Reward sensitivity and the D2 dopamine receptor gene: A case-control study of binge eating disorder

Mapping Treatment Advances in the Neurobiology of Binge Eating Disorder: A Concept Paper

Binge eating disorder (BED) is a complex and heritable mental health disorder, with genetic, neurobiological, neuroendocrinological, environmental and developmental factors all demonstrated to contribute to the aetiology of this illness. Although psychotherapy is the gold standard for treating BED, a significant subgroup of those treated do not recover. Neurobiological research highlights aberrances in neural regions associated with reward processing, emotion processing, self-regulation and executive function processes, which are clear therapeutic targets for future treatment frameworks. Evidence is emerging of the microbiota-gut-brain axis, which may mediate energy balance, high-lighting a possible underlying pathogenesis factor of BED, and provides a potential therapeutic strategy.

Prefrontal-Limbic Circuitry Is Associated With Reward Sensitivity in Nonhuman Primates

BACKGROUND

Abnormal reward sensitivity is a risk factor for psychiatric disorders, including eating disorders such as overeating and binge-eating disorder, but the brain structural mechanisms that underlie it are not completely understood. Here, we sought to investigate the relationship between multimodal whole-brain structural features and reward sensitivity in nonhuman primates.

METHODS

Reward sensitivity was evaluated through behavioral economic analysis in which monkeys (adult rhesus macaques; 7 female, 5 male) responded for sweetened condensed milk (10%, 30%, 56%), Gatorade, or water using an operant procedure in which the response requirement increased incrementally across sessions (i.e., fixed ratio 1, 3, 10). Animals were divided into high (n = 6) or low (n = 6) reward sensitivity groups based on essential value for 30% milk. Multimodal magnetic resonance imaging was used to measure gray matter volume and white matter microstructure. Brain structural features were compared between groups, and their correlations with reward sensitivity for various stimuli was investigated.

RESULTS

Animals in the high sensitivity group had greater dorsolateral prefrontal cortex, centromedial amygdaloid complex, and middle cingulate cortex volumes than animals in the low sensitivity group. Furthermore, compared with monkeys in the low sensitivity group, high sensitivity monkeys had lower fractional anisotropy in the left dorsal cingulate bundle connecting the centromedial amygdaloid complex and middle cingulate cortex to the dorsolateral prefrontal cortex, and in the left superior longitudinal fasciculus 1 connecting the middle cingulate cortex to the dorsolateral prefrontal cortex.

CONCLUSIONS

These results suggest that neuroanatomical variation in prefrontal-limbic circuitry is associated with reward sensitivity. These brain structural features may serve as predictive biomarkers for vulnerability to food-based and other reward-related disorders.

Genetic variation in the dopamine system is associated with mixed-strategy decision-making in patients with Parkinson's disease

Decision-making during mixed-strategy games requires flexibly adapting choice strategies in response to others' actions and dynamically tracking outcomes. Such decisions involve diverse cognitive processes, including reinforcement learning, which are affected by disruptions to the striatal dopamine system. We therefore investigated how genetic variation in dopamine function affected mixed-strategy decision-making in Parkinson's disease (PD), which involves striatal dopamine pathology. Sixty-six PD patients (ages 49-85, Hoehn and Yahr Stages 1-3) and 22 healthy controls (ages 54-75) competed in a mixed-strategy game where successful performance depended on minimizing choice biases (i.e., flexibly adapting choices trial by trial). Participants also completed a fixed-strategy task that was matched for sensory input, motor outputs and overall reward rate. Factor analyses were used to disentangle cognitive from motor aspects within both tasks. Using a within-subject, multi-centre design, patients were examined on and off dopaminergic therapy, and genetic variation was examined via a multilocus genetic profile score representing the additive effects of three single nucleotide polymorphisms (SNPs) that influence dopamine transmission: rs4680 (COMT Val158 Met), rs6277 (C957T) and rs907094 (encoding DARPP-32). PD and control participants displayed comparable mixed-strategy choice behaviour (overall); however, PD patients with genetic profile scores indicating higher dopamine transmission showed improved performance relative to those with low scores. Exploratory follow-up tests across individual SNPs revealed better performance in individuals with the C957T polymorphism, reflecting higher striatal D2/D3 receptor density. Importantly, genetic variation modulated cognitive aspects of performance, above and beyond motor function, suggesting that genetic variation in dopamine signalling may underlie individual differences in cognitive function in PD.

Appetitive and Aversive Motivation in Dysregulated Behaviors: A Meta-Analysis

Appetitive and aversive motivation are prominent in theories of dysregulated behaviors. The authors conducted a meta-analysis of the association between individual differences in appetitive and aversive motivation and several dysregulated behaviors (i.e., alcohol use, marijuana use, tobacco use, binge eating, aggression, gambling, and nonsuicidal self-injury). Alcohol use (r = .17, k = 141), marijuana use (r = .13, k = 23), aggression (r = .22, k = 52), and gambling (r = .08, k = 55) were all significantly positively related to appetitive motivation. Binge eating (r = .28, k = 34) and self-injury (r = .17, k = 10) were significantly positively related to aversive motivation. Effect sizes were similar to the median effect size in personality research. Together, these results provide some evidence that some dysregulated behaviors are more correlated with approach motivation, whereas others are more correlated with aversive motivation, which may indicate distinct etiological pathways.

Striatal dopamine D2 receptor availability as a predictor of subsequent alcohol use in social drinkers

BACKGROUND AND AIMS

Whereas striatal dopamine D2 receptor (D2R) availability has shown to be altered in individuals with alcohol use disorder (AUD) and in healthy individuals with a family history of AUD, the role of D2R in the development of AUD is unknown. In this positron emission tomography (PET) study, we measured whether D2R availability is associated with subsequent alcohol use and alcohol-related factors, at a follow-up 8 to 16 years post-PET scan, in social drinkers.

DESIGN

Longitudinal study investigating the association between PET data and later self-report measures in healthy individuals.

SETTING

Academic research imaging centre in Stockholm, Sweden.

PARTICIPANTS

There were 71 individuals (68 of whom had evaluable PET data, 5 females, 42.0 years mean age) from a series of previous PET studies.

MEASUREMENTS

One PET examination with the D2R antagonist radioligand [11 C]raclopride at baseline and self-report measures assessing alcohol use, drug use, impulsivity, reward sensitivity and family history of alcohol or substance use disorder at follow-up.

