The main effects of genotype indicate that individuals with a particular variant found to show association with Fagerström Test for Nicotine Dependence (FTND) score and number of cigarettes they smoke daily, and a significantly higher levels of HINT1 expression, while the genotype (rs3864283) × smoking status interaction suggests that this effect depends on smoking status, that is, smokers with the rs3864283 risk allele have higher HINT1 expression than never-smokers. The gene discussed is HINT1; the disease is substance dependence.