Dopamine D2 receptor gene and alcoholism among four aboriginal groups and Han in Taiwan

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.

Hypothesizing dopaminergic genetic antecedents in schizophrenia and substance seeking behavior

The dopamine system has been implicated in both substance use disorder (SUD) and schizophrenia. A recent meta-analysis suggests that A1 allele of the DRD2 gene imposes genetic risk for SUD, especially alcoholism and has been implicated in Reward Deficiency Syndrome (RDS). We hypothesize that dopamine D2 receptor (DRD2) gene Taq1 A2 allele is associated with a subtype of non-SUD schizophrenics and as such may act as a putative protective agent against the development of addiction to alcohol or other drugs of abuse. Schizophrenics with SUD may be carriers of the DRD2 Taq1 A1 allele, and/or other RDS reward polymorphisms and have hypodopaminergic reward function. One plausible mechanism for alcohol seeking in schizophrenics with SUD, based on previous research, may be a deficiency of gamma type endorphins that has been linked to schizophrenic type psychosis. We also propose that alcohol seeking behavior in schizophrenics, may serve as a physiological self-healing process linked to the increased function of the gamma endorphins, thereby reducing abnormal dopaminergic activity at the nucleus accumbens (NAc). These hypotheses warrant further investigation and cautious interpretation. We, therefore, encourage research involving neuroimaging, genome wide association studies (GWAS), and epigenetic investigation into the relationship between neurogenetics and systems biology to unravel the role of dopamine in psychiatric illness and SUD.

The association between DRD2/ANKK1 and genetically informed measures of alcohol use and problems

In 1990, Blum and colleagues first reported an association between DRD2 and alcoholism. While there have been subsequent replications of this genetic association, there have also been numerous studies that failed to detect an association between DRD2 and alcohol dependence. We propose that one aspect contributing to this inconsistency is the variation in alcohol phenotype used across studies. Within the population-based Finnish twin sample, FinnTwin16, we previously performed multivariate twin analyses to extract latent genetic factors, which account for the variation across seven measures of alcohol consumption (frequency of drinking, frequency × quantity, frequency of heavy drinking, frequency of intoxication and maximum drinks in a 24-hour period) and problems (the Rutgers Alcohol Problem Index-RAPI and the Mälmö-modified Michigan Alcohol Screen Test-MmMAST) in 3065 twins. In the present study, we examined the association between 31 DRD2/ANKK1 single-nucleotide polymorphisms (SNPs) and the genetic factor scores generated by twin analyses in a subset of FinnTwin16 (n = 602). We focus on two of the genetic factors: a general alcohol consumption and problems factor score, which represents shared genetic variance across alcohol measures, and a alcohol problems genetic factor score, which loads onto the two indices of problematic drinking (MAST and RAPI). After correction for multiple testing across SNPs and phenotypes, of the 31 SNPs genotyped across DRD2/ANKK1, one SNP (rs10891549) showed significant association with the general alcohol consumption and problems factor score (P = 0.004), and four SNPs (rs10891549, rs1554929, rs6275, rs6279), representing two independent signals after accounting for linkage disequilibrium, showed significant association with the alcohol problems genetic factor score (P = 0.005, P = 0.005, P = 0.003, P = 0.003). In this study, we provide additional positive evidence for the association between DRD2/ANKK1 and alcohol outcomes, including frequency of drinking and drinking problems. Additionally, post hoc analyses indicate stronger association signals using genetic factor scores than individual measures, which suggest that accounting for the genetic architecture of the alcohol measures reduces genetic heterogeneity in alcohol dependence outcomes in this sample and enhances the ability to detect association.

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.