FINDINGS

We found no evidence for an association between D2R availability and later alcohol use (B = -0.019, B 95% CI = -0.043 to -0.006, P = 0.147) nor for the majority of the alcohol-related factors (B 95% CI = -0.034 to 0.004, P = 0.273-0.288). A negative association with a small effect size was found between D2R availability and later impulsivity (B = -0.017, B 95% CI = -0.034 to -0.001, P = 0.046).

CONCLUSIONS

Low striatal dopamine D2 receptor availability may not be a strong predictor in the development of alcohol use disorder.

Gene variants in eating disorders. Focus on anorexia nervosa, bulimia nervosa, and binge-eating disorder

Eating disorders such as anorexia nervosa, bulimia nervosa and binge-eating disorder, have a deep social impact, concluding with death in cases of severe disease. Eating disorders affect up to 5% of the population in the industrialized countries, but probably the phenomenon is under-detection and under-diagnosis. Eating disorders are multifactorial disorders, resulting from the interaction between environmental triggers, psychological factors, but there is also a strong genetic component. In fact, genetic factors predispose for approximately 33-84% to anorexia nervosa, 28-83% to bulimia nervosa, and 41-57% to binge eating disorder. Twins and family studies have provided an unassailable proof on the heritability of these disorders. Other types of genetic studies, including genome-wide association studies, whole genome sequencing and linkage analysis, allowed to identify the genes and their variants associated with eating disorders and moreover global collaborative efforts have led to delineate the etiology of these disorders. Next Generation Sequencing technologies can be considered as an ideal diagnostic approach to identify not only the common variants, such as single nucleotide polymorphism, but also rare variants. Here we summarize the present knowledge on the molecular etiology and genetic determinants of eating disorders including serotonergic genes, dopaminergic genes, opioid genes, appetite regulation genes, endocannabinoid genes and vitamin D3.

Prenatal Effects of Nicotine on Obesity Risks: A Narrative Review

Nicotine usage by mothers throughout pregnancy has been observed to relate to numerous deleterious effects in children, especially relating to obesity. Children who have prenatally been exposed to nicotine tend to have lower birth weights, with an elevated risk of becoming overweight throughout development and into their adolescent and adult life. There are numerous theories as to how this occurs: catch-up growth theory, thrifty phenotype theory, neurotransmitter or endocrine imbalances theory, and a more recent examination on the genetic factors relating to obesity risk. In addition to the negative effect on bodyweight and BMI, individuals with obesity may also suffer from numerous comorbidities involving metabolic disease. These may include type 1 and 2 diabetes, high cholesterol levels, and liver disease. Predisposition for obesity with nicotine usage may also be associated with genetic risk alleles for obesity, such as the DRD2 A1 variant. This is important for prenatally nicotine-exposed individuals as an opportunity to provide early prevention and intervention of obesity-related risks.

DRD2 and BDNF polymorphisms are associated with binge eating disorder in patients with weight regain after bariatric surgery

AIM

The aim of this study was to analyze the association and susceptibility of Single Nucleotide Polymorphisms (SNPs) in the DRD2 and BDNF genes with BED in patients with weight regain in the postoperative period of bariatric surgery.

METHODS

One hundred and seventy-seven individuals who underwent bariatric surgery with weight regain were evaluated and divided into two groups according to the BED diagnostic. The individuals were submitted to an anthropometric evaluation, analysis of the presence of BED using a validated questionnaire, and blood collection for genotyping of the polymorphisms rs6265 (BDNF) and rs1800497 (DRD2) by real-time polymerase chain reaction (RT-PCR).

RESULTS

The presence of wild-type alleles for rs1800497 (CC) and rs6265 (GG) was more frequent in patients without BED. Nevertheless, the presence of one or two variant alleles for rs1800497 (CT + TT) and rs6265 (GA + AA) was more frequent in patients with BED. The combination of the two studied SNPs prevailed in patients with BED.

CONCLUSIONS

The presence of allele frequency of rs1800497 SNP in the DRD2 gene and rs6265 SNP in the BDNF gene, isolated and/or combined, indicated an additional risk for the development of BED in patients with obesity, especially in the context of weight regain.

LEVEL OF EVIDENCE

III (evidence obtained from the case-control analytic study).

Nutrient intake, dietary patterns, and anthropometric variables of children with ADHD in comparison to healthy controls: a case-control study

BACKGROUND

Poor health behaviors and variables are recently more documented in attention-deficit hyperactivity disorder (ADHD) lifestyle which might be relevant to the pathophysiology of this disorder. The objective of this case-control study was to assess the nutrient intake, dietary patterns, and anthropometric variables in children with ADHD compared to normal peers.

METHOD

One hundred children diagnosed with ADHD were included and compared to 100 healthy, sex-matched normal children as the control group. Anthropometric indices, macronutrients, and micronutrients were measured and compared in both groups.

RESULTS

ADHD children were significantly consuming more simple sugars, tea, ready-made meals but less protein, vitamin B1, vitamin B2, vitamin C, zinc and calcium compared to the control group. The body mass index (BMI) and waist circumference of children with ADHD were significantly higher and were related to the severity and type of the disease.

CONCLUSION

Unhealthy eating behavior is more frequent in children with ADHD, compared to normal children which might warrant lifestyle intervention in this disorder.

Taste of Fat and Obesity: Different Hypotheses and Our Point of View

Obesity results from a temporary or prolonged positive energy balance due to an alteration in the homeostatic feedback of energy balance. Food, with its discriminative and hedonic qualities, is a key element of reward-based energy intake. An alteration in the brain reward system for highly palatable energy-rich foods, comprised of fat and carbohydrates, could be one of the main factors involved in the development of obesity by increasing the attractiveness and consumption of fat-rich foods. This would induce, in turn, a decrease in the taste of fat. A better understanding of the altered reward system in obesity may open the door to a new era for the diagnosis, management and treatment of this disease.

Hypothesizing in the Face of the Opioid Crisis Coupling Genetic Addiction Risk Severity (GARS) Testing with Electrotherapeutic Nonopioid Modalities Such as H-Wave Could Attenuate Both Pain and Hedonic Addictive Behaviors

In the United States, amid the opioid overdose epidemic, nonaddicting/nonpharmacological proven strategies are available to treat pain and manage chronic pain effectively without opioids. Evidence supporting the long-term use of opioids for pain is lacking, as is the will to alter the drug-embracing culture in American chronic pain management. Some pain clinicians seem to prefer classical analgesic agents that promote unwanted tolerance to analgesics and subsequent biological induction of the "addictive brain". Reward genes play a vital part in modulation of nociception and adaptations in the dopaminergic circuitry. They may affect various sensory and affective components of the chronic pain syndromes. The Genetic Addiction Risk Severity (GARS) test coupled with the H-Wave at entry in pain clinics could attenuate pain and help prevent addiction. The GARS test results identify high-risk for both drug and alcohol, and H-Wave can be initiated to treat pain instead of opioids. The utilization of H-Wave to aid in pain reduction and mitigation of hedonic addictive behaviors is recommended, notwithstanding required randomized control studies. This frontline approach would reduce the possibility of long-term neurobiological deficits and fatalities associated with potent opioid analgesics.

