This stunning result created a surge of GWA studies using the new microarray technology that made GWA feasible. The first of these reported an association between SNPs in the interleukin-23 gene and inflammatory bowel disease using a 300,000-SNP microarray with about 500 cases and 500 controls (Duerr, Taylor, Brant, Rioux, Silverberg et al., 2006). This association was much smaller than the association found for age-related macular degeneration; the odds ratio was about 1.5 between cases and controls in two independent samples with about 500 individuals in each group. Nonetheless, the association has been replicated in several subsequent studies (Cho & Weaver, 2007).
