Two-part random effects growth modeling to identify risks associated with alcohol and cannabis initiation, initial average use and changes in drug consumption in a sample of adult, male twins

The genetic aetiology of cannabis use: from twin models to genome-wide association studies and beyond

Cannabis is among the most widely consumed psychoactive substances worldwide. Individual differences in cannabis use phenotypes can partly be explained by genetic differences. Technical and methodological advances have increased our understanding of the genetic aetiology of cannabis use. This narrative review discusses the genetic literature on cannabis use, covering twin, linkage, and candidate-gene studies, and the more recent genome-wide association studies (GWASs), as well as the interplay between genetic and environmental factors. Not only do we focus on the insights that these methods have provided on the genetic aetiology of cannabis use, but also on how they have helped to clarify the relationship between cannabis use and co-occurring traits, such as the use of other substances and mental health disorders. Twin studies have shown that cannabis use is moderately heritable, with higher heritability estimates for more severe phases of use. Linkage and candidate-gene studies have been largely unsuccessful, while GWASs so far only explain a small portion of the heritability. Dozens of genetic variants predictive of cannabis use have been identified, located in genes such as CADM2, FOXP2, and CHRNA2. Studies that applied multivariate methods (twin models, genetic correlation analysis, polygenic score analysis, genomic structural equation modelling, Mendelian randomisation) indicate that there is considerable genetic overlap between cannabis use and other traits (especially other substances and externalising disorders) and some evidence for causal relationships (most convincingly for schizophrenia). We end our review by discussing implications of these findings and suggestions for future work.

Parental protective and risk factors regarding cannabis use in adolescence: A national sample from the Chilean school population

Background: Research has increased our understanding of the parental factors associated with the initiation and development of cannabis use disorder in adolescents, but few studies about this have been performed in middle- or low-income countries.

Objective: First, to examine whether perceived past parental drug use, parental monitoring, and attitude toward adolescent cannabis use are associated with general and problematic cannabis use in Chilean adolescents. Second, to explore whether perceived past parental drug use weakens the associations of protective factors with general and problematic adolescent cannabis use.

Methods: Regression analyses were performed on cross-sectional data from a multistage probabilistic sample stratified by clusters (municipalities, school and grade) of 43,060 students (47% male, mean age 15.5 years) from grades 8 to 12, which was collected from the Chilean National School Survey on Drug Use (2013).

Results: Perceived past parental drug use increased the likelihood of adolescent cannabis use in general, but not its problematic use. Parental monitoring of adolescents' whereabouts and parental opposition to adolescent cannabis use decreased the likelihood of adolescent cannabis use in general, as well as problematic use. Perceived past parental drug use only interacted with parental monitoring of school activities.

Conclusions: In line with research from the United States, the Netherlands and Spain, parental monitoring of adolescents' whereabouts and a strong parental opposition to cannabis use appear to be protective factors, irrespective of past parental use. However, the effectiveness of monitoring adolescents' school activities seems to decrease when parents are perceived as having used drugs in the past.

Cessation of cannabis use: A retrospective cohort study

Given recent findings of a worldwide increase in cannabis use, a better understanding of the factors associated with cannabis use is needed. Most previous studies have focused on factors that predict the initiation of cannabis use, but less is known about factors associated with cessation. The present study is a retrospective cohort study of 6467 current or former cannabis users aged 15 to 46 years (mean age 22.5, SD = 4.8). Data were collected via an online survey advertised in social media. All analyzed participants had used cannabis for at least three years. Approximately 16.3% (n = 1055) of the sample population had not used cannabis in the previous 12 months and were classified as quitters; all others (83.7%, n = 5412) reported at least monthly use. Cessation was predicted by older current age, being female, nonmigrant status, less sensation seeking, using psychological treatment, more peer cannabis use during youth and more negative first experience with cannabis. An additional predictor was a nonincrease in the frequency of cannabis use in the first three years of use, indicating that trajectories of cannabis use are set early on and might be used to identify risk groups for early preventive measures.

