Association between serotonin transporter gene polymorphism and anxiety-related traits

Validation of serotonin transporter mRNA as a quantitative biomarker of heavy drinking and its comparison to ethyl glucuronide/ethyl sulfate: A randomized, double-blind, crossover trial

BACKGROUND

The serotonin transporter (SERT) mRNA was previously reported to be a quantitative and pathophysiology-based biomarker of heavy drinking in 5HTTLPR:LL genotype-carriers treated with ondansetron. Here, we validated the potential use of SERT mRNA for quantitative prediction of recent alcohol consumption (in the absence of treatment) and compared it with the known biomarkers ethyl glucuronide (EtG) and ethyl sulfate (EtS).

METHODS

Binge drinking men and women of European ancestry aged 21 to 65 years were enrolled in a 12-day, in-patient, randomized, double-blind, crossover study, where they were administered three beverage doses (placebo, 0.5 g/kg [0.4 g/kg] ethanol, and 1 g/kg [0.9 g/kg] ethanol for men [women]) individually in three 4-day periods (experiments), separated by minimum 7-day washout period. Diet, sleep, and physical activity were controlled throughout the inpatient experiments. Twenty-nine participants were randomized to receive beverage doses counterbalancing the sequence of treatment and gender within subgroups stratified by SERT genotypes 5HTTLPR:LL+rs25531:AA (LA LA ) versus 5HTTLPR:LS/SS. Peripheral venous blood was collected daily for (1) quantification of SERT mRNA (the primary outcome measure) using qRT-PCR and (2) plasma EtG and EtS levels using tandem mass-spectrometry.

RESULTS

The association between administered beverage dose and SERT mRNA from completers of at least one 4-day experiment (N = 18) assessed by a linear mixed model was not statistically significant. Significant positive associations were found with beverage dose and plasma EtG, EtS and EtG/EtS ratio (β = 5.8, SE = 1.2, p < 0.0001; β = 1.3, SE = 0.6, p = 0.023; and β = 3.0, SE = 0.7, p < 0.0001, respectively; the C-statistics for discriminating outcomes were 0.97, 0.8, and 0.92, respectively). Additionally, we observed a sequence effect with a greater placebo effect on SERT mRNA when it was administered during the first experiment (p = 0.0009), but not on EtG/EtS measures.

CONCLUSION

The findings do not validate the use of SERT as a biomarker of heavy drinking. Larger and more innovative studies addressing the effects of placebo, race, gender, and response to treatment with serotonergic agents are needed to fully assess the utility of SERT as a biomarker of heavy and binge drinking.

Specific temperament in patients with nevoid basal cell carcinoma syndrome

BACKGROUND

Nevoid basal cell carcinoma syndrome (NBCCS) is a neurocutaneous disease, characterized by tumorigenesis and developmental anomalies due to aberrant sonic hedgehog (Shh) signaling. Patients with NBCCS typically appear calm and carefree, suggesting that a specific personality in these patients may be associated with an enhanced hedgehog pathway. Our study aimed to determine the personality type in these patients.

METHODS

We enrolled 14 mentally normal patients with genetically confirmed NBCCS (seven males and seven females; mean age = 25.2 years) and 20 controls (10 males and 10 females; mean age = 27.9 years). The patients were assessed with the Japanese version of the Temperament and Character Inventory, based on the seven-dimensional model of temperament and character, and their clinical symptoms were evaluated. The amygdala volumes of six patients with NBCCS were measured using magnetic resonance imaging with image-processing software.

RESULTS

Patients with NBCCS scored significantly lower on harm avoidance (0.89) than controls (1.00; P = 0.0084). Moreover, patients with NBCCS and developmental malformations such as rib anomalies, who may have experienced Shh signaling enhancement from the prenatal period, scored significantly lower on harm avoidance (0.80 [P = 0.0031]). The left amygdala volume was also significantly reduced in patients with NBCCS (P = 0.0426).

CONCLUSIONS

Patients with NBCCS who experienced increased Shh signaling from the prenatal period showed significantly lower harm avoidance related to serotonin. The left amygdala volume was significantly reduced in these patients. Our results indicate that Shh signaling may influence the human personality.

Resilience to fear: The role of individual factors in amygdala response to stressors

Resilience to stress is an adaptive process that varies individually. Resilience refers to the adaptation, or the ability to maintain or regain mental health, despite being subject to adverse situation. Resilience is a dynamic concept that reflects a combination of internal individual factors, including age and gender interacting with external factors such as social, cultural and environmental factors. In the last decade, we have witnessed an increase in the prevalence of anxiety disorders, including post-traumatic stress disorder. Given that stress in unavoidable, it is of great interest to understand the neurophysiological mechanisms of resilience, the individual factors that may contribute to susceptibility and promote efficacious approaches to improve resilience. Here, we address this complex question, attempting at defining clear and operational definitions that may allow us to improve our analysis of behavior incorporating individuality. We examine how individual perception of the stressor can alter the outcome of an adverse situation using as an example, the fear-conditioning paradigm and discuss how individual differences in the reward system can contribute to resilience. Given the central role of the endocannabinoid system in regulating fear responses and anxiety, we discuss the evidence that polymorphisms in several molecules of this signaling system contribute to different anxiety phenotypes. The endocannabinoid system is highly interconnected with the serotoninergic and dopaminergic modulatory systems, contributing to individual differences in stress perception and coping mechanisms. We review how the individual variability in these modulatory systems can be used towards a multivariable assessment of stress risk. Incorporating individuality in our research will allow us to define biomarkers of anxiety disorders as well as assess prognosis, towards a personalized clinical approach to mental health.

Sex differences modulating serotonergic polymorphisms implicated in the mechanistic pathways of risk for depression and related disorders

Despite consistent observations of sex differences in depression and related emotional disorders, we do not yet know how these sex differences modulate the effects of genetic polymorphisms implicated in risk for these disorders. This Mini-Review focuses on genetic polymorphisms of the serotonergic system to illustrate how sex differences might modulate the neurobiological pathways involved in the development of depression. We consider the interacting role of environmental factors such as early-life stress. Given limited current knowledge about this topic, we highlight methodological considerations, challenges, and guidelines for future research. © 2016 Wiley Periodicals, Inc.

Neural basis of individual differences in the response to mental stress: a magnetoencephalography study

Stress is a risk factor for the onset of mental disorders. Although stress response varies across individuals, the mechanism of individual differences remains unclear. Here, we investigated the neural basis of individual differences in response to mental stress using magnetoencephalography (MEG). Twenty healthy male volunteers completed the Temperament and Character Inventory (TCI). The experiment included two types of tasks: a non-stress-inducing task and a stress-inducing task. During these tasks, participants passively viewed non-stress-inducing images and stress-inducing images, respectively, and MEG was recorded. Before and after each task, MEG and electrocardiography were recorded and subjective ratings were obtained. We grouped participants according to Novelty seeking (NS) - tendency to be exploratory, and Harm avoidance (HA) - tendency to be cautious. Participants with high NS and low HA (n = 10) assessed by TCI had a different neural response to stress than those with low NS and high HA (n = 10). Event-related desynchronization (ERD) in the beta frequency band was observed only in participants with high NS and low HA in the brain region extending from Brodmann's area 31 (including the posterior cingulate cortex and precuneus) from 200 to 350 ms after the onset of picture presentation in the stress-inducing task. Individual variation in personality traits (NS and HA) was associated with the neural response to mental stress. These findings increase our understanding of the psychological and neural basis of individual differences in the stress response, and will contribute to development of the psychotherapeutic approaches to stress-related disorders.

