Allelic and genotypic associations of DRD2 TaqI A polymorphism with heroin dependence in Spanish subjects: a case control study

Role of antioxidants in the neurobiology of drug addiction: An update

Relationships between protective enzymatic and non-enzymatic pro-antioxidant mechanisms and addictive substances use disorders (SUDs) are analyzed here, based on the results of previous research, as well as on the basis of our current own studies. This review introduces new aspects of comparative analysis of associations of pro-antixidant and neurobiological effects in patients taking psychoactive substances and complements very limited knowledge about relationships with SUDs from different regions, mainly Europe. In view of the few studies on relations between antioxidants and neurobiological processes acting in patients taking psychoactive substances, this review is important from the point of view of showing the state of knowledge, directions of diagnosis and treatment, and further research needed explanation. We found significant correlations between chemical elements, pro-antioxidative mechanisms, and lipoperoxidation in the development of disorders associated with use of addictive substances, therefore elements that show most relations (Pr, Na, Mn, Y, Sc, La, Cr, Al, Ca, Sb, Cd, Pb, As, Hg, Ni) may be significant factors shaping SUDs. The action of pro-antioxidant defense and lipid peroxidation depends on the pro-antioxidative activity of ions. We explain the strongest correlations between Mg and Sb, and lipoperoxidation in addicts, which proves their stimulating effect on lipoperoxidation and on the induction of oxidative stress. We discussed which mechanisms and neurobiological processes change susceptibility to SUDs. The innovation of this review is to show that addicted people have lower activity of dismutases and peroxidases than healthy ones, which indicates disorders of antioxidant system and depletion of enzymes after long-term tolerance of stressors. We explain higher level of catalases, reductases, ceruloplasmin, bilirubin, retinol, α-tocopherol and uric acid of addicts. In view of poorly understood factors affecting addiction, analysis of interactions allows for more effective understanding of pathogenetic mechanisms leading to formation of addiction and development the initiation of directed, more effective treatment (pharmacological, hormonal) and may be helpful in the diagnosis of psychoactive changes.

Single Nucleotide Variants (SNVs) of the Mesocorticolimbic System Associated with Cardiovascular Diseases and Type 2 Diabetes: A Systematic Review

The mesocorticolimbic (MCL) system is crucial in developing risky health behaviors which lead to cardiovascular diseases (CVDs) and type 2 diabetes (T2D). Although there is some knowledge of the MCL system genes linked to CVDs and T2D, a comprehensive list is lacking, underscoring the significance of this review. This systematic review followed PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. The PubMed and Web of Science databases were searched intensively for articles related to the MCL system, single nucleotide variants (SNVs, formerly single nucleotide polymorphisms, SNPs), CVDs, T2D, and associated risk factors. Included studies had to involve a genotype with at least one MCL system gene (with an identified SNV) for all participants and the analysis of its link to CVDs, T2D, or associated risk factors. The quality assessment of the included studies was performed using the Q-Genie tool. The VEP and DAVID tools were used to annotate and interpret genetic variants and identify enriched pathways and gene ontology terms associated with the gene list. The review identified 77 articles that met the inclusion criteria. These articles provided information on 174 SNVs related to the MCL system that were linked to CVDs, T2D, or associated risk factors. The COMT gene was found to be significantly related to hypertension, dyslipidemia, insulin resistance, obesity, and drug abuse, with rs4680 being the most commonly reported variant. This systematic review found a strong association between the MCL system and the risk of developing CVDs and T2D, suggesting that identifying genetic variations related to this system could help with disease prevention and treatment strategies.

Genetic Addiction Risk and Psychological Profiling Analyses for "Preaddiction" Severity Index

Since 1990, when our laboratory published the association of the DRD2 Taq A1 allele and severe alcoholism in JAMA, there has been an explosion of genetic candidate association studies, including genome-wide association studies (GWAS). To develop an accurate test to help identify those at risk for at least alcohol use disorder (AUD), a subset of reward deficiency syndrome (RDS), Blum's group developed the genetic addiction risk severity (GARS) test, consisting of ten genes and eleven associated risk alleles. In order to statistically validate the selection of these risk alleles measured by GARS, we applied strict analysis to studies that investigated the association of each polymorphism with AUD or AUD-related conditions, including pain and even bariatric surgery, as a predictor of severe vulnerability to unwanted addictive behaviors, published since 1990 until now. This analysis calculated the Hardy-Weinberg Equilibrium of each polymorphism in cases and controls. Pearson's χ2 test or Fisher's exact test was applied to compare the gender, genotype, and allele distribution if available. The statistical analyses found the OR, 95% CI for OR, and the post risk for 8% estimation of the population's alcoholism prevalence revealed a significant detection. Prior to these results, the United States and European patents on a ten gene panel and eleven risk alleles have been issued. In the face of the new construct of the "preaddiction" model, similar to "prediabetes", the genetic addiction risk analysis might provide one solution missing in the treatment and prevention of the neurological disorder known as RDS.

