Modulation of a number of genes on personality traits in a sample of healthy subjects

The Relationship between Character Traits and In Vivo Cerebral Serotonin Transporter Availability in Healthy Subjects: A High-Resolution PET Study with C-11 DASB

To elucidate the potential roles of serotonergic activity in human character traits (i.e., self-directedness, cooperativeness, and self-transcendence), we investigated the relationship between these character traits and serotonin transporter (5-HTT) in healthy subjects. Twenty-four participants underwent High-Resolution Research Tomograph-positron emission tomography scans with [¹¹C]DASB. To quantify 5-HTT availability, binding potential (BP_ND) of [¹¹C]DASB was obtained using the simplified reference tissue model. The Temperament and Character Inventory was used to assess subjects' levels of three character traits. There were no significant correlations between the three character traits. Self-directedness was significantly positively correlated with [¹¹C]DASB BP_ND in the left hippocampus, left middle occipital gyrus, bilateral superior parietal gyrus, left inferior parietal gyrus, left middle temporal gyrus (MTG), and left inferior temporal gyrus (ITG). Cooperativeness was significantly negatively correlated with [¹¹C]DASB BP_ND in the median raphe nucleus. Self-transcendence was significantly negatively correlated with [¹¹C]DASB BP_ND in the right MTG and right ITG. Our results show significant correlations between the three character traits and 5-HTT availability in specific brain regions. In particular, self-directedness was significantly positively correlated with 5-HTT availability, suggesting that a goal-oriented, self-confident, and resourceful character may be related to higher serotonergic neurotransmission.

Temperament and Character Inventory in Bipolar Disorder versus Healthy Controls and Modulatory Effects of 3 Key Functional Gene Variants

BACKGROUND

Bipolar disorder (BD) has been associated with temperamental and personality traits, although the relationship is still to be fully elucidated. Several studies investigated the genetic basis of temperament and character, identifying catechol-O-methyltransferase (COMT), brain derived neurotrophic factor (BDNF), and serotonin transporter (5-HTT) gene variants as strong candidates.

METHODS

In the GECO-BIP study, 125 BD patients and 173 HC were recruited. Subjects underwent to a detailed assessment and the temperament and character inventory 125 items (TCI) was administrated. Three functional genetic variants within key candidate genes (COMT rs4680, BDNF rs6265, and the serotonin-transporter-linked polymorphic region (5-HTTLPR)) were genotyped. Univariate and multivariate analyses were performed.

RESULTS

Compared to HC, BD patients showed higher scores in novelty seeking (NS; p = 0.001), harm avoidance (HA; p < 0.001), and self transcendence (St; p < 0.001), and lower scores in self directness (p < 0.001) and cooperativeness (p < 0.001) TCI dimensions. Concerning the genetic analyses, COMT rs4680 was associated with NS in the total sample (p = 0.007) and in the male subsample (p = 0.022). When performing the analysis in the HC and BD samples, the association was confirmed only in HC (p = 0.012), and in the HC male subgroup in particular (p = 0.004). BDNF rs6265 was associated with St in the BD group (p = 0.017).

CONCLUSION

COMT rs4680 may modulate NS in males in the general population. This effect was not detected in BD patients, probably because BD alters the neurobiological basis of some TCI dimensions. BDNF rs6265 seems to modulate St TCI dimension only in BD patients, possibly modulating the previously reported association between rs6265 and BD treatment response. Further studies are needed to confirm our findings.

The association between the serotonin and dopamine neurotransmitters and personality traits

Evidence from previous studies has reported that complex traits, including psychiatric disorders, are moderately to highly heritable. Moreover, it has also been shown that specific personality traits may increase the risk to develop mental illnesses. Therefore the focus of the research shifted towards the identification of the biological mechanisms underpinning these traits by exploring the effects of a constellation of genetic polymorphisms in healthy subjects. Indeed, studying the effect of genetic variants in normal personality provides a unique means for identifying candidate genes which may increase the risk for psychiatric disorders. In this review, we discuss the impact of two of the most frequently studied genetic polymorphisms on personality in healthy subjects, the 5-HTT polymorphism of the serotonin transporter and the DRD2/DRD4 polymorphisms of the D2/D4 dopamine's receptors. The main aims are: (a) to highlight that the study of candidate genes provides a fruitful ground for the identification of the biological underpinnings of personality without, though, reaching a general consensus about the strength of this relationship; and (b) to outline that the research in personality genetics should be expanded to provide a clearer picture of the heritability of personality traits.

The influence of genes on "positive valence systems" constructs: A systematic review

In 2009, the U.S. National Institute of Mental Health (NIMH) proposed an approach toward the deconstruction of psychiatric nosology under the research domain criteria (RDoC) framework. The overarching goal of RDoC is to identify robust, objective measures of behavior, emotion, cognition, and other domains that are more closely related to neurobiology than are diagnoses. A preliminary framework has been constructed, which has connected molecules, genes, brain circuits, behaviors, and other elements to dimensional psychiatric constructs. Although the RDoC framework has salience in emerging studies, foundational literature that pre-dated this framework requires synthesis and translation to the evolving objectives and nomenclature of RDoC. Toward this end, we review the candidate-gene association, linkage, and genome-wide studies that have implicated a variety of loci and genetic polymorphisms in selected Positive Valence Systems (PVS) constructs. Our goal is to review supporting evidence to currently listed genes implicated in this domain and novel candidates. We systematically searched and reviewed literature based on keywords listed under the June, 2011, edition of the PVS matrix on the RDoC website (http://www.nimh.nih.gov/research-priorities/rdoc/positive-valence-systems-workshop-proceedings.shtml), which were supplemented with de novo keywords pertinent to the scope of our review. Several candidate genes linked to the PVS framework were identified from candidate-gene association studies. We also identified novel candidates with loose association to PVS traits from genome-wide studies. There is strong evidence suggesting that PVS constructs, as currently conceptualized under the RDoC initiative, index genetically influenced traits; however, future research, including genetic epidemiological, and psychometric analyses, must be performed.

Personality and genes: remarks from a biological perspective

Although there is no doubt that genes’ functions influence human personality, years of studies provided no clear picture on regulation of particular traits by specific genes. In this article, an overview of the complexity of the system of genetic control of personality is presented, and the level of complications of biological processes operating in this system is underlined. The methodology of studies devoted to determine effects of genes on personality traits is discussed, and limitations of various methods in such studies are indicated. Finally, suggestions for further research are listed and commented on. It is likely that to increase the level of our understanding of genetic mechanisms that modulate human personality, researchers conducting further studies will have to focus on using large sample sizes, performing independent replications, considering experiments on animal models, integrating cross-cultural data and epigenetic measures, and performing interdisciplinary experiments which combine methods of various disciplines, such as biology and psychology.