Genomics of human aggression: current state of genome-wide studies and an automated systematic review tool

Automation of systematic reviews of biomedical literature: a scoping review of studies indexed in PubMed

BACKGROUND

The demand for high-quality systematic literature reviews (SRs) for evidence-based medical decision-making is growing. SRs are costly and require the scarce resource of highly skilled reviewers. Automation technology has been proposed to save workload and expedite the SR workflow. We aimed to provide a comprehensive overview of SR automation studies indexed in PubMed, focusing on the applicability of these technologies in real world practice.

METHODS

In November 2022, we extracted, combined, and ran an integrated PubMed search for SRs on SR automation. Full-text English peer-reviewed articles were included if they reported studies on SR automation methods (SSAM), or automated SRs (ASR). Bibliographic analyses and knowledge-discovery studies were excluded. Record screening was performed by single reviewers, and the selection of full text papers was performed in duplicate. We summarized the publication details, automated review stages, automation goals, applied tools, data sources, methods, results, and Google Scholar citations of SR automation studies.

RESULTS

From 5321 records screened by title and abstract, we included 123 full text articles, of which 108 were SSAM and 15 ASR. Automation was applied for search (19/123, 15.4%), record screening (89/123, 72.4%), full-text selection (6/123, 4.9%), data extraction (13/123, 10.6%), risk of bias assessment (9/123, 7.3%), evidence synthesis (2/123, 1.6%), assessment of evidence quality (2/123, 1.6%), and reporting (2/123, 1.6%). Multiple SR stages were automated by 11 (8.9%) studies. The performance of automated record screening varied largely across SR topics. In published ASR, we found examples of automated search, record screening, full-text selection, and data extraction. In some ASRs, automation fully complemented manual reviews to increase sensitivity rather than to save workload. Reporting of automation details was often incomplete in ASRs.

CONCLUSIONS

Automation techniques are being developed for all SR stages, but with limited real-world adoption. Most SR automation tools target single SR stages, with modest time savings for the entire SR process and varying sensitivity and specificity across studies. Therefore, the real-world benefits of SR automation remain uncertain. Standardizing the terminology, reporting, and metrics of study reports could enhance the adoption of SR automation techniques in real-world practice.

Genetics of child aggression, a systematic review

Excessive and persistent aggressiveness is the most common behavioral problem that leads to psychiatric referrals among children. While half of the variance in childhood aggression is attributed to genetic factors, the biological mechanism and the interplay between genes and environment that results in aggression remains elusive. The purpose of this systematic review is to provide an overview of studies examining the genetics of childhood aggression irrespective of psychiatric diagnosis. PubMed, PsycINFO, and MEDLINE databases were searched using predefined search terms for aggression, genes and the specific age group. From the 652 initially yielded studies, eighty-seven studies were systematically extracted for full-text review and for further quality assessment analyses. Findings show that (i) investigation of candidate genes, especially of MAOA (17 studies), DRD4 (13 studies), and COMT (12 studies) continue to dominate the field, although studies using other research designs and methods including genome-wide association and epigenetic studies are increasing, (ii) the published articles tend to be moderate in sizes, with variable methods of assessing aggressive behavior and inconsistent categorizations of tandem repeat variants, resulting in inconclusive findings of genetic main effects, gene-gene, and gene-environment interactions, (iii) the majority of studies are conducted on European, male-only or male-female mixed, participants. To our knowledge, this is the first study to systematically review the effects of genes on youth aggression. To understand the genetic underpinnings of childhood aggression, more research is required with larger, more diverse sample sets, consistent and reliable assessments and standardized definition of the aggression phenotypes. The search for the biological mechanisms underlying child aggression will also benefit from more varied research methods, including epigenetic studies, transcriptomic studies, gene system and genome-wide studies, longitudinal studies that track changes in risk/ameliorating factors and aggression-related outcomes, and studies examining causal mechanisms.