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

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

DRD2 and ANKK1 genes associate with late-onset heroin dependence in men

Objectives: Dopamine plays an important role in reward system of heroin dependence (HD), and dopaminergic D2 receptor (DRD2) gene is a candidate for the aetiology of HD. Ankyrin repeat and kinase domain containing 1 (ANKK1) gene is proximal to DRD2 and may influence its expression. We explored whether DRD2 and ANKK1 associate with occurrence of HD, and whether the genetic variants influence personality traits in male patients with HD.Methods:DRD2/ANKK1 polymorphisms were analysed in 950 unrelated Han Chinese male participants (601 HD patients and 349 healthy controls). All participants were screened using the same assessment tools and all patients met the diagnostic criteria of HD. Personality traits were assessed in 274 patients and 142 controls using the Tridimensional Personality Questionnaire.Results: According to the allele, genotype and haplotype frequency analysis, we observed an association between HD and several DRD2/ANKK1 polymorphisms (rs1800497, rs1800498, rs1079597 and rs4648319); this was most notable in the late-onset HD subgroup. However, these DRD2/ANKK1 polymorphisms did not associate with specific personality traits in HD patients and controls.Conclusions:DRD2/ANKK1 may play an important role in occurrence of late-onset HD, but does not mediate the relationship between personality traits and HD in Han Chinese male population.

The genetic epidemiology of substance use disorder: A review

BACKGROUND

Substance use disorder (SUD) remains a significant public health issue. A greater understanding of how genes and environment interact to regulate phenotypes comprising SUD will facilitate directed treatments and prevention.

METHODS

The literature studying the neurobiological correlates of SUD with a focus on the genetic and environmental influences underlying these mechanisms was reviewed. Results from twin/family, human genetic association, gene-environment interaction, epigenetic literature, phenome-wide association studies are summarized for alcohol, nicotine, cannabinoids, cocaine, and opioids.

RESULTS

There are substantial genetic influences on SUD that are expected to influence multiple neurotransmission pathways, and these influences are particularly important within the dopaminergic system. Genetic influences involved in other aspects of SUD etiology including drug processing and metabolism are also identified. Studies of gene-environment interaction emphasize the importance of environmental context in SUD. Epigenetic studies indicate drug-specific changes in gene expression as well as differences in gene expression related to the use of multiple substances. Further, gene expression is expected to differ by stage of SUD such as substance initiation versus chronic substance use. While a substantial literature has developed for alcohol and nicotine use disorders, there is comparatively less information for other commonly abused substances.

CONCLUSIONS

A better understanding of genetically-mediated mechanisms involved in the neurobiology of SUD provides increased opportunity to develop behavioral and biologically based treatment and prevention of SUD.

Dopaminergic pathway polymorphisms and heroin addiction: further support for association of CSNK1E variants

BACKGROUND & AIM

The dopaminergic pathways have been implicated in the etiology of drug addictions. The aim of this study was to determine if variants in dopaminergic genes are associated with heroin addiction.

MATERIALS & METHODS

The study includes 828 former heroin addicts and 232 healthy controls, of predominantly European ancestry. Ninety seven SNPs (13 genes) were analyzed.

RESULTS

Nine nominally significant associations were observed at CSNK1E, ANKK1, DRD2 and DRD3.

CONCLUSION

The results support our previous report of association of CSNK1E SNP rs1534891 with protection from heroin addiction. CSNK1E interacts with circadian rhythms and DARPP-32 and has been implicated in negative regulation of sensitivity to opioids in rodents. It may be a target for drug addiction treatment. Original submitted 8 August 2014; Revision submitted 8 October 2014.

Neural substrates of cognitive flexibility in cocaine and gambling addictions

BACKGROUND

Individuals with cocaine and gambling addictions exhibit cognitive flexibility deficits that may underlie persistence of harmful behaviours.

AIMS

We investigated the neural substrates of cognitive inflexibility in cocaine users v. pathological gamblers, aiming to disambiguate common mechanisms v. cocaine effects.

METHOD

Eighteen cocaine users, 18 pathological gamblers and 18 controls performed a probabilistic reversal learning task during functional magnetic resonance imaging, and were genotyped for the DRD2/ANKK Taq1A polymorphism.

RESULTS

Cocaine users and pathological gamblers exhibited reduced ventrolateral prefrontal cortex (PFC) signal during reversal shifting. Cocaine users further showed increased dorsomedial PFC (dmPFC) activation relative to pathological gamblers during perseveration, and decreased dorsolateral PFC activation relative to pathological gamblers and controls during shifting. Preliminary genetic findings indicated that cocaine users carrying the DRD2/ANKK Taq1A1+ genotype may derive unique stimulatory effects on shifting-related ventrolateral PFC signal.

CONCLUSIONS

Reduced ventrolateral PFC activation during shifting may constitute a common neural marker across gambling and cocaine addictions. Additional cocaine-related effects relate to a wider pattern of task-related dysregulation, reflected in signal abnormalities in dorsolateral and dmPFC.

Overlapping dopaminergic pathway genetic susceptibility to heroin and cocaine addictions in African Americans

Drugs of abuse activate the mesolimbic dopaminergic pathway. Genetic variations in the dopaminergic system may contribute to drug addiction. Several processes are shared between cocaine and heroin addictions but some neurobiological mechanisms may be specific. This study examined the association of 98 single nucleotide polymorphisms in 13 dopamine-related genes with heroin addiction (OD) and/or cocaine addiction (CD) in a sample of 801 African Americans (315 subjects with OD ± CD, 279 subjects with CD, and 207 controls). Single-marker analyses provided nominally significant evidence for associations of 24 SNPs) in DRD1, ANKK1/DRD2, DRD3, DRD5, DBH, DDC, COMT and CSNK1E. A DRD2 7-SNPs haplotype that includes SNPs rs1075650 and rs2283265, which were shown to alter D2S/D2L splicing, was indicated in both addictions. The Met allele of the functional COMT Val158Met was associated with protection from OD. None of the signals remained significant after correction for multiple testing. The study results are in accordance with the results of previous studies, including our report of association of DRD1 SNP rs5326 with OD. The findings suggest the presence of an overlap in genetic susceptibility for OD and CD, as well as shared and distinct susceptibility for OD in subjects of African and European descent.

