Tourette's syndrome and related disorders.

The past two decades of research have demonstrated that Tourette's syndrome (TS) is likely to be more genetically heterogeneous than initially appreciated. Nonetheless, important progress toward the understanding of genetic influences in TS has been made by the combination of family and twin studies, segregation analyses, parametric and nonparametric linkage analyses, and association studies. The identification of genetic factors involved in TS will have important implications for clinical research. Once it is possible to stratify patients meaningfully with respect to known genetic markers, a reassessment of diagnostic nosology, neuroimaging findings, psychopharmacology, and disease course will be possible. Another result of gene identification will be the rapid clarification of additional environmental factors influencing the development of the disorder. Because it may be easier to influence the environment and behavior rather than to change genes, exploration of such gene-environment interactions may lead to the most significant clinical contributions in the near term.