Common single nucleotide variants underlying drug addiction: more than a decade of research

A multi-ancestry cerebral cortex transcriptome-wide association study identifies genes associated with smoking behaviors

Transcriptome-wide association studies (TWAS) have provided valuable insight in identifying genes that may impact cigarette smoking. Most of previous studies, however, mainly focused on European ancestry. Limited TWAS studies have been conducted across multiple ancestries to explore genes that may impact smoking behaviors. In this study, we used cis-eQTL data of cerebral cortex from multiple ancestries in MetaBrain, including European, East Asian, and African samples, as reference panels to perform multi-ancestry TWAS analyses on ancestry-matched GWASs of four smoking behaviors including smoking initiation, smoking cessation, age of smoking initiation, and number of cigarettes per day in GWAS & Sequencing Consortium of Alcohol and Nicotine use (GSCAN). Multiple-ancestry fine-mapping approach was conducted to identify credible gene sets associated with these four traits. Enrichment and module network analyses were further performed to explore the potential roles of these identified gene sets. A total of 719 unique genes were identified to be associated with at least one of the four smoking traits across ancestries. Among those, 249 genes were further prioritized as putative causal genes in multiple ancestry-based fine-mapping approach. Several well-known smoking-related genes, including PSMA4, IREB2, and CHRNA3, showed high confidence across ancestries. Some novel genes, e.g., TSPAN3 and ANK2, were also identified in the credible sets. The enrichment analysis identified a series of critical pathways related to smoking such as synaptic transmission and glutamate receptor activity. Leveraging the power of the latest multi-ancestry GWAS and eQTL data sources, this study revealed hundreds of genes and relevant biological processes related to smoking behaviors. These findings provide new insights for future functional studies on smoking behaviors.

Association of TOP2A and ADH1B with lipid levels and prognosis in patients with lung adenocarcinoma and squamous cell carcinoma

BACKGROUND

Although lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) have different pathological and clinical features, they may share common driver genes. It was found that lipid levels can be used for early diagnosis of NSCLC; however, the relationship between driver genes and genes regulating lipid metabolism and their relationship with patient prognosis needs further investigation.

METHODS

Genes whose expression was up- or down-regulated in both LUAD and LUSC were identified using the GEO database. Online tools like GEPIA 2, PrognoScan, UALCAN, and TIMER2.0 were used to investigate the association of these gene expressions with the patient's prognosis and lipid regulatory genes. The association between clinical lipid levels and the risk of LUAD and LUSC was analyzed by using a multiple logistic regression model.

RESULTS

Topoisomerase II alpha (TOP2A) and alcohol dehydrogenase 1B (ADH1B) were identified as the only genes up- and down-regulated in both LUAD and LUSC. TOP2A and ADH1B expression levels significantly correlated with the patient's gender, age, individual cancer stage, histological subtype, nodal metastasis status, and TP53 mutation status. Additionally, only LUAD patients with higher TOP2A or lower ADH1B expressions displayed poor overall and relapse-free survival rates. Moreover, TOP2A levels exhibited a negative correlation with adipose triglyceride lipase (ATGL) and ATP-binding cassette transporter A1 (ABCA1) in both LUAD and LUSC. However, ADH1B showed inverse associations with the above-mentioned genes when compared to TOP2A expressions in both LUAD and LUSC. Furthermore, elevated triglyceride (OR = 1.59; 95% CI = 1.01 to 2.49; P < 0.05) and total cholesterol (OR = 2.45; 95% CI = 1.08 to 5.57; P < 0.05) levels might increase the risk of LUAD.

CONCLUSIONS

TOP2A and ADH1B can be used as diagnostic markers for LUAD and LUSC, but only as independent prognostic factors for LUAD, and may be involved in lipid metabolism in LUAD patients but not in LUSC. Thus, combining genetic diagnostics with lipid panel tests might be an effective method for an early diagnosis and improved prognosis of LUAD.

Signatures of Convergent Evolution and Natural Selection at the Alcohol Dehydrogenase Gene Region are Correlated with Agriculture in Ethnically Diverse Africans

The alcohol dehydrogenase (ADH) family of genes encodes enzymes that catalyze the metabolism of ethanol into acetaldehyde. Nucleotide variation in ADH genes can affect the catalytic properties of these enzymes and is associated with a variety of traits, including alcoholism and cancer. Some ADH variants, including the ADH1B*48His (rs1229984) mutation in the ADH1B gene, reduce the risk of alcoholism and are under positive selection in multiple human populations. The advent of Neolithic agriculture and associated increase in fermented foods and beverages is hypothesized to have been a selective force acting on such variants. However, this hypothesis has not been tested in populations outside of Asia. Here, we use genome-wide selection scans to show that the ADH gene region is enriched for variants showing strong signals of positive selection in multiple Afroasiatic-speaking, agriculturalist populations from Ethiopia, and that this signal is unique among sub-Saharan Africans. We also observe strong selection signals at putatively functional variants in nearby lipid metabolism genes, which may influence evolutionary dynamics at the ADH region. Finally, we show that haplotypes carrying these selected variants were introduced into Northeast Africa from a West-Eurasian source within the last ∼2,000 years and experienced positive selection following admixture. These selection signals are not evident in nearby, genetically similar populations that practice hunting/gathering or pastoralist subsistence lifestyles, supporting the hypothesis that the emergence of agriculture shapes patterns of selection at ADH genes. Together, these results enhance our understanding of how adaptations to diverse environments and diets have influenced the African genomic landscape.

FOXN3 and GDNF Polymorphisms as Common Genetic Factors of Substance Use and Addictive Behaviors

Epidemiological and phenomenological studies suggest shared underpinnings between multiple addictive behaviors. The present genetic association study was conducted as part of the Psychological and Genetic Factors of Addictions study (n = 3003) and aimed to investigate genetic overlaps between different substance use, addictive, and other compulsive behaviors. Association analyses targeted 32 single-nucleotide polymorphisms, potentially addictive substances (alcohol, tobacco, cannabis, and other drugs), and potentially addictive or compulsive behaviors (internet use, gaming, social networking site use, gambling, exercise, hair-pulling, and eating). Analyses revealed 29 nominally significant associations, from which, nine survived an FDRbl correction. Four associations were observed between FOXN3 rs759364 and potentially addictive behaviors: rs759364 showed an association with the frequency of alcohol consumption and mean scores of scales assessing internet addiction, gaming disorder, and exercise addiction. Significant associations were found between GDNF rs1549250, rs2973033, CNR1 rs806380, DRD2/ANKK1 rs1800497 variants, and the “lifetime other drugs” variable. These suggested that genetic factors may contribute similarly to specific substance use and addictive behaviors. Specifically, FOXN3 rs759364 and GDNF rs1549250 and rs2973033 may constitute genetic risk factors for multiple addictive behaviors. Due to limitations (e.g., convenience sampling, lack of structured scales for substance use), further studies are needed. Functional correlates and mechanisms underlying these relationships should also be investigated.

Behavioral consequences of the downstream products of ethanol metabolism involved in alcohol use disorder

Research concerning Alcohol Use Disorder (AUD) has previously focused primarily on either the behavioral or chemical consequences experienced following ethanol intake, but these areas of research have rarely been considered in tandem. Compared with other drugs of abuse, ethanol has been shown to have a unique metabolic pathway once it enters the body, which leads to the formation of downstream metabolites which can go on to form biologically active products. These metabolites can mediate a variety of behavioral responses that are commonly observed with AUD, such as ethanol intake, reinforcement, and vulnerability to relapse. The following review considers the preclinical and chemical research implicating these downstream products in AUD and proposes a chemobehavioral model of AUD.

