In contrast, candidate gene studies in the field of genetics rarely genotype a single genetic marker in the gene of interest; in fact, this would generally not be publishable in any respectable genetics journal (Pettersson et al., 2009). Rather, with data from the Human Genome Project and the HapMap project, we now know something about the structure of most genes in the human genome (Manolio et al., 2008). Further, there are many polymorphic markers available across most genes of interest. It is possible that multiple locations in a gene could have various forms that lead to differential function of that gene contributing to differential susceptibility to an outcome (McClellan & King, 2010). In fact, we know this to be the case in single gene Mendelian disorders, such as cystic fibrosis, where more than 1,000 different mutations have been discovered in the cystic fibrosis gene that lead to the disease phenotype! Accordingly, to truly evaluate the role of a hypothesized gene of interest it is absolutely necessary to understand the genomic structure in and around that gene (see Dick et al.,