The role of dopamine transporter (SLC6A3) and dopamine D2 receptor/ankyrin repeat and kinase domain containing 1 (DRD2/ANKK1) gene polymorphisms in personality traits

Variations in personality traits are caused by interactions between multiple genes of small effect and environmental factors. To date, gender- and ethnicity-specific variations in personality have been established. In the present study, we aimed to test: (1) the effects of four polymorphisms of dopamine system genes: ANKK1/DRD2 Taq1A, DRD2 rs6275, SLC6A3 40-bp VNTR and rs27072, on personality traits; (2) whether these effects differ between men and women and between Russians and Tatars. A sample of 652 healthy individuals (222 men and 430 women) of Caucasian origin (233 Russians and 419 Tatars) from Russia was subjected to personality traits assessment with Eysenck Personality Inventory (EPI) and Temperament and Character Inventory-125 (TCI-125). The associations between each personality trait and polymorphisms were assessed with regression models adjusted for gender and ethnicity. There were significant effects of ANKK1/DRD2 Taq1A on Neuroticism (p=0.016) and of SLC6A3 rs27072 on Persistence (p=0.021) in both genders. The association between ANKK1/DRD2 Taq1A A2/A2-genotype and higher Novelty Seeking and lower Reward Dependence was shown in men only (p for gender interaction=0.018). In women only, there was a significant association between SLC6A3 10R*G-haplotype and higher Persistence (p=0.002). Our findings provide evidence for a modifying effect of gender on the associations between dopamine system genes and approach-related traits (in men) and Persistence (in women).

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.

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.

[Genetic factors of alcohol-dependence]

INTRODUCTION

Alcohol dependence is a complex and multifactorial disease resulting both from neurobiological mechanisms and environmental factors. It is frequently associated with comorbid psychiatric disorders or with specific personality or behavioral features. Although action can be taken on the environment in order to decrease the risk of the illness, current methods used to prevent or to treat this pathology show moderate efficacy: problematic consumption of ethanol in the general population as well as relapse rates under treatment in dependent patients remain indeed very high.

LITERATURE FINDINGS

It is therefore of major importance to broaden our knowledge of alcohol dependence and its comorbidities so as to improve both their prevention and treatment. In this perspective, recent progress in the field of neurosciences may contribute to achieve this goal. Precisely, genetics is a promising way benefiting from many advances in genetic epidemiology, cellular and molecular biology, neuroimaging and pharmacology. In parallel with a better understanding of the neurobiology of addictions and associated behaviors, these techniques led to the identification of brain mechanisms in which a genetic variation may influence the individual vulnerability towards alcohol dependence. Moreover, there is growing evidence that alcoholism results from the interaction of genetic and environmental factors influencing both its expression and its course. Given the fact that alcohol-dependence seems highly heritable (50 to 60% of the variance in both men and women), this review assesses the role of some of the genomic regions linked with the disease, as well as the principal variants of candidate genes identified as specifically involved in the predisposition. Polymorphisms of genes influencing alcohol metabolism, GABAergic, dopaminergic and serotonergic neurotransmission seem, indeed, at stake in the development of alcohol-dependence and its related features such as personality, behavior, impulse control or craving. In the future, a better characterization of the links between genotypes and phenotypes will probably increase our ability to treat alcoholic patients.

Meta-analysis of the association of the Taq1A polymorphism with the risk of alcohol dependency: a HuGE gene-disease association review

The human dopamine 2 receptor Taq1A allele has been implicated as a vulnerability factor for alcohol dependence in a number of studies and reviews. To determine whether this allele is associated with alcoholism, the authors conducted a Human Genome Epidemiology review and meta-analysis. Forty-four studies with 9,382 participants were included. An odds ratio of 1.38 (95% confidence interval: 1.20, 1.58; heterogeneity, 50.5%) was found for the A1A1 + A1A2 versus the A2A2 genotype. Sensitivity analyses suggested lack of ethnic matching as a possible source of heterogeneity; a small, significant association was detected in studies with ethnic-matched controls (odds ratio = 1.26, 95% confidence interval: 1.02, 1.56; heterogeneity, 37%). Significant associations were also found in analyses restricted to studies reporting use of blinding and those with adequate screening of controls for alcohol dependency. For the A1A1 versus the A1A2 + A2A2 genotype, the odds ratio was 1.22 (95% confidence interval: 1.05, 1.43; heterogeneity, 0%). Sensitivity analyses on groups of studies reporting use of ethnic-matched controls and those that screened controls for alcohol dependency still showed significant associations. The relatively small effect for the association of the A1 allele, or another genetic variant linked to it, with alcohol dependence indicates a multigene causality for this complex disorder.

