Commonest lifetime comorbidities differed across adult and paediatric subgroups. Anxiety disorders were the most common in children, vs. mood disorders in adults. These perhaps reflect etiopathological origins and natural history of these disorders. Anxious temperament traits such as high harm avoidance (78) and shyness/behavioural inhibition (79) are seen in children with anxiety disorders and OCD. As such, a shared developmental/temperamental vulnerability may lead to emergence of both disorder types at a young age (80, 81). Compulsive behaviours possibly provide anxious youth with increased perceived control over uncertainty, given that they have less direct control over their environment than adults (80). A shared vulnerability to anxiety could also explain our findings of an association between lower AOO of OCD and higher comorbid rates of GAD. In comparison, onset of mood disorders (regardless of OCD comorbidity) tends to occur after that of anxiety disorders, and often in adulthood (82). The high lifetime prevalence of mood disorders in adults could suggest a secondary impact of OCD over time, i.e., resultant from cumulative patterns of avoidance, increased negative emotional states, impairment, and reduced quality of life.
