The current findings from the few published GWAS studies of schizophrenia and bipolar disorder, along with the data from leading candidate genes that predate the era, are supportive of the hypothesis that common variants contribute. However, no locus has yet been reported for schizophrenia that in any single or combined study reaches genome-wide levels of significance17. For bipolar disorder, there are 3 such loci18,19 but these have yet to receive support in independent studies. The issue of whether there is wide-scale involvement of common variants is not moot; if the vast majority of genetic risk is conferred almost exclusively by rare alleles, approaches based upon indirect genetic association may not be very informative. Given the challenges in obtaining appropriate sized samples to conduct GWAS studies, it would be preferable to have strong evidence as to whether doing so is likely to be rewarded with a significant degree of success.
