The serotonin transporter promoter variant (5-HTTLPR), stress, and depression meta-analysis revisited: evidence of genetic moderation

Mood and personality effects in healthy participants after chronic administration of sertraline

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) are utilised in the treatment of a wide range of disorders but the neuropsychological basis of their therapeutic efficacy remains unclear. In this study we examine the impact of 3 weeks administration of sertraline, an SSRI, on mood and personality in a group of healthy volunteers to understand the effect of these agents in the absence of clinical disorder.

METHODS

Thirty-eight healthy women and men, with no personal or familial history of Axis I disorder were randomised to receive either a placebo or sertraline (50mg/day p.o.) for an average of 23 days, in a double-blind design. Self-report indices of mood and personality, and genotype (5-HTTLPR) and sertraline bioavailability were assessed.

RESULTS

Chronic administration of an SSRI was found to alter mood and personality. The SSRI group experienced a significant decrease in negative affect (NA), guilt and attentiveness, and significant increases in positive affect (PA), joviality, self-assurance and serenity. Genotype and bioavailability of sertraline did not moderate these findings, however gender did. Only females demonstrated increased PA and joviality, and decreased NA; whereas, only males demonstrated decreased attentiveness.

LIMITATIONS

Greater power and a more specific manipulation of serotonergic functioning would help clarify the neurochemical basis of these findings.

CONCLUSIONS

Results from the current study demonstrate that longer term administration of SSRIs alters aspects of mood and personality in the absence of disorder. This suggests that these agents have effects on basic psychological processes that may in turn form the basis of their therapeutic efficacy.

Interactive effects of corticotropin releasing hormone receptor 1, serotonin transporter linked polymorphic region, and child maltreatment on diurnal cortisol regulation and internalizing symptomatology

Within an allostatic load framework, the effect of Gene × Environment (G × E) interactions on diurnal cortisol regulation and internalizing symptomatology were investigated. Variation in the corticotropin releasing hormone receptor 1 (CRHR1) TAT haplotype and serotonin transporter linked polymorphic region (5-HTTLPR) was determined in a sample of maltreated (n = 238, 21.4% with early physical and sexual abuse) and nonmaltreated (n = 255) children (M age = 10.08) participating in a summer research camp. Internalizing and depressive symptoms were assessed by other and self-report. G × E effects for CRHR1 and maltreatment and early abuse on diurnal cortisol regulation were observed; CRHR1 variation was related to cortisol dysregulation only among maltreated children. Early abuse and high internalizing symptoms also interacted to predict atypical diurnal cortisol regulation. The interaction of CRHR1, 5-HTTLPR, and child maltreatment (G × G × E) identified a subgroup of maltreated children with high internalizing symptoms who shared the same combination of the two genes. The findings support an allostatic load perspective on the effects of the chronic stress associated with child maltreatment on cortisol regulation and internalizing symptomatology as moderated by genetic variation.

Community attitudes to genetic susceptibility-based mental health interventions for healthy people in a large national sample

BACKGROUND

Despite an apparent high interest in predictive genetic testing for common multifactorial disorders, few data describe anticipated health behaviour as a consequence of such testing.

METHODS

A large population-based public survey with community dwelling adults (N = 1046) ascertained through random digit dialling. Attitudes were assessed via structured interviews.

RESULTS

Intention to start therapies or courses to learn to develop better strategies to cope with stress (80%) was significantly and positively associated with self-estimation of risk for major depressive disorder as higher than average (ß = 0.12, p = 0.001); endorsement of family environment as a causal attribution (ß = 0.11, p < 0.001); and endorsement of gene-environment interaction as a causal mechanism of mental illness (ß = 0.12, p = 0.017). Intention to modify potential life stressors (84%) was significantly and positively associated with self-estimation of risk for depression as higher than average (ß = 0.07, p = 0.029); endorsement of 'abuse' as a causal attribution (ß = 0.10, p = 0.003); and endorsement of 'gene-environment interaction' as a causal mechanism (ß = 0.10, p = 0.002).

LIMITATIONS

The hypothetical nature of the genetic risk scenario may have weakened participants' sensitivity to the potential personal impact of such a genetic test result.

CONCLUSIONS

Perceptions that modifiable environmental factors strongly contribute to overall risk of major depressive disorder appeared to drive willingness to engage in risk-modifying interventions in the hypothetical scenario of a genetic predisposition. Our results suggest that screening for genetic risk in consort with environmental risk factor assessment has potential community acceptability and clinical value as an early intervention and preventive tool for high risk groups.

Serotonin transporter genotype moderates the link between children's reports of overprotective parenting and their behavioral inhibition

The goal of the current study was to examine environmental and genetic correlates of children's levels of behavioral inhibition (BI). Participants were 100 mother child pairs drawn from the community who were part of a larger study of the intergenerational transmission of depression. Results indicated that higher levels of maternal overprotection, as reported by the child, were associated with elevations in BI among children carrying two copies of the lower expressing 5-HTTLPR alleles (S or L(G)), but not among those carrying only one copy or those homozygous for the L(A) allele. In addition, this interaction was specific for the social component of BI, not the nonsocial component. This relation was maintained even after statistically controlling for children's and mother's psychopathology. Together, these findings add to emerging research demonstrating that G × E interactions predict variation in BI during childhood.

Interaction between BDNF Val66Met and childhood stressful life events is associated to affective memory bias in men but not women

Recent meta-analyses point towards a pathogenic role of the Val66Met variant of the brain-derived neurotrophic factor (BDNF) in major depressive disorder, specifically in males. We investigated whether BDNF Val66Met shows a male-specific interaction with childhood stressful life events on affective memory bias, a cognitive susceptibility factor for depression. Healthy volunteers (n=430; 272 females and 158 males) were genotyped for BDNF Val66Met (rs6265) and completed the self-referent encoding task and a childhood stressful life events scale. BDNF Met carriers reporting childhood events tended to recall a lower proportion of positive words compared to Val/Val homozygotes reporting childhood events. Sex-specific analyses revealed that the BDNF genotype×childhood events interaction was significant in male participants and not in female participants. The results suggest that in males, BDNF Val66Met interacts with childhood life events, increasing the cognitive susceptibility markers of depression. In females, this effect may be independent of BDNF Val66Met.

