Dopamine D2 receptor polymorphisms and susceptibility to alcohol dependence in Indian males: a preliminary study

Probiotics-role in alleviating the impact of alcohol liver disease and alcohol deaddiction: a systematic review

Background

There are few efficient treatment options for alcohol addiction, which continues to be a serious public health concern. The possible contribution of gut microbiota to the onset and progression of alcohol addiction has been brought to light by recent studies. Probiotics have become a cutting-edge intervention in the treatment of alcohol consumption disorder because of its favorable effects on gut health. The purpose of this systematic review is to assess the body of research on the advantages of probiotics in treating alcoholism and associated neuroinflammatory conditions.

Methods

To find pertinent research published from January 2012 to 2023, a thorough search of electronic databases, including PubMed, Scopus, Google Scholar and Web of Science, was carried out. Included were studies looking at how probiotics affect neuroinflammation, gut- brain axis regulation, alcohol addiction, and related behaviors.

Findings

Several investigations have shown how beneficial probiotics are in reducing systemic inflammation and alcoholic liver disease (ALD). Probiotic treatments successfully corrected the imbalance of microbiota, decreased intestinal permeability, and stopped the passage of bacterial constituents such lipopolysaccharides (LPS) into the bloodstream. Additionally, probiotics helped to regulate neurotransmitter pathways, especially those connected to GABA, glutamate, and dopamine, which are intimately linked to behaviors related to addiction. Furthermore, it was shown that probiotics altered the expression of neurotransmitter signaling and dopamine receptors.

Conclusion

There is strong evidence from this systematic study that probiotics have potential advantages in treating alcohol addiction. The potential of probiotic therapies is demonstrated by the way they modulate important neurotransmitter pathways implicated in addiction, decrease neuroinflammation, and restore the balance of gut flora. To fully investigate the therapeutic potential of probiotics in treating alcohol addiction and enhancing the general wellbeing of those afflicted by this condition, more research is necessary.

Evaluation of the Relationship Between Dopamine Receptor D2 Gene TaqIA1 Polymorphism and Alcohol Dependence Risk

Several studies are published, that investigated dopamine receptor 2 (DRD2) gene TaqIA polymorphism as a risk factor for alcohol dependence (AD) with positive and negative associations. To derive a more precise estimation of the relationship, a meta-analysis of case-control studies that examined the association between DRD2 gene Taq1A polymorphism and alcohol dependence was performed. Eligible articles were identified through a search of databases including PubMed, Science Direct, Springer link, and Google Scholar. The association between the DRD2 TaqIA polymorphism and AD susceptibility was conducted using odds ratios (ORs) and 95% confidence intervals (95% CIs) as association measures. A total of 69 studies with 9125 cases and 9123 healthy controls were included in the current meta-analysis. Results of the present analysis showed significant association between DRD2 TaqIA polymorphism and AD risk using five genetic modes (allele contrast model-OR 1.22, 95% CI 1.13-1.32, p < 0.0001; homozygote model-OR 1.35, 95%CI 1.18-1.55; p ≤ 0.0001; dominant model-OR 1.29; 95% CI 1.20-1.39; p < 0.0001; recessive model-OR 1.21; 95% CI 1.08-1.36; p = 0.0006). There was no significant association found in subgroup analysis, TaqIA polymorphism was not significantly associated with AD risk in the Asian population under all genetic models, but in the Caucasian population, TaqIA polymorphism was significantly associated with AD risk. Overall, results support the hypothesis that DRD2 Taq1A polymorphism plays a role in alcohol dependence.

Alcohol use disorder research in India: An update

Background

Despite alcohol use being a risk factor for numerous health-related conditions and alcohol use disorder (AUD) recognized as a disease, there was limited research in India until 2010. This narrative review aims to evaluate AUD-related research in India from 2010 to July 2023.

Methods

A PubMed search used key terms for AUD in India after 2010. Indian and international journals with regional significance that publish alcohol-related research were searched by each author individually. These were then collated, and duplicates were removed. In addition, we also conducted a gray literature search on focused areas related to AUD.

Results

The alcohol-related research in India after 2010 focused on diverse areas associated with alcohol use. Some areas of research have received more attention than others. Two major epidemiological surveys conducted in the past decade reveal that around 5% have a problematic alcohol use pattern. Factors associated with alcohol use, like genetic, neurobiological, psychological, and sociocultural, were studied. The studies focused on the clinical profile of AUD, including their correlates, such as craving, withdrawal, alcohol-related harm, and comorbid psychiatric and medical illnesses. During this period, minimal research was conducted to understand AUD's laboratory biomarkers, course, and prognosis. While there was a focus on generating evidence for different psychological interventions for alcohol dependence in management-related research, pharmacological studies centered on anticraving agents like baclofen. Research on noninvasive brain stimulation, such as rTMS, has shown preliminary usefulness in treating alcohol dependence. Very little research has been conducted regarding alcohol policy.

Conclusion

In the past decade, Indian research on alcohol has focused on diverse areas. Epidemiological and psychological management-related research received maximum attention. Considering the magnitude of the alcohol-related burden, it is essential to prioritize research to other less studied areas like pharmacological management of alcohol dependence and alcohol policy.

The Roles of Endogenous D2R Dopamine and μ-opioid Receptors of the Brain in Alcohol use Disorder

Alcohol use disorder (AUD) affects millions of people worldwide. It is characterized by a strong physiological and psychological craving to consume large amounts of alcohol despite adverse consequences. Alcohol use disorder carries a large health and economic burden on society. Despite its prevalence, AUD is still severely undertreated. The precise molecular mechanisms of how alcohol addiction forms are yet unknown. However, previous studies on animal models show that along with the μ-opioid receptors, the D2R dopamine receptors may also be involved in alcohol craving and reward pathways. Currently, there is a limited number of treatment strategies for alcohol use disorder, which include several medications and therapy. By understanding the limitations of current treatment options and exploring new potential targets, it could be possible to find more effective ways of treating AUD in the future.

