Risk factors for cannabis use disorders in Caucasian and American population

Abstract

Marijuana is the most commonly used illicit drug globally and its use is associated with dependence, craving, and drug-seeking behaviour. Compared with other drugs of abuse, less is known about the susceptibility to cannabis use disorders. Hence, the aim of the present work was to identify potential genetic and environmental risk factors associated with cannabis use, comparing a group of marijuana users and control subjects in both Caucasian (93 controls and 92 marijuana users) and American (96 controls and 40 marijuana users) populations. Genetic association studies on polymorphisms involved in dopaminergic and endocannabinoid pathways were performed through gel electrophoresis based analysis and TaqMan genotyping Assay (Thermo). Psychometric tests (ACES, CECA-q, PBI) and a sociodemographic data analysis (gender, marital status, level of education, BMI evaluation) were used to assess environmental influences on cannabis use in the Caucasian and American groups respectively. MeDIP-qPCR finally investigated DNA methylation variations that can alter or trigger drugs of abuse response in the American population. In Caucasian population differences in allelic frequencies and genotype distributions of the SNP rs1800497 (Taq1A) (p<0.03) of ANKK1 gene were observed and heterozygous G/A carriers were found more frequent among marijuana users than controls (p<0.051) for the SNP rs1049353 (G1359A) of CNR1 gene. In addition, G allele of the SNP rs1049353 may represent a risk factor for cannabis use in American population, since G allele (p<0.002) and homozygous GG genotype (p<0.01) were found significantly higher in marijuana users compared to control subjects. In American population differences were also observed in the genotypes distribution (p<0.058) for the SNP rs2501431, CNR2 gene. In our study, homozygous A/A genotype was found more frequent in the marijuana group compared to controls. Using logistic regression models the psychometric variables were evaluated in Caucasian population and the optimal parenting was observed as protective factor against cannabis use. Emotional neglect and physical neglect were confirmed as specific risk factors to this condition. In American population, an increase in education by one level drops the risk of marijuana use by approximately half. In both the populations, the gender difference affected cannabis use, with males tending to use at a higher rate than females. DNA methylation status was found significantly higher in marijuana users compared to control subjects in two of the genes analyzed: hypermethylation at the exon 8 (+66.7 kb from TSS) of DRD2 gene (p<0.034) and hypermethylation at the CpG-rich region, +3 kb from TSS, in the NCAM1 gene (p<0.0004). This study is one of the first to investigate the association between environmental factors, genetic polymorphisms, DNA methylation and marijuana use. Further to explore and replicate these results would be important to understand if genetic polymorphisms, stressful life events and differences in DNA methylation of marijuana-associated genes could be used as biomarkers for the prevention and treatment of marijuana use disorders.