In February 2009, the catalogue of genome-wide association studies at the NHGRI listed more than 250 publications with results of GWAS and more than 1,000 SNPs that were discovered as associated with a variety of traits and disease [44]. This large number proves that the GWAS approach works and can indeed discover common variants related to common diseases, but it is much smaller than expected. Several issues have become apparent [8,95] and will have a substantial impact on the best way to follow up these initial GWAS.
