TaqI-A polymorphism linked to the DRD2 gene and P300 in alcoholic patients

Psychobiological traits in the risk profile for overeating and weight gain

Our dramatically changed food environment--since periods in our history when food sources were highly constrained--has presented new challenges for obesity research. For example, these alterations have strongly emphasized the physiological differences between the homeostatic and the hedonic regulation of food intake--the latter being largely responsible for the pronounced increase in obesity in the past few decades. There is also increasing agreement that compulsive overeating shares many parallels with addiction disorders such as drug abuse. These factors have also fostered a renewed interest in identifying individual differences in personality and motivational systems that increase the risk for overeating and weight gain in our population. Reward sensitivity has been the focus of a recent body of compelling research, with evidence favoring two seemingly opposite points of view. On the one hand, studies have found support for a link between low reward sensitivity and obesity, whereas other evidence suggests that a strong appetitive motivation leads to overeating and weight gain. Arguments are provided to reconcile these apparently disparate theories. Finally, the role of impulsivity and its links with symptoms of attention deficit/hyperactivity disorder are discussed, as well as their respective roles in the risk profile for obesity.

The ANKK1 gene associated with addictions is expressed in astroglial cells and upregulated by apomorphine

BACKGROUND

TaqIA, the most widely analyzed genetic polymorphism in addictions, has traditionally been considered a gene marker for association with D2 dopamine receptor gene (DRD2). TaqIA is located in the coding region of the ANKK1 gene that overlaps DRD2 and encodes a predicted kinase ANKK1. The ANKK1 protein nonetheless had yet to be identified. This study examined the ANKK1 expression pattern as a first step to uncover the biological bases of TaqIA-associated phenotypes.

METHODS

Northern blot and quantitative reverse-transcriptase polymerase chain reaction analyses were performed to analyze the ANKK1 mRNA. To study ANKK1 protein expression, we developed two polyclonal antibodies to a synthetic peptides contained in the putative Ser/Thr kinase domain.

RESULTS

We demonstrate that ANKK1 mRNA and protein were expressed in the adult central nervous system (CNS) in human and rodents, exclusively in astrocytes. Ankk1 mRNA level in mouse astrocyte cultures was upregulated by apomorphine, suggesting a potential relationship with the dopaminergic system. Developmental studies in mice showed that ANKK1 protein was ubiquitously located in radial glia in the CNS, with an mRNA expression pick around embryonic Day 15. This time expression pattern coincided with that of the Drd2 mRNA. On induction of differentiation by retinoic acid, a sequential expression was found in human neuroblastoma, where ANKK1 was expressed first, followed by that of DRD2. An opposite time expression pattern was found in rat glioma.

CONCLUSIONS

Spatial and temporal regulation of the expression of ANKK1 suggest an involvement of astroglial cells in TaqIA-related neuropsychiatric phenotypes both during development and adult life.

Dopamine for "wanting" and opioids for "liking": a comparison of obese adults with and without binge eating

Obesity research suffers from an overinclusion paradigm whereby all participants with a BMI beyond a certain cutoff value (e.g., 30) are typically combined in a single group and compared to those of normal weight. There has been little attempt to identify meaningful subgroups defined by their salient biobehavioral differences. In order to address this limitation, we examined genetic and psychological indicators of hedonic eating in obese adults with (n=66) and without (n=70) binge eating disorder (BED). Our analyses focused on dopamine (DA) and opioid genetic markers because of their conjoint association with the functioning of brain reward mechanisms. We targeted three functional polymorphisms related to the D2 receptor (DRD2) gene, as well as the functional A118G polymorphism of the mu-opioid receptor (OPRM1) gene. We found that significantly more obese controls had the "loss-of-function" A1 allele of Taq1A compared to their BED counterparts, whereas the "gain-of-function" G allele of A118G occurred with greater frequency in the BED group. A significant gene-gene combination chi2 analysis also indicated that of those participants with the gain-gain genotype (G+ and A1), 80% were in the BED group whereas only 35% with the loss-loss genotype (G- and A1+) were in this group. Finally, BED subjects had significantly higher scores on a self-report measure of hedonic eating. Our findings suggest that BED is a biologically based subtype of obesity and that the proneness to binge eating may be influenced by a hyper-reactivity to the hedonic properties of food--a predisposition that is easily exploited in our current environment with its highly visible and easily accessible surfeit of sweet and fatty foods.

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

OBJECTIVE

The sensitivity of dopamine reward pathways has been implicated in the risk for various psychiatric disorders including compulsive overeating. The evidence is divided, however, about the direction of causal association. One argument is that a Reward Deficiency Syndrome is the risk factor, while others contend that hyper-sensitivity to reward enhances the motivation for pleasurable activities like eating. Unfortunately, little human research has bridged the gap between psychological and neurobiological approaches to brain reward functioning and disorder. The present study addressed this issue by implementing psychological and biological markers of reward sensitivity in the assessment protocol.

METHODS

Adults with binge eating disorder (BED) were compared to samples of normal-weight and obese controls on two personality measures of reward sensitivity and were genotyped for six markers of the DRD2 dopamine receptor gene.

RESULTS

Genotype x Group ANOVAs revealed significant main effects and an interaction on the personality measures for Taq1A. BED and obese subjects reported greater reward sensitivity than normal-weight controls, but only among those carrying the A1 allele. We also found that normal-weight controls with at least one copy of the T allele of the C957T marker had significantly lower reward sensitivity scores than any of the other groups who did not differ from each other.

CONCLUSIONS

Given evidence linking the A1 allele with reduced receptor density, an inverse relationship was expected between psychological measures of reward sensitivity and presence of the A1 allele. One explanation for our findings could be that the BED and obese participants possess another genetic variant that interacts with the A1 allele to produce higher dopamine activity. These findings have implications for future studies of the molecular genetics of BED and obesity, and for behavioural and pharmacologic therapies targeting these conditions.