Affect-modulated startle reflex and dopamine D4 receptor gene variation

Genetics of human startle reactivity: A systematic review to acquire targets for an anxiety endophenotype

OBJECTIVES

Startle response is an objective physiological measure integral to the human defense system and a promising target for endophenotype investigations of anxiety. Given the alterations in startle reactivity observed among anxiety and related disorders, we searched for genetic variants associated with startle reactivity as they may be further involved in pathological anxiety risk.

METHODS

A systematic literature review was performed to identify genetic variants associated with startle reactivity in humans, specifically baseline and fear- or anxiety-potentiated startle.

RESULTS

The polymorphisms Val66Met (rs6265) from brain-derived neurotrophic factor (BDNF), Val158Met (rs4680) from catechol-O-methyltransferase (COMT), and the serotonin transporter-linked polymorphic region (5-HTTLPR) from the serotonin transporter gene (SLC6A4) were most commonly studied in human startle. In addition, several other genetic variants have also been identified as potential candidates that warrant further research, especially given their novelty in in the context of anxiety.

CONCLUSIONS

Similar to psychiatric genetic studies, the studies on startle reactivity primarily focus on candidate genes and are plagued by non-replication. Startle reactivity is a promising endophenotype that requires concerted efforts to collect uniformly assessed, large, well-powered samples and hypothesis-free genome-wide strategies. To further support startle as an endophenotype for anxiety, this review suggests advanced genetic strategies for startle research.

The effects of the CACNA1C rs1006737 A/G on affective startle modulation in healthy males

Background:

The CACNA1C rs1006737 risk A allele has been associated with affective psychoses and functional studies indicate that it is associated with increased hippocampal/amygdala activity during emotional face-processing. Here we studied the impact of the risk A allele on affective startle modulation.

Methods:

Hundred and ninety-four healthy males stratified for their CACNA1C rs1006737 genotype (GG:111, GA:67, AA:16) were presented with 18 pleasant, 18 unpleasant and 18 neutral pictures with acoustic probes (104 dB) occurring during 12 pictures in each affective category. Baseline startle was assessed during blank screens. State mood was self-rated on arrival, pre- and post-test and the emotional valence and arousal of affective pictures at post-test.

Results:

Relative to the other genotypes, risk A allele homozygotes presented with higher anxiety/negative affect at pre-test, reduced and exaggerated physiological responses to the pleasant and negative pictures respectively, negative affect with reduced arousal at post-test and rated the affective pictures as less arousing and inconsistently to their physiological responses (all P < 0.05). Sustained contextual negative mood predicted reduced baseline and affective startle reactivity in the AA group.

Conclusions:

Healthy homozygous males for the risk A allele appear to have marked contextual sensitivity, affective reactivity akin to anxiety and depression and inefficient emotional appraisal. Our findings provide phenotypic detail of the CACNA1C AA genotype in non-symptomatic individuals, which suggest primary effects in emotional circuitry, consistent with previously documented alterations in hippocampal/amygdala processing.

Neurogenetic Approaches to Stress and Fear in Humans as Pathophysiological Mechanisms for Posttraumatic Stress Disorder

In this review article, genetic variation associated with brain responses related to acute and chronic stress reactivity and fear learning in humans is presented as an important mechanism underlying posttraumatic stress disorder. We report that genes related to the regulation of the hypothalamic-pituitary-adrenal axis, as well as genes that modulate serotonergic, dopaminergic, and neuropeptidergic functions or plasticity, play a role in this context. The strong overlap of the genetic targets involved in stress and fear learning suggests that a dimensional and mechanistic model of the development of posttraumatic stress disorder based on these constructs is promising. Genome-wide genetic analyses on fear and stress mechanisms are scarce. So far, reliable replication is still lacking for most of the molecular genetic findings, and the proportion of explained variance is rather small. Further analysis of neurogenetic stress and fear learning needs to integrate data from animal and human studies.

