Collections of large samples, including case and control individuals as well as families containing affected individuals, are enhancing our ability to identify DNA variants affecting risk for disease. It has become the standard to search for genetic variants associated with complex disease using genome-wide association studies (GWAS). As of March 2010, 2403 associations for common diseases/phenotypes have been validated [1, 2]. Using combined data from three studies, genome-wide association has identified more than 30 variants for Crohn's disease [3]. Yet, even with these successes, many more variants are yet to be discovered [4]. In the pursuit of unexplained heritability more samples from many collections are being combined to increase the power to detect additional risk variants.