Associations of externalizing polygenic scores with externalizing disorders among Mexican youth

Several studies have examined the association of externalizing polygenic scores (PGS) with externalizing symptoms in samples of European ancestry. However, less is known about the associations of externalizing polygenic vulnerability in relation to phenotypic externalizing disorders among individuals of different ancestries, such as Mexican youth. Here, we leveraged the largest genome-wide association study on externalizing behaviors that included over 1 million individuals of European ancestry to examine associations of externalizing PGS with a range of externalizing disorders in Mexican adolescents, and investigated whether adversity exposure in childhood moderated these associations. Participants (N = 1064; age range 12-17 years old; 58.8% female) were adolescents recruited for a general population survey on adolescent mental health in the Mexico City Metropolitan region and were genotyped. Childhood adversity exposure and externalizing disorders, specifically attention-deficit hyperactivity disorder (ADHD), conduct disorder, oppositional defiant disorder, and substance use disorder, were assessed via the computer-assisted World Mental Health Composite International Diagnostic Interview for adolescents. A greater externalizing PGS was associated with a greater odds of any externalizing disorder (OR = 1.29 [1.12, 1.48]; p < 0.01) and ADHD (OR = 1.40 [1.15, 1.70]; p < 0.01) in the whole sample, and in females in particular. There were no main effects of the externalizing PGS on conduct disorder, oppositional defiant disorder, or substance use disorder, nor did adversity exposure moderate these associations. Our results suggest that greater genetic propensity for externalizing disorders is associated with increased odds of any externalizing disorders and ADHD among Mexican adolescents, furthering our understanding of externalizing disorder manifestation in this population.

The influence of the COMT Val158Met polymorphism on prefrontal TDCS effects on aggression

Increasing dorsolateral prefrontal cortex (DLPFC) activity by anodal transcranial direct current stimulation (tDCS) enhances cognitive control and might reduce aggression. The Val158Met polymorphism within the catechol-O-methyltransferase gene (rs4680) plays a pivotal role in prefrontal dopamine signaling, displaying associations with aggressive behavior, and potentially influencing the effects of tDCS. In a double-blind, sham-controlled study, we investigated the influence of rs4680 on tDCS effects on aggression. While undergoing functional magnetic resonance imaging, 89 healthy male participants performed the Taylor aggression paradigm before and immediately after tDCS. Actively stimulated participants (n = 45) received anodal tDCS (1.5 mA) for 20 min targeting the right DLPFC. Carriers of the val-allele (val+; n = 46; active tDCS n = 23) were compared to met-allele homozygotes (val-; n = 43; active tDCS n = 22). Analysis revealed decreased aggressive behavior in the val- group following active tDCS (p < 0.001). The val+ group showed increased aggression during the second session (p < 0.001) with an even higher increase following active as compared to sham tDCS (p < 0.001). No effects of stimulation or rs4680 on brain activation were found. Our study provides evidence for opposite tDCS effects on aggressive behavior in val-carriers and val-noncarriers. By shedding light on genetic factors predicting tDCS responsivity, the study will help to pave the way toward individualized-and thus more effective-tDCS treatment options.

Increased burden of rare protein-truncating variants in constrained, brain-specific and synaptic genes in extremely impulsively violent males with antisocial personality disorder

The genetic correlates of extreme impulsive violence are poorly understood, and there have been few studies that have characterized a large group of affected individuals both clinically and genetically. We performed whole exome sequencing (WES) in 290 males with the life-course-persistent, extremely impulsively violent form of antisocial personality disorder (APD) and analyzed the spectrum of rare protein-truncating variants (rPTVs). Comparisons were made with 314 male controls and publicly available genotype data. Functional annotation tools were used for biological interpretation. Participants were significantly more likely to harbor rPTVs in genes that are intolerant to loss-of-function variants (odds ratio [OR] 2.06; p < 0.001), specifically expressed in brain (OR 2.80; p = 0.036) and enriched for those involved in neurotransmitter transport and synaptic processes. In 60 individuals (20%), we identified rPTVs that we classified as clinically relevant based on their clinical associations, biological function and gene expression patterns. Of these, 37 individuals harbored rPTVs in 23 genes that are associated with a monogenic neurological disorder, and 23 individuals harbored rPTVs in 20 genes reportedly intolerant to loss-of-function variants. The analysis presents evidence in support of a model where presence of either one or several private, functionally relevant mutations contribute significantly to individual risk of life-course-persistent APD and reveals multiple individuals who could be affected by clinically unrecognized neuropsychiatric Mendelian disease. Thus, Mendelian diseases and increased rPTV burden may represent important factors for the development of extremely impulsive violent life-course-persistent forms of APD irrespective of their clinical presentation.

