MAOA-VNTR genotype affects structural and functional connectivity in distributed brain networks

MAOA methylation is associated with impulsive and antisocial behaviour: dependence on allelic variation, family environment and diet

Congenital absence of monoamine oxidase A (MAO-A) activity predisposes to antisocial impulsive behaviour, and the MAOA uVNTR low-expressing genotype (MAOA-L) together with childhood maltreatment is associated with similar phenotypes in males. A possible explanation of how family environment may lead to such behaviour involves DNA methylation. We have assessed MAOA methylation and impulsive/antisocial behaviour in 121 males from the Estonian Children Personality Behaviour and Health Study. Of the 12 CpG sites measured, methylation levels at the locus designated CpG3 were significantly lower in subjects with antisocial behaviour involving police contact. CpG3 methylation was lower in subjects with alcohol use disorder by age 25, but only in MAOA-H genotype. No correlation between MAOA CpG3 methylation levels and adaptive impulsivity was found at age 15, but in MAOA-L genotype a positive correlation appeared by age 18. By age 25, this positive correlation was no longer observed in subjects with better family relationships but had increased further with experience of adversity within the family. MAOA CpG3 methylation had different developmental dynamics in relation to maladaptive impulsivity. At age 18, a positive correlation was observed in MAOA-L genotype with inferior family relationships and a negative correlation was found in MAOA-H with superior home environment; both of these associations had disappeared by age 25. CpG3 methylation was associated with dietary intake of several micronutrients, most notable was a negative correlation with the intake of zinc, but also with calcium, potassium and vitamin E; a positive correlation was found with intake of phosphorus. In conclusion, MAOA CpG3 methylation is related to both maladaptive and adaptive impulsivity in adolescence in MAOA-L males from adverse home environment. By young adulthood, this relationship with maladaptive impulsivity had disappeared but with adaptive impulsivity strengthened. Thus, MAOA CpG3 methylation may serve as a marker for adaptive developmental neuroplasticity in MAOA-L genotype. The mechanisms involved may include dietary factors.

Relating Cognition to both Brain Structure and Function: A Systematic Review of Methods

Introduction: Cognitive neuroscience explores the mechanisms of cognition by studying its structural and functional brain correlates. Many studies have combined structural and functional neuroimaging techniques to uncover the complex relationship between them. In this study, we report the first systematic review that assesses how information from structural and functional neuroimaging methods can be integrated to investigate the brain substrates of cognition. Procedure: Web of Science and Scopus databases were searched for studies of healthy young adult populations that collected cognitive data and structural and functional neuroimaging data. Results: Five percent of screened studies met all inclusion criteria. Next, 50% of included studies related cognitive performance to brain structure and function without quantitative analysis of the relationship. Finally, 31% of studies formally integrated structural and functional brain data. Overall, many studies consider either structural or functional neural correlates of cognition, and of those that consider both, they have rarely been integrated. We identified four emergent approaches to the characterization of the relationship between brain structure, function, and cognition; comparative, predictive, fusion, and complementary. Discussion: We discuss the insights provided in each approach about the relationship between brain structure and function and how it impacts cognitive performance. In addition, we discuss how authors can select approaches to suit their research questions. Impact statement The relationship between structural and functional brain networks and their relationship to cognition is a matter of current investigations. This work surveys how researchers have studied the relationship between brain structure and function and its impact on cognitive function in healthy adult populations. We review four emergent approaches of quantitative analysis of this multivariate problem; comparative, predictive, fusion, and complementary. We explain the characteristics of each approach, discuss the insights provided in each approach, and how authors can combine approaches to suit their research questions.

MAOA-LPR polymorphism and math anxiety: A marker of genetic susceptibility to social influences in girls?

Math anxiety (MA) seems to result from an interaction of genetic vulnerability with negative experiences learning mathematics. Although mathematics achievement does not substantially differ between the sexes, MA levels are usually higher in girls. Molecular genetic markers of MA vulnerability have been seldom explored. This article examines the contribution of the monoamine oxidase A gene (MAOA) to MA and to sex differences in MA. Five hundred and sixty-eight third to fifth graders were genotyped for the MAOA-LPR polymorphism (a repetitive element in MAOA promoter that has been associated with MAOA enzymatic activity), and assessed on general cognitive ability, mathematics achievement, and the cognitive and affective dimensions of MA. MAOA-LPR genotypes were classified as high (MAOA-H) or low (MAOA-L) according to their predicted enzymatic activity. Mixed models controlling for effects of school, sex, general cognitive ability, and mathematics achievement were evaluated. The best fitting model included school, math achievement, sex, MAOA-LPR, and the MAOA-LPR by sex interaction. This indicated that under the MAOA-H dominant model, anxiety toward mathematics interacted with the MAOA genotype: girls with an MAOA-L genotype exhibited higher levels of MA, with a small but significant effect. The association between MAOA-L genotype and MA in girls may represent an example of developmental plasticity.