Epigenetic Mechanisms Mediate Nicotine-Induced Reward and Behaviour in Zebrafish

Nicotine induces long-term changes in the neural activity of the mesocorticolimbic reward pathway structures. The mechanisms involved in this process have not been fully characterized. The hypothesis discussed here proposed that epigenetic regulation participates in the installation of persistent adaptations and long-lasting synaptic plasticity generated by nicotine action on the mesolimbic dopamine neurons of zebrafish. The epigenetic mechanisms induced by nicotine entail histone and DNA chemical modifications, which have been described to lead to changes in gene expression. Among the enzymes that catalyze epigenetic chemical modifications, histone deacetylases (HDACs) remove acetyl groups from histones, thereby facilitating DNA relaxation and making DNA more accessible to gene transcription. DNA methylation, which is dependent on DNA methyltransferase (DNMTs) activity, inhibits gene expression by recruiting several methyl binding proteins that prevent RNA polymerase binding to DNA. In zebrafish, phenylbutyrate (PhB), an HDAC inhibitor, abolishes nicotine rewarding properties together with a series of typical reward-associated behaviors. Furthermore, PhB and nicotine alter long- and short-term object recognition memory in zebrafish, respectively. Regarding DNA methylation effects, a methyl group donor L-methionine (L-met) was found to dramatically reduce nicotine-induced conditioned place preference (CPP) in zebrafish. Simultaneous treatment with DNMT inhibitor 5-aza-2’-deoxycytidine (AZA) was found to reverse the L-met effect on nicotine-induced CPP as well as nicotine reward-specific effects on genetic expression in zebrafish. Therefore, pharmacological interventions that modulate epigenetic regulation of gene expression should be considered as a potential therapeutic method to treat nicotine addiction.

Transition to substance use disorders: impulsivity for reward and learning from reward

Substance dependence constitutes a profound societal burden. Although large numbers of individuals use licit or illicit substances, few transition to dependence. The specific factors influencing this transition are not well understood. Substance-dependent individuals tend to be swayed by the immediate rewards of drug taking, but are often insensitive to delayed negative consequences of their behavior. Dependence is consequently associated with impulsivity for reward and atypical learning from feedback. Behavioral impulsivity is indexed using tasks measuring spontaneous decision-making and capacity to control impulses. While evidence indicates drug taking exacerbates behavioral impulsivity for reward, animal and human studies of drug naïve populations demonstrate it might precede any drug-related problems. Research suggests dependent individuals are also more likely to learn from rewarding (relative to punishing) feedback. This may partly explain why substance-dependent individuals fail to modify their behavior in response to negative outcomes. This enhanced learning from reward may constitute a further pre-existing risk factor for substance dependence. Although impulsivity for reward and preferential learning from rewarding feedback are both underpinned by a compromised dopaminergic system, few studies have examined the relationship between these two mechanisms. The interplay of these processes may help enrich understanding of why some individuals transition to substance dependence.

Marijuana use/nonuse among those aged 50+: comparisons of use-to-nonuse, initiation/reinitiation, and continued use over 24 months

OBJECTIVES

To examine: (1) correlates of use-to-nonuse (use 13-24 months ago, but no past-year use), initiation/reinitiation (no use 13-24 months ago, but past-year use), and continued use over a 24-month period; and (2) associations of past-year marijuana use disorder with use/nonuse among older adults.

METHOD

The 2015-2017 National Survey on Drug Use and Health provided data (N = 26,322 aged 50+). We used multinomial and binary logistic regression analyses to compare users-to-nonusers and initiators/reinitiators to continued users (N = 2304).

RESULTS

In the 50-64 age group, 2.1% were users-to-nonusers, 2.2% initiators/reinitiators, and 7.2% continued users. In the 65+ age group, the corresponding percentages were 0.7%, 0.7%, and 2.4%. Residence in states with medical marijuana laws, nicotine dependence, and other illicit drug use were associated with a lower likelihood of use-to-nonuse than continued use. Alcohol use disorder was associated with a higher likelihood of initiation/reinitiation. Parole/probation status was associated with higher likelihood of use-to-nonuse. Moderate/great marijuana risk perceptions were associated with a higher likelihood of both use-to-nonuse and initiation/reinitiation. The odds of marijuana use disorder did not differ between continued users and initiators/reinitiators or between medical and recreational users.

CONCLUSION

Most older users continued using over 24 months. Substantial numbers had marijuana and other substance use problems that require treatment.

Endocannabinoid Gene × Gene Interaction Association to Alcohol Use Disorder in Two Adolescent Cohorts

Genetic markers of the endocannabinoid system have been linked to a variety of addiction-related behaviors that extend beyond cannabis use. In the current study we investigate the relationship between endocannabinoid (eCB) genetic markers and alcohol use disorder (AUD) in European adolescents (14-18 years old) followed in the IMAGEN study (n = 2,051) and explore replication in a cohort of North American adolescents from Canadian Saguenay Youth Study (SYS) (n = 772). Case-control status is represented by a score of more than 7 on the Alcohol Use Disorder Identification Test (AUDIT). First a set-based test method was used to examine if a relationship between the eCB system and AUDIT case/control status exists at the gene level. Using only SNPs that are both independent and significantly associated to case-control status, we perform Fisher's exact test to determine SNP level odds ratios in relation to case-control status and then perform logistic regressions as post-hoc analysis, while considering various covariates. Generalized multifactor dimensionality reduction (GMDR) was used to analyze the most robust SNP×SNP interaction of the five eCB genes with positive AUDIT screen. While no gene-sets were significantly associated to AUDIT scores after correction for multiple tests, in the case/control analysis, 7 SNPs were significantly associated with AUDIT scores of > 7 (p < 0.05; OR<1). Two SNPs remain significant after correction by false discovery rate (FDR): rs9343525 in CNR1 (pcorrected =0.042, OR = 0.73) and rs507961 in MGLL (pcorrected = 0.043, OR = 0.78). Logistic regression showed that both rs9353525 (CNR1) and rs507961 (MGLL) remained significantly associated with positive AUDIT screens (p < 0.01; OR < 1) after correction for multiple covariables and interaction of covariable × SNP. This result was not replicated in the SYS cohort. The GMDR model revealed a significant three-SNP interaction (p = 0.006) involving rs484061 (MGLL), rs4963307 (DAGLA), and rs7766029 (CNR1) predicted case-control status, after correcting for multiple covariables in the IMAGEN sample. A binomial logistic regression of the combination of these three SNPs by phenotype in the SYS cohort showed a result in the same direction as seen in the IMAGEN cohort (BETA = 0.501, p = 0.06). While preliminary, the present study suggests that the eCB system may play a role in the development of AUD in adolescents.

AddictGene: An integrated knowledge base for differentially expressed genes associated with addictive substance

Addiction, a disorder of maladaptive brain plasticity, is associated with changes in numerous gene expressions. Nowadays, high-throughput sequencing data on addictive substance-induced gene expression have become widely available. A resource for comprehensive annotation of genes that show differential expression in response to commonly abused substances is necessary. So, we developed AddictGene by integrating gene expression, gene-gene interaction, gene-drug interaction and epigenetic regulatory annotation for over 70,156 items of differentially expressed genes associated with 7 commonly abused substances, including alcohol, nicotine, cocaine, morphine, heroin, methamphetamine, and amphetamine, across three species (human, mouse, rat). We also collected 1,141 addiction-related experimentally validated genes by techniques such as RT-PCR, northern blot and in situ hybridization. The easy-to-use web interface of AddictGene (http://159.226.67.237/sun/addictgedb/) allows users to search and browse multidimensional data on DEGs of their interest: 1) detailed gene-specific information extracted from the original studies; 2) basic information about the specific gene extracted from NCBI; 3) SNP associated with substance dependence and other psychiatry disorders; 4) expression alteration of specific gene in other psychiatric disorders; 5) expression patterns of interested gene across 31 primary and 54 secondary human tissues; 6) functional annotation of interested gene; 7) epigenetic regulators involved in the alteration of specific genes, including histone modifications and DNA methylation; 8) protein-protein interaction for functional linkage with interested gene; 9) drug-gene interaction for potential druggability. AddictGene offers a valuable repository for researchers to study the molecular mechanisms underlying addiction, and might provide valuable insights into potential therapies for drug abuse and relapse.

