To detect potentially different effects of disease with age, we performed all analyses separately for pediatric and adult participants. We performed stratified analyses comparing the medicated group and unmedicated group of OCD patients separately to controls and to each other. Likewise, stratified analyses were performed to investigate effect of comorbid major depressive disorder, comorbid anxiety disorders, and OCD symptom dimensions (using the Yale-Brown Obsessive Compulsive Scale [Y-BOCS] and the Children’s Yale-Brown Obsessive Compulsive Scale [CY-BOCS] symptom checklist; see Supplementary Information SI2). To study the neurodevelopmental aspects of illness within the adult samples, we performed separate stratified analyses comparing childhood-onset OCD patients (onset <18 years) and adult-onset OCD patients (onset ≥18 years). Furthermore, we examined associations with age at onset, illness duration and illness severity (using the total severity score from the (C)Y-BOCS (23; 24)) as continuous variables. In these analyses, effect sizes were expressed as partial-correlation Pearson’s r after removing nuisance variables (age, sex, site and ICV). Throughout the manuscript, we report P-values corrected for multiple comparisons using the Benjamini-Hochberg procedure to ensure a false-discovery rate (FDR) limited at 5% for 70 cortical measures.