Behavioural and functional evidence revealing the role of RBFOX1 variation in multiple psychiatric disorders and traits

Common variation in the gene encoding the neuron-specific RNA splicing factor RNA Binding Fox-1 Homolog 1 (RBFOX1) has been identified as a risk factor for several psychiatric conditions, and rare genetic variants have been found causal for autism spectrum disorder (ASD). Here, we explored the genetic landscape of RBFOX1 more deeply, integrating evidence from existing and new human studies as well as studies in Rbfox1 knockout mice. Mining existing data from large-scale studies of human common genetic variants, we confirmed gene-based and genome-wide association of RBFOX1 with risk tolerance, major depressive disorder and schizophrenia. Data on six mental disorders revealed copy number losses and gains to be more frequent in ASD cases than in controls. Consistently, RBFOX1 expression appeared decreased in post-mortem frontal and temporal cortices of individuals with ASD and prefrontal cortex of individuals with schizophrenia. Brain-functional MRI studies demonstrated that carriers of a common RBFOX1 variant, rs6500744, displayed increased neural reactivity to emotional stimuli, reduced prefrontal processing during cognitive control, and enhanced fear expression after fear conditioning, going along with increased avoidance behaviour. Investigating Rbfox1 neuron-specific knockout mice allowed us to further specify the role of this gene in behaviour. The model was characterised by pronounced hyperactivity, stereotyped behaviour, impairments in fear acquisition and extinction, reduced social interest, and lack of aggression; it provides excellent construct and face validity as an animal model of ASD. In conclusion, convergent translational evidence shows that common variants in RBFOX1 are associated with a broad spectrum of psychiatric traits and disorders, while rare genetic variation seems to expose to early-onset neurodevelopmental psychiatric disorders with and without developmental delay like ASD, in particular. Studying the pleiotropic nature of RBFOX1 can profoundly enhance our understanding of mental disorder vulnerability.

Revisiting tandem repeats in psychiatric disorders from perspectives of genetics, physiology, and brain evolution

Genome-wide association studies (GWASs) have revealed substantial genetic components comprised of single nucleotide polymorphisms (SNPs) in the heritable risk of psychiatric disorders. However, genetic risk factors not covered by GWAS also play pivotal roles in these illnesses. Tandem repeats, which are likely functional but frequently overlooked by GWAS, may account for an important proportion in the "missing heritability" of psychiatric disorders. Despite difficulties in characterizing and quantifying tandem repeats in the genome, studies have been carried out in an attempt to describe impact of tandem repeats on gene regulation and human phenotypes. In this review, we have introduced recent research progress regarding the genomic distribution and regulatory mechanisms of tandem repeats. We have also summarized the current knowledge of the genetic architecture and biological underpinnings of psychiatric disorders brought by studies of tandem repeats. These findings suggest that tandem repeats, in candidate psychiatric risk genes or in different levels of linkage disequilibrium (LD) with psychiatric GWAS SNPs and haplotypes, may modulate biological phenotypes related to psychiatric disorders (e.g., cognitive function and brain physiology) through regulating alternative splicing, promoter activity, enhancer activity and so on. In addition, many tandem repeats undergo tight natural selection in the human lineage, and likely exert crucial roles in human brain evolution. Taken together, the putative roles of tandem repeats in the pathogenesis of psychiatric disorders is strongly implicated, and using examples from previous literatures, we wish to call for further attention to tandem repeats in the post-GWAS era of psychiatric disorders.