Methylphenidate and emotional-motivational processing in attention-deficit/hyperactivity disorder

In line with the assumption that emotional-motivational deficits are one core dysfunction in ADHD, in one of our previous studies we observed a reduced reactivity towards pleasant pictures in adult ADHD patients as compared to controls. This was indicated by a lack of attenuation of the startle reflex specifically during pleasant pictures in ADHD patients. The first choice medical agents in ADHD, methylphenidate (MPH), is discussed to normalize these dysfunctions. However, experimental evidence in the sense of double-blind placebo-controlled study designs is lacking. Therefore, we investigated 61 adult ADHD patients twice, one time with placebo and one time with MPH with the same experimental design as in our study previously and assessed emotion processing during the presentation of pleasant, neutral and unpleasant pictures. We obtained startle reflex data as well as valence and arousal ratings in association with the pictures. As previously shown, ADHD patients showed a diminished startle attenuation during pleasant pictures while startle potentiation during unpleasant pictures was normal. Valence and arousal ratings unsuspiciously increased with increasing pleasantness and arousal of the pictures, respectively. There were no significant influences of MPH. The study replicates that ADHD patients show a reduced reactivity towards pleasant stimuli. MPH did not normalize this dysfunction. Possibly, MPH only influences emotions during more complex behavioural tasks that involve executive functions in adults with ADHD. Our results emphasize the importance for the use of double-blind placebo-controlled designs in psychopharmacological research.

Genetic influences on the neural and physiological bases of acute threat: A research domain criteria (RDoC) perspective

The NIMH Research Domain Criteria (RDoC) initiative aims to describe key dimensional constructs underlying mental function across multiple units of analysis-from genes to observable behaviors-in order to better understand psychopathology. The acute threat ("fear") construct of the RDoC Negative Valence System has been studied extensively from a translational perspective, and is highly pertinent to numerous psychiatric conditions, including anxiety and trauma-related disorders. We examined genetic contributions to the construct of acute threat at two units of analysis within the RDoC framework: (1) neural circuits and (2) physiology. Specifically, we focused on genetic influences on activation patterns of frontolimbic neural circuitry and on startle, skin conductance, and heart rate responses. Research on the heritability of activation in threat-related frontolimbic neural circuitry is lacking, but physiological indicators of acute threat have been found to be moderately heritable (35-50%). Genetic studies of the neural circuitry and physiology of acute threat have almost exclusively relied on the candidate gene method and, as in the broader psychiatric genetics literature, most findings have failed to replicate. The most robust support has been demonstrated for associations between variation in the serotonin transporter (SLC6A4) and catechol-O-methyltransferase (COMT) genes with threat-related neural activation and physiological responses. However, unbiased genome-wide approaches using very large samples are needed for gene discovery, and these can be accomplished with collaborative consortium-based research efforts, such as those of the Psychiatric Genomics Consortium (PGC) and Enhancing Neuro Imaging Genetics through Meta-Analysis (ENIGMA) Consortium.

5HTT is associated with the phenotype psychological flexibility: results from a randomized clinical trial

Adaption to changing environments is evolutionarily advantageous. Studies that link genetic and phenotypic expression of flexible adjustment to one's context are largely lacking. In this study, we tested the importance of psychological flexibility, or goal-related context sensitivity, in an interaction between psychotherapy outcome for panic disorder with agoraphobia (PD/AG) and a genetic polymorphism. Given the established role of the 5HTT-LPR polymorphism in behavioral flexibility, we tested whether this polymorphism (short group vs. long group) impacted therapy response as a function of various endophenotypes (i.e., psychological flexibility, panic, agoraphobic avoidance, and anxiety sensitivity). Patients with PD/AG were recruited from a large multicenter randomized controlled clinical trial on cognitive-behavioral therapy. Pre- to post-treatment changes by 5HTT polymorphism were analyzed. 5HTT polymorphism status differentiated pre- to post-treatment changes in the endophenotype psychological flexibility (effect size difference d = 0.4, p < 0.05), but none of the specific symptom-related endophenotypes consistently for both the intent-to-treat sample (n = 228) and the treatment completers (n = 194). Based on the consistency of these findings with existing theory on behavioral flexibility, the specificity of the results across phenotypes, and the consistency of results across analyses (i.e., completer and intent to treat), we conclude that 5HTT polymorphism and the endophenotype psychological flexibility are important variables for the treatment of PD/AG. The endophenotype psychological flexibility may help bridge genetic and psychological literatures. Despite the limitation of the post hoc nature of these analyses, further study is clearly warranted.

Multilevel impact of the dopamine system on the emotion-potentiated startle reflex

RATIONALE/OBJECTIVES

The pathogenetic mechanism of emotion-related disorders such as anxiety disorders is considered to be complex with an interaction of genetic, biochemical, and environmental factors. Particular evidence has accumulated for alterations in the dopaminergic system-partly conferred by catechol-O-methyltransferase (COMT) gene variation-and for distorted emotional processing to constitute risk factors for anxiety and anxiety-related disorders.