The impact of serotonin transporter (5-HTTLPR) genotype on the development of resting-state functional connectivity in children and adolescents: a preliminary report

A fundamental component of brain development is the formation of large-scale networks across the cortex. One such network, the default network, undergoes a protracted development, displaying weak connectivity in childhood that strengthens in adolescence and becomes most robust in adulthood. Little is known about the genetic contributions to default network connectivity in adulthood or during development. Alterations in connectivity between posterior and frontal portions of the default network have been associated with several psychological disorders, including anxiety, autism spectrum disorders, schizophrenia, depression, and attention-deficit/hyperactivity disorder. These disorders have also been linked to variants of the serotonin transporter linked polymorphic region (5-HTTLPR). The LA allele of 5-HTTLPR results in higher serotonin transporter expression than the S allele or the rarer LG allele. 5-HTTLPR may influence default network connectivity, as the superior medial frontal region has been shown to be sensitive to changes in serotonin. Also, serotonin as a growth factor early in development may alter large-scale networks such as the default network. The present study examined the influence of 5-HTTLPR variants on connectivity between the posterior and frontal structures and its development in a cross-sectional study of 39 healthy children and adolescents. We found that children and adolescents homozygous for the S allele (S/S, n=10) showed weaker connectivity in the superior medial frontal cortex compared to those homozygous for the LA allele (LA/LA, n=13) or heterozygotes (S/LA, S/LG, n=16). Moreover, there was an age-by-genotype interaction, such that those with LA/LA genotype had the steepest age-related increase in connectivity between the posterior hub and superior medial frontal cortex, followed by heterozygotes. In contrast, individuals with the S/S genotype had the least age-related increase in connectivity strength. This preliminary report expands our understanding of the genetic influences on the development of large-scale brain connectivity and lays down the foundation for future research and replication of the results with a larger sample.

Affect-related behaviors in mice selectively bred for high and low voluntary alcohol consumption

There is considerable evidence for the existence of comorbidity between alcohol-use disorders and depression in humans. One strategy to elucidate hereditary factors affecting the comorbidity of these disorders is to use genetic animal models, such as mouse lines selectively bred for voluntary ethanol consumption. We hypothesized that mice from lines that were bred for high-alcohol preference would manifest increased depression-like phenotypes compared to low-alcohol preferring mice. Mice that were bi-directionally selected and bred on the basis of their High- (HAP) or Low-Alcohol Preference (LAP) were tested in the open-field (OFT), dark-light box (DLB), forced swim (FST), and learned helplessness tests (LH). The study was conducted in two independently derived replicates. In the OFT, both HAP2 and HAP3 mice showed higher levels of general locomotion compared to LAP mice. However, only HAP2 mice spent more time in the center compared to LAP2 mice. In the DLB, there was a slightly higher anxiety-like phenotype in HAP mice. In both FST and LH, we observed higher depression-like behaviors in HAP mice compared to LAP mice, but this was limited to the Replicate 2 mice. Overall, we identified affect-related behavioral changes in mouse lines bred for high-alcohol preference. Notably, the Replicate 3 lines that showed fewer depression-like behaviors also manifest smaller differences in alcohol intake. These data suggest that there may be overlap between genes that predispose to excessive alcohol intake and those underlying affect-related behaviors in the mouse.

Portrayal of psychiatric genetics in Australian print news media, 1996-2009

OBJECTIVE

To investigate how Australian print news media portray psychiatric genetics.

DESIGN AND SETTING

Content and framing analysis of a structured sample of print news items about psychiatric genetics published in Australian newspapers between 1996 and 2009.

MAIN OUTCOME MEASURES

Identify dominant discourses about aetiology of mental illness, and perceived clinical outcomes and implications of psychiatric genetics research.

RESULTS

We analysed 406 eligible items about the genetics of psychiatric disorders. News coverage of psychiatric genetics has steadily increased since 1996. Items attributing the aetiology of psychiatric disorders to gene-environment interactions (51%) outnumbered items attributing only genetic (30%) or only environmental factors (20%). Of items that referred to heritability of mental illness, frames of genetic determinism (78%) occurred more frequently than probabilistic frames (22%). Of frames related to genetic prophesy, genetic optimism frames (78%) were used more frequently than frames of genetic pessimism (22%). Psychosocial and ethical implications of psychiatric genetics received comparatively relatively little coverage (23%). The analysis identified 22 predictions about psychiatric genetic discoveries and the availability of molecular-based interventions in psychiatry, most of which (20/22, 91%) failed to manifest by the predicted year.

CONCLUSIONS

Excessive optimism about the power of genetic technology in psychiatric health care, perceived clinical benefits, and largely unfulfilled predictions about availability of these benefits could encourage unrealistic expectations about future molecular-based treatment options for mental health.

Serotonin transporter gene polymorphism and psychiatric disorders: is there a link?

Though still in infancy, the field of psychiatric genetics holds great potential to contribute to the development of new diagnostic and therapeutic options to treat these disorders. Among a large number of existing neurotransmitter systems, the serotonin system dysfunction has been implicated in many psychiatric disorders and therapeutic efficacy of many drugs is also thought to be based on modulation of serotonin. Serotonin transporter gene polymorphism is one of the most extensively studied polymorphisms in psychiatric behavioral genetics. In this article, we review the status of evidence for association between the serotonin gene polymorphism and some common mental disorders like affective disorders, post-traumatic stress disorder, obsessive-compulsive disorder, suicide, autism, and other anxiety and personality disorders. Going beyond traditional association studies, gene-environment interaction, currently gaining momentum, is also discussed in the review. While the existing information of psychiatric genetics is inadequate for putting into practice genetic testing in the diagnostic work-up of the psychiatric patient, if consistent in future research attempts, such results can be of great help to improve the clinical care of a vast majority of patients suffering from such disorders.