Toward a multiscale modeling framework for understanding serotonergic function

Despite its importance in regulating emotion and mental wellbeing, the complex structure and function of the serotonergic system present formidable challenges toward understanding its mechanisms. In this paper, we review studies investigating the interactions between serotonergic and related brain systems and their behavior at multiple scales, with a focus on biologically-based computational modeling. We first discuss serotonergic intracellular signaling and neuronal excitability, followed by neuronal circuit and systems levels. At each level of organization, we will discuss the experimental work accompanied by related computational modeling work. We then suggest that a multiscale modeling approach that integrates the various levels of neurobiological organization could potentially transform the way we understand the complex functions associated with serotonin.

Affective changes during the postpartum period: Influences of genetic and experiential factors

This article is part of a Special Issue "Parental Care". The postpartum period involves some truly transformational changes in females' socioemotional behaviors. For most female laboratory rodents and women, these changes include an improvement in their affective state, which has positive consequences for their ability to sensitively care for their offspring. There is heterogeneity among females in the likelihood of this positive affective change, though, and some women experience elevated anxiety or depression (or in rodents anxiety- or depression-related behaviors) after giving birth. We aim to contribute to the understanding of this heterogeneity in maternal affectivity by reviewing selected components of the scientific literatures on laboratory rodents and humans examining how mothers' physical contact with her infants, genetics, history of anxiety and depression and early-life and recent-life experiences contribute to individual differences in postpartum affective states. These studies together indicate that multiple biological and environmental factors beyond female maternal state shape affective responses during the postpartum period, and probably do so in an interactive manner. Furthermore, the similar capacity of some of these factors to modulate anxiety and depression in human and rodent mothers suggests cross-species conservation of mechanisms regulating postpartum affectivity.

Association of Anxiety Symptoms in Offspring of Bipolar Parents with Serotonin Transporter-Linked Polymorphic Region (5-HTTLPR) Genotype

OBJECTIVE

Offspring of parents with bipolar disorder (BD) have been shown to be at high risk for BD. Anxiety symptoms, even at subclinical levels, have been associated with increased risk for BD in these youth. The s-allele of the serotonin transporter-linked polymorphic region (5-HTTLPR) has been implicated in the pathophysiology of both BD and anxiety disorders and has been associated with pharmacological treatment response and increased risk for antidepressant side effects. Therefore, we aimed to explore 1) whether anxiety symptoms in offspring of BD parents were associated with presence of the 5-HTTLPR s-allele and 2) whether anxiety symptoms in the offspring of BD parents according to the 5-HTTLPR genotypes are related to antianxiety medication status.

METHODS

A total of 64 offspring of BD parents (mean age: 13.7 years) and 51 healthy controls (HC) (mean age: 13.7 years) were compared genetically and on the Multidimensional Anxiety Scale for Children (MASC).

RESULTS

Offspring of BD parents showed higher levels of overall anxiety than did the HC group. Only antianxiety medication naïve offspring of BD parents were found to have an association between 5-HTTLPR genotypes and anxiety symptoms. The antianxiety medication naïve offspring of BD parents with the s-allele showed higher level of overall anxiety than offspring of BD parents with the l/l genotype. No significant differences in anxiety symptoms or their association with the 5-HTTLPR genotype were found in the HC group.

CONCLUSIONS

This study indicated that there may be an association between 5-HTTLPR genotypes and anxiety symptoms in offspring of BD parents, and that antianxiety medication status may affect anxiety symptoms in the offspring of BD patients according to genotype.

Serotonin transporter gene polymorphism (5-HTTLPR) influences trait anxiety by modulating the functional connectivity between the amygdala and insula in Han Chinese males

A functional polymorphism (5-hydroxytryptamine transporter linked polymorphic region [5-HTTLPR]) in the promoter region of human serotonin transporter gene has been found to be associated with several dimensions of neuroticism and psychopathology, especially anxiety. However, the neural basis underlying the association between 5-HTTLPR and anxiety is less clear. Here, we explored how 5-HTTLPR influenced anxiety by modulating the spontaneous brain activities in Han Chinese. First, we found an association between 5-HTTLPR and anxiety only in the male and not in the female population, where male S/S homozygotes had a significantly higher level of anxiety than male L allele carriers. Then, we examined how 5-HTTLPR influenced anxiety at both regional and network levels in the brain at rest. At the regional level, we found a significantly higher fractional amplitude of low-frequency fluctuations in the amygdala in male S/S homozygotes relative to male L allele carriers. At the network level, male S/S homozygotes showed a weaker resting-state functional connectivity (RSFC) between the amygdala and various regions, including the insula, Heschl's gyrus, lateral occipital cortex, superior temporal gyrus, and hippocampus, and a stronger RSFC between the amygdala and various regions, including the supramariginal gyrus and middle frontal gyrus. However, at both levels, only was the amygdala-insula RSFC correlated with anxiety. Mediation analyses further revealed that the amygdala-insula RSFC mediated the association between 5-HTTLPR and anxiety. In short, our study provided the first empirical evidence that the amygdala-insula RSFC served as the neural basis underlying the association between 5-HTTLPR and anxiety, suggesting a potential neurogenetic susceptibility mechanism for anxiety.

Relationship between serotonin transporter gene polymorphism and constipation in cancer patients

INTRODUCTION

To assess the potential association between serotonin transporter gene insertion/deletion polymorphism and the cancer-related constipation phenotype.

MATERIAL AND METHODS

A total of 120 patients diagnosed with malignant solid tumors were subjected to genotyping. For the two groups - patients with constipation and constipation-free patients with non-gastrointestinal cancer, 60 cases in each group - we collected the peripheral venous blood. We extracted genomic DNA, and used polymerase chain reaction (PCR) to analyze the serotonin transporter (5-HT) link polymorphic region (5-HTTLPR) polymorphism of the serotonin transporter gene.

RESULTS

The frequency of S/S genotype in cancer patients with constipation was 66.67% (40/60), and the frequency of the S allele was 79.17% (95/120); the frequency of S/S genotype in cancer patients without constipation was 48.33% (29/60), and the frequency of the S allele was 65.83% (79/120). There was a significant difference between the two groups (p < 0.05).

CONCLUSIONS

The presence of 5-HTTLPRS/S genotype and the S allele in patients with cancers probably carry an increased risk of constipation. However, its role as a cause of cancer-related constipation needs to be further investigated.