Association between DRD2/ANKK1 TaqIA polymorphism and common illicit drug dependence: evidence from a meta-analysis

BACKGROUND

Growing evidence indicated conflicting results about the dopamine receptor D2 (DRD2)/kinase domain containing 1 gene (ANKK1) TaqIA single nucleotide polymorphism (rs1800497) and common illicit drug dependence risk including stimulants, opioid and marijuana. We conducted a meta-analysis to evaluate the association between the polymorphism and common illicit drug dependence risk.

METHOD

A total of 25 available studies (26 subgroups) testing the association between the polymorphism and common illicit drug dependence were examined through Oct 2013. Pooled odds ratios (ORs) and 95% confidence intervals (CI) were estimated using fixed- and random-effects models when appropriate. Heterogeneity and publication bias were evaluated.

RESULTS

We found the DRD2/ANKK1 TaqIA polymorphism was significantly associated with increased risk of opioid dependence under homozygote, dominant, and recessive genetic model, respectively (homozygote: OR=1.546, 95%CI=1.279-1.87; dominant: OR=1.265, 95%CI=1.055-1.516; recessive: OR=1.409, 95%CI=1.182-1.680). Subgroup analyses were similar to the results of the total population by ethnicity and quality score. Besides, we also found that Caucasian and low-quality studies were major sources of heterogeneity for opioid dependence. We failed to find any significant association between the polymorphism and stimulants or marijuana neither in total population nor subgroup analyses under any genetic model.

CONCLUSIONS

The current meta-analysis suggested that DRD2/ANKK1 TaqIA polymorphism might be associated with opioid dependence risk, but not associated with stimulants or marijuana dependence.

Association of dopamine receptor D2 TaqI A polymorphism and cannabis use disorder in Lagos, Nigeria

TaqI A polymorphism (rs1800497) has been linked to many substance use disorders but there is a shortage of data on cannabis use disorder. Nigeria has a huge burden of cannabis use disorder, prompting our investigation of the relation between cannabis use disorder and the TaqI A polymorphism among males in Lagos, Nigeria. We recruited 106 males with cannabis use disorder based on International Classification of Diseases, version 10 (ICD-10) and 98 cannabis-naive males for the study. Cannabis use disorder was assessed using the Severity of Dependence Scale (SDS) and Cannabis Use Disorder Identification Test (CUDIT). Genotyping was done using the Restriction Fragment Length Polymorphism (RFLP). The frequency of the A1 allele was higher among the cannabis users (57.8%) compared with the nonusers (42.2%). The genotype distribution was found to be in Hardy-Weinberg equilibrium in both populations. The homozygous A1 genotype alone contributed 11.8% to the variance in the SDS scores. However, both A1/A1 and A1/A2 genotypes contributed to the variance in the CUDIT scores (10.2% and 5.1%, respectively). In conclusion, the distribution of the A1 allele among the general population in this study correlates with the previously reported findings in a southwestern Nigerian population. We also found that carrying an A1 allele appears to be a significant predictor of cannabis use disorder. The result suggests that carrying just a single allele of the A1 is enough to predict cannabis abuse, as shown by the allele association with CUDIT scores. However, double A1 alleles seem to be necessary for the prediction of dependence.

HIV-related cognitive impairment shows bi-directional association with dopamine receptor DRD1 and DRD2 polymorphisms in substance-dependent and substance-independent populations

It has been postulated that drugs of abuse act synergistically with HIV, leading to increased neurotoxicity and neurocognitive impairment. The CNS impacts of HIV and drug use converge on the mesocorticolimbic dopamine (DA) system, which contains two main receptor subtypes: dopamine receptors 1 (DRD1) and 2 (DRD2). DRD1 and DRD2 have been linked to substance dependence; whether they predict HIV-associated neurocognitive disorder (HAND) is unclear. Using an advanced-stage HIV+ population, we sought to determine if drug dependence impacts the contribution of DA receptor polymorphisms on neurocognition. We observed that both DRD1 and DRD2 polymorphisms were associated with opiate and cocaine dependence (P < 0.05) in Caucasian subjects, but not African-American individuals. Using linear regression analysis, we examined the polymorphisms for associations with neuropsychological performance in global and cognitive domain T-scores (Motor, Processing Speed, Verbal Fluency, Learning, Memory, Executive Functioning, Working Memory) while controlling for opiate and cocaine dependency. In the Motor domain, we observed an association for two DRD2 polymorphisms (P < 0.05) in Caucasian subjects. The effects differed for substance dependence groups as the direction of the correlations with DRD2 were opposite to what was seen in subjects without these dependencies. In African-American subjects, associations were observed in nearly every domain, and again, the direction of the correlation differed between substance-dependent and substance-independent groups. We conclude that studies to examine genetic risk for HAND must carefully account for substance dependence patterns when assaying dopaminergic systems, as the neurobiological substrates of cognition in HIV populations may vary with tonic alterations secondary to chronic substance exposures.