Identification of novel risk loci with shared effects on alcoholism, heroin, and methamphetamine dependence

Different substance dependences have common effects on reward pathway and molecular adaptations, however little is known regarding their shared genetic factors. We aimed to identify the risk genetic variants that are shared for substance dependence (SD). First, promising genome-wide significant loci were identified from 3296 patients (521 alcoholic/1026 heroin/1749 methamphetamine) vs 2859 healthy controls and independently replicated using 1954 patients vs 1904 controls. Second, the functional effects of promising variants on gene expression, addiction characteristics, brain structure (gray and white matter), and addiction behaviors in addiction animal models (chronic administration and self-administration) were assessed. In addition, we assessed the genetic correlation among the three SDs using LD score regression. We identified and replicated three novel loci that were associated with the common risk of heroin, methamphetamine addiction, and alcoholism: ANKS1B rs2133896 (P_meta = 3.60 × 10^-9), AGBL4 rs147247472 (P_meta = 3.40 × 10^-12), and CTNNA2 rs10196867 (P_meta = 4.73 × 10^-9). Rs2133896 in ANKS1B was associated with ANKS1B gene expression and had effects on gray matter of the left calcarine and white matter of the right superior longitudinal fasciculus in heroin dependence. Overexpression of anks1b gene in the ventral tegmental area decreased addiction vulnerability for heroin and methamphetamine in self-administration rat models. Our findings could shed light on the root cause for substance dependence and will be helpful for the development of cost-effective prevention strategies for general addiction disorders.

Exploring allele specific methylation in drug dependence susceptibility

Drug dependence is a neuropsychiatric condition that involves genetic, epigenetic and environmental factors. Allele-specific methylation (ASM) is a common and stable epigenetic mechanism that involves genetic variants correlating with differential levels of methylation at CpG sites. We selected 182 single-nucleotide polymorphisms (SNPs) described to influence cis ASM in human brain regions to evaluate their possible contribution to drug dependence susceptibility. We performed a case-control association study in a discovery sample of 578 drug-dependent patients (including 428 cocaine-dependent subjects) and 656 controls from Spain, and then, we followed-up the significant associations in an independent sample of 1119 cases (including 589 cocaine-dependent subjects) and 1092 controls. In the discovery sample, we identified five nominal associations, one of them replicated in the follow-up sample (rs6020251). The pooled analysis revealed an association between drug dependence and rs6020251 but also rs11585570, both overcoming the Bonferroni correction for multiple testing. We performed the same analysis considering only cocaine-dependent patients and obtained similar results. The rs6020251 variant correlates with differential methylation levels of cg17974185 and lies in the first intron of the CTNNBL1 gene, in a genomic region with multiple histone marks related to enhancer and promoter regions in brain. Rs11585570 is an eQTL in brain and blood for the SCP2 and ECHDC2 genes and correlates with differential methylation of cg27535305 and cg13461509, located in the promoter regions of both genes. To conclude, using an approach that combines genetic and epigenetic data, we highlighted the CTNNBL1, SCP2 and ECHDC2 genes as potential contributors to drug dependence susceptibility.

Enhancing Research Through the Use of the Genotype-Tissue Expression (GTEx) Database

Despite a growing interest in multi-omic research, individual investigators may struggle to collect large-scale omic data, particularly from human subjects. Publicly available datasets can help to address this problem, including those sponsored by the NIH Common Fund, such as the Genotype-Tissue Expression (GTEx) database. This database contains genotype and expression data obtained from 54 non-diseased tissues in human subjects. But these data are often underutilized, because users may find the browsing tools to be counterintuitive or have difficulty navigating the procedures to request controlled data access. Furthermore, there is limited knowledge of these resources among nurse scientists interested in incorporating such information into their programs of research. This article outlines the procedures for using the GTEx database. Next, we provide one exemplar of using this resource to enhance existing research by investigating expression of dopamine receptor type 2 (DRD2) across brain tissues in human subjects.

Expression of Dopamine-Related Genes in Four Human Brain Regions

A better understanding of dopaminergic gene expression will inform future treatment options for many different neurologic and psychiatric conditions. Here, we utilized the National Institutes of Health’s Genotype-Tissue Expression project (GTEx) dataset to investigate genotype by expression associations in seven dopamine pathway genes (ANKK1, DBH, DRD1, DRD2, DRD3, DRD5, and SLC6A3) in and across four human brain tissues (prefrontal cortex, nucleus accumbens, substantia nigra, and hippocampus). We found that age alters expression of DRD1 in the nucleus accumbens and prefrontal cortex, DRD3 in the nucleus accumbens, and DRD5 in the hippocampus and prefrontal cortex. Sex was associated with expression of DRD5 in substantia nigra and hippocampus, and SLC6A3 in substantia nigra. We found that three linkage disequilibrium blocks of SNPs, all located in DRD2, were associated with alterations in expression across all four tissues. These demographic characteristic associations and these variants should be further investigated for use in screening, diagnosis, and future treatment of neurological and psychiatric conditions.

Nicotinic acetylcholine receptors and nicotine addiction: A brief introduction

Nicotine is a highly addictive drug found in tobacco that drives its continued use despite the harmful consequences. The initiation of nicotine abuse involves the mesolimbic dopamine system, which contributes to the rewarding sensory stimuli and associative learning processes in the beginning stages of addiction. Nicotine binds to neuronal nicotinic acetylcholine receptors (nAChRs), which come in a diverse collection of subtypes. The nAChRs that contain the α4 and β2 subunits, often in combination with the α6 subunit, are particularly important for nicotine's ability to increase midbrain dopamine neuron firing rates and phasic burst firing. Chronic nicotine exposure results in numerous neuroadaptations, including the upregulation of particular nAChR subtypes associated with long-term desensitization of the receptors. When nicotine is no longer present, for example during attempts to quit smoking, a withdrawal syndrome develops. The expression of physical withdrawal symptoms depends mainly on the α2, α3, α5, and β4 nicotinic subunits in the epithalamic habenular complex and its target regions. Thus, nicotine affects diverse neural systems and an array of nAChR subtypes to mediate the overall addiction process. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.

Opioid use disorder research and the Council for the Advancement of Nursing Science priority areas

BACKGROUND

Chronic diseases, such as opioid use disorder (OUD) require a multifaceted scientific approach to address their evolving complexity. The Council for the Advancement of Nursing Science's (Council) four nursing science priority areas (precision health; global health, determinants of health, and big data/data analytics) were established to provide a framework to address current complex health problems.

PURPOSE

To examine OUD research through the nursing science priority areas and evaluate the appropriateness of the priority areas as a framework for research on complex health conditions.

METHOD

OUD was used as an exemplar to explore the relevance of the nursing science priorities for future research.

FINDINGS

Research in the four priority areas is advancing knowledge in OUD identification, prevention, and treatment. Intersection of OUD research population focus and methodological approach was identified among the priority areas.

DISCUSSION

The Council priorities provide a relevant framework for nurse scientists to address complex health problems like OUD.

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.

Association of CHRNA5 Gene Variants with Crack Cocaine Addiction

Genome-wide studies provide increasing evidence of association of genetic variants with different behaviors. However, there is a growing need for replication and subsequent characterization of specific findings. In this sense, the CHRNA5 gene has been associated with nicotine (with genome-wide significance), alcohol and cocaine addictions. So far, this gene has not been evaluated in smoked (crack) cocaine. We aimed to analyze the influence of CHRNA5 variants in crack addiction susceptibility and severity. The sample includes 300 crack-addicted patients and 769 non-addicted individuals. The CHRNA5 SNPs evaluated were rs588765, rs16969968, and rs514743. Homozygosity for rs16969968 and rs588765 major alleles was nominally associated with a risk to crack addiction (GG, P = 0.032; CC, P = 0.036, respectively). Haplotype analyses reveal significant associations (rs588765|rs16969968|rs514743 p_{global-corrected} = 7.66 × 10^-5) and suggest a substantial role for rs16969968. These findings corroborate previous reports in cocaine addiction-in line with the expected effects of cocaine in the cholinergic system-and in the opposite direction of significant GWAS findings for nicotine addiction susceptibility. These results are strengthened by the first report of an association of rs588765 with crack addiction and by the haplotype findings. In summary, our study highlights the relevance of the α5 subunit on crack cocaine addiction, replicating previous results relating CHRNA5 with the genetics and pathophysiology of addiction of different drugs.

