The D2 dopamine receptor gene variant C957T affects human fear conditioning and aversive priming

Ankyrin Repeat and Kinase Domain Containing 1 Gene, and Addiction Vulnerability

The TaqIA single nucleotide variant (SNV) has been tested for association with addictions in a huge number of studies. TaqIA is located in the ankyrin repeat and kinase domain containing 1 gene (ANKK1) that codes for a receptor interacting protein kinase. ANKK1 maps on the NTAD cluster along with the dopamine receptor D2 (DRD2), the tetratricopeptide repeat domain 12 (TTC12) and the neural cell adhesion molecule 1 (NCAM1) genes. The four genes have been associated with addictions, although TTC12 and ANKK1 showed the strongest associations. In silico and in vitro studies revealed that ANKK1 is functionally related to the dopaminergic system, in particular with DRD2. In antisocial alcoholism, epistasis between ANKK1 TaqIA and DRD2 C957T SNVs has been described. This clinical finding has been supported by the study of ANKK1 expression in peripheral blood mononuclear cells of alcoholic patients and controls. Regarding the ANKK1 protein, there is direct evidence of its location in adult and developing central nervous system. Together, these findings of the ANKK1 gene and its protein suggest that the TaqIA SNV is a marker of brain differences, both in structure and in dopaminergic function, that increase individual risk to addiction development.

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.

[A pharmacogenetic analysis of dopaminergic and opioidergic genes in opioid addicts treated with the combination of naltrexone and guanfacine]

AIM

To evaluate an effect of opioid receptor and dopamine system gene polymorphisms on the efficacy of combined treatment with oral naltrexone and guanfacine in a randomized double blinded double dummy placebo controlled clinical trial.

MATERIAL AND METHODS

Three hundred and one patients with opioid dependence were randomized into 4 treatment groups: naltrexone 50 mg/day + guanfacine 1 mg/day (N+G); naltrexone + placebo guanfacine (N+GP); placebo naltrexone + guanfacine (NP+G); double placebo (NP+GP). The primary outcome was treatment retention. All enrolled participants were genotyped for polymorphisms in the following genes: mu- (OPRM1), kappa-opioid receptors (OPRK1), catechol-O-methyltransferase (COMT), dopamine receptors types 2 (DRD2) and 4 (DRD4), dopamine-beta-hydroxylase, and dopamine transporter (SLC6A3, DAT1) and alpha-2-adrenoreceptor (ADRA2A) a pharmacological target of guanfacine.

RESULTS

The efficacy of the combination of naltrexone and guanfacine was comparable to naltrexone monotherapy. Regardless of treatment, several gene polymorphisms were associated with higher chance to complete the treatment program: allele Т DRD4 - 521 С/Т (rs1800955) (р=0.039; OR (95% CI)=3.7 (1.1-12.7); log-rank test: р=0.01); allele С DRD2 С957Т (rs6277) (р=0.03; HR=0.6 (0.34-0.95); genotype combination: DRD4 VNTR (LL) + OPRM1 A118G (rs1799971) (AA), р=0.051; DRD2 C957T (ТТ) + OPRM1 (rs1074287) (СС), р=0.025; DRD2 - 141С (II) + OPRM1 (rs510769) (АА), р=0.035; DBH Fau(СС) + OPRM1 (rs1074287) (СС), р=0.0497. Regardless of treatment several polymorphisms were associated with high risk of relapse: allele Т (rs510769) OPRM1 (р=0.053), allele А (rs1799971, A118G) OPRM1 (р=0.056), allele S exon III 48 bp DRD4 VNTR (р=0.001; HR=3.1 (ДИ 95% 1.57-6.18); genotype combinations: DRD4 - 521 С/Т (ТТ) + DRD2 Nco I (TT), р=0.026; DRD4 -521 С/Т (ТТ) + DRD2 -141 С (II), р=0.011; DRD4 - 521 С/Т (ТТ) + OPRM1 A118G (rs1799971) (AA), р=0.011; DRD2 Nco I(ТТ) + ADRA2A (СС), р=0.012; DRD2 Nco I(ТТ) + OPRM1 A118G (AA), р=0.02. The effects dependent on the treatment group were as follows: 1) in the N+G group, patients with the DRD4 -521 С/Т TT genotype had higher probability of completion of treatment program in comparison with other genotypes (CC and CT) (log-rank test: p=0.002); 2) in NP + GP group, patients with the OPRM1 rs510769 T allele had higher risk of relapse compared to the genotype GG (p=0.008) (FDR p<0.0125).