Association of dopamine receptor gene polymorphism and psychological personality traits in liability for opioid addiction

There is a clear evidence that same psychoactive substance may cause various individual physiological reactions in same environmental conditions. Although there is a general attitude on equal liability to opioid addiction, latest genetic analysis findings imply there are certain quantifiable factors that could lead to elevated individual liability towards development of opioid addiction. The goal of this study was to investigate association of certain personality traits and genetic factors (separately and in combination) with heroin addiction. Total of 200 individuals participated in the study: 100 patients on Metadone Maintenance Treatment (MMT) and 100 age and sex matched healthy volunteers. All were medically examined, interviewed and psychologically evaluated using Eysenck personality questionnaire (EPQ) and genotyped for DRD2 (rs1800497) using PCR-RFLP method. Overrepresentation of certain personality traits (neuroticism, psychoticism and extraversion/ intraversion), together with environemental risk factors such as: upbringing within incomplete families and familial history of psychotropic substances abuse, are associated with high-risk development of opioid addiction.

A variant in ANKK1 modulates acute subjective effects of cocaine: a preliminary study

This study aimed to evaluate whether functional variants in the ankyrin repeat and kinase domain-containing 1 (ANKK1) gene and/or the dopamine receptor D2 (DRD2) gene modulate the subjective effects (reward or non-reward response to a stimulus) produced by cocaine administration. Cocaine-dependent participants (N = 47) were administered 40 mg of cocaine or placebo at time 0, and a subjective effects questionnaire (visual analog scale) was administered 15 min prior to cocaine administration, and at 5, 10, 15 and 20 min following administration. The influence of polymorphisms in the ANKK1 and DRD2 genes on subjective experience of cocaine in the laboratory was tested. Participants with a T allele of ANKK1 rs1800497 experienced greater subjective 'high' (P = 0.00006), 'any drug effect' (P = 0.0003) and 'like' (P = 0.0004) relative to the CC genotype group. Although the variant in the DRD2 gene was shown to be associated with subjective effects, linkage disequilibrium analysis revealed that this association was driven by the ANKK1 rs1800497 variant. A participant's ANKK1 genotype may identify individuals who are likely to experience greater positive subjective effects following cocaine exposure, including greater 'high' and 'like', and these individuals may have increased vulnerability to continue using cocaine or they may be at greater risk to relapse during periods of abstinence. However, these results are preliminary and replication is necessary to confirm these findings.

ANKK1 and DRD2 pharmacogenetics of disulfiram treatment for cocaine abuse

OBJECTIVE

Disulfiram is a potential cocaine addiction pharmacotherapy. Since dopamine deficiency has been found with cocaine addiction, our objective was to examine whether functional variants in the ankyrin repeat and kinase domain-containing 1 (ANKK1) and/or the dopamine receptor D2 (DRD2) genes interact with response to treatment with disulfiram.

MATERIALS AND METHODS

Cocaine and opioid codependent (DSM-IV) patients were stabilized on methadone and subsequently randomized into treatment groups - disulfiram (250 mg/day, N=31) or placebo (N=37). They were genotyped for ANKK1 (rs1800497) and DRD2 (rs2283265) polymorphisms, and the data were evaluated for an association between a cocaine-free state, as assessed by cocaine-free urine samples, and disulfiram treatment. Data were analyzed using repeated measures analysis of variance corrected for population structure.

RESULTS

Patients with CT or TT ANKK1 genotypes dropped from 80 to 52% cocaine-positive urines on disulfiram (N=13; P≤0.0001), whereas those on placebo (N=20) showed no treatment effect. Patients carrying the CC ANKK1 genotype showed no effect on treatment with disulfiram (N=18) or placebo (N=17). The GT/TT DRD2 genotype group showed a significant decrease in the number of cocaine-positive urine samples on disulfiram (N=9; 67-48%; P ≤ 0.0001), whereas the GG DRD2 genotype group showed only a marginal decrease (N=23; 84-63%; P=0.04). Genotype pattern analysis revealed that individuals carrying at least one minor allele in either gene responded better to disulfiram treatment (N=13; P ≤ 0.0001) compared with individuals carrying only the major alleles (N=17).

CONCLUSION

A patient's genotype for ANKK1, DRD2, or both, may be used to identify individuals for whom disulfiram may be an effective pharmacotherapy for cocaine dependence.

Multivariate analysis of dopaminergic gene variants as risk factors of heroin dependence

BACKGROUND

Heroin dependence is a debilitating psychiatric disorder with complex inheritance. Since the dopaminergic system has a key role in rewarding mechanism of the brain, which is directly or indirectly targeted by most drugs of abuse, we focus on the effects and interactions among dopaminergic gene variants.

OBJECTIVE

To study the potential association between allelic variants of dopamine D2 receptor (DRD2), ANKK1 (ankyrin repeat and kinase domain containing 1), dopamine D4 receptor (DRD4), catechol-O-methyl transferase (COMT) and dopamine transporter (SLC6A3) genes and heroin dependence in Hungarian patients.