Initial Study on COMT and DRD2 Gene Polymorphisms as Well as the Influence of Temperament and Character Trait on the Severity of Alcohol Craving in Alcohol-Dependent Patients

The main aim of this work was to determine the impact of COMT and DRD2 gene polymorphisms together with temperament and character traits on alcohol craving severity alcohol-dependent persons. The sample comprised of 89 men and 16 women (aged 38±7). For the sake of psychological assessment various analytic methods have been applied like the Short Alcohol Dependence Data Questionnaire (SADD), Penn Alcohol Craving Scale (PACS) or Temperament and Character Inventory (TCI) test. The SNP polymorphism of the analyzed genes was determined by Real Time PCR test. The results showed, that the COMT polymorphismmay have an indirected relationship with the intensity and changes in alcohol craving during abstinence. The DRD2 receptor gene polymorphisms are related with the intensity of alcohol craving. It seems that the character traits like “self-targeting”, including “self-acceptance”, are more closely related to the severity of alcohol craving and polymorphic changes in the DRD2 receptor than temperamental traits. Although this is a pilot study the obtained results appeared to be promising and clearly indicate the link betweengene polymorphisms alcohol craving and its severity.

A review on association and correlation of genetic variants with eating disorders and obesity

Background

Now, eating disorders and obesity and their correlations are danger signal in worldwide which is caused by multifactor and associated with significant mortality and morbidity.

Main body

Every aspect of a patient’s life is influenced by eating disorders and obesity and their correlations. Due to frequent seeing of obese patients, eating disorders have been included in the review as they can sometimes be associated with obesity. However, it should be noted that most patients having eating disorder are at risk to be obese or overweight. This research explores the risk factors for the two disorders, as well as the assessment of medical complications and treatment recommendations for the disorders. In these two disorders, there is also a correlation. The essential consideration is that eating disorders are impulse-control disorders which are similar to addictive behaviors in some aspects. So it is a crying need to treat a patient with obesity and eating disorders simultaneously to ensure success. Genome-wide association studies (GWASs) have increased our knowledge of the pathophysiology of eating disorders (EDs) and obesity and their correlation.

Conclusion

This review enlightens on the summary of eating disorder, obesity, genotypic traits, molecular relations, interaction, correlation, and effect of eating disorder and obesity which outline potential future directions and clinical implications for patients with EDs and obesity.

Neuronal activities during palatable food consumption in the reward system of binge-like eating female rats

Binge eating disorder (BED), characterized by bingeing episodes and compulsivity, is the most prevalent eating disorder; however, little is known about its neurobiological underpinnings. In humans, BED is associated with desensitization of the reward system, specifically, the medial prefrontal cortex (mPFC), nucleus accumbens (Acb), and ventral tegmental area (VTA). Additionally, BED patients feel relieved during bingeing, suggesting that bingeing helps to decrease the negative emotions they were feeling prior to the binge episode. However, the mechanisms that underlie this feeling of relief in BED patients have not been well investigated. To investigate neuronal activity before and during palatable food consumption in BED, we performed in vivo electrophysiological recordings in a binge-like eating rat model (bingeing, n = 12 and non-bingeing, n = 14) and analyzed the firing rate of neurons in the mPFC, Acb, and VTA before and during access to sucrose solution. We also investigated changes in the firing rate of neurons in these regions during and between active bingeing, which may underlie the feeling of relief in BED patients. We found that neuronal firing rates of mPFC and VTA neurons in bingeing rats were lower than those in non-bingeing rats before and during sucrose consumption. Palatable food consumption increased neuronal firing rates during and between active bingeing in bingeing rats. Our results suggest a desynchronization in the activity of reward system regions, specifically in the mPFC, in bingeing rats, which may also contribute to BED. These results are consistent with those of functional magnetic resonance imaging (fMRI) studies that reported decreased activity in the reward system in BED patients. We propose that increased neuronal activity in the mPFC, Acb, or VTA produces an antidepressant effect in rats, which may underlie the sense of relief patients express during bingeing episodes.

A Systematic Review of Genetic Polymorphisms Associated with Binge Eating Disorder

The genetic polymorphisms involved in the physiopathology of binge eating disorder (BED) are currently unclear. This systematic review aims to highlight and summarize the research on polymorphisms that is conducted in the BED. We looked for observational studies where there was a genetic comparison between adults with BED, in some cases also with obesity or overweight, and healthy controls or obesity/overweight without BED. Our protocol was written using PRISMA. It is registered at PROSPERO (identification: CRD42020198645). To identify potentially relevant documents, the following bibliographic databases were searched without a time limit, but until September 2020: PubMed, PsycINFO, Scopus, and Web of Science. In total, 21 articles were included in the qualitative analysis of the systematic review, as they met the eligibility criteria. Within the selected studies, 41 polymorphisms of 17 genes were assessed. Overall, this systematic review provides a list of potentially useful genetic polymorphisms involved in BED: 5-HTTLPR (5-HTT), Taq1A (ANKK1/DRD2), A118G (OPRM1), C957T (DRD2), rs2283265 (DRD2), Val158Met (COMT), rs6198 (GR), Val103Ile (MC4R), Ile251Leu (MC4R), rs6265 (BNDF), and Leu72Met (GHRL). It is important to emphasize that Taq1A is the polymorphism that showed, in two different research groups, the most significant association with BED. The remaining polymorphisms need further evidence to be confirmed.

Associations of the ANKK1 and DRD2 gene polymorphisms with overweight, obesity and hedonic hunger among women from the Northwest of Iran

BACKGROUND

Pleasure from palatable foods can stimulate hedonic eating and, therefore, might be a major culprit for obesity. Dopamine receptor polymorphisms, especially variants in the genes regulating the D2 receptor, including ANKK1 and DRD2, are the prime candidates for assessing the individual differences in hedonic eating. This study was carried out to investigate the possible associations of the T (rs1800497) and Del (rs1799732) alleles with body mass index (BMI) and hedonic hunger among Iranian Azeri women.