Population disparities in mental health: insights from cultural neuroscience

By 2050, nearly 1 in 5 Americans (19%) will be an immigrant, including Hispanics, Blacks, and Asians, compared to the 1 in 8 (12%) in 2005. They will vary in the extent to which they are at risk for mental health disorders. Given this increase in cultural diversity within the United States and costly population health disparities across cultural groups, it is essential to develop a more comprehensive understanding of how culture affects basic psychological and biological mechanisms. We examine these basic mechanisms that underlie population disparities in mental health through cultural neuroscience. We discuss the challenges to and opportunities for cultural neuroscience research to determine sociocultural and biological factors that confer risk for and resilience to mental health disorders across the globe.

Anxiety sensitivity in adolescence and young adulthood: the role of stressful life events, 5HTTLPR and their interaction

BACKGROUND

Cognitive biases have long been hypothesized to influence the development and maintenance of symptoms of internalizing problems. Anxiety sensitivity represents one such bias and refers to sensitivity to the physical and emotional symptoms of anxiety and the belief that these are harmful. Twin studies indicate a role for both environmental and genetic influences on anxiety sensitivity. However, little work has been done specifying environments or genes involved in this phenotype. In light of this, we looked at the association between stressful life events, the serotonin transporter gene polymorphism (5HTTLPR), and anxiety sensitivity in a longitudinal sample of adolescents.

METHODS

Stressful life events and anxiety sensitivity were measured in over 1,500 individuals at three time points (mean ages 15, 17, and 20 years). 5HTTLPR was genotyped in 1,109 participants.

RESULTS

There was consistent evidence for an association between stressful life events and both anxiety sensitivity and change in anxiety sensitivity over time. Although the effect of independent stressful life events was relatively short lived, dependent stressful life events were associated with anxiety sensitivity over time. There was no evidence for a main effect of 5HTTLPR on anxiety sensitivity. 5HTTLPR genotype did not moderate the effect of stressful life events on anxiety sensitivity.

CONCLUSIONS

The current study extends previous work by showing that stressful life events, independent of the individual, explained change in cognitions associated with anxiety and depression. This effect does not, however, appear to be moderated by genotype.

A single nucleotide polymorphism of the neuropeptide B/W receptor-1 gene influences the evaluation of facial expressions

Neuropeptide B/W receptor-1 (NPBWR1) is expressed in discrete brain regions in rodents and humans, with particularly strong expression in the limbic system, including the central nucleus of the amygdala. Recently, Nagata-Kuroiwa et al. reported that Npbwr1(-/-) mice showed changes in social behavior, suggesting that NPBWR1 plays important roles in the emotional responses of social interactions.The human NPBWR1 gene has a single nucleotide polymorphism at nucleotide 404 (404A>T; SNP rs33977775). This polymorphism results in an amino acid change, Y135F. The results of an in vitro experiment demonstrated that this change alters receptor function. We investigated the effect of this variation on emotional responses to stimuli of showing human faces with four categories of emotional expressions (anger, fear, happiness, and neutral). Subjects' emotional levels on seeing these faces were rated on scales of hedonic valence, emotional arousal, and dominance (V-A-D). A significant genotype difference was observed in valence evaluation; the 404AT group perceived facial expressions more pleasantly than did the 404AA group, regardless of the category of facial expression. Statistical analysis of each combination of [V-A-D and facial expression] also showed that the 404AT group tended to feel less submissive to an angry face than did the 404AA group. Thus, a single nucleotide polymorphism of NPBWR1 seems to affect human behavior in a social context.

[Familial transmission of depression: the importance of harm avoidance]

BACKGROUND

Previous research about the aetiology of depression has analysed how depression-associated personality traits influence familial transmission. Using the community-based sample of the Greifswald Family Study, we investigated longitudinally to which extent the temperament factor harm avoidance influences the correlation between parent's depression and the depression of their offspring (with regard to possible sex differences).

METHODS

To test this familial transmission a structural equation model was conducted with the data of 193 children (mean age 19.5, SD=2.41) and their biological parents. Depression was assessed with structured clinical interviews, and harm avoidance with Cloninger's Temperament and Character Inventory (TCI, JTCI).

RESULTS

The harm avoidance scores of the mothers were significantly correlated with the harm avoidance scores of their children, but the correlation of the father's and children's scores did not reach significance. The extent of harm avoidance at the first assessment of the 14-year-old children predicted depression 5 years later.

CONCLUSION

These results indicate the importance of personality as a vulnerability marker for developing affective disorders. The results are discussed with respect to prevention programmes for children and parents with depression, especially if they exhibit strongly avoidant or anxious behaviour.

Behavioural genetics of the serotonin transporter

The serotonin transporter is a key regulator of the bioavailability of serotonin and therefore any modulation in the expression or action of the transporter would be expected to have consequences on behaviour. The transporter has therefore become a target for pharmaceutical intervention in behavioural and mood disorders. The search for polymorphic variants in the transporter that would associate with neurological disorders has been extensive but has become focused on two domains which are both termed variable number tandem repeat (VNTR)polymorphisms. Both of these VNTRs are in non-coding DNA and therefore proposed to be mechanistically involved in a disorder through their ability to modulate transcriptional or post-transcriptional regulation of the transporter. The most extensively studied is in the promoter and is a bi-allelic insertion/deletion found in the 50 promoter region of the gene 1.2 kb upstream of the transcriptional start site. This VNTR, termed, 5-HTTLPR was initially identified as two variants containing either, 14 (short/deletion) or 16 (long/insertion) copies of a 22 bp repeat. A second widely studied VNTR found in the non-coding region of the transporter is located within intron 2 and comprises 9, 10 or 12 copies of a16–17 bp repeat termed, STin2.9, STin2.10 and STin2.12, respectively. These VNTR polymorphisms have been associated with a range of behavioural and psychiatric disorders including depression, OCD, anxiety and schizophrenia, however often the lack of reproducibility in different cohorts has led to debate on the actual association of the polymorphisms with this extensive range of neurological conditions. Here we review these two polymorphic VNTRs in depth and relate that to pharmaceutical response, their ability to regulate differential transporter expression, their core involvement in gene-environment interaction and their genetic association with specific disorders.

Serotonin transporter gene and childhood trauma--a G × E effect on anxiety sensitivity

BACKGROUND

Genetic factors and environmental factors are assumed to interactively influence the pathogenesis of anxiety disorders. Thus, a gene-environment interaction (G × E) study was conducted with respect to anxiety sensitivity (AS) as a promising intermediate phenotype of anxiety disorders.

METHOD

Healthy subjects (N = 363) were assessed for AS, childhood maltreatment (Childhood Trauma Questionnaire), and genotyped for functional serotonin transporter gene variants (5-HTTLPR/5-HTT rs25531). The influence of genetic and environmental variables on AS and its subdimensions was determined by a step-wise hierarchical regression and a multiple indicator multiple cause (MIMIC) model.

