the multiple comparisons challenges of relating high-dimensional phenotypes to high-dimensional genotypes and interactions are even more daunting than for regular GWA studies. Alternatively, stand-alone studies or external databases can be used to construct prior covariates to inform G×E analyses of epidemiologic studies. For example, GWA data on immunologic markers for a challenge study of allergen and diesel exhaust particles are being used to define a set of immunologic covariates associated with each SNP as priors in a hierarchical model for a GWA study of asthma. Associations of genome-wide expression with genome-wide SNPs143 could be used in a similar manner, and would likely be even more promising for G×E interactions if based on expression studies conducted under a range of environmental conditions.
