Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2017 Apr 19.
Published in final edited form as: Pharmacogenet Genomics. 2013 Jul;23(7):333–340. doi: 10.1097/FPC.0b013e328361c39d

ANKK1 and DRD2 pharmacogenetics of disulfiram treatment for cocaine abuse

Catherine J Spellicy 1,*, Thomas R Kosten 1, Sara C Hamon 2, Mark J Harding 1, David A Nielsen 1
PMCID: PMC5396392  NIHMSID: NIHMS622771  PMID: 23635803

Abstract

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 gene (ANKK1) and/or the dopamine receptor D2 gene (DRD2) interact with response to treatment with disulfiram.

Methods

Cocaine and opioid co-dependent (DSM-IV) patients were stabilized on methadone and subsequently randomized into treatment groups, disulfiram (250 mg/day, N = 31) or placebo (N = 37), genotyped for ANKK1 (rs1800497) and DRD2 (rs2283265) polymorphisms, and the data evaluated for association with cocaine-free urines in the presence or absence of disulfiram. Data was analyzed using repeated measures analysis of variance (ANOVA) 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) while those on placebo (N = 20) showed no treatment effect. Patients carrying the CC ANKK1 genotype showed no effect from disulfiram (N = 18) or placebo (N = 17). The GT/TT DRD2 genotype group showed a significant decrease in cocaine-positive urines on disulfiram (N = 9; 67% – 48%; p ≤ 0.0001), while the GG DRD2 genotype group showed 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) than individuals carrying only the major alleles (N = 17).

Conclusions

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.

Keywords: ANKK1, DRD2, disulfiram, cocaine, treatment, dependence

Introduction

Cocaine is the third most commonly used drug of addiction with over 1.5 million addicts in 2010 [1]. Cocaine dependence (CD) has significant social and economic impact and is also currently without an FDA-approved pharmacotherapy. CD often occurs in tandem with alcohol dependence and frequently within methadone maintenance programs, where rates of cocaine use may range from 30% to 50%. CD may also lead to HIV risk behaviors, illicit opioid use, and overdoses requiring emergency department utilization [1–13]. Various pharmacological approaches have been evaluated to reduce CD, but with limited success [e.g. 14, 15]. Disulfiram has shown some initial promise in treating CD, including among opioid-dependent patients [16–20].

Disulfiram is a pharmacotherapy originally used to treat alcoholism and is also known as Antabuse. Disulfiram blocks the conversion of acetaldehyde (a metabolite of ethanol) into acetic acid, thereby inducing aversive physiological symptoms such as nausea and vomiting after alcohol consumption. The exact mechanism by which disulfiram exerts its effect to reduce cocaine cravings or use is not known, but may be via dopamine availability and signaling in the brain. Disulfiram inhibits dopamine β-hydroxylase (DβH), which converts dopamine (DA) to norepinephrine [21, 22]. Inhibiting DβH increases brain DA levels, which in turn increases stimulation of dopamine D2 receptors, part of the brain’s ‘reward circuitry’ [23, 24].

Given that disulfiram influences dopamine levels in the brain, and given the strong genetic basis of CD with heritability estimated at up to 72% [25], we adopted a molecular genetic approach examining genes in, or peripheral to, the dopaminergic pathway to investigate disulfiram’s efficacy in CD patients [26–29]. We recently showed that a polymorphism in the dopamine β-hydroxylase gene (DBH) that associates with normal DβH levels (rs1611115, T allele) identified CD patients who reduce their cocaine use with disulfiram [30]. This finding led us to examine other genes coding for proteins involved in dopamine signaling such as the dopamine receptor D2 (DRD2) and the ankyrin repeat and kinase domain-containing 1 (ANKK1) genes.

DRD2 and ANKK1 are both located on chromosome 11q22-23 in human. The genes are approximately ten-thousand nucleotides apart and variants in these genes frequently have some degree of linkage disequilibrium with each other [e.g. 31, 32]. DRD2 encodes the G-protein coupled dopamine D2 receptor. Given the involvement of dopamine in several psychiatric disorders it is not surprising that variants in DRD2 have been found to be associated with several psychiatric conditions, including alcohol and nicotine addiction, schizophrenia, and migraine [33–43]. The T allele of the rs2283265 variant in the DRD2 gene has been shown to be overrepresented in cocaine addicts as well as associated with decreased expression of the D2S form of the D2 receptor [44, 45].

The ANKK1 gene, which encodes the ankyrin repeat and kinase domain-containing 1 protein, has a functional variant, rs1800497 (C→T, also known as TaqIA) that encodes a glutamate to lysine substitution at amino acid position 713. ANKK1 alters D2 receptor stimulation via D2 receptor density, with the T allele found to be associated with lower receptor density than with the C allele [46]. ANKK1 spans about thirteen-thousand nucleotides and is expressed in astroglial cells [47]. The T allele of rs1800497 has been shown to be associated with alcohol addiction, several psychiatric disorders [e.g. 39, 41, 48], as well as with cocaine addiction [49]. Because disulfiram increases dopamine concentration in the synapse via inhibition of DβH, and because variants in ANKK1 and DRD2 have been found to be in association with cocaine addiction, dopamine signaling, and D2 dopamine receptor density in the brain, we hypothesized that ANKK1 rs1800497 and DRD2 rs2283265 may mediate response to disulfiram pharmacotherapy in CD individuals.

