Heterogeneity in effects across studies exists due to the different design and case ascertainment of cross-sectional studies contributing to earlier GWAS [19]. In addition, heterogeneity in effects of established or yet unidentified loci between population subgroups is likely, due to the multifaceted aetiology of type 2 diabetes. Varying effects between subgroups defined by disease characteristics such as early versus late diabetes onset or with versus without positive family history may reflect different relative contributions of genetic versus lifestyle factors. Not accounting for potential sources of heterogeneity may lead to important subgroup effects being overlooked, genetic variants not being identified and the genetic variance explained being underestimated.