Brunner syndrome associated MAOA mutations result in NMDAR hyperfunction and increased network activity in human dopaminergic neurons

Monoamine neurotransmitter abundance affects motor control, emotion, and cognitive function and is regulated by monoamine oxidases. Among these, Monoamine oxidase A (MAOA) catalyzes the degradation of dopamine, norepinephrine, and serotonin into their inactive metabolites. Loss-of-function mutations in the X-linked MAOA gene have been associated with Brunner syndrome, which is characterized by various forms of impulsivity, maladaptive externalizing behavior, and mild intellectual disability. Impaired MAOA activity in individuals with Brunner syndrome results in bioamine aberration, but it is currently unknown how this affects neuronal function, specifically in dopaminergic (DA) neurons. Here we generated human induced pluripotent stem cell (hiPSC)-derived DA neurons from three individuals with Brunner syndrome carrying different mutations and characterized neuronal properties at the single cell and neuronal network level in vitro. DA neurons of Brunner syndrome patients showed reduced synaptic density but exhibited hyperactive network activity. Intrinsic functional properties and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated synaptic transmission were not affected in DA neurons of individuals with Brunner syndrome. Instead, we show that the neuronal network hyperactivity is mediated by upregulation of the GRIN2A and GRIN2B subunits of the N-methyl-d-aspartate receptor (NMDAR), resulting in increased NMDAR-mediated currents. By correcting a MAOA missense mutation with CRISPR/Cas9 genome editing we normalized GRIN2A and GRIN2B expression, NMDAR function and neuronal population activity to control levels. Our data suggest that MAOA mutations in Brunner syndrome increase the activity of dopaminergic neurons through upregulation of NMDAR function, which may contribute to the etiology of Brunner syndrome associated phenotypes.

The Modulatory Role of Serotonin on Human Impulsive Aggression

The hypothesis of chronically low brain serotonin levels as pathophysiologically linked to impulsive aggression has been around for several decades. Whereas the theory was initially based on indirect methods to probe serotonin function, our understanding of the neural mechanisms involved in impulsive aggression has progressed with recent advances in neuroimaging. The review integrates evidence based on data from several neuroimaging domains in humans. In vivo molecular neuroimaging findings demonstrate associations between impulsive aggression and high serotonin 1B and serotonin 4 receptor binding, high serotonin transporter levels, and low monoamine oxidase A levels, suggesting that low interstitial serotonin levels are a neurobiological risk factor for impulsive aggressive behavior. Imaging genetics suggests that serotonergic-related genetic polymorphisms associate with antisocial behavior, and some evidence indicates that the low-expressing monoamine oxidase A genotype specifically predisposes to impulsive aggression, which may be mediated by effects on corticolimbic function. Interventions that (presumably) alter serotonin levels have effects on brain activity within brain regions involved in impulsive aggression, notably the amygdala, dorsal striatum, anterior cingulate, insula, and prefrontal cortex. Based on these findings, we propose a model for the modulatory role of serotonin in impulsive aggression. Future studies should ensure that clinical features unique for impulsive aggression are appropriately assessed, and we propose investigations of knowledge gaps that can help confirm, refute, or modify our proposed model of impulsive aggression.

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.

MAOA-VNTR genotype affects structural and functional connectivity in distributed brain networks

Previous studies have linked the low expression variant of a variable number of tandem repeat polymorphism in the monoamine oxidase A gene (MAOA‐L) to the risk for impulsivity and aggression, brain developmental abnormalities, altered cortico‐limbic circuit function, and an exaggerated neural serotonergic tone. However, the neurobiological effects of this variant on human brain network architecture are incompletely understood. We studied healthy individuals and used multimodal neuroimaging (sample size range: 219–284 across modalities) and network‐based statistics (NBS) to probe the specificity of MAOA‐L‐related connectomic alterations to cortical‐limbic circuits and the emotion processing domain. We assessed the spatial distribution of affected links across several neuroimaging tasks and data modalities to identify potential alterations in network architecture. Our results revealed a distributed network of node links with a significantly increased connectivity in MAOA‐L carriers compared to the carriers of the high expression (H) variant. The hyperconnectivity phenotype primarily consisted of between‐lobe (“anisocoupled”) network links and showed a pronounced involvement of frontal‐temporal connections. Hyperconnectivity was observed across functional magnetic resonance imaging (fMRI) of implicit emotion processing (p_FWE = .037), resting‐state fMRI (p_FWE = .022), and diffusion tensor imaging (p_FWE = .044) data, while no effects were seen in fMRI data of another cognitive domain, that is, spatial working memory (p_FWE = .540). These observations are in line with prior research on the MAOA‐L variant and complement these existing data by novel insights into the specificity and spatial distribution of the neurogenetic effects. Our work highlights the value of multimodal network connectomic approaches for imaging genetics.