Preliminary evidence for an association of a dinucleotide repeat polymorphism at the MAOA gene with early onset alcoholism/substance abuse

"Weeding out" violence? Translational perspectives on the neuropsychobiological links between cannabis and aggression

Recent shifts in societal attitudes towards cannabis have led to a dramatic increase in consumption rates in many Western countries, particularly among young people. This trend has shed light on a significant link between cannabis use disorder (CUD) and pathological reactive aggression, a condition involving disproportionate aggressive and violent reactions to minor provocations. The discourse on the connection between cannabis use and aggression is frequently enmeshed in political and legal discussions, leading to a polarized understanding of the causative relationship between cannabis use and aggression. However, integrative analyses from both human and animal research indicate a complex, bidirectional interplay between cannabis misuse and pathological aggression. On the one hand, emerging research reveals a shared genetic and environmental predisposition for both cannabis use and aggression, suggesting a common underlying biological mechanism. On the other hand, there is evidence that cannabis consumption can lead to violent behaviors while also being used as a self-medication strategy to mitigate the negative emotions associated with pathological reactive aggression. This suggests that the coexistence of pathological aggression and CUD may result from overlapping vulnerabilities, potentially creating a self-perpetuating cycle where each condition exacerbates the other, escalating into externalizing and violent behaviors. This article aims to synthesize existing research on the intricate connections between these issues and propose a theoretical model to explain the neurobiological mechanisms underpinning this complex relationship.

Candidate gene-environment interactions in substance abuse: A systematic review

BACKGROUND

The abuse of psychogenic drugs can lead to multiple health-related problems. Genetic and environmental vulnerabilities are factors in the emergence of substance use disorders. Empirical evidence regarding the gene-environment interaction in substance use is mixed. Summaries of the latest findings from a candidate gene approach will be useful for revealing the significance of particular gene contributions. Thus, we aim to identify different gene-environment interactions in patterns of substance use and investigate whether any effects trend notably across different genders and races.

METHODS

We reviewed published studies, until March 1, 2022, on substance use for candidate gene-environment interaction. Basic demographics of the included studies, target genes, environmental factors, main findings, patterns of gene-environment interaction, and other relevant information were collected and summarized.

RESULTS

Among a total of 44 studies, 38 demonstrated at least one significant interaction effect. About 61.5% of studies on the 5-HTTLPR gene, 100% on the MAOA gene, 42.9% on the DRD2 gene, 50% on the DRD4 gene, 50% on the DAT gene, 80% on the CRHR1 gene, 100% on the OPRM1 gene, 100% on the GABRA1 gene, and 50% on the CHRNA gene had a significant gene-environment interaction effect. The diathesis-stress model represents a dominant interaction pattern (89.5%) in the studies with a significant interaction effect; the remaining significant effect on substance use is found in the differential susceptibility model. The social push and swing model were not reported in the included studies.

CONCLUSION

The gene-environment interaction research on substance use behavior is methodologically multidimensional, which causes difficulty in conducting pooled analysis, or stated differently-making it hard to identify single sources of significant influence over maladaptive patterns of drug taking. In decreasing the heterogeneity and facilitating future pooled analysis, researchers must (1) replicate the existing studies with consistent study designs and measures, (2) conduct power calculations to report gene-environment correlations, (3) control for covariates, and (4) generate theory-based hypotheses with factorial based experiments when designing future studies.

Forensically relevant challenging behaviors and the genetics domain

Impulsive and aggressive behaviors along with intellectual disabilities often manifest in the context of genetic disorders and are a persisting challenge to professionals in the forensic psychiatric and psychological setting. The following chapter comprises an overview of relevant factors in the gene-context-behavior interaction such as monoamine oxidase A activity and specific epileptic phenomena. It presents several examples of monogenetic disorders with behaviors from the aggression spectrum and summarizes emerging strategies for treatment and clinical management thereof. The final part focuses on challenges and future developments in this field with relevance for the judicial and forensic systems. It is concluded that the relationship between a genetic syndrome and forensically relevant and/or violent behaviors should typically be addressed within a multidisciplinary framework that also includes the application of modern genetic techniques.

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.

Sex-Dimorphic Interactions of MAOA Genotype and Child Maltreatment Predispose College Students to Polysubstance Use

Polysubstance use (PSU) is highly prevalent among college students. Recent evidence indicates that PSU is based on gene x environment (G×E) interactions, yet the specific biosocial factors underlying this problem remain elusive. We recently reported that lifetime use of tobacco and cannabis in college students is influenced by the interaction of the X-linked MAOA (monoamine oxidase A) gene and child maltreatment. Building on these premises, here we evaluated whether the same G×E interaction may also predict PSU in this population. Students of a large Midwestern university (n = 470; 50.9% females) took part in a computer survey for substance use, as well as childhood trauma exposure, using the Child Trauma Questionnaire (CTQ). DNA was extracted from their saliva samples and genotyped for MAOA variable-number of tandem repeat (VNTR) variants. Findings indicated that the highest number of substances were used by male students harboring low-activity MAOA alleles with a history of childhood emotional abuse. In contrast, female homozygous high-activity MAOA carriers with a history of emotional and physical abuse reported consumption of the greatest number of substances. Our results indicate that PSU among college students is influenced by the interaction of MAOA and child maltreatment in a sex-specific fashion. Further studies are warranted to understand the mechanisms of sex differences in the biosocial interplays underlying PSU in this at-risk group.