Molecular mechanisms of alcohol's effects on the human body: A review and update

Alcohol consumption has been linked to numerous negative health outcomes although it has some beneficial effects on moderate dosages, the most severe of which being alcohol-induced hepatitis. The number of people dying from this liver illness has been shown to climb steadily over time, and its prevalence has been increasing. Researchers have found that alcohol consumption primarily affects the brain, leading to a wide range of neurological and psychological diseases. High-alcohol-consumption addicts not only experienced seizures, but also ataxia, aggression, social anxiety, and variceal hemorrhage that ultimately resulted in death, ascites, and schizophrenia. Drugs treating this liver condition are limited and can cause serious side effects like depression. Serine-threonine kinases, cAMP protein kinases, protein kinase C, ERK, RACK 1, Homer 2, and more have all been observed to have their signaling pathways disrupted by alcohol, and alcohol has also been linked to epigenetic changes. In addition, alcohol consumption induces dysbiosis by changing the composition of the microbiome found in the gastrointestinal tract. Although more studies are needed, those that have been done suggest that probiotics aid in keeping the various microbiota concentrations stable. It has been argued that reducing one's alcohol intake may seem less harmful because excessive drinking is a lifestyle disorder.

Craving among patients seeking treatment for substance use disorder

BACKGROUND

Craving has been implicated as a central feature of addiction and a predictor of relapse. However, a complete understanding of how craving varies across patient populations is lacking. This study aimed to better inform the effective and accurate use of craving as a clinical prognostic tool for patients with substance use disorders (SUD).

METHODS

This cross-sectional study utilized information gathered on patients (n = 112) entering specialty treatment for a SUD. Craving in the prior 30 days was assessed with a single item with other intake questionnaires.

RESULTS

Patients who reported substance use in the last 30 days were more likely to report craving compared to patients who did not report substance use in the last 30 days (AOR = 6.86 [95% CI 2.17-21.7], p-value = 0.001). Patients who reported Hispanic/Latinx ethnicity were less likely to report craving compared to patients who did not report Hispanic/Latinx ethnicity (AOR = 0.28 [95% CI 0.08-0.95], p-value = 0.04). There was no association between craving and Adverse Childhood Events (OR = 1.03 [95% CI 0.84-1.25], p-value = 0.81).

CONCLUSION

The association between recent substance use and craving supports previous findings. The observed variation in craving among patients who report Hispanic/Latinx ethnicity is novel and suggests socio-cultural influences and possibly genetic factors influencing reported craving amongst patients. Additional research is needed to further understand the underlying factors leading to this finding, in order for better utilization of craving as a clinical indicator across patient populations.

Association between opioid and dopamine receptor gene polymorphisms OPRM1 rs1799971, DAT VNTR 9-10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 and alcohol dependence: an ethnicity oriented meta-analysis

OBJECTIVE

We carried out a meta-analysis of four opioid and dopamine candidate gene polymorphisms having conflicting results in prior literature, namely OPRM1 rs1799971, DAT VNTR 9-10 repeat, DRD1 rs4532 and DRD2 rs1799732, to clarify their association with alcohol dependence and further stratified results by ethnicity to analyze possible ethnicity-mediated effects.

METHODS

Inclusion criteria: case-control studies assessing the association between OPRM1 rs1799971, DAT VNTR 9/10 repeat allele, DRD1 rs4532 and DRD2 rs1799732 with alcohol dependence, with sufficient data available to calculate the odds ratio (OR) within a 95% confidence interval. Exclusion criteria: studies of quantitative measures of alcohol consumption, response to medications or analyses of other markers in the candidate genes, studies without controls, animal studies and lack of genotyping data. Information sources were PubMed, Google Scholar and ScienceDirect databases, all of which were searched for articles published till 2021. Heterogeneity between studies and publication bias, subgroup analyses and sensitivity analyses were carried out.

RESULTS

A total of 41 published studies were included in the current meta-analysis. For the OPRM1 gene, there was a statistically significant association in the Asian population with a pooled OR of 1.707 (95% CI, 1.32-2.20 P  < 0.0001) and 1.618 (95% CI, 1.16-2.26 P  = 0.005) in the additive and dominant genetic models. For DAT VNTR 9/10 repeat, a statistically significant association of the risk vs. common allele was observed in AD with a pooled OR of 1.104 (95% CI, 1.00-1.21 P  = 0.046) in the allele model and the additive genetic model in the Caucasian population with pooled OR of 1.152 (95% CI, 1.01-1.31 P  = 0.034).

CONCLUSION

Results indicate that some of the effects may be ethnicity-specific.

OTHER

The meta-analysis has been registered in the CRD PROSPERO (CRD42023411576).

DRD2, DRD3, and HTR2A Single-Nucleotide Polymorphisms Involvement in High Treatment Resistance to Atypical Antipsychotic Drugs

BACKGROUND

The objective of this study was to investigate the DRD2 rs1800497, rs1799732, rs1801028, DRD3 rs6280, and HTR2A rs6314, rs7997012, and rs6311 single-nucleotide polymorphism (SNP) correlations with resistance to second-generation antipsychotics (SGAs) in a real-world sample of patients with treatment-resistant mental disorders.

METHODS

We divided 129 participants into a high treatment resistance (HTR) group (current treatment with two SGAs, or clozapine, or classic neuroleptics for a failure of previous SGAs trials) and a low treatment resistance (LTR) group (current treatment with one atypical antipsychotic). We used Next-Generation Sequencing on DNA isolated from peripheral blood samples to analyze the polymorphisms. We performed logistic regression to search for predictors of HTR membership.

