Genetics of obsessive-compulsive spectrum disorder: Does a major gene account for familial transmission?

Obsessive Compulsive Disorder (OCD) is a heterogeneous group of disorders probably due to a basal ganglia dysfunction such as Tourette's Syndrome (TS) and Idiopatic Dystonia (ID). It has been observed that some patients affected with ID have an increased risk for OCD and OC symptoms. We hypothesized a common etiologic basis for these disorders (spectrum OCD, TS, ID with OCD) and we evaluated the morbidity risk (MR) for OCD and TS/tic in first degree relatives. 110 OCD patients, 47 OCD patients with tics, 39 TS patients, 12 ID patients with OCD and 46 ID patients without OCD have been collected. In all patients' groups the MR for OCD ranges from 9.19% (TS patients) to 15.55% (OCD patients), while the OCD+tic/TS MR ranges from 17.86%(OCD patients) to 28.82% (TS patients), while the MR for ID patients without OCD is similar to general population. ID patients with OCD have an OCD MR (13.8%) similar to that of OCD+tic patients (12.35%). We applied a complex segregation analysis to these families and preliminary results indicates that a Mendelian model of transmission account for the role of a major gene in OCD+tic/TS and ID+OCD families (qA=0.034, AA penetrance = 100%, Aa and aa penetrance=0%).