CHRNA6 and nicotine dependence: To understand the genetic mechanisms mediating these effects, human association studies have indicated that a single-nucleotide polymorphism (SNP) in the 3′-untranslated region (UTR) of the α6 nAChR subunit gene (CHRNA6) is associated with increased cigarette smoking, drug experimentation during adolescence, and nicotine dependence and unsuccessful quit attempts in adulthood [18,19,20,21].