Tobacco and cannabis use in college students are predicted by sex-dimorphic interactions between MAOA genotype and child abuse

BACKGROUND

Postsecondary students in Western countries exhibit a high prevalence of cannabis and tobacco use disorders. The etiology of these problems is contributed by several psychosocial factors, including childhood adversity and trauma; however, the mechanisms whereby these environmental determinants predispose to the use of these substances remain elusive, due to our poor knowledge of genetic and biological moderators. Converging evidence points to the monoamine oxidase A (MAOA) gene as a moderator of the effects of lifetime stress on the initiation of substance use.

AIMS

Building on these premises, in this study, we analyzed whether MAOA upstream variable number tandem repeat (uVNTR) alleles interact with child maltreatment history to predict for lifetime cannabis and tobacco consumption.

MATERIALS AND METHODS

Five hundred college students (age: 18-25 years) from a large Midwestern University were surveyed for their child maltreatment history (encompassing emotional, physical, and sexual abuse, as well as emotional and physical neglect) and lifetime consumption of cannabis and tobacco. Saliva samples were obtained to determine the MAOA uVNTR genotype of each participant.

RESULTS

In female students, lifetime tobacco and cannabis use was predicted by the interaction of physical and emotional abuse with high-activity MAOA allelic variants; conversely, in males, the interaction of low-activity MAOA alleles and physical abuse was associated with lifetime use of tobacco, but not cannabis.

DISCUSSION

These findings collectively suggest that the vulnerability to smoke tobacco and cannabis is predicted by sex-dimorphic interactions of MAOA gene with childhood abuse.

CONCLUSION

These biosocial underpinnings of tobacco and cannabis use may prove important in the development of novel personalized preventive strategies for substance use disorders in adolescents.

Clinical features of drug abuse that reflect genetic risk

BACKGROUND

Drug abuse (DA) is a clinically heterogeneous syndrome. Can we, in a large epidemiological sample, identify clinical features of DA cases that index genetic risk?

METHOD

Using registration in medical, legal or pharmacy records, we identified four kinds of relative pairs (n=935,854) starting with a proband with DA: monozygotic co-twins; full siblings; half-siblings; and cousins. Using linear hazard regression, we examined the interaction between three clinical features of DA in the proband and risk for DA in these four relative pairs, ordered by degree of genetic relationship.

RESULTS

Increased risk for DA in relatives was robustly predicted by early age at first registration, total number of registrations, and ascertainment in the criminal versus the medical or pharmacy registry. In multivariate models, all three of these variables remained significant and in aggregate strongly predicted DA risk in relatives. The risk for DA in siblings of DA probands in the highest decile of genetic risk predicted by our three indices was more than twice as great as that predicted in siblings of probands in the lowest decile of risk.

CONCLUSIONS

In an epidemiological sample, genetic risk for DA can be substantially indexed by simple clinical and historical variables.

Polymorphisms in genes encoding dopamine signalling pathway and risk of alcohol dependence: a systematic review

BACKGROUND

Alcohol dependence (AD) is one of the major elements that significantly influence drinking pattern that provoke the alcohol-induced organ damage. The structural and neurophysiologic abnormalities in the frontal lobes of chronic alcoholics were revealed by magnetic resonance imaging scans. It is well known that candidate genes involved in dopaminergic pathway are of immense interest to the researchers engaged in a wide range of addictive disorders. Dopaminergic pathway gene polymorphisms are being extensively studied with respect to addictive and behavioral disorders.

METHODS

From the broad literature available, the current review summarizes the specific polymorphisms of dopaminergic genes that play a role in alcohol dependence.

RESULTS

No evidence indicating any strong association between AD and polymorphisms of dopamine pathway genes has emerged from the literature.

DISCUSSION

Further studies are warranted, considering a range of alcohol-related traits to determine the genes that influence alcohol dependence.

P2RX7 gene is associated consistently with mood disorders and predicts clinical outcome in three clinical cohorts

We investigated the effect of nine candidate genes on risk for mood disorders, hypothesizing that predisposing gene variants not only elevate the risk for mood disorders but also result in clinically significant differences in the clinical course of mood disorders. We genotyped 178 DSM-IV bipolar I and II and 272 major depressive disorder patients from three independent clinical cohorts carefully diagnosed with semistructured interviews and prospectively followed up with life charts for a median of 60 (range 6-83) months. Healthy control subjects (n = 1322) were obtained from the population-based national Health 2000 Study. We analyzed 62 genotyped variants within the selected genes (BDNF, NTRK2, SLC6A4, TPH2, P2RX7, DAOA, COMT, DISC1, and MAOA) against the presence of mood disorder, and in post-hoc analyses, specifically against bipolar disorder or major depressive disorder. Estimates for time ill were based on life charts. The P2RX7 gene variants rs208294 and rs2230912 significantly elevated the risk for a familial mood disorder (OR = 1.35, P = 0.0013, permuted P = 0.06, and OR = 1.44, P = 0.0031, permuted P = 0.17, respectively). The results were consistent in all three cohorts. The same risk alleles predicted more time ill in all cohorts (OR 1.3, 95% CI 1.1-1.6, P = 0.0069 and OR 1.7, 95% CI 1.3-2.3, P = 0.0002 with rs208294 and rs2230912, respectively), so that homozygous carriers spent 12 and 24% more time ill. P2RX7 and its risk alleles predisposed to mood disorders consistently in three independent clinical cohorts. The same risk alleles resulted in clinically significant differences in outcome of patients with major depressive and bipolar disorder.

