than SNP by SNP GXE analyses, given the small effect sizes anticipated for the latter). Isolated reports of GXE effects in individual samples have in general not yet led to the coordinated efforts at cross-study replication, including meta-analyses, that would make findings convincing both in terms of confirmation of GXE effects, and through clarification of the specific aspects of environmental exposure (e.g. of the many environmental differences associated with urban versus rural residence) that may be contributing to interaction effects.