Impulsivities and addictions: a multidimensional integrative framework informing assessment and interventions for substance use disorders

Impulse control is becoming a critical survival skill for the twenty-first century. Impulsivity is implicated in virtually all externalizing behaviours and disorders, and figures prominently in the aetiology and long-term sequelae of substance use disorders (SUDs). Despite its robust clinical and predictive validity, the study of impulsivity is complicated by its multidimensional nature, characterized by a variety of trait-like personality dimensions, as well as by more state-dependent neurocognitive dimensions, with variable convergence across measures. This review provides a hierarchical framework for linking self-report and neurocognitive measures to latent constructs of impulsivity and, in turn, to different psychopathology vulnerabilities, including substance-specific addictions and comorbidities. Impulsivity dimensions are presented as novel behavioural targets for prevention and intervention. Novel treatment approaches addressing domains of impulsivity are reviewed and recommendations for future directions in research and clinical interventions for SUDs are offered. This article is part of the theme issue 'Risk taking and impulsive behaviour: fundamental discoveries, theoretical perspectives and clinical implications'.

Predictors of initiation of nicotine, alcohol, cannabis, and cocaine use: Results of the National Epidemiologic Survey on Alcohol and Related Conditions (NESARC)

BACKGROUND AND OBJECTIVES

There may be substantial overlap in the risk factors for substance use and substance use disorders (SUD). Identifying risk factors for substance use initiation is essential for understanding the etiology and natural history of SUD and to develop empirically-based preventive interventions to reduce initiation.

METHODS

Analyses were done on Wave 1 participants of the National Epidemiological Survey of Alcohol and Related Conditions (NESARC) (n = 43,093). Estimates of the cumulative probability of substance use initiation were obtained separately for nicotine, alcohol, cannabis, and cocaine. Survival analyses with time-varying covariates were implemented to identify risk factors for substance initiation.

RESULTS

The lifetime cumulative probabilities of substance initiation were 45.5% for nicotine, 82% for alcohol, 19.6% for cannabis, and 6.4% for cocaine. Among respondents with lifetime nicotine use, 50% had used it by age 15.3, whereas for alcohol, cannabis, and cocaine the respective ages were 17.8, 16.6, and 19.8. Previous use of another substance, being male, having a cluster B personality disorder, family history of SUD, and being separated, divorced, or widowed increased the risk of use of all the substances assessed, whereas social anxiety disorder and some personality disorders were associated with specific substances.

DISCUSSION AND CONCLUSIONS

Although the age of substance use initiation varies by substance, in more than 50% of cases initiation of use occurs in the first two decades of life. Although most risk factors for substance use initiation are common across substances, some are substance-specific.

SCIENTIFIC SIGNIFICANCE

This information may help in the development of empirically-based preventive interventions. (Am J Addict 2018;27:477-484).

The Genetic and Environmental Association Between Parental Monitoring and Risk of Cannabis, Stimulants, and Cocaine Initiation in a Sample of Male Twins: Does Parenting Matter?

Our aim was to test the direction of causation between self-report parental monitoring (PM) and the liability to illicit drug initiation (DI) as indicated by cannabis, cocaine, and stimulants. We fitted a multiple indicator model to test causal and non-causal models based on a large, genetically informative cross-sectional sample of male twins. The sample comprised 1,778 males aged 24-62 years from the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders. Data came from self-report measures of lifetime cannabis, stimulants, and cocaine initiation, and retrospective assessment of PM between ages 8-17 years. Multivariate modeling showed that familial aggregation in PM and DI were both explained by a combination of additive genetic and shared environmental effects. Moreover, the significant association between PM and DI was best explained by a correlated liability model versus causal models. PM has typically been assumed to be an environmental, causal risk factor for drug use and has been shown to be among the more salient environmental risk factors for illicit DI. Our data were not consistent with this causal hypothesis. Instead, a correlated liability model in which PM and risk of DI share common genetic and environmental risks provided a better fit to the data.