Association of VNTR polymorphisms in the MAOA promoter and DRD4 exon 3 with heroin dependence in male Chinese addicts

OBJECTIVE

To explore the involvement of variable number tandem repeat (VNTR) polymorphisms in the monoamine oxidase A (MAOA) promoter and exon 3 of the dopamine D4 receptor (DRD4) gene in heroin addiction modulate the vulnerability of individuals to heroin addiction.

METHODS

Eight hundred and ninety-four male heroin addicts without other psychiatric disorders, were recruited as subjects. Another community 180 males were selected randomly as controls.

RESULTS

The geno-distribution of the DRD4 exon 3 VNTR polymorphism in controls was in Hardy-Weinberg equilibrium (HWEchi(2)=0.925), but the distribution in heroin addicts was not (HWEchi(2)=28.35). The long-repeat alleles of the DRD4 exon 3 VNTR polymorphism were found more frequently in the heroin addicts (P=0.019). However, the long-repeat alleles of the MAOA promoter VNTR polymorphism were not (P=0.828). No interaction between these two VNTR polymorphisms was found by using multiple logistic regression analysis (P=0.261).

CONCLUSION

The long-repeat allelic variants (>4-repeats) and 2-repeat allele of the DRD4 exon 3 VNTR polymorphism might be risk alleles for individual vulnerability to heroin addiction in Chinese men, but the MAOA promoter VNTR polymorphism does not mean that the partial dominant inherited mode might involved in the genetics of heroin dependence.

Upregulation of serotonin transporter by alcohol in human dendritic cells: possible implication in neuroimmune deregulation

BACKGROUND

Alcohol is the most widely abused substance and its chronic consumption causes neurobehavioral disorders. It has been shown that alcohol affects the function of immune cells. Dendritic cells (DC) serve as the first line of defense against infections and are known to accumulate neurotransmitters such as 5-hydroxytryptamine (5-HT). The enzyme monoamine oxidase-A (MAO-A) degrades 5-HT that is associated with clinical depression and other neurological disorders. 5-HT is selectively transported into neurons through the serotonin transporter (SERT), which is a member of the sodium- and chloride-dependent neurotransmitter transporter (SLC6) family. SERT also serves as a receptor for psychostimulant recreational drugs. It has been demonstrated that several drugs of abuse such as amphetamine and cocaine inhibit the SERT expression; however, the role of alcohol is yet to be elucidated. We hypothesize that alcohol can modulate SERT and MAO-A expression in DC, leading to reciprocal downregulation of 5-HT in extracellular medium.

METHODS

Dendritic cells were treated with different concentrations (0.05% to 0.2%v/v) of alcohol for 24-72 hours and processed for SERT and MAO-A expression using Q-PCR and Western blots analysis. In addition, SERT function in DC treated with alcohol both in the presence and absence of imipramine, a SERT inhibitor was measured using 4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide uptake assay. 5-HT levels in culture supernatant and intracellular 5-hydroxy indole acetic acid (5-HIAA) and cyclic AMP were also quantitated using ELISA.

RESULTS

Dendritic cells treated with 0.1% alcohol for 24 hours showed significant upregulation of SERT and MAO-A expression compared with untreated DC. We also observed that 0.1% alcohol enhanced the function of SERT and decreased extracellular 5-HT levels compared with untreated DC cultures, and this was associated with the elevation of intracellular 5-HIAA and cyclic AMP levels.

CONCLUSIONS

Our study suggests that alcohol upregulates SERT and MAO-A by elevating cyclic AMP, which may lead to decreased concentration of 5-HT in the extracellular medium. As 5-HT is a major neurotransmitter and an inflammatory mediator, its alcohol-mediated depletion may cause both neurological and immunological deregulation.

MAOA gene polymorphisms and response to mirtazapine in major depression

BACKGROUND

Polymorphisms in the monoamine oxidase A (MAOA) gene may influence treatment outcomes in major depression disorder (MDD).

OBJECTIVE

To investigate the association of MAOA genetic polymorphisms and response to mirtazapine in patients with MDD.

METHOD

Fifty-eight adult patients in Taiwan who met the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) diagnostic criteria for MDD were given mirtazapine for 7 weeks and evaluated on days 0, 7, 14, 21, 49 using the 24-item Hamilton Rating Scale for Depression (HRSD). Remission was defined as a final HRSD <or= 10 and a 50% reduction in baseline HRSD score. Patients provided venous blood for DNA testing. The patients' response to mirtazapine treatment was compared between those who had the long-form polymorphism in the MAOA gene promoter and the short-form polymorphism.

RESULT

The total HRSD scores after mirtazapine treatment were significantly lower than baseline (p < 0.001). There were 10 cases (38.5%) in short from and 6 (18.8%) in long from group touched the remission stage. Patients with the short-form group had a greater response to mirtazapine (p < 0.001) than those with the long-form polymorphism after controlling for age, sex, and apolipoprotein E genetic (APOE) polymorphism.

CONCLUSION

The genetic polymorphisms in the MAOA promoter region may be associated with treatment response to mirtazapine.

