underlying behaviors, such as novelty-seeking and conduct disorder. Future studies aimed at disentangling possible unique genetic contributions to these phenotypes are merited. An alternative explanation for these findings could be biological. Age at initiation is related to behavioral traits such as Attention Deficit Hyperactivity Disorder (ADHD), Conduct Disorder (CD), Oppositional Deviant Disorder (ODD), delinquency, and criminal behavior [Armstrong and Costello, 2002; Flory et al., 2003; Han et al., 1999; Krueger et al., 2002; McGue and Iacono, 2008; McGue et al., 2001; Sihvola et al., 2011; Tarter et al., 2003; Young et al., 2000], while the time from initiation to regular smoking could be related to individual differences in neuroadaptation to nicotine and other psychoactive components of tobacco. Thus, it is reasonable to propose that nicotinic receptor properties are related to the neuroadaptation process and consequently to CHRN gene polymorphisms.