Direct and Indirect Genetic Effects on Aggression

Background

Family members resemble each other in their propensity for aggression. In twin studies, approximately 50% of the variance in aggression can be explained by genetic influences. However, if there are genotype-environment correlation mechanisms, such as environmental manifestations of parental and sibling genotypes, genetic influences may partly reflect environmental influences. In this study, we investigated the importance of indirect polygenic score (PGS) effects on aggression.

Methods

We modeled the effect of PGSs based on 3 genome-wide association studies: early-life aggression, educational attainment, and attention-deficit/hyperactivity disorder (ADHD). The associations with aggression were tested in a within- and between-family design (37,796 measures from 7740 individuals, ages 3-86 years [mean = 14.20 years, SE = 12.03], from 3107 families, 55% female) and in a transmitted/nontransmitted PGS design (42,649 measures from 6653 individuals, ages 3-61 years [mean = 11.81 years, SE = 8.68], from 3024 families, 55% female). All participants are enrolled in the Netherlands Twin Register.

Results

We found no evidence for contributions of indirect PGS effects on aggression in either a within- and between-family design or a transmitted/nontransmitted PGS design. Results indicate significant direct effects on aggression for the PGSs based on early-life aggression, educational attainment, and ADHD, although explained variance was low (within- and between-family: early-life aggression R2 = 0.3%, early-life ADHD R2 = 0.6%, educational attainment R2 = 0.7%; transmitted/nontransmitted PGSs: early-life aggression R2 = 0.2%, early-life ADHD R2 = 0.9%, educational attainment R2 = 0.5%).

Conclusions

PGSs included in the current study had a direct (but no indirect) effect on aggression, consistent with results of previous twin and family studies. Further research involving other PGSs for aggression and related phenotypes is needed to determine whether this conclusion generalizes to overall genetic influences on aggression.

Reducing Literature Screening Workload With Machine Learning

Abstract. In our era of accelerated accumulation of knowledge, the manual screening of literature for eligibility is increasingly becoming too labor-intensive for summarizing the current state of knowledge in a timely manner. Recent advances in machine learning and natural language processing promise to reduce the screening workload by automatically detecting unseen references with a high probability of inclusion. As a variety of tools have been developed, the current review provides an overview of their characteristics and performance. A systematic search in various databases yielded 488 eligible reports, revealing 15 tools for screening automation that differed in methodology, features, and accessibility. For the review on the performance of screening tools, 21 studies could be included. In comparison to sampling records randomly, active screening with prioritization approximately halves the screening workload. However, a comparison of tools under equal or at least similar conditions is needed to derive clear recommendations.

Integrative Multi-omics Analysis of Childhood Aggressive Behavior

This study introduces and illustrates the potential of an integrated multi-omics approach in investigating the underlying biology of complex traits such as childhood aggressive behavior. In 645 twins (cases = 42%), we trained single- and integrative multi-omics models to identify biomarkers for subclinical aggression and investigated the connections among these biomarkers. Our data comprised transmitted and two non-transmitted polygenic scores (PGSs) for 15 traits, 78,772 CpGs, and 90 metabolites. The single-omics models selected 31 PGSs, 1614 CpGs, and 90 metabolites, and the multi-omics model comprised 44 PGSs, 746 CpGs, and 90 metabolites. The predictive accuracy for these models in the test (N = 277, cases = 42%) and independent clinical data (N = 142, cases = 45%) ranged from 43 to 57%. We observed strong connections between DNA methylation, amino acids, and parental non-transmitted PGSs for ADHD, Autism Spectrum Disorder, intelligence, smoking initiation, and self-reported health. Aggression-related omics traits link to known and novel risk factors, including inflammation, carcinogens, and smoking.

Intergenerational continuity of crime: A comparison between children of discordant siblings

BACKGROUND

Various studies have shown that fathers and children show similarities in criminal behaviour, but little is known about the nature of this relationship. By using a family-based research design, this study controls for familial confounders and gives a better estimate of the extent to which paternal crime has a direct effect on offspring offending.

AIMS

To test the extent of any relationship between paternal offending during the childhood of offspring and adolescent offending by those offspring and to examine the effect of potential confounders of this relationship.