METHODS

303 heroin dependent subjects and 555 healthy controls were genotyped for 7 single nucleotide polymorphisms (SNPs) rs4680 of the COMT gene; rs1079597 and rs1800498 of the DRD2 gene; rs1800497 of the ANKK1 gene; rs1800955, rs936462 and rs747302 of the DRD4 gene. Four variable number of tandem repeats (VNTRs) were also genotyped: 120 bp duplication and 48 bp VNTR in exon 3 of DRD4 and 40 bp VNTR and intron 8 VNTR of SLC6A3. We also perform a multivariate analysis of associations using Bayesian networks in Bayesian multilevel analysis (BN-BMLA).

FINDINGS AND CONCLUSIONS

In single marker analysis the TaqIA (rs1800497) and TaqIB (rs1079597) variants were associated with heroin dependence. Moreover, -521 C/T SNP (rs1800955) of the DRD4 gene showed nominal association with a possible protective effect of the C allele. After applying the Bonferroni correction TaqIB was still significant suggesting that the minor (A) allele of the TaqIB SNP is a risk component in the genetic background of heroin dependence. The findings of the additional multiple marker analysis are consistent with the results of the single marker analysis, but this method was able to reveal an indirect effect of a promoter polymorphism (rs936462) of the DRD4 gene and this effect is mediated through the -521 C/T (rs1800955) polymorphism in the promoter.

ANKK1, TTC12, and NCAM1 polymorphisms and heroin dependence: importance of considering drug exposure

CONTEXT

The genetic contribution to liability for opioid dependence is well established; identification of the responsible genes has proved challenging.

OBJECTIVE

To examine association of 1430 candidate gene single-nucleotide polymorphisms (SNPs) with heroin dependence, reporting here only the 71 SNPs in the chromosome 11 gene cluster (NCAM1, TTC12, ANKK1, DRD2) that include the strongest observed associations.

DESIGN

Case-control genetic association study that included 2 control groups (lacking an established optimal control group).

SETTING

Semistructured psychiatric interviews.

PARTICIPANTS

A total of 1459 Australian cases ascertained from opioid replacement therapy clinics, 531 neighborhood controls ascertained from economically disadvantaged areas near opioid replacement therapy clinics, and 1495 unrelated Australian Twin Registry controls not dependent on alcohol or illicit drugs selected from a twin and family sample.

MAIN OUTCOME MEASURE

Lifetime heroin dependence.

RESULTS

Comparison of cases with Australian Twin Registry controls found minimal evidence of association for all chromosome 11 cluster SNPs (P ≥ .01); a similar comparison with neighborhood controls revealed greater differences (P ≥ 1.8 × 10(-4)). Comparing cases (n = 1459) with the subgroup of neighborhood controls not dependent on illicit drugs (n = 340), 3 SNPs were significantly associated (correcting for multiple testing): ANKK1 SNP rs877138 (most strongly associated; odds ratio = 1.59; 95% CI, 1.32-1.92; P = 9.7 × 10(-7)), ANKK1 SNP rs4938013, and TTC12 SNP rs7130431. A similar pattern of association was observed when comparing illicit drug-dependent (n = 191) and nondependent (n = 340) neighborhood controls, suggesting that liability likely extends to nonopioid illicit drug dependence. Aggregate heroin dependence risk associated with 2 SNPs, rs877138 and rs4492854 (located in NCAM1), varied more than 4-fold (P = 2.7 × 10(-9) for the risk-associated linear trend).

CONCLUSIONS

Our results provide further evidence of association for chromosome 11 gene cluster SNPs with substance dependence, including extension of liability to illicit drug dependence. Our findings highlight the necessity of considering drug exposure history when selecting control groups for genetic investigations of illicit drug dependence.

The aldehyde dehydrogenase 2 gene is associated with heroin dependence

BACKGROUND

Determining the influences of genes involved in metabolizing dopamine and encoding dopamine receptors, such as the aldehyde dehydrogenase 2 (ALDH2) and dopamine D2 receptor/ankyrin repeat and kinase domain containing 1 (DRD2/ANKK1) genes, is critical for understanding addictive behavior. Therefore, we investigated the association between the ALDH2 and DRD2/ANKK1 Taq IA polymorphisms and heroin dependence.

METHODS

Heroin-dependent Han Chinese patients (250) and healthy controls (312) were recruited. ALDH2 and DRD2/ANKK1 Taq IA polymorphisms were genotyped.

RESULTS

The frequency of ALDH2*1/*2 and *2/*2 genotypes was significantly higher in heroin-dependent patients than in controls, but the frequency of DRD2 Taq IA genotypes was not significantly different. Logistic regression analysis showed no significant interaction between ALDH2 and DRD2 Taq IA genotypes in patients.

CONCLUSIONS

The ALDH2 polymorphism, but not the DRD2, was associated with heroin dependence.

Generational association studies of dopaminergic genes in reward deficiency syndrome (RDS) subjects: selecting appropriate phenotypes for reward dependence behaviors

Abnormal behaviors involving dopaminergic gene polymorphisms often reflect an insufficiency of usual feelings of satisfaction, or Reward Deficiency Syndrome (RDS). RDS results from a dysfunction in the "brain reward cascade," a complex interaction among neurotransmitters (primarily dopaminergic and opioidergic). Individuals with a family history of alcoholism or other addictions may be born with a deficiency in the ability to produce or use these neurotransmitters. Exposure to prolonged periods of stress and alcohol or other substances also can lead to a corruption of the brain reward cascade function. We evaluated the potential association of four variants of dopaminergic candidate genes in RDS (dopamine D1 receptor gene [DRD1]; dopamine D2 receptor gene [DRD2]; dopamine transporter gene [DAT1]; dopamine beta-hydroxylase gene [DBH]).