Materials and methods

Participants

Ninety-three cocaine and opioid-dependent patients were stabilized on methadone maintenance during a two-week screening period at Yale University (N = 40) and Baylor College of Medicine (N = 53) from 2004 to 2008 [30]. Patients were selected based on the presence of at least one cocaine-positive urine sample. Eleven patients were excluded for lack of positive urine samples. Eight patients dropped out during this two week screening, and six others were eliminated due to indeterminate genotyping for a final cohort of 68 subjects. A psychiatric interview, which included the administration of the ASI [50] and MINI (English Version 5.0.0, July 1, 2006) [51], confirmed DSM-IV opioid and cocaine dependence. Exclusion criteria included a current diagnosis of other drug or alcohol physical dependence (other than tobacco), current major medical illness unstablized on medications, a history of major psychiatric disorder (e.g. psychosis, schizophrenia, or bipolar), current suicidality, and an inability to read and understand the consent form. Women of childbearing age required an initial negative urine pregnancy test, use of adequate contraception to prevent pregnancy during the study, and monthly pregnancy tests throughout the study. All signed an informed consent approved by Yale University and the Baylor College of Medicine Institutional Review Boards that gave specific consent for genetic studies. Ethnicity was based on self-report of ethnic/cultural background of the patients.

The 68 patients were stabilized on methadone maintenance at 60 mg daily and were assigned randomly to placebo or disulfiram (250 mg daily, which was dissolved into their daily methadone dose to assure medication compliance) groups. Methadone dose increased 5 mg per day from an initial 25 mg/day until patients reached a 60 mg/day maintenance dose. Individual manual-driven cognitive behavioral therapy [52] was provided weekly to all patients. Supervised urine samples were obtained thrice weekly and tested for the presence of the cocaine metabolite benzoylecgonine using an Olympus AU 640 Emit system (Olympus America Inc., Melville, NY) with a cut-off concentration of 300 ng/ml. We obtained saliva samples for DNA isolation.

Genotyping and statistical analyses

DNA purification, genotyping, and statistical analyses were performed as previously described [30, 53]. Briefly, DNA was isolated using the Gentra Puregene Buccal Cell Kit (Qiagen, Valencia, CA) following the manufacturer’s recommendations from pelleted buccal cells that were obtained by the centrifugation of 10 ml Scope® mouthwash that was used to rinse the subject’s mouth for 60 seconds.

Genotypes were determined using 5′-fluorogenic exonuclease assays (TaqMan®, Applied Biosystems, Foster City, CA). The ANKK1 rs1800497 variant was genotyped using the TaqMan® primer-probe sets (Applied Biosystems) assay ID C_7486676_10, and the DRD2 rs2283265 variant with assay ID C__16070796_10. PCR amplifications were performed using Platinum® quantitative PCR SuperMix-UDG (Invitrogen, Carlsbad, CA) on a GeneAmp® PCR system 9700 (Applied Biosystems).

A repeated measures analysis of variance (ANOVA) was used to analyze the number of cocaine positive urines over the total number of samples (six) for each two week period. Data from the disulfiram treatment group was compared to the placebo group over time to determine if the effect of disulfiram is modulated by the ANKK1 locus, the DRD2 locus, or both, using R version 2.9.1 [54]. We compared condition (disulfiram or placebo), ANKK1 genotype (0 = CC genotype, 1 = all other genotypes), DRD2 genotype (0 = GG genotype, 1 = all other genotypes), ANKK1 plus DRD2 genotype (0 = CC/GG genotype, 1 = all other genotypes), time (each two week period), and interactions between condition and time, and between condition and genotypes. We analyzed all individuals who had complete data (N = 55) and unbalanced repeated measures ANOVA for all individuals (N = 68). The two analyses yielded similar results. ANOVA was also used to analyze demographic and MINI/ASI data.

To determine population structure, our cohort was compared against CEPH-HGDP samples (1,035 subjects of 51 populations) as previously described [30, 53]. Gender, recruitment site, and population structure were run as covariates in the statistical model. We calculated effect size as a partial eta-squared statistic using condition or SNP variance over residual variance. The three general cut-offs for effect size are the following: a large effect is 0.14, a medium effect is 0.06, and a small effect is 0.01. Hardy-Weinberg equilibrium was calculated for each genetic variant and resulted in non-significant p-values indicating that the genotypes were observed in the expected ratios (ANKK1, rs1800497; p = 0.567976 and DRD2, rs2283265; p = 0.3588037).

Results

Baseline characteristics by treatment and ANKK1/DRD2 genetics

Genotyping failed for six patients thereby providing a sample of 68 patients; 31 in the disulfiram group and 37 in the placebo group. The patients included thirty-five CC; twenty-four CT; and nine TT genotypes for ANKK1 and twenty-three GG; thirty GT; and fifteen TT genotypes for DRD2 (See Table 1). The patients were mostly Caucasian males with a mean age of 39 years. Forty (54%) patients previously had been treated with methadone maintenance. On average, participants used cocaine for 13 years, and for 19 days in the month prior to entering this study. Only 30 patients (40%) reported any alcohol abuse history reflecting our exclusion criteria, and 39 patients (53%) reported marijuana use. As shown in Table 1, we found no significant baseline differences among the four treatment by genotype groups in any clinical characteristics (p >.05).

Table 1.