METHODS

Applying a multilevel approach, we analyzed the main and interactive effects of the functional COMT val158met polymorphism and L-dopa (single-dose 50 mg levodopa and 12.5 mg carbidopa; double-blind, placebo-controlled design) on the emotion-potentiated (unpleasant, neutral, and pleasant IAPS pictures) startle response as an intermediate phenotype of anxiety in a sample of 100 healthy probands (f = 52, m = 48).

RESULTS

The COMT 158val allele was associated with an increased startle potentiation by unpleasant stimuli as compared with neutral stimuli irrespective of L-dopa or placebo intervention. COMT 158met/met genotype carriers, while displaying no difference in startle magnitude in response to unpleasant or neutral pictures in the placebo condition, showed startle potentiation by unpleasant pictures under L-dopa administration only.

CONCLUSIONS

The present proof-of-concept study provides preliminary support for a complex, multilevel impact of the dopaminergic system on the emotion-potentiated startle reflex suggesting increased phasic dopamine transmission driven by the more active COMT 158val allele and/or a single dose of L-dopa to predispose to maladaptive emotional processing and thereby potentially also to anxiety-related psychopathological states.

Heritability and molecular genetic basis of acoustic startle eye blink and affectively modulated startle response: a genome-wide association study

Acoustic startle responses have been studied extensively in relation to individual differences and psychopathology. We examined three indices of the blink response in a picture-viewing paradigm-overall startle magnitude across all picture types, and aversive and pleasant modulation scores-in 3,323 twins and parents. Biometric models and molecular genetic analyses showed that half the variance in overall startle was due to additive genetic effects. No single nucleotide polymorphism was genome-wide significant, but GRIK3 produced a significant effect when examined as part of a candidate gene set. In contrast, emotion modulation scores showed little evidence of heritability in either biometric or molecular genetic analyses. However, in a genome-wide scan, PARP14 produced a significant effect for aversive modulation. We conclude that, although overall startle retains potential as an endophenotype, emotion-modulated startle does not.

Imaging genetics in adult attention-deficit/hyperactivity disorder (ADHD): a way towards pathophysiological understanding?

Attention-deficit/hyperactivity disorder (ADHD) is a common, early-onset and enduring developmental disorder whose underlying etiological and neurobiological processes are the current focus of major research. Research strategies have made considerable effort in elucidating the complex genetic architecture of ADHD and indicate various pathways from genotype to phenotype. Understanding ADHD as a neuropsychiatric disorder enabled to investigate markers of neural activity as endophenotypes to better explain the link from gene to symptomatology (the so-called imaging genetics approach). Overcoming the originally rather restrictive requirements for an endophenotype, imaging genetics studies are supposed to offer a much more flexible and hypothesis-driven approach towards the etiology of ADHD. Although 1) ADHD often persists into adulthood, thus remaining a prevalent disorder, and 2) imaging genetics provides a promising research approach, a review on imaging genetics in adult ADHD - as available for childhood ADHD (Durston 2010) - is lacking. In this review, therefore, findings from the few available imaging genetics studies in adult ADHD will be summarized and complemented by relevant findings from healthy controls and children with ADHD that are considered important for the adult ADHD imaging genetics approach. The studies will be reviewed regarding implications for basic research and possible practical applications. Imaging genetics studies in adult ADHD have the potential to further clarify pathophysiological pathways and mechanisms, to derive new testable hypotheses, to investigate genetic interaction effects and to partly influence practical applications. In combination with other research strategies, they can incrementally foster the understanding of relevant processes in a more comprehensive way. Current limitations comprise the incapability to discover new genes, a high genetic load in patients potentially obscuring the effect of single candidate genes, the mostly unknown heritability of the endophenotype and the heterogeneous manifestation of ADHD.

Influence of catechol-O-methyltransferase Val158Met polymorphism on startle response in the presence of high estradiol levels

INTRODUCTION

both human and animal studies have shown a somewhat complex COMT-by-sex interaction effect on brain function and dysfunction. A functional variation in the gene coding for the catechol-O-methyltransferase (COMT) enzyme, which metabolizes dopamine and noradrenaline, has been related to executive and emotional functions, and to sex dimorphism.

AIM

to investigate if COMT Val158Met genotype influences startle response in pregnant women, given their physiologically elevated estradiol levels.

