Although this is the first study to examine the interaction between specific genes and peer smoking for nicotine dependence, twin studies of related measures of peer influence and the total additive genetic effects on related phenotypes have been reported. These studies have found that the similarity in substance use and substance abuse symptoms between individuals and their peers has been largely attributable to additive genetic variance components [12, 14–16]. Harden et al. [14] and Dick et al. [32] observed that the genetic variance component for adolescent substance use or alcohol use was greater when peer use was greater, that is a GxE, adjusting for rGE. Testing a series of GxE models for perceived peer deviance Button et al. [16] found that the genetic variance component contributing to substance dependence symptoms during adolescence was greatest where peer deviance was high (social expression model) and where peer deviance was low (social distinction model). Our GxE finding between rs16969968 and H.S. peer smoking wherein the effects of the AA genotype on probability of nicotine dependence were most obvious at lower numbers of smoking
