Nearly all GWAS to date have concentrated on detecting and characterizing main effects of genes and have underemphasized the potential role the environment plays in modifying genetic risk [Clayton and McKeigue, 2001; Dempfle et al., 2008; Martinez, 2008]. This decreased attention may, in part, be due to the paucity of established methods for the study of G × E interactions in a GWAS context. GWAS present many common challenges in analysis and interpretation that are likely to have common solutions [Manolio et al., 2007; Wellcome Trust Case Control Consortium, 2007]. These solutions and the potential for combining phenotype and genotype data across studies to enhance statistical power are best developed through collaborative approaches, as demonstrated by the Wellcome Trust Case Control Consortium (WTCCC), Genetic Association Information Network (GAIN) and the Psychiatric Genetics Consortium [Manolio et al., 2007; Psychiatric GWAS Consortium Steering Committee, 2009; Wellcome Trust Case Control Consortium, 2007].
