Obsessive-compulsive disorder (OCD) [MIM 164230] and Tourette Syndrome (TS) [MIM 137580] are highly familial neuropsychiatric disorders with complex overlapping genetic etiologies (1–3). 20–60% of TS-affected individuals have co-occurring OCD, and 10–20% of those initially diagnosed with OCD have TS or chronic tics (CT), well over what is expected based on their respective population prevalences (4–6). Both disorders are characterized by the presence of repetitive, ritualized or stereotyped behaviors (tics and compulsions), often preceded by cognitive or sensory phenomena (premonitory urges and obsessions), and clinical differentiation of compulsions versus complex tics can be challenging (7). Genetic epidemiological studies suggest up to 90% shared genetic variance between TS/CT and OCD (8–10), and abnormalities in cortico-striatal-thalamo-cortical (CSTC) circuitry have been identified in both conditions (1).
