The Interplay of Genes, Peers, and Cohort on Patterns of Cigarette Use

Genetic factors are a known culprit influencing the choice of individuals to smoke. However, the way in which these genetic factors may contribute to smoking behavior through peers, depending upon the specific stage of smoking, and change in relation to birth cohort further compounds the complexity of understanding the mechanisms that link genetic makeup to smoking behavior. Here we addressed: (1) what mechanism(s) are responsible for peer similarity in smoking behavior, (2) at what stage of the smoking trajectory, from initiation to progression, are these peer mechanisms most salient, (3) from whole-genome SNP data, to what extent is smoking initiation related to more regular smoking behaviors, and (4) to what degree do the genetic factors influencing smoking for one generation correspond to those of another. We utilized two twin samples, the 1962 National Merit twins and the more recent Add Health twins. We also conducted genome-wide analyses of data from the Atherosclerosis Risk in Communities Study (ARIC) and the Multi-Ethnic Study of Atherosclerosis (MESA). Our results indicated that homophily, or the tendency to associate with individuals that are like oneself, may explain peer homogeneity for smoking behaviors, and if this homophily is accompanied by additional peer influence, active gene-environment correlation may be in part responsible for peer resemblance in smoking behavior. While it was unclear whether this mechanism is relevant to both initiation and persistent smoking in the National Merit Twins, analysis on the Add Health sample demonstrated that this mechanism may be important at both the stages of experimentation and regular use. Genome-wide analysis on unrelated individuals revealed that common genetic variation, as indexed by genome-wide SNPs, contributed to cigarette smoking liability, and the genetic factors that influenced smoking initiation were largely shared with those that impacted quantity smoked. Additionally, the genetic factors influencing smoking may change as a function of birth cohort