MAOA and persistent, pervasive childhood aggression

Genetic determinants of longitudinal behavioural trajectories in rare conditions: The case of fragile X syndrome

Despite being a monogenic condition, individual variability in the phenotypic profile of fragile X syndrome (FXS) is substantial, with behavioural outcomes differing in severity and frequency. Existing studies have revealed that common variation in 5-HTTLPR (serotonin) and COMT (dopamine) single nucleotide polymorphisms (SNPs) is associated with behavioural variation in FXS when measured cross-sectionally. However, the associations between SNPs and longitudinal behavioural trajectories in FXS remain unknown. This study explored relationships between three SNPs, selected a priori (5-HTTLPR, COMT and monoamine oxidase A (MAOA)), and trajectories of clinically relevant behaviours in 42 males with FXS. Autistic characteristics, property destruction, aggression, stereotyped behaviour, self-injury, repetitive behaviour, and mood/interest and pleasure were measured at two time points across three years via a series of standardised informant questionnaires. DNA was extracted from saliva samples and a combination of PCR and TaqMan genotyping was performed for genetic confirmation of FXS, and COMT, 5-HTTLPR and MAOA analyses. Results revealed that males with FXS with AA COMT genotype were less likely to display persistent stereotyped behaviour compared to AG or GG genotypes. Participants with the S/S 5-HTTLPR genotype displayed a steeper decline in repetitive and stereotyped behaviours compared to the L/S or L/L genotypes. Participants with the three-repeat MAOA genotype demonstrated a steeper decline in communication skills over three years compared to those with four repeats. This study documents the association between common genetic variation and behavioural trajectories in males with FXS. Results suggest specific SNPs play an important role in longitudinal behavioural patterns in FXS. This work may facilitate an understanding of individual trajectories for people with FXS, and, therefore, support future tailored interventions.

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.

Association of the MAOA-uVNTR polymorphism with psychopathic traits may change from childhood to adolescence

Psychopathic traits can lead to violence, making it a serious public health concern. Genetic factors contribute to the aetiology of psychopathy. We examined whether monoamine oxidase A (MAOA-uVNTR) was associated with psychopathic traits measured quantitatively from controls through clinically aggressive youth (n = 336). Subjects were sub-categorized into at or above, and below age 13 years. Results reveal that males below age 13 were more likely to display psychopathic traits with the MAOA long variant, whereas males above age 13 years were more likely to display with the short variant. This suggests that developmental factors may be crucial for understanding the role of the MAOA polymorphism in psychopathic traits in males.

Exploring the association of interleukin polymorphisms with aggression and internalizing behaviors in children and adolescents

BACKGROUND

There is growing evidence that inflammation influences mental health. Blood interleukin levels, which regulate inflammation, have been linked to aggression and internalizing behaviors. We performed a hypothesis-driven genetic study to (1) evaluate the association of IL1B, IL2, and IL6 gene variants with aggression and internalizing behaviors and (2) explore gene-environment interactions with childhood adversity in a deeply phenotyped childhood-onset aggression sample including 255 cases and 226 controls of European ancestry.

METHODS

We evaluated the association of putative functional and tag SNPs within IL1B, IL2, and IL6 with aggression case status, parent-reported internalizing problems, self-reported anxiety symptoms, and self-reported depressive symptoms in our sample. We also performed exploratory GxE analyses within cases, testing for statistical interaction between interleukin SNP genotype and childhood adversity for depressive symptoms.

RESULTS

No significant association was observed between any of the interleukin SNPs and childhood-onset aggression. We observed association of IL6 variant rs2069827 with depressive symptoms (p = 7.15×10^-4 ), and trends for an interaction between severe childhood adversity and SNPs in IL1B and IL2 for depressive symptoms.

CONCLUSIONS

Our findings provide preliminary evidence that common variation in IL6 may be associated with depressive symptoms in children and adolescents, and that common variation in interleukin genes may sensitize individuals to the depressogenic effects of traumatic life experiences. Replication in independent samples is needed.

COMT Val/Met and Psychopathic Traits in Children and Adolescents: A Systematic Review and New Evidence of a Developmental Trajectory toward Psychopathy

Psychopathic traits in youth may lead to adult criminal behaviors/psychopathy. The Val158Met polymorphism of catechol-O-methyltransferase (COMT) may influence the risk for psychopathy-related behaviors, while acting as a biomarker for predicting treatment response to dopaminergic medications. The literature shows inconsistent findings, making the interpretation of COMT's role difficult. The aims of this article are (i) to conduct a systematic review to analyze the effects of COMT Val158Met on psychopathic traits in children and adolescents, and (ii) to present new evidence on the developmental trajectory of the association of Val158Met and youth psychopathic traits. For the systematic review, a literature search was conducted using PubMed, EMBASE, OVID Medline and PsychINFO with the search terms for psychopathic traits, Val158Met and age of interest. In our genotype study, the COMT Val158Met genotype of 293 youth with European ancestry was analyzed in association with the psychopathy-related behavior scores from the Child Behavior Checklist and the Psychopathy Screening Device. To examine the potential influence of developmental changes, the sample was split into at or above and below age 13, and analyses were performed in males and females separately. The literature search yielded twenty-eight articles to be included in the systematic review, which demonstrated mixed results on the association depending on environmental factors, sex ratios, age groups and behavioral disorder diagnoses. The results from our genotype study revealed that Met homozygous youth in the below age 13 group and conversely Val carrier youth in the above age 13 group were more likely to display psychopathic traits. To our knowledge, this is the first study to systematically review the effects of COMT Val158Met on psychopathic traits in childhood and adolescence, and to provide new evidence on the changing effects of Val158Met on psychopathy-related behaviors with development. Elucidating the role of the COMT genotype in conjunction with the child versus adolescent stage of development for psychopathic traits may help predict treatment response, and may lead to early intervention and prevention strategies.

Evidence for association of vasopressin receptor 1A promoter region repeat with childhood onset aggression

OBJECTIVE

Childhood onset aggression can cause major suffering to affected families and is associated with many negative outcomes in the child's later life, including poor academic performance, adolescent delinquency, drug abuse, depression and antisocial personality disorder. Currently available prevention and intervention strategies have limited efficacy, but a better understanding of underlying genetic and neurobiological factors can lead to more effective prevention and treatment strategies, through genetic screening programs and novel therapies.

METHOD

This study examined the RS1 (n = 299 aggression, n = 192 controls) and RS3 (n = 291 aggression, n = 189 controls) microsatellite repeats within the promoter region of the vasopressin receptor 1A gene (AVPR1A) and their association with extreme childhood aggression, as assessed by the Child Behavior Checklist (CBCL), as well as the Teacher Report Form (TRF) and Youth Self Report (YSR). Binary logistic regression was used to model the relationship between microsatellite length and childhood aggression. Age and sex were used as covariates.