METHODS

Data were from records held by Statistics Netherlands for 1,155,771 individuals born in the Netherlands between 1996 and 2001. Police data were used to measure paternal offending during the childhood (age 0-11) of this cohort and their adolescent offending (age 12-18). Logistic regression analyses were used to estimate the bivariate relationship between paternal and offspring offending, as well as this relationship after controlling for various demographic and socio-economic variables. Conditional logistic regression analyses were used to compare children of discordant brothers (N = 9232). By comparing within families rather than between unrelated individuals, all unmeasured familial factors that are shared between these cousins were controlled for.

RESULTS

Offending during adolescence was about three times as likely among offspring whose fathers had offended while they were 11 years old or younger than among adolescents with no such paternal problem (OR: 3.21, CI 3.17-3.26). This relationship was attenuated after controlling for measured confounders (OR: 1.78, CI 1.75-1.81) and for unmeasured familial confounders (OR: 1.47, CI 1.36-1.59), but remained significant.

CONCLUSIONS

Paternal offending has an association with offspring offending, but this is small after controlling for measured socio-economic and unmeasured familial confounders. Previous studies that did not control for unmeasured familial confounders seem likely to have overestimated the effect of paternal crime on their offspring's offending. This has implications for interventions for the offspring. If confined to mitigating the negative consequences of paternal offending, they are likely to have limited effectiveness.

Dysfunction of AMPA receptor GluA3 is associated with aggressive behavior in human

Inappropriate aggression in humans hurts the society, families and individuals. The genetic basis for aggressive behavior, however, remains largely elusive. In this study, we identified two rare missense variants in X-linked GRIA3 from male patients who showed syndromes featuring aggressive outbursts. Both G630R and E787G mutations in AMPA receptor GluA3 completely lost their ion channel functions. Furthermore, a guanine-repeat single nucleotide polymorphism (SNP, rs3216834) located in the first intron of human GRIA3 gene was found to regulate GluA3 expression with longer guanine repeats (rs3216834-10G/-11G) suppressing transcription compared to the shorter ones (-7G/-8G/-9G). Importantly, the distribution of rs3216834-10G/-11G was elevated in a male violent criminal sample from Chinese Han population. Using GluA3 knockout mice, we showed that the excitatory neurotransmission and neuronal activity in the medial prefrontal cortex (mPFC) was impaired. Expressing GluA3 back into the mPFC alleviated the aggressive behavior of GluA3 knockout mice, suggesting that the defects in mPFC explained, at least partially, the neural mechanisms underlying the aggressive behavior. Therefore, our study provides compelling evidence that dysfunction of AMPA receptor GluA3 promotes aggressive behavior.

No causal relationship between early motherhood and offspring adolescent offending: Empirical evidence from a genetically-informed study

Previous studies have consistently shown that young maternal age at birth is associated with an increased risk for problematic behavior in offspring. Less is known about the mechanisms underlying this association, as it could either reflect a causal effect or a spurious relationship. This study aims to gain more insights in these underlying mechanisms by studying the relationship between early motherhood and offspring adolescent offending. The sample includes all individuals who were born in the Netherlands between 1991 and 2001 (N=2,098,815). All variables were extracted from register data of Statistics Netherlands, including police registrations to measure adolescent offending. Logistic regression analyses were used to examine the relationship between maternal age at birth and offspring adolescent offending, with and without control variables. Moreover, a children of discordant siblings model was applied to further control for unmeasured familial confounders (i.e., shared environmental and genetic confounders). In line with previous studies, the results show a significant negative relationship between early motherhood and offspring offending. However, no significant effect was found in the children of discordant siblings analysis, which suggests that this relationship is confounded by unmeasured familial factors. These results illustrate the importance of applying genetically informed research designs when studying intergenerational relationships.