The epigenetic legacy of illicit drugs: developmental exposures and late-life phenotypes

The effects of in utero exposure to illicit drugs on adult offspring are a significant and widespread but understudied global health concern, particularly in light of the growing opioid epidemic and emerging therapeutic uses for cannabis, ketamine, and MDMA. Epigenetic mechanisms including DNA methylation, histone modifications, and expression of non-coding RNAs provide a mechanistic link between the prenatal environment and health consequences years beyond the original exposure, and shifts in the epigenome present in early life or adolescence can lead to disease states only appearing during adulthood. The current review summarizes the literature assessing effects of perinatal illicit drug exposure on adult disease phenotypes as mediated by perturbations of the epigenome. Both behavioral and somatic phenotypes are included and studies reporting clinical data in adult offspring, epigenetic readouts in offspring of any age, or both phenotypic and epigenetic measures are prioritized. Studies of licit substances of abuse (i.e. alcohol, nicotine) are excluded with a focus on cannabis, psychostimulants, opioids, and psychedelics; current issues in the field and areas of interest for further investigation are also discussed.

Genome-wide association meta-analysis of cocaine dependence: Shared genetics with comorbid conditions

Cocaine dependence is a complex psychiatric disorder that is highly comorbid with other psychiatric traits. Twin and adoption studies suggest that genetic variants contribute substantially to cocaine dependence susceptibility, which has an estimated heritability of 65-79%. Here we performed a meta-analysis of genome-wide association studies of cocaine dependence using four datasets from the dbGaP repository (2085 cases and 4293 controls, all of them selected by their European ancestry). Although no genome-wide significant hits were found in the SNP-based analysis, the gene-based analysis identified HIST1H2BD as associated with cocaine-dependence (10% FDR). This gene is located in a region on chromosome 6 enriched in histone-related genes, previously associated with schizophrenia (SCZ). Furthermore, we performed LD Score regression analysis with comorbid conditions and found significant genetic correlations between cocaine dependence and SCZ, ADHD, major depressive disorder (MDD) and risk taking. We also found, through polygenic risk score analysis, that all tested phenotypes are significantly associated with cocaine dependence status: SCZ (R² = 2.28%; P = 1.21e-26), ADHD (R² = 1.39%; P = 4.5e-17), risk taking (R² = 0.60%; P = 2.7e-08), MDD (R² = 1.21%; P = 4.35e-15), children's aggressive behavior (R² = 0.3%; P = 8.8e-05) and antisocial behavior (R² = 1.33%; P = 2.2e-16). To our knowledge, this is the largest reported cocaine dependence GWAS meta-analysis in European-ancestry individuals. We identified suggestive associations in regions that may be related to cocaine dependence and found evidence for shared genetic risk factors between cocaine dependence and several comorbid psychiatric traits. However, the sample size is limited and further studies are needed to confirm these results.

On the utilization of polygenic risk scores for therapeutic targeting

The promise of personalized genomic medicine is that knowledge of a person's gene sequences and activity will facilitate more appropriate medical interventions, particularly drug prescriptions, to reduce the burden of disease. Early successes in oncology and pediatrics have affirmed the power of positive diagnosis and are mostly based on detection of one or a few mutations that drive the specific pathology. However, genetically more complex diseases require the development of polygenic risk scores (PRSs) that have variable accuracy. The rarity of events often means that they have necessarily low precision: many called positives are actually not at risk, and only a fraction of cases are prevented by targeted therapy. In some situations, negative prediction may better define the population at low risk. Here, I review five conditions across a broad spectrum of chronic disease (opioid pain medication, hypertension, type 2 diabetes, major depression, and osteoporotic bone fracture), considering in each case how genetic prediction might be used to target drug prescription. This leads to a call for more research designed to evaluate genetic likelihood of response to therapy and a call for evaluation of PRS, not just in terms of sensitivity and specificity but also with respect to potential clinical efficacy.

Genome-wide association study of alcohol use disorder identification test (AUDIT) scores in 20 328 research participants of European ancestry

Genetic factors contribute to the risk for developing alcohol use disorder (AUD). In collaboration with the genetics company 23andMe, Inc., we performed a genome-wide association study of the alcohol use disorder identification test (AUDIT), an instrument designed to screen for alcohol misuse over the past year. Our final sample consisted of 20 328 research participants of European ancestry (55.3% females; mean age = 53.8, SD = 16.1) who reported ever using alcohol. Our results showed that the 'chip-heritability' of AUDIT score, when treated as a continuous phenotype, was 12%. No loci reached genome-wide significance. The gene ADH1C, which has been previously implicated in AUD, was among our most significant associations (4.4 × 10-7 ; rs141973904). We also detected a suggestive association on chromosome 1 (2.1 × 10-7 ; rs182344113) near the gene KCNJ9, which has been implicated in mouse models of high ethanol drinking. Using linkage disequilibrium score regression, we identified positive genetic correlations between AUDIT score, high alcohol consumption and cigarette smoking. We also observed an unexpected positive genetic correlation between AUDIT and educational attainment and additional unexpected negative correlations with body mass index/obesity and attention-deficit/hyperactivity disorder. We conclude that conducting a genetic study using responses to an online questionnaire in a population not ascertained for AUD may represent a cost-effective strategy for elucidating aspects of the etiology of AUD.

Genetic and Environmental Risk Factors for Cannabis Use: Preliminary Results for the Role of Parental Care Perception

BACKGROUND

Vulnerability to cannabis use (CU) initiation and problematic use have been shown to be affected by both genetic and environmental factors, with still inconclusive and uncertain evidence.

OBJECTIVE

Aim of the present study was to investigate the possible interplay between gene polymorphisms and psychosocial conditions in CU susceptibility.

METHODS

Ninety-two cannabis users and ninety-three controls have been included in the study. Exclusion criteria were serious mental health disorders and severe somatic disorders, use of other drugs and alcohol abuse; control subjects were not screened to remove Reward Deficiency Syndrome (RDS) behaviors. A candidate gene association study was performed, including variants related to dopaminergic and endocannabinoids pathways. Adverse childhood experiences and quality of parental care have been retrospectively explored utilizing ACES (Adverse Children Experience Scale), CECA-q (Child Experience of Care and Abuse Questionnaire), PBI (Parental Bonding Instrument).

RESULTS

Our findings evidenced a significant association between rs1800497 Taq1A of ANKK1 gene and CU. Parental care was found to be protective factor, with emotional and physical neglect specifically influencing CU. Gender also played a role in CU, with males smoking more than females. However, when tested together genotypes and psychosocial variables, the significance of observed genetic differences disappeared.

CONCLUSIONS

Our results confirm a significant role of Taq1A polymorphism in CU vulnerability. A primary role of environmental factors in mediating genetic risk has been highlighted: parental care could be considered the main target to design early prevention programs and strategies.

NOP Receptor Agonist Ro 64-6198 Decreases Escalation of Cocaine Self-Administration in Rats Genetically Selected for Alcohol Preference

Cocaine dependence is a psychiatric condition for which effective medications are still lacking. Published data indicate that an increase in nociceptin/orphanin FQ (N/OFQ) transmission by NOP receptor activation attenuates cocaine-induced place conditioning and the locomotor sensitization effects of cocaine. This suggests that the activation of the N/OFQ receptor (NOP) may attenuate the motivation for psychostimulants. To further explore this possibility, we investigated the effect of the potent and selective NOP receptor agonist Ro 64-6198 on cocaine intake under 1 h short access (ShA) and 6 h long access (LgA) operant self-administration conditions in rats. We used Marchigian Sardinian alcohol-preferring (msP) rats and Wistar control rats. msP rats were used because we recently found that this rat line, originally selected for excessive alcohol drinking and preference, exhibits a greater propensity to escalate cocaine self-administration following LgA training. msP rats are also characterized by innate overexpression of the N/OFQ-NOP system compared with Wistar rats. Wistar and msP rats both exhibited an increase in cocaine self-administration under LgA conditions, with a higher trend toward escalation in msP rats. In Wistar rats, the intraperitoneal administration of Ro 64-6198 (0. 1 and 3 mg/kg) significantly decreased ShA cocaine self-administration. In Wistar rats that underwent LgA cocaine self-administration training, Ro 64-6198 induced no significant effect either during the first hour of self-administration or after the entire 6 h session. In msP rats, Ro 64-6198 significantly reduced cocaine self-administration both under ShA conditions and in the first hour of the LgA session. At the end of the 6 h session, the effect of Ro 64-6198 was no longer observed in msP rats. The highest dose of Ro 64-6198 (3 mg/kg) did not affect saccharin self-administration in msP rats but reduced saccharin self-administration in Wistar rats. Altogether, these data suggest that NOP receptor activation attenuates cocaine self-administration, and this effect tends to be more pronounced in a rat line with innately higher NOP receptor expression and that more robustly escalates cocaine intake.

