The genetic and environmental architecture of substance use development from early adolescence into young adulthood: a longitudinal twin study of comorbidity of alcohol, tobacco and illicit drug use

Generalized genetic liability to substance use disorders

Lifetime and temporal co-occurrence of substance use disorders (SUDs) is common and compared with individual SUDs is characterized by greater severity, additional psychiatric comorbidities, and worse outcomes. Here, we review evidence for the role of generalized genetic liability to various SUDs. Coaggregation of SUDs has familial contributions, with twin studies suggesting a strong contribution of additive genetic influences undergirding use disorders for a variety of substances (including alcohol, nicotine, cannabis, and others). GWAS have documented similarly large genetic correlations between alcohol, cannabis, and opioid use disorders. Extending these findings, recent studies have identified multiple genomic loci that contribute to common risk for these SUDs and problematic tobacco use, implicating dopaminergic regulatory and neuronal development mechanisms in the pathophysiology of generalized SUD genetic liability, with certain signals demonstrating cross-species and translational validity. Overlap with genetic signals for other externalizing behaviors, while substantial, does not explain the entirety of the generalized genetic signal for SUD. Polygenic scores (PGS) derived from the generalized genetic liability to SUDs outperform PGS for individual SUDs in prediction of serious mental health and medical comorbidities. Going forward, it will be important to further elucidate the etiology of generalized SUD genetic liability by incorporating additional SUDs, evaluating clinical presentation across the lifespan, and increasing the granularity of investigation (e.g., specific transdiagnostic criteria) to ultimately improve the nosology, prevention, and treatment of SUDs.

Addiction-Associated Genetic Variants Implicate Brain Cell Type- and Region-Specific Cis-Regulatory Elements in Addiction Neurobiology

Recent large genome-wide association studies have identified multiple confident risk loci linked to addiction-associated behavioral traits. Most genetic variants linked to addiction-associated traits lie in noncoding regions of the genome, likely disrupting cis-regulatory element (CRE) function. CREs tend to be highly cell type-specific and may contribute to the functional development of the neural circuits underlying addiction. Yet, a systematic approach for predicting the impact of risk variants on the CREs of specific cell populations is lacking. To dissect the cell types and brain regions underlying addiction-associated traits, we applied stratified linkage disequilibrium score regression to compare genome-wide association studies to genomic regions collected from human and mouse assays for open chromatin, which is associated with CRE activity. We found enrichment of addiction-associated variants in putative CREs marked by open chromatin in neuronal (NeuN+) nuclei collected from multiple prefrontal cortical areas and striatal regions known to play major roles in reward and addiction. To further dissect the cell type-specific basis of addiction-associated traits, we also identified enrichments in human orthologs of open chromatin regions of female and male mouse neuronal subtypes: cortical excitatory, D1, D2, and PV. Last, we developed machine learning models to predict mouse cell type-specific open chromatin, enabling us to further categorize human NeuN+ open chromatin regions into cortical excitatory or striatal D1 and D2 neurons and predict the functional impact of addiction-associated genetic variants. Our results suggest that different neuronal subtypes within the reward system play distinct roles in the variety of traits that contribute to addiction.SIGNIFICANCE STATEMENT We combine statistical genetic and machine learning techniques to find that the predisposition to for nicotine, alcohol, and cannabis use behaviors can be partially explained by genetic variants in conserved regulatory elements within specific brain regions and neuronal subtypes of the reward system. Our computational framework can flexibly integrate open chromatin data across species to screen for putative causal variants in a cell type- and tissue-specific manner for numerous complex traits.

Development of individuals' own and perceptions of peers' substance use from early adolescence to adulthood

This study evaluated how individuals' own substance use and their perception of peers' substance use predict each other across development from early adolescence to middle adulthood. Participants were from two longitudinal studies: Fast Track (FT; N = 463) and Child Development Project (CDP; N = 585). Participants reported on their own and peers' substance use during early and middle adolescence and early adulthood, and their own substance use in middle adulthood. From adolescence to early adulthood, individuals' reports of their own substance use in a given developmental period predicted reports of their peers' substance use in the next developmental period more than peers' substance use in a given developmental period predicted individuals' own substance use in the next. In the higher-risk FT sample, individuals' own substance use in early adulthood predicted alcohol, cannabis, and other substance use in middle adulthood, and peers' substance use in early adulthood predicted cannabis use in middle adulthood. In the lower-risk CDP sample, participants' own substance use in early adulthood predicted only their own cannabis use in middle adulthood, whereas peers' substance use in early adulthood predicted participants' alcohol, cannabis, opioid, and other substance use in middle adulthood. The findings suggest that peer substance use in early adulthood may indicate a greater propensity for subsequent substance use in lower-risk groups, whereas those in higher-risk groups may remain more stable in substance use, with less variability explained by peer contexts.

