Several features of the genome led to the ability to perform GWA studies; i) that most common genetic variation is shared amongst individuals, particularly within the same ethnic group, and also ii) that segments of chromosomes are often inherited intact, resulting in batches of correlated markers. However, these features also bias this approach towards detecting association with common genetic markers (44). To examine this empirically, we examined the frequency distribution of SNPs that reach genome-wide association in studies of > 10,000 individuals, SNPs typically examined in GWAS studies including imputation and HapMap SNPs (Figure 1A) and there is a clear excess of common variants in the category of associated variants.