Genetics of addictive behavior: the example of nicotine dependence

The majority of addictive disorders have a significant heritability—roughly around 50%. Surprisingly, the most convincing association (a nicotinic acetylcholine receptor CHRNA5-A3-B4 gene cluster in nicotine dependence), with a unique attributable risk of 14%, was detected through a genome-wide association study (GWAS) on lung cancer, although lung cancer has a low heritability. We propose some explanations of this finding, potentially helping to understand how a GWAS strategy can be successful. Many endophenotypes were also assessed as potentially modulating the effect of nicotine, indirectly facilitating the development of nicotine dependence. Challenging the involved phenotype led to the demonstration that other potentially overlapping disorders, such as schizophrenia and Parkinson disease, could also be involved, and further modulated by parent monitoring or the existence of a smoking partner. Such a complex mechanism of action is compatible with a gene-environment interaction, most clearly explained by epigenetic factors, especially as such factors were shown to be, at least partly, genetically driven.

Selective breeding for high alcohol consumption and response to nicotine: locomotor activity, dopaminergic in the mesolimbic system, and innate genetic differences in male and female alcohol-preferring, non-preferring, and replicate lines of high-alcohol drinking and low-alcohol drinking rats

RATIONALE

There is evidence for a common genetic link between alcohol and nicotine dependence. Rodents selectively bred for high alcohol consumption/responsivity are also more likely to self-administer nicotine than controls.

OBJECTIVES

The experiments examined the response to systemic nicotine, the effects of nicotine within the drug reward pathway, and innate expression of nicotine-related genes in a brain region regulating drug reward/self-administration in multiple lines of rats selectively bred for high and low alcohol consumption.

METHODS

The experiments examined the effects of systemic administration of nicotine on locomotor activity, the effects of nicotine administered directly into the (posterior ventral tegmental area; pVTA) on dopamine (DA) release in the nucleus accumbens shell (AcbSh), and innate mRNA levels of acetylcholine receptor genes in the pVTA were determined in 6 selectively bred high/low alcohol consuming and Wistar rat lines.

RESULTS

The high alcohol-consuming rat lines had greater nicotine-induced locomotor activity compared to low alcohol-consuming rat lines. Microinjections of nicotine into the pVTA resulted in DA release in the AcbSh with the dose response curves for high alcohol-consuming rats shifted leftward and upward. Genetic analysis of the pVTA indicated P rats expressed higher levels of α2 and β4.

CONCLUSION

Selective breeding for high alcohol preference resulted in a genetically divergent behavioral and neurobiological sensitivity to nicotine. The observed behavioral and neurochemical differences between the rat lines would predict an increased likelihood of nicotine reinforcement. The data support the hypothesis of a common genetic basis for drug addiction and identifies potential receptor targets.

MiR-9, miR-153 and miR-124 are down-regulated by acute exposure to cocaine in a dopaminergic cell model and may contribute to cocaine dependence

Cocaine is one of the most used psychostimulant drugs worldwide. MicroRNAs are post-transcriptional regulators of gene expression that are highly expressed in brain, and several studies have shown that cocaine can alter their expression. In a previous study, we identified several protein-coding genes that are differentially expressed in a dopaminergic neuron-like model after an acute exposure to cocaine. Now, we used the prediction tool WebGestalt to identify miRNA molecules potentially involved in the regulation of these genes. Using the same cellular model, we found that seven of these miRNAs are down-regulated by cocaine: miR-124-3p, miR-124-5p, miR-137, miR-101-3p, miR-9-5p, miR-369-3p and miR-153-3p, the last three not previously related to cocaine. Furthermore, we found that three of the miRNA genes that are differentially expressed in our model (hsa-miR-9-1, hsa-miR-153-1 and hsa-miR-124-3) are nominally associated with cocaine dependence in a case-control study (2,085 cases and 4,293 controls). In summary, we highlighted novel miRNAs that may be involved in those cocaine-induced changes of gene expression that underlie addiction. Moreover, we identified genetic variants that contribute to cocaine dependence in three of these miRNA genes, supporting the idea that genes differentially expressed under cocaine may play an important role in the susceptibility to cocaine dependence.

[The interaction effect of ANKK1/DRD2 TaqIA and HTR2C Cys23Ser on approach motivation in schizophrenic patients and normals]

AIM

To evaluate the association of the DRD2 gene and DRD2 x HTR2C interaction with hedonic and activational aspects of approach motivation in schizophrenia.

MATERIAL AND METHODS

Genotypes at polymorphic loci DRD2 rs1800497 and HTR2C rs6318 (Cys23Ser) were identified in a sample that included 174 patients with schizophrenic spectrum disorders and 268 healthy subjects without a family history of psychoses. The participants completed the BIS/BAS and Temporal Experience of Pleasure Scale (TEPS).

RESULTS AND CONCLUSION

A MANCOVA with sex and age as covariates revealed the effect of the 'DRD2 x HTR2C x diagnosis' interaction on the BAS scores (p=0.033). The effect was significant for the Fun-Seeking and Drive scales. Among patients, the carriers of the DRD2 TT/CT x HTR2C GG/G genotype showed the highest scores on the both scales, and those with the minor alleles in the two loci had the lowest ones. Differences between these groups were nominally significant for both the Fun-Seeking and Drive, but did not survive the correction for multiple comparisons. Among controls, subjects without minor alleles demonstrated the highest scores on these two scales. They differed significantly from the carriers of the DRD2 TT/CT+HTR2C GG/G genotype on the Fun-Seeking (p=0.008). No effects of DRD2 and HTR2C on TEPS scores were found. In general, the results of the study can be interpreted in favor of the hypothesis about the role of the HTR2C and DRD2 genes interaction in the variability of the activational aspects of approach motivation in schizophrenia and healthy subjects. However, the lack of differences survived correction for multiple comparisons makes it difficult to interpret the revealed effects.

Knockout of alpha 5 nicotinic acetylcholine receptors subunit alters ethanol-mediated behavioral effects and reward in mice

Evidence suggests that there is an association between polymorphisms in the α5 nicotinic acetylcholine receptor (nAChR) subunit and risk of developing alcohol dependence in humans. The α5 nAChR subunit has also recently been shown to modulate some of the acute response to ethanol in mice. The aim of the current study was to further characterize the role of α5-containing (α5*) nAChRs in acute ethanol responsive behaviors, ethanol consumption and ethanol preference in mice. We conducted a battery of tests in male α5 knockout (KO) mice for a range of ethanol-induced behaviors including hypothermia, hypnosis, and anxiolysis. We also investigated the effects of α5* nAChR on ethanol reward using the Conditioned Place Preference (CPP) assay. Further, we tested the effects of gene deletion on drinking behaviors using the voluntary ethanol consumption in a two-bottle choice assay and Drinking in the Dark (DID, with or without stress) paradigm. We found that deletion of the α5 nAChR subunit enhanced ethanol-induced hypothermia, hypnosis, and an anxiolytic-like response in comparison to wild-type controls. The α5 KO mice showed reduced CPP for ethanol, suggesting that the rewarding properties of ethanol are decreased in mutant mice. Interestingly, Chrna5 gene deletion had no effect on basal ethanol drinking behavior, or ethanol metabolism, but did decrease ethanol intake in the DID paradigm following restraint stress. Taken together, we provide new evidence that α5 nAChRs are involved in some but not all of the behavioral effects of ethanol. Our results highlight the importance of nAChRs as a possible target for the treatment of alcohol dependence.