Genetic and Environmental Factors Associated with Cannabis Involvement

Approximately 50-70% of the variation in cannabis use and use disorders can be attributed to heritable factors. For cannabis use, the remaining variance can be parsed in to familial and person-specific environmental factors while for use disorders, only the latter contribute. While numerous candidate gene studies have identified the role of common variation influencing liability to cannabis involvement, replication has been elusive. To date, no genomewide association study has been sufficiently powered to identify significant loci. Despite this, studies adopting polygenic techniques and integrating genetic variation with neural phenotypes and measures of environmental risk, such as childhood adversity, are providing promising new leads. It is likely that the small effect sizes associated with variants related to cannabis involvement will only be robustly identified in substantially larger samples. Results of such large-scale efforts will provide valuable single variant targets for translational research in neurogenetic, pharmacogenetic and non-human animal models as well as polygenic risk indices that can be used to explore a host of other genetic hypotheses related to cannabis use and misuse.

Clinical and Social/Environmental Characteristics in a Community Sample of Children With and Without Family Histories of Substance Use Disorder in the San Antonio Area: A Descriptive Study

This is a descriptive study of the recruitment and clinical/environmental characteristics of a child cohort (ages 10-12) established to test transmission of impulsivity in children with (FH+; n = 305) and without (FH-; n = 81) family history of substance use disorder. Among this cohort FH⁺ children had more emotional and behavioral symptoms, worse family relationships, and more deviant peers compared to FH^- children. This cohort of children was established prior to the initiation of regular substance use and significant clinical problems, which will allow the opportunity to examine reciprocal relations between development of impulse control and substance use development.

Genome-wide association study of lifetime cannabis use based on a large meta-analytic sample of 32 330 subjects from the International Cannabis Consortium

Cannabis is the most widely produced and consumed illicit psychoactive substance worldwide. Occasional cannabis use can progress to frequent use, abuse and dependence with all known adverse physical, psychological and social consequences. Individual differences in cannabis initiation are heritable (40-48%). The International Cannabis Consortium was established with the aim to identify genetic risk variants of cannabis use. We conducted a meta-analysis of genome-wide association data of 13 cohorts (N=32 330) and four replication samples (N=5627). In addition, we performed a gene-based test of association, estimated single-nucleotide polymorphism (SNP)-based heritability and explored the genetic correlation between lifetime cannabis use and cigarette use using LD score regression. No individual SNPs reached genome-wide significance. Nonetheless, gene-based tests identified four genes significantly associated with lifetime cannabis use: NCAM1, CADM2, SCOC and KCNT2. Previous studies reported associations of NCAM1 with cigarette smoking and other substance use, and those of CADM2 with body mass index, processing speed and autism disorders, which are phenotypes previously reported to be associated with cannabis use. Furthermore, we showed that, combined across the genome, all common SNPs explained 13-20% (P<0.001) of the liability of lifetime cannabis use. Finally, there was a strong genetic correlation (rg=0.83; P=1.85 × 10(-8)) between lifetime cannabis use and lifetime cigarette smoking implying that the SNP effect sizes of the two traits are highly correlated. This is the largest meta-analysis of cannabis GWA studies to date, revealing important new insights into the genetic pathways of lifetime cannabis use. Future functional studies should explore the impact of the identified genes on the biological mechanisms of cannabis use.

Impulsivity in abstinent alcohol and polydrug dependence: a multidimensional approach

RATIONALE

Dependence on drugs and alcohol is associated with impaired impulse control, but deficits are rarely compared across individuals dependent on different substances using several measures within a single study.

OBJECTIVES

We investigated impulsivity in abstinent substance-dependent individuals (AbD) using three complementary techniques: self-report, neuropsychological and neuroimaging. We hypothesised that AbDs would show increased impulsivity across modalities, and that this would depend on length of abstinence.

METHODS

Data were collected from the ICCAM study: 57 control and 86 AbDs, comprising a group with a history of dependence on alcohol only (n = 27) and a group with history of dependence on multiple substances ("polydrug", n = 59). All participants completed self-report measures of impulsivity: Barratt Impulsiveness Scale, UPPS Impulsive Behaviour Scale, Behaviour Inhibition/Activation System and Obsessive-Compulsive Inventory. They also performed three behavioural tasks: Stop Signal, Intra-Extra Dimensional Set-Shift and Kirby Delay Discounting; and completed a Go/NoGo task during fMRI.