Regulation of monoamine oxidase A by circadian-clock components implies clock influence on mood

The circadian clock has been implicated in addiction and several forms of depression [1, 2], indicating interactions between the circadian and the reward systems in the brain [3-5]. Rewards such as food, sex, and drugs influence this system in part by modulating dopamine neurotransmission in the mesolimbic dopamine reward circuit, including the ventral tegmental area (VTA) and the ventral striatum (NAc). Hence, changes in dopamine levels in these brain areas are proposed to influence mood in humans and mice [6-10]. To establish a molecular link between the circadian-clock mechanism and dopamine metabolism, we analyzed the murine promoters of genes encoding key enzymes important in dopamine metabolism. We find that transcription of the monoamine oxidase A (Maoa) promoter is regulated by the clock components BMAL1, NPAS2, and PER2. A mutation in the clock gene Per2 in mice leads to reduced expression and activity of MAOA in the mesolimbic dopaminergic system. Furthermore, we observe increased levels of dopamine and altered neuronal activity in the striatum, and these results probably lead to behavioral alterations observed in Per2 mutant mice in despair-based tests. These findings suggest a role of circadian-clock components in dopamine metabolism highlighting a role of the clock in regulating mood-related behaviors.

Early developmental processes and the continuity of risk for underage drinking and problem drinking

Developmental pathways to underage drinking emerge before the second decade of life. Many scientists, however, as well as the general public, continue to focus on proximal influences surrounding the initiation of drinking in adolescence, such as social, behavioral, and genetic variables related to availability and ease of acquisition of the drug, social reinforcement for its use, and individual differences in drug responses. In the past 20 years, a considerable body of evidence has accumulated on the early (often much earlier than the time of the first drink) predictors and pathways of youthful alcohol use and abuse. These early developmental influences involve numerous risk, vulnerability, promotive, and protective processes. Some of these factors are not related directly to alcohol use, whereas others involve learning and expectancies about later drug use that are shaped by social experience. The salience of these factors (identifiable in early childhood) for understanding the course and development of adult alcohol and other drug use disorders is evident from the large and growing body of findings on their ability to predict adult clinical outcomes. This review summarizes the evidence on early pathways toward and away from underage drinking, with a particular focus on the risk and protective factors and the mediators and moderators of risk for underage drinking that become evident during the preschool and early school years. It is guided by a developmental perspective on the aggregation of risk and protection and examines the contributions of biological, psychological, and social processes within the context of normal development. Implications of this evidence for policy, intervention, and future research are discussed.

The MAOA promoter polymorphism, disruptive behavior disorders, and early onset substance use disorder: gene-environment interaction

OBJECTIVES

Conduct, oppositional defiant, and attention deficit hyperactivity disorders, reflecting early antisociality and behavior dysregulation, are predictive of substance use disorders. Liabilities to these disorders share genetic and environmental variance. Parenting characteristics have been shown to influence development of antisociality, moderated by variation at the MAOA gene, which has also been associated with the risk for substance use disorders. To extend these findings, we tested the relationships between the MAOA promoter polymorphism (variable number tandem repeat), indices of child's perception of paternal and maternal parenting, and disruptive behavior disorders and substance use disorders.

METHODS

A sample of 148 European-American males was assessed prospectively at ages from 10-12 to 18-19 years and genotyped for the monoamine oxidase A variable number tandem repeat. The Diagnostic and statistical manual of mental disorder-III-R diagnoses were obtained using standard methodology. Parenting was assessed using a scale summarizing the child's evaluation of the parenting style (parent's behavior toward him, parental emotional distance and involvement). Correlation, logistic regression, and Cox proportional hazard regression analysis was used to determine the relationships between the variables.

RESULTS

The strength of association between parenting index and conduct and attention deficit hyperactivity disorders depended on the MAOA genotype. Unlike earlier findings, the parenting-risk relationships were observed in the 'high-' rather than 'low-activity' genotypes. The strength and direction of relationships depended on the parental sex. The MAOA polymorphism's association with the risk for substance use disorders was detected when parenting was controlled for.

CONCLUSIONS

The results are consistent with the contribution of the MAOA gene, parenting style and their interactions to variation in the risk for early onset behavior disorders and liability to substance use disorders.

Approach to the genetics of alcoholism: A review based on pathophysiology

Alcohol dependence is a common disorder with a heterogenous etiology. The results of family, twin and adoption studies on alcoholism are reviewed. These studies have revealed a heritability of alcoholism of over 50%. After evaluating the results, it was epidemiologically stated that alcoholism is heterogenous complex disorder with a multiple genetic background. Modern molecular genetic techniques allow examining specific genes involved in the pathophysiology of complex diseases such as alcoholism. Strategies for gene identification are introduced to the reader, including family-based and association studies. The susceptibility genes that are in the focus of this article have been chosen because they are known to encode for underlying mechanisms that are linked to the pathophysiology of alcoholism or that are important for the pharmacotherapeutic approaches in the treatment of alcohol dependence. Postulated candidate genes of the metabolism of alcohol and of the involved neurotransmitter systems are introduced. Genetic studies on alcoholism examining the metabolism of alcohol and the dopaminergic, GABAergic, glutamatergic, opioid, cholinergic and serotonergic neurotransmitter systems as well as the neuropeptide Y are presented. The results are critically discussed followed by a discussion of possible consequences.

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.

