Effect of COMT genotype on aggressive behaviour in a community cohort of schizophrenic patients

Drosophila mutants lacking the glial neurotransmitter-modifying enzyme Ebony exhibit low neurotransmitter levels and altered behavior

Inhibitors of enzymes that inactivate amine neurotransmitters (dopamine, serotonin), such as catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), are thought to increase neurotransmitter levels and are widely used to treat Parkinson's disease and psychiatric disorders, yet the role of these enzymes in regulating behavior remains unclear. Here, we investigated the genetic loss of a similar enzyme in the model organism Drosophila melanogaster. Because the enzyme Ebony modifies and inactivates amine neurotransmitters, its loss is assumed to increase neurotransmitter levels, increasing behaviors such as aggression and courtship and decreasing sleep. Indeed, ebony mutants have been described since 1960 as "aggressive mutants," though this behavior has not been quantified. Using automated machine learning-based analyses, we quantitatively confirmed that ebony mutants exhibited increased aggressive behaviors such as boxing but also decreased courtship behaviors and increased sleep. Through tissue-specific knockdown, we found that ebony's role in these behaviors was specific to glia. Unexpectedly, direct measurement of amine neurotransmitters in ebony brains revealed that their levels were not increased but reduced. Thus, increased aggression is the anomalous behavior for this neurotransmitter profile. We further found that ebony mutants exhibited increased aggression only when fighting each other, not when fighting wild-type controls. Moreover, fights between ebony mutants were less likely to end with a clear winner than fights between controls or fights between ebony mutants and controls. In ebony vs. control fights, ebony mutants were more likely to win. Together, these results suggest that ebony mutants exhibit prolonged aggressive behavior only in a specific context, with an equally dominant opponent.

Biological Aspects of Aggression and Violence in Schizophrenia

Although the majority of patients with schizophrenia are not actually violent, an increased tendency toward violent behaviors is known to be associated with schizophrenia. There are several factors to consider when identifying the subgroup of patients with schizophrenia who may commit violent or aggressive acts. Comorbidity with substance abuse is the most important clinical indicator of increased aggressive behaviors and crime rates in patients with schizophrenia. Genetic studies have proposed that polymorphisms in the promoter region of the serotonin transporter gene and in the catechol-O-methyltransferase gene are related to aggression. Neuroimaging studies have suggested that fronto-limbic dysfunction may be related to aggression or violence. By identifying specific risk factors, a more efficient treatment plan to prevent violent behavior in schizophrenia will be possible. Management of comorbid substance use disorder may help prevent violent events and overall aggression. Currently, clozapine may be the only effective antipsychotic medication to repress aggressive behavior. With the current medical field moving toward tailored medicine, it is important to identify vulnerable schizophrenia populations and provide efficient treatment.

Biomarkers in aggression

Aggressive behavior exerts an enormous impact on society remaining among the main causes of worldwide premature death. Effective primary interventions, relying on predictive models of aggression that show adequate sensitivity and specificity are currently lacking. One strategy to increase the accuracy and precision of prediction would be to include biological data in the predictive models. Clearly, to be included in such models, biological markers should be reliably associated with the specific trait under study (i.e., diagnostic biomarkers). Aggression, however, is phenotypically highly heterogeneous, an element that has hindered the identification of reliable biomarkers. However, current research is trying to overcome these challenges by focusing on more homogenous aggression subtypes and/or by studying large sample size of aggressive individuals. Further advance is coming by bioinformatics approaches that are allowing the integration of inter-species biological data as well as the development of predictive algorithms able to discriminate subjects on the basis of the propensity toward aggressive behavior. In this review we first present a brief summary of the available evidence on neuroimaging of aggression. We will then treat extensively the data on genetic determinants, including those from hypothesis-free genome-wide association studies (GWAS) and candidate gene studies. Transcriptomic and neurochemical biomarkers will then be reviewed, and we will dedicate a section on the role of metabolomics in aggression. Finally, we will discuss how biomarkers can inform the development of new pharmacological tools as well as increase the efficacy of preventive strategies.