RESULTS

AbDs scored significantly higher than controls on self-report measures, but alcohol and polydrug dependent groups did not differ significantly from each other. Polydrug participants had significantly higher discounting scores than both controls and alcohol participants. There were no group differences on the other behavioural measures or on the fMRI measure.

CONCLUSIONS

The results suggest that the current set of self-report measures of impulsivity is more sensitive in abstinent individuals than the behavioural or fMRI measures of neuronal activity. This highlights the importance of developing behavioural measures to assess different, more relevant, aspects of impulsivity alongside corresponding cognitive challenges for fMRI.

Can cannabis use be prevented by targeting personality risk in schools? Twenty-four-month outcome of the adventure trial on cannabis use: a cluster-randomized controlled trial

AIMS

To examine the effectiveness of a personality-targeted intervention program (Adventure trial) delivered by trained teachers to high-risk (HR) high-school students on reducing marijuana use and frequency of use.

DESIGN

A cluster-randomized controlled trial.

SETTING

Secondary schools in London, UK.

PARTICIPANTS

Twenty-one secondary schools were randomized to intervention (n = 12) or control (n = 9) conditions, encompassing a total of 1038 HR students in the ninth grade [mean (standard deviation) age = 13.7 (0.33) years].

INTERVENTIONS

Brief personality-targeted interventions to students with one of four HR profiles: anxiety sensitivity, hopelessness, impulsivity and sensation-seeking.

PRIMARY OUTCOME

marijuana use. Secondary outcome: frequency of use. Assessed using the Reckless Behaviour Questionnaire at intervals of 6 months for 2 years. Personality risk was measured with the Substance Use Risk Profile Scale.

FINDINGS

Logistic regression analysis revealed significant intervention effects on cannabis use rates at the 6-month follow-up in the intent-to-treat sample [odds ratio (OR) = 0.67, P = 0.05, 95% confidence interval (CI) = 0.45-1.0] and significant reductions in frequency of use at 12- and 18-month follow-up (β = -0.14, P ≤ 0.05, 95% CI = -0.6 to -0.01; β = -0.12, P ≤ 0.05, 95% CI = -0.54 to 0.0), but this was not supported in two-part latent growth models. Subgroup analyses (both logistic and two-part models) reveal that the sensation-seeking intervention delayed the onset of cannabis use among sensation seekers (OR = 0.25, β = -0.833, standard error = 0.342, P = 0.015).

CONCLUSIONS

Personality-targeted interventions can be delivered effectively by trained school staff to delay marijuana use onset among a subset of high-risk teenagers: sensation-seekers.

Oral operant ethanol self-administration in the absence of explicit cues, food restriction, water restriction and ethanol fading in C57BL/6J mice

RATIONALE

Mouse models of ethanol (EtOH) self-administration are useful to identify genetic and biological underpinnings of alcohol use disorder.

OBJECTIVES

These experiments developed a novel method of oral operant EtOH self-administration in mice without explicitly paired cues, food/water restriction, or EtOH fading.

METHODS

Following magazine and lever training for 0.2 % saccharin (SAC), mice underwent nine weekly overnight sessions with lever pressing maintained by dipper presentation of 0, 3, 10, or 15 % EtOH in SAC or water vehicle. Ad libitum water was available from a bottle.

RESULTS

Water vehicle mice ingested most fluid from the water bottle in contrast to SAC vehicle mice, which despite lever pressing demands, drank most of their fluid from the liquid dipper. Although EtOH in SAC vehicle mice showed concentration-dependent increases of g/kg EtOH intake, lever pressing decreased with increasing EtOH concentration and did not exceed that of SAC vehicle alone at any EtOH concentration. Mice reinforced with EtOH in water ingested less EtOH than mice reinforced with EtOH in SAC. EtOH in water mice, however, showed concentration-dependent increases in g/kg EtOH intake and lever presses. Fifteen percent EtOH in water mice showed significantly greater levels of lever pressing than water vehicle mice and a significant escalation of responding across weeks of exposure. Naltrexone pretreatment reduced EtOH self-administration and intake in these mice without altering responding in the vehicle control condition during the first hour of the session.