RESULTS

A diagnosis of schizophrenia significantly predicted the HTR membership compared to other diagnoses. Other predictors were the DRD3 rs6280 C|T (OR = 22.195) and T|T (OR = 18.47) vs. C|C, HTR2A rs7997012 A|G vs. A|A (OR = 6.859) and vs. G|G (OR = 2.879), and DRD2 rs1799732 I|I vs. D|I (OR = 12.079) genotypes.

CONCLUSIONS

A diagnosis of schizophrenia and the DRD2 rs1799732, DRD3 rs6280, and HTR2A rs7997012 genotypes can predict high treatment resistance to SGAs.

No association of the dopamine D2 receptor genetic bilocus score (rs1800497/rs1799732) on food addiction and food reinforcement in Chilean adults

Purpose: Different systems regulate food intake. In the reward system, dopamine (DA) is the main neurotransmitter, and a variety of genetic variants (rs1799732 and rs1800497) are associated with addiction. Addiction is a highly polygenic disease, where each allelic variant adds a small amount of vulnerability. Polymorphisms rs1799732 and rs1800497 are associated with eating behavior and hedonic hunger, but links to food addiction remain unclear.

Aim: To evaluate the association between the bilocus profile (rs1799732-rs1800497) of the dopaminergic pathway with food reinforcement and food addiction in Chilean adults.

Methods: A cross-sectional study recruited a convenience sample of 97 obese, 25 overweight, and 99 normal-weight adults (18–35 years). Anthropometric measurements were performed by standard procedures and eating behavior was assessed using the: Food Reinforcement Value Questionnaire (FRVQ) and Yale Food Addiction scale (YFAS). The DRD2 genotypes were determined by TaqMan assays (rs1800497 and rs1799732). A bilocus composite score was calculated.

Results: In the normal weight group, individuals who were heterozygous for the rs1977932 variant (G/del) showed higher body weight (p-value 0.01) and abdominal circumference (p-value 0.01) compared to those who were homozygous (G/G). When analyzing rs1800497, a significant difference in BMI was observed for the normal weight group (p-value 0.02) where heterozygous showed higher BMI. In the obese group, homozygous A1/A1 showed higher BMI in comparison to A1/A2 and A2/A2 (p-value 0.03). Also, a significant difference in food reinforcement was observed in the rs1800497, where homozygous for the variant (A1A1) show less reinforcement (p-value 0.01).In relation to the bilocus score in the total sample, 11% showed “very low dopaminergic signaling”, 24.4% were “under”, 49.7% showed “intermediate signaling”, 12.7% showed “high” and 1.4% showed “very high”. No significant genotypic differences were observed in food reinforcement and food addiction by bilocus score.

Conclusions: The results indicate that the genetic variants rs1799732 and rs1800497 (Taq1A) were associated with anthropometric measurements but not with food addiction or food reinforcement in Chilean university students. These results suggest that other genotypes, such as rs4680 and rs6277, which affect DA signaling capacity through a multilocus composite score, should be studied. Level V: Evidence obtained from a cross-sectional descriptive study.

Molecular genetics of neurotransmitters and neuropeptides involved in Internet use disorders including first insights on a potential role of hypothalamus' oxytocin hormone

This chapter covers the phenomenon of Internet use disorders (IUDs) and putative associations with different neurotransmitter and neuropeptide systems. Genes coding for such messengers can be seen as an important starting point in the complicated quest to understand human behavior including new phenomena such as IUDs. Therefore, a special focus of this chapter will lie on individual differences in molecular genetic underpinnings of neurotransmitter and neuropeptide systems and their associations with individual differences in tendencies towards IUDs. By shedding light on these associations, putative predisposing molecular genetic factors for the emergence and maintenance of IUDs can be carved out. Therefore, first an introduction to IUDs and a model that can guide research on putative associations of IUDs with different specific neurotransmitters and neuropeptides will be presented. Subsequently, twin studies on the heritability of IUDs are reviewed. Finally, studies on differences in molecular genetic predispositions and their associations with differences in IUDs will be presented and discussed, including targets related to the dopaminergic and serotonergic system as well as the hypothalamic neuropeptide oxytocin. The chapter closes with a conclusion about what is already known and what needs to be investigated in future studies to gain further insights into putative associations between molecular genetic markers and IUDs.

Spontaneous Ultrasonic Vocalization Transmission in Adult, Male Long-Evans Rats Is Age-Dependent and Sensitive to EtOH Modulation

Ultrasonic vocalizations (USVs) are well-established markers of motivational and emotional status. Recent work from our lab has provided novel evidence for a role of USVs in models of ethanol (EtOH) use. For instance, USV acoustic characteristics can be used to accurately discriminate between rats selectively bred for high EtOH intake (e.g., alcohol-preferring (P) and high-alcohol-drinking (HAD)) versus EtOH-avoiding (e.g., alcohol-non-preferring (NP) and low-alcohol-drinking (LAD)) strains, as well as differentiate between male and female rats. In the present study we sought to explore the effect of age and alcohol availability on spontaneously emitted 50–55 kHz frequency modulated (FM) and 22–28 kHz USVs in adult, male Long–Evans rats. With the hypothesis that age and alcohol experience influence spontaneous USV emissions, we examined USV data collected across a 24-week intermittent EtOH access experiment in male Long–Evans rats. USV counts and acoustic characteristic (i.e., mean frequency, duration, bandwidth and power) data revealed distinct age-dependent phenotypes in both 50–55 kHz FM and 22–28 kHz USV transmission patterns that were modulated by EtOH exposure. These results highlight the influence of age and EtOH experience on the unique emotional phenotypes of male Long–Evans rats.