A critical review of the first 10 years of candidate gene-by-environment interaction research in psychiatry

OBJECTIVE

Gene-by-environment interaction (G×E) studies in psychiatry have typically been conducted using a candidate G×E (cG×E) approach, analogous to the candidate gene association approach used to test genetic main effects. Such cG×E research has received widespread attention and acclaim, yet cG×E findings remain controversial. The authors examined whether the many positive cG×E findings reported in the psychiatric literature were robust or if, in aggregate, cG×E findings were consistent with the existence of publication bias, low statistical power, and a high false discovery rate.

METHOD

The authors conducted analyses on data extracted from all published studies (103 studies) from the first decade (2000-2009) of cG×E research in psychiatry.

RESULTS

Ninety-six percent of novel cG×E studies were significant compared with 27% of replication attempts. These findings are consistent with the existence of publication bias among novel cG×E studies, making cG×E hypotheses appear more robust than they actually are. There also appears to be publication bias among replication attempts because positive replication attempts had smaller average sample sizes than negative ones. Power calculations using observed sample sizes suggest that cG×E studies are underpowered. Low power along with the likely low prior probability of a given cG×E hypothesis being true suggests that most or even all positive cG×E findings represent type I errors.

CONCLUSIONS

In this new era of big data and small effects, a recalibration of views about groundbreaking findings is necessary. Well-powered direct replications deserve more attention than novel cG×E findings and indirect replications.

Differential susceptibility in youth: evidence that 5-HTTLPR x positive parenting is associated with positive affect 'for better and worse'

Positive affect has been implicated in the phenomenological experience of various psychiatric disorders, vulnerability to develop psychopathology and overall socio-emotional functioning. However, developmental influences that may contribute to positive affect have been understudied. Here, we studied youths' 5-HTTLPR genotype and rearing environment (degree of positive and supportive parenting) to investigate the differential susceptibility hypothesis (DSH) that youth carrying short alleles of 5-HTTLPR would be more influenced and responsive to supportive and unsupportive parenting, and would exhibit higher and lower positive affect, respectively. Three independent studies tested this gene-environment interaction (GxE) in children and adolescents (age range 9-15 years; total N=1874). In study 1 (N=307; 54% girls), positive/supportive parenting was assessed via parent report, in study 2 (N=197; 58% girls) via coded observations of parent-child interactions in the laboratory and in study 3 (N=1370; 53% girls) via self report. Results from all the three studies showed that youth homozygous for the functional short allele of 5-HTTLPR were more responsive to parenting as environmental context in a 'for better and worse' manner. Specifically, the genetically susceptible youth (that is, S'S' group) who experienced unsupportive, non-positive parenting exhibited low levels of positive affect, whereas higher levels of positive affect were reported by genetically susceptible youth under supportive and positive parenting conditions. These GxE findings are consistent with the DSH and may inform etiological models and interventions in developmental psychopathology focused on positive emotion, parenting and genetic susceptibility.

Excess of serotonin affects neocortical pyramidal neuron migration

The serotonin transporter (SERT) is a key molecule involved in the homeostasis of extracellular levels of serotonin and is regulated developmentally. Genetic deletion of SERT in rodents increases extracellular levels of serotonin and affects cellular processes involved in neocortical circuit assembly such as barrel cortex wiring and cortical interneuron migration. Importantly, pharmacological blockade of SERT during brain development leads to phenotypes relevant to psychiatry in rodents and to an increased risk for autism spectrum disorders in humans. Furthermore, developmental adversity interacts with genetically-driven variations of serotonin function in humans and nonhuman primates to increase the risk for a variety of stress-related phenotypes. In this study, we investigate whether an excess of serotonin affects the migration of neocortical pyramidal neurons during development. Using in utero electroporation combined with time-lapse imaging to specifically monitor pyramidal neurons during late mouse embryogenesis, we show that an excess of serotonin reversibly affects the radial migration of pyramidal neurons. We further identify that the serotonin receptor 5-HT(6) is expressed in pyramidal neuron progenitors and that 5-HT(6) receptor activation replicates the effects of serotonin stimulation. Finally, we show that the positioning of superficial layer pyramidal neurons is altered in vivo in SERT knockout mice. Taken together, these results indicate that a developmental excess of serotonin decreases the migration speed of cortical pyramidal neurons, affecting a fundamental step in the assembly of neural circuits. These findings support the hypothesis that developmental dysregulation of serotonin homeostasis has detrimental effects on neocortical circuit formation and contributes to increased vulnerability to psychiatric disorders.

Understanding risk for psychopathology through imaging gene-environment interactions

Examining the interplay of genes, experience and the brain is crucial to understanding psychopathology. We review the recent gene-environment interaction (G×E) and imaging genetics literature with the goal of developing models to bridge these approaches within single imaging gene-environment interaction (IG×E) studies. We explore challenges inherent in both G×E and imaging genetics and highlight studies that address these limitations. In specifying IG×E models, we examine statistical methods for combining these approaches, and explore plausible biological mechanisms (e.g. epigenetics) through which these conditional mechanisms can be understood. Finally, we discuss the potential contribution that IG×E studies can make to understanding psychopathology and developing more personalized and effective prevention and treatment.

Genetics of emotion

Emotion is critical to most aspects of human behavior, and individual differences in systems recruited to process emotional stimuli, expressed as variation in emotionality, are characteristic of several neuropsychiatric disorders. We examine the genetic origins of individual differences in emotion processing by focusing on functional variants at five genes: catechol-O-methyltransferase (COMT), serotonin transporter (SLC6A4), neuropeptide Y (NPY), a glucocorticoid receptor-regulating co-chaperone of stress proteins (FKBP5) and pituitary adenylate cyclase-activating polypeptide receptor (ADCYAP1R1). These represent a range of effects of genes on emotion as well as the variety of mechanisms and factors, such as stress, that modify these effects. The new genomic era of genome-wide association studies (GWAS) and deep sequencing may yield a wealth of new loci modulating emotion. The effects of these genes can be validated by neuroimaging, neuroendocrine and other studies accessing intermediate phenotypes, deepening our understanding of mechanisms of emotion and variation in emotionality.