CONCLUSION

The additive effect of opioid receptor genes and dopaminergic system genes on outcomes of treatment opioid dependence with oral naltrexone and guanfacine was shown. Pharmacological effects of naltrexone and guanfacine were associated with genetic variants of the DRD4 - 521C/T polymorphism, since its effect was shown only in the N+G group. The effect of the OPRM1 rs510769 polymorphism was demonstrated in the double placebo group that was associated with personality traits (temperament, character) and determined compliance. Genetic analysis is useful for determining potential responders to treatment of opioid dependence; genotyping can increase the efficacy of pharmacotherapy.

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.

The ANKK1/DRD2 locus is a genomic substrate for affective priming and recognition of angry faces

INTRODUCTION

Ankyrin repeat and kinase domain containing I (ANKK1) and dopamine D2 receptor (DRD2) genes have been associated with psychopathic traits in clinical samples. On the other hand, individuals high in psychopathy show reduced affective priming and deficits in facial expression recognition. We have hypothesized that these emotion-related cognitive phenomena are associated with Taq IA (rs18000497) SNP (single nucleotide polymorphism) of the ANKK1 gene and with C957T (rs6277) SNP of the DRD2 gene.

METHODS

We performed a genetic association analysis in 94 self-reported Caucasian healthy volunteers. The participants completed 144 trials of an affective priming task, in which primes and targets were emotional words. They also had to recognize 64 facial expressions of happiness, sadness, anger, and fear in an expression recognition task. Regarding the genetic analyses, Taq IA and C957T SNPs were genotyped.

RESULTS

We found that the C957T SNP TT genotype was associated with a stronger priming effect and a better recognition of angry expressions. No associations were found for the Taq IA SNP. In addition, in silico analysis demonstrated that C957T SNP is a marker of a regulatory sequence at the 5' UTR of ANKK1 gene, thus suggesting the involvement of the whole ANKK1/DRD2 locus in cognitive-emotional processing.

CONCLUSIONS

These results suggest that affective priming and recognition of angry facial expressions are endophenotypes that lie on the pathway between the ANKK1/DRD2 locus and some deviant phenotypes.

[Stabilization of remission in patients with opioid dependence with naltrexone implant: a pharmacogenetic approach]

AIM

To evaluate the effect of opioid receptor genes and dopamine system genes polymorphisms on treatment outcomes of opioid dependence with implantable and oral naltrexone.

MATERIAL AND METHODS

Authors carried out a randomized double-blind, double-dummy, placebo-controlled clinical trial. Three hundred and six patients with opioid dependence were randomized into 3 equal treatment groups. The first group received implantation of 1000 mg naltrexone every 2 months during 6 months + oral naltrexone placebo; the second group - placebo implant every 2 months + oral naltrexone (50mg/day) and the third group - placebo implant + oral naltrexone placebo. It was genotyped polymorphisms in the following genes: mu-opioid receptor (OPRM1), kappa-opioid receptor (OPRK1), catechol-O-methyltransferase (COMT), dopamine receptors types 2 (DRD2) and 4 (DRD4), dopamine-beta-hydroxylase, and dopamine transporter (DAT1).

RESULTS

Regardless of treatment several polymorphisms of these genes were associated with high risk of relapse: an allele L (2R) DRD4 120bp (p=0.05; OR (95% CI)=3.3(1.1-10.1)); an allele С DRD2 NcoI (р=0,051; OR (95% CI)=2,86 (1,09-7,52)); the genotype 9.9 DAT VNTR 40bp (р=0,04; OR (95% CI)=1,4 (1,3-1,5)); on the contrary, (СС+СТ)-(ТТ)) variants of OPRK1-DRD2Ncol increased a chance to complete treatment program (р=0,004; OR (95% CI)=7.4 (1.8-30.4)), Kaplan-Meier survival analysis (р=0,016). The probability of completing treatment program by the carriers of these variants was higher in the oral naltrexone group (p=0.016), lower in the double placebo group (p=0.015), but did not influence on treatment outcomes in the naltrexone-implant group.

CONCLUSION

Naltrexone-implant is a highly effective medication for treatment of opioid dependence and its effectiveness exceeds that of oral naltrexone and placebo. The study has shown the joint influence of opioid receptor genes and genes of dopaminergic system on treatment outcomes of opioid dependence. Genetic analysis is useful for determining potential responders to naltrexone treatment of opioid dependence.