Genetic Polymorphisms on OPRM1, DRD2, DRD4, and COMT in Young Adults: Lack of Association With Alcohol Consumption

Background: Risk behaviors for young adults such as alcohol use are associated with increased risk of morbidity and mortality. Patterns of risk behavior may be genetically determined and vary between genders. Previous studies in both young adults and heavy drinking adult samples have demonstrated that some genotypes, such as OPRM1 A118G, COMT Val158Met and DRD2 Taq1A and DRD4 C52IT, may predict addictive behaviors including alcohol consumption and impulsivity, although results have been mixed. Methods: This study aimed to investigate the predictive relationship of these four single nucleotide polymorphisms (SNPs) prospectively on student patterns of drinking using a micro-longitudinal daily diary design in a sample of 628 young adults ages 18-25 of predominantly of European ethnicity. Linear mixed models were used to examine the effect of SNPs on the number of drinks per drinking session with gender as a moderating variable. Results: There were no main effects for genotype on alcohol consumption, nor for gender × genotype for any of the SNPs. There was a trend for an effect of the DRD2 Taq1A on the number of drinks per drinking day and for the interaction of gender and DRD2 Taq1A on the number of drinks per drinking day. Conclusion: These findings suggest that the DRD2 Taq1A, OPRM1 A118G, DRD4 C521T, or COMT Val158Met polymorphisms, are not associated with alcohol consumption in young adults, although there may be a relationship between DRD2 Taq1A and alcohol consumption in young adult males.

Assessment of the Association of D2 Dopamine Receptor Gene and Reported Allele Frequencies With Alcohol Use Disorders: A Systematic Review and Meta-analysis

IMPORTANCE

The association between the D2 dopamine receptor gene (DRD2) Taq1A locus (rs1800497) and alcohol use disorder (AUD) is enduring but the subject of long-standing controversy; meta-analysis of studies across 3 decades shows an association between rs1800497 and AUD, but genome-wide analyses have detected no role for rs1800497 in any phenotype. No evidence has emerged that rs1800497, which is located in ANKK1, perturbs the expression or function of DRD2.

OBJECTIVE

To resolve contradictions in previous studies by identifying hidden confounders and assaying for functional effects of rs1800497 and other loci in the DRD2 region.

DATA SOURCES

PubMed (882 studies), Embase (1056 studies), and Web of Science (501 studies) databases were searched through August 2018. Three clinical populations-Finnish, Native American, and African American participants-were genotyped for 208 to 277 informative single-nucleotide polymorphisms (SNPs) across the DRD2 region to test the associations of SNPs in this region with AUD.

STUDY SELECTION

Eligible studies had diagnosis of AUD made by accepted criteria, reliable genotyping methods, sufficient genotype data to calculate odds ratios and 95% CIs, and availability of control allele frequencies or genotype frequencies.

DATA EXTRACTION AND SYNTHESIS

After meta-analysis of 62 studies, metaregression was performed to detect between-study heterogeneity and to explore the effects of moderators, including deviations of cases and controls from allele frequencies in large population databases (ExAC and 1000 Genomes). Linkage to AUD and the effect on gene expression of rs1800497 were evaluated in the context of other SNPs in the DRD2 region. Data analysis was performed from August 2018 to March 2019. This study follows the Preferred Reporting Items for Systematic Reviews and Meta-analyses reporting guideline.

MAIN OUTCOMES AND MEASURES

The effects of rs1800497 and other SNPs in the DRD2 region on gene expression were measured in human postmortem brain samples via differential allelic expression and evaluated in other tissues via publicly available expression quantitative locus data.

RESULTS

A total of 62 studies of DRD2 and AUD with 16 294 participants were meta-analyzed. The rs1800497 SNP was associated with AUD (odds ratio, 1.23; 95% CI, 1.14-1.31; P < .001). However, the association was attributable to spuriously low allele frequencies in controls in positive studies, which also accounted for some between-study heterogeneity (I2 = 43%; 95% CI, 23%-58%; Q61 = 107.20). Differential allelic expression of human postmortem brain and analysis of expression quantitative loci in public data revealed that a cis-acting locus or loci perturb the DRD2 transcript level; however, rs1800497 does not and is not in strong disequilibrium with such a locus. Across the DRD2 region, other SNPs are more strongly associated with AUD than rs1800497, although no DRD2 SNP was significantly associated in these 3 clinical samples.

CONCLUSIONS AND RELEVANCE

In this meta-analysis, the significant association of DRD2 with AUD was reassessed. The DRD2 association was attributable to anomalously low control allele frequencies, not function, in positive studies. For genetic studies, statistical replication is not verification.

Evaluation of association of DRD2 TaqIA and -141C InsDel polymorphisms with food intake and anthropometric data in children at the first stages of development

The reward sensation after food intake may be different between individuals and variants in genes related to the dopaminergic system may indicate a different response in people exposed to the same environmental factors. This study investigated the association of TaqIA (rs1800497) and -141C InsDel (rs1799732) variants in DRD2/ANKK1 gene with food intake and adiposity parameters in a cohort of children. The sample consisted of 270 children followed until 7 to 8 years old. DNA was extracted from blood and polymorphisms were detected by PCR-RFLP analysis. Food intake and nutritional status were compared among individuals with different SNP genotypes. Children carrying the A1 allele (TaqIA) had higher energy of lipid dense foods (LDF) when compared with A2/A2 homozygous children at 7 to 8 years old (GLM p=0.004; Mann Whitney p=0.005). No association was detected with -141C Ins/Del polymorphism. To our knowledge, this is the first association study of the DRD2 TaqIA and -141C Ins/Del polymorphism with food intake and anthropometric parameters in children. DRD2 TaqIA polymorphism has been associated with a reduction in D₂ dopamine receptor availability. Therefore, the differences observed in LDF intake in our sample may occur as an effort to compensate the hypodopaminergic functioning.