Family-Based Association Analyses of Alcohol Dependence Phenotypes Across DRD2 and Neighboring Gene ANKK1

BACKGROUND

There is an extensive and inconsistent literature on the association of the dopamine D2 receptor gene (DRD2) with alcohol dependence. Conflicting results have been attributed to differences in the severity of the alcohol dependence phenotype across studies, failure to exclude related disorders from comparison groups, and artifacts of population-stratification. Recently the genetic polymorphism most widely analyzed in DRD2, Taq1A, has been discovered to reside in a neighboring gene, ankyrin repeat and kinase domain containing 1 (ANKK1), located 10 kb downstream from DRD2.

METHODS

To more carefully characterize evidence for association across this region, we genotyped 26 single nucleotide polymorphisms (SNPs) spanning DRD2 and ANKK1 in a sample of 219 Caucasian families (n = 1,923) from the Collaborative Study on the Genetics of Alcoholism (COGA), making this the most extensive analysis to date of association between this region and alcohol dependence. We used family-based analyses robust to population-stratification, and we made use of rich phenotypic data to analyze alcohol dependence and subtypes hypothesized in the literature to be more directly influenced by DRD2.

RESULTS

We found that the evidence for association is strongest in the 5' linkage disequilibrium block of ANKK1 (that does not contain Taq1A), with weak evidence of association with a small number of SNPs in DRD2. The association in ANKK1 is strongest among the subsets of alcoholics with medical complications and with antisocial personality disorder.

CONCLUSIONS

More extensive genotyping across DRD2 and ANKK1 suggests that the association with alcohol dependence observed in this region may be due to genetic variants in the ANKK1 gene. ANKK1 is involved in signal transduction pathways and is a plausible biological candidate for involvement in addictive disorders.

Association of the DRD2 gene Taq1A polymorphism and alcoholism: a meta-analysis of case-control studies and evidence of publication bias

We investigated the association of the dopamine D2 receptor (DRD2) Taq1A polymorphism and alcoholism, using meta-analytic techniques, and specifically undertook an investigation of possible publication bias. Potential publication bias represents a genuine risk to the integrity of published research, but its impact has rarely been documented. We observed a small effect of the DRD2 Taq1A polymorphism on risk of alcoholism, indicating increased alcoholism in individuals possessing the A1 allele of the Taq1A polymorphism (OR=1.21, 95% CI 1.13-1.30, P<0.001). This association remained significant when data from samples of European and East Asian ancestry were analyzed separately. We did not find evidence for association in high-severity alcoholism compared to low-severity alcoholism. Removing the first published study significantly reduced the magnitude of the pooled effect size estimate, although the association remained significant. In addition, we observed evidence for possible publication bias and for the strength of individual study effect size to be inversely related to year of publication. These results support the association of the DRD2 Taq1A polymorphism with alcoholism. This conclusion is qualified by the possibility of publication bias in the literature and the observed between-study heterogeneity, which indicates that the observed association may differ in strength between populations or may not exist at all in some populations.

Prevalence and detection of alcohol use disorders among general hospital inpatients in eastern Taiwan

OBJECTIVE

To examine (1) the prevalence of alcohol use disorders (AUD) and its various correlates, and (2) the detection rate of AUD by nonpsychiatric physicians and its related factors associated with increased chances of detection among inpatients in a general hospital in rural eastern Taiwan.

METHODS

A well-trained psychiatrist interviewed all adult patients admitted during a 1-month period using the Alcohol Inventory and reviewed all medical records for alcohol-related diagnoses.

RESULTS

A total of 303 inpatients aged 18 to 93 years were evaluated, of whom 78 (25.7%) were diagnosed by the psychiatrist as having AUD within the past year. Males, aborigines, middle-aged, current smokers and betel quid chewers had a significantly higher odds ratio for AUD. Nonpsychiatric physicians detected only 14.1% patients with recent AUD. Internists identified AUD nearly four times as often as surgeons. Better detection was associated with higher level of alcohol intake.

CONCLUSIONS

This study demonstrates the high prevalence of AUD among hospitalized patients in eastern Taiwan and the frequent failure of physicians to identify the disorder. These findings suggest that more effort should be directed toward increasing medical professionals' awareness of AUD in general hospital settings, especially among high-risk groups.