Sleep quality and diurnal preference in a sample of young adults: associations with 5HTTLPR, PER3, and CLOCK 3111

Research investigating associations between specific genes and individual differences with regards to the quality and timing of sleep has primarily focussed on serotonin-related and clock genes. However, there are only a few studies of this type and most of those to date have not considered the possibility of gene-environment interaction. Here, we describe associations between sleep quality and diurnal preference and three functional polymorphisms: 5HTTLPR, PERIOD3, and CLOCK 3111. Furthermore, we assessed whether associations between genotypes and sleep phenotypes were moderated by negative life events-a test of gene-environment interaction. DNA from buccal swabs was collected from 947 individuals [mean age = 20.3 years (SD = 1.77), age range = 18-27 years; 61.8% female] and genotyped for the three polymorphisms. Participants completed the Pittsburgh Sleep Quality Index and the Morningness-Eveningness Questionnaire. There was a significant main effect of 5HTTLPR on sleep quality, indicating that "long-long" homozygotes experienced significantly poorer sleep quality (mean = 6.35, SD = 3.36) than carriers of at least one "short" allele (mean = 5.67, SD = 2.96; β = -0.34, P = 0.005). There were no main effects of 5HTTLPR on diurnal preference; no main effects of PERIOD3 or CLOCK on sleep quality or diurnal preference; and no significant interactions with negative life events. The main effect of the "long" 5HTTLPR allele contradicts previous research, suggesting that perhaps the effects of this gene are heterogeneous in different populations. Failure to replicate previous research in relation to PERIOD3 and CLOCK concurs with previous research suggesting that the effects of these genes are small and may be related to population composition.

Interaction of early environment, gender and genes of monoamine neurotransmission in the aetiology of depression in a large population-based Finnish birth cohort

Objectives Depression is a worldwide leading cause of morbidity and disability. Genetic studies have recently begun to elucidate its molecular aetiology. The authors investigated candidate genes of monoamine neurotransmission and early environmental risk factors for depressiveness in the genetically isolated population-based Northern Finland Birth Cohort 1966 (12 058 live births). Design The authors ascertained and subdivided the study sample (n=5225) based on measures of early development and of social environment, and examined candidate genes of monoamine neurotransmission, many of which have shown prior evidence of a gene-environment interaction for affective disorders, namely SLC6A4, TPH2, COMT, MAOA and the dopamine receptor genes DRD1-DRD5. Results and conclusion The authors observed no major genetic effects of the analysed variants on depressiveness. However, when measures of early development and of social environment were considered, some evidence of interaction was observed. Allelic variants of COMT interacted with high early developmental risk (p=0.005 for rs2239393 and p=0.02 for rs4680) so that the association with depression was detected only in individuals at high developmental risk group (p=0.0046 and β=0.056 for rs5993883-rs2239393-rs4680 risk haplotype CGG including Val158), particularly in males (p=0.0053 and β=0.083 for the haplotype CGG). Rs4274224 from DRD2 interacted with gender (p=0.017) showing a significant association with depressiveness in males (p=0.0006 and β=0.0023; p=0.00005 and β=0.069 for rs4648318-rs4274224 haplotype GG). The results support the role of genes of monoamine neurotransmission in the aetiology of depression conditional on environmental risk and sex, but not direct major effects of monoaminergic genes in this unselected population.

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.

Establishing a learned-helplessness effect paradigm in C57BL/6 mice: behavioural evidence for emotional, motivational and cognitive effects of aversive uncontrollability per se

Uncontrollability of major life events has been proposed to be central to depression onset and maintenance. The learned helplessness (LH) effect describes a deficit in terminating controllable aversive stimuli in individuals that experienced aversive stimuli as uncontrollable relative to individuals that experienced the same stimuli as controllable. The LH effect translates across species and therefore can provide an objective-valid readout in animal models of depression. Paradigms for a robust LH effect are established and currently applied in rat but there are few reports of prior and current study of the LH effect in mouse. This includes the C57BL/6 mouse, typically the strain of choice for application of molecular-genetic tools in pre-clinical depression research. The aims of this study were to develop a robust paradigm for the LH effect in BL/6 mice, provide evidence for underlying psychological processes, and study the effect of a depression-relevant genotype on the LH effect. The apparatus used for in/escapable electro-shock exposure and escape test was a two-way shuttle arena with continuous automated measurement of locomotion, compartment transfers, e-shock escapes, vertical activity and freezing. Brother-pairs of BL/6 mice were allocated to either escapable e-shocks (ES) or inescapable e-shocks (IS), with escape latencies of the ES brother used as e-shock durations for the IS brother. The standard two-way shuttle paradigm was modified: the central gate was replaced by a raised divider and e-shock escape required transfer to the distal part of the safe compartment. These refinements yielded reduced superstitious, pre-adaptive e-shock transfers in IS mice and thereby increased the LH effect. To obtain a robust LH effect in all brother pairs, pre-screening for minor between-brother ES differences was necessary and did not confound the LH effect. IS mice developed reduced motor responses to e-shock, consistent with a motivational deficit, and absence of a learning curve for escapes at escape test, consistent with a cognitive deficit. When a tone CS was used to predict e-shock, IS mice exhibited increased reactivity to the CS, consistent with hyper-emotionality. There was no ES-IS difference in pain sensitivity. Mice heterozygous knockout for the 5-HTT gene exhibited an increased LH effect relative to wildtype mice. This mouse model will allow for the detailed molecular study of the aetiology, psychology, neurobiology and neuropharmacology of uncontrollability of aversive stimuli, a potential major aetiological factor and state marker in depression. This article is part of a Special Issue entitled 'Anxiety and Depression'.