Polymorphisms of dopamine receptor genes DRD2 and DRD4 in African populations of Hadza and Datoga differing in the level of culturally permitted aggression

The key regulator in the control of aggressive behavior is dopamine receptors. Association of variants in these genes with aggression has been shown in modern populations. However, these studies have not been conducted in traditional cultures. The aim of our study was to investigate population features in distributions of allele and genotype frequencies of DRD2 rs1800497, DRD4 120 bp Ins, and DRD4 exon III polymorphisms and their associations with aggressive behavior in the traditional African populations of Hadza and Datoga, which display a contrast in their culturally permitted aggression. Overall, 820 healthy unrelated Hadza and Datoga individuals were studied. Self-rated scores of aggression were collected using Buss and Perry's Aggression Questionnaire. Polymerase chain reaction-Restriction fragment length polymorphism (PCR-RFLP) was used to determine the genotype of each individual. We show that the Hadza and the Datoga differed significantly in allele and genotype frequencies of all studied loci. Our association analysis detected that only ethnicity and sex of individuals significantly influenced their aggression rank, but we failed to identify any associations of DRD2 rs1800497, DRD4 120 bp Ins, or DRD4 exon III polymorphisms with aggression. Thus, our data have no strong evidence to support the involvement of polymorphisms of DRD2 and DRD4 in controlling aggressive behavior.

Association of ankyrin repeats & kinase domain containing 1 (ANKK1) gene polymorphism with co-morbid alcohol & nicotine dependence: A pilot study from a tertiary care treatment centre in north India

BACKGROUND & OBJECTIVES

The frequently encountered co-morbidity of alcohol dependence (AD) with nicotine dependence (ND) increases the risk for various diseases. Ankyrin repeats and kinase domain containing 1 (ANKK1) gene polymorphism is reported to be associated with both ND and AD. This study was undertaken to investigate the possible association of alcohol and tobacco use variables with ANKK1 polymorphism in co-morbid alcohol- and nicotine-dependent treatment seekers visiting a tertiary care centre in north India.

METHODS

Seventy nine male participants (18-65 yr old) fulfilling diagnostic criteria for ND and AD were included in the study. The socio-demographic data, along with alcohol and tobacco use profile, was recorded and ANKK1 profiling was carried out. Both the allele groups, A1 and A2, were compared with respect to demographic and substance dependence profile. Univariate binary logistic regression analysis was performed to determine the risk of high nicotine and alcohol consumption with genotype.

RESULTS

The A1 carrier group (n=33) reported a significantly higher amount of alcohol and tobacco consumed per day. The scores on parameters of ND were found to be significantly higher in this group. The logistic regression analysis revealed that participants with A1 genotype were 2.5 times more likely to report higher amount of alcohol and nicotine consumption than A2 carriers.

INTERPRETATION & CONCLUSIONS

The study provides an indication for the association of ANKK1 polymorphism in the form of higher substance consumption among alcohol dependent smokers, who are A1 carriers and thus may require higher attention of the treatment provider.

An association study of Taq1A ANKK1 and C957T and - 141C DRD2 polymorphisms in adults with internet gaming disorder: a pilot study

BACKGROUND

Though Internet gaming disorder (IGD) is considered to share similar genetic vulnerability with substance addictions, little has been explored about the role of the genetic variants on IGD. This pilot study was designed to investigate the association of the Taq1A polymorphism of the ankyrin repeat and kinase domain containing 1 (ANKK1) gene and C957T and - 141C of the dopamine D2 receptor (DRD2) with IGD and their role on the personality and temperament traits in IGD among adult population.

METHODS

Sixty-three subjects with IGD and 87 control subjects who regularly played Internet games were recruited. Self-administered questionnaires on self-control, dysfunctional impulsivity, and temperament and character domains were done. The Taq1A ANKK1 and the C957T and - 141C ins/del from the DRD2 genes were genotyped using the specific TaqMan PCR assay.

RESULTS

The distributions of allele and genotype frequencies were not significantly different between the IGD and control groups in both genders. In male, excessive gaming and use of gaming to escape from a negative feeling were associated with the del- genotype of the - 141C. Among IGD, the del+ genotype was associated with higher novelty seeking. Logistic regression showed no predictive value of these polymorphisms for IGD when using age and gender as covariates.

CONCLUSIONS

Though no direct association of the Taq1A ANKK1 and C957T DRD2 variants with IGD were observed, the - 141C polymorphism may play a role in IGD via mediating symptoms or temperament traits.

Paraphilic Sexual Offenders Do Not Differ From Control Subjects With Respect to Dopamine- and Serotonin-Related Genetic Polymorphisms

INTRODUCTION

Rape and pedophilic child molestation are the most commonly convicted sexual offenses in Poland. Recent studies have suggested a possible genetic contribution toward pathologic sexual interests and behaviors.

AIM

To analyze and compare functional polymorphisms of genes associated with the activity of the serotonin and dopamine systems in a group of paraphilic sexual offenders and control subjects.

METHODS

The study sample (n = 97) consisted of two groups: paraphilic sexual offenders (65 pedophilic child molesters and 32 rapists) and controls (n = 76). Genetic polymorphisms previously associated with behavioral control, addictive behaviors, and sexual functions were chosen for analyses. Specifically, functional polymorphisms in dopamine receptors genes (DRD1, DRD2, DRD4), catechol-O-methyltransferase gene (COMT), dopamine transporter gene (DAT), serotonin transporter gene (SLC6A4), serotonin type 2A receptor gene (5HTR2A), tryptophan hydroxylase 2 gene (TPH2), monoamine oxidase A gene (MAOA), and brain-derived neurotrophic factor gene (BDNF) were analyzed.

