Under the synthetic associations model, common variant signals reflecting single or multiple rare alleles are unlikely to be consistent across populations of different ancestry. This is based on the fact that many of these rare variants would have arisen recently and will therefore not be shared across diverged populations. The majority of GWAS to date have focused on populations of European descent. However, data on more diverse populations are now starting to arise. For example, a study from early 2010 clearly demonstrated that common variant signals for T2D are reproducible and have similar effect sizes across East Asian populations including Chinese, Malays and Asian-Indians in Singapore (57). In fact, T2D-associated variants have been found to be associated with disease in diverse populations (ranging from African-Americans to Chinese) by several studies (58–62). Similarly, in RA, the STAT4 locus, as an example, has shown reproducible association with disease in the USA (63), UK (64), Spanish, Swedish, Dutch (65), Korean (66), Colombian (67), Japanese (68) and Greek (69) populations.