METHODS

seventy-three pregnant women were assessed in gestational week 38 for acoustic startle response, measured by electromyography of the blink reflex, during control condition, positive and negative anticipation stimuli, and pleasant and unpleasant image stimuli. A blood sample was taken for measurement of estradiol levels and genetic analysis.

RESULTS

the results indicated a COMT Val158Met effect on startle response across all conditions (main effect of genotype, F(2,70=3.58), p=0.033), where Val/Val women displayed higher startle magnitudes than Val/Met carriers (Cohen's d=0.71). No significant difference by genotype was found in affective modulation. The findings also suggested an estrogen dose-dependent effect of COMT Val158Met on startle reflex. Among women with higher pregnancy-induced estradiol levels, Val/Val carriers had markedly higher startle response across conditions than heterozygotes (Cohen's d=1.36; F(4,21=11.07); p=0.003), while this effect was not present in women with estradiol levels under the median concentration.

CONCLUSIONS

the observed effect of COMT Val158Met by estradiol on overall startle response is likely to be due to a variable noradrenergic transmission depending on COMT activity in a possible interaction with estradiol.

Human fear acquisition deficits in relation to genetic variants of the corticotropin releasing hormone receptor 1 and the serotonin transporter

The ability to identify predictors of aversive events allows organisms to appropriately respond to these events, and failure to acquire these fear contingencies can lead to maladaptive contextual anxiety. Recently, preclinical studies demonstrated that the corticotropin-releasing factor and serotonin systems are interactively involved in adaptive fear acquisition. Here, 150 healthy medication-free human subjects completed a cue and context fear conditioning procedure in a virtual reality environment. Fear potentiation of the eyeblink startle reflex (FPS) was measured to assess both uninstructed fear acquisition and instructed fear expression. All participants were genotyped for polymorphisms located within regulatory regions of the corticotropin releasing hormone receptor 1 (CRHR1 - rs878886) and the serotonin transporter (5HTTLPR). These polymorphisms have previously been linked to panic disorder and anxious symptomology and personality, respectively. G-allele carriers of CRHR1 (rs878886) showed no acquisition of fear conditioned responses (FPS) to the threat cue in the uninstructed phase, whereas fear acquisition was present in C/C homozygotes. Moreover, carrying the risk alleles of both rs878886 (G-allele) and 5HTTLPR (short allele) was associated with increased FPS to the threat context during this phase. After explicit instructions regarding the threat contingency were given, the cue FPS and context FPS normalized in all genotype groups. The present results indicate that genetic variability in the corticotropin-releasing hormone receptor 1, especially in interaction with the 5HTTLPR, is involved in the acquisition of fear in humans. This translates prior animal findings to the human realm.

Effects of ADORA2A gene variation and caffeine on prepulse inhibition: a multi-level risk model of anxiety

The complex pathogenesis of anxiety and panic disorder in particular has been suggested to be influenced by genetic factors such as the adenosine A2A receptor gene (ADORA2A) 1976T>C polymorphism (rs5751876) as well as neuropsychological factors such as early information processing deficits. In 114 healthy individuals (males=57, females=57) controlled for anxiety sensitivity (AS), a multi-level risk model of the development of anxiety was applied: Genetic (ADORA2A 1976T>C variant) and biochemical (300 mg of caffeine citrate vs. placebo) factors were hypothesized to influence early information processing as measured by the prepulse inhibition/facilitation paradigm (stimulus onset asynchronies (SOAs) of 60, 120, 240, 480 and 2000ms between prepulses and startle stimuli). A fourfold interaction of genotype, intervention, gender, and SOAs was discerned. Stratification by SOAs revealed that at 120 ms and 240 ms SOAs in the caffeine condition, PPI was impaired in female ADORA2A 1976TT risk genotype carriers as compared to male ADORA2A 1976TT homozygotes, while no significant effects were observed in the ADORA2A 1976CC/CT non-risk genotype or placebo group. Only in high anxiety sensitive probands, a significant intervention effect was discerned with impaired prepulse facilitation (PPF) due to caffeine. The present results point to an impaired ability to selectively process very early information and to gate irrelevant sensory information, respectively, in female ADORA2A 1976TT homozygotes in response to caffeine, providing further evidence for the adenosinergic system to be involved in the pathogenesis of anxiety.