Cluster B personality disorders are associated with allelic variation of monoamine oxidase A activity

Genetic variants of the monoamine oxidase A (MAOA) have been associated with aggression-, anxiety-, and addiction-related behavior in several nonclinical and clinical populations. Here, we investigated the influence of allelic variation of MAOA activity on aggression-related personality traits and disease risk in patients with personality disorders. Personality disorders were diagnosed with the Structured Clinical Interview of DSM-IV and were allocated to cluster A, B, and C. Personality features were assessed by the revised NEO Personality Inventory and the Tridimensional Personality Questionnaire. The genotype of the MAOA gene-linked polymorphic region (MAOA-LPR) was determined in 566 patients with personality disorders and in 281 healthy controls. MAOA genotype was significantly associated with cluster B personality disorders (chi2=7.77, p=0.005, df=1) but not with cluster C personality disorders. In total, 26.0% of cluster B patients were hemi- or homozygous for the low-activity variant of the MAOA genotype, compared to 16.4% in the control group. Associations between MAOA variants and personality domains related to impulsivity and aggressiveness were inconsistent. Our findings further support the notion that allelic variation of MAOA activity contributes modestly to the balance of hyper- (impulsive-aggressive) and hyporeactive (anxious-depressive) traits.

Association of MAO A polymorphism and alcoholism in Brazilian females

Among the different possible genes involved in the alcoholism etiology, the X-linked monoamine oxidase A gene is a good candidate. The aim of this study was to assess whether a functional VNTR polymorphism in the promoter region of the monoamine oxidase A gene is associated with alcoholism, comparing patients of both sexes. Ninety-three alcohol-dependent patients (51 males, 42 females) and 93 sex-matched normal controls were engaged. In the total sample, the genotype containing at least one three-repeat allele was significantly more frequent among alcohol-dependent patients than controls (P=0.01). However, when the two sexes were analyzed separately, the difference was statistically significant only for females. This is of particular interest as rates of alcoholism in Brazil are markedly lower in females. Our results suggest that this monoamine oxidase A polymorphism could play a role in susceptibility to alcoholism, which may differ across sexes.

Genes associated with addiction: alcoholism, opiate, and cocaine addiction

Drug addiction is a complex disorder that has a large spectrum of causes. Vulnerability to addiction has been shown in twin studies to have a robust genetic component. This genetic basis for addiction has general and specific components for each drug abused. Although many genes have been implicated in drug addiction, only a handful have either been replicated to have an association or to have an identified functional mechanism related to specific effects of abused drugs. A few selected genetic variants that currently look promising for the study of alcohol, opiate, and cocaine addiction are discussed in this article.

Haplotypes of the monoamine oxidase genes and the risk for substance use disorders

Monoamine oxidase A (MAOA) locus is an attractive candidate for exploring genetic contribution to the variation in the risk for substance use disorders (SUD) because of its important role in the metabolism of neurotransmitters, including dopamine and serotonin. Prior findings have suggested an association of the MAOA gene with the risk for early onset SUD. To extend this research, we genotyped four MAOA markers (two VNTR polymorphisms and two SNPs) and built a cladogram reflecting the evolutionary history of MAOA haplotypes [Nguyen et al., under review]. The cladogram served as the framework for nested ANOVA and logit analyses of association between MAOA and indices of liability to SUD (diagnosis, age of onset, and a dimensional index of substance use related problems) in a sample of adult males of European ancestry. Whereas no association was found for the categorical diagnosis, a significant relationship was detected between the dimensional liability indices and MAOA haplotypes. Overall, our results, albeit not definitive, are consistent with the hypothesis that variants in MAOA account for a small portion of the variance of SUD risk, possibly mediated by liability to early onset behavioral problems.

Neurobehavior disinhibition in childhood predisposes boys to substance use disorder by young adulthood: direct and mediated etiologic pathways

OBJECTIVE

The development of substance use disorder (SUD) was prospectively investigated in 66 boys having fathers with SUD and 104 boys having fathers with no adult Axis I or II psychiatric disorder. Evaluations were conducted to determine the context in which neurobehavior disinhibition in relation to parental SUD, parental neglect of the child and child's social maladjustment culminated in a DSM-III-R diagnosis of SUD.

METHODS

A neurobehavior disinhibition latent trait was derived using indicators of behavior undercontrol, affect dysregulation and executive cognitive functioning in the boys when they were 10-12 and again at 16 years of age. These latter characteristics have been frequently observed in individuals who have a prefrontal cortex disturbance. The data were analyzed to determine whether the score on the neurobehavior disinhibition construct mediates the association between father's and mother's SUD and son's SUD.

RESULTS

SUD in the mother and father predicted neurobehavior disinhibition in the son. The neurobehavior disinhibition score in the sons predicted SUD between ages 10-12 and 19. Neurobehavior disinhibition, in conjunction with social maladjustment and drug use frequency, mediated the association between paternal and maternal SUD and son's SUD. Neurobehavior disinhibition was unrelated to neglect of the child by either the father or mother; however, paternal but not maternal neglect at age 10-12 predicted SUD at age 19.

CONCLUSIONS

The association of neurobehavior disinhibition in childhood and SUD by young adulthood suggests that a prefrontal cortex dysfunction contributes to SUD liability. The results extend previous findings demonstrating that neurobehavior disinhibition is an important component of the liability to SUD.

