However, we are unable to conclude from some small GxE studies that the phenotypes are not genetically the same, as long as GWAS on the same phenotypes do not come up with the same list of associated genes. As such, we remain unable to make definitive claims regarding the nature of changing gene-environment interaction contributing to cigarette use due to the limited availability of studies investigating this phenomenon. Each study reviewed here examined the association between specific cigarette use phenotypes and a given environmental measure within either adolescents or adults. This made it difficult to determine how environmental contexts differentially influence genetic factors that contribute to cigarette use phenotypes such as initiation, daily use, nicotine dependence, and cessation and demonstrates how the use of various cigarette use phenotypes may complicate the literature and comparability of findings across studies. Added layers of complexity are found in the fact that there is a great deal of variability in heritability across each cigarette use phenotype (96) and heritability estimates may be contingent on social and institutional characteristics of the environment, such as temporal