RESULTS

Logistic regression revealed a nominally significant association between one specific RS3 repeat and non-aggressive status. No association was found for any of the RS1 repeats. In a separate model, grouping repeats into short and long, carriers of long RS3 repeats were nominally significantly associated with non-aggressive status.

CONCLUSIONS

These findings suggest a role for AVPR1A and its RS3 microsatellite in extreme childhood aggression and could lead to a better understanding of the biological pathways of aggressive behavior. However, independent replication and further research into the functionality of studied genetic variants is required.

From warrior genes to translational solutions: novel insights into monoamine oxidases (MAOs) and aggression

The pervasive and frequently devastating nature of aggressive behavior calls for a collective effort to understand its psychosocial and neurobiological underpinnings. Regarding the latter, diverse brain areas, neural networks, neurotransmitters, hormones, and candidate genes have been associated with antisocial and aggressive behavior in humans and animals. This review focuses on the role of monoamine oxidases (MAOs) and the genes coding for them, in the modulation of aggression. During the past 20 years, a substantial number of studies using both pharmacological and genetic approaches have linked the MAO system with aggressive and impulsive behaviors in healthy and clinical populations, including the recent discovery of MAALIN, a long noncoding RNA (lncRNA) regulating the MAO-A gene in the human brain. Here, we first provide an overview of the MAOs and their physiological functions, we then summarize recent key findings linking MAO-related enzymatic and gene activity and aggressive behavior, and, finally, we offer novel insights into the mechanisms underlying this association. Using the existing experimental evidence as a foundation, we discuss the translational implications of these findings in clinical practice and highlight what we believe are outstanding conceptual and methodological questions in the field. Ultimately, we propose that unraveling the specific role of MAO in aggression requires an integrated approach, where this question is pursued by combining psychological, radiological, and genetic/genomic assessments. The translational benefits of such an approach include the discovery of novel biomarkers of aggression and targeting the MAO system to modulate pathological aggression in clinical populations.

The role of monoamine oxidase A in the neurobiology of aggressive, antisocial, and violent behavior: A tale of mice and men

Over the past two decades, research has revealed that genetic factors shape the propensity for aggressive, antisocial, and violent behavior. The best-documented gene implicated in aggression is MAOA (Monoamine oxidase A), which encodes the key enzyme for the degradation of serotonin and catecholamines. Congenital MAOA deficiency, as well as low-activity MAOA variants, has been associated with a higher risk for antisocial behavior (ASB) and violence, particularly in males with a history of child maltreatment. Indeed, the interplay between low MAOA genetic variants and early-life adversity is the best-documented gene × environment (G × E) interaction in the pathophysiology of aggression and ASB. Additional evidence indicates that low MAOA activity in the brain is strongly associated with a higher propensity for aggression; furthermore, MAOA inhibition may be one of the primary mechanisms whereby prenatal smoke exposure increases the risk of ASB. Complementary to these lines of evidence, mouse models of Maoa deficiency and G × E interactions exhibit striking similarities with clinical phenotypes, proving to be valuable tools to investigate the neurobiological mechanisms underlying antisocial and aggressive behavior. Here, we provide a comprehensive overview of the current state of the knowledge on the involvement of MAOA in aggression, as defined by preclinical and clinical evidence. In particular, we show how the convergence of human and animal research is proving helpful to our understanding of how MAOA influences antisocial and violent behavior and how it may assist in the development of preventative and therapeutic strategies for aggressive manifestations.

Association Analysis of Monoamine Oxidase-A Gene Promoter Polymorphism (MAOA uVNTR) for Antisocial Behavior: Absence of the Counting Number Repeats in Central Iran

Background: The MAOA gene is located on the X chromosome (Xp11.23). Several studies have established a VNTR (Variable Number Tandem Repeat) polymorphism in the upstream of the MAOA gene transcriptional initiation region named uVNTR which is correlated with the risk of antisocial behavior. Objectives: This study aimed to investigate the association between MAOA genotypes and the risk of violent behavior in a cohort of violent and age-matched non-violent individuals. Methods: In the current case-control study, MAOA uVNTR was genotyped in a cohort of 88 violent and 95 age-matched non-violent individuals. Individuals were genotyped for the MAOA uVNTR by performing PCR, gel electrophoresis, and sequencing. Furthermore, a chi-square test was performed using SPSS, and a p-value of less than 0.05 was considered statistically significant. Results: We identified three MAOA uVNTR allelic variants: They were harboring 3.5, 4.5, and 5.5 repeated sequences. Alleles with 2, 3, 4, 5, and 6 repeats were not observed in any of the two examined groups. Conclusions: We did not detect a statistically appreciable association between antisocial behavior and allele frequencies in the studied population in central Iran.

The effect of polymorphisms in startle-related genes on anxiety symptom severity

Given the limited effectiveness of treatments for pathological anxiety, there is a pressing need to identify genetic markers that can aid the precise selection of treatments and optimize treatment response. Anxiety and startle response levels demonstrate a direct relationship, and previous literature suggests that exaggerated startle reactivity may serve as an endophenotype of pathological anxiety. In addition, genetic variants related to startle reactivity may play a role in the etiology of pathological anxiety. In the current study, we selected 22 single nucleotide polymorphisms (SNPs) related to startle reactivity in the literature, and examined their association with anxiety symptom severity across psychiatric disorders (n = 508), and in a subset of patients with an anxiety disorder (n = 298). Overall, none of the SNPs pass correction for multiple independent tests. However, across psychiatric patients, rs6323 from the monoamine oxidase A (MAOA) gene and rs324981 from the neuropeptide S receptor 1 (NPSR1) gene were nominally associated with baseline anxiety symptom severity (p = 0.017, 0.023). These preliminary findings provide support for investigating startle-related genetic variants to identify biomarkers of anxiety symptom severity.

Low Resting Heart Rate and Stalking Perpetration

There is consistent evidence to suggest that individuals with low resting heart rate are more likely to engage in a variety of antisocial behaviors. The present study examines whether this finding can be extended to stalking perpetration. Drawing from fearlessness theory and stimulation-seeking theory, as well as conceptual work of Meloy and Fisher, we find that individuals with low resting heart rates had significantly greater odds of engaging in stalking behavior, net of controls for sex, age, race, self-control, parental affection, delinquent peers, attitudes/beliefs toward crime, and aggression. When disaggregated by sex, the heart rate-stalking relationship was found to be significant for males, but not for females. The implications of these findings are discussed from a biosocial perspective.