METHODS

A total of 372 healthy overweight/obese subjects (BMI ≥ 25 kg/m²) and 159 normal weight individuals (BMI 18.5-24.9 kg/m²) were genotyped for the polymorphisms of ANNK1 and DRD2 genes using PCR-RFLP. BMI and hedonic hunger were also evaluated.

RESULTS

Three hundred and sixty-three (68.36%), 152 (28.63%), and 16 (3.01%) of the participants had CC, CT, and TT genotypes for ANNK1 gene, respectively. Of 515 samples genotyped for DRD2 gene, 315 (60.51%), 173 (33.59%), and 27 (5.24%) had Ins/Ins, Ins/Del, and Del/Del genotypes, respectively. The genotype and genotype frequencies were significantly different between the groups (p = 0.04). Significant differences were observed between the T+ genotype (TT + TC) and the T- genotype (CC) regarding the BMI and hedonic hunger scores (p < 0.05). In addition, Del+ group (Del/Del + Ins/Del) had higher BMI and hedonic hunger scores compared to Del- group (Ins/Ins) (p < 0.05).

CONCLUSIONS

Our findings showed that the frequencies of T and Del alleles were greater in the overweight/obese individuals. Also, the polymorphism of ANKK1 (rs1800497) and polymorphism of the DRD2 gene (rs1799732) showed significant associations with BMI and hedonic hunger.

LEVEL OF EVIDENCE

Level III, case-control study.

Behavior and Substance Addictions in Children: A Behavioral Model and Potential Solutions

Behavior and substance use addictions are increasingly prevalent in children with increased risk for substance abuse and mental health diagnoses in adulthood. This article proposes a comprehensive model of addiction to inform research on the prevention and treatment of childhood addiction, emphasizing skills training, mindfulness training, and broader treatment strategies consistent with acceptance and commitment therapy.

Investigating the relationship between reward sensitivity, impulsivity, and food addiction: A systematic review

OBJECTIVE

The aim of the current research was to identify the extent to which reward sensitivity and impulsivity were related to food addiction.

METHOD

Forty-five studies, published from 2009 to June 2019, investigating reward sensitivity and/or impulsivity with food addiction as measured by the Yale Food Addiction Scale were reviewed.

RESULTS

Reward sensitivity, as measured by the Sensitivity to Reward (SR) scale, was positively associated with food addiction in two studies, but failed to yield consistent results in other studies when measured with the Behavioral Inhibition/Behavioral Activation Scales. Self-report impulsivity, as measured by the Barratt Impulsiveness Scale (BIS-11), was consistently associated with food addiction, with attentional impulsivity and motor impulsivity the most consistent subscales. Similarly, food addiction was also consistently associated with Negative Urgency, Positive Urgency, and Lack of Perseverance as measured by the UPPS-P Impulsive Behavior Scale. Food addiction was inconsistently associated with disinhibition, as measured by behavioral tasks, indicating food addiction appears more aligned with self-report measures of impulsivity.

CONCLUSIONS

Research in this field is dominated by university student, overweight and obese samples. Additional research is required to further tease out these relationships.

Individual differences in dopamine D2 receptor availability correlate with reward valuation

Reward valuation, which underlies all value-based decision-making, has been associated with dopamine function in many studies of nonhuman animals, but there is relatively less direct evidence for an association in humans. Here, we measured dopamine D₂ receptor (DRD2) availability in vivo in humans to examine relations between individual differences in dopamine receptor availability and neural activity associated with a measure of reward valuation, expected value (i.e., the product of reward magnitude and the probability of obtaining the reward). Fourteen healthy adult subjects underwent PET with [¹⁸F]fallypride, a radiotracer with strong affinity for DRD2, and fMRI (on a separate day) while performing a reward valuation task. [¹⁸F]fallypride binding potential, reflecting DRD2 availability, in the midbrain correlated positively with neural activity associated with expected value, specifically in the left ventral striatum/caudate. The present results provide in vivo evidence from humans showing midbrain dopamine characteristics are associated with reward valuation.

Shared Behavioral and Neurocircuitry Disruptions in Drug Addiction, Obesity, and Binge Eating Disorder: Focus on Group I mGluRs in the Mesolimbic Dopamine Pathway

Accumulated data from clinical and preclinical studies suggest that, in drug addiction and states of overeating, such as obesity and binge eating disorder (BED), there is an imbalance in circuits that are critical for motivation, reward saliency, executive function, and self-control. Central to these pathologies and the extensive topic of this Review are the aberrations in dopamine (DA) and glutamate (Glu) within the mesolimbic pathway. Group I metabotropic glutamate receptors (mGlus) are highly expressed in the mesolimbic pathway and are poised in key positions to modulate disruptions in synaptic plasticity and neurotransmitter release observed in drug addiction, obesity, and BED. The use of allosteric modulators of group I mGlus has been studied in drug addiction, as they offer several advantages over traditional orthosteric agents. However, they have yet to be studied in obesity or BED. With the substantial overlap between the neurocircuitry involved in drug addiction and eating disorders, group I mGlus may also provide novel targets for obesity and BED.

The effect of ANKK1 Taq1A and DRD2 C957T polymorphisms on executive function: A systematic review and meta-analysis

Research in healthy adults suggests that C957T polymorphism of the dopamine D2 receptor encoding DRD2 and the Taq1A polymorphism of the neighbouring gene ankyrin repeat and kinase domain containing 1 (ANKK1) alter dopaminergic signalling and may influence prefrontally-mediated executive functions. A systematic review and meta-analysis was carried out on the evidence for the association of DRD2 C957T and ANKK1 Taq1A polymorphisms in performance on tasks relating to the three core domains of executive function: working memory, response inhibition and cognitive flexibility in healthy adults. CINAHL, MEDLINE, PsycARTICLES and PsychINFO databases were searched for predefined key search terms associated with the two polymorphisms and executive function. Studies were included if they investigated a healthy adult population with the mean age of 18-65 years, no psychiatric or neurological disorder and only the healthy adult arm were included in studies with any case-control design. Data from 17 independent studies were included in meta-analysis, separated by the Taq1A and C957T polymorphisms and by executive function tests: working memory (Taq1A, 6 samples, n = 1270; C957 T, 6 samples, n = 977), cognitive flexibility (C957 T, 3 samples, n = 620), and response inhibition (C957 T, 3 samples, n = 598). The meta-analyses did not establish significant associations between these gene polymorphisms of interest and any of the executive function domains. Theoretical implications and methodological considerations of these findings are discussed.