Genetically selected alcohol-preferring msP rats to study alcohol use disorder: Anything lost in translation?

For several decades, genetically selected alcohol-preferring rats have been successfully used to mimic and study alcohol use disorders (AUD). These rat lines have been instrumental in advancing our understanding of the neurobiology of alcoholism and enabling pharmacological studies to evaluate drug efficacy on alcohol drinking and relapse. Moreover, the results of these studies have identified genetic variables that are linked to AUD vulnerability. This is an up-to-date review that focuses on genetically selected Marchigian Sardinian alcohol-preferring (msP) rats. To support the translational relevance of the findings that are obtained from msP rats and highlight important similarities to AUD patients, we also discuss the results of recent brain imaging studies. Finally, to demonstrate the importance of studying sex differences in animal models of AUD, we present original data that highlight behavioral differences in the response to alcohol in male and female rats. Female msP rats exhibited higher alcohol consumption compared with males. Furthermore, msP rats of both sexes exhibit higher anxiety- and depressive-like behaviors in the elevated plus maze and forced swim test, respectively, compared with unselected Wistar controls. Notably, voluntary alcohol drinking decreases foot-shock stress and depressive-like behavior in both sexes, whereas anxiety-like behavior in the elevated plus maze is attenuated only in males. These findings suggest that male and female msP rats both drink high amounts of alcohol to self-medicate negative affective symptoms. For females, this behavior may be driven by an attempt to treat stress and depressive-like conditions. For males, generalized anxiety appears to be an important additional factor in the motivation to drink alcohol. This article is part of the special issue on 'Vulnerabilities to Substance Abuse.'

Preadult polytoxicomania-strong environmental underpinnings and first genetic hints

Considering the immense societal and personal costs and suffering associated with multiple drug use or "polytoxicomania", better understanding of environmental and genetic causes is crucial. While previous studies focused on single risk factors and selected drugs, effects of early-accumulated environmental risks on polytoxicomania were never addressed. Similarly, evidence of genetic susceptibility to particular drugs is abundant, while genetic predisposition to polytoxicomania is unexplored. We exploited the GRAS data collection, comprising information on N~2000 deep-phenotyped schizophrenia patients, to investigate effects of early-life environmental risk accumulation on polytoxicomania and additionally provide first genetic insight. Preadult accumulation of environmental risks (physical or sexual abuse, urbanicity, migration, cannabis, alcohol) was strongly associated with lifetime polytoxicomania (p  = 1.5 × 10^-45; OR = 31.4), preadult polytoxicomania with OR = 226.6 (p = 1.0 × 10^-33) and adult polytoxicomania with OR = 17.5 (p = 3.4 × 10^-24). Parallel accessibility of genetic data from GRAS patients and N~2100 controls for genome-wide association (GWAS) and phenotype-based genetic association studies (PGAS) permitted the creation of a novel multiple GWAS-PGAS approach. This approach yielded 41 intuitively interesting SNPs, potentially conferring liability to preadult polytoxicomania, which await replication upon availability of suitable deep-phenotyped cohorts anywhere world-wide. Concisely, juvenile environmental risk accumulation, including cannabis and alcohol as starter/gateway drugs, strongly predicts polytoxicomania during adolescence and adulthood. This pivotal message should launch more effective sociopolitical measures to prevent this deleterious psychiatric condition.

