GWA studies have been defined by the National Institutes of Health (NIH) as any studies of common genetic variation across the entire human genome designed to identify genetic associations with observable traits (10). Implicit in this definition is that sufficient numbers of SNPs are typed to capture the vast majority of common variations (as noted above, these are alleles with a frequency of at least 5% in a population) throughout the entire genome. Such studies typically involve hundreds of thousands of SNPs and are not limited to known genes or regulatory regions. Instead, they assess genetic variation genome-wideinanalmost “agnostic” fashion, unconstrained by current imperfect understanding of genome structure and function (11).
