However, peer smoking influence plays out against a backdrop of individual variability in genetic vulnerability to smoking and nicotine dependence. From a genetic perspective the interplay of peer and genetic influences on smoking may follow two mechanisms: gene-environment interactions (GxE) and/or gene-environment correlation (rGE) [11]. In the case of GxE the effects of peer smoking may differ (being lesser or greater) by individual genetic risk for smoking. Genes may also influence the degree to which individuals associate with smoking peers by influencing an individuals selection of peers (active rGE) or peer groups selection of an individual (evocative rGE) based on genetically influenced traits and behaviors [11–12]. Twin studies examining peer behaviors and genetic factors for substance use phenotypes have found evidence for both rGE and GxE [12–16]. These studies provide important insights into the interplay between the peer social context and a general genetic predisposition toward substance use and abuse symptoms. However, none of these studies specifically examined cigarette smoking or nicotine dependence, and there are no studies examining specific genetic variants associated with nicotine dependence and the influence of peer smoking.
