Challenges in OCD research: Overcoming heterogeneity

Introduction Obsessive–compulsive disorder (OCD) is a neuro-psychiatric condition characterized by recurrent, intrusive, and distressing thoughts, images, or impulses (obsessions) and repetitive mental or behavioral acts that the individual feels driven to perform (compulsions) to prevent or reduce distress. OCD typically starts in childhood or adolescence, persists throughout a person's life (Skoog & Skoog 1999), and produces substantial impairment in social, family, and work functioning (Koran 2000). With a lifetime prevalence of up to 2–3% (Kessler et al. 2005), the World Health Organization characterizes OCD among the 10 most disabling of all medical and psychiatric conditions in the industrialized world (Murray & Lopez 1996). Obsessions and compulsions are remarkably diverse, and are expressed with great variability both within and across patients over time (Rasmussen & Eisen 1988). Besides differing in the content of their symptoms, OCD patients differ in their course of illness (e.g., early versus late onset) and comorbidity (e.g., tic-related versus non-tic-related OCD). This heterogeneity in the clinical phenotype significantly complicates research on OCD, potentially obscuring findings and reducing power in studies of pathophysiology (including the search for vulnerability genes), course, and treatment outcome. >To advance our understanding of the clinical, neurobiological, and genetic features of OCD, researchers have been actively pursuing strategies for dissecting the heterogeneous phenotype into less complex, more homogeneous components.