COMT polymorphism regulates the hippocampal subfield volumes in first-episode, drug-naive patients with major depressive disorder

Purpose: Compared with healthy subjects (HS), patients with major depressive disorder (MDD) exhibit volume differences that affect the volume changes in several areas such as the limbic, cortical, subcortical, and white matter. Catechol-O-methyltransferase (COMT) is a methylation enzyme that catalyzes endogenous catecholamines. The Val158Met polymorphism of COMT has been reported to affect the dopamine (DA) levels, which plays an important role in psychiatric diseases. However, the relationships among both DA levels, COMT genotype, and brain morphology are complicated and controversial. In previous studies that investigated the hippocampal subfields, the greatest brain abnormalities in MDD patients were observed in Cornu Ammonis (CA)1 and the subiculum, followed by that in CA2-3. We have prospectively demonstrated the relationship between the single-nucleotide polymorphism of the Val158Met COMT gene (rs4680) and the hippocampal subfields in drug-naive MDD patients. Patients and methods: In this study, we compared 27 MDD patients and 42 HS who were divided into groups based on their COMT genotype. The effects of the diagnosis, genotype, and genotype-diagnosis interaction related to CA1 and the subiculum volumes, as well as the whole-brain cortical thickness, were evaluated by performing a FreeSurfer statistical analysis of high-resolution magnetic resonance imaging (MRI) findings. Results: The results revealed that there was a statistically significant interaction between the effects of diagnosis and genotype on the right subiculum (a component of the hippocampus). Conclusion: This Val158Met COMT polymorphism may influence the subiculum volume in drug-naive, first-episode MDD patients.

Targeting aggression in severe mental illness: The predictive role of genetic, epigenetic, and metabolomic markers

Human aggression is a complex and widespread social behavior that is overrepresented in individuals affected by severe mental illness (SMI), such as schizophrenia (SCZ), bipolar disorder (BD), autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD). A substantial proportion of the liability threshold for aggressive behavior is determined by genetic factors, and environmental moderators might precipitate the manifestation of this behavioral phenotype through modification of gene expression via the epigenetic machinery. These specific alterations in the genetic and epigenetic make-up of aggressive individuals might determine distinct biochemical signatures detectable through metabolomics. An additional pathophysiological component playing a role in aggressive behavior might be determined by alterations of gut microbiota. Here, we present a selective review of human data on genetic, epigenetic, and metabolomic markers of aggressive behavior in SMI, discussing also the available evidence on the role of microbiome alterations. Clinical implication of these evidences, as well as future perspectives, will be discussed.

The Role of the Catechol-o-Methyltransferase (COMT) GeneVal158Met in Aggressive Behavior, a Review of Genetic Studies

Aggressive behaviors have become a major public health problem, and early-onset aggression can lead to outcomes such as substance abuse, antisocial personality disorder among other issues. In recent years, there has been an increase in research in the molecular and genetic underpinnings of aggressive behavior, and one of the candidate genes codes for the catechol-O-methyltransferase (COMT). COMT is involved in catabolizing catecholamines such as dopamine. These neurotransmitters appear to be involved in regulating mood which can contribute to aggression. The most common gene variant studied in the COMT gene is the Valine (Val) to Methionine (Met) substitution at codon 158. We will be reviewing the current literature on this gene variant in aggressive behavior.

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.

Val158Met COMT polymorphism and risk of aggression in alcohol dependence

Aggression, violence and antisocial behavior are common in alcoholism, but their biological basis is poorly understood. Several studies and recent meta-analyses indicate that in schizophrenia the catecholamine-O-methyltransferase (COMT) Val158Met genotype may be associated with aggression, most often in methionine allele carriers. We tested this hypothesis in a sample of treatment-seeking alcohol-dependent in-patients (293 German patients and 499 controls, and additional 190 Polish patients as replication sample). As expected, patients with a history of violent or non-violent crime were more often male, had an earlier onset of alcoholism and more withdrawal seizures and delirium tremens, and were more likely to have a history of suicide attempts. COMT genotype was not associated with a history of violent or non-violent crime. More studies are needed on the neurobiological basis of aggression and violence in alcoholism.