Polygenic risk scores for antisocial behavior in relation to amygdala morphology across an attention deficit hyperactivity disorder case-control sample with and without disruptive behavior

Antisocial and aggressive behaviors show considerable heritability and are central to disruptive behavior disorders (DBDs), but are also frequently observed in attention deficit hyperactivity disorder (ADHD). While the amygdala is implicated as a key neural structure, it remains unclear whether common genetic variants underlie this brain-behavior association. We hypothesized that polygenic (risk) scores for antisocial and aggressive behaviors (ASB-PRS) would be related to amygdala morphology. Using the Broad Antisocial Behavior Consortium genome-wide association study (GWAS; mostly population based cohorts), we calculated ASB-PRS in the NeuroIMAGE I ADHD case-control sample with varying levels of DBD symptomatology (n=679 from 379 families, aged 7 - 29). We first investigated associations of several ASB-PRS p value thresholds with the presence of DBD symptoms and self-reported antisocial behavior (ASB) to determine the threshold for further analyses. This PRS was then related to amygdala volume and shape using regression and vertex-wise analyses. Our results showed associations of ASB-PRS with the presence of DBD symptoms, self-reported ASB, and left basolateral amygdala shape, independent of ADHD symptom severity and ADHD-PRS, with a relative outward displacement of the vertices. No associations of ASB-PRS, DBD symptoms or self-reported ASB with amygdala volume were found. Our results indicate that genetic risk for antisocial and aggressive behaviors is related to amygdala shape alterations, and point to genetic sharing across different DBD and ASB and aggression-related phenotypes as a spectrum of genetically related quantitative traits. Additionally, our findings support the utility of vertex-based shape analyses in genetic studies of ASB, aggression, and DBDs.

Melatonin and aggressive behavior: A systematic review of the literature on preclinical and clinical evidence

The melatonin system and circadian disruption have well-established links with aggressive behaviors; however, the biological underpinnings have not been thoroughly investigated. Here, we aimed at examining the current knowledge regarding the neurobiological and psychopharmacological involvement of the melatonin system in aggressive/violent behaviors. To this end, we performed a systematic review on Embase and Pubmed/MEDLINE of preclinical and clinical evidence linking the melatonin system, melatonin, and melatoninergic drugs with aggressive/violent behaviors. Two blinded raters performed an independent screening of the relevant literature. Overall, this review included 38 papers distributed between clinical and preclinical models. Eleven papers specifically addressed the existing evidence in rodent models, five in fish models, and 21 in humans. The data indicate that depending on the species, model, and timing of administration, melatonin may exert a complex influence on aggressive/violent behaviors. Particularly, the apparent contrasting findings on the link between the melatonin system and aggression/violence (with either increased, no, or decreased effect) shown in preclinical models underscore the need for further research to develop more accurate and fruitful translational models. Likewise, the significant heterogeneity found in the results of clinical studies does not allow yet to draw any firm conclusion on the efficacy of melatonin or melatonergic drugs on aggressive/violent behaviors. However, findings in children and in traits associated with aggressive/violent behavior, including irritability and anger, are emerging and deserve empirical attention given the low toxicity of melatonin and melatonergic drugs.

Multivariate Genetic Structure of Externalizing Behavior and Structural Brain Development in a Longitudinal Adolescent Twin Sample

Externalizing behavior in its more extreme form is often considered a problem to the individual, their families, teachers, and society as a whole. Several brain structures have been linked to externalizing behavior and such associations may arise if the (co)development of externalizing behavior and brain structures share the same genetic and/or environmental factor(s). We assessed externalizing behavior with the Child Behavior Checklist and Youth Self Report, and the brain volumes and white matter integrity (fractional anisotropy [FA] and mean diffusivity [MD]) with magnetic resonance imaging in the BrainSCALE cohort, which consisted of twins and their older siblings from 112 families measured longitudinally at ages 10, 13, and 18 years for the twins. Genetic covariance modeling based on the classical twin design, extended to also include siblings of twins, showed that genes influence externalizing behavior and changes therein (h² up to 88%). More pronounced externalizing behavior was associated with higher FA (observed correlation r_ph up to +0.20) and lower MD (r_ph up to −0.20), with sizeable genetic correlations (FA r_a up to +0.42; MD r_a up to −0.33). The cortical gray matter (CGM; r_ph up to −0.20) and cerebral white matter (CWM; r_ph up to +0.20) volume were phenotypically but not genetically associated with externalizing behavior. These results suggest a potential mediating role for global brain structures in the display of externalizing behavior during adolescence that are both partially explained by the influence of the same genetic factor.

Genetics and Brain Transcriptomics of Completed Suicide

OBJECTIVE

The authors sought to study the transcriptomic and genomic features of completed suicide by parsing the method chosen, to capture molecular correlates of the distinctive frame of mind of individuals who die by suicide, while reducing heterogeneity.

