A genome-wide association study of cocaine use disorder accounting for phenotypic heterogeneity and gene–environment interaction

BACKGROUND

Phenotypic heterogeneity and complicated gene–environment interplay in etiology are among the primary factors that hinder the identification of genetic variants associated with cocaine use disorder.

METHODS

To detect novel genetic variants associated with cocaine use disorder, we derived disease traits with reduced phenotypic heterogeneity using cluster analysis of a study sample (n = 9965). We then used these traits in genome-wide association tests, performed separately for 2070 African Americans and 1570 European Americans, using a new mixed model that accounted for the moderating effects of 5 childhood environmental factors. We used an independent sample (918 African Americans, 1382 European Americans) for replication.

RESULTS

The cluster analysis yielded 5 cocaine use disorder subtypes, of which subtypes 4 (n = 3258) and 5 (n = 1916) comprised heavy cocaine users, had high heritability estimates (h2 = 0.66 and 0.64, respectively) and were used in association tests. Seven of the 13 identified genetic loci in the discovery phase were available in the replication sample. In African Americans, rs114492924 (discovery p = 1.23 × E−8), a single nucleotide polymorphism in LINC01411, was replicated in the replication sample (p = 3.63 × E−3). In a meta-analysis that combined the discovery and replication results, 3 loci in African Americans were significant genome-wide: rs10188036 in TRAK2 (p = 2.95 × E−8), del-1:15511771 in TMEM51 (p = 9.11 × E−10) and rs149843442 near LPHN2 (p = 3.50 × E−8).

LIMITATIONS

Lack of data prevented us from replicating 6 of the 13 identified loci.

CONCLUSION

Our results demonstrate the importance of considering phenotypic heterogeneity and gene–environment interplay in detecting genetic variations that contribute to cocaine use disorder, because new genetic loci have been identified using our novel analytic method.

Latent classes of heroin and cocaine users predict unique HIV/HCV risk factors

BACKGROUND

Patterns of heroin and cocaine use vary and may be associated with unique risk factors for bloodborne infections.

METHODS

Latent class analysis identified sub-populations of 552 heroin and cocaine users in Baltimore, Maryland. Using latent class regression, these classes were analyzed for associations with demographic characteristics, risky behaviors, Hepatitis C, and HIV.

RESULTS

Three classes were found: Crack/Nasal-Heroin users (43.5%), Polysubstance users (34.8%), and Heroin Injectors (21.8%). Compared to Polysubstance users, Crack/Nasal-Heroin users were almost 7 times more likely to identify as Black (OR=6.97, 95% CI=4.35-11.2). Sharing needles was over 2.5 times more likely among Polysubstance users than among Heroin Injectors (OR=2.66, 95% CI=1.49-4.75). Crack/Nasal-Heroin users were 2.5 times more likely than Polysubstance users to exchange drugs for sex (OR=2.50, 95% CI=1.22-5.13). Crack/Nasal-Heroin users were less likely than Heroin Injectors to have Hepatitis C (OR=0.10, 95% CI=0.06-0.18), but no significant differences were found for HIV.

CONCLUSIONS

Subpopulations of cocaine and heroin users differed in demographic classifications, HIV-risk behaviors, and Hepatitis C infection. All subpopulations included substantial numbers of HIV-positive individuals. Findings provide further evidence that non-injection drug users face significant infectious disease risk.

[Subtypes of cocaine addicts with and without associated problematic alcohol use: towards a neuropsychology of personality applied to clinical practice]

It is important to know which personality factors are associated with addiction so to distinguish addicts that require specialized treatment from those who do not, and to identify those addicts who achieve abstinence from those who continue their substance use despite the negative consequences. Cloninger's model includes biological and psychosocial variables that can be characterized in neuropsychological terms. Two samples were analyzed: individuals who had begun cocaine addiction treatment (n=183) and a non-clinical population sample (n = 183), matched for sex, age and educational level. Alcohol abuse/dependence was monitored as an independent variable. Significant differences and large effect size were found between addicts and non-clinical population in Novelty Seeking and Self-Directedness, and to a lesser extent, in Harm Avoidance. These differences increase when problematic use of alcohol is added. According to the profile of traits, clusters of addicts were established and differences were obtained in variables such as functional/dysfunctional impulsivity, dysexecutive symptoms and perceived stress. Six clusters were identified, some of minor severity, the most severely problematic clusters being characterized by higher levels of dysfunctional impulsivity, more dysexecutive symptoms and higher levels of perceived stress. Self-Directedness seems to reflect the deficit of prefrontal systems in the regulation of behavior, as well as in emotion and impulse control. It is proposed that evaluation of the personality is more useful than the mere assessment of symptoms for classifying addicts, determining their needs and designing a therapeutic itinerary.

