Obsessive-compulsive disorder (OCD) is now recognized as a frequent and disabling disorder among children and adolescents. The phenomenology is similar to adult OCD, but several reports have indicated that compulsions are more prominent in children and that children are more inclined than adults to include their family surroundings in ritualistic behavior. It is also clear that young children engage in a significant amount of repetitive, ritualistic compulsive activity that appears to be a normal part of their behavioral repertoire.
Although the cause of childhood-onset OCD is unknown, many factors are likely to contribute to the heterogenous clinical phenotypes, including both genetic and environmental factors. The neurobiological circuitry involved in childhood-onset OCD is likely to involve alterations to the same cortico-striatothalamic circuitry implicated in adult OCD, but the develop-mental differences have yet to be fully delineated. The treatment response patterns of adults and children are generally inconsis-tent with each other, and specific OCD subtypes may also respond differentially.
Phenotypic characterization can be undertaken either categorically, as seen with traditional diagnostic categories, or dimensionally. Extended phenotypes can be defined in terms of symptoms and course of the illness, or neuroimaging and neurobiologic study findings, or treatment responses. Phenotypic characterization must also reflect an understanding of the rituals and repetitive behaviors that are associated with normal development. (A proposed categorization of OCD subtypes appears in the “Table library.”)