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.

MAOA-VNTR Genotype Effects on Ventral Striatum-Hippocampus Network in Alzheimer's Disease: Analysis Using Structural Covariance Network and Correlation with Neurobehavior Performance

Functional polymorphisms in the promoter region of the monoamine oxidase A (MAOA) gene are associated with brain MAOA activity and transcriptional efficiency in patients with Alzheimer's disease (AD). This study investigated structural covariance networks mediated by MAOA-variable number tandem repeat (VNTR) genotypes in patients with AD, and assessed whether this effect was associated with sex. A total of 193 patients with AD were classified into four genotype groups based on MAOA transcriptional efficiency (female low [L], low-high + high activity groups [LH + H]; male L, male H groups). Structural covariance networks were constructed focusing on triple-network and striatal networks. Covariance strength was analyzed in the four groups, and the genotype and sex main effects and their interactions were analyzed. Significant peak cluster volumes were correlated with neurobehavioral scores to establish the clinical significance. MAOA genotypes mediated the structural covariance strength on the dorsolateral prefrontal cortex (dLPFC)-caudate axis in both sexes, but a higher covariance strength was shown in the female L group and male H group. The independent effect of male sex was related to higher covariance strength in the frontal medial superior region in the dLPFC, dorsal caudate (DC), and ventral superior striatum (VSs) seeds. In contrast, female sex had higher covariance strength in the frontal opercular areas anchored by the dLPFC, DC, and VSs seeds. Topographies showing higher covariance strength with sex interactions were found in the male H group and female L group in the dLPFC supplementary motor axis, DC-SMA, and DC-precentral axis. In our patients with AD, MAOA-VNTR polymorphisms and sex had independent and interactive effects on structural covariance networks, of which the dLPFC-, VSs-, and DC-anchored networks represented major endophenotypes that determined cognitive outcomes. The sex-genotype interaction model suggested that male high activity and female low activity may modulate brain morphometric connectivity and determine cognitive scores.

Interacting Effect of Catechol-O-Methyltransferase (COMT) and Monoamine Oxidase A (MAOA) Gene Polymorphisms, and Stressful Life Events on Aggressive Behavior in Chinese Male Adolescents

Numerous studies have demonstrated that both catechol-O-methyltransferase (COMT) gene and monoamine oxidase A (MAOA) gene have been involved in aggressive behavior, as have stressful life events (SLEs). However, most of available evidence was based upon single gene or single gene–environment design, which is limited in accounting for the variance of aggressive behavior, a complex phenotype. This study examined the possible gene × gene × environment interactions between SLE (interpersonal problems and academic pressure) and two genetic polymorphisms (MAOA T941G and COMT Ala22/72Ser) correlated with aggressive behaviors in a sample of 658 Chinese male adolescents. Mothers and teachers reported on adolescents’ aggressive behavior using Achenbach’s Child Behavior Checklist and Teacher Report Form, respectively. Adolescents completed Self-Rating Life Events Checklist. Saliva samples were collected for DNA analysis. The results revealed no main effects of MAOA T941G and COMT Ala22/72Ser polymorphisms on male adolescents’ aggressive behaviors. However, a two-way interactive effect of interpersonal problems and MAOA T941G genotype on teacher-reported aggressive behavior was observed: adolescents with lower activity of MAOA T allele, but not those with MAOA G allele, exhibited greater aggressive behavior with an increase in interpersonal problems. A three-way interaction among COMT Ala22/72Ser and MAOA T941G polymorphisms, and SLE in the academic pressure on aggressive behavior was also identified. Among adolescents with lower activity of COMT GT/TT genotype and MAOA T allele, the higher level of academic pressure was significantly linked with an amplification of aggressive behavior, whereas this association didn’t exist among those with other genotypes. The present study presents the first evidence of COMT × MAOA × SLE interaction effect on male adolescents’ aggressive behavior, highlights the importance of considering distinct domains of stressful events and information bias when examining the effect of MAOA and COMT on aggressive behavior, and thereby contributes to MAOA gene-aggression and COMT gene-aggression literature.

Sex differences modulating serotonergic polymorphisms implicated in the mechanistic pathways of risk for depression and related disorders

Despite consistent observations of sex differences in depression and related emotional disorders, we do not yet know how these sex differences modulate the effects of genetic polymorphisms implicated in risk for these disorders. This Mini-Review focuses on genetic polymorphisms of the serotonergic system to illustrate how sex differences might modulate the neurobiological pathways involved in the development of depression. We consider the interacting role of environmental factors such as early-life stress. Given limited current knowledge about this topic, we highlight methodological considerations, challenges, and guidelines for future research. © 2016 Wiley Periodicals, Inc.

Blunted insula activation reflects increased risk and reward seeking as an interaction of testosterone administration and the MAOA polymorphism

Testosterone, a male sex hormone, has been suggested to partly explain mixed findings in males and females when investigating behavioral tendencies associated with the MAOA polymorphism. Prior studies indicated that the MAOA polymorphism represents a vulnerability factor for financial risk-taking and harm avoidance and that testosterone increases human risk-taking. We therefore assumed an interactive influence of the MAOA polymorphism and testosterone application on decision making and corresponding neural correlates in a risk and reward context. Stratified for the MAOA polymorphism (S =short, L =long), 103 healthy males were assigned to a placebo or testosterone group (double blind, randomized) receiving a topical gel containing 50 mg testosterone. During a functional MRI scan, the participants performed a sequential decision making task. Our results indicate that testosterone and the MAOA polymorphism jointly influence sequential decision making. The MAOA-S variant was associated with less automatic harm avoidance as reflected in response times on safe decisions. Moreover, after testosterone administration, MAOA-S carriers were more risk-taking. Overall activity in the anterior cingulate cortex, anterior insula and inferior frontal gyrus increased with growing risk for losses. In the anterior insula, testosterone administration mitigated this effect solely in MAOA-S carriers. This might be a reflection of an improved coping during risk-reward conflicts subsequently modulating risky decision making. While the molecular basis is not well defined so far, our results support the assumption of testosterone as a modulatory factor for previously reported sex differences of behavioral associations with the MAOA-S variant. Hum Brain Mapp 38:4574-4593, 2017. © 2017 Wiley Periodicals, Inc.