The contribution of imaging genetics to the development of predictive markers for addictions

A key challenge for intervention and prevention of addictions is the identification of genetic, neurobiological and cognitive risk profiles that can predict which adolescents are at risk for addiction. Abnormalities in reinforcement behaviour have been linked to addiction vulnerability and imaging genetic studies have begun to elucidate the mechanisms by which genetic and environmental factors influence brain function underlying individual variability in reinforcement behaviour. Most studies have examined associations between a few well-characterised candidate polymorphisms and task-related brain activation differences in individual regions of interest. Here we propose that integrating the imaging genetic strategy with biological network approaches and longitudinal adolescent designs in large multi-centre samples may offer promising opportunities to identify risk markers for early diagnosis, progression and prediction of addictions.

Biomarkers for major depression and its delineation from neurodegenerative disorders

Major depressive disorders (MDD) are among the most debilitating diseases worldwide and occur with a high prevalence in elderly individuals. Neurodegenerative diseases (in particular Alzheimer's disease, AD) do also show a strong age-dependent increase in incidence and prevalence among the elderly population. A high number of geriatric patients with MDD show cognitive deficits and a very high proportion of AD patients present co-morbid MDD, which poses difficult diagnostic and prognostic questions. Especially in prodromal and in very early stages of AD, it is almost impossible to differentiate between pure MDD and MDD with underlying AD. Here, we give a comprehensive review of the literature on the current state of candidate biomarkers for MDD ("positive MDD markers") and briefly refer to established and validated diagnostic AD biomarkers in order to rule out underlying AD pathophysiology in elderly MDD subjects with cognitive impairments ("negative MDD biomarkers"). In summary, to date there is no evidence for positive diagnostic MDD biomarkers and the only way to delineate MDD from AD is to use "negative MDD" biomarkers. Because of this highly unsatisfactory current state of MDD biomarker research, we propose a research strategy targeting to detect and validate positive MDD biomarkers, which is based on a complex (genetic, molecular and neurophysiological) biological model that incorporates current state of the art knowledge on the pathobiology of MDD. This model delineates common pathways and the intersection between AD and MDD. Applying these concepts to MDD gives hope that positive MDD biomarkers can be successfully identified in the near future.

5-HTTLPR and BDNF Val66Met polymorphisms moderate effects of stress on rumination

This study examined whether polymorphisms in the serotonin transporter (SLC6A4, 5-HTTLPR) and brain-derived neurotropic factor (BDNF Val66Met, rs6265) genes moderate the relationship between life stress and rumination. Participants were a large homogenous group of healthy, unmedicated, never depressed individuals with few current symptoms of depression (N = 273). Results indicate that individuals with two short (S) alleles of the 5-HTTLPR polymorphism or two Met alleles of the BDNF Val66Met polymorphism ruminate more under conditions of life stress, compared to the other genotypes. Moreover, the accumulation of risk alleles (i.e. S and Met alleles) across genes is associated with significantly greater rumination in the context of life stress. These results suggest that both 5-HTTLPR and BDNF Val66Met moderate the relationship between life stress and rumination. These findings support the notion that variation in these genes is associated with biological sensitivity to the negative effects of stress.

Maternal depression and child and adolescent depression symptoms: an exploratory test for moderation by CRHR1, FKBP5 and NR3C1 gene variants

This study investigated moderation of the association between recurrent maternal depression and offspring depression symptoms by a selection of biologically relevant gene variants. 271 children/adolescents (aged 9.00 to 16.00 years) whose mothers had experienced at least two episodes of DSM-IV major depression and 165 controls (aged 12.25 to 16.67 years) drawn from a population-based twin register were used. Seven single nucleotide polymorphisms (SNPs) from three genes were genotyped in children. The genes were the Corticotropin Receptor Type 1 gene (CRHR1), the gene coding for the FK506 binding protein 5 (FKBP5) and the Glucocorticoid receptor gene (NR3c1) along with a haplotype formed by the SNPs in CRHR1. A significant association was found between recurrent maternal depression and depression symptoms in offspring. None of the SNPs were associated with offspring depression symptoms and associations did not differ according to the presence of recurrent maternal depression. However, caution is required due to a relatively small sample size.

Fibromyalgia: from pathophysiology to therapy

Individuals with fibromyalgia generally experience chronic widespread pain, which can be accompanied by further symptoms including fatigue, sleep disturbances, cognitive dysfunction, anxiety and depressive episodes. As the recognition and diagnosis of fibromyalgia has improved, the availability of therapeutic options for patients has increased. Furthermore, research into the neurobiological mechanisms that contribute to the chronic pain and concomitant symptoms experienced by patients with fibromyalgia has advanced our understanding of this debilitating disorder. In this Review, we aim to provide an overview of existing pathophysiological concepts. The roles of biological and psychological stress, genetic factors, and pain and sensory processing in the pathophysiology of fibromyalgia and related conditions are discussed. In addition, pharmacological treatments, including monoamine modulators, calcium channel modulators and γ-aminobutyric acid modulators, as well as nonpharmacological treatment options are considered.

The truth about genetic variation in the serotonin transporter gene and response to stress and medication

The question of whether a functional variant in the promoter of the serotonin transporter gene (5-HTTLPR) influences response to adversity and/or antidepressants has generated great interest and controversy. A review of the literature suggests that the issue is complicated by differences in methodology and sample ethnicity. When these confounders are accounted for, there probably is a real, if small, effect of 5-HTTLPR on response to both serotonin reuptake inhibitors and environmental adversity.

Role of mother's genes and environment in postpartum depression

Most studies of human molecular genetics and social environment interactions on health have relied heavily on the classic diathesis-stress model that treats genetic variations and environments as being either "risky" or "protective." The biological susceptibility model posits that some individuals have greater genetic reactivity to stress, leading to worse outcomes in poor environments, but better outcomes in rich environments. Using a nontruncated measure of a chronic environmental stressor--socioeconomic status--measured by education, and two polymorphisms (5-HTTLPR and STin2 VNTR) of the serotonin transporter gene (5-HTT), we find strong evidence that some women are genetically more reactive to the environment, resulting in a crossover of risks of postpartum depression for the most reactive groups. We discuss how our approach and findings provide a framework for understanding some of the confusion in the gene-environment interaction literature on stress, 5-HTT, and depression.