Modification of caffeine effects on the affect-modulated startle by neuropeptide S receptor gene variation

RATIONALE/OBJECTIVES

Both the neuropeptide S (NPS) system and antagonism at the adenosine A2A receptor (e.g., by caffeine) were found to play a crucial role in the mediation of arousal and anxiety/panic in animal and human studies. Furthermore, a complex interaction of the neuropeptide S and the adenosinergic system has been suggested with administration of the adenosine A2A receptor antagonist caffeine downregulating NPS levels (Lage et al., 2006) and attenuating the stimulatory effects of NPS in rodents (Boeck et al., 2010).

METHODS

Thus, in the present study, the impact of the functional neuropeptide S receptor (NPSR) A/T (Asn(107)Ile; rs324981) variant on affect-modulated (neutral, unpleasant, and pleasant IAPS pictures) startle response depending on the administration of 300 mg caffeine citrate was investigated in a sample of 124 (m = 58, f = 66) healthy probands using a double-blind, placebo-controlled design.

RESULTS

ANOVA revealed a significant interaction between NPSR genotype, challenge condition, and picture valence. Comparing startle magnitudes upon stimulation with neutral or emotional pictures between the placebo and caffeine condition, in AA/AT non-risk genotype carriers no significant difference was discerned, while TT risk genotype carriers showed a significantly increased startle magnitude in response to neutral stimuli (p = .02) and a significantly decreased startle magnitude in response to unpleasant stimuli (p = .02) in the caffeine condition as compared to the placebo condition.

CONCLUSIONS

In summary, the present findings - extending previous evidence from rodent studies - for the first time provide support for a complex, non-linear interaction of the neuropeptide S and adenosinergic systems affecting the affect-modulated startle response as an intermediate phenotype of anxiety in humans.

Affect-modulated startle: interactive influence of catechol-O-methyltransferase Val158Met genotype and childhood trauma

The etiology of emotion-related disorders such as anxiety or affective disorders is considered to be complex with an interaction of biological and environmental factors. Particular evidence has accumulated for alterations in the dopaminergic and noradrenergic system--partly conferred by catechol-O-methyltransferase (COMT) gene variation--for the adenosinergic system as well as for early life trauma to constitute risk factors for those conditions. Applying a multi-level approach, in a sample of 95 healthy adults, we investigated effects of the functional COMT Val158Met polymorphism, caffeine as an adenosine A2A receptor antagonist (300 mg in a placebo-controlled intervention design) and childhood maltreatment (CTQ) as well as their interaction on the affect-modulated startle response as a neurobiologically founded defensive reflex potentially related to fear- and distress-related disorders. COMT val/val genotype significantly increased startle magnitude in response to unpleasant stimuli, while met/met homozygotes showed a blunted startle response to aversive pictures. Furthermore, significant gene-environment interaction of COMT Val158Met genotype with CTQ was discerned with more maltreatment being associated with higher startle potentiation in val/val subjects but not in met carriers. No main effect of or interaction effects with caffeine were observed. Results indicate a main as well as a GxE effect of the COMT Val158Met variant and childhood maltreatment on the affect-modulated startle reflex, supporting a complex pathogenetic model of the affect-modulated startle reflex as a basic neurobiological defensive reflex potentially related to anxiety and affective disorders.

ADORA2A Gene variation, caffeine, and emotional processing: a multi-level interaction on startle reflex

There is converging evidence for genetic, biochemical, and neuropsychological factors to increase the risk for anxiety and anxiety disorders. The pathogenesis of anxiety disorders is assumed to be influenced by a complex interaction of these individual risk factors on several levels, affecting intermediate phenotypes of anxiety such as the startle reflex. Thus, in the present double-blind, placebo-controlled study we attempted to paradigmatically investigate a multi-level pathogenetic model of anxiety by testing the effect of 300 mg caffeine citrate as an antagonist at the adenosine A2A receptor vs placebo on the emotion-potentiated (unpleasant, neutral, and pleasant International Affective Picture System pictures) startle reflex in 110 healthy individuals (male=56, female=54) stratified for the adenosine A2A receptor (ADORA2A) 1976T>C polymorphism (rs5751876). In addition to the expected main effect of picture category (highest startle amplitude for unpleasant, lowest for pleasant pictures) groups across all ADORA2A 1976T>C genotype and intervention (caffeine vs placebo) groups, an interaction effect of genotype, intervention, and picture category was discerned: In ADORA2A 1976TT risk genotype carriers, highest startle magnitudes were observed after caffeine administration in response to unpleasant pictures, with this effect arising particularly from the female subgroup. Our data point to a complex, multi-level, and potentially gender-specific pathogenetic model of anxiety, with genetic and biochemical factors interactively increasing the risk of maladaptive emotional processing and thereby possibly also anxiety disorders. The present findings may eventually aid in improving primary and secondary prevention by sharpening the risk profiles of anxiety-prone individuals.