Demographic and clinical characteristics by ANKK1 and DRD2 genotype

Gene ANKK1
 DRD2
 ANKK1/DRD2
Treatment Placebo
 Disulfiram
 Placebo
 Disulfiram
 Placebo
 Disulfiram
CT/TT CC CT/TT CC GT/TT GG GT/TT GG CC/GG others CC/GG others
Characteristic
N 20 17 13 18 14 22 9 23 17 19 17 13
% Male 65.0 70.6 61.5 61.1 71.4 68.2 44.4 69.5 70.6 61.5 58.8 68.4
%Caucasian 65.0 76.5 69.2 83.3 64.3 72.7 66.7 82.6 76.5 63.2 82.4 69.2
%African American 23.5 10.5 0.0 12.5 21.4 22.7 0.0 8.7 17.7 26.3 5.9 7.7
%Hispanic 11.8 0.0 18.8 16.7 14.3 4.5 33.3 8.7 5.9 5.9 28.6 23.1
% Employed 45.0 71.0 69.0 67.0 42.9 63.6 66.6 69.6 70.6 42.1 64.7 69.2
Average age (s.d) 42.7 (10.6) 36.7 (10.5) 39.7 (9.5) 37.8 (11.0) 42.7 (12.0) 37.7 (9.9) 38.9 (9.1) 38.2 (10.7) 36.6 (10.5) 42.4 (10.8) 38.5 (10.9) 39.7 (9.5)
Cocaine use, past 30 days (s.d.) 20.3 (8.2) 18.6 (7.4) 17.9 (8.2) 18.6 (9.2) 19.7 (9.9) 18.7 (8.8) 17.9 (9.4) 16.3 (10.9) 17.1 (8.3) 20.8 (9.6) 18.5 (10.8) 16.8 (9.1)
Cocaine use, years (s.d.) 13.7 (8.5) 12.7 (9.3) 14.3 (6.8) 10.4 (7.6) 14.6 (9.4) 14.4 (8.0) 11.6 (6.6) 8.8 (7.3) 14.1 (8.8) 14.9 (8.4) 9.1 (7.3) 11.5 (6.6)
% any alcohol use in lifetime 25.0 48.8 38.5 38.9 28.6 50.0 44.4 34.8 58.8 26.3 41.2 38.5
% any marijuana use in lifetime 30.0 64.7 61.5 52.9 45.8 46.2 66.7 52.2 64.7 31.6 58.8 53.9
Open in a new tab

No significant baseline differences among the two treatment groups by genotype in any clinical characteristics after adjusting for multiple testing (p > 0.05).

Treatment outcomes by ANKK1 genotype

To examine whether ANKK1 genotypes would be found to associate with response to disulfiram, we divided the 68 patients who had been genotyped for the ANKK1 rs1800497 variant into two groups based on presence of the minor T allele. The CT/TT genotype group showed significantly fewer cocaine-positive urines during the twelve weeks of disulfiram treatment (F = 21.69; df = 1,175; p < 0.0001, with an effect size of .0365) compared to placebo, while the CC genotype group showed no difference between disulfiram and placebo (F = 2.09; df = 1,176; p = 0.15, with an effect size of .0117). As shown in Figure 1A, cocaine-positive urines for the CT/TT genotype group during the two baseline weeks were 74% and 82% for disulfiram and placebo, respectively. These percentages dropped to 52% for the disulfiram group during the last two weeks of treatment and were unchanged for placebo. In contrast, cocaine-positive urines for the CC genotype group during the two baseline weeks were 88% for disulfiram and 80% for placebo. These rates were relatively unchanged during the last two weeks of treatment (71% for disulfiram and to 76% for placebo) (see Figure 1B). When only the fifty-five subjects who completed the study were included in the analyses, the disulfiram treatment effect remained highly significant in the CT/TT genotype group (F = 17.46; df = 1,186; p < 0.0001, with an effect size of .0995).

Figure 1. Response of ANKK1 or DRD2 genotype groups to disulfiram pharmacotherapy (N = 68).

Figure 1

Open in a new tab

Cocaine-positive urine toxicology data are shown for each two-week time period across the 12-week trial in percent-positive urines. Time points for the placebo group are represented by the solid line, and time points for the disulfiram treatment group (250 mg/day) are represented by the dashed line. Each panel shows data for specific genotype groups: A – DRD2 GT/TT genotypes, B – DRD2 GG genotype, C– ANKK1 CT/TT genotypes, D – ANKK1 CC genotype, E – genotypes including a minor allele from ANKK1, DRD2, or both, F – genotypes with only the major allele from DRD2 and ANKK1 (GG/CC). Standard error bars are shown for each time point.

Treatment outcomes by DRD2 genotype

We next examined response to disulfiram in relation to DRD2 genotype. Patients genotyped for the DRD2 rs2283265 variant were separated into two groups based on presence of the minor T allele. Individuals with GT/TT genotypes showed a decreased number of cocaine-positive urines during the twelve week treatment with disulfiram while the GG genotype group showed only a marginal decrease. Specifically, cocaine-positive urines dropped from 67% to 48% in the GT/TT genotype group with disulfiram, compared to the GT/TT genotype group under placebo conditions who showed no significant decrease in cocaine positive urines (80% to 79%; F = 26.12; df = 1,121; p < .0001, with an effect size of .1775) (see Figure 3A). Within the GG genotype group there was only a small difference between treatment groups; at baseline the placebo GG group had 80% cocaine positive urines, which dropped to 75% at 12 weeks, while the disulfiram group had 84% positive urines which dropped to 63% at 12 weeks (F = 4.16; df = 1,234; p = 0.04, with an effect size of .0174) (see Figure 3B). When only the individuals with complete urine toxicology data were analyzed, the effect remained highly significant for the GT/TT genotype group (F = 23.23; df = 1,121; p < 0.0001, with an effect size of .1775) and less so for the GG genotype group (F = 8.26; df = 1,110; p = 0.004, with an effect size of .1743).