Role of eating disorders-related polymorphisms in obesity pathophysiology

Human biological system provides innumerable neuroendocrine inputs for food intake control, with effects on appetite's modulation and the satiety signs. Its regulation is very complex, engaging several molecular interactions with many tissues, hormones, and neural circuits. Thus, signaling molecules that control food intake are critical for normal energy homeostasis and a deregulation of these pathways can lead to eating disorders and obesity. In line of this, genetic factors have a significantly influence of the regulation of neural circuits controlling the appetite and satiety pathways, as well as the regulation of brain reward systems. Single Nucleotide Polymorphisms (SNPs) in genes related to hypothalamic appetite and satiety mechanisms, further in multiple neurotransmitter systems may contribute to the development of major Eating Disorders (EDs) related to obesity, among them Binge Eating Disorder (BED) and Bulimia Nervosa (BN), which are discussed in this review.

Molecular dynamics simulation of biased agonists at the dopamine D2 receptor suggests the mechanism of receptor functional selectivity

The dopamine D2 receptor (D2R) is the primary target for antipsychotic drugs. Besides schizophrenia, this receptor is linked to dementia, Parkinson's disease, and depression. Recent studies have shown that β-arrestin biased agonists at this receptor treat schizophrenia with less side effects. Although the high resolution structure of this receptor exists, the mechanism of biased agonism at the receptor is unknown. In this study, dopamine, the endogenous unbiased G-protein agonist, MLS1547, a G-protein biased agonist, and UNC9975, a G-protein antagonist and a β-arrestin biased agonist, were docked to a homology model of the whole D2R including all flexible loops, and molecular dynamics simulations were conducted to study the potential mechanisms of biased agonism. Our thorough analysis on the protein-ligand interaction, secondary structure, tertiary structure, structure dynamics, and molecular switches of all three systems indicates that ligand binding to transmembrane 3 might be essential for G-protein recruitment, while ligand binding to transmembrane 6 might be essential for β-arrestin recruitment. Our analysis also suggests changes in both the secondary and the tertiary structures of TM5 and TM7, molecular switches and ICL3 flexibility are important in biased signaling. Communicated by Ramaswamy H. Sarma.

[The interaction effect of ANKK1/DRD2 TaqIA and HTR2C Cys23Ser on approach motivation in schizophrenic patients and normals]

AIM

To evaluate the association of the DRD2 gene and DRD2 x HTR2C interaction with hedonic and activational aspects of approach motivation in schizophrenia.

MATERIAL AND METHODS

Genotypes at polymorphic loci DRD2 rs1800497 and HTR2C rs6318 (Cys23Ser) were identified in a sample that included 174 patients with schizophrenic spectrum disorders and 268 healthy subjects without a family history of psychoses. The participants completed the BIS/BAS and Temporal Experience of Pleasure Scale (TEPS).

RESULTS AND CONCLUSION

A MANCOVA with sex and age as covariates revealed the effect of the 'DRD2 x HTR2C x diagnosis' interaction on the BAS scores (p=0.033). The effect was significant for the Fun-Seeking and Drive scales. Among patients, the carriers of the DRD2 TT/CT x HTR2C GG/G genotype showed the highest scores on the both scales, and those with the minor alleles in the two loci had the lowest ones. Differences between these groups were nominally significant for both the Fun-Seeking and Drive, but did not survive the correction for multiple comparisons. Among controls, subjects without minor alleles demonstrated the highest scores on these two scales. They differed significantly from the carriers of the DRD2 TT/CT+HTR2C GG/G genotype on the Fun-Seeking (p=0.008). No effects of DRD2 and HTR2C on TEPS scores were found. In general, the results of the study can be interpreted in favor of the hypothesis about the role of the HTR2C and DRD2 genes interaction in the variability of the activational aspects of approach motivation in schizophrenia and healthy subjects. However, the lack of differences survived correction for multiple comparisons makes it difficult to interpret the revealed effects.

Complete sequence of the ANKK1 gene in Mexican-Mestizo individuals with obesity, with or without binge eating disorder

BACKGROUND

The aim of this study was to investigate if Mexican-Mestizo individuals with obesity, with or without binge eating disorder (BED), exhibited mutations or other type of genetic variants in the sequence of ANKK1.

SUBJECTS AND METHODS

Fifty unrelated individuals (21-53 years of age) with obesity, of Mexican-Mestizo ethnic origin were included; 25 of them had BED and 25 presented obesity without BED. The diagnosis of BED was based on criteria proposed in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5). Besides, we also analyzed 100 individuals with normal body mass index. DNA from blood leukocytes was amplified by the polymerase chain reaction and all exons of ANKK1 were sequenced.

RESULTS

After ANKK1 sequencing we did not find any mutations; however, we observed various polymorphisms. One polymorphism, rs4938013 in exon 2 showed an association with obesity, whilst rs1800497 (also known as Taq1A) in exon 8, showed an association with BED (P = 0.020). Remarkable, for this study, the number of individuals for both polymorphisms for and additive model was sufficient to derive strong statistical power (80%, with a P < 0.05).

CONCLUSIONS

To our knowledge, this constitutes the first report where the complete sequences of ANKK1 has been analyzed in individuals with obesity, with or without BED. No mutations were found; however, one polymorphism was associated with obesity, with or without BED, and another one was associated with BED.

Nutritional Health Considerations for Persons with Spinal Cord Injury

Chronic spinal cord injury (SCI) often results in morbidity and mortality due to all-cause cardiovascular disease (CVD) and comorbid endocrine disorders. Several component risk factors for CVD, described as the cardiometabolic syndrome (CMS), are prevalent in SCI, with the individual risks of obesity and insulin resistance known to advance the disease prognosis to a greater extent than other established risks. Notably, adiposity and insulin resistance are attributed in large part to a commonly observed maladaptive dietary/nutritional profile. Although there are no evidence-based nutritional guidelines to address the CMS risk in SCI, contemporary treatment strategies advocate more comprehensive lifestyle management that includes sustained nutritional guidance as a necessary component for overall health management. This monograph describes factors in SCI that contribute to CMS risks, the current nutritional profile and its contribution to CMS risks, and effective treatment strategies including the adaptability of the Diabetes Prevention Program (DPP) to SCI. Establishing appropriate nutritional guidelines and recommendations will play an important role in addressing the CMS risks in SCI and preserving optimal long-term health.

