Despite the tremendous success of GWAS in the last few years there remain skeptics of the value of the approach. Some question the value of observing associations of DNA variants to disease in the absence of knowledge of the underlying biology. The answer to such reservations is simple. GWAS should only be considered a first step toward the identification of causal relationships between gene biology and disease. There is much work that needs to be done after a GWAS in order to move the knowledge through basic research to translational research and into the clinic. Others argue that, since the identified genetic variants only explain a small fraction of the disease heritability, they are of limited value. It is true that the heritability explained by variants identified through GWAS is most often less than 2–3% of the disease heritability (20), a phenomenon that has triggered much discussion about the underlying reasons, which might include a great number of small effect variants, gene-gene interactions, multiple individually rare variables that are not detectable by GWAS, copy number variations (a type of variation