Early intervention following trauma may mitigate genetic risk for PTSD in civilians: a pilot prospective emergency department study

BACKGROUND

Civilian posttraumatic stress disorder (PTSD) and combat PTSD are major public health concerns. Although a number of psychosocial risk factors have been identified related to PTSD risk, there are no accepted, robust biological predictors that identify who will develop PTSD or who will respond to early intervention following trauma. We wished to examine whether genetic risk for PTSD can be mitigated with an early intervention.

METHOD

65 emergency department patients recruited in 2009-2010 at Grady Memorial Hospital in Atlanta, Georgia, who met criterion A of DSM-IV PTSD received either 3 sessions of an exposure intervention, beginning in the emergency department shortly after trauma exposure or assessment only. PTSD symptoms were assessed 4 and 12 weeks after trauma exposure. A composite additive risk score was derived from polymorphisms in 10 previously identified genes associated with stress-response (ADCYAP1R1, COMT, CRHR1, DBH, DRD2, FAAH, FKBP5, NPY, NTRK2, and PCLO), and gene x treatment effects were examined. The intervention included 3 sessions of imaginal exposure to the trauma memory and additional exposure homework. The primary outcome measure was the PTSD Symptom Scale-Interview Version or DSM-IV-based PTSD diagnosis in patients related to genotype and treatment group.

RESULTS

A gene x intervention x time effect was detected for individual polymorphisms, in particular the PACAP receptor, ADCYAP1R1, as well as with a combined genotype risk score created from independent SNP markers. Subjects who did not receive treatment had higher symptoms than those who received intervention. Furthermore, subjects with the "risk" genotypes who did not receive intervention had higher PTSD symptoms compared to those with the "low-risk" or "resilience" genotypes or those who received intervention. Additionally, PTSD symptoms correlated with level of genetic risk at week 12 (P < .005) in the assessment-only group, but with no relationship in the intervention group, even after controlling for age, sex, race, education, income, and childhood trauma. Using logistic regression, the number of risk alleles was significantly associated with likelihood of PTSD diagnosis at week 12 (P < .05).

CONCLUSIONS

This pilot prospective study suggests that combined genetic variants may serve to predict those most at risk for developing PTSD following trauma. A psychotherapeutic intervention initiated in the emergency department within hours of the trauma may mitigate this risk. The role of genetic predictors of risk and resilience should be further evaluated in larger, prospective intervention and prevention trials.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00895518.

Dopamine and glucose, obesity, and reward deficiency syndrome

Obesity as a result of overeating as well as a number of well described eating disorders has been accurately considered to be a world-wide epidemic. Recently a number of theories backed by a plethora of scientifically sound neurochemical and genetic studies provide strong evidence that food addiction is similar to psychoactive drug addiction. Our laboratory has published on the concept known as Reward Deficiency Syndrome (RDS) which is a genetic and epigenetic phenomena leading to impairment of the brain reward circuitry resulting in a hypo-dopaminergic function. RDS involves the interactions of powerful neurotransmitters and results in abnormal craving behavior. A number of important facts which could help translate to potential therapeutic targets espoused in this focused review include: (1) consumption of alcohol in large quantities or carbohydrates binging stimulates the brain’s production of and utilization of dopamine; (2) in the meso-limbic system the enkephalinergic neurons are in close proximity, to glucose receptors; (3) highly concentrated glucose activates the calcium channel to stimulate dopamine release from P12 cells; (4) a significant correlation between blood glucose and cerebrospinal fluid concentrations of homovanillic acid the dopamine metabolite; (5) 2-deoxyglucose (2DG), the glucose analog, in pharmacological doses is associated with enhanced dopamine turnover and causes acute glucoprivation. Evidence from animal studies and fMRI in humans support the hypothesis that multiple, but similar brain circuits are disrupted in obesity and drug dependence and for the most part, implicate the involvement of DA-modulated reward circuits in pathologic eating behaviors. Based on a consensus of neuroscience research treatment of both glucose and drug like cocaine, opiates should incorporate dopamine agonist therapy in contrast to current theories and practices that utilizes dopamine antagonistic therapy. Considering that up until now clinical utilization of powerful dopamine D2 agonists have failed due to chronic down regulation of D2 receptors newer targets based on novel less powerful D2 agonists that up-regulate D2 receptors seems prudent. We encourage new strategies targeted at improving DA function in the treatment and prevention of obesity a subtype of reward deficiency.