Positive symptoms in first-episode psychosis patients experiencing low maternal care and stressful life events: a pilot study to explore the role of the COMT gene

COMT Val(158)Met moderates the effect of stress on psychotic symptoms. Exposure to stress is also associated with mesolimbic dopamine release in individuals experiencing low maternal care. We therefore test the hypothesis that recent stressful life events are associated with more severe positive symptoms (associated with mesolimbic dopamine release) in first-episode psychosis (FEP) patients who experienced low maternal care during childhood. We hypothesized that COMT Val(158)Met moderates this association. A total of 149 FEP patients recruited within the Psychosis Incident Cohort Outcome Study (PICOS) participated in the present study. Maternal care was assessed by the Parental Bonding Instrument (PBI), stressful life events were collected by the List of Events Scale and positive symptoms were assessed by the Positive and Negative Syndrome Scale (PANSS). We found that low maternal care and recent stressful life events were associated with higher level of positive symptoms at the onset (analysis of variance [ANOVA], p = 0.012), and that patients who were also homozygotes for the COMT Val(158) allele had the highest level of positive symptoms (ANOVA, p = 0.024). Low maternal care and severe stressful life events may contribute to a symptomatology characterized by more severe positive symptoms at the onset, possibly due to an increased mesolimbic dopamine release. Homozygosity for the COMT Val(158) allele seems to confer a biological predisposition to the stress-related hyperactivity of the mesolimbic dopaminergic system. The data imply that the mesolimbic dopaminergic system is involved in the mediation/modulation of the effect of stressful events on the vulnerability for psychosis.

Molecular genetics and antisocial behavior: where do we stand?

Over the last two decades, it has become increasingly evident that control of aggressive behavior is modulated by the individual genetic profile as well. Several candidate genes have been proposed to play a role in the risk to develop antisocial behavior, and distinct brain imaging studies have shown that specific cortical areas may be functionally and/or structurally impaired in impulsive violent subjects on the basis of their genotypes. In this paper, we review the findings regarding four polymorphisms-MAOA (Monoamine oxidase A) uVNTR, SLC6A4 (solute carrier family 6 (neurotransmitter transporter), member 4) 5HTTLPR, COMT (Catechol-O-methyltransferase) Val158Met and DRD4 (dopamine D4 receptor) VNTR 1-11-that all have been found to be associated with an increased vulnerability for antisocial and impulsive behavior in response to aversive environmental conditions. These results, however, have not been replicated by other studies, likely because of crucial methodological discrepancies, including variability in the criteria used to define antisocial behavior and assessment of environmental factors. Finally, it has been recently proposed that these genetic variants may actually increase the individual susceptibility not merely to the negative environmental factors, but to the positive ones as well. In this view, such alleles would play a wider modulatory role, by acting as "plasticity" rather than "vulnerability" genes. Overall, these findings have potential important implications that span well outside of neuroscience and psychiatry, to embrace ethics, philosophy, and the law itself, as they pose new challenges to the very notion of Free Will. Novel properly controlled studies that examine multi-allelic genetic profiles, rather than focusing on distinct single variants, will make it possible to achieve a clearer understanding of the molecular underpinnings of the nature by nurture interaction.

Gene-sex interactions in schizophrenia: focus on dopamine neurotransmission

Schizophrenia is a severe mental disorder, with a highly complex and heterogenous clinical presentation. Our current perspectives posit that the pathogenic mechanisms of this illness lie in complex arrays of gene × environment interactions. Furthermore, several findings indicate that males have a higher susceptibility for schizophrenia, with earlier age of onset and overall poorer clinical prognosis. Based on these premises, several authors have recently begun exploring the possibility that the greater schizophrenia vulnerability in males may reflect specific gene × sex (G×S) interactions. Our knowledge on such G×S interactions in schizophrenia is still rudimentary; nevertheless, the bulk of preclinical evidence suggests that the molecular mechanisms for such interactions are likely contributed by the neurobiological effects of sex steroids on dopamine (DA) neurotransmission. Accordingly, several recent studies suggest a gender-specific association of certain DAergic genes with schizophrenia. These G×S interactions have been particularly documented for catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), the main enzymes catalyzing DA metabolism. In the present review, we will outline the current evidence on the interactions of DA-related genes and sex-related factors, and discuss the potential molecular substrates that may mediate their cooperative actions in schizophrenia pathogenesis.