Treatment outcomes in Caucasians by ANKK1 and DRD2 genotype

To examine if there was a treatment effect in individual ethnic groups without correcting for population structure, we examined the data by self-reported ethnicity. The only group with enough individuals to make analysis possible was the Caucasian group (N = 50 for both genes). The analyses showed results similar to the previous analyses including all individuals that were corrected for population structure. Specifically, the analyses within the Caucasians for ANKK1 remained significant (F=9.499 (1,262), p = 0.00228) and trended towards significance for DRD2 (F=3.383, (1,266), p = 0.0670) indicating that the CT/TT or GT/TT genotypes in ANKK1 and DRD2, respectively, showed fewer cocaine-positive urines when treated with disulfiram. Hence, the results with Caucasians only demonstrate that it is unlikely that the results with the total cohort were due to population stratification.

Treatment outcomes by ANKK1/DRD2 genotype pattern

We went on to analyze disulfiram response in relation to genotype patterns of the ANKK1 and DRD2 genotypes combined. We divided the patients into two genotype pattern groups: individuals carrying the genotype homozygous for the major alleles only (ANKK1 CC/DRD2 GG), versus all other possible genotype patterns. Individuals in the latter group who carried at least one minor allele in ANKK1, DRD2, or both genes showed significantly reduced cocaine-positive urines as compared to individuals with a ANKK1 CC/DRD2 GG genotype pattern (see Figure 1) when treated with disulfiram (F = 20.72; df = 1,173; p < 0.0001, with an effect size of 0.1187). Linkage disequilibrium analysis showed that the two loci (rs2283265 and rs1800497) had medium linkage disequilibrium in our cohort (r2 = 0.57).

Discussion

In this study, we found that the T allele of rs1800497 (also known as the TaqIA1 allele) in the ANKK1 gene, the T allele of rs2283265 in the DRD2 gene, and the genotype patterns including at least one minor allele from either gene, were found to be associated with significant reduction in cocaine-positive urines when in combination with disulfiram treatment for CD. We speculate that the increased dopamine levels as a result of disulfiram therapy more easily saturate the lower density of D2 receptors in individuals carrying the minor T allele of rs1800497 and/or rs2283265, therefore eliciting a better response compared to individuals carrying only the major alleles who would have a higher density of D2 receptors.

Both DRD2 and ANKK1 gene products function in the dopaminergic pathway of the brain and studies have linked variants in these genes to several addictive disorders relating to alcohol, heroin, nicotine, cocaine, opioids, gambling, methamphetamine, and polysubstance addiction [39, 42, 55–59], as well as to psychiatric disorders such as eating disorders, schizophrenia, obsessive-compulsive disorder (OCD), attention-deficit hyperactivity disorder (ADHD), and others [35, 36, 60–62].

The TaqIA variant is one of the most frequently studied variants in relation to psychiatric conditions since its initial association to alcoholism in 1990 [63]. Initially thought to be a promoter variant of DRD2, TaqIA has subsequently been shown to reside in the last exon of the upstream ANKK1 gene [64]. This variant codes for an amino acid substitution (Glu713Lys) in the 11th of 12 ankyrin repeats, but the functional consequences of this substitution have yet to be identified. Similarly, the DRD2 gene is one of the most frequently examined genes in relation to psychiatric disorders. The rs2283265 variant examined in this study is a G→T transversion in intron 5 of the DRD2 gene. There are two forms of the D2 dopamine receptor that result from alternative splicing of intron 6, known as D2S and D2L, for the short and long forms, respectively. The D2S protein is thought to be a presynaptic autoreceptor and may be involved in dopamine release and D2 receptor regulation [65]. The rs2283265 variant probably alters the ratio of long (D2L) to short (D2S) D2 receptor isoforms [44], the function of which is still unclear.

The gene product of DRD2, the D2 dopamine receptor, is central to the ‘reward circuitry’ in the brain and is therefore integral to addictive and psychiatric conditions. Low D2 receptor availability has been shown to predict increased cocaine self-administration in primates [66], and the ANKK1 rs1800497 and DRD2 rs2283265 T allele have both been shown to associate with lower DA receptor density [67–69]. Given these data, the response of patients carrying these alleles may be related to the interaction of disulfiram and D2 receptor availability [16–20].

Given the close proximity of ANKK1 to the DRD2 gene, one might surmise that the association with the ANKK1 rs1800497 variant may simply be due to linkage disequilibrium with the DRD2 rs2283265 variant. Studies that have examined haplotypes in and across both genes sometimes show linkage between the two [32], but statistical associations of phenotypes relating to these genes are often distinct as well [e.g. 32–34, 70, 71]. Our data show a similar phenotype association, but with a low LD of r2 = 0.57, therefore the two variants appear to have independent genetic influences. However, the two variants may affect response to disulfiram treatment via moderating the same pathway (e.g. dopamine signaling).

