of the MAOA-uVNTR, 5-HTTLPR, and BDNF Val66Met, either alone or in interaction with each other, may be best conceptualized as modifying sensitivity to environmental factors that confer either risk or protection for teenage delinquency.