RESULTS

A significant G × E effect of the more active 5-HTT genotypes and childhood maltreatment on AS was observed. Furthermore, genotype (LL)-childhood trauma interaction particularly influenced somatic AS subdimensions, whereas cognitive subdimensions were affected by childhood maltreatment only.

CONCLUSIONS

Results indicate a G × E effect of the more active 5-HTT genotypes and childhood maltreatment on AS, with particular impact on its somatic subcomponent.

Mapping functional brain activation using [14C]-iodoantipyrine in male serotonin transporter knockout mice

Background

Serotonin transporter knockout mice have been a powerful tool in understanding the role played by the serotonin transporter in modulating physiological function and behavior. However, little work has examined brain function in this mouse model. We tested the hypothesis that male knockout mice show exaggerated limbic activation during exposure to an emotional stressor, similar to human subjects with genetically reduced transcription of the serotonin transporter.

Methodology/Principal Findings

Functional brain mapping using [¹⁴C]-iodoantipyrine was performed during recall of a fear conditioned tone. Regional cerebral blood flow was analyzed by statistical parametric mapping from autoradiographs of the three-dimensionally reconstructed brains. During recall, knockout mice compared to wild-type mice showed increased freezing, increased regional cerebral blood flow of the amygdala, insula, and barrel field somatosensory cortex, decreased regional cerebral blood flow of the ventral hippocampus, and conditioning-dependent alterations in regional cerebral blood flow in the medial prefrontal cortex (prelimbic, infralimbic, and cingulate). Anxiety tests relying on sensorimotor exploration showed a small (open field) or paradoxical effect (marble burying) of loss of the serotonin transporter on anxiety behavior, which may reflect known abnormalities in the knockout animal's sensory system. Experiments evaluating whisker function showed that knockout mice displayed impaired whisker sensation in the spontaneous gap crossing task and appetitive gap cross training.

Conclusions

This study is the first to demonstrate altered functional activation in the serotonin transporter knockout mice of critical nodes of the fear conditioning circuit. Alterations in whisker sensation and functional activation of barrel field somatosensory cortex extend earlier reports of barrel field abnormalities, which may confound behavioral measures relying on sensorimotor exploration.

Serotonin transporter gene polymorphism may be associated with functional dyspepsia in a Japanese population

Background

Although familial clustering of functional dyspepsia (FD) has been reported, the role of genetics in the susceptibility to FD is still not well understood. In the present study, the association between serotonin transporter (SERT) gene (SLC6A4) polymorphism and FD was explored.

Methods

Subjects were divided into either a postprandial distress syndrome (PDS) group or an epigastric pain syndrome (EPS) group according to the Rome III criteria. The healthy controls were those who had visited a hospital for an annual health check-up. The presence of the SLC6A4 promoter polymorphism, 5-hydroxytryptamin transporter gene linked polymorphic region (5-HTTLPR), was then evaluated, and logistic regression analysis was used to test all variables.

Results

The 5-HTTLPR genotype distribution was 448 SS, 174 SL, and 24 LL in controls and 30 SS, 20 SL, and 3 LL in FD subjects. No significant correlation was found between the 5-HTTLPR genotype and FD. When the genotypes and subtypes of FD were exploratory evaluated, the SL genotype was significantly associated with PDS [odds ratio (OR) = 2.24, 95% confidence interval (CI); 1.16-4.32, P = 0.034 after Bonferroni correction] compared to the SS genotype adjusted for sex and age. Comparison of the SS genotype with the SL/LL genotype also showed a significant association of genotype with PDS (OR = 2.32, 95% CI; 1.23-4.37, P = 0.009).

Conclusion

The present results suggest that 5-HTTLPR L allele may influence the susceptibility to PDS.

The influence of psychiatric screening in healthy populations selection: a new study and meta-analysis of functional 5-HTTLPR and rs25531 polymorphisms and anxiety-related personality traits

BACKGROUND

A genetic liability for anxiety-related personality traits in healthy subjects has been associated with the functional serotonin transporter promoter polymorphism (5-HTTLPR), although the data are somewhat conflicting. Moreover, only one study has investigated the functional significance of the 5-HTTLPR/rs25531 haplotypes in relation to anxiety traits in healthy subjects. We tested whether the 5-HTTLPR polymorphism and the 5-HTTLPR/rs25531 haplotypes are linked to Harm Avoidance (HA) using an association study (STUDY I) and a meta-analytic approach (STUDY II).

METHODS

STUDY I: A total of 287 unrelated Italian volunteers were screened for DSM-IV Axis I disorders and genotyped for the 5-HTTLPR and rs25531 (A/G) polymorphisms. Different functional haplotype combinations were also analyzed. STUDY II: A total of 44 studies were chosen for a meta-analysis of the putative association between 5-HTTLPR and anxiety-related personality traits.

RESULTS

STUDY I: In the whole sample of 287 volunteers, we found that the SS genotype and S'S' haplotypes were associated with higher scores on HA. However, because the screening assessed by Mini-International Neuropsychiatric Interview (M.I.N.I.) showed the presence of 55 volunteers affected by depression or anxiety disorders, we analyzed the two groups ("disordered" and "healthy") separately. The data obtained did indeed confirm that in the "healthy" group, the significant effects of the SS genotype and S'S' haplotypes were lost, but they remained in the "disordered" group. STUDY II: The results of the 5-HTTLPR meta-analysis with anxiety-related traits in the whole sample confirmed the association of the SS genotype with higher anxiety-related traits scores in Caucasoids; however, when we analyzed only those studies that used structured psychiatric screening, no association was found.

CONCLUSIONS

This study demonstrates the relevance to perform analyses on personality traits only in DSM-IV axis I disorder-free subjects. Furthermore, we did not find an association between functional serotonin transporter gene polymorphisms and anxiety traits in healthy subjects screened through a structured psychiatric interview.

5-HTTLPR status moderates the effect of early adolescent substance use on risky sexual behavior

OBJECTIVE

A longitudinal, prospective design was used to investigate a moderation effect in the association between early adolescent substance use and risky sexual behavior 2 years later. A genetic vulnerability factor, a variable nucleotide repeat polymorphism (VNTR) in the promoter region of the serotonin transporter gene SLC6A4, known as 5-HTTLPR, was hypothesized to moderate the link between substance use at age 14 and risky sexual behavior at age 16. This VNTR has been associated with risk-taking behavior.

DESIGN

African American youths in rural Georgia (N = 185) provided 2 waves of data on their substance use and sexual behavior. Genetic data were obtained via saliva samples.

MAIN OUTCOME MEASURES

Substance use and sexual risk behavior were assessed using youth self-report items developed for this investigation.

RESULTS

Multiple regression analyses indicated that the presence of 1 or 2 copies of the short allele of the VNTR interacted with substance use to predict sexual behavior. Substance use had little effect on sexual behavior for youths without the short allele; this effect was greatly increased for youths with the short allele.