Dopamine D2 receptor polymorphism (C957T) is associated with sugar consumption and triglyceride levels in West Mexicans

Genetic variations in the dopamine receptor D2 (DRD2) may alter dopamine signaling and modify the rewarding effects of food. This study aimed to analyze the association of the C957T DRD2 polymorphism with sugar consumption in West Mexican subjects. In a cross-sectional and analytical study, a total of 215 Mexican subjects were enrolled. DRD2 genotyping was performed by an allelic discrimination assay. Habitual dietary intake and the biochemical profile were evaluated. Genotype frequencies of the C957T DRD2 polymorphism were CC (12.1%), CT (40.9%) and TT (47.0%). Carriers of the CC genotype had a higher intake of sugar (g/day) than heterozygotes (67.4 g vs. 41.3 g, p = 0.001) and TT homozygotes (67.4 g vs. 45.2 g, p = 0.004). Also, the habitual consumption of soda (daily or at least 3 times per week) was more frequent among CC genotype carriers compared with heterozygotes (81% vs. 51%, p = 7.5 × 10^-6) and TT homozygotes (81% vs. 57%, p = 2.4 × 10^-4). Furthermore, the CC genotype was associated with elevated serum triglyceride levels (>150 mg/dL) than the CT genotype (OR = 2.80, 95% CI 1.08-7.24, p = 0.034). In conclusion, our results suggest a genetic background associated with sugar consumption among West Mexicans, which may contribute to increases in serum triglyceride levels.

Evaluation of motor proficiency and adiponectin in adolescent students with attention deficit hyperactivity disorder after high-intensity intermittent training

Attention deficit hyperactivity disorder (ADHD) is a chronic condition with frequent comorbidities such as obesity, troubled relationships, low self-esteem, and difficulty in motor proficiency. This study aims to elucidate the effect of high-intensity intermittent training on motor proficiency, adiponectin, and insulin resistance in adolescent students with ADHD disorder. Fifty adolescent students of both genders with ADHD diagnosis participated and assigned into four experimental groups (each group with 15 girls and 10 boys students; two experimental and two control groups). High-intensity intermittent training was performed continuously 3 times a week for 6 weeks in experimental groups. Serum adiponectin level significantly increased in the experimental groups of both genders after 6 weeks intermittent training while insulin resistance levels were markedly decreased. Furthermore, motor proficiency score were significantly improved in the experimental groups of both genders. In addition gender had no significant impact on adiponectin, insulin resistance and motor proficiency rating. The findings of this study suggest that high intensity intermittent training improved physiological systems in ADHD population that leads to reduce risk factors for future development of comorbidities.

Eating disorders: Insights from imaging and behavioral approaches to treatment

Understanding factors that contribute to eating disorders, which affect 13% of females, is critical to developing effective prevention and treatment programs. In this paper, we summarize results from prospective studies that identified factors predicting onset and persistence of eating disorders and core symptom dimensions. Next, implications for intervention targets for prevention, and treatment interventions from the risk- and maintenance-factor findings are discussed. Third, given that evidence suggests eating disorders are highly heritable, implying biological risk and maintenance factors for eating disorders, we offer working hypotheses about biological factors that might contribute to eating disorders, based on extant risk factor findings, theory, and cross-sectional studies. Finally, potentially fruitful directions for future research are presented. We suggest that it would be useful for experimental therapeutics trials to evaluate the effects of reducing the risk factors on future onset of eating pathology and on reducing maintenance factors on the risk for persistence of eating pathology, and encourage researchers to utilize prospective high-risk studies so that knowledge regarding potential intervention targets for prevention and treatment interventions for eating disorders can be advanced. Using the most rigorous research designs should help improve the efficacy of prevention and treatment interventions for eating disorders.

Cognitive impairment and gene expression alterations in a rodent model of binge eating disorder

Binge eating disorder (BED) is defined as recurrent, distressing over-consumption of palatable food (PF) in a short time period. Clinical studies suggest that individuals with BED may have impairments in cognitive processes, executive functioning, impulse control, and decision-making, which may play a role in sustaining binge eating behavior. These clinical reports, however, are limited and often conflicting. In this study, we used a limited access rat model of binge-like behavior in order to further explore the effects of binge eating on cognition. In binge eating prone (BEP) rats, we found novel object recognition (NOR) as well as Barnes maze reversal learning (BM-RL) deficits. Aberrant gene expression of brain derived neurotrophic factor (Bdnf) and tropomyosin receptor kinase B (TrkB) in the hippocampus (HPC)-prefrontal cortex (PFC) network was observed in BEP rats. Additionally, the NOR deficits were correlated with reductions in the expression of TrkB and insulin receptor (Ir) in the CA3 region of the hippocampus. Furthermore, up-regulation of serotonin-2C (5-HT_2C) receptors in the orbitoprefrontal cortex (OFC) was associated with BM-RL deficit. Finally, in the nucleus accumbens (NAc), we found decreased dopamine receptor 2 (Drd2) expression among BEP rats. Taken together, these data suggest that binge eating vegetable shortening may induce contextual and reversal learning deficits which may be mediated, at least in part, by the altered expression of genes in the CA3-OFC-NAc neural network.

Brain on Fire: Incentive Salience, Hedonic Hot Spots, Dopamine, Obesity, and Other Hunger Games

This review examines human feeding behavior in light of psychological motivational theory and highlights the importance of midbrain dopamine (DA). Prospective evidence of both reward surfeit and reward deficit pathways to increased body weight are evaluated, and we argue that it is more complex than an either/or scenario when examining DA's role in reward sensitivity, eating, and obesity. The Taq1A genotype is a common thread that ties the contrasting models of DA reward and obesity; this genotype related to striatal DA is not associated with obesity class per se but may nevertheless confer an increased risk of weight gain. We also critically examine the concept of so-called food addiction, and despite growing evidence, we argue that there is currently insufficient human data to warrant this diagnostic label. The surgical and pharmacological treatments of obesity are discussed, and evidence is presented for the selective use of DA-class drugs in obesity treatment.