Examining human behavior in video games: The development of a computational model to measure aggression

Video games with violent content have raised considerable concern in popular media and within academia. Recently, there has been considerable attention regarding the claim of the relationship between aggression and video game play. The authors of this study propose the use of a new class of tools developed via computational models to allow examination of the question of whether there is a relationship between violent video games and aggression. The purpose of this study is to computationally model and compare the General Aggression Model with the Diathesis Mode of Aggression related to the play of violent content in video games. A secondary purpose is to provide a method of measuring and examining individual aggression arising from video game play. Total participants examined for this study are N = 1065. This study occurs in three phases. Phase 1 is the development and quantification of the profile combination of traits via latent class profile analysis. Phase 2 is the training of the artificial neural network. Phase 3 is the comparison of each model as a computational model with and without the presence of video game violence. Results suggest that a combination of environmental factors and genetic predispositions trigger aggression related to video games.

FKBP5 interacts with maltreatment in children with extreme, pervasive, and persistent aggression

Genetic variation in stress response protein FKBP5 is associated with adult psychopathology, but little is known about its role in children's mental health. 5 polymorphisms were genotyped in 170 high aggression cases and 170 age- and sex-matched controls. The rs9470080 polymorphism was associated with physiological anxiety, while rs4713916 polymorphism interacted with maltreatment to influence externalizing traits. These results suggest that genetic variation in FKBP5 has a role in children's vulnerability to stress-related behaviours.

The role of MAO in personality and drug use

Monoamine oxidases, both MAO-A and MAO-B, have been implicated in personality traits and complex behaviour, including drug use. Findings supporting the involvement of MAO-A and MAO-B in shaping personality and in the development of strategies of making behavioural choices come from a variety of studies that have examined either prevalence of gene variants in clinical groups or population-derived samples, estimates of enzyme activity in blood or, by positron emission tomography, in the brain and, most recently, measurement of methylation of the gene. Most of the studies converge in associating MAO-A and MAO-B with impulsive, aggressive or antisocial personality traits or behaviours, including alcohol-related problems, and for MAO-A available evidence strongly supports interaction with adverse environmental exposures in childhood. What is known about genotype effects, and on expression and activity of the enzyme in the brain and in blood has not yet been possible to unite into a mechanistic model of the role of monoamine systems, but the reason for this low degree of generalization is likely caused by the cross-sectional nature of investigation that has not incorporated the developmental effects of MAO-s in critical time windows, including the foetal period. The "risk variants" of both MAO-s appear to increase behavioural plasticity, as supportive environments may particularly well enhance the hidden potential of their carriers. Importantly, male and female brain and behaviours have been found very different with regard to MAO×life events interaction. Future studies need to take into consideration these developmental aspects and sex/gender, as well as to specify the role of different types of environmental factors.

Monoamine oxidase and agitation in psychiatric patients

Subjects with schizophrenia or conduct disorder display a lifelong pattern of antisocial, aggressive and violent behavior and agitation. Monoamine oxidase (MAO) is an enzyme involved in the degradation of various monoamine neurotransmitters and neuromodulators and therefore has a role in various psychiatric and neurodegenerative disorders and pathological behaviors. Platelet MAO-B activity has been associated with psychopathy- and aggression-related personality traits, while variants of the MAOA and MAOB genes have been associated with diverse clinical phenotypes, including aggressiveness, antisocial problems and violent delinquency. The aim of the study was to evaluate the association of platelet MAO-B activity, MAOB rs1799836 polymorphism and MAOA uVNTR polymorphism with severe agitation in 363 subjects with schizophrenia and conduct disorder. The results demonstrated significant association of severe agitation and smoking, but not diagnosis or age, with platelet MAO-B activity. Higher platelet MAO-B activity was found in subjects with severe agitation compared to non-agitated subjects. Platelet MAO-B activity was not associated with MAOB rs1799836 polymorphism. These results suggested the association between increased platelet MAO-B activity and severe agitation. No significant association was found between severe agitation and MAOA uVNTR or MAOB rs1799836 polymorphism, revealing that these individual polymorphisms in MAO genes are not related to severe agitation in subjects with schizophrenia and conduct disorder. As our study included 363 homogenous Caucasian male subjects, our data showing this negative genetic association will be a useful addition to future meta-analyses.

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.

Identification of genomic variants putatively targeted by selection during dog domestication

BACKGROUND

Dogs [Canis lupus familiaris] were the first animal species to be domesticated and continue to occupy an important place in human societies. Recent studies have begun to reveal when and where dog domestication occurred. While much progress has been made in identifying the genetic basis of phenotypic differences between dog breeds we still know relatively little about the genetic changes underlying the phenotypes that differentiate all dogs from their wild progenitors, wolves [Canis lupus]. In particular, dogs generally show reduced aggression and fear towards humans compared to wolves. Therefore, selection for tameness was likely a necessary prerequisite for dog domestication. With the increasing availability of whole-genome sequence data it is possible to try and directly identify the genetic variants contributing to the phenotypic differences between dogs and wolves.

RESULTS

We analyse the largest available database of genome-wide polymorphism data in a global sample of dogs 69 and wolves 7. We perform a scan to identify regions of the genome that are highly differentiated between dogs and wolves. We identify putatively functional genomic variants that are segregating or at high frequency [> = 0.75 Fst] for alternative alleles between dogs and wolves. A biological pathways analysis of the genes containing these variants suggests that there has been selection on the 'adrenaline and noradrenaline biosynthesis pathway', well known for its involvement in the fight-or-flight response. We identify 11 genes with putatively functional variants fixed for alternative alleles between dogs and wolves. The segregating variants in these genes are strong candidates for having been targets of selection during early dog domestication.

CONCLUSIONS

We present the first genome-wide analysis of the different categories of putatively functional variants that are fixed or segregating at high frequency between a global sampling of dogs and wolves. We find evidence that selection has been strongest around non-synonymous variants. Strong selection in the initial stages of dog domestication appears to have occurred on multiple genes involved in the fight-or-flight response, particularly in the catecholamine synthesis pathway. Different alleles in some of these genes have been associated with behavioral differences between modern dog breeds, suggesting an important role for this pathway at multiple stages in the domestication process.

The role of genetic variants in genes regulating the oxytocin-vasopressin neurohumoral system in childhood-onset aggression

OBJECTIVE

The genetic etiology of aggressive behaviors remains elusive, but growing evidence suggests that they are heritable, and certain genetic variants have been implicated as contributing factors. The oxytocin-vasopressin (OXT-AVP) neurohumoral system has recently been implicated in social behaviors. Oxytocin, especially, has been linked to prosocial behaviors such as trust and social bonds. Hence, the aim of this study was to determine whether genes regulating this system were also associated with childhood-onset aggressive behaviors.

