It is also notable that SNPs that have been implicated in this region also lie within genes encoding an iron regulatory protein (IREB2), an α4 proteosome subunit protein (PSMA4) and a putative protein of unknown function (LOC123688) that may also be important in cell proliferation and apoptosis (12). Further research, such as behavioral tests in animal models and targeted re-sequencing of this gene cluster, will help clarify the role of these genes and their variants in mediating smoking phenotypes. This also provides the basis for the hypothesis-driven testing of gene-gene interactions, for example, by conditioning analyses on a known functional SNP.
