Candidate gene studies have focused mainly on genes involved in the dopaminergic pathway due to the fact that dopamine antagonists are the most effective medications for tic suppression. As shown in Table 1, similar to findings in other complex disorders [84], candidate gene association studies in GTS have not yielded any clearly replicated results that unequivocally identify a causative GTS susceptibility gene. It is likely that most of these candidate genes tested are not involved in the etiology of GTS, since candidate gene selection is a subjective process, complicated by the lack of clear understanding of the biological pathways involved in GTS. In addition small study sizes are significantly underpowered to detect genes with small-to-medium effect sizes.