METHODS

Our sample included 182 White children showing extreme, persistent, and pervasive aggressive behavior. These cases were matched with 182 White controls on the basis of sex and age. We used PCR to determine the genotype for 28 single nucleotide polymorphisms within eight genes regulating the OXT-AVP system, including CD38 polymorphisms. Genotypic analyses were carried out using STATA, whereas differences in haplotypic and allelic frequencies were analyzed using Unphased.

RESULTS

None of the results reached significance after correction for multiple testing. However, nominally significant allelic effects were observed for OXTR rs6770632T (P=0.028) and AVPR1A rs11174811G (P=0.040) in females, and OXTR rs237898A (P=0.006), rs237902C (P=0.007), and AVP rs3761249A (P=0.008) in males.

CONCLUSION

Genetic variants regulating the OXT-AVP system may be associated with childhood-onset aggression.

Monoamine oxidase a promoter variable number of tandem repeats (MAOA-uVNTR) in alcoholics according to Lesch typology

Background: The aim of this study was to examine the association between the MAOA-uVNTR gene polymorphism in a homogeneous subgroups of patients with alcohol dependence categorized according to Lesch’s typology. Methods: DNA was provided from alcohol dependent (AD) patients (n = 370) and healthy control subjects (n = 168) all of Polish descent. The history of alcoholism was obtained using the Polish version of the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA). Samples were genotyped using PCR methods. Results: We found no association between alcohol dependence and MAOA gene polymorphism. Conclusions: Lesch typology is a clinical consequence of the disease and its phenotypic description is too complex for a simple genetic analysis.

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.

Candidate genes for aggression and antisocial behavior: a meta-analysis of association studies of the 5HTTLPR and MAOA-uVNTR

Variation in central serotonin levels due to genetic mutations or experimental modifications has been associated with the manifestation of aggression in humans and animals. Many studies have examined whether common variants in serotonergic genes are implicated in aggressive or antisocial behaviors (ASB) in human samples. The two most commonly studied polymorphisms have been the serotonin transporter linked polymorphic region of the serotonin transporter gene (5HTTLPR) and the 30 base pair variable number of tandem repeats of the monoamine oxidase A gene (MAOA-uVNTR). Despite the aforementioned theoretical justification for these polymorphisms, findings across studies have been mixed and are thus difficult to interpret. A meta-analysis of associations of the 5HTTLPR and MAOA-uVNTR with ASB was conducted to determine: (1) the overall magnitude of effects for each polymorphism, (2) the extent of heterogeneity in effect sizes across studies and the likelihood of publication bias, and (3) whether sample-level or study-level characteristics could explain observed heterogeneity across studies. Both the 5HTTLPR and the MAOA-uVNTR were significantly associated with ASB across studies. There was also significant and substantial heterogeneity in the effect sizes for both markers, but this heterogeneity was not explained by any sample-level or study-level characteristics examined. We did not find any evidence for publication bias across studies for the MAOA-uVNTR, but there was evidence for an oversampling of statistically significant effect sizes for the 5HTTLPR. These findings provide support for the modest role of common serotonergic variants in ASB. Implications regarding the role of serotonin in antisocial behavior and the conceptualization of antisocial and aggressive phenotypes are discussed.

The association of 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR gene polymorphisms and borderline personality disorder in female heroin-dependent Chinese subjects

OBJECTIVE

To explore the association between the 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR polymorphisms with co-morbid borderline personality disorder (BPD) in female heroin-dependent patients.

SUBJECTS AND METHODS

In a case control study, we compared the polymorphic distributions of 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR in 296 female heroin-dependent patients (including 61 patients with BPD and 235 without BPD) and 101 normal females by genotypes, alleles, and interaction between genes.

RESULTS

Female heroin-dependent subjects with BPD have lower frequency of the high activity allele (L: 4 repeats (4R)) of MAOA-LPR than those female heroin-dependent subjects without BPD, and have higher 5-HTTVNTR 10R/10R genotype frequency than normal female controls, with adjusted P-value<0.05 (after adjusted for multiple testing by 1000-fold permutation tests) respectively. By MDR (Multifactor Dimensionality Reduction) analyses, the interactive effects between MAOA-LPR and 5-HTTVNTR, and among MAOA-LPR, 5-HTTVNTR and rs6311 were close to the significance level (P=0.05) in predicting the risk of co-morbidity of BPD and heroin dependence relative to normal female controls, with 1000-fold permutation testing P-value<0.06 however >0.05 respectively.

CONCLUSION

5-HTTVNTR and MAOA-LPR may have independent predictive effects on co-morbid BPD in female heroin-dependent patients; the gene-gene interactions between MAOA-LPR and 5-HTTVNTR, and among MAOA-LPR, 5-HTTVNTR and rs6311 might also be involved in the etiology of this co-morbidity.

Testing for association of the monoamine oxidase A promoter polymorphism with brain structure volumes in both autism and the fragile X syndrome

BACKGROUND

Autism and the fragile X syndrome (FXS) are related to each other genetically and symptomatically. A cardinal biological feature of both disorders is abnormalities of cerebral cortical brain volumes. We have previously shown that the monoamine oxidase A (MAOA) promoter polymorphism is associated with cerebral cortical volumes in children with autism, and we now sought to determine whether the association was also present in children with FXS.

METHODS

Participants included 47 2-year-old Caucasian boys with FXS, some of whom also had autism, as well as 34 2-year-old boys with idiopathic autism analyzed in a previous study. The MAOA promoter polymorphism was genotyped and tested for relationships with gray and white matter volumes of the cerebral cortical lobes and cerebro-spinal fluid volume of the lateral ventricles.

RESULTS

MAOA genotype effects in FXS children were the same as those previously observed in idiopathic autism: the low activity MAOA promoter polymorphism allele was associated with increased gray and white matter volumes in all cerebral lobes. The effect was most pronounced in frontal lobe gray matter and all three white matter regions: frontal gray, F = 4.39, P = 0.04; frontal white, F = 5.71, P = 0.02; temporal white, F = 4.73, P = 0.04; parieto-occipital white, F = 5.00, P = 0.03. Analysis of combined FXS and idiopathic autism samples produced P values for these regions <0.01 and effect sizes of approximately 0.10.

CONCLUSIONS

The MAOA promoter polymorphism is similarly associated with brain structure volumes in both idiopathic autism and FXS. These data illuminate a number of important aspects of autism and FXS heritability: a genetic effect on a core biological trait of illness, the specificity/generalizability of the genetic effect, and the utility of examining individual genetic effects on the background of a single gene disorder such as FXS.