Of sound mind and body: depression, disease, and accelerated aging

Major depressive disorder (MDD) is associated with a high rate of developing serious medical comorbidities such as cardiovascular disease, stroke, dementia, osteoporosis, diabetes, and the metabolic syndrome. These are conditions that typically occur late in life, and it has been suggested that MDD may be associated with “accelerated aging.” We review several moderators and mediators that may accompany MDD and that may give rise to these comorbid medical conditions. We first review the moderating effects of psychological styles of coping, genetic predisposition, and epigenetic modifications (eg, secondary to childhood adversity). We then focus on several interlinked mediators occurring in MDD (or at least in subtypes of MDD) that may contribute to the medical comorbidity burden and to accelerated aging: limbic-hypothalamic-pituitary-adrenal axis alterations, diminution in glucocorticoid receptor function, altered glucose tolerance and insulin sensitivity, excitotoxicity, increases in intracellular calcium, oxidative stress, a proinflammatory milieu, lowered levels of “counter-regulatory” neurosteroids (such as allopregnanolone and dehydroepiandrosterone), diminished neurotrophic activity, and accelerated cell aging, manifest as alterations in telomerase activity and as shortening of telomeres, which can lead to apoptosis and cell death. In this model, MDD is characterized by a surfeit of potentially destructive mediators and an insufficiency of protective or restorative ones. These factors interact in increasing the likelihood of physical disease and of accelerated aging at the cellular level. We conclude with suggestions for novel mechanism-based therapeutics based on these mediators.

Genes, environment, and individual differences in responding to treatment for depression

A principal weakness of evidence-based psychiatry is that it does not account for the individual variability in therapeutic response among individuals with the same diagnosis. The aim of personalized psychiatry is to remediate this shortcoming and to use predictors to select treatment that is most likely to be beneficial for an individual. This article reviews the evidence that genetic variation, environmental exposures, and gene-environment interactions shape mental illness and influence treatment outcomes, with a primary focus on depression. Several genetic polymorphisms have been identified that influence the outcome of specific treatments, but the strength and generalizability of such influences are not sufficient to justify personalized prescribing. Environmental exposures in early life, such as childhood maltreatment, exert long-lasting influences that are moderated by inherited genetic variation and mediated through stable epigenetic mechanisms such as tissue- and gene-specific DNA methylation. Pharmacological and psychological treatments act on and against the background of genetic disposition, with epigenetic annotation resulting from previous experiences. Research in animal models suggests the possibility that epigenetic interventions may modify the impact of environmental stressors on mental health. Gaps in evidence are identified that need to be bridged before knowledge about cause can inform cure in personalized psychiatry.

Serotonin transporter genotype x construction stress interaction in rats

A well-known example for gene x environment interactions in psychiatry is the one involving the low activity (s) allelic variant of the serotonin transporter (5-HTT) promoter polymorphism (5-HTTLPR) that in the context of stress increases risk for depression. In analogy, 5-HTT knockout rodents are highly responsive to early life, but also adult external stressors, albeit conflicting data have been obtained. In our study on emotion and cognition using homozygous 5-HTT knockout (5-HTT(-/-)) and wild-type (5-HTT(+/+)) rats we have been confronted with animal facility construction, which were associated with severe lifetime stress (noise and vibrations). To assess the impact of construction stress on well-established 5-HTT(-/-) rat phenotypes we conducted ad hoc analyses of 5-HTT(-/-) and 5-HTT(+/+) rats that grew up before and during the construction. The reproductive capacity of the parents of the experimental 5-HTT(+/-) rats was significantly decreased. Further, 5-HTT(-/-) anxiety-related phenotypes in the elevated plus maze and social interaction tests were abolished after construction noise exposure, due to increased anxiety in 5-HTT(+/+) rats and decreased anxiety in 5-HTT(-/-) rats (social interaction test only). In addition, reversal learning was improved in 5-HTT(+/+) and, to a milder extent, decreased in 5-HTT(-/-) rats. Finally, construction stress genotype-independently increased behavioural despair in the forced swim test. In conclusion, severe construction stress induces 5-HTT genotype-dependent 'for-better-and-for-worse' effects. These data importantly contribute to the understanding of 5-HTT gene x environment interactions and show the risk of losing genotype effects by construction stress.

Gene–Culture Interaction

Research has demonstrated that certain genotypes are expressed phenotypically in different forms depending on the social environment. To examine sensitivity to cultural norms regarding emotion regulation, we explored the expression of the oxytocin receptor polymorphism ( OXTR) rs53576, a gene previously related to socioemotional sensitivity, in conjunction with cultural norms. Emotional suppression is normative in East Asian cultures but not in American culture. Consequently, we predicted an interaction of Culture and OXTR in emotional suppression. Korean and American participants completed assessments of emotion regulation and were genotyped for OXTR. We found the predicted interaction: Among Americans, those with the GG genotype reported using emotional suppression less than those with the AA genotype, whereas Koreans showed the opposite pattern. These findings suggest that OXTR rs53576 is sensitive to input from cultural norms regarding emotion regulation. These findings also indicate that culture is a moderator that shapes behavioral outcomes associated with OXTR genotypes.

Annual Research Review: Developmental considerations of gene by environment interactions

Biological development is driven by a complex dance between nurture and nature, determined not only by the specific features of the interacting genetic and environmental influences but also by the timing of their rendezvous. The initiation of large-scale longitudinal studies, ever-expanding knowledge of genetics, and increasing availability of neuroimaging data to provide endophenotypic bridges between molecules and behavior are beginning to provide some insight into interactions of developmental stage, genes, and the environment, although daunting challenges remain. Prominent amongst these challenges are difficulties in identifying and quantifying relevant environmental factors, discerning the relative contributions to multiply determined outcomes, and the likelihood that brain development is a non-linear dynamic process in which small initial differences may yield large later effects. Age-sensitive mechanisms include developmental changes in gene expression, epigenetic modifications, synaptic arborization/pruning, and maturational improvements in our capacity to seek out environments of our choosing. Greater understanding of how genetic and environmental factors interact differently across ages is an important step toward elucidating the mechanisms by which phenotypes are created - and how they may differ in health and disease. This knowledge may also provide clues to guide the type and timing of interventions to maximize outcomes.