From Pavlov to PTSD: the extinction of conditioned fear in rodents, humans, and anxiety disorders

Nearly 100 years ago, Ivan Pavlov demonstrated that dogs could learn to use a neutral cue to predict a biologically relevant event: after repeated predictive pairings, Pavlov's dogs were conditioned to anticipate food at the sound of a bell, which caused them to salivate. Like sustenance, danger is biologically relevant, and neutral cues can take on great salience when they predict a threat to survival. In anxiety disorders such as posttraumatic stress disorder (PTSD), this type of conditioned fear fails to extinguish, and reminders of traumatic events can cause pathological conditioned fear responses for decades after danger has passed. In this review, we use fear conditioning and extinction studies to draw a direct line from Pavlov to PTSD and other anxiety disorders. We explain how rodent studies have informed neuroimaging studies of healthy humans and humans with PTSD. We describe several genes that have been linked to both PTSD and fear conditioning and extinction and explain how abnormalities in fear conditioning or extinction may reflect a general biomarker of anxiety disorders. Finally, we explore drug and neuromodulation treatments that may enhance therapeutic extinction in anxiety disorders.

Hatching the behavioral addiction egg: Reward Deficiency Solution System (RDSS)™ as a function of dopaminergic neurogenetics and brain functional connectivity linking all addictions under a common rubric

BACKGROUND

Following the first association between the dopamine D2 receptor gene polymorphism and severe alcoholism, there has been an explosion of research reports in the psychiatric and behavioral addiction literature and neurogenetics. With this increased knowledge, the field has been rife with controversy. Moreover, with the advent of Whole Genome-Wide Studies (GWAS) and Whole Exome Sequencing (WES), along with Functional Genome Convergence, the multiple-candidate gene approach still has merit and is considered by many as the most prudent approach. However, it is the combination of these two approaches that will ultimately define real, genetic allelic relationships, in terms of both risk and etiology. Since 1996, our laboratory has coined the umbrella term Reward Deficiency Syndrome (RDS) to explain the common neurochemical and genetic mechanisms involved with both substance and non-substance, addictive behaviors.

METHODS

This is a selective review of peer-reviewed papers primary listed in Pubmed and Medline.

RESULTS

A review of the available evidence indicates the importance of dopaminergic pathways and resting-state, functional connectivity of brain reward circuits.

DISCUSSION

Importantly, the proposal is that the real phenotype is RDS and impairments in the brain's reward cascade, either genetically or environmentally (epigenetically) induced, influence both substance and non-substance, addictive behaviors. Understanding shared common mechanisms will ultimately lead to better diagnosis, treatment and prevention of relapse. While, at this juncture, we cannot as yet state that we have "hatched the behavioral addiction egg", we are beginning to ask the correct questions and through an intense global effort will hopefully find a way of "redeeming joy" and permitting homo sapiens live a life, free of addiction and pain.

Updated findings of the association and functional studies of DRD2/ANKK1 variants with addictions

Both nicotine and alcohol addictions are severe public health hazards worldwide. Various twin and family studies have demonstrated that genetic factors contribute to vulnerability to these addictions; however, the susceptibility genes and the variants underlying them remain largely unknown. Of susceptibility genes investigated for addictions, DRD2 has received much attention. Considering new evidence supporting the association of DRD2 and its adjacent gene ankyrin repeat and kinase domain containing 1 (ANKK1) with various addictions, in this paper, we provide an updated view of the involvement of variants in DRD2 and ANKK1 in the etiology of nicotine dependence (ND) and alcohol dependence (AD) based on linkage, association, and molecular studies. This evidence shows that both genes are significantly associated with addictions; however the association with ANKK1 appears to be stronger. Thus, both more replication studies in independent samples and functional studies of some of these variants are warranted.