Evaluation of previous substance dependence genome-wide significant findings in a Spanish sample

BACKGROUND

Substance dependence is a chronic and relapsing disorder explained by genetic and environmental risk factors. The aim of our study is to replicate previous genome-wide significant (GWS) hits identified in substance dependence in general or in cocaine dependence in particular using an independent sample from Spain.

METHODS

We evaluated, in a Spanish sample of 1711 subjects with substance dependence (1011 of them cocaine dependent) and 1719 control individuals, three SNPs identified as GWS in previous studies: rs1868152 and rs2952621 (located near LINC02052 and LINC01854, respectively), associated with substance dependence, and rs2629540 (in the first intron of FAM53B), associated with cocaine dependence.

RESULTS

We replicated the association between rs2952621 and substance dependence under the dominant model (P = 0.020), with the risk allele (T) being the same in our sample and in those two reported previously. We then performed a meta-analysis of the two samples used in the original study that reported the association of rs2952621 with substance dependence (Collaborative Studies on Genetics of Alcoholism (COGA) and Study of Addiction: Genetics and Environment (SAGE)) together with our Spanish sample. The meta-analysis of 3747 cases and 4043 controls confirmed the association (OR = 1.26, 95% CI = 1.15-1.39).

CONCLUSIONS

The rs2952621 variant, located downstream from the yet uncharacterized gene LINC01854, is associated with substance dependence in our Spanish sample. Further research is needed to understand its contribution to the susceptibility to substance dependence.

Short-Term Genetic Selection for Adolescent Locomotor Sensitivity to Delta9-Tetrahydrocannabinol (THC)

Cannabis use is linked to positive and negative outcomes. Identifying genetic targets of susceptibility to the negative effects of cannabinoid use is of growing importance. The current study sought to complete short-term selective breeding for adolescent sensitivity and resistance to the locomotor effects of a single 10 mg/kg THC dose in the open field. Selection for THC-locomotor sensitivity was moderately heritable, with the greatest estimates of heritability seen in females from the F2 to S3 generations. Selection for locomotor sensitivity also resulted in increased anxiety-like activity in the open field. These results are the first to indicate that adolescent THC-locomotor sensitivity can be influenced via selective breeding. Development of lines with a genetic predisposition for THC-sensitivity or resistance to locomotor effects allow for investigation of risk factors, differences in consequences of THC use, identification of correlated behavioral responses, and detection of genetic targets that may contribute to heightened cannabinoid sensitivity.

ADH1B: From alcoholism, natural selection, and cancer to the human phenome

The ADH1B (Alcohol Dehydrogenase 1B (class I), Beta Polypeptide) gene and its best-known functional alleles, Arg48His (rs1229984, ADH1B*2) and Arg370Cys (rs2066702, ADH1B*3), have been investigated in relation to many phenotypic traits; most frequently including alcohol metabolism and alcohol drinking behaviors, but also human evolution, liver function, cancer, and, recently, the comprehensive human phenome. To understand ADH1B functions and consequences, we provide here a bioinformatic analysis of its gene regulation and molecular functions, literature review of studies focused on this gene, and a discussion regarding future research perspectives. Certain ADH1B alleles have large effects on alcohol metabolism, and this relationship particularly encourages further investigations in relation to alcoholism and alcohol-associated cancer to understand better the mechanisms by which alcohol metabolism contributes to alcohol abuse and carcinogenesis. We also observed that ADH1B has complex mechanisms that regulate its expression across multiple human tissues, and these may be involved in cardiac and metabolic traits. Evolutionary data strongly suggest that the selection signatures at the ADH1B locus are primarily related to effects other than those on alcohol metabolism. This is also supported by the involvement of ADH1B in multiple molecular pathways and by the findings of our recent phenome-wide association study. Accordingly, future studies should also investigate other functions of ADH1B potentially relevant for the human phenome. © 2017 Wiley Periodicals, Inc.

Alcohol Misuse Across the Lifespan: Insights from Developmental Studies in Behavior Genetics

Alcohol misuse, one of today's greatest public health challenges, is a developmentally dynamic, complex behavior at the intersection of genetic and environmental influences. This review examines such influences from a behavior genetics perspective and discusses implications for public policy. Alcohol misuse is moderately heritable with genetic influences accounting for around 50% of its variance, but to date few specific genes have been identified. However, numerous environmental and social factors moderate genetic risk, including parents, peers, romantic partners, family dynamics, employment, laws, and cultural influences. These moderating factors change in salience across development, and, accordingly, no one-size-fits-all approach is suitable for reducing alcohol misuse at a large scale. We provide examples of some effective prevention and intervention programs and discuss a framework for using the behavior genetics evidence to inform future public policy efforts.

Focusing on the Opioid System for Addiction Biomarker Discovery

Substance use disorders (SUD) and behavioral addictions are devastating conditions that impose a severe burden on all societies, and represent difficult challenges for clinicians. Therefore, biomarkers are urgently needed to help predict vulnerability, clinical course, and response to treatment. Here, we elaborate on the potential for addiction biomarker discovery of the opioid system, particularly within the emerging framework aiming to probe opioid function in peripheral tissues. Mu, delta, and kappa opioid receptors all critically regulate neurobiological and behavioral processes that define addiction, and are also targeted by major pharmacotherapies used in the management of patients with SUD. We propose that opioid biomarkers may have the potential to improve and guide diagnosis and therapeutic decisions in the addiction field.

Comorbidity of Alcohol Use Disorder and Chronic Pain: Genetic Influences on Brain Reward and Stress Systems

Alcohol use disorder (AUD) is highly comorbid with chronic pain (CP). Evidence has suggested that neuroadaptive processes characterized by reward deficit and stress surfeit are involved in the development of AUD and pain chronification. Neurological data suggest that shared genetic architecture associated with the reward and stress systems may contribute to the comorbidity of AUD and CP. This monograph first delineates the prevailing theories of the development of AUD and pain chronification focusing on the reward and stress systems. It then provides a brief summary of relevant neurological findings followed by an evaluation of evidence documented by molecular genetic studies. Candidate gene association studies have provided some initial support for the genetic overlap between AUD and CP; however, these results must be interpreted with caution until studies with sufficient statistical power are conducted and replications obtained. Genomewide association studies have suggested a number of genes (e.g., TBX19, HTR7, and ADRA1A) that are either directly or indirectly related to the reward and stress systems in the AUD and CP literature. Evidence reviewed in this monograph suggests that shared genetic liability underlying the comorbidity between AUD and CP, if present, is likely to be complex. As the advancement in molecular genetic methods continues, future studies may show broader central nervous system involvement in AUD-CP comorbidity.

Using the research domain criteria (RDoC) to conceptualize impulsivity and compulsivity in relation to addiction

Nomenclature for mental disorder was updated in 2013 with the publication of the fifth edition of the Diagnostic and Statistical Manual (DSM-5). In DSM-5, substance use disorders are framed as more dimensional. First, the distinction between abuse and dependence is replaced by substance use. Second, the addictions section now covers both substances and behavioral addictions. This contemporary move toward dimensionality and transdiagnosis in the addictions and other disorders embrace accumulating cognitive-affective neurobiological evidence that is reflected in the United States' National Institutes of Health Research Domain Criteria (NIH RDoC). The RDoC calls for the further development of transdiagnostic approaches to psychopathy and includes five domains to improve research. Additionally, the RDoC suggests that these domains can be measured in terms of specific units of analysis. In line with these suggestions, recent publications have stimulated updated neurobiological conceptualizations of two transdiagnostic concepts, namely impulsivity and compulsivity and their interactions that are applicable to addictive disorders. However, there has not yet been a review to examine the constructs of impulsivity and compulsivity in relation to addiction in light of the research-oriented RDoC. By doing so it may become clearer as to whether impulsivity and compulsivity function antagonistically, complementarily or in some other way at the behavioral, cognitive, and neural level and how this relationship underpins addiction. Thus, here we consider research into impulsivity and compulsivity in light of the transdiagnostic RDoC to help better understand these concepts and their application to evidence-based clinical intervention for addiction.