Evolution of the DRD2 gene haplotype and its association with alcoholism in Mexican Americans

The human D2 dopamine receptor gene (DRD2) plays a central role in the neuromodulation of appetitive behaviors and is implicated in having a possible role in susceptibility to alcoholism. We genotyped an SNP in DRD2 Exon 8 in 251 nonalcoholic, unrelated, healthy controls and 200 alcoholic Mexican Americans. The DRD2 haplotypes were analyzed using the Exon 8 genotype in combination with five other SNP genotypes, which were obtained from our previous study. The ancestral origins of the DRD2 polymorphisms have been determined by sequencing the homologous region in other higher primates. Twenty DRD2 haplotypes, defined as H1 to H20 based on their frequency from high to low, were obtained in this major minority population. The ancestral haplotype "I-B2-G-C-G-A1" and two one-step mutation haplotypes were absent in our study population. The haplotype H1, "I-B1-T-C-A-A1", with the highest frequency in the population, is a three-step mutation from the ancestral form. The first five or eight major haplotypes make up 87% or 95% of the entire population, respectively. The prevalence of the haplotype H1+ (H1/H1 and H1/Hn genotypes) is significantly higher in alcoholics and alcoholic subgroups, including early onset drinkers and benders, than in their respective control groups. The Promoter -141C allele is in linkage disequilibrium (LD) with five other loci in the nonalcoholic group, but not in the alcoholic group. All of the other five loci are in LD in both the alcoholic and control groups. The DRD2 TaqI B allele is in complete LD with the allele located in intron 6. Five SNPs, Promoter -141C, TaqI B (or Intron 6), Exon 7, Exon 8, and TaqI A, are sufficient to define the DRD2 haplotypes in Mexican Americans. Our data indicate that the DRD2 haplotypes are associated with alcoholism in Mexican Americans.

Advances in molecular genetics and the prevention and treatment of substance misuse: Implications of association studies of the A1 allele of the D2 dopamine receptor gene

Substance misuse is influenced by multiple genetic and environmental factors. Recent research has identified a number of potential genetic markers of risk and those associated with drug reward substrates show particular promise. The current study reexamines the extant published data of the association between the D2 dopamine receptor (DRD2) gene minor Taq 1A (A1) allele and substance misuse risk. A series of meta-analyses was performed on 64 studies examining DRD2 A1+ allelic status and substance misuse. In addition, personality was examined as a possible endophenotype. Significant association was found between the A1 allele and severe substance dependence in both Caucasian and non-Caucasian groups. The data did not support a significant association between the A1 allele and personality features. While the specific mechanism underlying these associations requires further elucidation, this genetic marker shows promise as a marker of brain reinforcement processes. Possible ways of utilising the A1 allele to inform prevention and treatment initiatives are discussed.

Possible interaction of alcohol dehydrogenase and aldehyde dehydrogenase genes with the dopamine D2 receptor gene in anxiety-depressive alcohol dependence

BACKGROUND

The role of the dopamine D2 receptor (DRD2) gene in the development of alcohol abuse or dependence is controversial. The controversy is due in part to the disparate definitions pertaining to the control groups used and to the definitions of subtypes in alcohol dependence. In the Han Chinese population, the alcohol dehydrogenase 1B*2/*2 (ADH1B*2/*2) genotype and the aldehyde dehydrogenase 2*2 (ALDH2*2) allele have been considered as protective factors against alcohol abuse or dependence. Moreover, the ADH1B and ALDH2 genes might be involved in dopamine metabolism. We hypothesized that the ADH1B and ALDH2 genes might interact with the DRD2 gene and that the association between the DRD2 gene and alcohol dependence might be affected by different ADH1B and ALDH2 genotypes. This study examined whether the DRD2 gene is associated with specific subtypes of alcohol dependence and evaluated the relationship between the DRD2 gene and alcohol-metabolizing genes in a specific subtype of alcohol dependence.

METHODS

Of the 465 Han Chinese subjects who were recruited for the study, 71 were classified with pure alcohol dependence, 113 with both alcohol dependence and anxiety-depression (ANX/DEP ALC), and 129 with anxiety-depression but without alcohol dependence (ANX/DEP). The remaining 152 subjects were supernormal controls. All subjects were interviewed with the Chinese version of the modified Schedule of Affective Disorders and Schizophrenia-Lifetime; all alcohol dependence, anxiety, and major depressive diagnoses were made according to DSM-IV criteria.