Aversive priming: cognitive processing of threatening stimuli is facilitated by aversive primes

It would be reasonable to expect that our previous experience regarding a stimulus that predicts harm would make the subsequent identification of that stimulus easier when harm happens again. Forty-eight volunteers were submitted to both phases of this sequence of events: learning of the predictive relationship and later priming. A face with neutral expression (CS+) was paired with a moderately aversive electric shock and another (CS-) with a neutral tone. Subsequently, these two faces, as well as other known and new faces, were presented for familiarity judgments. Both the CS+ and the CS- faces were preceded by an aversive stimulus (aversive prime) in one occasion and by a neutral stimulus (neutral prime) in another. The familiarity judgment regarding the CS+ was faster after the aversive prime than after the neutral prime, but there was no difference regarding the CS-. The differential effect of the aversive prime over the CS+ and the CS- showed a significant but small correlation with the differential skin conductance response to CS+ and CS- (signal learning), and with the differential evaluation of those stimuli in terms of like-dislike (evaluative learning). The scope of these results, as well as the usefulness of this methodological model, is discussed.

C957T polymorphism of the dopamine D2 receptor gene is associated with motor learning and heart rate

Genetic variants that are related to the dopaminergic system have been frequently found to be associated with various neurological and mental disorders. Here, we studied the relationships between some of these genetic variants and some cognitive and psychophysiological processes that are implicated in such disorders. Two single nucleotide polymorphisms were chosen: one in the dopamine D2 receptor gene (rs6277-C957T) and one in the catechol-O-methyltransferase gene (rs4680-Val158Met), which is involved in the metabolic degradation of dopamine. The performance of participants on two long-term memory tasks was assessed: free recall (declarative memory) and mirror drawing (procedural motor learning). Heart rate (HR) was also monitored during the initial trials of the mirror-drawing task, which is considered to be a laboratory middle-stress generator (moderate stress), and during a rest period (low stress). Data were collected from 213 healthy Caucasian university students. The C957T C homozygous participants showed more rapid learning than the T allele carriers in the procedural motor learning task and smaller differences in HR between the moderate- and the low-stress conditions. These results provide useful information regarding phenotypic variance in both healthy individuals and patients.

Catecholaminergic depletion in nucleus accumbens enhances trace conditioning

PURPOSE

To examine the effect of dopamine depletion in nucleus accumbens on trace conditioning; to distinguish the role of core and shell sub-regions, as far as possible.

MATERIAL/METHODS

6-hydroxydopamine was used to lesion dopamine terminals within the core and shell accumbens. Experiment 1 assessed conditioning to a tone conditioned stimulus that had previously been paired with footshock (unconditioned stimulus) at a 30s trace interval. Experiment 2 subsequently assessed contiguous conditioning (at 0s trace) using a light conditioned stimulus directly followed by the unconditioned stimulus.

RESULTS

Both sham and shell-lesioned animals showed the normal trace effect of reduced conditioning to the trace conditioned stimulus but 6-hydroxydopamine injections targeted on the core subregion of the nucleus accumbens abolished this effect and enhanced conditioning to the trace conditioned stimulus. However, the depletion produced by this lesion placement extended to the shell. In Experiment 2 (at 0s trace), there was no effect of either lesion placement as all animals showed comparable levels of conditioning to the light conditioned stimulus. Neurochemical analysis across core, shell and comparison regions showed some effects on noradrenalin as well as dopamine.

CONCLUSIONS

The pattern of changes in noradrenalin did not systematically relate to the observed behavioural changes after core injections. The pattern of changes in dopamine suggested that depletion in core mediated the increased conditioning to the trace conditioned stimulus seen in the present study. However, the comparison depletion restricted to the shell subregion was less substantial, and a role for secondarily affected brain regions cannot be excluded.

A review on experimental and clinical genetic associations studies on fear conditioning, extinction and cognitive-behavioral treatment

Fear conditioning and extinction represent basic forms of associative learning with considerable clinical relevance and have been implicated in the pathogenesis of anxiety disorders. There is considerable inter-individual variation in the ability to acquire and extinguish conditioned fear reactions and the study of genetic variants has recently become a focus of research. In this review, we give an overview of the existing genetic association studies on human fear conditioning and extinction in healthy individuals and of related studies on cognitive-behavioral treatment (CBT) and exposure, as well as pathology development after trauma. Variation in the serotonin transporter (5HTT) and the catechol-o-methyltransferase (COMT) genes has consistently been associated with effects in pre-clinical and clinical studies. Interesting new findings, which however require further replication, have been reported for genetic variation in the dopamine transporter (DAT1) and the pituitary adenylate cyclase 1 receptor (ADCYAP1R1) genes, whereas the current picture is inconsistent for variation in the brain-derived neurotrophic factor (BDNF) gene. We end with a discussion of the findings and their limitations, as well as future directions that we hope will aid the field to develop further.