MAIN OUTCOME MEASURES

An association between a history of sexual offense and the distribution of genotypes and alleles in the analyzed polymorphisms.

RESULTS

Our results found no association between a history of sexual offense and the distribution of genotypes or alleles in the analyzed polymorphisms.

CONCLUSION

Although these results are limited by the small sample and are exploratory, they highlight a novel approach to sample selection in a population that is difficult to access and study. Future research should include larger samples and other relevant polymorphisms to advance this field of study.

-141C insertion/deletion polymorphism of the dopamine D2 receptor gene is associated with schizophrenia in Chinese Han population: Evidence from an ethnic group-specific meta-analysis

Accumulate evidence has implicated dopamine D2 receptor gene polymorphisms in the etiology of schizophrenia. A single nucleotide polymorphism, -141C insertion/deletion (Ins/Del) (rs1799732), in the promoter region of the dopamine D2 receptor gene has been linked to schizophrenia; however, the data are inconclusive. This study investigated whether the -141C polymorphism is associated with the risk of schizophrenia in different ethnic groups by performing a meta-analysis. A total of 24 case-control studies examining the association between -141C Ins/Del polymorphism and schizophrenia were identified according to established inclusion criteria. Significant association was revealed between -141C Ins/Del polymorphism and schizophrenia risk in dominant genetic model (Ins/Ins + Ins/Del versus Del/Del) (odds ratio = 0.33, 95% confidence interval = 0.14-0.81, z = 2.41, P = 0.02) in Chinese Han but not in Caucasian, Japanese or India populations. Our results indicate that -141C Ins/Del polymorphism might be a susceptibility factor for schizophrenia in Chinese Han population.

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.

Neurotransmitters in alcoholism: A review of neurobiological and genetic studies

Recent advances in the study of alcoholism have thrown light on the involvement of various neurotransmitters in the phenomenon of alcohol addiction. Various neurotransmitters have been implicated in alcohol addiction due to their imbalance in the brain, which could be either due to their excess activity or inhibition. This review paper aims to consolidate and to summarize some of the recent papers which have been published in this regard. The review paper will give an overview of the neurobiology of alcohol addiction, followed by detailed reviews of some of the recent papers published in the context of the genetics of alcohol addiction. Furthermore, the author hopes that the present text will be found useful to novices and experts alike in the field of neurotransmitters in alcoholism.

Alcohol abuse and HIV infection: role of DRD2

According to a survey from the HIV Cost and Services Utilization Study (HCSUS), approximately 53% of HIV-infected patients reported drinking alcohol and 8% were classified as heavy drinkers. The role of alcohol as a risk factor for HIV infection has been widely studied and recent research has found a significant association between heavy alcohol consumption and lower levels of CD4 T cells among HIV-infected alcoholics. Although there is evidence on the role of alcohol as a risk factor for HIV transmission and disease progression, there is a need for population studies to determine the genetic mechanisms that affect alcohol's role in HIV disease progression. One of the mechanisms of interest is the dopaminergic system. To date, the effects of dopamine on HIV neuroimmune pathogenesis are not well understood; however, dopaminergic neural degeneration due to HIV is known to occur by viral invasion into the brain via immune cells, and modulation of dopamine in the CNS may be a common mechanism by which different types of substances of abuse impact HIV disease progression. Although previous studies have shown an association of D(2) dopamine receptor (DRD2) polymorphisms with severity of alcohol dependence, the expression of this allele risk on HIV patients with alcohol dependence has not been systematically explored. In the current study, DRD2 Taq1A and C957T SNP genotyping analyses were performed in 165 HIV-infected alcohol abusers and the results were examined with immune status and CD4 counts.

Alcoholism and liver disease in Mexico: Genetic and environmental factors

Alcoholism and cirrhosis, which are two of the most serious health problems worldwide, have a broad spectrum of clinical outcomes. Both diseases are influenced by genetic susceptibility and cultural traits that differ globally but are specific for each population. In contrast to other regions around the world, Mexicans present the highest drinking score and a high mortality rate for alcoholic liver disease with an intermediate category level of per capita alcohol consumption. Mexico has a unique history of alcohol consumption that is linked to profound anthropological and social aspects. The Mexican population has an admixture genome inherited from different races, Caucasian, Amerindian and African, with a heterogeneous distribution within the country. Thus, genes related to alcohol addiction, such as dopamine receptor D2 in the brain, or liver alcohol-metabolizing enzymes, such as alcohol dehydrogenase class I polypeptide B, cytochrome P450 2E1 and aldehyde dehydrogenase class 2, may vary from one individual to another. Furthermore, they may be inherited as risk or non-risk haplogroups that confer susceptibility or resistance either to alcohol addiction or abusive alcohol consumption and possibly liver disease. Thus, in this era of genomics, personalized medicine will benefit patients if it is directed according to individual or population-based data. Additional association studies will be required to establish novel strategies for the prevention, care and treatment of liver disease in Mexico and worldwide.

Case-control association analysis of dopamine receptor polymorphisms in alcohol dependence: a pilot study in Indian males

Background

Brain imaging studies and knock-out animal models have derived substantial abetment for dopamine receptor (DR) subtypes as potential candidates in susceptibility to addictive disorders, including alcohol dependence (AD). Various association studies that compared the frequencies of alleles of the dopamine D1, D2, D3 and D4 receptor genes between alcohol dependent and control subjects have produced suggestive results, though some of them are discordant in nature. In the absence of genetic data from Indian population, we evaluated genetic association of three polymorphisms namely rs4532 in DRD1, rs6280 in DRD3 and 120 bp duplication in 1.2 kb upstream region of DRD4 with AD.