CONCLUSIONS

SAC facilitated EtOH intake but prevented observation of EtOH reinforcement. Water vehicle unmasked EtOH's reinforcing effects.

The temporal "pulse" of drinking: Tracking 5 years of binge drinking in emerging adults

Binge drinking is associated with clinically significant individual-level and public health consequences. The topography of binge drinking may influence the emergence of consequences, but studies of topography require a higher level of temporal resolution than is typically available in epidemiological research. To address topography across the 5 "peak" years of binge drinking (18 to 23 years), we assessed daily binge drinking via successive 90-day timeline follow-back interviews of 645 young adults (resulting in almost 700,000 data points). Results showed a weekend "pulse" of binge drinking that remained consistent across the entire 5 year span, with occasional holiday-based perturbations. Two-part latent growth curve modeling applied to this dataset showed that the often-observed decrease in drinking associated with "maturing out" was due more to decreased participation in binge drinking occasions, rather than to amounts consumed when drinking (intensity). Similarly, the number of binge drinkers varied by day of the week, but the intensity of binge drinking, for those drinking, varied little by day of the week. This approach also showed distinctive predictors for participation and intensity; baseline expectancies and sociability accounted for individual differences in participation, whereas impulsivity-sensation seeking predicted intensity. Individual patterns of binge drinking participation and intensity also predicted drinking consequences over the 5 years of the study. Given these results, binge drinking patterns may serve as a useful phenotype for future research on pathological drinking.

Dopamine modulates risk-taking as a function of baseline sensation-seeking trait

Trait sensation-seeking, defined as a need for varied, complex, and intense sensations, represents a relatively underexplored hedonic drive in human behavioral neuroscience research. It is related to increased risk for a range of behaviors including substance use, gambling, and risky sexual practice. Individual differences in self-reported sensation-seeking have been linked to brain dopamine function, particularly at D2-like receptors, but so far no causal evidence exists for a role of dopamine in sensation-seeking behavior in humans. Here, we investigated the effects of the selective D2/D3 agonist cabergoline on performance of a probabilistic risky choice task in healthy humans using a sensitive within-subject, placebo-controlled design. Cabergoline significantly influenced the way participants combined different explicit signals regarding probability and loss when choosing between response options associated with uncertain outcomes. Importantly, these effects were strongly dependent on baseline sensation-seeking score. Overall, cabergoline increased sensitivity of choice to information about probability of winning; while decreasing discrimination according to magnitude of potential losses associated with different options. The largest effects of the drug were observed in participants with lower sensation-seeking scores. These findings provide evidence that risk-taking behavior in humans can be directly manipulated by a dopaminergic drug, but that the effectiveness of such a manipulation depends on baseline differences in sensation-seeking trait. This emphasizes the importance of considering individual differences when investigating manipulation of risky decision-making, and may have relevance for the development of pharmacotherapies for disorders involving excessive risk-taking in humans, such as pathological gambling.

Marijuana: current concepts(†)

Marijuana (cannabis) remains a controversial drug in the twenty-first century. This paper considers current research on use of Cannabis sativa and its constituents such as the cannabinoids. Topics reviewed include prevalence of cannabis (pot) use, other drugs consumed with pot, the endocannabinoid system, use of medicinal marijuana, medical adverse effects of cannabis, and psychiatric adverse effects of cannabis use. Treatment of cannabis withdrawal and dependence is difficult and remains mainly based on psychological therapy; current research on pharmacologic management of problems related to cannabis consumption is also considered. The potential role of specific cannabinoids for medical benefit will be revealed as the twenty-first century matures. However, potential dangerous adverse effects from smoking marijuana are well known and should be clearly taught to a public that is often confused by a media-driven, though false message and promise of benign pot consumption.