METHODS

The authors analyzed gene expression (RNA sequencing) from postmortem dorsolateral prefrontal cortex of patients who died by suicide with violent compared with nonviolent means, nonsuicide patients with the same psychiatric disorders, and a neurotypical group (total N=329). They then examined genomic risk scores (GRSs) for each psychiatric disorder included, and GRSs for cognition (IQ) and for suicide attempt, testing how they predict diagnosis or traits (total N=888).

RESULTS

Patients who died by suicide by violent means showed a transcriptomic pattern remarkably divergent from each of the other patient groups but less from the neurotypical group; consistently, their genomic profile of risk was relatively low for their diagnosed illness as well as for suicide attempt, and relatively high for IQ: they were more similar to the neurotypical group than to other patients. Differentially expressed genes (DEGs) associated with patients who died by suicide by violent means pointed to purinergic signaling in microglia, showing similarities to a genome-wide association study of Drosophila aggression. Weighted gene coexpression network analysis revealed that these DEGs were coexpressed in a context of mitochondrial metabolic activation unique to suicide by violent means.

CONCLUSIONS

These findings suggest that patients who die by suicide by violent means are in part biologically separable from other patients with the same diagnoses, and their behavioral outcome may be less dependent on genetic risk for conventional psychiatric disorders and be associated with an alteration of purinergic signaling and mitochondrial metabolism.

Continuity of Genetic Risk for Aggressive Behavior Across the Life-Course

We test whether genetic influences that explain individual differences in aggression in early life also explain individual differences across the life-course. In two cohorts from The Netherlands (N = 13,471) and Australia (N = 5628), polygenic scores (PGSs) were computed based on a genome-wide meta-analysis of childhood/adolescence aggression. In a novel analytic approach, we ran a mixed effects model for each age (Netherlands: 12-70 years, Australia: 16-73 years), with observations at the focus age weighted as 1, and decaying weights for ages further away. We call this approach a 'rolling weights' model. In The Netherlands, the estimated effect of the PGS was relatively similar from age 12 to age 41, and decreased from age 41-70. In Australia, there was a peak in the effect of the PGS around age 40 years. These results are a first indication from a molecular genetics perspective that genetic influences on aggressive behavior that are expressed in childhood continue to play a role later in life.

Genetic Moderation of the Association Between Early Family Instability and Trajectories of Aggressive Behaviors from Middle Childhood to Adolescence

The present study tested models of polygenic by environment interaction between early childhood family instability and polygenic risk for aggression predicting developmental trajectories of aggression from middle childhood to adolescence. With a longitudinal sample of 515 racially and ethnically diverse children from low-income families, primary caregivers reported on multiple components of family instability annually from child ages 2-5 years. A conservative polygenic risk score (p = 0.05) was generated based on a prior meta-genome wide association study. Trajectories of aggression were identified using a curve of factors model based on a composite of primary caregiver, alternate caregiver, and teacher reports at five ages from 7.5 to 14 years. The family instability by polygenic interaction predicted growth in children's aggression such that children with lower levels of family instability and lower polygenic risk exhibited a steeper decline in aggression from 7.5 to 14. Findings support the need to model gene-environment interplay to elucidate the role of genetics in the development of aggressive behaviors.

Genetic association study of childhood aggression across raters, instruments, and age

Childhood aggressive behavior (AGG) has a substantial heritability of around 50%. Here we present a genome-wide association meta-analysis (GWAMA) of childhood AGG, in which all phenotype measures across childhood ages from multiple assessors were included. We analyzed phenotype assessments for a total of 328 935 observations from 87 485 children aged between 1.5 and 18 years, while accounting for sample overlap. We also meta-analyzed within subsets of the data, i.e., within rater, instrument and age. SNP-heritability for the overall meta-analysis (AGGoverall) was 3.31% (SE = 0.0038). We found no genome-wide significant SNPs for AGGoverall. The gene-based analysis returned three significant genes: ST3GAL3 (P = 1.6E-06), PCDH7 (P = 2.0E-06), and IPO13 (P = 2.5E-06). All three genes have previously been associated with educational traits. Polygenic scores based on our GWAMA significantly predicted aggression in a holdout sample of children (variance explained = 0.44%) and in retrospectively assessed childhood aggression (variance explained = 0.20%). Genetic correlations (rg) among rater-specific assessment of AGG ranged from rg = 0.46 between self- and teacher-assessment to rg = 0.81 between mother- and teacher-assessment. We obtained moderate-to-strong rgs with selected phenotypes from multiple domains, but hardly with any of the classical biomarkers thought to be associated with AGG. Significant genetic correlations were observed with most psychiatric and psychological traits (range [Formula: see text]: 0.19-1.00), except for obsessive-compulsive disorder. Aggression had a negative genetic correlation (rg = ~-0.5) with cognitive traits and age at first birth. Aggression was strongly genetically correlated with smoking phenotypes (range [Formula: see text]: 0.46-0.60). The genetic correlations between aggression and psychiatric disorders were weaker for teacher-reported AGG than for mother- and self-reported AGG. The current GWAMA of childhood aggression provides a powerful tool to interrogate the rater-specific genetic etiology of AGG.

