It seems likely that, considering the scale of studies so far carried out and the wide range of SNPs used, most of the associations with ORs around 1.2 or greater for the diseases so far studied may already have been found, at least in populations of European origin. There is always the possibility that positive interactions between one or more common variants may give rise to a much increased OR. This is, however, very difficult to test for, unless the marginal effects of the variants being tested for their interactions are themselves significant. Even then, the number of pairwise combinations to be assessed is likely to be prohibitive. Furthermore, it seems a priori unlikely that variants with small primary effects would give rise to significant interactions.