CONCLUSION

Genetic vulnerability affected the implications of early onset substance use for later sexual behavior.

Serotonin transporter gene-linked polymorphic region (5-HTTLPR) influences decision making under ambiguity and risk in a large Chinese sample

Risky decision making is a complex process that involves weighing the probabilities of alternative options that can be desirable, undesirable, or neutral. Individuals vary greatly in how they make decisions either under ambiguity and/or under risk. Such individual differences may have genetic bases. Based on previous studies on the genetic basis of decision making, two decision making tasks [i.e., the Iowa Gambling Task (IGT) and Loss Aversion Task (LAT)] were used to test the effect of 5-HTTLPR polymorphism on decision making under ambiguity and under risk in a large Han Chinese sample (572 college students, 312 females). Basic intelligence and memory tests were also included to control for the influence of basic cognitive abilities on decision making. We found that 5-HTTLPR polymorphism significantly influenced performance in both IGT and LAT. After controlling for intelligence and memory abilities, subjects homozygous for s allele had lower IGT scores than l carriers in the first 40 trials of the IGT task. They also exhibited higher loss aversion than l carriers in the LAT task. Moreover, the effects of 5-HTTLPR were stronger for males than for females. These results extend the literature on the important role of emotion in decision making under ambiguity and risk, and shed additional lights on how decision making is influenced by culture as well as sex differences. Combining our results with existing literature, we propose that these effects might be mediated by a neural circuitry that comprises the amygdala, ventromedial prefrontal cortex, and insular cortex. Understanding the genetic factors affecting decision making in healthy subjects may allow us to better identify at-risk individuals, and better target the development of new potential treatments for specific disorders such as schizophrenia, addiction, and depression.

How possible is the development of an operational psychometric method to assess the presence of the 5-HTTLPR s allele? Equivocal preliminary findings

OBJECTIVE

The s allele of the 5-hydroxytryptamine transporter-linked promoter region (5-HTTLPR) polymorphism of the serotonin transporter gene has been found to be associated with neuroticism-related traits, affective temperaments and response to selective serotonin reuptake inhibitor (SSRI) treatment. The aim of the current study was to develop a psychometric tool that could at least partially substitute for laboratory testing and could predict the presence of the s allele.

METHODS

The study included 138 women of Caucasian origin, mean 32.20 +/- 1.02 years old. All subjects completed the Hungarian standardised version of the Temperament Evaluation of the Memphis, Pisa, Paris, and San Diego Autoquestionnaire (TEMPS-A) instrument and were genotyped for 5-HTTLPR using PCR. The statistical analysis included the calculation of the Index of Discrimination (D), Discriminant Function Analysis, creation of scales on the basis of the above and then item analysis and calculation of sensitivity and specificity.

RESULTS

Four indices were eventually developed, but their psychometric properties were relatively poor and their joint application did not improve the outcome.

CONCLUSIONS

We could not create a scale that predicts the 5-HTTLPR genotype with sufficient sensitivity and specificity, therefore we could not substitute a psychometric scale for laboratory genetic testing in predicting genotype, and also possibly affective disorder characterisation and treatment.

Serotonin transporter genotype and action monitoring dysfunction: a possible substrate underlying increased vulnerability to depression

A variable number of tandem repeats (short (S) vs long (L)) in the promoter region of the serotonin transporter gene (5-HTTLPR) and a functional variant of a single-nucleotide polymorphism (rs25531) in 5-HTTLPR have been recently associated with increased risk for major depressive disorder (MDD). In particular, relative to L/L or L(A) homozygotes (hereafter referred to as L' participants), S carriers or L(g)-allele carriers (S' participants) have been found to have a higher probability of developing depression after stressful life events, although inconsistencies abound. Previous research indicates that patients with MDD are characterized by executive dysfunction and abnormal activation within the anterior cingulate cortex (ACC), particularly in situations requiring adaptive behavioral adjustments following errors and response conflict (action monitoring). The goal of this study was to test whether psychiatrically healthy S' participants would show abnormalities similar to those of MDD subjects. To this end, 19 S' and 14 L' participants performed a modified Flanker task known to induce errors, response conflict, and activations in various ACC subdivisions during functional magnetic resonance imaging. As hypothesized, relative to L' participants, S' participants showed (1) impaired post-error and post-conflict behavioral adjustments; (2) larger error-related rostral ACC activation; and (3) lower conflict-related dorsal ACC activation. As similar behavioral and neural dysfunctions have been recently described in MDD patient samples, the current results raise the possibility that impaired action monitoring and associated ACC dysregulation may represent risk factors increased vulnerability to depression.

Race/ethnicity and internalizing disorders in youth: a review

This review examines the impact of race/ethnicity and cultural differences in the presentation and prevalence rates of internalizing disorders in youth, as well as a variety of associated factors. There is robust support for higher prevalence rates of depression and anxiety in ethnic minority youth living in the United States. Gender differences are consistent across ethnicity, but symptom presentation, biological factors, and family processes vary somewhat by ethnic group. Environmental factors and acculturation are considered in relation to internalizing disorders in ethnic minority youth. Several problems with the literature are outlined. Several recommendations are made including better operationalization of internalizing disorders in the DSM and key issues that warrant being added to background text in the DSM. A research agenda is outlined to address possible mechanisms by which culture and race/ethnicity impact internalizing symptomatology.

Serotonin transporter promoter variant: Analysis in Indian IBS patients and control population

BACKGROUND

Studies of serotonin reuptake transporter (SERT-P) polymorphism and irritable bowel syndrome (IBS) have shown diverse results among different populations, which might be due to racial and ethnic difference.

AIM

This study was to investigate the potential association between the SERT-P polymorphism and clinical subtypes of IBS patients in the Indian population.

METHOD

This prospective case-control study included 151 IBS patients. Ninety-two patients were diarrhea-predominant IBS, 44 were constipation-predominant IBS (C-IBS), 15 were alternating diarrhea and constipation IBS, and 100 were healthy controls. SERT gene polymorphism was studied by polymerase chain reaction.

RESULT

A genotypic association was observed between SS genotype of SERT-P polymorphism and C-IBS (P<0.05). When the L/S and L/L genotypes were combined into one group, the frequency of the S/S genotype was significantly higher than that of the non-S/S genotype between C-IBS and the control group (P<0.05). There was no significant difference in the SERT-P genotype and allele frequency between c-ibs, alternating diarrhea and constipation IBS, all types of IBS cases, and controls.

CONCLUSIONS

A significant association was observed between the SS genotype of SERT-P polymorphism and C-IBS in the Indian population.