DNA methylation signatures of aggression and closely related constructs: A meta-analysis of epigenome-wide studies across the lifespan

DNA methylation profiles of aggressive behavior may capture lifetime cumulative effects of genetic, stochastic, and environmental influences associated with aggression. Here, we report the first large meta-analysis of epigenome-wide association studies (EWAS) of aggressive behavior (N = 15,324 participants). In peripheral blood samples of 14,434 participants from 18 cohorts with mean ages ranging from 7 to 68 years, 13 methylation sites were significantly associated with aggression (alpha = 1.2 × 10-7; Bonferroni correction). In cord blood samples of 2425 children from five cohorts with aggression assessed at mean ages ranging from 4 to 7 years, 83% of these sites showed the same direction of association with childhood aggression (r = 0.74, p = 0.006) but no epigenome-wide significant sites were found. Top-sites (48 at a false discovery rate of 5% in the peripheral blood meta-analysis or in a combined meta-analysis of peripheral blood and cord blood) have been associated with chemical exposures, smoking, cognition, metabolic traits, and genetic variation (mQTLs). Three genes whose expression levels were associated with top-sites were previously linked to schizophrenia and general risk tolerance. At six CpGs, DNA methylation variation in blood mirrors variation in the brain. On average 44% (range = 3-82%) of the aggression-methylation association was explained by current and former smoking and BMI. These findings point at loci that are sensitive to chemical exposures with potential implications for neuronal functions. We hope these results to be a starting point for studies leading to applications as peripheral biomarkers and to reveal causal relationships with aggression and related traits.

Genetically Informed Regression Analysis: Application to Aggression Prediction by Inattention and Hyperactivity in Children and Adults

We present a procedure to simultaneously fit a genetic covariance structure model and a regression model to multivariate data from mono- and dizygotic twin pairs to test for the prediction of a dependent trait by multiple correlated predictors. We applied the model to aggressive behavior as an outcome trait and investigated the prediction of aggression from inattention (InA) and hyperactivity (HA) in two age groups. Predictions were examined in twins with an average age of 10 years (11,345 pairs), and in adult twins with an average age of 30 years (7433 pairs). All phenotypes were assessed by the same, but age-appropriate, instruments in children and adults. Because of the different genetic architecture of aggression, InA and HA, a model was fitted to these data that specified additive and non-additive genetic factors (A and D) plus common and unique environmental (C and E) influences. Given appropriate identifying constraints, this ADCE model is identified in trivariate data. We obtained different results for the prediction of aggression in children, where HA was the more important predictor, and in adults, where InA was the more important predictor. In children, about 36% of the total aggression variance was explained by the genetic and environmental components of HA and InA. Most of this was explained by the genetic components of HA and InA, i.e., 29.7%, with 22.6% due to the genetic component of HA. In adults, about 21% of the aggression variance was explained. Most was this was again explained by the genetic components of InA and HA (16.2%), with 8.6% due to the genetic component of InA.