The Brisbane Longitudinal Twin Study: Pathways to Cannabis Use, Abuse, and Dependence project-current status, preliminary results, and future directions

We describe the data being collected from the Brisbane Longitudinal Twin Study in Australia as part of the US National Institute on Drug Abuse (NIDA)-funded project, Pathways to Cannabis Use, Abuse and Dependence. The history, recruitment, assessment, and retention of twin families in this project are described in detail, along with preliminary findings and plans for future research. The goal of this NIDA project is to make a significant contribution to the discovery of quantitative trait loci influencing cannabis use disorders. Although the focus is cannabis use, abuse, and dependence in young adults, measures of comorbid illicit drug use disorders are also being collected. In addition, a variety of internalizing and externalizing disorders are being assessed, funded by support from the Australian National Health and Medical Research Council. Because these same twins have participated in numerous twin studies since 1992, future plans will include linking different phenotypes to investigate relationships between drug use, psychiatric disorders, and psychological phenotypes within cross-sectional and longitudinal or developmental frameworks.

The detrimental effects of emotional process dysregulation on decision-making in substance dependence

Substance dependence is complex and multifactorial, with many distinct pathways involved in both the development and subsequent maintenance of addictive behaviors. Various cognitive mechanisms have been implicated, including impulsivity, compulsivity, and impaired decision-making. These mechanisms are modulated by emotional processes, resulting in increased likelihood of initial drug use, sustained substance dependence, and increased relapse during periods of abstinence. Emotional traits, such as sensation-seeking, are risk factors for substance use, and chronic drug use can result in further emotional dysregulation via effects on reward, motivation, and stress systems. We will explore theories of hyper and hypo sensitivity of the brain reward systems that may underpin motivational abnormalities and anhedonia. Disturbances in these systems contribute to the biasing of emotional processing toward cues related to drug use at the expense of natural rewards, which serves to maintain addictive behavior, via enhanced drug craving. We will additionally focus on the sensitization of the brain stress systems that result in negative affect states that continue into protracted abstinence that is may lead to compulsive drug-taking. We will explore how these emotional dysregulations impact upon decision-making controlled by goal-directed and habitual action selections systems, and, in combination with a failure of prefrontal inhibitory control, mediate maladaptive decision-making observed in substance dependent individuals such that they continue drug use in spite of negative consequences. An understanding of the emotional impacts on cognition in substance dependent individuals may guide the development of more effective therapeutic interventions.

The CHRNA5/A3/B4 gene cluster and tobacco, alcohol, cannabis, inhalants and other substance use initiation: replication and new findings using mixture analyses

Multiple studies have provided evidence for genetic associations between single nucleotide polymorphisms (SNPs) located on the CHRNA5/A3/B4 gene cluster and various phenotypes related to Nicotine Dependence (Greenbaum et al. 2009). Only a few studies have investigated other substances of abuse. The current study has two aims, (1) to extend previous findings by focusing on associations between the CHRNA5/A3/B4 gene cluster and age of initiation of several different substances, and (2) to investigate heterogeneity in age of initiation across the different substances. All analyses were conducted with a subset of the Add Health study with available genetic data. The first aim was met by modeling onset of tobacco, alcohol, cannabis, inhalants, and other substance use using survival mixture analysis (SMA). Ten SNPs in CHRNA5/A3/B4 were used to predict phenotypic differences in the risk of onset, and differences between users and non-users. The survival models aim at investigating differences in the risk of initiation across the 5-18 age range for each phenotype separately. Significant or marginally significant genetic effects were found for all phenotypes. The genetic effects were mainly related to the risk of initiation and to a lesser extent to discriminating between users and non-users. To address the second goal, the survival analyses were complemented by a latent class analysis that modeled all phenotypes jointly. One of the ten SNPs was found to predict differences between the early and late onset classes. Taken together, our study provides evidence for a general role of the CHRNA5/A3/B4 gene cluster in substance use initiation that is not limited to nicotine and alcohol.