Genetic covariation of neuroticism with monoamine oxidase activity and smoking

The role of MAO in personality and drug use

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

Platelet monoamine oxidase activity in children with attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a highly heritable developmental disorder characterized by symptoms of impulsivity, hyperactivity and/or inattention, and associated with structural and biochemical abnormalities in cortical and limbic structures innervated by dopamine, noradrenalin and serotonin. The enzyme monoamine oxidase, type B (MAO-B), is expressed in platelets, and metabolizes endogenous amines. Its activity has been proposed to represent a peripheral marker of various traits and forms of psychopathology. This study evaluated platelet MAO activity with a spectrofluorimetric method in 72 boys and 12 girls with predominantly hyperactive, predominantly inattentive, and combined subtype of ADHD (DSM-IV criteria), and in 64 control children. The results showed significantly lower platelet MAO activity in children with hyperactive, inattentive, and combined subtype of ADHD than in control children. There was no significant association between platelet MAO activity and gender or age. The limitation of the study was in the small sample of girls with ADHD (N=12), and in the determination of only one peripheral marker. In line with hypotheses of lower platelet MAO activity in different types of psychopathology, children with different subtypes of ADHD had significantly lower platelet MAO-B activity than control children.

Do Health Behaviors Explain the Effect of Neuroticism on Mortality? Longitudinal Findings from the VA Normative Aging Study

Studies have shown that higher levels of neuroticism are associated with greater risk of mortality. Yet what accounts for this association? One major theoretical position holds that persons higher in neuroticism engage in poorer health behaviors, such as smoking and excessive drinking, thus leading to earlier death. We tested this hypothesis using 30-year mortality in 1,788 men from the VA Normative Aging Study. Using proportional hazards (Cox) models we found that one health behavior, smoking, attenuated the effect of neuroticism on mortality by 40%. However, 60% remained unexplained, suggesting that the effects of other pathways (e.g., biological) also influence the relationship between neuroticism and mortality.

[Psychosomatic concept of hyperthyroidism-Graves type--behavioral and biochemical characteristics]

INTRODUCTION

In this study we test the hypothesis that specific behavioral and biochemical vulnerabilities characterize individuals with hyperthyroidism-Graves type, one of the classically cited "psychosomatic disorders".

MATERIAL AND METHODS

The sample included 24 subjects with Graves disease and 34 controls. All participants were evaluated for personality and temperament characteristics and for platelet MAO activity. A smaller group of panic disorder patients was tested with the same set of measures to ensure a validity of the study, especially regarding results on personality tests.

RESULTS

Individuals with hyperthyroidism had lower platelet MAO activity and higher scores on histrionic (Hy), depressive (D) and hypochondriac (H) subscale on the MMPI-201 than normal controls. Their TPQ temperament scores were characterized by high Harm Avoidance, whereas other temperament traits were average. Platelet MAO activity was inversely correlated with the MMPI-201 psychopatic deviance scale (Pd) and positively correlated with the TPQ Reward Dependence scale.

CONCLUSIONS

Our results provide support for the psychosomatic concept of Graves' disease. Personality features, temperament traits, and platelet MAO activity of hyperthyroid individuals are different from those in normal controls and correspond to those observed in anxiety disorders. We propose that the observed behavioral and biochemical similaritites between hyperthyroid and anxiety disorder patients represent an equicausality phenomenon, where the same underlying heritable factors, such as variable central monoaminergic activity coupled with temperament-related susceptibility to stress, facilitate phenotypic manifestation of a number of psychosomatic and psychialric disorders--including Graves disease. The observed correlations between personality traits and MAO activity provide support for the hypothesized functional relationship between the underlying central monoaminergic activity and temperament traits associated with anxiety, depression, and impulsivity.

Impulsivity and cigarette craving: differences across subtypes

RATIONALE

Cigarette smoking has been linked to a number of personality characteristics, including impulsivity. Smokers tend to endorse high levels of impulsivity, and more impulsive smokers have greater difficulty quitting, but little is known about potential explanatory mechanisms. Although indirect evidence suggests craving as a candidate mechanism, direct evidence has been mixed.

MATERIALS AND METHODS

This study assessed whether specific aspects of impulsivity (sensation seeking, lack of premeditation, lack of perseverance, and urgency) were associated with cue-induced craving. Regular smokers (n = 60; 50% female) were exposed to a smoking cue and a neutral cue in a repeated measure counter-balanced design.

RESULTS

Mixed effects regression models indicated that smokers who were high in sensation seeking reported greater increases in appetitive craving after smoking cue exposure, whereas, smokers who were high in urgency and lack of perseverance reported greater increases in negative affect craving.

CONCLUSIONS

Findings suggest a complex relationship between impulsivity and cue-induced craving that may be masked by single construct conceptualizations of impulsivity.