COMT, neuropsychological function and brain structure in schizophrenia: a systematic review and neurobiological interpretation

BACKGROUND

Endophenotypes in genetic psychiatry may increase our understanding of the molecular mechanisms underlying disease risk and its manifestations. We sought to investigate the link between neuropsychological impairments and brain structural abnormalities associated with the COMT Val(158)Met polymorphism in patients with schizophrenia to improve understanding of the pathophysiology of this disorder.

METHODS

We performed a systematic review using studies identified in PubMed and MEDLINE (from the date of the first available article to July 2012). Our review examined evidence of an association between the COMT Val(158)Met polymorphism and both neuropsychological performance and brain structure in patients with psychosis, in their relatives and in healthy individuals (step 1). The review also explored whether the neuropsychological tasks and brain structures identified in step 1 met the criteria for an endophenotype (step 2). Then we evaluated evidence that the neuropsychological endophenotypes identified in step 2 are associated with the brain structure endophenotypes identified in that step (step 3). Finally, we propose a neurobiological interpretation for this evidence.

RESULTS

A poorer performance on the n-back task and the Continuous Performance Test (CPT) and smaller temporal and frontal brain areas were associated with the COMT Val allele in patients with schizophrenia and their relatives and met most of the criteria for an endophenotype. It is possible that the COMT Val(158)Met polymorphism therefore contributes to the development of these neuropsychological and brain structural endophenotypes of schizophrenia, in which the prefrontal cortex may represent the neural substrate underlying both n-back and CPT performances.

LIMITATIONS

The association between a single genetic variant and an endophenotype does not necessarily imply a causal relationship between them.

CONCLUSION

This evidence and the proposed interpretation contribute to explain, at least in part, the biological substrate of 4 important endophenotypes that characterize schizophrenia.

The COMT Met158 allele and violence in schizophrenia: a meta-analysis

BACKGROUND

The Met158 allele of catechol-O-methyl transferase (COMT) gene is associated with increased levels of catecholamines in the prefrontal cortex and may increase the likelihood of aggressiveness. We conducted a meta-analysis to test the hypothesis that the Met158 allele of the COMT gene is associated with aggressive and violent behavior in schizophrenia.

METHODS

MEDLINE search (12/31/11) yielded 14 studies examining the association of the COMT gene polymorphism (rs4680) and aggression in schizophrenia (total n=2219). Three separate analyses were conducted using a random effects model for Met allele carriers vs. Val/Val homozygotes, Met/Met homozygotes vs. Val allele carriers, and Met allele vs. Val allele, respectively. Primary outcome was frequency of patients with aggressive behavior and odds ratio (OR) was the effect size measure.

RESULTS

The frequency of violent patients in the sample ranged from 20% to 75%. The pooled effect sizes for the Met homozygotes vs. Val allele carriers, Met allele carriers vs. Val homozygotes and the Met allele vs. Val allele comparisons were 1.74, 1.65 and 1.35, ps<.05, respectively, suggesting that the Met 158 allele of the COMT gene is associated with higher risk for violence in schizophrenia. Results remained significant after examining heterogeneity among samples and potential publication biases.

CONCLUSIONS

The Met158 allele of the COMT gene confers a significantly increased risk for aggressive and violent behavior in schizophrenia. These data may provide basis for developing informative strategies for reducing violence in patients with schizophrenia.

Genetics of aggression

Aggression mediates competition for food, mating partners, and habitats and, among social animals, establishes stable dominance hierarchies. In humans, abnormal aggression is a hallmark of neuropsychiatric disorders and can be elicited by environmental factors acting on an underlying genetic susceptibility. Identifying the genetic architecture that predisposes to aggressive behavior in people is challenging because of difficulties in quantifying the phenotype, genetic heterogeneity, and uncontrolled environmental conditions. Studies on mice have identified single-gene mutations that result in hyperaggression, contingent on genetic background. These studies can be complemented by systems genetics approaches in Drosophila melanogaster, in which mutational analyses together with genome-wide transcript analyses, artificial selection studies, and genome-wide analysis of epistasis have revealed that a large segment of the genome contributes to the manifestation of aggressive behavior with widespread epistatic interactions. Comparative genomic analyses based on the principle of evolutionary conservation are needed to enable a complete dissection of the neurogenetic underpinnings of this universal fitness trait.