Congenital central hypoventilation syndrome (CCHS) and sudden infant death syndrome (SIDS): kindred disorders of autonomic regulation

Congenital central hypoventilation syndrome (CCHS) and sudden infant death syndrome (SIDS) were long considered rare disorders of respiratory control and more recently have been highlighted as part of a growing spectrum of disorders within the rubric of autonomic nervous system (ANS) dysregulation (ANSD). CCHS typically presents in the newborn period with a phenotype including alveolar hypoventilation, symptoms of ANSD and, in a subset of cases, Hirschsprung disease and later tumors of neural crest origin. Study of genes related to autonomic dysregulation and the embryologic origin of the neural crest led to the discovery of PHOX2B as the disease-defining gene for CCHS. Like CCHS, SIDS is thought to result from central deficits in control of breathing and ANSD, although SIDS risk is most likely defined by complex multifactorial genetic and environmental interactions. Some early genetic and neuropathological evidence is emerging to implicate serotonin systems in SIDS risk. The purpose of this article is to review the current understanding of the genetic basis for CCHS and SIDS, and discuss the impact of this information on clinical practice and future research directions.

5-HTTLPR genotype and anxiety-related personality traits: a meta-analysis and new data

We investigated the strength of evidence for association of the 5-HTTLPR polymorphism and the personality trait of Harm Avoidance. We used new primary data from a large sample of adults drawn from the Finnish population. We also applied meta-analytic techniques to synthesize existing published data. The large number of studies of the 5-HTTLPR polymorphism allowed us to apply a formal test of publication bias, as well as formally investigate the impact of potential moderating factors such as measurement instrument. Univariate ANOVA of primary data (n = 3,872), with 5-HTTLPR genotype as a between-groups factor, indicated no evidence of association with Harm Avoidance (P = 0.99). Meta-analysis indicated no evidence of significant association of 5-HTTLPR with Harm Avoidance (d = 0.02, P = 0.37), or EPQ Neuroticism (d = 0.01, P = 0.71), although there was evidence of association with NEO Neuroticism (d = 0.18, P < 0.001). Our analyses indicate that the 5-HTTLPR variant is not associated with Harm Avoidance. Together with our previous analyses of a large sample of participants with extreme Neuroticism scores (defined by the EPQ), we have data that excludes a meaningful genetic effect of the 5-HTTLPR on two measures of anxiety-related personality traits. There remains the possibility that the variant influences the NEO personality questionnaire measure of Neuroticism. However, a large, well-powered primary study is required to test this hypothesis directly and adequately.

Association of the s allele of the 5-HTTLPR with neuroticism-related traits and temperaments in a psychiatrically healthy population

INTRODUCTION

Research concerning the genetic background of traits, temperaments and psychiatric disorders has been rapidly expanding. One of the most frequently studied genetic polymorphisms in the background of psychological and psychiatric phenomena is the 5-HTTLPR polymorphism of the serotonin transporter gene which has earlier been found to be associated with neuroticism and neuroticism-related traits and disorders. However, both the neuroticism trait and psychiatric disorders are complex and composed of several subfacets. The aim of our study was to investigate the association of the 5-HTTLPR polymorphism with several smaller, distinct and better characterisable phenomena related to the neuroticism trait.

METHODS

169 healthy females participated in the study. All participants completed the Buss-Durkee Hostility Inventory (BDHI), the State-Trait Anxiety Inventory (STAI), The Zung Self-rating Depression Scale (ZSDS), the Beck Hopelessness Scale, the SCL-51, the Temperament and Character Inventory (TCI) and the Temperament Evaluation of Memphis, Pisa, Paris and San Diego (TEMPS-A) questionnaire. All subjects were genotyped for the 5-HTTLPR using PCR. Data were analysed with ANOVA and MANCOVA with age as a covariate.

RESULTS

We found that the presence of the s allele was significantly associated with anxiety, depression, hopelessness, guilt, hostility, aggression, presence of neurotic symptoms, self-directedness and affective temperaments carrying a depressive component even when controlling for age.

CONCLUSIONS

Our study is the first that confirms that traits and characteristics related to neuroticism, such as increased anxiety, depression, hopelessness, somatization, feeling of guilt, hostility, aggression, lack of self-directedness and affective temperament are consistently and independently associated with the 5-HTTLPR polymorphism of the serotonin transporter gene. Our study therefore suggests that neuroticism can be considered a unified construct not only from a phenotypical but also from a genetic point of view and 5HTTLPR can be considered one component of its polygenic background. Our results thus yield further insight into the role of the 5-HTTLPR in the background of neuroticism and neuroticism-related psychiatric disorders.

Towards a genetically validated new affective temperament scale: a delineation of the temperament phenotype of 5-HTTLPR using the TEMPS-A

BACKGROUND

Although it has been described that affective temperaments are associated with the 5-HTTLPR, less attention was paid to the association between this polymorphism and subscales and items related to each affective temperament. The aim of our study was to investigate the association of affective temperament subscales and individual items with the s allele of the 5-HTTLPR.

METHOD

138 psychiatrically healthy women completed the TEMPS-A questionnaire and were genotyped for 5-HTTLPR. Scores of subjects on the temperament scales, subscales and items in the three genotype and the two phenotype groups were compared using ANOVA. We selected items with significantly different mean scores between the three genotype groups and the two phenotype groups separately and performed item analysis.

RESULTS

Subjects in the different 5-HTTLPR genotype and phenotype groups have significantly different score on scales measuring depressive, cyclothymic, irritable and anxious temperaments, and several subscales composing these temperamental scales. Subjects in the three genotype groups scored significantly different on 11 items, 8 of these remained in a derived genotype scale after item analysis. Subjects in the two phenotype groups had significantly different scores on 12 items, 9 of them were retained in a derived phenotype scale after item analysis.

LIMITATIONS

Our sample was relatively small and included only women.

CONCLUSIONS

Our data provide support for the association of affective temperaments with the s allele. Although the cyclothymic temperament shows the strongest association, all temperaments within the depressive superfactor have a similar share in this association. The newly derived 5-HTTLPR Phenotype Scale shows strong association with 5-HTTLPR genotype and phenotype, therefore this scale should be further investigated in relation to psychiatric disorders, as well as psychological traits and temperaments.

Evidence for attenuated affective processing in obesity

Attenuated affective processing is hypothesized to play a role in the development and maintenance of obesity. Using an affective priming task measuring automatic affective processing of verbal stimuli, a group of 30 obese participants in a weight-loss program at the Psychosomatic University Clinic Bonn (M age = 48.3, SD = 10.7) was compared with a group of 25 participants of normal weight (M age = 43.6, SD = 12.5). A smaller affective priming effect was observed for participants with obesity, indicating less pronounced reactions to valenced adjectives. The generally reduced affective processing in obese participants was discussed as a possible factor in the etiology of obesity. Individuals who generally show less pronounced affective reactions to a given stimulus may also react with less negative affect when confronted with weight gain or less positive affect when weight is lost. Consequently, they could be expected to be less motivated to stop overeating or to engage in dieting and will have a higher risk of becoming or staying obese.