Monoamine oxidase (MAO) intron 13 polymorphism and platelet MAO-B activity in combat-related posttraumatic stress disorder

BACKGROUND

The neurobiology of posttraumatic stress disorder (PTSD) involves alterations in multiple neuroendocrine and neurotransmitter systems. Platelet monoamine oxidase (MAO-B) has been associated with susceptibility to various psychiatric disorders, personality traits and behaviors.

METHODS

Platelet MAO-B activity and MAO-B intron 13 polymorphism (a G/A substitution) were determined in male war veterans (n=106) with DSM-IV diagnosed current and chronic PTSD, divided into subgroups of PTSD patients with (n=28) or without (n=78) psychotic features, combat exposed veterans (n=41) who did not develop PTSD, and healthy control men (n=242).

RESULTS

Two-way ANOVAs revealed a significant effect of diagnosis and smoking, a significant effect of smoking, no significant effect of genotype, and no significant interaction between genotype, smoking or diagnosis, on platelet MAO-B activity. One-way ANOVAs showed significantly lower platelet MAO-B activity in smokers than in nonsmokers. After controlling for smoking, veterans with psychotic PTSD had significantly higher platelet MAO-B activity than veterans with or without PTSD, or healthy subjects.

LIMITATIONS

The results were obtained on peripheral biochemical marker, i.e. platelet MAO activity.

CONCLUSIONS

The MAO-B intron 13 polymorphism was not functional, and did not affect platelet MAO-B activity. The allele frequencies of the MAO-B genotype were similarly distributed among healthy controls and veterans with or without PTSD and/or psychotic symptoms. The results suggest that platelet MAO-B activity, controlled for smoking status, might be used as a peripheral marker of the psychotic symptoms in PTSD.

Características psicológicas associadas ao comportamento de fumar tabaco

Este artigo apresenta uma revisão da literatura sobre a psicologia do tabagismo, destacando características de personalidade do fumante como um dos obstáculos à cessação do tabagismo. Descreve-se a relação entre tabagismo e personalidade e, a seguir, a relação do tabagismo com os principais transtornos psiquiátricos. Estudos revelam que os fumantes tendem a ser mais extrovertidos, ansiosos, tensos, impulsivos e com mais traços de neuroticismo e psicoticismo, em comparação a ex-fumantes e não fumantes. A literatura revela, ainda, forte associação entre tabagismo e transtornos mentais, como esquizofrenia e depressão, entre outros. A compreensão dos fatores de natureza psicológica associados ao consumo e à dependência pode contribuir para a elaboração e aperfeiçoamento de estratégias terapêuticas para o tratamento da dependência e/ou programas de cunho educativo/preventivo.

Adaptive and maladaptive impulsivity, platelet monoamine oxidase (MAO) activity and risk-admitting in different types of risky drivers

RATIONALE

Platelet monoamine oxidase (MAO) activity reflects serotonergic functioning associated with impulsive behaviour, but the significance of these associations to real-life impulsive behaviour in healthy subjects is not clear.

OBJECTIVES

The present study explores impulsivity and platelet MAO activity among people with driving violations.

MATERIALS AND METHODS

We compared facets of impulsivity and platelet MAO activity in 1,004 male drivers, out of whom 203 had been caught by the police driving drunk and 292 had been caught exceeding speed limits and committing other non-alcohol-related driving violations. Subjects with speeding and other non-alcohol-related violations were further divided according to their self-reported risk-admitting of exceeding speed limits.

RESULTS

While drunk driving was associated only with maladaptive types of impulsivity, exceeding speed limits was associated with functional impulsivity and excitement seeking and, to a lesser degree, with dysfunctional impulsivity. Drunk drivers had lower platelet MAO activity. Risk-admitting high-risk drivers had higher platelet MAO activity, neuroticism-related impulsivity, dysfunctional impulsivity and excitement seeking compared to all other groups and higher functional impulsivity compared to controls. Risk-denying high-risk drivers had only higher functional impulsivity compared to controls.

CONCLUSIONS

This study demonstrates different expressions of functional and dysfunctional impulsivity in behaviour. While platelet MAO activity is lower in alcohol-related risky behaviour, non-alcohol-related self-acknowledged risky behaviour is related to higher platelet MAO activity. Thus, deviance towards lower as well as higher end of central serotonergic functioning may lead to impulsive behaviour. While self-reported impulsivity did not correlate with MAO activity, both MAO activity and impulsivity were related to risky behaviour.

MAOA haplotypes associated with thrombocyte-MAO activity

Background

The aim was to ascertain whether thrombocyte MAO (trbc-MAO) activity and depressed state are genetically associated with the MAO locus on chromosome X (Xp11.3 – 11.4). We performed novel sequencing of the MAO locus and validated genetic variants found in public databases prior to constructing haplotypes of the MAO locus in a Swedish sample (N = 573 individuals).