Effect of MAOA Genotype on Resting-State Networks in Healthy Participants

Up to now, it remains unclear how monoamine oxidase A (MAOA), which has been repeatedly linked to aggression, affects brain activity within resting-state networks (RSN). Here, we used functional magnetic resonance imaging (fMRI) to test whether the MAOA genotype might influence activity within the common RSN. Our results demonstrate that during rest, participants with the low-activity genotype (MAOA-L) exhibit more activity within frontoparietal and temporal parts of the default mode network (DMN) and the cerebellum. The executive control and salience RSN revealed reduced activity for the MAOA-L group in several areas related to executive control, namely the right middle frontal gyrus (BA 6 and BA 9), and the dorsal part of the anterior cingulate cortex. Participants with the high-activity genotype (MAOA-H) showed increased activity in the posterior cingulate part of the DMN. Taken together, we found widespread hyperactivity within the DMN and reduced activity in brain areas related to executive and inhibitory control for the MAOA-L group. We discuss how these first results examining the influence of MAOA on the resting brain might be related to previous findings regarding the genetics of aggression, while acknowledging that this is an exploratory study which needs further confirmation.

Neurobiological mechanisms for impulsive-aggression: the role of MAOA

Aggression may be present across a large part of the spectrum of psychopathology, and underlies costly criminal antisocial behaviors. Human aggression is a complex and underspecified construct, confounding scientific discovery. Nevertheless, some biologically tractable subtypes are apparent, and one in particular-impulsive (reactive) aggression-appears to account for many facets of aggression-related dysfunction in psychiatric illness. Impulsive-aggression is significantly heritable, suggesting genetic transmission. However, the specific neurobiological mechanisms that mediate genetic risk for impulsive-aggression remain unclear. Here, we review extant data on the genetics and neurobiology of individual differences in impulsive-aggression, with particular attention to the role of genetic variation in Monoamine Oxidase A (MAOA) and its impact on serotonergic signaling within corticolimbic circuitry.

The neurobiology of oppositional defiant disorder and conduct disorder: altered functioning in three mental domains

This review discusses neurobiological studies of oppositional defiant disorder and conduct disorder within the conceptual framework of three interrelated mental domains: punishment processing, reward processing, and cognitive control. First, impaired fear conditioning, reduced cortisol reactivity to stress, amygdala hyporeactivity to negative stimuli, and altered serotonin and noradrenaline neurotransmission suggest low punishment sensitivity, which may compromise the ability of children and adolescents to make associations between inappropriate behaviors and forthcoming punishments. Second, sympathetic nervous system hyporeactivity to incentives, low basal heart rate associated with sensation seeking, orbitofrontal cortex hyporeactiviy to reward, and altered dopamine functioning suggest a hyposensitivity to reward. The associated unpleasant emotional state may make children and adolescents prone to sensation-seeking behavior such as rule breaking, delinquency, and substance abuse. Third, impairments in executive functions, especially when motivational factors are involved, as well as structural deficits and impaired functioning of the paralimbic system encompassing the orbitofrontal and cingulate cortex, suggest impaired cognitive control over emotional behavior. In the discussion we argue that more insight into the neurobiology of oppositional defiance disorder and conduct disorder may be obtained by studying these disorders separately and by paying attention to the heterogeneity of symptoms within each disorder.

XM: association testing on the X-chromosome in case-control samples with related individuals

Genetic variants on the X-chromosome could potentially play an important role in some complex traits. However, development of methods for detecting association with X-linked markers has lagged behind that for autosomal markers. We propose methods for case-control association testing with X-chromosome markers in samples with related individuals. Our method, XM, appropriately adjusts for both correlation among relatives and male-female allele copy number differences. Features of XM include: (1) it is applicable to and computationally feasible for completely general combinations of family and case-control designs; (2) it allows for both unaffected controls and controls of unknown phenotype to be included in the same analysis; (3) it can incorporate phenotype information on relatives with missing genotype data; and (4) it adjusts for sex-specific trait prevalence values. We propose two other tests, Xχ and XW, which can also be useful in certain contexts. We derive the best linear unbiased estimator of allele frequency, and its variance, for X-linked markers. In simulation studies with related individuals, we demonstrate the power and validity of the proposed methods. We apply the methods to X-chromosome association analysis of (1) asthma in a Hutterite sample and (2) alcohol dependence in the GAW 14 COGA data. In analysis (1), we demonstrate computational feasibility of XM and the applicability of our robust variance estimator. In analysis (2), we detect significant association, after Bonferroni correction, between alcohol dependence and single nucleotide polymorphism rs979606 in the monoamine oxidases A gene, where this gene has previously been found to be associated with substance abuse and antisocial behavior.

The association of 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR gene polymorphisms and antisocial personality disorder in male heroin-dependent Chinese subjects

OBJECTIVE

To explore the association between the 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR polymorphisms with comorbidity of antisocial personality disorder in male heroin-dependent patients.

SUBJECTS AND METHODS

In case control study, we compared the polymorphic distributions of 5-HTR2A-1438A/G, COMTVal158Met, MAOA-LPR, DATVNTR and 5-HTTVNTR in 588 male heroin-dependent patients (including 311 patients with antisocial personality disorder and 277 patients without antisocial personality disorder) and 194 normal males by genotypes, alleles, and interaction between genes.

RESULTS

Between male heroin-dependent patients with antisocial personality disorder and normal males, and between male heroin-dependent patients with and without antisocial personality disorder, the distributions of 5-HTTVNTR polymorphic genotypes and alleles were in statistical significance. Individuals carrying 10R allele were in higher risk of the comorbidity of antisocial personality disorder and heroin dependence. By MDR analyses, the interaction between 5-HTTVNTR and DATVNTR was close to statistical significance in predicting the risk of antisocial personality disorder in male heroin dependent patients. In male heroin dependent patients, individuals carrying 5-HTTVNTR 10R allele or/and DATVNTR 9R allele were in higher risks of co-occurring antisocial personality disorder, while individuals with 5-HTTVNTR 12R/12R and DATVNTR 10R/10R genotypes together were in lower risks of antisocial personality disorder.

CONCLUSION

5-HTTVNTR, and the interaction between 5-HTTVNTR and DATVNTR may be associated with the comorbidity of antisocial personality disorder in male heroin-dependent patients.