Diagnosis of brain abnormality using both structural and functional MR images

A number of neurological diseases are associated with structural and functional alterations in the brain. This paper presents a method of using both structural and functional MR images for brain disease diagnosis, by machine learning and high-dimensional template warping. First, a high-dimensional template warping technique is used to complete morphological and functional representation for each individual brain in a template space, within a mass preserving framework. Then, statistical regional features are extracted to reduce the dimensionality of morphological and functional representation , as well as to achieve the robustness to registration errors and inter-subject variations. Finally, the most discriminative regional features are selected by a hybrid feature method for brain classification, using a nonlinear support vector machine. The proposed method has been applied to classifying the brain images of prenatally cocaine-exposed young adults from those of socioeconomically matched controls, resulting in 91.8% correct classification rate using a leave-one-out cross-validation. Comparison results show the effectiveness of our method and also the importance of simultaneously using both structural and functional images for brain classification.

Genomewide linkage scan for cocaine dependence and related traits: significant linkages for a cocaine-related trait and cocaine-induced paranoia

Risk for cocaine dependence (CD) is genetically influenced. We recruited a sample of small nuclear families (528 full and 155 half sibpairs) with at least one subject affected with CD. The sample was classified via Bayesian clustering as 45.5% European American (EA) and 54.5% African American (AA). Assessment, via the Semi-Structured Assessment for Drug Dependence and Alcoholism, allowed for detailed evaluation of substance dependence-related traits. To define subgroups with increased genetic homogeneity, consistent with our a priori analytic plan, we used cluster analytic methods to identify six cocaine-related symptom clusters; membership was shown to be significantly heritable. We then completed a genomewide linkage scan (409 markers) for the CD diagnosis, cocaine-induced paranoia (CIP; an outcome that occurs in some cocaine users) and the clusters (three of which contained >80% of the CD subjects). We observed a "suggestive" linkage signal on chromosome 10 for the trait of CD in the full sample; and two "suggestive" linkage signals at different locations on chromosome 3, in the EA part of the sample. We observed a genomewide-significant lod score of 3.65 for the trait of CIP on chromosome 9, in the AA part of the sample only. Our strongest results were observed for the cluster membership traits, including a lod score of 4.66 for membership in the "Heavy Use, Cocaine Predominant" cluster on chromosome 12 (in EAs only) and a lod score of 3.35 for membership in the "Moderate Cocaine and Opioid Abuse" cluster on chromosome 18. These results provide a basis for the identification of specific genes contributing to risk for these traits.

Injection drug use and crack cocaine smoking: independent and dual risk behaviors for HIV infection

PURPOSE

Previous studies have examined the practices of injecting drugs or smoking crack cocaine as high-risk, but independent, factors for HIV transmission. To explore the independent and dual risks of injection practices and crack smoking, this study examined HIV seroprevalence rates among distinct drug user groups, based on patterns of daily administration.

METHODS

A sample of 3,555 drug users and neighborhood controls in urban Miami, FL and rural Belle Glade and Immokalee, FL were partitioned into four mutually-exclusive groups: 1) injection drug users (IDUs); 2) crack-cocaine smokers; 3) dual users who both smoked crack and injected drugs; and 4) non-drug-user controls.

RESULTS

HIV seroprevalence rates were 45.1% for IDUs, 30.5% for dual users, 20.1% for crack smokers and 7.3% for controls. Multivariate logistic regression analysis found that when compared with controls odds ratios for HIV seropositivity were 9.81 for IDUs, 5.27 for dual users, and 2.24 for crack smokers.

CONCLUSIONS

These findings provide evidence of: 1) behavioral and structural co-factors that influence HIV exposure patterns among drug users; and 2) the substantially higher risk of HIV infection among IDUs compared with other drug users. Intervention strategies must be tailored for the specific drug use subpopulations to optimize efficacy.