Genetic variation in serotonin transporter function affects human fear expression indexed by fear-potentiated startle

The serotonin transporter (SERT) plays a crucial role in anxiety. Accordingly, variance in SERT functioning appears to constitute an important pathway to individual differences in anxiety. The current study tested the hypothesis that genetic variation in SERT function is associated with variability in the basic reflex physiology of defense. Healthy subjects (N=82) were presented with clearly instructed cues of shock threat and safety to induce robust anxiety reactions. Subjects carrying at least one short allele for the 5-HTTLPR polymorphism showed stronger fear-potentiated startle compared to long allele homozygotes. However, short allele carriers showed no deficit in the downregulation of fear after the offset of threat. These results suggest that natural variation in SERT function affects the magnitude of defensive reactions while not affecting the capacity for fear regulation.

Startle response related genes

The startle reaction (also known as the startle response, the startle reflex, or the alarm reaction) is the psychological and physiological response to a sudden unexpected stimulus, such as a flash of light, a loud noise (acoustic startle reflex), or a quick movement near the face. Abnormalities of startle response have been observed in many stress-related mental disorders, such as schizophrenia and post-traumatic stress disorder (PTSD). However, the molecular mechanisms of startle in stress-associated conditions--for example, whether the startle reaction is associated with any gene variance--is still unknown. In this paper, we will carry out a systematic review by retrieving, assessing, and combining, when applicable, individual studies investigating association of the molecular variation of candidate gene with the startle response. The systematic review is based on the search for numerous publications using the keywords "startle gene" on September 15, 2010 using PubMed, which comprises more than 20 million citations for biomedical literature from MEDLINE and life science journals. A total of 486 publications regarding genes associated with startle have been obtained and reviewed here. There are fewer than 20 publications associating genes with the startle response between 1979, when the first valuable paper was published, and 1999. However, publications have dramatically increase from 2001 and reaches over 70 in 2009. We have characterized them into three categories: startle-associated gene studies in humans, in animals, as well as in both human and animals. This review of research strategy may provide the information for identifying a biomarker for startle response, with the objective of translating research into clinical utility: diagnosis and treatment of stress-induced mental disorders.

Variation in genes involved in dopamine clearance influence the startle response in older adults

The dopamine transporter (DAT) and the enzyme catechol-O-methyltransferase (COMT) both terminate synaptic dopamine action. Here, we investigated the influence of two polymorphisms in the respective genes: DAT1 (SLC6A3) VNTR and COMT val(158)met (rs4680). Startle magnitudes to intense noise bursts as measured with the eye blink response were recorded during the presentation of pictures of three valence conditions (unpleasant, pleasant and neutral) and during baseline without additional pictorial stimulation in a sample of healthy older adults (N = 94). There was a significant Bonferroni corrected main effect of COMT genotype on the overall startle responses, with met/met homozygotes showing the highest and participants with the val/val genotype showing the lowest startle response, while participants with the val/met genotype displayed intermediate reactions. There was also a DAT1 VNTR main effect, which, after Bonferroni correction, still showed a tendency toward significance with carriers of at least one 9-repeat (R) allele showing smaller overall startle responses compared to 10R/10R homozygotes. Thus, older adult carriers of COMT variants, which result in lower enzyme activity and therefore probably enhanced dopamine signaling, showed stronger startle activity. Although the functional significance of DAT1 VNTR is less defined, our results point to a potential influence of SLC6A3 on startle magnitude.

L-DRD4 genotype not associated with sensation seeking, gambling performance and startle reactivity in adolescents: the TRAILS study

The purpose of the present study was to investigate whether a length polymorphism in the dopamine receptor D4 gene (DRD4) was associated with approach related traits in adolescents. Data were used from TRAILS (TRacking Adolescents' Individual Lives Survey), a population based cohort of Dutch adolescents. Sensation seeking, assessed with personality questionnaires from the participants themselves and their biological father and mother (n=1282) was not associated with DRD4 genotype. Gambling performance (n=591) and startle reactivity (n=432) were not associated with DRD4 genotype either. Explanations for the dissociation might be sought in differences in development of the limbic system and the prefrontal cortex, both with high dopamine receptor D4 densities and both involved in approach related behaviours.