RESULTS

The DRD2 gene was not found to be associated with pure alcohol dependence or ANX/DEP, but was found to be associated with ANX/DEP ALC. Furthermore, the association between the DRD2 gene and ANX/DEP ALC was shown to be under the control of the ALDH2*1/*1 and ADH1B*1/*2 genotypes.

CONCLUSIONS

ANX/DEP ALC is a specific subtype of alcohol dependence. Because ANX/DEP ALC was associated with the DRD2 gene only under the stratification of ADH1B*1/*2 or ALDH2*1/*1, the DRD2 gene might interact with the ADH1B gene and the ALDH2 gene, respectively, in the development of ANX/DEP ALC in the Taiwan Han Chinese population.

Genetic polymorphisms of the promoter region of dopamine D2 receptor and dopamine transporter genes and alcoholism among four aboriginal groups and Han Chinese in Taiwan

This study aims to examine the relationship between the functional polymorphism at the promoter region of the dopamine D2 receptor (DRD2) gene (i.e. -141C Ins/Del) and variable number of tandem repeat polymorphism at the 3' untranslated region of the dopamine transporter (DAT) gene (SLC6A3) with alcoholism in a case-control study. The cases (n = 203) were alcohol dependents with withdrawal symptoms, and the controls (n = 213) were sex- and ethnicity-matched individuals who were screened to exclude those with alcohol problems among four aboriginal groups (Atayal, Ami, Bunun, and Paiwan) and Han Chinese in Taiwan. To control for potential confounding factors, we excluded tobacco abusers from control subjects in part of the analysis and compared the distribution of the genetic polymorphisms in alcoholics with severe medical complications versus those with less severe medical complications. There were no differences in allele and genotype frequencies of these two distinct genetic markers between alcoholics and control subjects in these five different ethnic groups. There was no significant linkage disequilibrium between the -141C polymorphism and two other DRD2 polymorphisms (TaqI A and NcoI). The results remained unchanged when cases were limited to alcoholics with more severe medical complications or when tobacco abusers were excluded from control subjects. The results suggest that both the DRD2 promoter region and the DAT gene do not play a significant role in conferring vulnerability to alcoholism.

Alcoholism, ALDH2*2 allele and the A1 allele of the dopamine D2 receptor gene: an association study

The inactive form of aldehyde dehydrogenase-2 (ALDH2) is regarded as a protective factor against the development of alcoholism, and alcoholics with inactive ALDH2 are considered to be relatively homogeneous. This examination of a possible allelic association of the dopamine D2 receptor (DRD2) gene TaqI A polymorphism failed to detect significant differences between 583 Japanese alcoholics and 295 unrelated Japanese controls, or between alcoholic subjects with different ALDH2 genotypes. Despite the significantly higher frequency of the DRD2 A1 allele in the 207 alcoholics with inactive ALDH2 than in the 376 alcoholics with active ALDH2, multiple logistic regression analysis (controlled for the ALDH2 genotype) revealed no association between the TaqI A polymorphism and alcoholism. Nor did the frequency of the DRD2 TaqI A polymorphism differ in alcoholic subjects grouped by several pertinent clinical characteristics, including severity of alcoholism. Although there remains a possibility that the DRD2 TaqI A polymorphism plays some role in modifying the phenotype of the disease, these results suggest that neither the A1 allele nor the homozygous A1 genotype is associated with alcoholism.

Linked polymorphisms (-333G>T and -286A>G) in the promoter region of the CCK-A receptor gene may be associated with schizophrenia

Cholecystokinin A receptors (CCKAR) modulate CCK-stimulated dopamine release, and mutations in the CCKAR gene may predispose affected individuals to schizophrenia. Our previous study suggested that -286A>G polymorphism (previously named 201A>G) in the CCKAR gene promoter is associated with schizophrenia. In the present study, we carried out a further investigation of the promoter and intron 1 of the CCKAR gene. In addition to polymorphisms reported previously (-333G>T, -286A>G, -241G>A, 773A>T, and 779T>C), two novel polymorphisms (-388(GT)(8)>(GT)(9) and -85C>G) were identified. These polymorphisms were in a linkage disequilibrium. Association analyses between schizophrenic patients and controls revealed that the frequencies of the A allele and AA genotype at the -286 loci, as well as the frequency of the GG genotype at the -333 loci, were significantly higher in patients than in controls. Furthermore, patients with paranoid type schizophrenia, auditory hallucinations, or a positive family history had a significantly higher frequency of the -286A allele than the control group. The results supported our previous data, and suggest the possible involvement of the -333G>T and the -286A>G polymorphisms in the promoter region of the CCKAR gene in the predisposition to schizophrenia.