Functional variation in promoter region of monoamine oxidase A and subtypes of alcoholism: haplotype analysis

Monoamine oxidase (MAO) is a mitochondrial enzyme involved in the degradation of certain neurotransmitter amines. MAO-A, due to its function in central nervous system, has been one of the important candidate genes involved in the development of neuropsychiatric disorders. A functional polymorphism in the promoter region of the MAO-A gene has been identified. This variation affects the transcriptional efficiency of the gene. To determine the role of this MAO-A functional polymorphism in the development of subtypes of alcoholism, a sample of alcoholics and normal controls were screened with this marker. The allele frequency differences between total alcoholics, Types I and II alcoholics, and normal controls was not significant. Comparison of male alcoholics to male normal controls for the frequencies of two-loci and three-loci haplotypes was statistically significant. After Bonferroni's correction for multiple tests none of the results remained significant at P < 0.05. Our results indicate that MAO-A may play a role in the development of alcoholism but the gene effect is very small.

No association between a polymorphism in the promoter region of the MAOA gene with antisocial personality traits in alcoholics

AIMS

We analysed the MAOAuVNTR functional polymorphism in the promoter region of the X-chromosomal monoamine oxidase A (MAOA) gene. Genotypes with three-repeat alleles were reported to be associated with antisocial as well as impulsive traits.

METHODS

The repeat number (3-5) of the MAOA polymorphism was determined in 169 male alcoholic subjects and 72 controls of German descent. Behavioural and personality traits were evaluated using the Brown-Goodwin Assessment for History of Lifetime Aggression, the Buss Durkee Hostility Inventory, as well as the Barrat Impulsiveness Score. A median split in Brown-Goodwin, Buss Durkee Irritability, Buss Durkee Assault and Barrat Impulsiveness Score was conducted.

RESULTS

High scores were found, i.e. 47.9% in Brown-Goodwin, 65.7% in Buss Durkee Irritability, 63.3% in Buss Durkee Assault and 59.8% in Barrat Impulsiveness Scale, indicating high impulsiveness, irritability and antisocial behaviour. Based on the results of these questionnaires, we detected no significant differences between the frequency of the three-repeat allele and high or low scores in alcoholics and controls.

CONCLUSIONS

Taken together, these findings suggest that the three-repeat allele of the MAOAuVNTR 30-bp polymorphism is not associated with impulsive and aggressive personality traits.

Assessing the molecular genetics of attention networks

BACKGROUND

Current efforts to study the genetic underpinnings of higher brain functions have been lacking appropriate phenotypes to describe cognition. One of the problems is that many cognitive concepts for which there is a single word (e.g. attention) have been shown to be related to several anatomical networks. Recently, we have developed an Attention Network Test (ANT) that provides a separate measure for each of three anatomically defined attention networks.

RESULTS

In this study we have measured the efficiency of neural networks related to aspects of attention using the ANT in a population of 200 adult subjects. We then examined genetic polymorphisms in four candidate genes (DRD4, DAT, COMT and MAOA) that have been shown to contribute to the risk of developing various psychiatric disorders where attention is disrupted. We find modest associations of several polymorphisms with the efficiency of executive attention but not with overall performance measures such as reaction time.

CONCLUSIONS

These results suggest that genetic variation may underlie inter-subject variation in the efficiency of executive attention. This study also shows that genetic influences on executive attention may be specific to certain anatomical networks rather than affecting performance in a global or non-specific manner. Lastly, this study further validates the ANT as an endophenotypic assay suitable for assessing how genes influence certain anatomical networks that may be disrupted in various psychiatric disorders.

Antisocial alcoholism and serotonin-related polymorphisms: association tests

Central serotonin dysfunction appears to be related to a subtype of alcoholism with antisocial impulsive features (type II; antisocial alcoholism). The serotonergic deficit may be associated with greater impulsivity, which in turn facilitates both alcohol dependence and antisocial behavior. The present study tested association of antisocial impulsive alcoholism with candidate genes related to serotonergic neurotransmission, using families. Eight markers were assayed using polymerase chain reaction: tryptophan hydroxylase (intron 7), the serotonin transporter SLC6A4 (VNTR 9/12), HTTLPR, the three serotonin receptor types HTR1B (G861C), HTR2A (T102C) and HTR2C (Cys23Ser), monoamine oxidase A (T1460C), and (CA)(n). Eligible probands had early age of onset of alcoholism, child conduct disorder, and two or more symptoms of adult Antisocial Personality Disorder. This sample included 35 probands, their parents, and some siblings (n = 116). Association tests were conducted using the Haplotype Relative Risk method for antisocial alcoholism diagnosis and the George-Elston regression method (the S.A.G.E. program ASSOC) for quantitative antisocial alcoholism severity. Haplotype Relative Risk analyses were not significant at the 0.05 level for any of the markers. Trends suggestive for future research occurred for tryptophan hydroxylase and HTR2A. Quantitative ASSOC analyses showed significant marker effects (P < 0.05) for both monoamine oxidase A markers, which were in linkage disequilibrium. Antisocial alcoholism symptom severity was higher with monoamine oxidase A C homozygotes or hemizygotes, indicating that low monoamine oxidase activity may be important. Future studies are needed to examine joint and interactive effects of serotonin-related markers.