A meta-analysis of the Val158Met COMT polymorphism and violent behavior in schizophrenia

We conducted a meta-analysis of studies examining the association between the Val158Met COMT polymorphism and violence against others in schizophrenia. A systematic search current to November 1, 2011 was conducted using MEDLINE, EMBASE, CINAHL, PsycINFO, ProQuest, and the National Criminal Justice Reference Service and identified 15 studies comprising 2,370 individuals with schizophrenia for inclusion. Bivariate analyses of study sensitivities and specificities were conducted. This methodology allowed for the calculation of pooled diagnostic odds ratios (DOR). Evidence of a significant association between the presence of a Met allele and violence was found such that men's violence risk increased by approximately 50% for those with at least one Met allele compared with homozygous Val individuals (DOR = 1.45; 95% CI = 1.05-2.00; z = 2.37, p = 0.02). No significant association between the presence of a Met allele and violence was found for women or when outcome was restricted to homicide. We conclude that male schizophrenia patients who carry the low activity Met allele in the COMT gene are at a modestly elevated risk of violence. This finding has potential implications for the pharmacogenetics of violent behavior in schizophrenia.

Pathways to aggression in schizophrenia affect results of treatment

Schizophrenia elevates the risk for aggressive behavior and violent crime, and different approaches have been used to manage this problem. The results of such treatments vary. One reason for this variation is that aggressive behavior in schizophrenia is heterogeneous in origin. This heterogeneity has usually not been accounted for in treatment trials nor is it adequately appreciated in routine clinical treatment planning. Here, we review pathways that may lead to the development of aggressive behavior in patients with schizophrenia and discuss their impact on treatment. Elements in these pathways include predisposing factors such as genotype and prenatal toxic effects, development of psychotic symptoms and neurocognitive impairments, substance abuse, nonadherence to treatment, childhood maltreatment, conduct disorder, comorbid antisocial personality disorder/psychopathy, and stressful experiences in adult life. Clinicians' knowledge of the patient's historical trajectory along these pathways may inform the choice of optimal treatment of aggressive behavior. Clozapine has superior antiaggressive activity in comparison with other antipsychotics and with all other pharmacological treatments. It is usually effective when aggressive behavior is related to psychotic symptoms. However, in many patients, aggression is at least partly based on other factors such as comorbid substance use disorder, comorbid antisocial personality disorder/psychopathy, or current stress. These conditions which are sometimes underdiagnosed in clinical practice must be addressed by appropriate adjunctive psychosocial approaches or other treatments. Treatment adherence has a crucial role in the prevention of aggressive behavior in schizophrenia patients.

Neurobiology of aggression and violence in schizophrenia

There is much evidence that schizophrenia patients have an increased risk for aggression and violent behavior, including homicide. The neurobiological basis and correlates of this risk have not been much studied. While genome-wide association studies are lacking, a number of candidate genes have been investigated. By far, the most intensively studied is the catechol-O-methyltransferase (COMT) gene on chromosome 22. COMT is involved in the metabolism of dopamine, a key neurotransmitter in schizophrenia pathophysiology. Several studies suggest that the Val158Met polymorphism of this gene affects COMT activity. Methionine (Met)/Met homozygote schizophrenia patients show 4- to 5-fold lower COMT activity than valine (Val)/Val homozygotes, and some but not all studies have found an association with aggression and violence. Recently, a new functional single-nucleotide polymorphism in the COMT gene, Ala72Ser, was found to be associated with homicidal behavior in schizophrenia, but this finding warrants further replication. Studies published so far indicate that an association with the monoamine oxidase A, B, or tryptophan hydroxylase 1 genes is unlikely. Data for the brain-derived neurotrophic factor gene are conflicting and limited. Data from the limited number of neuroimaging studies performed to date are interesting. Frontal and temporal lobe abnormalities are found consistently in aggressive schizophrenia patients. Positron emission tomography and single photon-emission computed tomography (SPECT) data indicate deficits also in the orbitofrontal and temporal cortex. Some functional magnetic resonance imaging studies found a negative association of violent behavior with frontal and right-sided inferior parietal activity. Neuroimaging studies may well help further elucidate the interrelationship between neurocognitive functioning, personality traits, and antisocial and violent behavior.