Polymorphisms at the DRD2 locus in early-onset alcohol dependence in the Indian population

The susceptibility to alcohol dependence is probably of polygenic origin. Association studies have attempted to identify possible candidate genes that may contribute to the risk to developing dependence. Severe forms of the alcoholism phenotype have been associated with an increased frequency of the Taq A1 allele at the DRD2 locus. Ethnic stratification and non-comparable phenotype may have contributed to the contradictory results in previous studies. We identified probands, using the Schedules of Assessment of Neuropsychiatry (SCAN) schedule, who had onset of alcohol dependence (ICD-10) before 25 years of age. Family members were interviewed using the Family Interview for Genetic Studies (FIGS) schedule to identify patients who had two first-degree relatives with alcohol dependence. Fifty subjects who fulfilled the criteria were selected for the study. These were compared to a normal population from a similar background. The allele frequencies did not differ between the two groups. The Taq1a polymorphism does not seem to be associated with alcoholism in this group of severely affected, young age of onset probands in the southern Indian population.

No association between DLST gene and Alzheimer's disease or Wernicke-Korsakoff syndrome

Among many candidate genes for the genetically heterogeneous Alzheimer's disease (AD), only apolipoprotein E (ApoE) has been confirmed. Another candidate is the dihydrolipoyl succinyltransferase (DLST) gene, one of three components of thiamine-dependent mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC), because KGDHC activity is reported reduced in AD patients. Also characterized by reduced KGDHC activity is another neuropsychiatric disease, Wernicke-Korsakoff syndrome (WKS), which results from thiamine deficiency. Examination of specific DLST gene polymorphism in 247 Japanese AD patients, 53 alcoholic WKS patients, and 368 nondemented Japanese control subjects revealed no significant differences in DLST genotypes and failed to replicate the findings of earlier studies indicating an association between DLST gene polymorphism and AD.

Polymorphism of the neuropeptide Y gene: an association study with alcohol withdrawal

BACKGROUND

Neuropeptide Y (NPY) exists in both the central and peripheral nervous system and is thought to modulate many functions such as feeding behavior, anxiety-associated behavior, circadian rhythm, seizure modulation, and hormone secretion. Recent studies have revealed that NPY influences alcohol consumption in mice and that alcohol-preferring rats showed lower concentrations of NPY-like immunoreactivity compared with alcohol-nonpreferring rats in several brain regions.

METHODS

In the present study, we analyzed the whole coding region and 5'-untranslating region of the NPY gene for 163 Japanese male alcoholics with different withdrawal symptoms (93 with delirium tremens, 71 with seizures, 49 with hallucinations) and 98 Japanese male controls. ALDH2 genotypes of all subjects tested were ALDH2*1 homozygote.

RESULTS

Three polymorphic nucleotide substitutions, namely -121C/A (promoter), 1258G/A (exon 2), and 5671C/T (exon 3), were detected in both groups. Substituting C to A in the -121 locus produced a putative binding site of GATA-1 and GATA-2. Also, -90G/A (promoter) as a rare variant and 5642-5651 single nucleotide repeats T10/T11 (intron 2) were found. Polymorphism (C/T) at the 1128 locus has been reported to be associated with a higher serum cholesterol level in obese white subjects, but such a polymorphism was not found in our samples. The genotypical distributions for these polymorphic loci (-121C/A, 1258G/A, 5642-5651 T10/T11, and 5671C/T) were not significantly different between the alcoholics and controls. However, frequency of the T allele and frequency of the genotype that possessed T alleles (CT, TT) at the 5671 locus were significantly higher in patients with seizure than in those without seizure (p < 0.05, p < 0.02).

CONCLUSION

Our data suggested that a C to T substitution at the 5671 locus of the NPY gene may be associated with seizure during alcohol withdrawal.