METHODOLOGY

We genotyped an experimental group of 55 subjects derived from up to five generations of two independent multiple-affected families compared to rigorously screened control subjects (e.g., N = 30 super controls for DRD2 gene polymorphisms). Data related to RDS behaviors were collected on these subjects plus 13 deceased family members.

RESULTS

Among the genotyped family members, the DRD2 Taq1 and the DAT1 10/10 alleles were significantly (at least p < 0.015) more often found in the RDS families vs. controls. The TaqA1 allele occurred in 100% of Family A individuals (N = 32) and 47.8% of Family B subjects (11 of 23). No significant differences were found between the experimental and control positive rates for the other variants.

CONCLUSIONS

Although our sample size was limited, and linkage analysis is necessary, the results support the putative role of dopaminergic polymorphisms in RDS behaviors. This study shows the importance of a nonspecific RDS phenotype and informs an understanding of how evaluating single subset behaviors of RDS may lead to spurious results. Utilization of a nonspecific "reward" phenotype may be a paradigm shift in future association and linkage studies involving dopaminergic polymorphisms and other neurotransmitter gene candidates.

Association between polymorphisms of DRD2 and DRD4 and opioid dependence: evidence from the current studies

Several studies have assessed the association between genetic polymorphisms of DRD2 and DRD4 genes and opioid dependence risk, while the results were inconsistent. We performed a meta-analysis, including 6,846 opioid dependence cases and 4,187 controls from 22 individual studies, to evaluate the roles of four variants (DRD2 -141ins/delC, rs1799732; DRD2 311 Ser > Cys, rs1801028; DRD2-related TaqI A, rs1800497 and DRD4 exon III VNTR) in opioid dependence for the first time. We found that the -141delC polymorphism was significantly associated with increased risk of opioid dependence (homozygote comparison: odds ratios [OR], 2.71; 95% confidence interval [CI], 1.74-4.22; dominant comparison: OR, 1.27; 95% CI, 1.09-1.48). Similarly, the TaqI A1 polymorphism was also significantly increased opioid dependence risk (homozygote comparison: OR, 2.06; 95% CI, 1.25-3.42; dominant comparison: OR, 1.34; 95% CI, 1.08-1.67). Moreover, long allele (≥5-repeat) and 7-repeat allele of DRD4 exon III VNTR were found to be associated with significantly increased opioid dependence risk (OR, 1.50; 95% CI, 1.24-1.80 and OR, 1.57; 95%, 1.18-2.09, respectively). However, no association was detected between the DRD2 311 Ser > Cys polymorphism and opioid dependence. In conclusion, our results suggested that DRD2 -141ins/delC, DRD2-related TaqI A and DRD4 exon III VNTR polymorphisms might play important roles in the development of opioid dependence.

Genetic diagnostics of functional variants of the human dopamine D2 receptor gene

INTRODUCTION

The importance of dopamine D2 receptors (DRD2) for central nervous dopaminergic signalling makes variants in the DRD2 gene potential modulators of the risk or course of various behavioural, psychiatric or neurologic diseases (e.g. addiction, schizophrenia, Parkinson's disease). We developed Pyrosequencing genetic screening assays for single nucleotide polymorphisms spanning the whole range of the DRD2 gene locus up to the functionally related ankyrin repeat and kinase domain containing 1 gene (ANKK1) located at approximately 10 kb downstream of DRD2.

METHODS

Assays for 11 genetic variants with reported functional association were developed in DNA samples from 300 unrelated healthy Caucasians and validated by independent conventional sequencing.

RESULTS

In all DNA samples the DRD2/ANKK1 genetic variants were identified correctly as verified by the control samples. The observed frequencies of homozygous, heterozygous and noncarriers of the minor alleles were in agreement with the Hardy-Weinberg equilibrium. Observed minor allele frequencies were DRD2 rs12364283T>C: 6.5%, rs1799978A>G: 4.8%, rs1799732C del: 14.2%, rs4648317C>T: 12.8%, rs1079597G>A: 13.8%, rs1076560G>T: 14.5%, rs1800496C>T: 0.2%, rs1801028C>G: 3.0%, rs6275C>T: 32.7%, rs6277C>T: 53.0% and ANKK1 rs1800497C>T: 17.5%.

CONCLUSION

The presently developed Pyrosequencing assays are provided to facilitate further research toward personalized approaches to pathophysiological conditions involving behavioural, psychiatric and neurologic disorders including addiction, schizophrenia and Parkinson's disease.

