From associated SNP to causal gene/mutation. There are at least three ways to go from an associated SNP in a GWAS to the causal mutation(s) and causal gene. The first is to perform dense genotyping to identify the set of common SNPs that yield the strongest signal of association, followed by hypothesis-driven functional studies. The second is to perform deep re-sequencing to search for rare mutations that are independent of the common mutation and that alter protein function. The third is to use bioinformatics approaches to establish connections among genes across associated loci.