The relationship between obsessive-compulsive symptoms and PARKIN genotype: The CORE-PD study

Background: Few studies have systematically investigated the association between PARKIN genotype and psychiatric co-morbidities of Parkison's disease (PD). PARKIN-associated PD is characterized by severe nigral dopaminergic neuronal loss, a finding that may have implications for behaviors rooted in dopaminergic circuits such as obsessive-compulsive symptoms (OCS). Methods: The Schedule of Compulsions and Obsessions Patient Inventory (SCOPI) was administered to 104 patients with early-onset PD and 257 asymptomatic first-degree relatives. Carriers of one and two PARKIN mutations were compared with noncarriers. Results: Among patients, carriers scored lower than noncarriers in adjusted models (one-mutation: 13.9 point difference, P=0.03; two-mutation: 24.1, P=0.001), where lower scores indicate less OCS. Among asymptomatic relatives, a trend toward the opposite was seen: mutation carriers scored higher than noncarriers (one mutation, P=0.05; two mutations, P=0.13). Conclusions: First, a significant association was found between PARKIN mutation status and obsessive-compulsive symptom level in both PD and asymptomatic patients, suggesting that OCS might represent an early non-motor dopamine-dependent feature. Second, irrespective of disease status, heterozygotes were significantly different from noncarriers, suggesting that PARKIN heterozygosity may contribute to phenotype.