Association of the PLCB1 gene with drug dependence

Genetic factors involved in the susceptibility to drug addiction still remain largely unknown. MiRNAs seem to play key roles in the drug-induced plasticity of the brain that likely drives the emergence of addiction. In this work we explored the role of miRNAs in drug addiction. With this aim, we selected 62 SNPs located in the 3'UTR of target genes that are predicted to alter the binding of miRNA molecules and performed a case-control association study in a Spanish sample of 735 cases (mainly cocaine-dependent subjects with multiple drug dependencies) and 739 controls. We found an association between rs1047383 in the PLCB1 gene and drug dependence that was replicated in an independent sample (663 cases and 667 controls). Then we selected 9 miRNAs predicted to bind the rs1047383 region, but none of them showed any effect on PLCB1 expression. We also assessed two miRNAs binding a region that contains a SNP in linkage disequilibrium with rs1047383, but although one of them, hsa-miR-582, was found to downregulate PLCB1, no differences were observed between alleles. Finally, we explored the possibility that PLCB1 expression is altered by cocaine and we observed a significant upregulation of the gene in the nucleus accumbens of cocaine abusers and in human dopaminergic-like neurons after cocaine treatment. Our results, together with previous studies, suggest that PLCB1 participates in the susceptibility to drug dependence.

Seeing through the smoke: Human and animal studies of cannabis use and endocannabinoid signalling in corticolimbic networks

Public opinion surrounding the recreational use and therapeutic potential of cannabis is shifting. This review describes new work examining the behavioural and neural effects of cannabis and the endocannabinoid system, highlighting key regions within corticolimbic brain circuits. First, we consider the role of human genetic factors and cannabis strain chemotypic differences in contributing to interindividual variation in the response to cannabinoids, such as THC, and review studies demonstrating that THC-induced impairments in decision-making processes are mediated by actions at prefrontal CB1 receptors. We further describe evidence that signalling through prefrontal or ventral hippocampal CB1 receptors modulates mesolimbic dopamine activity, aberrations of which may contribute to emotional processing deficits in schizophrenia. Lastly, we review studies suggesting that endocannabinoid tone in the amygdala is a critical regulator of anxiety, and report new data showing that FAAH activity is integral to this response. Together, these findings underscore the importance of cannabinoid signalling in the regulation of cognitive and affective behaviours, and encourage further research given their social, political, and therapeutic implications.

Independent and Interactive Effects of OPRM1 and DAT1 Polymorphisms on Alcohol Consumption and Subjective Responses in Social Drinkers

BACKGROUND

The current study examined independent and interactive effects of polymorphisms of the mu opioid receptor gene (OPRM1, A118G) and variable number tandem repeats of the dopamine transporter gene (DAT1, SLC6A3) on alcohol consumption and subjective responses to alcohol in 127 young, healthy, social drinkers.

METHODS

Participants completed an in-person assessment, which included self-reported alcohol drinking patterns and blood sampling for DNA, and in a second visit, a cumulative alcohol dosing procedure with subjective ratings across multiple time points and breath alcohol contents (0.03 to 0.1%). DNA was analyzed for OPRM1 AA versus AG/GG (*G) genotypes, DAT1 10-repeat allele (A10) versus 9 or lesser alleles (A9), and ancestral informative markers.

RESULTS

There were significant epistatic interactions between OPRM1 and DAT1 genotypes. Subjective High Assessment Scale scores after alcohol consumption were highest in *G and A9 carriers, and lowest in *G and A10 carriers. Negative subjective effects were also highest in *G and A9 carriers. Effects were similar in a sensitivity analysis limited to Caucasian subjects. There were independent and epistatic interactions on drinking. The OPRM1 *G allele was independently associated with fewer heavy drinking days. The A9 allele was associated with a greater number of drinking days, which was attenuated in carriers of the *G allele.

CONCLUSIONS

These findings highlight the biological importance of interactions between these 2 genes and interactions between brain opioid and dopamine systems.

Promising pharmacogenetic targets for treating alcohol use disorder: evidence from preclinical models

Inherited genetic variants contribute to risk factors for developing an alcohol use disorder, and polymorphisms may inform precision medicine strategies for treating alcohol addiction. Targeting genetic mutations linked to alcohol phenotypes has provided promising initial evidence for reducing relapse rates in alcoholics. Although successful in some studies, there are conflicting findings and the reports of adverse effects may ultimately limit their clinical utility, suggesting that novel pharmacogenetic targets are necessary to advance precision medicine approaches. Here, we describe promising novel genetic variants derived from preclinical models of alcohol consumption and dependence that may uncover disease mechanisms that drive uncontrolled drinking and identify novel pharmacogenetic targets that facilitate therapeutic intervention for the treatment of alcohol use disorder.

Deep Sequencing of 71 Candidate Genes to Characterize Variation Associated with Alcohol Dependence

BACKGROUND

Previous genomewide association studies (GWASs) have identified a number of putative risk loci for alcohol dependence (AD). However, only a few loci have replicated and these replicated variants only explain a small proportion of AD risk. Using an innovative approach, the goal of this study was to generate hypotheses about potentially causal variants for AD that can be explored further through functional studies.

METHODS

We employed targeted capture of 71 candidate loci and flanking regions followed by next-generation deep sequencing (mean coverage 78X) in 806 European Americans. Regions included in our targeted capture library were genes identified through published GWAS of alcohol, all human alcohol and aldehyde dehydrogenases, reward system genes including dopaminergic and opioid receptors, prioritized candidate genes based on previous associations, and genes involved in the absorption, distribution, metabolism, and excretion of drugs. We performed single-locus tests to determine if any single variant was associated with AD symptom count. Sets of variants that overlapped with biologically meaningful annotations were tested for association in aggregate.

RESULTS

No single, common variant was significantly associated with AD in our study. We did, however, find evidence for association with several variant sets. Two variant sets were significant at the q-value <0.10 level: a genic enhancer for ADHFE1 (p = 1.47 × 10^-5 ; q = 0.019), an alcohol dehydrogenase, and ADORA1 (p = 5.29 × 10^-5 ; q = 0.035), an adenosine receptor that belongs to a G-protein-coupled receptor gene family.

CONCLUSIONS

To our knowledge, this is the first sequencing study of AD to examine variants in entire genes, including flanking and regulatory regions. We found that in addition to protein coding variant sets, regulatory variant sets may play a role in AD. From these findings, we have generated initial functional hypotheses about how these sets may influence AD.

Differential potassium channel gene regulation in BXD mice reveals novel targets for pharmacogenetic therapies to reduce heavy alcohol drinking

Alcohol (ethanol) dependence is a chronic relapsing brain disorder partially influenced by genetics and characterized by an inability to regulate harmful levels of drinking. Emerging evidence has linked genes that encode K_V7, K_IR, and K_Ca2 K⁺ channels with variation in alcohol-related behaviors in rodents and humans. This led us to experimentally test relations between K⁺ channel genes and escalation of drinking in a chronic-intermittent ethanol (CIE) exposure model of dependence in BXD recombinant inbred strains of mice. Transcript levels for K⁺ channel genes in the prefrontal cortex (PFC) and nucleus accumbens (NAc) covary with voluntary ethanol drinking in a non-dependent cohort. Transcripts that encode K_V7 channels covary negatively with drinking in non-dependent BXD strains. Using a pharmacological approach to validate the genetic findings, C57BL/6J mice were allowed intermittent access to ethanol to establish baseline consumption before they were treated with retigabine, an FDA-approved K_V7 channel positive modulator. Systemic administration significantly reduced drinking, and consistent with previous evidence, retigabine was more effective at reducing voluntary consumption in high-drinking than low-drinking subjects. We evaluated the specific K⁺ channel genes that were most sensitive to CIE exposure and identified a gene subset in the NAc and PFC that were dysregulated in the alcohol-dependent BXD cohort. CIE-induced modulation of nine genes in the NAc and six genes in the PFC covaried well with the changes in drinking induced by ethanol dependence. Here we identified novel candidate genes in the NAc and PFC that are regulated by ethanol dependence and correlate with voluntary drinking in non-dependent and dependent BXD mice. The findings that Kcnq expression correlates with drinking and that retigabine reduces consumption suggest that K_V7 channels could be pharmacogenetic targets to treat individuals with alcohol addiction.