Polymorphisms in dopamine receptors: what do they tell us?

Many genetic studies have focussed on dopamine receptors and their relationship to neuropsychiatric disease. Schizophrenia, bipolar disorder, and substance abuse have been the most studied, but no conclusive linkage or association has been found. The possible influence of dopamine receptor variants on drug response has not received as much attention. While there is some evidence that polymorphisms and mutations in dopamine receptors can alter functional activity and pharmacological profiles, no conclusive data link these gene variants to drug response or disease. The lack of unequivocal findings may be related, in part, to the subtle changes in receptor pharmacology that these polymorphisms and mutations mediate. These subtle effects may be obscured by the influence of genes controlling drug metabolism and kinetics. Further insight into the pharmacogenetics of dopamine receptors may require not just more studies, but novel approaches to the study of complex genetic traits and diseases.

Reward deficiency syndrome: a biogenetic model for the diagnosis and treatment of impulsive, addictive, and compulsive behaviors

The dopaminergic system, and in particular the dopamine D2 receptor, has been implicated in reward mechanisms. The net effect of neurotransmitter interaction at the mesolimbic brain region induces "reward" when dopamine (DA) is released from the neuron at the nucleus accumbens and interacts with a dopamine D2 receptor. "The reward cascade" involves the release of serotonin, which in turn at the hypothalmus stimulates enkephalin, which in turn inhibits GABA at the substania nigra, which in turn fine tunes the amount of DA released at the nucleus accumbens or "reward site." It is well known that under normal conditions in the reward site DA works to maintain our normal drives. In fact, DA has become to be known as the "pleasure molecule" and/or the "antistress molecule." When DA is released into the synapse, it stimulates a number a DA receptors (D1-D5) which results in increased feelings of well-being and stress reduction. A consensus of the literature suggests that when there is a dysfunction in the brain reward cascade, which could be caused by certain genetic variants (polygenic), especially in the DA system causing a hypodopaminergic trait, the brain of that person requires a DA fix to feel good. This trait leads to multiple drug-seeking behavior. This is so because alcohol, cocaine, heroin, marijuana, nicotine, and glucose all cause activation and neuronal release of brain DA, which could heal the abnormal cravings. Certainly after ten years of study we could say with confidence that carriers of the DAD2 receptor A1 allele have compromised D2 receptors. Therefore lack of D2 receptors causes individuals to have a high risk for multiple addictive, impulsive and compulsive behavioral propensities, such as severe alcoholism, cocaine, heroin, marijuana and nicotine use, glucose bingeing, pathological gambling, sex addiction, ADHD, Tourette's Syndrome, autism, chronic violence, posttraumatic stress disorder, schizoid/avoidant cluster, conduct disorder and antisocial behavior. In order to explain the breakdown of the reward cascade due to both multiple genes and environmental stimuli (pleiotropism) and resultant aberrant behaviors, Blum united this hypodopaminergic trait under the rubric of a reward deficiency syndrome.

Novel polymorphisms of the human cholecystokinin A receptor gene: an association analysis with schizophrenia

The cholecystokinin A receptor (CCK-AR) modulates CCK-stimulated dopamine release in the posterior nucleus accumbens, and its gene is mapped to 4p15.2-15.1 with the dopamine receptor 5 (DR5) gene. We speculated that alterations in the CCK-AR lead to an increase in dopamine release, which may in turn constitute a predisposition in schizophrenia. We investigated genetic variations in the promoter region and the coding region of the CCK-AR gene. An association analysis was conducted between 83 unrelated schizophrenic patients and 80 healthy controls. Novel polymorphisms (201A-->G, 246G-->A in the promoter region, 1260T-->A, 1266T-->C in intron 1 within the 3' mRNA splice acceptor site consensus sequence, and Leu306Leu in exon 5) were found in addition to the variants (608G-->A in intron 1, 3849C-->T [Ile296Ile] in exon 5) reported previously. Significant differences were found in the allele frequencies of the 201A-->G nucleotide substitution in the promoter region between patients and controls (P = 0.0181, odds ratio: 1.972, after Bonferroni correction: P = 0.0543). These differences were also found between the patients with paranoid type and controls (P = 0.0274, odds ratio = 3.667, after Bonferroni correction: P = 0.0822). Our analyses suggest that the 201A allele frequency was higher in the schizophrenic group, especially in the paranoid type, than in the control group at a rate that was not quite significant after Bonferroni correction. Am J. Med Genet. (Neuropsychiatr. Genet.) 96:141-145, 2000.