Conditioned pain modulation is associated with common polymorphisms in the serotonin transporter gene

Background

Variation in the serotonin transporter (5-HTT) gene (SLC6A4) has been shown to influence a wide range of affective processes. Low 5-HTT gene-expression has also been suggested to increase the risk of chronic pain. Conditioned pain modulation (CPM) - i.e. ‘pain inhibits pain’ - is impaired in chronic pain states and, reciprocally, aberrations of CPM may predict the development of chronic pain. Therefore we hypothesized that a common variation in the SLC6A4 is associated with inter-individual variation in CPM. Forty-five healthy subjects recruited on the basis of tri-allelic 5-HTTLPR genotype, with inferred high or low 5-HTT-expression, were included in a double-blind study. A submaximal-effort tourniquet test was used to provide a standardized degree of conditioning ischemic pain. Individualized noxious heat and pressure pain thresholds (PPTs) were used as subjective test-modalities and the nociceptive flexion reflex (NFR) was used to provide an objective neurophysiological window into spinal processing.

Results

The low, as compared to the high, 5-HTT-expressing group exhibited significantly reduced CPM-mediated pain inhibition for PPTs (p = 0.02) and heat-pain (p = 0.02). The CPM-mediated inhibition of the NFR, gauged by increases in NFR-threshold, did not differ significantly between groups (p = 0.75). Inhibition of PPTs and heat-pain were correlated (Spearman’s rho = 0.35, p = 0.02), whereas the NFR-threshold increase was not significantly correlated with degree of inhibition of these subjectively reported modalities.

Conclusions

Our results demonstrate the involvement of the tri-allelic 5-HTTLPR genotype in explaining clinically relevant inter-individual differences in pain perception and regulation. Our results also illustrate that shifts in NFR-thresholds do not necessarily correlate to the modulation of experienced pain. We discuss various possible mechanisms underlying these findings and suggest a role of regulation of 5-HT receptors along the neuraxis as a function of differential 5-HTT-expression.

Gene × environment vulnerability factors for PTSD: the HPA-axis

Post-traumatic stress disorder (PTSD) is a severely debilitating psychiatric condition. Although a lifetime trauma incidence of 40-90% has been reported in the general population, the overall lifetime prevalence for PTSD ranges between 7-12%, suggesting individual-specific differences towards the susceptibility to PTSD. While studies investigating main genetic effects associated with PTSD have yielded inconsistent findings, there is growing evidence supporting the role of gene-environment (G × E) interactions in PTSD. The hypothalamus pituitary adrenal (HPA) axis is one of the main systems activated after exposure to a trauma and perturbations in this system are one of the more consistent neurobiological abnormalities observed in PTSD. Genes regulating the HPA-axis are therefore interesting candidates for G × E studies in PTSD. This article will review the concept and initial results of G × E interactions with polymorphisms in these genes for PTSD. In addition, the use of alternate phenotypes and more complex interaction models such as G × G × E or G × E × E will be explored. Finally, putative molecular mechanisms for these interactions will be presented. The research presented in this article indicates that a combined analysis of environmental, genetic, endophenotype and epigenetic data will be necessary to better understand pathomechanisms in PTSD. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

The serotonin transporter is an exclusive client of the coat protein complex II (COPII) component SEC24C

The transporters for serotonin (SERT), dopamine, and noradrenaline have a conserved hydrophobic core but divergent N and C termini. The C terminus harbors the binding site for the coat protein complex II (COPII) cargo-binding protein SEC24. Here we explored which SEC24 isoform was required for export of SERT from the endoplasmic reticulum (ER). Three lines of evidence argue that SERT can only exit the ER by recruiting SEC24C: (i) Mass spectrometry showed that a peptide corresponding to the C terminus of SERT recruited SEC24C-containing COPII complexes from mouse brain lysates. (ii) Depletion of individual SEC24 isoforms by siRNAs revealed that SERT was trapped in the ER only if SEC24C was down-regulated, in both, cells that expressed SERT endogenously or after transfection. The combination of all siRNAs was not more effective than that directed against SEC24C. A SERT mutant in which the SEC24C-binding motif ((607)RI(608)) was replaced by alanine was insensitive to down-regulation of SEC24C levels. (iii) Overexpression of a SEC24C variant with a mutation in the candidate cargo-binding motif (SEC24C-D796V/D797N) but not of the corresponding mutant SEC24D-D733V/D734N reduced SERT surface levels. In contrast, noradrenaline and dopamine transporters and the more distantly related GABA transporter 1 relied on SEC24D for ER export. These observations demonstrate that closely related transporters are exclusive client cargo proteins for different SEC24 isoforms. The short promoter polymorphism results in reduced SERT cell surface levels and renders affected individuals more susceptible to depression. By inference, variations in the Sec24C gene may also affect SERT cell surface levels and thus be linked to mood disorders.

Perception of thermal pain and the thermal grill illusion is associated with polymorphisms in the serotonin transporter gene

Aim

The main aim of this study was to assess if the perception of thermal pain thresholds is associated with genetically inferred levels of expression of the 5-HT transporter (5-HTT). Additionally, the perception of the so-called thermal grill illusion (TGI) was assessed. Forty-four healthy individuals (27 females, 17 males) were selected a-priori based on their 5-HTTLPR/rs25531 (‘tri-allelic 5-HTTLPR’) genotype, with inferred high or low 5-HTT expression. Thresholds for heat- and cold-pain were determined along with the sensory and affective dimensions of the TGI.

Results

Thresholds to heat- and cold-pain correlated strongly (rho  = −0.58, p<0.001). Individuals in the low 5-HTT-expressing group were significantly less sensitive to heat-pain (p = 0.02) and cold-pain (p = 0.03), compared to the high-expressing group. A significant gender-by-genotype interaction also emerged for cold-pain perception (p = 0.02); low 5-HTT-expressing females were less sensitive. The TGI was rated as significantly more unpleasant (affective-motivational dimension) than painful (sensory-discriminatory dimension), (p<0.001). Females in the low 5-HTT expressing group rated the TGI as significantly less unpleasant than high 5-HTT expressing females (p<0.05), with no such differences among men.