Parental Alcohol Use and the Alcohol Misuse of their Offspring in a Finnish Birth Cohort: Investigation of Developmental Timing

There is a positive association between parental alcohol use and the alcohol use of their offspring. It is less clear whether this relation exists at different developmental periods. The purpose of the current study was to examine the associations between parental alcohol use at two developmental periods (prenatal and adolescence) and the alcohol misuse of their offspring at two developmental periods (adolescence and young adulthood). Data from the Northern Finland Birth Cohort 1986 (NFBC1986; n = 6963; 51% of offspring were girls) were used. The NFBC1986 is a population-based study of individuals born during a 1-year period in Finland. Multi-informant (parent, teacher, and youth) and multi-method (surveys and population registers) data were collected at four developmental periods (prenatal, childhood, adolescence, and young adulthood). The findings indicated that parents' alcohol use was stable from the prenatal period to adolescence. Mothers' and fathers' (based on mothers' perceptions) alcohol use during the prenatal period and adolescence were directly related to adolescents' heavy drinking. Prenatal alcohol use by mothers and fathers were related to young adults' alcohol use disorder indirectly (but not directly) through mothers' and fathers' alcohol use during adolescence and then through adolescents' heavy drinking. The results suggest that early and ongoing screening for alcohol use by mothers and fathers could help identify individuals at risk for heavy drinking and alcohol-related problems during adolescence and young adulthood.

DSM-5 Maladaptive Personality Domains among Treatment-Seeking Individuals with Alcohol Use Disorder: The Role of Disinhibition and Negative Affectivity

Background: Dimensional models of personality and personality disorders (PDs) have been widely investigated among individuals with alcohol use disorders (AUD). Nevertheless, DSM-5 maladaptive personality domains showed mixed associations with AUD. Furthermore, no studies have explored the role of DSM-5 maladaptive personality domains on the comorbidity between AUD and different PDs. Objective(s): This study aims at investigating whether DSM-5 maladaptive personality dimensions could differentiate individuals with AUD from normative and healthy controls (HCs) subjects. The study also investigated relationships between these personality dimensions and AUD clinical features (i.e. onset, severity of concurrent substance use disorders), as well as their role in accounting for the comorbidity between AUD and PDs. Methods: This study administered the personality inventory for DSM-5 (PID-5) to 99 treatment-seeking individuals (male 68.8%; female 31.2%; age: 48.12 (14.32)) with AUD (41 AUD only; 58 AUD with PDs), comparing the participants' levels of PID-5 domains with normative data and the data from a HC sample (N = 40; male 50%; female 50%; age: 48.12 (14.32)). Results: Disinhibition and negative affectivity were relevant maladaptive personality dimensions of AUD, even when controlling for the impact of PD diagnoses. Disinhibition and negative affectivity were associated to the onset of AUD and the severity of concurrent substance use disorders. The co-occurrence of AUD and PDs is related to other two domains, namely antagonism and detachment. Conclusions: AUD is a complex psychopathological disorder in which both externalizing and internalizing aspects determine relevant clinical features.

Longitudinal associations between youth tobacco and substance use in waves 1 and 2 of the Population Assessment of Tobacco and Health (PATH) Study

BACKGROUND

While evidence suggests bidirectional associations between cigarette use and substance (alcohol or drug) use, how these associations are reflected across the range of currently available tobacco products is unknown. This study examined whether ever tobacco use predicted subsequent substance use, and ever substance use predicted subsequent tobacco use among 11,996 U.S. youth (12-17 years) from Waves 1 (2013-2014) and 2 (2014-2015) of the Population Assessment of Tobacco and Health (PATH) Study.

METHODS

Ever use of cigarettes, e-cigarettes, traditional cigars, cigarillos, filtered cigars, pipe, hookah, snus pouches, smokeless tobacco excluding snus pouches, dissolvable tobacco, bidis, kreteks, alcohol, marijuana, prescription drugs, and other drugs (cocaine and other stimulants, heroin, inhalants, solvents, and hallucinogens) was assessed at Wave 1 followed by past 12-month use assessments at Wave 2. The analyses included covariates (demographics, mental health, sensation seeking, prior use) to mitigate confounding.

RESULTS

Ever tobacco use predicted subsequent substance use. The magnitude of the associations was lowest for alcohol, higher for marijuana, and highest for other drugs. Ever substance use also predicted subsequent tobacco use. Specifically, ever alcohol, marijuana, and non-prescribed Ritalin/Adderall use predicted tobacco-product use. Ever e-cigarette and cigarette use exclusively and concurrently predicted subsequent any drug (including and excluding alcohol) use. E-cigarette and cigarette use associations in the opposite direction were also significant; the strongest associations were observed for exclusive cigarette use.

CONCLUSION

Tobacco and substance use prevention efforts may benefit from comprehensive screening and interventions across tobacco products, alcohol, and drugs, and targeting risk factors shared across substances.