age (34.4 vs. 40.1 years) and gender distribution (males 52.7 and 45%) within their samples. In comparing comorbid anxiety disorder rates, studies by Deacon et al. (17) and Mancebo et al. (16) differ with respect to age (35.8 vs. 40.1 year mean), age of onset of OCD (16.7 vs. 18.5 year mean), gender distribution (51 vs. 45%), and illness severity [Yale-Brown Obsessive Compulsive Scale (Y-BOCS) (22, 23) mean score 24 vs. 20.6]. Studies conducted with a primary aim to examine clinical variations by age, gender, etc., echo these observations (24–27), with differences particularly notable between paediatric samples (e.g., higher rates of NDDs like attention deficit hyperactivity disorder (ADHD) (28, 29) and adult samples (e.g., higher rates of mood disorders and anxiety disorders) (30, 31). Observed differences in comorbidity profiles across age possibly reflect variations in the relative etiopathological roles of genetic, neurobiological, and environmental factors (27, 32, 33). OCD presenting with comorbid illnesses tends to be more severe, with a more chronic course, and higher negative consequences on daily life functioning (34). It is also possible that changing diagnostic criteria and conceptualizations over time influence comorbidity rates.