Methods

A total of 90 cases (alcohol dependent males) and 122 age and ethnicity matched healthy male controls were recruited in the study by following DSM-IV criteria. Three polymorphisms, namely rs4532 in DRD1, rs6280 in DRD3 and 120 bp duplication in 1.2 kb upstream region of DRD4 were selected (based on minor allele frequency and available literature) for genotyping by PCR-RFLP/LP method. Allele and genotype frequencies of these genetic markers were compared using Pearson’s χ² test followed by risk assessment using odds ratio. Statistical analysis of clinical parameters such as AUDIT scores of case subjects was also performed.

Results

Statistically significant associations of polymorphisms in DRD1 and DRD4 with alcoholism were found.

Conclusions

Our results underscore that genetic variations in dopamine receptors D1 and D4 may influence genetic predisposition to alcoholism. Unavailability of comparative data from Indian population and small sample size necessitate replication of results in an independent cohort.

Catecholaminergic gene variants: contribution in ADHD and associated comorbid attributes in the eastern Indian probands

Contribution of genes in attention deficit hyperactivity disorder (ADHD) has been explored in various populations, and several genes were speculated to contribute small but additive effects. We have assessed variants in four genes, DDC (rs3837091 and rs3735273), DRD2 (rs1800496, rs1801028, and rs1799732), DRD4 (rs4646984 and rs4646983), and COMT (rs165599 and rs740603) in Indian ADHD subjects with comorbid attributes. Cases were recruited following the Diagnostic and Statistical Manual for Mental Disorders-IV-TR after obtaining informed written consent. DNA isolated from peripheral blood leukocytes of ADHD probands (N = 170), their parents (N = 310), and ethnically matched controls (n = 180) was used for genotyping followed by population- and family-based analyses by the UNPHASED program. DRD4 sites showed significant difference in allelic frequencies by case-control analysis, while DDC and COMT exhibited bias in familial transmission (P < 0.05). rs3837091 “AGAG,” rs3735273 “A,” rs1799732 “C,” rs740603 “G,” rs165599 “G” and single repeat alleles of rs4646984/rs4646983 showed positive correlation with co-morbid characteristics (P < 0.05). Multi dimensionality reduction analysis of case-control data revealed significant interactive effects of all four genes (P < 0.001), while family-based data showed interaction between DDC and DRD2 (P = 0.04). This first study on these gene variants in Indo-Caucasoid ADHD probands and associated co-morbid conditions indicates altered dopaminergic neurotransmission in ADHD.

DRD2 and ANKK1 gene polymorphisms and alcohol dependence: a case-control study among a Mendelian population of East Asian ancestry

AIMS

Dopamine receptors are extensively studied in association with alcohol dependence (AD), since they are thought to be the key neural substrate for alcohol and other drug-related reinforcement and reward behaviours. The present study aims to understand the role of dopamine receptors in susceptibility to AD with respect to three sites of DRD2 gene (-141C Ins/Del, TaqIB and TaqID) and TaqIA site of ANKK1 gene among Meiteis of Manipur, a Mendelian population of India.

METHODS

A total of 129 individuals who all met the DSM-IV criteria for AD and 286 controls were screened for four single-nucleotide polymorphisms (SNPs) -141C Ins/Del, TaqIB TaqID and TaqIA. Both AD cases and controls were unrelated up to first cousin.

RESULTS

Early age of onset of alcohol consumption and smoking status were significantly associated with AD. Improvement in education and occupation statuses showed decreased risk of AD. The heterozygous and mutant homozygous conditions of ANKK1 TaqIA polymorphism were found to be significantly associated with AD (odds ratio = 2.13, 95% confidential interval 1.04-4.39, P < 0.05), whereas a borderline significance of the -141C Del allele was observed (P = 0.059). Such a trend was not observed between AD and the other polymorphism, i.e., TaqIB and TaqID.

CONCLUSIONS

Individuals carrying the A1 allele of ANKK1 TaqIA polymorphism may be relatively more susceptible to AD. Interaction of both ANKK1 TaqIA and -141C Ins/Del polymorphism is likely to increase risk of AD phenotypes among Meiteis of Manipur, India.

A large-scale meta-analysis of the association between the ANKK1/DRD2 Taq1A polymorphism and alcohol dependence

Alcohol dependence (AD) is a common neuropsychiatric disorder with high heritability. A number of studies have analyzed the association between the Taq1A polymorphism (located in the gene cluster ANKK1/DRD2) and AD. In the present study, we conducted a large-scale meta-analysis to confirm the association between the Taq1A polymorphism and the risk for AD in over 18,000 subjects included in 61 case-control studies that were published up to August 2012. Our meta-analysis demonstrated both allelic and genotypic association between the Taq1A polymorphism and AD susceptibility [allelic: P(Z) = 1.1 × 10(-5), OR = 1.19; genotypic: P(Z) = 3.2 × 10(-5), OR = 1.24]. The association remained significant after adjustment for publication bias using the trim and fill method. Sensitivity analysis showed that the effect size of the Taq1A polymorphism on AD risk was moderate and not influenced by any individual study. The pooled odds ratio from published studies decreased with the year of publication, but stabilized after the year 2001. Subgroup analysis indicated that publication bias could be influenced by racial ancestry. In summary, this large-scale meta-analysis confirmed the association between the Taq1A polymorphism and AD. Future studies are required to investigate the functional significance of the ANKK1/DRD2 Taq1A polymorphism in AD.