The impact of common dopamine D2 receptor gene polymorphisms on D2/3 receptor availability: C957T as a key determinant in putamen and ventral striatum

Dopamine function is broadly implicated in multiple neuropsychiatric conditions believed to have a genetic basis. Although a few positron emission tomography (PET) studies have investigated the impact of single-nucleotide polymorphisms (SNPs) in the dopamine D2 receptor gene (DRD2) on D2/3 receptor availability (binding potential, BP_ND), these studies have often been limited by small sample size. Furthermore, the most commonly studied SNP in D2/3 BP_ND (Taq1A) is not located in the DRD2 gene itself, suggesting that its linkage with other DRD2 SNPs may explain previous PET findings. Here, in the largest PET genetic study to date (n=84), we tested for effects of the C957T and -141C Ins/Del SNPs (located within DRD2) as well as Taq1A on BP_ND of the high-affinity D2 receptor tracer ¹⁸F-Fallypride. In a whole-brain voxelwise analysis, we found a positive linear effect of C957T T allele status on striatal BP_ND bilaterally. The multilocus genetic scores containing C957T and one or both of the other SNPs produced qualitatively similar striatal results to C957T alone. The number of C957T T alleles predicted BP_ND in anatomically defined putamen and ventral striatum (but not caudate) regions of interest, suggesting some regional specificity of effects in the striatum. By contrast, no significant effects arose in cortical regions. Taken together, our data support the critical role of C957T in striatal D2/3 receptor availability. This work has implications for a number of psychiatric conditions in which dopamine signaling and variation in C957T status have been implicated, including schizophrenia and substance use disorders.

Dietary Protein Modifies the Effect of the MC4R Genotype on 2-Year Changes in Appetite and Food Craving: The POUNDS Lost Trial

Background: The melanocortin-4 receptor (MC4R) plays a pivotal role in the regulation of appetite and eating behavior. Variants in the MC4R gene have been related to appetite and obesity.Objective: We aimed to examine whether weight-loss diets modified the effect of the "obesity-predisposing" MC4R genotype on appetite-related measures in a randomized controlled trial.Methods: A total of 811 overweight and obese subjects [25 ≤ body mass index (BMI; kg/m²) ≤ 40] aged 30-70 y were included in the 2-y POUNDS Lost (Preventing Overweight Using Novel Dietary Strategies) trial. We genotyped MC4R rs7227255 in 735 overweight adults and assessed appetite-related characteristics, including craving, fullness, hunger, and prospective consumption, as well as a composite appetite score. We examined the effects of the genotype-by-weight-loss diet intervention interaction on appetite variables by using general linear models in both the whole population and in white participants only.Results: We found that dietary protein intake (low compared with high: 15% of energy compared with 25% of energy, respectively) significantly modified MC4R genetic effects on changes in appetite score and craving (P-interaction = 0.03 and 0.02, respectively) at 2 y, after adjustment for age, sex, ethnicity, baseline BMI, weight change, and baseline perspective phenotype. The obesity-predisposing A allele was associated with a greater increase in overall appetite score (β = 0.10, P = 0.05) and craving (β = 0.13, P = 0.008) compared with the non-A allele among participants who consumed a high-protein diet. MC4R genotype did not modify the effects of fat or carbohydrate intakes on appetite measures. Similar interaction patterns were observed in whites.Conclusion: Our data suggest that individuals with the MC4R rs7227255 A allele rather than the non-A allele might experience greater increases in appetite and food craving when consuming a high-protein weight-loss diet. This trial was registered at clinicaltrials.gov as NCT00072995.

A meta-analysis of the relationship between brain dopamine receptors and obesity: a matter of changes in behavior rather than food addiction?

Addiction to a wide range of substances of abuse has been suggested to reflect a ‘Reward Deficiency Syndrome'. That is, drugs are said to stimulate the reward mechanisms so intensely that, to compensate, the population of dopamine D₂ receptors (DD2R) declines. The result is that an increased intake is necessary to experience the same degree of reward. Without an additional intake, cravings and withdrawal symptoms result. A suggestion is that food addiction, in a similar manner to drugs of abuse, decrease DD2R. The role of DD2R in obesity was therefore examined by examining the association between body mass index (BMI) and the Taq1A polymorphism, as the A1 allele is associated with a 30–40% lower number of DD2R, and is a risk factor for drug addiction. If a lower density of DD2R is indicative of physical addiction, it was argued that if food addiction occurs, those with the A1 allele should have a higher BMI. A systematic review found 33 studies that compared the BMI of those who did and did not have the A1 allele. A meta-analysis of the studies compared those with (A1/A1 and A1/A2) or without (A2/A2) the A1 allele; no difference in BMI was found (standardized mean difference 0.004 (s.e. 0.021), variance 0.000, Z=0.196, P<0.845). It was concluded that there was no support for a reward deficiency theory of food addiction. In contrast, there are several reports that those with the A1 allele are less able to benefit from an intervention that aimed to reduce weight, possibly a reflection of increased impulsivity.

Specific Reaction Patterns to Distinct Positive Emotional Cues Related to Incentive Motivation in Dependence of the Taq1A-Polymorphism: Molecular Genetic Associations of Early and Late Event-Related Potentials

BACKGROUND/AIMS

Early and late event-related potential (ERP) responses, representing early subconscious and late motivational processes, were recorded for positive emotional words related to 'wanting' and 'liking', in dependence of the dopamine-related Taq1A genotype (ANKK1/DRD2). Research suggests that 'wanting' as opposed to 'liking' is related to dopaminergic processes. Therefore, it was hypothesized that risk allele carriers of the Taq1A polymorphism exhibit late ERP changes in reaction to words representing incentive motivation, i.e. 'wanting' (word categories 'lust' and 'anticipation'), but not to words representing 'liking' ('closeness').

METHODS

Seventy-two male participants performed an emotional-word Stroop task during EEG recording and were genotyped according to the Taq1A polymorphism of ANKK1/DRD2.

RESULTS

Positive emotional words related to anticipation and lust revealed blunted responses in the late positive potential (LPP) in carriers of the A1 allele, an effect absent in response to 'liking'-related words. These differences were not evident in the earlier posterior negativity (EPN).

CONCLUSION

As no differences in dependence of the Taq1A genotype were observed in reaction to 'wanting'- and 'liking'-related words in the EPN, but merely in the LPP, it can be assumed that incentive-motivational stimuli only modify motivation-related ERP responses in carriers of the A1 allele of the Taq1A polymorphism, indicating the role of dopamine in late ERP components.