Association of positive and negative parenting behavior with childhood ADHD: interactions with offspring monoamine oxidase A (MAO-A) genotype

Relatively little is known about the potential interplay between genetic and environmental influences on attention-deficit/hyperactivity disorder (ADHD), including gene-environment interaction (G×E). There is evidence that parenting behavior interacts with offspring genotype in the development of externalizing problems, but studies have largely focused on explicit maltreatment rather than differentiated measures of parenting behavior, including positive and negative parenting. We tested the interactive effects of the 30-base pair variable number tandem repeat (VNTR) polymorphism of the monoamine oxidase A gene (MAO-A) with positive and negative parenting behavior on parent- and teacher ratings of inattention and hyperactivity symptoms among 150 6-9 year-old boys with and without ADHD. Negative parenting predicted parent and teacher ratings of inattention symptoms, but only among boys with high-activity MAO-A genotype. MAO-A genotype did not moderate the association of positive parenting and parent- and teacher ratings of ADHD. We discuss the potential role of interactive exchanges between parenting behavior and child genotype in the development and persistence of ADHD and related behavior problems.

Childhood aggression, callous-unemotional traits and oxytocin genes

Given the known behavior effects of oxytocin,and in particular its putative effect on trust, affiliation and anxiety, we hypothesized that oxytocin may be involved in the development and expression of callous-unemotional traits in children with aggressive antisocial behavior. We recruited 162 children between the ages of 6 and 16. The majority of subjects were Caucasian (84.0%) compared to African-Canadian (4.9%) and others (11.1%). The oxytocin and oxytocin receptor gene polymorphisms were genotyped and analyzed for possible association with child aggression in a case–control study design as well as with callous-unemotional traits in a within cases analysis. We did not have significant findings with our tested OXTR markers in the case–control analysis. We found the OXTR_rs237885 AA genotype carriers to score higher than AC or CC genotype carriers on the callous-unemotional traits. This result remained significant following correction for multiple testing. No other markers were found to be significant. However, the haplotype consisting of the OXTR_rs237885 A allele and OXTR_rs2268493 A allele was associated with significantly higher callous-unemotionals cores than other haplotypes. This is the first known study to show a significant association between callous unemotional traits in children and adolescents with extreme, persistent pervasive aggression and a polymorphism on the oxytocin receptor. Given the small sample size and the possibility of false positive effects, the need to replicate and verify these findings is required.

Deviant peer affiliation and antisocial behavior: interaction with Monoamine Oxidase A (MAOA) genotype

Although genetic and environmental factors are separately implicated in the development of antisocial behavior (ASB), interactive models have emerged relatively recently, particularly those incorporating molecular genetic data. Using a large sample of male Caucasian adolescents and young adults from the National Longitudinal Study of Adolescent Health (Add Health), the association of deviant peer affiliation, the 30-base pair variable number tandem repeat polymorphism in promoter region of the monoamine oxidase-A (MAOA) gene, and their interaction, with antisocial behavior (ASB) was investigated. Weighted analyses accounting for over-sampling and clustering within schools as well as controlling for age and wave suggested that deviant peer affiliation and MAOA genotype were each significantly associated with levels of overt ASB across a 6-year period. Only deviant peer affiliation was significantly related to covert ASB, however. Additionally, there was evidence suggestive of a gene-environment interaction (G × E) where the influence of deviant peer affiliation on overt ASB was significantly stronger among individuals with the high-activity MAOA genotype than the low-activity genotype. MAOA was not significantly associated with deviant peer affiliation, thus strengthening the inference of G × E rather than gene-environment correlation (rGE). Different forms of gene-environment interplay and implications for future research on ASB are discussed.

Harsh discipline, childhood sexual assault, and MAOA genotype: an investigation of main and interactive effects on diverse clinical externalizing outcomes

We studied the impact of MAOA genotype, childhood sexual assault, and harsh discipline on clinical externalizing symptoms (substance problems, adult antisocial behavior, and conduct disorder). Participants were 841 individual twins from the Minnesota Twin Family Study assessed through age 25. MAOA genotype was not associated with differences in any phenotype, nor was there a significant interaction between MAOA and harsh discipline for any phenotype or a significant interaction between MAOA and childhood sexual assault for substance problems. We found evidence that childhood sexual assault interacted with MAOA genotype to predict antisocial behavior and conduct disorder symptoms. Individuals with the low MAOA activity genotype who reported childhood sexual assault had more symptoms than individuals with either the high MAOA activity genotype and/or no history of childhood sexual assault. These findings suggest that the previously reported interaction between MAOA and childhood maltreatment may be specific to the antisocial subset of externalizing disorders.

MAOA alters the effects of heavy drinking and childhood physical abuse on risk for severe impulsive acts of violence among alcoholic violent offenders

BACKGROUND

A polymorphism in the promoter region of the monoamine oxidase A gene (MAOA) has been shown to alter the effect of persistent drinking and childhood maltreatment on the risk for violent and antisocial behaviors. These findings indicate that MAOA could contribute to inter-individual differences in stress resiliency.

METHODS

Recidivism in severe violent crimes was assessed after 8 years of nonincarcerated follow-up in a male sample of 174 impulsive Finnish alcoholic violent offenders, the majority of whom exhibited antisocial (ASPD) or borderline personality disorder (BPD) or both. We examined whether MAOA genotype alters the effects of heavy drinking and childhood physical abuse (CPA) on the risk for committing impulsive recidivistic violent crimes.

RESULTS

Logistic regression analyses showed that both heavy drinking and CPA were significant independent predictors of recidivism in violent behavior (OR 5.2, p = 0.004 and OR 5.3, p = 0.003) among offenders having the high MAOA activity genotype (MAOA-H), but these predictors showed no effect among offenders carrying the low MAOA activity genotype (MAOA-L).

CONCLUSION

Carriers of the MAOA-H allele have a high risk to commit severe recidivistic impulsive violent crimes after exposure to heavy drinking and CPA.

Effects of MAOA-genotype, alcohol consumption, and aging on violent behavior

BACKGROUND

Environmental factors appear to interact with a functional polymorphism (MAOA-LPR) in the promoter region of the monoamine oxidase A gene (MAOA) in determining some forms of antisocial behavior. However, how MAOA-LPR modulates the effects of other factors such as alcohol consumption related to antisocial behavior is not completely understood.

METHODS

This study examines the conjunct effect of MAOA-LPR, alcohol consumption, and aging on the risk for violent behavior. Recidivism in severe impulsive violent behavior was assessed after 7 to 15 years in a sample of 174 Finnish alcoholic offenders, the majority of whom exhibited antisocial or borderline personality disorder or both, and featured impulsive temperament traits.

RESULTS

The risk for committing new acts of violence increased by 2.3% for each kilogram of increase in yearly mean alcohol consumption (p = 0.004) and decreased by 7.3% for every year among offenders carrying the high activity MAOA genotype. In contrast, alcohol consumption and aging failed to affect violent behavior in the low activity MAOA genotyped offenders. MAOA-LPR showed no main effect on the risk for recidivistic violence.