We have recently published two studies showing that associations exist between response to disulfiram and genes in the serotonergic pathway as well. Variants in the dopamine-β hydroxylase (DBH) [30], the serotonin transporter (5-HTTLPR) and the tryptophan hydroxylase (TPH2) [53] genes all were shown to be associated with response to disulfiram treatment for CD. Specifically, the first study found that the carrier group with only the major C allele of DBH showed decreased cocaine-positive urines in treatment with disulfiram, while the minor T allele showed no change. The second study, Nielsen et.al. 2012, showed that subjects with at least one copy of the minor allele of 5-HTTLPR or TPH2, or both, responded to disulfiram therapy, while the genotype groups with the major alleles of both genes did not show reduced cocaine-positive urines. The same clinical cohort was used for these studies as well as the current study. We anticipate that data from studies such as these, taken together will ultimately lead us to define ‘responder’ or ‘non-responder’ genotype patterns and may allow for the more accurate prediction of individuals for whom disulfiram may be an effective therapy.

A potential limitation of this study was the small sample size of the patient cohort. Additionally, since patients in the cohort were opioid co-dependent these findings may or may not translate to cocaine-dependent individuals who are not opioid co-dependent. Further studies will be required to confirm these findings.

In summary, this study identifies the rs1800497 T allele in the ANKK1 gene, the rs2283265 T allele in the DRD2 gene, and the genotype patterns including at least one of these two alleles as increasing the pharmacotherapeutic response to disulfiram pharmacotherapy for CD. This finding may be useful in personalizing treatment of CD to an individual based on their genetic makeup. Again, this ‘personalized medicine’ strategy may help increase the efficacy of CD pharmacotherapy.

Acknowledgments

Funding sources: Supported by: NIH/NIDA 5 P50 DA018197-05 (TK, DN) through MD Anderson's Cancer Center Support Grant DA026120 NIH/NIDA DA026120, the Veterans Health Administration, and the Toomim Family Fund. This material is the result of work supported with resources and the use of facilities at the Michael E. DeBakey VA Medical Center, Houston, TX.

Footnotes

Statement of conflict of interest: None declared

Clinical Trial: Pharmacogenetics of Disulfiram for Cocaine, clinicaltrials.gov/ct2/show/NCT00149630, NIDA-18197-2, NCT00149630