Neurogenetics of dopaminergic receptor supersensitivity in activation of brain reward circuitry and relapse: proposing "deprivation-amplification relapse therapy" (DART)

BACKGROUND AND HYPOTHESIS

It is well known that after prolonged abstinence, individuals who use their drug of choice experience a powerful euphoria that often precipitates relapse. While a biological explanation for this conundrum has remained elusive, we hypothesize that this clinically observed "supersensitivity" might be tied to genetic dopaminergic polymorphisms. Another therapeutic conundrum relates to the paradoxical finding that the dopaminergic agonist bromocriptine induces stronger activation of brain reward circuitry in individuals who carry the DRD2 A1 allele compared with DRD2 A2 allele carriers. Because carriers of the A1 allele relative to the A2 allele of the DRD2 gene have significantly lower D2 receptor density, a reduced sensitivity to dopamine agonist activity would be expected in the former. Thus, it is perplexing that with low D2 density there is an increase in reward sensitivity with the dopamine D2 agonist bromocriptine. Moreover, under chronic or long-term therapy with D2 agonists, such as bromocriptine, it has been shown in vitro that there is a proliferation of D2 receptors. One explanation for this relates to the demonstration that the A1 allele of the DRD2 gene is associated with increased striatal activity of L-amino acid decarboxylase, the final step in the biosynthesis of dopamine. This appears to be a protective mechanism against low receptor density and would favor the utilization of an amino acid neurotransmitter precursor like L-tyrosine for preferential synthesis of dopamine. This seems to lead to receptor proliferation to normal levels and results in significantly better treatment compliance only in A1 carriers.

PROPOSAL AND CONCLUSION

We propose that low D2 receptor density and polymorphisms of the D2 gene are associated with risk for relapse of substance abuse, including alcohol dependence, heroin craving, cocaine dependence, methamphetamine abuse, nicotine sensitization, and glucose craving. With this in mind, we suggest a putative physiological mechanism that may help to explain the enhanced sensitivity following intense acute dopaminergic D2 receptor activation: "denervation supersensitivity." Rats with unilateral depletions of neostriatal dopamine display increased sensitivity to dopamine agonists estimated to be 30 to 100 x in the 6-hydroxydopamine (6-OHDA) rotational model. Given that mild striatal dopamine D2 receptor proliferation occurs (20%-40%), it is difficult to explain the extent of behavioral supersensitivity by a simple increase in receptor density. Thus, the administration of dopamine D2 agonists would target D2 sensitization and attenuate relapse, especially in D2 receptor A1 allele carriers. This hypothesized mechanism is supported by clinical trials utilizing amino acid neurotransmitter precursors, enkephalinase, and catechol-O-methyltransferase (COMT) enzyme inhibition, which have resulted in attenuated relapse rates in reward deficiency syndrome (RDS) probands. If future translational research reveals that dopamine agonist therapy reduces relapse in RDS, it would support the proposed concept, which we term "deprivation-amplification relapse therapy" (DART). This term couples the mechanism for relapse, which is "deprivation-amplification," especially in DRD2 A1 allele carriers with natural D2 agonist therapy utilizing amino acid precursors and COMT and enkepalinase inhibition therapy.

Genetic variants altering dopamine D2 receptor expression or function modulate the risk of opiate addiction and the dosage requirements of methadone substitution

AIM

Addictive behavior is importantly mediated by mesolimbic dopaminergic signaling. Here, we comprehensively analyzed the DRD2 gene locus, and in addition, the ANKK1 rs1800497C>T single nucleotide polymorphism (SNP), formerly known as 'dopamine D2 receptor Taq1A C>T polymorphism', for associations with the risk of opiate addiction and the methadone dosage requirements.

METHODS

Allelic frequencies of DRD2/ANKK1 polymorphisms were compared between 85 methadone-substituted Caucasian patients and a random sample of 99 healthy Caucasian controls. Within patients, the average and maximum daily methadone dose during the first year of treatment and the time when that maximum dose was reached were analyzed for an association with DRD2/ANKK1 genetics.

RESULTS

Compared with the control group, drug users carried more frequently the minor allele of DRD2 SNP rs1076560G>T SNP (P=0.022, odds ratio 2.343) or the ATCT haplotype of DRD2 rs1799978A>G, rs1076560G>T, rs6277C>T, ANKK1 rs1800497C>T (P=0.048, odds ratio 2.23), with similar tendencies for ANKK1 rs1800497C>T (P=0.056, odds ratio 2.12) and the TCCTCTT haplotype of DRD2 rs12364283T>C, rs1799732C del, rs4648317C>T, rs1076560G>T, rs6275C>T, rs6277C>T, and ANKK1 rs1800497C>T (P=0.059, odds ratio 2.31). The average and maximum daily methadone doses were significantly associated with the DRD2 rs6275C>T SNP (P=0.016 and 0.005 for average and maximum dose, respectively). Carriers of the variant rs6275T allele needed higher methadone doses than noncarriers. In addition, this variant was associated with a longer time to reach the maximum methadone dose (P=0.025).

CONCLUSION

On the basis of an analysis spanning the whole gene locus, from the DRD2 promoter to the ANKK1 rs1800497C>T polymorphism, DRD2 genetic polymorphisms modulate both the risk of opiate addiction, leading to the necessity of methadone substitution therapy, and the course of this therapy in terms of dosage requirements.