Epistatic interactions involving DRD2, DRD4, and COMT polymorphisms and risk of substance abuse in women with binge-purge eating disturbances

Substance abuse is common in individuals with bulimia-spectrum (binge-purge) eating disturbances, a co-occurrence that has been attributed to shared neurobiological substrates--notably alterations in dopaminergic activity. We examined the implications of variations of selected, dopamine-relevant polymorphisms (DRD2 Taq1A, DRD4 7R, and COMT) for risk of substance abuse in women with binge-purge eating syndromes. We genotyped 183 women (66.1% showing full-threshold BN and 33.9% showing sub-syndromic variants), and assessed lifetime presence of alcohol, cannabis, cocaine, and stimulant abuse or dependence using structured interviews. Tests for main and interaction effects of various allele combinations revealed that individuals who carried high function COMT and low-function DRD4 7R alleles (a combination expected to be associated with higher risk) did indeed show more lifetime substance abuse and, specifically, more cannabis abuse. Our findings suggest that a gene combination that, in theory, codes for low levels of dopaminergic neurotransmission coincides with sensitivity to substance abuse in a sample displaying binge-purge eating-disorder variants.

Fuel not fun: Reinterpreting attenuated brain responses to reward in obesity

There is a well-established literature linking obesity to altered dopamine signaling and brain response to food-related stimuli. Neuroimaging studies frequently report enhanced responses in dopaminergic regions during food anticipation and decreased responses during reward receipt. This has been interpreted as reflecting anticipatory "reward surfeit", and consummatory "reward deficiency". In particular, attenuated response in the dorsal striatum to primary food rewards is proposed to reflect anhedonia, which leads to overeating in an attempt to compensate for the reward deficit. In this paper, we propose an alternative view. We consider brain response to food-related stimuli in a reinforcement-learning framework, which can be employed to separate the contributions of reward sensitivity and reward-related learning that are typically entangled in the brain response to reward. Consequently, we posit that decreased striatal responses to milkshake receipt reflect reduced reward-related learning rather than reward deficiency or anhedonia because reduced reward sensitivity would translate uniformly into reduced anticipatory and consummatory responses to reward. By re-conceptualizing reward deficiency as a shift in learning about subjective value of rewards, we attempt to reconcile neuroimaging findings with the putative role of dopamine in effort, energy expenditure and exploration and suggest that attenuated brain responses to energy dense foods reflect the "fuel", not the fun entailed by the reward.

Shared and unique mechanisms underlying binge eating disorder and addictive disorders

Scientific interest in "food addiction" is growing, but the topic remains controversial. One critique of "food addiction" is its high degree of phenotypic overlap with binge eating disorder (BED). In order to examine associations between problematic eating behaviors, such as binge eating and "food addiction," we propose the need to move past examining similarities and differences in symptomology. Instead, focusing on relevant mechanisms may more effectively determine whether "food addiction" contributes to disordered eating behavior for some individuals. This paper reviews the evidence for mechanisms that are shared (i.e., reward dysfunction, impulsivity) and unique for addiction (i.e., withdrawal, tolerance) and eating disorder (i.e., dietary restraint, shape/weight concern) frameworks. This review will provide a guiding framework to outline future areas of research needed to evaluate the validity of the "food addiction" model and to understand its potential contribution to disordered eating.

The neurobiological basis of binge-eating disorder

Relatively little is known about the neuropathophysiology of binge-eating disorder (BED). Here, the evidence from neuroimaging, neurocognitive, genetics, and animal studies are reviewed to synthesize our current understanding of the pathophysiology of BED. Binge-eating disorder may be conceptualized as an impulsive/compulsive disorder, with altered reward sensitivity and food-related attentional biases. Neuroimaging studies suggest there are corticostriatal circuitry alterations in BED similar to those observed in substance abuse, including altered function of prefrontal, insular, and orbitofrontal cortices and the striatum. Human genetics and animal studies suggest that there are changes in neurotransmitter networks, including dopaminergic and opioidergic systems, associated with binge-eating behaviors. Overall, the current evidence suggests that BED may be related to maladaptation of the corticostriatal circuitry regulating motivation and impulse control similar to that found in other impulsive/compulsive disorders. Further studies are needed to understand the genetics of BED and how neurotransmitter activity and neurocircuitry function are altered in BED and how pharmacotherapies may influence these systems to reduce BED symptoms.

[Genetic aspects of binge eating disorder Part 2. Molecular genetics and pharmacogenetic approaches]

Genetic risk of binge eating disorder (ВЕD) is a consequence of joint participation of many genes, the contribution of each one is small, but the total (additive) effect is significant and greatly influences the age at onset, clinical dynamics and the level of treatment resistance. It is assumed that the carriers of different polymorphic variants of genes and their combinations have different levels of genetic risk. No Genom Wide Association studies of ВЕD has been performed and the analysis of the results of candidate genes studies gives reason to believe that pathogenetically substantiated panel of genes, including serotonin system, BDNF and, especially dopamine and endogenous opioid system, would be most useful, taking into account the mechanism of action of drugs for the ВЕD treatment. Genetic studies with this panel if using evidence-based design, detailed and quantitative analysis of the family history of binge eating can give good results for: 1) assessment of the genetic risk of ВЕD for primary prevention programs; 2) identification of the specific clinical forms of development and course of ВЕD with significant genetic influence; 3) identification of the specific genetic variants that increase the effectiveness of personalized pharmacotherapy of ВЕD within pharmacogenetic approach.

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

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

An Obesity-Predisposing Variant of the FTO Gene Regulates D2R-Dependent Reward Learning

Variations in the fat mass and obesity-associated (FTO) gene are linked to obesity. However, the underlying neurobiological mechanisms by which these genetic variants influence obesity, behavior, and brain are unknown. Given that Fto regulates D2/3R signaling in mice, we tested in humans whether variants in FTO would interact with a variant in the ANKK1 gene, which alters D2R signaling and is also associated with obesity. In a behavioral and fMRI study, we demonstrate that gene variants of FTO affect dopamine (D2)-dependent midbrain brain responses to reward learning and behavioral responses associated with learning from negative outcome in humans. Furthermore, dynamic causal modeling confirmed that FTO variants modulate the connectivity in a basic reward circuit of meso-striato-prefrontal regions, suggesting a mechanism by which genetic predisposition alters reward processing not only in obesity, but also in other disorders with altered D2R-dependent impulse control, such as addiction. Significance statement: Variations in the fat mass and obesity-associated (FTO) gene are associated with obesity. Here we demonstrate that variants of FTO affect dopamine-dependent midbrain brain responses and learning from negative outcomes in humans during a reward learning task. Furthermore, FTO variants modulate the connectivity in a basic reward circuit of meso-striato-prefrontal regions, suggesting a mechanism by which genetic vulnerability in reward processing can increase predisposition to obesity.