References

  • 1.SAMHSA. N.S. H-41, Editor. Rockville, MD: 2011. Results from the 2010 National Survey on Drug Use and Health (NSDUH) [Google Scholar]
  • 2.McLellan AT, et al. Drug dependence, a chronic medical illness: implications for treatment, insurance, and outcomes evaluation. JAMA. 2000;284(13):1689–1695. doi: 10.1001/jama.284.13.1689. [DOI] [PubMed] [Google Scholar]
  • 3.Wolf BC, et al. Methadone-related deaths in Palm Beach County. J Forensic Sci. 2004;49(2):375–378. [PubMed] [Google Scholar]
  • 4.Bux DA, Lamb RJ, Iguchi MY. Cocaine use and HIV risk behavior in methadone maintenance patients. Drug Alcohol Depend. 1995;37(1):29–35. doi: 10.1016/0376-8716(94)01058-s. [DOI] [PubMed] [Google Scholar]
  • 5.MacGowan RJ, et al. Factors associated with client-reported HIV infection among clients entering methadone treatment. AIDS Educ Prev. 1997;9(3):205–217. [PubMed] [Google Scholar]
  • 6.Meandzija B, et al. HIV infection and cocaine use in methadone maintained and untreated intravenous drug users. Drug Alcohol Depend. 1994;36(2):109–113. doi: 10.1016/0376-8716(94)90092-2. [DOI] [PubMed] [Google Scholar]
  • 7.Hartel DM, et al. Heroin use during methadone maintenance treatment: the importance of methadone dose and cocaine use. Am J Public Health. 1995;85(1):83–88. doi: 10.2105/ajph.85.1.83. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Bovasso G, Cacciola J. The long-term outcomes of drug use by methadone maintenance patients. J Behav Health Serv Res. 2003;30(3):290–303. doi: 10.1007/BF02287318. [DOI] [PubMed] [Google Scholar]
  • 9.Kosten TR, Rounsaville BJ, Kleber HD. Antecedents and consequences of cocaine abuse among opioid addicts. A 2.5-year follow-up. J Nerv Ment Dis. 1988;176(3):176–181. doi: 10.1097/00005053-198803000-00006. [DOI] [PubMed] [Google Scholar]
  • 10.Magura S, Rosenblum A, Rodriguez EM. Changes in HIV risk behaviors among cocaine-using methadone patients. J Addict Dis. 1998;17(4):71–90. doi: 10.1300/J069v17n04_07. [DOI] [PubMed] [Google Scholar]
  • 11.Magura S, et al. Treating cocaine-using methadone patients: predictors of outcomes in a psychosocial clinical trial. Subst Use Misuse. 2002;37(14):1927–1955. doi: 10.1081/ja-120016225. [DOI] [PubMed] [Google Scholar]
  • 12.Black JL, et al. The effect of increased cocaine use on drug treatment. Addict Behav. 1987;12(3):289–292. doi: 10.1016/0306-4603(87)90042-6. [DOI] [PubMed] [Google Scholar]
  • 13.Dunteman GH, Condelli WS, Fairbank JA. Predicting cocaine use among methadone patients: analysis of findings from a national study. Hosp Community Psychiatry. 1992;43(6):608–611. doi: 10.1176/ps.43.6.608. [DOI] [PubMed] [Google Scholar]
  • 14.Lima MS, et al. Antidepressants for cocaine dependence. Cochrane Database Syst Rev. 2003;(2):CD002950. doi: 10.1002/14651858.CD002950. [DOI] [PubMed] [Google Scholar]
  • 15.Lima AR, et al. Carbamazepine for cocaine dependence. Cochrane Database Syst Rev. 2002;(2):CD002023. doi: 10.1002/14651858.CD002023. [DOI] [PubMed] [Google Scholar]
  • 16.Carroll KM, et al. Efficacy of Disulfiram and Cognitive Behavior Therapy in Cocaine-Dependent Outpatients: A Randomized Placebo-Controlled Trial. Arch Gen Psychiatry. 2004;61(3):264–272. doi: 10.1001/archpsyc.61.3.264. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Carroll KM, et al. Treatment of cocaine and alcohol dependence with psychotherapy and disulfiram. Addiction. 1998;93(5):713–727. doi: 10.1046/j.1360-0443.1998.9357137.x. [DOI] [PubMed] [Google Scholar]
  • 18.Carroll KM. Psychotherapeutic treatment of cocaine abuse: models for its evaluation alone and in combination with pharmacotherapy. NIDA Res Monogr. 1993;135:116–132. [PubMed] [Google Scholar]
  • 19.George TP, et al. Disulfiram versus placebo for cocaine dependence in buprenorphine-maintained subjects: a preliminary trial. Biol Psychiatry. 2000;47(12):1080–1086. doi: 10.1016/s0006-3223(99)00310-8. [DOI] [PubMed] [Google Scholar]
  • 20.Petrakis IL, et al. Disulfiram treatment for cocaine dependence in methadone-maintained opioid addicts. Addiction. 2000;95(2):219–228. doi: 10.1046/j.1360-0443.2000.9522198.x. [DOI] [PubMed] [Google Scholar]
  • 21.Vaccari A, et al. Disulfiram and diethyldithiocarbamate intoxication affects the storage and release of striatal dopamine. Toxicol Appl Pharmacol. 1996;139(1):102–108. doi: 10.1006/taap.1996.0147. [DOI] [PubMed] [Google Scholar]
  • 22.Johnson SM, Fleming WW. Mechanisms of cellular adaptive sensitivity changes: applications to opioid tolerance and dependence. Pharmacol Rev. 1989;41(4):435–488. [PubMed] [Google Scholar]
  • 23.Bourdelat-Parks BN, et al. Effects of dopamine beta-hydroxylase genotype and disulfiram inhibition on catecholamine homeostasis in mice. Psychopharmacology (Berl) 2005;183(1):72–80. doi: 10.1007/s00213-005-0139-8. [DOI] [PubMed] [Google Scholar]
  • 24.Schank JR, et al. Dopamine beta-hydroxylase knockout mice have alterations in dopamine signaling and are hypersensitive to cocaine. Neuropsychopharmacology. 2006;31(10):2221–2230. doi: 10.1038/sj.npp.1301000. [DOI] [PubMed] [Google Scholar]
  • 25.Goldman D, Oroszi G, Ducci F. The genetics of addictions: uncovering the genes. Nat Rev Genet. 2005;6(7):521–532. doi: 10.1038/nrg1635. [DOI] [PubMed] [Google Scholar]
