Expression quantitative trait locus rs6356 is associated with the susceptibility of heroin addiction by potentially influencing the TH gene expression in the hippocampus and nucleus accumbens

Abstract Opioid addiction is a complicated and highly heritable brain disease. Dysfunction of dopaminergic signaling is involved in the pathogenesis of addictive disorders. Encoding the synthetase of dopamine, tyrosine hydroxylase (TH) gene has long been an interesting candidate in the genetic association studies for opioid addiction. However, the underlying mechanism of the association of risk gene variants and opioid addiction remains unknown. In the present study, we first analyzed the association between TH gene variants and susceptibility and traits of heroin addiction in 801 patients with heroin addiction and 930 healthy controls. The methylation level in the promoter region of the TH gene was detected and compared between the heroin addiction and healthy control groups. To reveal the potential mechanism of the association of TH gene variants and heroin addiction, correlation between the risk TH SNPs for heroin addiction and the methylation as well expression level of TH gene were examined. Our results demonstrated that SNP rs6356 was associated with the susceptibility of heroin addiction. CpG TH_15 was hypermethylated in the heroin addiction group compared with the healthy control group. Notably, SNP rs6356 was allele-specific correlated with the expression of TH gene in the hippocampus and nucleus accumbens, but not the methylation level of CpG TH_15. Our findings suggest that the eQTL rs6356 was associated with the risk of heroin addiction by potentially affecting the expression of TH gene in the mesocorticolimbic dopamine system brain regions including hippocampus and nucleus accumbens.