CONCLUSIONS

Violent offenders carrying the high activity MAOA genotype differ in several ways from carriers with the low activity MAOA risk allele previously associated with antisocial behavior. Finnish high activity MAOA genotyped risk alcoholics exhibiting antisocial behavior, high alcohol consumption, and abnormal alcohol-related impulsive and uncontrolled violence might represent an etiologically distinct alcohol dependence subtype.

Association study of MAO-A and DRD4 genes in schizophrenic patients with aggressive behavior

Genes involved in dopamine neurotransmission are interesting candidates to be analyzed in schizophrenia and aggressive behavior. Therefore, we analyzed the functional polymorphisms of the dopamine receptor D4 (DRD4) and monoamine oxidase A (MAO-A) genes in a sample of 71 schizophrenic patients assessed with the Overt Aggression Scale to measure aggressive behavior. CLUMP analysis of the DRD4 48-bp repeat-exon III polymorphism in schizophrenic patients showed significant differences between the aggressive behavior and the nonaggressive groups (T1 = 18.77, d.f. = 6, p = 0.0046; T3 = 6.54, p = 0.0195). However, analysis of the promoter polymorphism of the MAO-A gene revealed no significant association between aggressive and nonaggressive patients. Finally, analysis of Overt Aggression Scale dimensions exhibited significant differences for the DRD4 and MAO-A genes. Our preliminary findings suggest that the DRD4 and MAO-A genes may be involved in aggressive schizophrenic patients.

Neural mechanisms of aggression

Unchecked aggression and violence exact a significant toll on human societies. Aggression is an umbrella term for behaviours that are intended to inflict harm. These behaviours evolved as adaptations to deal with competition, but when expressed out of context, they can have destructive consequences. Uncontrolled aggression has several components, such as impaired recognition of social cues and enhanced impulsivity. Molecular approaches to the study of aggression have revealed biological signals that mediate the components of aggressive behaviour. These signals may provide targets for therapeutic intervention for individuals with extreme aggressive outbursts. This Review summarizes the complex interactions between genes, biological signals, neural circuits and the environment that influence the development and expression of aggressive behaviour.

Monoamine oxidase A gene is associated with borderline personality disorder

OBJECTIVE

Monoamine oxidase A is a mitochondrial enzyme involved in the degradation of certain neurotransmitter amines: serotonin and norepinephrine. As for its role in aggression, impulsivity, suicide and mood liability, monoamine oxidase A can be considered a functional candidate in borderline personality disorder.

METHODS

To test for this hypothesis we genotyped two polymorphic markers in monoamine oxidase A gene, a promoter VNTR and an rs6323 (T941G) in exon 8, in 111 Caucasian borderline personality disorder patients and 289 Caucasian healthy controls. Association analyses using individual marker and haplotype data were performed by a program of COCAPHASE in UNPHASED (MRC Human Genome Mapping Project Resource Centre, Cambridge, UK).

RESULTS

We found that the borderline personality disorder patients had a high frequency of the high activity VNTR alleles (chi=4.696, P=0.03) and a low frequency of the low activity haplotype (chi=5.089, P=0.02).

CONCLUSION

These results show that the monoamine oxidase A gene may play an important role in the etiological development of the borderline personality disorder.

The importance of stress and genetic variation in human aggression

Both genetic and environmental factors have key roles in determining aggressive tendencies. In particular, reaction to stress appears to be an important factor in precipitating aggressive episodes and individuals may vary in their ability to cope with stressful environments depending on their genetic make up. Evidence from humans and primates indicates that adverse rearing conditions may interact with variants in stress and neurotransmitter pathway genes leading to antisocial and/or violent behaviour. Common alleles of some serotonin pathway genes, including those involved in its degradation (monoamine oxidase A, MAOA), or its re-uptake into pre-synaptic neurones (serotonin transporter, SERT) have been shown to confer functional variation. Examination of the interaction between the alleles of such polymorphisms (in particular those affecting MAOA) and environmental stressors suggest that they may provide protection against, or increase sensitivity to, abusive upbringing; an observation that may explain part of the variability in developmental outcomes associated with maltreatment.

MAOA, maltreatment, and gene-environment interaction predicting children's mental health: new evidence and a meta-analysis

Previous research on adults has shown that a functional polymorphism in the promoter region of the monoamine oxidase A (MAOA) gene moderates the impact of childhood maltreatment on risk for developing antisocial behavior. Thus far, attempts to replicate this finding have been mixed. The current study (i) presents new data investigating this finding in a sample of 975 seven-year-old boys, and (ii) evaluates the extant data by conducting a meta-analysis of published findings. We replicated the original finding by showing that the MAOA polymorphism moderates the development of psychopathology after exposure to physical abuse, we extended the finding to childhood closer in time to the maltreatment experience, and we ruled-out the possibility of a spurious finding by accounting for passive and evocative gene-environment correlation. Moreover, meta-analysis demonstrated that across studies, the association between maltreatment and mental health problems is significantly stronger in the group of males with the genotype conferring low vs high MAOA activity. These findings provide the strongest evidence to date suggesting that the MAOA gene influences vulnerability to environmental stress, and that this biological process can be initiated early in life.

Structural variation of the monoamine oxidase A gene promoter repeat polymorphism in nonhuman primates

By conferring allele-specific transcriptional activity on the monoamine oxidase A (MAOA) gene in humans, length variation of a repetitive sequence [(variable number of tandem repeat (VNTR)] in the MAOA promoter influences a constellation of personality traits related to aggressive and antisocial behavior and increases the risk of neurodevelopmental and psychiatric disorders. Here, we have analyzed the presence and variability of this MAOA promoter repeat in several species of nonhuman primates. Sequence analysis of MAOA's transcriptional control region revealed the presence of the VNTR in chimpanzee (Pan troglodytes), bonobo (Pan paniscus), gorilla (Gorilla gorilla), orangutan (Pongo pygmaeus), rhesus macaque (Macaca mulatta) and Gelada baboon (Theropithecus gelada). The majority of P. troglodytes and P. paniscus showed a single repeat with a sequence identical to the VNTR sequence in humans. In contrast, analyses of the remaining species revealed shorter sequences similar to the first 18 bp of human VNTR. Compared with other nonhuman primates, the VNTR sequence of M. mulatta showed the highest length variability with allele frequencies of 35, 25 and 40% for the five, six and seven repeat variants, respectively. The extent of variability of the MAOA promoter repeat in both rhesus monkeys and humans supports the notion that there may be a relationship between functional MAOA expression and aggression-related traits in humans and rhesus macaque populations.