Results

Our results reveal a profound SNP desert in the MAOB gene. Both the MAOA and MAOB genes segregate as two distinct LD blocks. We found a significant association between two MAOA gene haplotypes and reduced trbc-MAO activity, but no association with depressed state.

Conclusion

The MAO locus seems to have an effect on trbc-MAO activity in the study population. The findings suggest incomplete X-chromosome inactivation at this locus. It is plausible that a gene-dosage effect can provide some insight into the greater prevalence of depressed state in females than males.

Correlation between striatal dopamine D2 receptor density and neuroticism in community volunteers

The central dopaminergic system, as well as the central serotonergic system, has been reported to be correlated with higher neuroticism. The present study examined the relationship between striatal dopamine D(2) receptor density and neuroticism. Neuroticism was assessed with the Maudsley Personality Inventory, and psychiatric morbidity was evaluated with both the Mini International Neuropsychiatric Interview and the Hamilton Depression Rating Scale (HAM-D). Single photon emission computed tomography with [(123)I]iodo-benzamide was used to measure striatal dopamine D(2) receptor density. HAM-D scores and psychiatric morbidity in high-neuroticism individuals were higher than in low-neuroticism individuals. Moreover, striatal dopamine D(2) receptor densities were significantly correlated with the neuroticism score of the 41 subjects. The central dopaminergic system may play an important role in the neurobiological characteristics of neuroticism.

Panic disorder: Psychobiological aspects of personality dimensions

Attempts to understand the underlying mechanisms of association between psychological factors and panic disorder have been mostly based on psychodynamic description. Evidence of the importance of serotonergic (5-HT) system in panic disorder (PD), however, has substanti ally increased in recent years. OBJECTIVE The objective of our study was to determine whether there was a specific personality profile of panic disorder patients and how it was related to possible neurobiological mechanisms underlying personality dimensions. PATIENTS AND METHODS Sample consisted of 14 inpatients with ICD-X diagnosis of panic disorder and 34 healthy control subjects. Personality dimensions were assessed by Minnesota Multiphasic Personality Inventory (MMPI-201) and Tridimensional Personality Questionnaire (TPQ). To assess central 5-HT function, platelet monoamine-oxidase (MAO) activity was measured. RESULTS In panic disorder group, higher scores of histrionic, depressive and hypochondriac subscales and significant increase of harm avoidance (HA) scale as well as low MAO activity were found. Negative correlation was established between MAO activity and psychopathic deviance MMPI scale. CONCLUSION The obtained results might indicate a specific personality profile of patients with panic disorder, which is characterized by high neuroticism, fearfulness, inhibition, shyness and apprehensive worry. Low MAO activity and high HA scores possibly indicate underlying hyperserotonergic state. The observed correlation between personality traits and MAO activity provide additional support for the hypothesized functional relationship between underlying central monoaminergic activity and temperament traits associated with anxiety, depression and impulsivity.

Both low and high activities of platelet monoamine oxidase increase the probability of becoming a smoker

Platelet monoamine oxidase (MAO) activity is a marker of personality and psychiatric vulnerability, but the direct inhibitory action of tobacco constituents on the enzyme distorts the association. In the present investigation, data from a prospective longitudinal study of smoking behaviour and platelet MAO activity in adolescents at ages 15 and 18 years were sequentially analysed using a second-order multiple logistic regression analysis. The odds of regular smoking at 18 years increased significantly with increasing absolute deviation of platelet MAO activity at 15 years from the mean. That is, both low and high platelet MAO activity at 15 years predicted a higher probability of becoming a smoker. These data suggest that smoking is associated with low platelet MAO activity not only because of the direct inhibitory effect of tobacco constituents on the enzyme, but also because subjects with low platelet MAO activity are more likely to become smokers. Furthermore, the possible association between above-average platelet MAO activity and behavioural phenotypes should be reexamined.

Genetics of personality: are we making progress?

For centuries, scientists are intrigued by the differences in personality between individuals. As early as in the ancient Greek civilization, people tried to formulate theories to systematize this diversity. With the increased interest in behavior genetics, personality was also considered a challenging phenotype. From the early start, studies suggested a heritable component in personality. After the successes of molecular genetic studies in unraveling the genetic basis of (mostly) monogenic diseases, the focus shifted towards complex traits, including psychiatric disorders. It was observed in several studies that personality measures differed between patients with psychiatric disorders and healthy controls. Therefore, normal personality was considered a viable endophenotype in the search for genes involved in psychiatric disorders such as affective disorders, ADHD and substance dependence. Genes that were to be found in studies on personality could be candidate genes for particular psychiatric disorders. In the course of time, however the study of genes for personality turned out to be at least as hard as the search for genes involved in other complex disorders. In this review, past studies, present problems and future directions concerning the study of personality genetics are discussed.