Recently, advances in genotyping technologies, reduction in genotyping costs and the availability of data regarding genome-wide sequence variation through the International HapMap Project and 1000 genomes project have made genome-wide association studies (GWAS) possible. GWAS have emerged as a powerful tool for identifying genetic variants associated with complex traits. In the past few years, more than 500 loci have been found to be associated with human common diseases and traits (1). GWAS have proven to be much more successful than linkage studies, which were underpowered to detect variants of modest effect (2), and candidate gene studies, which are non-systematic and biased due to our limited knowledge of the biological pathways implicated in disease pathogenesis (3).
