Such twins-based studies are highly informative for identifying the interplay between specific environmental risk factors and the general heritability of a phenotype. However, by their nature, these studies do not identify which specific genetic risks are modified by environmental exposures. Using data from the Collaborative Genetic Study of Nicotine Dependence (COGEND), we extend this research on the modifying effects of parent monitoring to examine nicotine dependence among adults and specific high priority genetic variants. With previous findings showing risk genotype (AA) for SNP rs16969968 and protective genotype (CC) for SNP rs3743078, a proxy for rs578776, associated with nicotine dependence as two distinct genetic risk factors (14), we test whether the genetic risks associated with these genotypes vary with level of parental monitoring during middle childhood. We test specifically if genetic and environmental risks are additive, and if there is a multiplicative interaction between them. Our key hypothesis on this relationship is that the known genetic risks will be highest among those with deviant parent monitoring, defined as lowest quartile in parent monitoring score. To the extent this hypothesis is supported, risk of nicotine dependence associated with these genes may be mitigated by interventions targeting parent monitoring.
