Gene-environment interactions for obesity-related phenotypes have been shown in candidate gene (Guo et al. 2007) and twin and sibling studies (Boardman et al. 2012). To date, though, no existing study has considered GxE associations for BMI using the GWGEI approach. Several recent studies have highlighted the usefulness of GWGEI methods (Cornelis et al. 2012; Mukherjee et al. 2012; Murcray et al. 2009; Thomas et al. 2012), but none of these approaches used trios to detect main and interactive genetic effects and to reduce the risk of gene-environment correlation. Our primary goal was to situate the GWGEI findings within the existing GxE theoretical framework to provide some structure as we sifted through hundreds of thousands of main environmental, main genetic, and GxE terms. Our results suggest that the search for specific alleles that are related to health outcomes of interest to demographers, such as physical weight, may not provide useful information, and the results from GWGEI analyses are also not likely to shed any light on the existing GxE typology, especially given sample sizes in the thousands. Even with a well-established