Gender effect on association between DRD2 polymorphism and substance dependence in a Spanish sample

Our aim was to examine a possible association between substance dependence and the TaqIA polymorphism of the D2 dopamine receptor (DRD2), a single nucleotide polymorphism (SNP) located at the 3' UTR region of the DRD2 gene. A case-control design stratified by gender was used to analyze the genotypes of this SNP in a sample of 125 substance-dependent patients according to DSM-IV and 203 blood donors recruited as controls in two general city hospitals in Madrid, Spain. Genomic DNA from peripheral blood samples was amplified through PCR to identify the variants of the SNP in the DRD2 gene. Analyses performed with Chi(2) tests revealed that the A1 allele (A1/A1 and A1/A2 genotypes) of the Taq 1A SNP of the DRD2 gene was significantly associated with substance dependence in males, but not in the whole sample. Male patients had significantly higher rates of the A1-containing genotypes than male controls. The finding of an association between substance dependence and the DRD2 gene TaqIA SNP only in males suggests the existence of gender-specific differences in the genetic underpinnings of substance dependence.

The ANKK1 kinase gene and psychiatric disorders

The TaqIA single nucleotide polymorphism (SNP, rs1800497), which is located in the gene that codes for the putative kinase ANKK1 (ANKK1) near the termination codon of the D2 dopamine receptor gene (DRD2; chromosome 11q22-q23), is the most studied genetic variation in a broad range of psychiatric disorders and personality traits. A large number of individual genetic association studies have found that the TaqIA SNP is linked to alcoholism and antisocial traits. In addition, it has also been related to other conditions such as schizophrenia, eating disorders, and some behavioral childhood disorders. The TaqIA A1 allele is mainly associated with addictions, antisocial disorders, eating disorders, and attention-deficit/hyperactivity disorders, while the A2 allele occurs more frequently in schizophrenic and obsessive-compulsive patients. Current data show that the TaqIA polymorphism may be a marker of both DRD2 and ANKK1 genetic variants. ANKK1 would belong to a family of kinases involved in signal transduction. This raises the question of whether signaling players intervene in the pathophysiology of psychiatric disorders. Basic research on the ANKK1 protein and its putative interaction with the D2 dopamine receptor could shed light on this issue.

Genetics of dopamine receptors and drug addiction: a comprehensive review

Drug dependence is a chronic, relapsing disorder in which compulsive drug-seeking and drug-taking behaviours persist despite serious negative consequences. Addictive substances, such as opioids, ethanol, psychostimulants and nicotine, induce pleasant states or relieve distress, effects that contribute to their recreational use. Dopamine is critically involved in drug addiction processes. However, the role of the various dopaminergic receptor subtypes has been difficult to delineate. Here, we will review the information collected implicating the receptors of the D1 family (DRD1 and DRD5) and of the D2 family (DRD2, DRD3 and DRD4) in drug addiction. We will summarize the distribution of these receptors in the brain, the preclinical experiments carried out with pharmacological and transgenic approaches and the genetic studies carried out linking genetic variants of these receptors to drug addiction phenotypes. A meta-analysis of the studies carried out evaluating DRD2 and alcohol dependence is also provided, which indicates a significant association. Overall, this review indicates that different aspects of the addiction phenotype are critically influenced by dopaminergic receptors and that variants of those genes seem to influence some addiction phenotypes in humans.

The interaction of DRD2 and violent victimization on depression: an analysis by gender and race

BACKGROUND

Recent research has shown that a polymorphism in the dopamine D2 receptor gene (DRD2) moderates the association between stressful life events and depression. The present study builds off this literature and examines whether DRD2 moderates the effect of violent victimization on depression. Furthermore, the current analyses investigate whether the effects of DRD2 and violent victimization vary by gender and by race for females.

METHODS

Respondents from waves II and III of the National Longitudinal Study of Adolescent Health (Add Health) completed questionnaires regarding their depressive symptoms and violent victimization experiences (n = 2380).

RESULTS

Multivariate regression results reveal that violent victimization has a strong independent effect on depressive symptoms for Caucasian females. In contrast, violent victimization is only associated with higher levels of depressive symptoms among African American females when they carry at least one A1 allele of DRD2. Results also show that DRD2 has a significant independent effect on depressive symptoms for males and African American females.

CONCLUSIONS

The results suggest that African American females who carry the A1 allele of DRD2 may be more vulnerable to the negative effects of violent victimization than African American females who do not carry at least one copy of the A1 allele.

LIMITATIONS

The current study's findings may not generalize to clinical populations, adults, and individuals residing in other countries. In addition, the effects of DRD2 may reflect other polymorphisms that are in linkage with DRD2.

Impulsivity as a vulnerability marker for substance-use disorders: review of findings from high-risk research, problem gamblers and genetic association studies

There is a longstanding association between substance-use disorders (SUDs) and the psychological construct of impulsivity. In the first section of this review, personality and neurocognitive data pertaining to impulsivity will be summarised in regular users of four classes of substance: stimulants, opiates, alcohol and 3,4-methylenedioxymethamphetamine (MDMA). Impulsivity in these groups may arise via two alternative mechanisms, which are not mutually exclusive. By one account, impulsivity may occur as a consequence of chronic exposure to substances causing harmful effects on the brain. By the alternative account, impulsivity pre-dates SUDs and is associated with the vulnerability to addiction. We will review the evidence that impulsivity is associated with addiction vulnerability by considering three lines of evidence: (i) studies of groups at high-risk for development of SUDs; (ii) studies of pathological gamblers, where the harmful consequences of the addiction on brain structure are minimised, and (iii) genetic association studies linking impulsivity to genetic risk factors for addiction. Within each of these three lines of enquiry, there is accumulating evidence that impulsivity is a pre-existing vulnerability marker for SUDs.