One Finnish twin study demonstrated that at age 14, the effect of genes on cigarette use increased and common environmental effects decreased as adolescents reported less parental monitoring. Specifically, genetic factors accounted for more than 60% of the variance at the extreme low end, but less than 15% at the extremely high end of parental monitoring. Meanwhile, common environmental effects accounted for 20% and 80% of the variance at extremely low and high ends of parental monitoring, respectively (8). Parental monitoring seems to have an effect on genes contributing to nicotine dependence as well, as demonstrated by a significant interaction found between rs169169968 and parental monitoring (p =0.009) in the Collaborative Genetic Study of Nicotine Dependence, whereby nicotine dependence increased with the risk genotype when combined with the lowest quartile of parental monitoring (33). This suggests that parents moderate the likelihood of an individual at genetic risk for adolescent smoking and nicotine dependence in later life, through the restrictiveness of the social environment provided by parents. Variation in rs3743078 did not contribute to this association, as no significant interaction was