Pathways to smoking behaviours: biological insights from the Tobacco and Genetics Consortium meta-analysis

By running gene and pathway analyses for several smoking behaviours in the Tobacco and Genetics Consortium (TAG) sample of 74 053 individuals, 21 genes and several chains of biological pathways were implicated. Analyses were carried out using the HYbrid Set-based Test (HYST) as implemented in the Knowledge-based mining system for Genome-wide Genetic studies software. Fifteen genes are novel and were not detected with the single nucleotide polymorphism-based approach in the original TAG analysis. For quantity smoked, 14 genes passed the false discovery rate of 0.05 (corrected for multiple testing), with the top association signal located at the IREB2 gene (P=1.57E-37). Three genomic loci were significantly associated with ever smoked. The top signal is located at the noncoding antisense RNA transcript BDNF-AS (P=6.25E-07) on 11p14. The SLC25A21 gene (P=2.09E-08) yielded the top association signal in the analysis of smoking cessation. The 19q13 noncoding RNA locus exceeded the genome-wide significance in the analysis of age at initiation (P=1.33E-06). Pathways belonging to the Neuronal system pathways, harbouring the nicotinic acetylcholine receptor genes expressing the α (CHRNA 1-9), β (CHRNB 1-4), γ, δ and ɛ subunits, yielded the smallest P-values in the pathway analysis of the quantity smoked (lowest P=4.90E-42). Additionally, pathways belonging to 'a subway map of cancer pathways' regulating the cell cycle, mitotic DNA replication, axon growth and synaptic plasticity were found significantly enriched for genetic variants in ever smokers relative to never smokers (lowest P=1.61E-07). In addition, these pathways were also significantly associated with the quantity smoked (lowest P=4.28E-17). Our results shed light on one of the world's leading causes of preventable death and open a path to potential therapeutic targets. These results are informative in decoding the biological bases of other disease traits, such as depression and cancers, with which smoking shares genetic vulnerabilities.

Phenome-Wide Association Study for Alcohol and Nicotine Risk Alleles in 26394 Women

To identify novel traits associated with alleles known to predispose to alcohol and nicotine use, we conducted a phenome-wide association study (PheWAS) in a large multi-population cohort. We investigated 7688 African-Americans, 1133 Asian-Americans, 14 081 European-Americans, and 3492 Hispanic-Americans from the Women's Health Initiative, analyzing alleles at the CHRNA3-CHRNA5 locus, ADH1B, and ALDH2 with respect to phenotypic traits related to anthropometric characteristics, dietary habits, social status, psychological traits, reproductive history, health conditions, and nicotine/alcohol use. In ADH1B trans-population meta-analysis and population-specific analysis, we replicated prior associations with drinking behaviors and identified multiple novel phenome-wide significant and suggestive findings related to psychological traits, socioeconomic status, vascular/metabolic conditions, and reproductive health. We then applied Bayesian network learning algorithms to provide insight into the causative relationships of the novel ADH1B associations: ADH1B appears to affect phenotypic traits via both alcohol-mediated and alcohol-independent effects. In an independent sample of 2379 subjects, we also replicated the novel ADH1B associations related to socioeconomic status (household gross income and highest grade finished in school). For CHRNA3-CHRNA5 risk alleles, we replicated association with smoking behaviors, lung cancer, and asthma. There were also novel suggestive CHRNA3-CHRNA5 findings with respect to high-cholesterol-medication use and distrustful attitude. In conclusion, the genetics of alcohol and tobacco use potentially has broader implications on physical and mental health than is currently recognized. In particular, ADH1B may be a gene relevant for the human phenome via both alcohol metabolism-related mechanisms and other alcohol metabolism-independent mechanisms.

Genetic variation in FAAH is associated with cannabis use disorders in a young adult sample of Mexican Americans

BACKGROUND

Cannabis is a commonly used drug and studies have shown that a significant portion of the variation in cannabis use disorders (CUDs) is heritable. Five genes known to play a role in the endocannabinoid system and CUDs were examined in a community sample of young adult Mexican Americans (MAs): CNR1, MGLL, FAAH, DAGLA, and DAGLB.

METHODS

Gene-based tests were run to test for association between each gene and two DSM-5 cannabis phenotypes. Subsequent linear regressions were run in PLINK using an additive model to determine which single nucleotide polymorphisms (SNPs) were driving the association.

RESULTS

FAAH was significantly associated with DSM-5 cannabis use disorder group count (DSM-5 CUD) using a gene-based test (p=0.0035). This association survived Bonferroni correction for multiple testing at p<0.004. Post hoc analyses suggested this association was driven by two common (minor allele frequency >5%) SNPs in moderate linkage disequilibrium, rs324420 and rs4141964, at p=0.0014 and p=0.0023, respectively. In both cases the minor allele increased risk for DSM-5 CUD.

CONCLUSIONS

Genetic variation in FAAH was associated with DSM-5 CUD in MAs. This association was primarily driven by the missense SNP rs324420. In vitro work has provided evidence that the risk allele generates an enzyme with decreased expression and cellular stability. Although this SNP has been previously associated with substance use in the literature, this is the first association in a young adult MA sample.

Pleiotropic effects of Chr15q25 nicotinic gene cluster and the relationship between smoking, cognition and ADHD

Polymorphisms in the CHRNA5-CHRNA3-CHRNB4 gene cluster (Chr15q25) have been robustly associated with nicotine dependence, including genome-wide studies, as well as with cognitive and neuropsychological measures. In addition, cognitive processes can be influenced by nicotine use through nicotinic acetylcholine receptors (nAChRs). Here, we evaluated the effect of polymorphisms in CHRNA5-CHRNA3-CHRNB4 gene cluster and their interaction with tobacco smoking status on cognition in patients with Attention Deficit/Hyperactivity Disorder (ADHD). Eight SNPs from the CHRNA5-CHRNA3-CHRNB4 gene cluster were evaluated on a clinical sample of 403 adults with ADHD. Cognitive performance was assessed using the Wechsler Adult Intelligence Scale-Revised (WAIS-R). Analyses of covariance were used to assess the influence of single markers and their interaction with smoking status in the Vocabulary and Block Design subtests of WAIS-R. Correction for multiple comparisons was applied. Lifetime smoking was associated to Vocabulary subtest. The TT genotypes of CHRNA5 SNPs rs588765 and rs514743 showed a trend towards association with, respectively, higher and lower scores on the Vocabulary subtest. There was a significant interaction between intergenic SNP rs8023462 and smoking on Vocabulary scores. Our results are consistent with an influence of variants in the CHRNA5-CHRNA3-CHRNB4 gene cluster on cognitive measures. The overall scenario suggests a pleiotropic role of Chr15q25 nicotinic gene cluster with complex influences in ADHD, tobacco smoking and cognitive performance, characteristics that can be partially interdependent and may share underlying genetic factors.

Genetics of Substance Use Disorders

Substance abuse disorders have a strong genetic component. Genetic risk factors associated with alcohol abuse include common variants in genes coding for alcohol-metabolizing enzymes and gamma-aminobutyric acid A receptors. Functional missense mutations in ADH1B and ALDH2 are protective against alcohol dependence. Nicotine use disorders are associated with polymorphisms in a cluster of nicotinic acetylcholine receptors on chromosome 15q24, and mutations that reduce the enzymatic activity of CYP2A6. Genetic risk factors for other illicit drug use have not been well-studied. Most genetic vulnerability toward substance use disorders remains unexplained. Future research will benefit from advanced whole-genome sequencing technologies.