Association between polymorphism of the cholecystokinin gene and idiopathic Parkinson's disease

Parkinson's disease (PD) is characterized by major alterations of neurotransmitter activity due to damage of the substantia nigra. Changes in neuropeptide concentration within the basal ganglia may play an important role in the putative dopaminergic-peptidergic interactions associated with the disease. Cholecystokinin (CCK) modulates the release of dopamine in the mesolimbic pathway and affects dopamine-related behavior. We analyzed genetic variations in the CCK gene, in both the coding and promoter region, in order to investigate the role of polymorphism in idiopathic PD. Four polymorphic sites of the CCK gene (-196G/A, -45C/T, 1270C/G, 6662C/T) were found in PD patients and controls. Complete linkage disequilibrium was observed between the -45 locus and the 1270 locus, and also a possible linkage disequilibrium was found between the -45 and -196 loci. A significant difference was found in the distributions of three identified genotypes at the -45 locus between 116 PD patients and 95 age-matched control subjects (chi2 = 7.95, p = 0.018, Bonferroni correction; p = 0.054). In addition, a significant difference was obtained amongst the three genotypic groups at the -45 locus when compared between PD patients who experienced hallucinations (n = 23) and those (n = 93) who did not (chi2 = 8.08, p = 0.018, Bonferroni correction, p = 0.126). Our data suggested that mutations at the -45 locus in the promoter region of the CCK gene may influence vulnerability to hallucinations in PD patients treated with L-dopa.

Polymorphism of dopamine D2 and D4 receptor genes and Slavic-surnamed alcoholic patients

The association between alcoholism and the Taq1 "A" and "B" polymorphic alleles at the DRD2 gene and 48-bp tandem repeat in exon 3 of dopamine D4 receptor (DRD4) gene in 42 unrelated Slavic-surnamed patients and 76 normal controls was examined. The frequency of the A1 allele was higher in alcoholic patients and in alcoholic patients with a family history of alcoholism than in controls (χ²= 3.45, p < 0.001 and χ²)= 3.97, p < 0.001, respectively). Moreover, the frequency of the A1 allele was higher in alcoholics with a family history of alcoholism than in alcoholics without a family history (χ²= 3.33, p < 0.001).The results of association analysis for both the Taq1 "B" and DRD4 alleles were negative for alcoholics in general, subgroups of alcoholics and normal controls. However, the 7-repeat allele (DRD4*7R) of DRD4 gene occurred at significantly higher frequency in alcoholics with a family history of alcoholism compared with those without a family history (χ²= 3.42, p < 0.01).The results indicate that the A1 allele of the DRD2 gene is associated with susceptibility to alcoholism in general.The A1 allele, as well as the DRD4*7R allele, is significantly prevalent among alcoholics with a family history, in comparison with alcoholics without a family history, reflecting different roles of genetic factors in development of alcoholism.

Alcohol use disorders among the Yami aborigines in Taiwan. An inter-ethnic comparison

BACKGROUND

Alcohol use disorders (AUDs) among the Yami aborigines in Taiwan were investigated and compared with four other taiwanese aboriginal groups.

METHOD

A sample survey was conducted using a semi-structured clinical interview for AUDs among 252 subjects, aged 15 and above, from two Yami villages on Orchid Island.

RESULTS

The prevalences of DSM-III-R and DSM-IV alcohol use disorders were 13.1% and 10.3% by one year, and 17.5% and 15.2% by lifetime, respectively, with a male excess. The risk for AUDs in Yami men was significantly associated with a lower educational level, a non-married status, and the length of stay in mainland Taiwan. A protective effect of Christian belief was evident for lifetime risk for AUDs.

CONCLUSIONS

The lower prevalences of AUDs in Yami than in other aboriginal groups in Taiwan might be explained by social isolation of the former, and differences in drinking tradition, availability of alcohol, biological vulnerability, and the extent of acculturation between these groups.