  • 26.Leshner AI. Addiction is a brain disease, and it matters. Science. 1997;278(5335):45–47. doi: 10.1126/science.278.5335.45. [DOI] [PubMed] [Google Scholar]
  • 27.Weisner C, Matzger H, Kaskutas LA. How important is treatment? One-year outcomes of treated and untreated alcohol-dependent individuals. Addiction. 2003;98(7):901–911. doi: 10.1046/j.1360-0443.2003.00438.x. [DOI] [PubMed] [Google Scholar]
  • 28.Simpson DD, Joe GW, Broome KM. A national 5-year follow-up of treatment outcomes for cocaine dependence. Arch Gen Psychiatry. 2002;59(6):538–565. doi: 10.1001/archpsyc.59.6.538. [DOI] [PubMed] [Google Scholar]
  • 29.Sofuoglu M, Kosten TR. Emerging pharmacological strategies in the fight against cocaine addiction. Expert Opin Investig Drugs. 2006;11(1):91–98. doi: 10.1517/14728214.11.1.91. [DOI] [PubMed] [Google Scholar]
  • 30.Kosten TR, et al. Pharmacogenetic randomized trial for cocaine abuse: disulfiram and dopamine beta-hydroxylase. Biol Psychiatry. 2013;73(3):219–224. doi: 10.1016/j.biopsych.2012.07.011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.McAllister T, et al. Single nucleotide polymorphisms in ANKK1 and the Dopamine D2 receptor gene affect cognitive outcome shortly after traumatic brain injury: A replication and extension study. Brain Injury. 2008;22(9):705–714. doi: 10.1080/02699050802263019. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Giegling I, et al. Influence of ANKK1 and DRD2 polymorphisms in response to haloperidol. Eur Arch Psychiatry Clin Neurosci. 2013;263(1):65–74. doi: 10.1007/s00406-012-0348-1. [DOI] [PubMed] [Google Scholar]
  • 33.Yang B, et al. Association of haplotypic variants in DRD2, ANKK1, TTC12 and NCAM1 to alcohol dependence in independent case control and family samples. Hum Mol Genet. 2007;16:2844–2853. doi: 10.1093/hmg/ddm240. [DOI] [PubMed] [Google Scholar]
  • 34.Yang B, et al. Haplotypic variants in DRD2, ANKK1, TTC12 and NCAM1 are associated with comorbid alcohol and drug dependence. Alcohol Clin Exp Res. 2008;32(12):2117–2127. doi: 10.1111/j.1530-0277.2008.00800.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 35.Golimbet V, et al. Analysis of the linkage of the Taq1A and Taq1B loci of the dopamine D2 receptor gene with schizophrenia in patients and their siblings. Neurosci Behav Physiol. 2003;(33):223–225. doi: 10.1023/a:1022191012698. [DOI] [PubMed] [Google Scholar]
  • 36.Glatt S, et al. Family-based association testing strongly implicates DRD2 as a risk gene for schizophrenia in Han Chinese from Taiwan. Mol Psychiatry. 2009;14(9):885–893. doi: 10.1038/mp.2008.30. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37.Comings D, et al. The dopamine D2 receptor locus as a modifying gene in neuropsychiatric disorders. JAMA. 1991;266(13):1793–1800. [PubMed] [Google Scholar]
  • 38.Voisey J, et al. A DRD2 and ANKK1 haplotype is associated with nicotine dependence. Psychiatry Res. 2012;196(2-3):285–289. doi: 10.1016/j.psychres.2011.09.024. [DOI] [PubMed] [Google Scholar]
  • 39.Blum K, et al. Association of the A1 allele of the D2 dopamine receptor gene with severe alcoholism. Alcohol. 1991;8(5):409–416. doi: 10.1016/0741-8329(91)90693-q. [DOI] [PubMed] [Google Scholar]
  • 40.Blum K, et al. Allelic association of human dopaine D2 receptor gene in alcoholism. JAMA. 1990;26:2055–2060. [PubMed] [Google Scholar]
  • 41.Connor J, et al. Heavy nicotine and alcohol use in alcohol dependence is associated with D2 dopamine receptor (DRD2) Addict Behav. 2007;32(2):310–319. doi: 10.1016/j.addbeh.2006.04.006. [DOI] [PubMed] [Google Scholar]
  • 42.Noble E. Polymorphisms of the D2 dopamine receptor gene and alcoholism and other substance use disorders. Alcohol and Alcoholism Supplement. 1994;2:35–43. [PubMed] [Google Scholar]
  • 43.Noble E, et al. Allelic association of the D2 dopamine receptor gene with receptor-binding characteristics in alcoholism. Arch Gen Psychiatry. 1991;48:648–654. doi: 10.1001/archpsyc.1991.01810310066012. [DOI] [PubMed] [Google Scholar]
  • 44.Zhang Y, et al. Polymorphisms in human dopamine D2 receptor gene affect gene expression, splicing, and neuronal activity during working memory. Proc Natl Acad Sci U S A. 2007;104(51):20552–20557. doi: 10.1073/pnas.0707106104. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 45.Moyer R, et al. Intronic polymorphisms affecting alternative splicing of human dopamine D2 receptor are associated with cocaine abuse. Neuropsychopharmacology. 2011;36:753–762. doi: 10.1038/npp.2010.208. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 46.Jonsson E, et al. Polymorphisms in the dopamine D2 receptor gene and their relationships to striatal dopamine receptor density of healthy voluneers. Mol Psychiatry. 1999;4(3):290–296. doi: 10.1038/sj.mp.4000532. [DOI] [PubMed] [Google Scholar]
  • 47.Hoenicka J, et al. The ANKK1 gene associated with addictions is expressed in astroglial cells and upregulated by apomorphine. Biol Psychiatry. 2010;67:3–11. doi: 10.1016/j.biopsych.2009.08.012. [DOI] [PubMed] [Google Scholar]
  • 48.Dubertret C, et al. Association and excess of transmission of a DRD2 haplotype in a sample of French schizophrenic patients. Schizophr Res. 2001;49(1-2):203–212. doi: 10.1016/s0920-9964(00)00085-2. [DOI] [PubMed] [Google Scholar]
