Candidate Gene Studies and Genome-Wide Association Studies
Genetic association studies use genetic variants. Given that there are millions of genetic variants in the genome, it is important to select carefully the variants to be used in association studies in order to obtain the correct answer to the research question and not to waste resources. Initial genetic association studies (candidate gene studies) only used one or a few variants from a candidate gene. Many contemporary genetic association studies are genome-wide association studies (GWASs), which use up to five million variants, but this is still not all the variants in the human genome. The ultimate aim is to encompass all variants, including previously unknown ones, which is only possible with whole-genome sequencing. In this sense, whole-genome sequencing can be viewed as the largest possible GWAS. It might be thought that candidate gene studies are now obsolete, but this is not the case and the place of candidate gene studies in the post-GWAS age will be discussed in this chapter. The advantages and disadvantages of GWASs will also be discussed. The chapter starts by describing the selection of candidate genes and variants, contrasting the requirements of candidate studies and GWASs.