Genetics of obsessive–compulsive disorder and Tourette’s syndrome

Obsessive–compulsive disorder (OCD) and Tourette Syndrome (TS) are two common psychiatric disorders affecting approximately 1–3% of the population. Over the years, considerable progress has been made in conceptualizing these disorders, both clinically and genetically, from simple manifestations of psychological disturbances to highly polygenic, heritable disorders. Family and twin studies have shown that both disorders are familial, and partly influenced by genetic factors. Heritability estimates range between 0.26 and 0.60 for OCD, and 0.25 and 0.54 for TS, but despite this steady progress, results remain inconclusive regarding specific etiological genetic causes. Currently, a remarkable increase in international collaborative efforts within psychiatric genetics has opened new research possibilities, with larger datasets and multiple sources of genetic information available. This chapter provides a broad and updated overview of the genetics of OCD and TS and their genetic association. Historical evidence from past literature and recent results in light of current research are summarized.