Ethnic differences in the serotonin transporter polymorphism (5-HTTLPR) in several European populations

The serotonin transporter (5-HTT) is a protein that has a major role in divergent psychiatric disorders, personality traits and behaviors, by regulating serotonergic synaptic function. Transcriptional activity of the 5-HTT gene (5-HTT or SLC6A4) is modulated by a polymorphic repetitive element (5-HTT gene-linked polymorphic region, 5-HTTLPR), which consists of a 44-base pairs insertion-deletion in the promoter region, creating a short (S) allele and a long (L) allele. Ethnic differences in the allele frequencies of the 5-HTTLPR exist between Caucasian and Asian populations. This study investigated ethnic differences in 5-HTTLPR in 1804 healthy Caucasian subjects from several European populations living in Croatia and the Russian Federation. The genotype and allele frequency of the 5-HTTLPR differed significantly (P<0.001) between male and female Croats, Russians, Tatars and Bashkirs, due to the lower frequency of the S allele (38% and 37%) and S/S genotype (14% and 15%) in Croat men and women compared to other studied groups. When male and female data were collapsed, Russians had marginally different allele and genotype distribution compared to Bashkirs and Tatars. Bashkirs and Tatars had similar allele and genotype frequency. The higher frequency of the S/S genotype was found in Tatars and Bashkirs compared to Croats and Russians. Gender related differences occurred only in the allele distribution within Bashkir population. These ethnic differences might be responsible for the inconsistent findings in the studies of the association between various psychiatric disorders, personality traits, behaviors and 5-HTTLPR across different ethnicities, and should be controlled to enable the generalization of results across various population groups.

Association study between reward dependence temperament and a polymorphism in the phenylethanolamine N-methyltransferase gene in a Japanese female population

Cloninger's theory is that specific dimensions of temperament are associated with single neurotransmitter systems, and it is based on neurophysiologic and genetic approaches to the human traits. It suggests that overexpression of temperament could cause psychiatric illness. Based on this theory, we examined the correlation between reward dependence (RD) trait, measured with the Temperament and Character Inventory, and 5 polymorphisms in genes of norepinephrine pathways, ADRB1, COMT, PNMT, SLC18A1, and SLC6A2, in 85 Japanese female nursing students. We found that rs3764351 in PNMT was significantly associated with RD on Fisher's exact test (P = .029, P(corr) = .236). When haplotype analysis was performed for rs3764351 and rs876493 polymorphisms in the 5' flanking region of PNMT, 3 haplotypes were identified. Rs3764351 itself appeared to be correlated with RD in the present study of a specific population, although we could not demonstrate an association between RD and any of the haplotypes. Our findings have implications for the understanding of temperament using neurophysiologic approaches.

Association of the serotonin transporter gene, neuroticism and smoking behaviours

Cigarette consumption and smoking cessation are influenced in part by genes. Personality traits have also been implicated in the aetiology of smoking. Neuroticism, a personality trait with a heritable component, correlates well with anxiety and depression, increasing the risk of being a smoker and decreasing the chance of smoking cessation. Several prior studies in non-British populations have given conflicting results as to whether some genetic polymorphisms affect the relationship between smoking and neuroticism. This study investigated the influence of serotonin transporter (5HTTLPR) genotypes on a composite measure of neuroticism and cigarette consumption/smoking cessation in a British population. Although neuroticism was significantly associated with cigarette consumption and smoking cessation, genotype did not affect this relationship. Our results do not support initial interest in utilising 5HTTLPR genotypes in combination with neuroticism ratings for predicting outcome in smoking cessation clinical settings.

Contribution of the serotoninergic system to anxious and depressive traits that may be partially responsible for the phenotypical variability of bulimia nervosa

Eating disorders (ED), such as anorexia nervosa (AN) and bulimia nervosa (BN), are complex psychiatric phenotypes influenced by both genetic and environmental factors. We investigated the genetic contribution of four single nucleotide polymorphisms (SNPs) within the serotonin receptor 5HT2C and two sequence variants within the serotonin transporter SLC6A4 to different ED-related psychopathological symptoms in a total sample of 82 ED patients. All patients were diagnosed according to DSM-IV criteria and underwent diagnostic and psychopathological assessments by means of structured clinical interviews and rating scales. We detected significant evidence of association between the -995A/-759T/-697C/Cys23 haplotype of the 5HT2C gene and different anxious and depressive subscales of the SCL90-R instrument, that included Somatization (p = 0.029), Obsessive-Compulsiveness (p = 0.021), Depression (p = 0.032), Anxiety (p = 0.004), Hostility (p = 0.028), Phobic Anxiety (p = 0.029) and Paranoid Ideation (p = 0.008), in BN patients. We also observed a strong association between the 5HTTLPR polymorphism of the SLC6A4 gene and Anxiety in the same group of BN patients (p = 0.004). However, no epistatic effects between the 5HT2C and SLC6A4 genes on the different anxious and depressive subscales were observed. Our preliminary data suggest that the serotoninergic system contributes to the different psychopathological symptoms that may be partially responsible for the phenotypical variability within the bulimic phenotype.

The association between serotonin transporter gene promoter polymorphism (5-HTTLPR), self-reported symptoms, and dental mercury exposure

The associations between a polymorphism of the serotonin transporter gene (5-HTTLPR), dental mercury exposure, and self-reported symptoms were evaluated among 157 male dentists and 84 female dental assistants. Self-reported symptoms and detailed work histories were obtained by computerized questionnaire. Spot urine samples were collected and analyzed for mercury concentrations to evaluate recent exposures, whereas a chronic mercury exposure index was created from the work histories. 5-HTTLPR polymorphism status was determined using a polymerase chain reaction (PCR)-based assay. Scores for current, recent, and chronic self-reported symptom groups were evaluated with respect to recent and chronic mercury exposure and 5-HTTLPR polymorphism status. Multiple regression analysis controlled for age, socioeconomic status, tobacco and alcohol use, self-reported health problems, and medications. Analyses were restricted to Caucasian subjects due to the highly skewed distribution of the 5-HTTLPR polymorphism. Separate evaluations were conducted for dentists and dental assistants. In contrast to previous reports, no consistent associations were found between either urinary mercury concentration or the chronic index of mercury exposure and any category of symptoms. However, both significant and consistent associations were observed between increased symptoms and the 5-HTTLPR polymorphism involving two copies of the short or "s" allele (full mutation), but not with the polymorphism involving only one copy (heterozygous), demonstrating a gene-dose relationship for symptom reporting. These findings suggest that within this restricted population increased symptoms of depression, anxiety, and memory are associated with the 5-HTTLPR polymorphism among both males and females.

Serotonin transporter gene polymorphism (5-HTTLPR) and anxiety reactivity in daily life: a daily process approach to gene-environment interaction

OBJECTIVE

To test whether individuals with at least one copy of the short (S) or long (L)(G) allele of the serotonin transporter polymorphism (5-HTTLPR) exhibit greater increases in anxiety, compared with L(A)L(A) individuals, under periods of high daily stress. Although this common polymorphism in the serotonin transporter gene has been identified as a vulnerability factor for anxiety, findings in the literature are mixed. Discrepant findings could be explained by recent research showing that 5-HTTLPR is functionally triallelic (L(A) versus L(G) or S), rather than biallelic (L versus S). Mixed findings could also result from a lack of attention to diathesis-stress models, whereby genetic vulnerability is considered latent until activated by stress (gene-environment interplay). Based on this model, we argue that genotype differences in anxiety should be stronger in the presence of stress.