Cocaine Dependence Severity Predicts Outcome in Outpatient Detoxification from Cocaine and Alcohol

This study compared the effects of alcohol and cocaine dependence severity on the outcome of outpatient detoxification from alcohol and cocaine. Subjects included 84 subjects with both alcohol and cocaine dependence admitted for outpatient detoxification. Fifty-three of the 84 subjects (63%) completed detoxification. Baseline cocaine use, cocaine craving, and cocaine withdrawal symptoms predicted detoxification outcome, whereas alcohol use, alcohol craving, and alcohol withdrawal symptoms did not. Among cocaine- and alcohol-dependent subjects, cocaine dependence severity appears to be a more important predictor of detoxification success than alcohol dependence severity.

Substance Dependence Severity Scale (SDSS): reliability and validity of a clinician-administered interview for DSM-IV substance use disorders

No existing diagnostic interview assesses severity of dependence based on DSM-IV criteria across a range of substances. The Substance Dependence Severity Scale (SDSS) was designed to serve this purpose, consisting of substance-specific scales of both severity and frequency of DSM-IV criteria. This study investigated the reliability and validity of the SDSS. The test-retest reliability of the SDSS in 175 (112 male and 63 female) treated substance users ranged from good to excellent for alcohol, cocaine, heroin and sedatives (interclass correlation coefficients (ICCs)=0.75-0.88 for severity, 0.67-0.85 for frequency). Results for cannabis were lower, ranging from fair to good (ICCs=0.50-0.62). Results for joint rating and internal consistency reliability were comparable to test-retest findings. In addition to indicators of concurrent validity, scale applications are presented and discussed.

Concurrent and predictive validity of the Substance Dependence Severity Scale (SDSS)

This study investigated the concurrent and predictive validity of the Substance Dependence Severity Scale (SDSS), a clinician-administered interview designed to assess the severity and frequency of DSM-IV dependence symptoms for a range of substances. A total of 172 (107 males and 66 females) treated substance users participated in the study. Of those, 89% (n=153) received at least one follow-up interview within 1-6 months of an initial assessment. For alcohol, cocaine and heroin, convergent and discriminant validity was supported by significant relationships between SDSS scores at baseline and other baseline measures of substance use consequences, such as the Addiction Severity Index (ASI), as well as significant relationships between SDSS change scores from baseline to follow-up and change scores of other measures of consequences. SDSS scores were significantly associated with time to first post treatment use of alcohol, cocaine and heroin, although the nature of the associations was complex. Scale applications and areas for further study are discussed.

Initial validation of the Voris Cocaine Craving Scale: a preliminary report

Although cocaine craving can persist for weeks after the last use and is thought to play a role in future relapses, few short, reliable, and valid instruments exist to measure craving. Therefore, we wished to examine the validity of the 4-item Voris Cocaine Craving Scale (VCCS), which was previously found reliable. A consecutive series of 41 recently withdrawn cocaine-dependent patients completed the 4-item VCCS and the Cocaine Craving Questionnaire (CCQ), which was used as the criterion measure. The VCCS items 1 "craving," 2 "mood," and 3 "health" were significant and highly correlated with the CCQ total craving score. The VCCS may prove to be useful in future outcome studies involving cocaine craving and in routine clinical treatment.

Congruence of the MCMI-II and MCMI-III in cocaine dependence

This study compared the MCMI-II and MCMI-III among 40 urban, poor, cocaine abusers in outpatient treatment. The mean group profiles had strikingly similar relative elevations on the Antisocial, Narcissistic, Aggressive-Sadistic, Alcohol Dependence, and Drug Dependence scales. However, the MCMI-III group profile was significantly lower in magnitude compared with the MCMI-II. Interval and rank-order correlations were moderate to low for most scales, and 90% of participants produced discrepant 2-point codetypes between the 2 tests. These results suggest that clinicians working in substance abuse settings should perhaps adjust MCMI-III profile elevations upward on most scales (particularly on the personality disorder scales) when comparing results to extant normative data and should use caution when referencing MCMI/MCMI-II interpretive manuals for descriptive correlates of MCMI-III scales and codetypes.

Validation of the criteria for DSM diagnosis of cocaine abuse and cocaine dependence

The concurrent external validity of the diagnosis of cocaine abuse, based on the DSM criteria, is shown to be established to an unexpectedly high degree, based on a method of determining the association between a summary score derived by quantifying the DSM criteria and another summary score derived from weighting several measures of frequency of use of cocaine and a measure of its mode of use. The degree of validity was cross-validated by performing the same analysis on two study samples: one of inpatients (N = 179) and one of urban-community African-Americans (N = 204).