Conclusion/Significance

We demonstrate an association between inferred low 5-HTT expression and elevated thresholds to thermal pain in healthy non-depressed individuals. Despite the fact that reduced 5-HTT expression is a risk factor for chronic pain we found it to be related to hypoalgesia for threshold thermal pain. Low 5-HTT expression is, however, also a risk factor for depression where thermal insensitivity is often seen. Our results may thus contribute to a better understanding of the molecular underpinnings of such paradoxical hypoalgesia. The results point to a differential regulation of thermoafferent-information along the neuraxis on the basis of 5-HTT expression and gender. The TGI, suggested to rely on the central integration of thermoafferent-information, may prove a valuable tool in probing the affective-motivational dimension of these putative mechanisms.

Human serotonin transporter gene (SLC6A4) variants: their contributions to understanding pharmacogenomic and other functional G×G and G×E differences in health and disease

Recent major findings from studies of SLC6A4 and its corresponding protein, the serotonin (5-HT) transporter (SERT) in humans, rodents and non-human primates indicate that combinations of SLC6A4 non-coding 5', 3' UTRs and intronic regions plus coding variants acting together can change 5HT transport as much as 40-fold in vitro. In vivo, SLC6A4 variants in humans and other species lead to marked physiological changes, despite mitigating neurodevelopmental adaptations in 5-HT receptors plus compensatory alterations in 5-HT synthesis and metabolism. Polymorphisms in SLC6A4 are associated with differences in emotional, endocrine, and personality characteristics as well as many diseases. This gene, in combinations with gene×gene (G×G) and gene×environment (G×E) interactions nonetheless remains incompletely understood, with some association findings remaining controversial. Considering its primary importance in the regulation and function of the entire serotonergic system (as evidenced by the consequences of SERT-mediated reuptake inhibition by SRIs like fluoxetine in humans and of genetically engineered changes in mice and rats), it seems likely that SLC6A4 and SERT will remain areas of high interest in our field's attempts to better understand and treat 5-HT-related disorders.

Of sound mind and body: depression, disease, and accelerated aging

Major depressive disorder (MDD) is associated with a high rate of developing serious medical comorbidities such as cardiovascular disease, stroke, dementia, osteoporosis, diabetes, and the metabolic syndrome. These are conditions that typically occur late in life, and it has been suggested that MDD may be associated with "accelerated aging." We review several moderators and mediators that may accompany MDD and that may give rise to these comorbid medical conditions. We first review the moderating effects of psychological styles of coping, genetic predisposition, and epigenetic modifications (eg, secondary to childhood adversity). We then focus on several interlinked mediators occurring in MDD (or at least in subtypes of MDD) that may contribute to the medical comorbidity burden and to accelerated aging: limbic-hypothalamic-pituitary-adrenal axis alterations, diminution in glucocorticoid receptor function, altered glucose tolerance and insulin sensitivity, excitotoxicity, increases in intracellular calcium, oxidative stress, a proinflammatory milieu, lowered levels of "counter-regulatory" neurosteroids (such as allopregnanolone and dehydroepiandrosterone), diminished neurotrophic activity, and accelerated cell aging, manifest as alterations in telomerase activity and as shortening of telomeres, which can lead to apoptosis and cell death. In this model, MDD is characterized by a surfeit of potentially destructive mediators and an insufficiency of protective or restorative ones. These factors interact in increasing the likelihood of physical disease and of accelerated aging at the cellular level. We conclude with suggestions for novel mechanism-based therapeutics based on these mediators.

Gene × environment interaction models in psychiatric genetics

Gene-environment (G × E) interaction research is an emerging area in psychiatry, with the number of G × E studies growing rapidly in the past two decades. This article aims to give a comprehensive introduction to the field, with an emphasis on central theoretical and practical problems that are worth considering before conducting a G × E interaction study. On the theoretical side, we discuss two fundamental, but controversial questions about (1) the validity of statistical models for biological interaction and (2) the utility of G × E research for psychiatric genetics. On the practical side, we focus on study characteristics that potentially influence the outcome of G × E interaction studies and discuss strengths and pitfalls of different study designs, including recent approaches like Genome-Environment Wide Interaction Studies (GEWIS). Finally, we discuss recent developments in G × E interaction research on the most heavily investigated example in psychiatric genetics, the interaction between a serotonin transporter gene promoter variant (5-HTTLPR) and stress on depression.

Impact of serotonin transporter gene polymorphism on brain activation by colorectal distention

Background and Aims

The 5-hydroxytryptamine transporter gene-linked polymorphic region (5-HTTLPR) has been linked to increased stress responsiveness and negative emotional states. During fearful face recognition individuals with the s allele of 5-HTTLPR show greater amygdala activation. We aimed to test the hypothesis that the 5-HTTLPR polymorphism differentially affects connectivity within brain networks during an aversive visceral stimulus.

Methods

Twenty-three healthy male subjects were enrolled. DNA was extracted from the peripheral blood. The genotype of 5-HTTLPR was determined using polymerase chain reaction. Subjects with the s/s genotype (n = 13) were compared to those with the l allele (genotypes l/s, l/l, n = 10). Controlled rectal distension from 0 to 40 mmHg was delivered in random order using a barostat. Radioactive H2[^15-O] saline was injected at time of distension followed by positron emission tomography (PET). Changes in regional cerebral blood flow (rCBF) were analyzed using partial least squares (PLS) and structural equation modeling (SEM).

Results

During baseline, subjects with s/s genotype demonstrated a significantly increased negative influence of pregenual ACC (pACC) on amygdala activity compared to l-carriers. During inflation, subjects with s/s genotype demonstrated a significantly greater positive influence of hippocampus on amygdala activity compared to l-carriers.

Conclusion

In male Japanese subjects, individuals with s/s genotype show alterations in the connectivity of brain regions involved in stress responsiveness and emotion regulation during aversive visceral stimuli compared to those with l carriers.