No association of the MAOA gene with alcoholism among Han Chinese males in Taiwan

A positive association of MAOA polymorphisms with alcoholism has been demonstrated in certain recent studies, however, this association is not universally supported. The haplotype status of the MAOA gene polymorphisms could provide more information than alleles at a single site alone tested for an association with a complex, heterogeous disorder. This study examines whether there is an association between alcoholism and either a variable number of tandem repeat located upstream of the MAOA gene or an EcoRV functional polymorphism of the MAOA gene. These are analyzed both individually and as haplotypes. The study consisted of 214 subjects meeting DSM-IV criteria for alcoholism from northern Taiwan and 77 control individuals without history of alcoholism from Taipei. All of the subjects were Chinese Han males. For the two polymorphic sites, significant linkage disequilibrium occurred. No significant intergroup difference was observed between the two subject groups with respect to the allele frequencies for the two polymorphisms at the MAO locus tested both individually and as haplotypes. This finding suggests that no association exists between genetic variation at the MAOA locus and alcoholism in Chinese Han males.

Analysis of monoamine oxidase A (MAOA) promoter polymorphism in Finnish male alcoholics

Alterations in monoamine oxidase A (MAOA) expression and enzyme activity may be associated with alcoholism and impulsive behavior. Therefore, functional polymorphisms in the MAOA gene would be good candidates to consider in the interindividual differences that exist in the susceptibility to alcoholism. One variant that has been considered as a candidate in alcoholism is a repeat polymorphism in the MAOA gene promoter. We analyzed a cohort of Finnish males with either type 1 or type 2 alcoholism, as well as controls, for differences in the distribution of MAOA promoter alleles. Based on other studies, we postulated that type 2 alcoholism, which is associated with antisocial behavior, but not type 1 alcoholism, would be correlated with the inheritance of the low promoter activity allele. However, we failed to find a difference in allele distribution in type 1 and type 2 alcoholics. In addition, there was no difference in the allele distribution when each group of alcoholics was compared with controls. However, when both groups of alcoholics were pooled and compared with controls, the difference in allele distribution reached a trend towards significance. Our results suggest a minimal association between the MAOA low activity promoter alleles and alcoholism, regardless of the presence or absence of antisocial behavior. Interestingly, approximately 3% of type 2 alcoholics were found to be heterozygous for the MAOA promoter polymorphism. Since MAOA is X-linked, the heterozygotes are probable cases of Klinefelter's syndrome (47,XXY) suggesting that X-chromosome aneuploidy may increase the risk for developing type 2 alcoholism.

Altered behavior and alcohol tolerance in transgenic mice lacking MAO A: a comparison with effects of MAO A inhibitor clorgyline

The influence of deficiency of monoamine oxidase A (MAO A) gene and the lack of enzyme MAO A on the behavior of transgenic mouse strain (Tg8) was studied. It was shown that MAO-A-lacking mice differed from mice of the wild-type strain C3H/HeJ (C3H) by an attenuated acoustic startle response, prepulse inhibition (PPI) was unchanged. In Tg 8 mice, the exploratory nose-poking in the holeboard test as well as exploratory line crossing in the "light-dark" test were decreased. No effect of MAO A deficiency on locomotor activity was found. No alcohol preference or difference between Tg8 and C3H in ethanol consumption in the free-choice test has been found, although an increase in alcohol tolerance has been demonstrated. Ethanol-induced (0.3 g/100 g ip) sleep latency was longer, duration of sleep was shorter and ethanol hypothermia was reduced in MAO-A-lacking mice. Comparison of effects of MAO A knockout with those of irreversible MAO A inhibitor clorgyline (5 and 10 mg/kg ip) on C3H mice showed a similar reducing effect on ethanol-induced sleep, but potentiated ethanol-induced hypothermia. Clorgyline administration provoked a tendency to decrease of exploratory activity in the nose-poking test and decreased the frequency of exploratory rearings in the light-dark test. Clorgyline (5 and 10 mg/kg) did not affect the acoustic startle response, but a dose of 5 mg/kg diminished PPI. Therefore, Tg8 mice exhibited a decreased startle response and exploratory activity and an increased tolerance to ethanol. A similar increase in tolerance to ethanol-induced sleep and a tendency to decrease exploratory behavior were displayed by clorgyline. Other effects on behavior were different, suggesting the influence of long-lasting action of MAO A knockout and the involvement of a compensatory mechanism in Tg8 mice.

Antisociality, substance dependence, and the DRD5 gene: a preliminary study

A pilot population-based study of a microsatellite polymorphism at the DRD5 locus in adult European-Americans showed its association with childhood symptom counts for oppositional defiant disorder (ODD) in males and females and adult antisocial personality disorder (ASPD) in females. No association with childhood conduct disorder symptom count was observed. ODD mediated the genotype-ASPD relationship in females. Neither ODD nor ASPD significantly mediated the relationship between the genotype and the liability to substance dependence (SD). The data suggest involvement of the DRD5 locus in the variation and sexual dimorphism of SD liability and antisociality and in the developmental continuity of antisociality.

Genetic studies of substance abuse

Genetic studies of substance abuse indicate that variation in the risk for the disorder in the population is contributed by differences in both individual genotypes and environment. Recent developments in genetics raise the possibility of disentangling the complex system of genotype-environment interaction that determines the development of the individual behavioral phenotype. This paper reviews the concepts, methods and results pertaining to genetic investigation of substance abuse.