METHODS

A total of 350 college students recorded their daily stressors and mood for two 30-day periods, separated by 1 year.

RESULTS

Across both years, diathesis-stress patterns were observed for reports of anxious mood as a function of 5-HTTLPR. Individuals with at least one copy of the S or L(G) allele at 5-HTTLPR experienced elevated anxious mood on days with more intense stressors, as compared with those who were L(A) homozygotes. Genotype differences in anxiety were less apparent on low stress days. No consistent allelic association of 5-HTTLPR was observed with any other mood states, trait anxiety, or neuroticism.

CONCLUSION

Our findings highlight the potential value of focusing on genetic vulnerability in the context of everyday environmental triggers.

Effects of environmental stress and gender on associations among symptoms of depression and the serotonin transporter gene linked polymorphic region (5-HTTLPR)

The short (s) variant of the serotonin transporter (5-HTT) gene linked functional polymorphic region (5-HTTLPR) is associated with depression. Stressful life events, gender, and race have been shown to moderate this association. We examined the relationship between 5-HTTLPR genotype and symptoms of depression in two samples. Study 1 = 288 participants from a study of caregiver stress; and Study 2 = 142 participants from a study examining psychosocial stressors, genetics, and health. Main effects of 5-HTTLPR on symptoms of depression were examined, along with moderation by stress (caregiving status or low childhood socioeconomic status (SES), gender, and race. The 5-HTTLPR x stress group x gender interaction was significant in both samples (P < 0.003, and P < 0.008, respectively). For females, the s allele, combined with caregiving stress (Study 1) or low childhood SES (Study 2), was associated with higher depression scores as compared to participants in the non-stressor group and those with the long (l) allele; whereas, in males, the l allele, combined with a stressor, was associated with higher depression scores as compared to those in the non-stressor group and those with the s allele. Findings from two independent samples suggest that the association of 5-HTTLPR with depression varies according to gender and stressful life events.

Sudden Infant Death Syndrome: review of implicated genetic factors

Genetic studies in Sudden Infant Death Syndrome (SIDS) have been motivated by clinical, epidemiological, and/or neuropathological observations in SIDS victims, with subsequent pursuit of candidate genes in five categories: (1) genes for ion channel proteins based on electrocardiographic evidence of prolonged QT intervals in SIDS victims, (2) gene for serotonin transporter based on decreased serotonergic receptor binding in brainstems of SIDS victims, (3) genes pertinent to the early embryology of the autonomic nervous system (ANS) (and with a link to the 5-HT system) based on reports of ANS dysregulation in SIDS victims, (4) genes for nicotine metabolizing enzymes based on evidence of cigarette smoking as a modifiable risk factor for SIDS, and (5) genes regulating inflammation, energy production, hypoglycemia, and thermal regulation based on reports of postnatal infection, low birth weight, and/or overheating in SIDS victims. Evidence for each of these classes of candidate genes is reviewed in detail. As this review indicates, a number of genetically controlled pathways appear to be involved in at least some cases of SIDS. Given the diversity of results to date, genetic studies support the clinical impression that SIDS is heterogeneous with more than one entity and with more than one possible genetic etiology. Future studies should consider expanded phenotypic features that might help clarify the heterogeneity and improve the predictive value of the identified genetic factors. Such features should be evaluated to the extent possible in both SIDS victims and their family members. With 2,162 infants dying from SIDS in 2003 in the U.S. alone, and improved but still imperfect parent and caretaker compliance with known modifiable risk factors for SIDS, it behooves clinicians, researchers, and parents to combine efforts to reach a common goal. The message of the "Back to Sleep" campaign needs to be re-introduced/re-engineered to reach families and caretakers of all ethnic groups. Clinicians and researchers need to gently inform new SIDS parents about the opportunity to contribute tissue to the NICHD-funded University of Maryland Brain and Tissue Bank. By expanding the network of clinicians, scientists, and families working together, and by combined efforts in a collaborative multi-center study of candidate genes and/or genomics, the discovery of the genetic profile of the infant at risk for SIDS can ultimately be determined.

Serotonin transporter density and anxiolytic-like effects of antidepressants in mice

BACKGROUND

Chronic treatment with the dual serotonin/noradrenaline reuptake inhibitor (SNRI) duloxetine reduces the density of serotonin transporter sites in cortex and engenders an anxiolytic-like response. To determine the reproducibility of these effects and their generality to other antidepressants we compared the effects of chronic duloxetine treatment with another SNRI, venlafaxine, and two selective serotonin reuptake inhibitors, paroxetine and fluoxetine.

METHODS

Separate groups of mice were administered vehicle, fluoxetine (15 mg/kg), paroxetine, duloxetine or venlafaxine (10 mg/kg) perorally twice daily for 28 days and tested in the mouse zero-maze and in motility cages on days 21 and 22, respectively, to determine effects on anxiety and motor activity. On day 28 brains were analysed for serotonin transporter (SERT) density in cortex and noradrenaline transporter (NET) density in cortex and hippocampus.

RESULTS

Duloxetine and fluoxetine both reduced SERT density in cortex and induced anxiolytic-like effects. Paroxetine had an identical profile, but it is unclear if this drug down-regulated the SERT since extensive washing of cortical tissue did not remove all drug. Venlafaxine had no effect on behavioural or biochemical parameters. Only duloxetine reduced NET density in cortex, although not hippocampus.

CONCLUSIONS

The reduction in SERT density and anxiolytic-like effects with duloxetine, fluoxetine and, potentially, paroxetine suggest that down-regulation of the SERT may be a relevant mechanism in therapeutic response to these antidepressants.

The functional impact of SLC6 transporter genetic variation

Solute carrier 6 (SLC6) is a gene family of ion-coupled plasma membrane cotransporters, including transporters of neurotransmitters, amino acids, and osmolytes that mediate the movement of their substrates into cells to facilitate or regulate synaptic transmission, neurotransmitter recycling, metabolic function, and fluid homeostasis. Polymorphisms in transporter genes may influence expression and activity of transporters and contribute to behavior, traits, and disease. Determining the relationship between the monoamine transporters and complex psychiatric disorders has been a particular challenge that is being met by evolving approaches. Elucidating the functional consequences of and interactions among polymorphic sites is advancing our understanding of this relationship. Examining the influence of environmental influences, especially early-life events, has helped bridge the gap between genotype and phenotype. Refining phenotypes, through assessment of endophenotypes, specific behavioral tasks, medication response, and brain network properties has also improved detection of the impact of genetic variation on complex behavior and disease.