Dopaminergic genes modulate response inhibition in alcohol abusing adults

Compulsion in alcohol use disorders (AUD) has been attributed to impairment in response inhibition. Because genes that regulate dopamine (DA) have been implicated not only for risk for AUD but also for impulsivity based on behavioral studies, we set out to examine the underlying neural mechanisms associated with these effects. We collected functional magnetic resonance imaging images on 53 heavy drinking but otherwise healthy adults while performing the Go/NoGo task. We predicted that genetic variants previously reported in the literature to be associated with substance abuse, specifically the DRD2 rs1799732 and DRD4 VNTR, will modulate neural processes underlying response inhibition. Our results showed differential neural response for the DRD4 VNTR during successful inhibition in the inferior frontal gyrus (IFG) (cluster-corrected P<0.05, z=1.9). Similarly, DRD2 rs1799732 groups were significantly different in the precuneus and cingulate gyrus during successful response inhibition (cluster-corrected P<0.05, z=1.9). These findings provide further evidence for the role of DAergic genes in modulating neural response in areas that underlie response inhibition and self-monitoring processes. Variants within these genes appear to influence processes related to impulsive behavior, which may increase one's risk for alcohol abuse and dependence.

Identification of a novel ANKK1 and other dopaminergic (DRD2 and DBH) gene variants in migraine susceptibility

The dopaminergic system plays an important role in migraine and its clinical subtypes. Hypersensitization of dopamine receptor type 2 (DRD2) in migraine led to successful administration of receptor antagonists in antimigraine therapy. Ankyrin repeats and kinase domain containing 1 (ANKK1) gene in DRD2 loci is linked to comorbid neurological disorders. Dopamine beta hydroxylase (DBH) is responsible for maintaining dopamine-to-norepinephrine ratio implicated in migraine pathophysiology. Therefore, we aimed to look for association of functional variants in ANKK1 (rs1800497), DRD2 (rs6275 and rs1799732) and DBH (rs7239728 and rs1611115) genes with migraine susceptibility. The present study was carried out in two dependent cohorts (n primary = 208, n secondary = 127, n controls = 200). The results of the cohorts were pooled by meta-analysis using Fisher's and Mantel-Haenszel test. Benjamini-Hochberg false discovery rate test was used to correct for multiple comparisons. Computer algorithm-based TANGO, WALTZ and LIMBO predictions were used to evaluate the effect of missense polymorphism (rs1800497). For ANKK1 polymorphism, variant genotype and allele showed significant associations with migraine risk. A significant protective effect of variant DRD2 rs6275 polymorphism was noticed. DBH rs7239728 imparted significant risk at genotypic, allelic and carrier analyses. We identified a risk haplotype in DRD2 loci. Two genotype interactions between ANKK1rs1800497 and DBHrs72393728 polymorphisms showed significant risks. The variant gene product of ANKK1 rs1800497 was predicted with decreased aggregation of ANKK1 protein. In conclusion, we identified novel genetic variants, haplotype and gene interactions in dopaminergic pathway as potential risk factors for migraine susceptibility.

Adenosinergic system: an assorted approach to therapeutics for drug addiction

Adenosine is an endogenous purine nucleoside and it is extensively present in the brain. It exerts several metabolic and neuromodulatory roles in the body. Adenosine also acts as an important messenger molecule for extracellular signaling and shows a homeostatic neuromodulatory function at the synaptic level. Extracellular adenosine exerts a wide variety of biological actions through four cell surface G-protein-coupled receptor subtypes, namely A1, A2A, A2B and A3 adenosine receptors. The extracellular levels of adenosine have been found to be enhanced in several neuropathological conditions, including drug addiction, and thus a neuroprotective role of adenosine was perceived by various experimental studies. The aversive withdrawal symptoms emanating from drug discontinuation provokes rebound drug intake patterns. In addition, alteration of neurotransmitter(s) release and changes in receptor expression contribute to the behavioral changes of drug withdrawal. Furthermore, the abuse of major drugs such as alcohol and opioids are reported to modulate extracellular adenosine levels. In this context, the neuromodulatory functions of adenosine would be valuable if projected to the clinical applications and thus, an increasing attention is currently given to the functional role of adenosine in human addictive disorders. This review will focus on recent clinical and experimental studies that reveal the actions of adenosine and related ligands in drug addiction and various drug-withdrawal syndromes. The evidence and reports provided in this review highlight the looming therapeutic potential of purinergic drugs, with a hope that new therapeutic interventions based on the adenosinergic concept will emerge in the coming years for the management of drug withdrawal syndrome.

Do alcohol-dependent individuals with DRD2 A1 allele have an increased risk of relapse? A pilot study

AIMS

The TaqIA polymorphism of the dopamine D2 receptor (DRD2) gene has been extensively studied in relation to alcoholism, and the TaqI A1 allele appears to be over-represented in alcohol-dependent individuals. In a recent study, this allele has also been associated with a highly increased mortality rate in alcohol-dependent individuals. In the present study, we investigated whether the TaqI A1 allele of the DRD2 gene region was associated with a higher relapse rate in alcohol-dependent individuals.

METHODS

Adult women (n = 10) and men (n = 40) with a diagnosis of alcohol-dependence were recruited from two Swedish 12-step treatment units for alcoholism. Subjects were genotyped for the TaqIA polymorphism. On average, 1&frac12; year after the end of the treatment program, subjects were re-interviewed by using the alcohol-related items from the Addiction Severity Index follow-up version.

RESULTS

Thirty-three (66%) subjects self-reported relapse and 17 (34%) abstinence during the follow-up period. Thirty-sex percent (18/50) were carriers of the A1 allele of the DRD2 gene region, and 64% (32/50) were non-carriers. Among the carriers of the A1 allele, 89% (16/18) reported relapse in contrast to 53% (17/32) in the non-carriers (P = 0.01; odds ratio = 7.1).

CONCLUSION

The present study is, to our knowledge, the first report of an association between the TaqI A1 allele and a substantially increased relapse rate. It should be emphasized that the number of subjects is relatively small, and this investigation should therefore be considered as a pilot study.