Genome polymorphism and alcoholism

Different gene variants have been identified as risk or protective factors in alcoholism. The genes coding for dopamine receptors, serotonin transporters, and dehydrogenases represent susceptibility loci for addictive behaviour. However, alcoholism represents a complex psychiatric symptomatology which is caused by multiple factors, both genetic and environmental. Furthermore, there are probably different subtypes of alcoholism each with a distinct pathophysiology, and thus a different genetic background. Genetic research can help to identify such subtypes, which may require different therapeutic approaches. However, gene polymorphisms are not only responsible for a predisposition to alcoholism, but also for personality traits which influence the likelihood of developing addictive behaviour. Moreover, genetic polymorphisms are probably involved in the way an individual responds to treatment. Also, the severity of secondary diseases resulting from chronic alcohol uptake may depend on the genetic makeup of an individual. New treatment strategies focusing on genes contributing towards drug and alcohol dependence (such as gene therapy) are already under examination in animal models. However, further research is required before these developments will considerably change today's clinical handling of alcoholism.

Pathological gambling and DNA polymorphic markers at MAO-A and MAO-B genes

This study was conducted to detect a possible association of MAOA and/or MAOB genes with pathological gambling (PG). DNA polymorphisms in MAOA and MAOB genes were screened by molecular analysis in 68 individuals (47 males and 21 females) meeting ICD-10 and DSM-IV criteria for pathological gambling and 68 healthy comparison controls matched for age and sex. There were no significant differences between pathological gamblers and healthy volunteers in overall allele distribution at the MAOA gene polymorphism. However there was a significant association between allele distribution and the subgroup of severe male gamblers (n = 31) compared to the males in the group of healthy volunteers (chi2 = 5246; df = 1; P < 0.05 [Bonferroni corrected]). No association was found between the MAOB polymorphic marker and PG. Allele variants at the MAOA, but not the MAOB gene may be a genetic liability factor in PG, at least in severe male gamblers. Molecular Psychiatry(2000) 5, 105-109.

Association of a regulatory polymorphism in the promoter region of the monoamine oxidase A gene with antisocial alcoholism

We analyzed a novel functional 30-bp repeat polymorphism in the promoter region of the X-chromosomal monoamine oxidase A gene (MAOA) to test whether length variation of the repeat polymorphism contributes to variation in the individual vulnerability to antisocial behavior and liability to alcohol dependence. The repeat number (3-5) of the MAOA polymorphism was assessed in 488 male subjects of German descent, a sample comprising 185 psychiatrically screened control subjects and 303 alcohol-dependent subjects including 59 alcoholics with antisocial personality disorder. The frequency of the low-activity 3-repeat allele was significantly increased in 59 antisocial alcoholics compared to 185 control subjects (51 vs. 35%; P = 0.031) and to 244 alcoholics without antisocial personality disorder (51 vs. 32%; P = 0.008), respectively. We found no significant difference in the frequency of the 3-repeat allele between 244 alcoholics without an antisocial personality disorder and the control subjects. Our findings suggest that the low-activity 3-repeat allele of the MAOA promoter polymorphism confers increased susceptibility to antisocial behavior rather than alcohol dependence per se in alcohol-dependent males.

Monoamine oxidase: from genes to behavior

Cloning of MAO (monoamine oxidase) A and B has demonstrated unequivocally that these enzymes are made up of different polypeptides, and our understanding of MAO structure, regulation, and function has been significantly advanced by studies using their cDNA. MAO A and B genes are located on the X-chromosome (Xp11.23) and comprise 15 exons with identical intron-exon organization, which suggests that they are derived from the same ancestral gene. MAO A and B knock-out mice exhibit distinct differences in neurotransmitter metabolism and behavior. MAO A knock-out mice have elevated brain levels of serotonin, norephinephrine, and dopamine and manifest aggressive behavior similar to human males with a deletion of MAO A. In contrast, MAO B knock-out mice do not exhibit aggression and only levels of phenylethylamine are increased. Mice lacking MAO B are resistant to the Parkinsongenic neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine. Both MAO A and B knock-out mice show increased reactivity to stress. These knock-out mice are valuable models for investigating the role of monoamines in psychoses and neurodegenerative and stress-related disorders.

Serotonin in early-onset alcoholism

This chapter examines current, common schemes to subgroup alcoholics to arrive at relatively homogeneous groups of patients to facilitate psychobiological and molecular genetic studies. Early-onset, male-limited alcoholism is commonly associated with antisocial personality disorder or antisocial behavioral traits. It is often preceded by early-onset aggressiveness, which is followed by conduct disorder. Early-onset alcoholism among men is associated with low central serotonin turnover rate. The data concerning platelet MAO activity and serotonin uptake to platelets among early-onset alcoholics are conflicting. Recent molecular genetic and brain imaging studies on early-onset alcoholics are preliminary but appear very promising.

A dinucleotide repeat polymorphism at the gene for monoamine oxidase A and measures of aggressiveness

The relationship between measures of aggressiveness (personality questionnaire scales, conduct disorder diagnosis, and symptom count) and a recently discovered dinucleotide repeat length polymorphism at the monoamine oxidase type A (MAOA) gene (MAOCA-1) as a candidate locus was examined in adolescents using polymerase chain reaction. No significant correlation between aggression scales and repeat length at the MAOCA-1 marker was found, whereas the categorical diagnosis of conduct disorder showed a nonsignificant trend for an association with the marker. Alternative explanations of this trend are discussed. The data obtained suggest that the polymorphism studied is not associated with the variation in aggressiveness.