  • 49.Noble E, et al. Allelic association of the D2 dopamine receptor gene with cocaine dependence. Drug Alcohol Depend. 1993;33(3):271–285. doi: 10.1016/0376-8716(93)90113-5. [DOI] [PubMed] [Google Scholar]
  • 50.McLellan A, et al. The Fifth Edition of the Addiction Severity Index. J Subst Abuse Treat. 1992;9(3):199–213. doi: 10.1016/0740-5472(92)90062-s. [DOI] [PubMed] [Google Scholar]
  • 51.Sheehan D, et al. The Mini-International Neuropsychiatric Interview (M.I.N.I.): the development and validation of a structured diagnostic psychiatric interview for DSM-IV and ICD-10. J Clin Psychiatry. 1998;59(20):22–33. [PubMed] [Google Scholar]
  • 52.Carroll KM. Manual-guided psychosocial treatment. A new virtual requirement for pharmacotherapy trials? Arch Gen Psychiatry. 1997;54(10):923–928. doi: 10.1001/archpsyc.1997.01830220041007. [DOI] [PubMed] [Google Scholar]
  • 53.Nielsen DA, et al. Modifying the role of serotonergic 5-HTTLPR and TPH2 variants on disulfiram treatment of cocaine addiction: a preliminary study. Genes Brain Behav. 2012 doi: 10.1111/j.1601-183X.2012.00839.x. [Epub ahead of print] [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 54.R_Development_Core_Team. R: A language and environment for statistical computing. Vienna, Austria: R Foundation for Statistical Computing; 2009. [Google Scholar]
  • 55.Comings D, et al. A study of the dopamine D2 receptor gene in pathological gambling. Pharmacogenetics. 1996;6(3):223–234. doi: 10.1097/00008571-199606000-00004. [DOI] [PubMed] [Google Scholar]
  • 56.Persico A, et al. D2 dopamine receptor gene TaqI A1 and B1 restriction fragment length polymorphisms: enhanced frequencies in psychostimulant-preferring polysubstance abusers. Biol Psychiatry. 1996;40:776–784. doi: 10.1016/0006-3223(95)00483-1. [DOI] [PubMed] [Google Scholar]
  • 57.Lawford B, et al. The D(2) dopamine receptor A(1) allele and opioid dependence: association with heroin use and response to methadone treatment. Am J Med Genet. 2000;96:592–598. doi: 10.1002/1096-8628(20001009)96:5<592::aid-ajmg3>3.0.co;2-y. [DOI] [PubMed] [Google Scholar]
  • 58.Munafo M, et al. The genetic basis for smoking behavior: a systematic review and meta-analysis. Nicotine Tob Res. 2004;6(4):583–597. doi: 10.1080/14622200410001734030. [DOI] [PubMed] [Google Scholar]
  • 59.Perez de los Cobos J, et al. Allelic and genotypic associations of DRD2 TaqI A polymorphism with heroin dependence in Spanish subjects: a case control study. Behav Brain Funct. 2007;3:25. doi: 10.1186/1744-9081-3-25. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 60.Denys D, et al. Association between the dopamine D2 receptor TaqIA A2 allele and low activity COMT allele with obsessive-compulsive disorder in males. Eur Neuropsychopharmacol. 2006;16(6):446–450. doi: 10.1016/j.euroneuro.2005.12.001. [DOI] [PubMed] [Google Scholar]
  • 61.Comings D, et al. The dopamine D2 receptor locus as a modifying gene in neuropsychiatric disorders. JAMA. 1991;266(13):1793–1800. [PubMed] [Google Scholar]
  • 62.Nisoli E, et al. D2 dopamine receptor (DRD2) gene Taq1A polymorphism and the eating-related psychological traits in eating disorders (anorexia nervosa and bulimia) and obesity. Eat Weight Disord. 2007;12:91–96. doi: 10.1007/BF03327583. [DOI] [PubMed] [Google Scholar]
  • 63.Blum K, et al. Allelic association of human dopaine D2 receptor geninni alcoholism. JAMA. 1990;26:2055–2060. [PubMed] [Google Scholar]
  • 64.Neville M, Johnstone E, RT W. Identification and characterization of ANKK1: A novel kinase gene closely linked to DRD2 on chromosome band 11p23.1. Hum Mutat. 2004;23(6):540–545. doi: 10.1002/humu.20039. [DOI] [PubMed] [Google Scholar]
  • 65.Khan Z, et al. Prominence of the dopamine D2 short isoform in dopaminergic pathways. Proc Natl Acad Sci U S A. 1998;95:7731–7736. doi: 10.1073/pnas.95.13.7731. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 66.Nader M, et al. PET imaging of dopamine D2 receptors during chronic cocaine self-administration in monkeys. Nat Neurosci. 2006;9(8):1050–1056. doi: 10.1038/nn1737. [DOI] [PubMed] [Google Scholar]
  • 67.Thompson J, et al. D2 dopamine receptor gene (DRD2) Taq1A polymorphism: reduced dopamine D2 receptor binding in the human striatum associated with the A1 allele. Pharmacogenetics. 1997;7:479–484. doi: 10.1097/00008571-199712000-00006. [DOI] [PubMed] [Google Scholar]
  • 68.Ritchie T, Noble E. Association of seven polymorphisms of the D2 dopamine receptor gene with brain receptor-binding characteristics. Neurochem Res. 2003;28:73–82. doi: 10.1023/a:1021648128758. [DOI] [PubMed] [Google Scholar]
  • 69.Pohjalainen T, et al. The A1 allele of the human D2 dopamine receptor gene predicts low D2 receptor availability in healthy volunteers. Mol Psychiatry. 1998;3(3):256–260. doi: 10.1038/sj.mp.4000350. [DOI] [PubMed] [Google Scholar]
  • 70.Dick D, et al. Family-based association analyses of alcohol dependence phenotypes across DRD1 and neighboring gene ANKK1. Alcohol Clin Exp Res. 2007;31(10):1645–1653. doi: 10.1111/j.1530-0277.2007.00470.x. [DOI] [PubMed] [Google Scholar]
  • 71.Gelernter J, et al. Haplotype spanning TTC12 and ANKK1, flanked by the DRD2 and NCAM1 loci, is strongly associated to nicotine dependence in two distinct American populations. Hum Mol Genet. 2006;15(24):3498–3507. doi: 10.1093/hmg/ddl426. [DOI] [PubMed] [Google Scholar]

RESOURCES