Ketone body 3-hydroxybutyrate as a biomarker of aggression

Human aggression is a complex behaviour, the biological underpinnings of which remain poorly known. To gain insights into aggression biology, we studied relationships with aggression of 11 low-molecular-weight metabolites (amino acids, ketone bodies), processed using ¹H nuclear magnetic resonance spectroscopy. We used a discovery sample of young adults and an independent adult replication sample. We studied 725 young adults from a population-based Finnish twin cohort born 1983-1987, with aggression levels rated in adolescence (ages 12, 14, 17) by multiple raters and blood plasma samples at age 22. Linear regression models specified metabolites as the response variable and aggression ratings as predictor variables, and included several potential confounders. All metabolites showed low correlations with aggression, with only one-3-hydroxybutyrate, a ketone body produced during fasting-showing significant (negative) associations with aggression. Effect sizes for different raters were generally similar in magnitude, while teacher-rated (age 12) and self-rated (age 14) aggression were both significant predictors of 3-hydroxybutyrate in multi-rater models. In an independent replication sample of 960 adults from the Netherlands Twin Register, higher aggression (self-rated) was also related to lower levels of 3-hydroxybutyrate. These exploratory epidemiologic results warrant further studies on the role of ketone metabolism in aggression.

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.

Content, diagnostic, correlational, and genetic similarities between common measures of childhood aggressive behaviors and related psychiatric traits

BACKGROUND

Given the role of childhood aggressive behavior (AGG) in everyday child development, precise and accurate measurement is critical in clinical practice and research. This study aims to quantify agreement among widely used measures of childhood AGG regarding item content, clinical concordance, correlation, and underlying genetic construct.

METHODS

We analyzed data from 1254 Dutch twin pairs (age 8-10 years, 51.1% boys) from a general population sample for whom both parents completed the A-TAC, CBCL, and SDQ at the same occasion.

RESULTS

There was substantial variation in item content among AGG measures, ranging from .00 (i.e., mutually exclusive) to .50 (moderate agreement). Clinical concordance (i.e., do the same children score above a clinical threshold among AGG measures) was very weak to moderate with estimates ranging between .01 and .43 for mother-reports and between .12 and .42 for father-reports. Correlations among scales were weak to strong, ranging from .32 to .70 for mother-reports and from .32 to .64 for father-reports. We found weak to very strong genetic correlations among the measures, with estimates between .65 and .84 for mother-reports and between .30 and .87 for father-reports.

CONCLUSIONS

Our results demonstrated that degree of agreement between measures of AGG depends on the type (i.e., item content, clinical concordance, correlation, genetic correlation) of agreement considered. Because agreement was higher for correlations compared to clinical concordance (i.e., above or below a clinical cutoff), we propose the use of continuous scores to assess AGG, especially for combining data with different measures. Although item content can be different and agreement among observed measures may not be high, the genetic correlations indicate that the underlying genetic liability for childhood AGG is consistent across measures.

Urinary Amine and Organic Acid Metabolites Evaluated as Markers for Childhood Aggression: The ACTION Biomarker Study

Biomarkers are of interest as potential diagnostic and predictive instruments in personalized medicine. We present the first urinary metabolomics biomarker study of childhood aggression. We aim to examine the association of urinary metabolites and neurotransmitter ratios involved in key metabolic and neurotransmitter pathways in a large cohort of twins (N = 1,347) and clinic-referred children (N = 183) with an average age of 9.7 years. This study is part of ACTION (Aggression in Children: Unraveling gene-environment interplay to inform Treatment and InterventiON strategies), in which we developed a standardized protocol for large-scale collection of urine samples in children. Our analytical design consisted of three phases: a discovery phase in twins scoring low or high on aggression (N = 783); a replication phase in twin pairs discordant for aggression (N = 378); and a validation phase in clinical cases and matched twin controls (N = 367). In the discovery phase, 6 biomarkers were significantly associated with childhood aggression, of which the association of O-phosphoserine (β = 0.36; SE = 0.09; p = 0.004), and gamma-L-glutamyl-L-alanine (β = 0.32; SE = 0.09; p = 0.01) remained significant after multiple testing. Although non-significant, the directions of effect were congruent between the discovery and replication analyses for six biomarkers and two neurotransmitter ratios and the concentrations of 6 amines differed between low and high aggressive twins. In the validation analyses, the top biomarkers and neurotransmitter ratios, with congruent directions of effect, showed no significant associations with childhood aggression. We find suggestive evidence for associations of childhood aggression with metabolic dysregulation of neurotransmission, oxidative stress, and energy metabolism. Although replication is required, our findings provide starting points to investigate causal and pleiotropic effects of these dysregulations on childhood aggression.