OBJECTIVE: Type 1 interferons (IFNs) have been identified as potentially important measures of disease activity in Juvenile Dermatomyositis (JDM). An Interferon Response Gene-score (IRG-score) has been defined using NanoString technology and appears to correlate with disease activity in cross-sectional samples of JDM patients. This study aimed to determine if there is evidence of a correlation between disease activity and IRG-score, in patients with JDM, both early in disease course and longitudinally. METHODS: All patients attending JDM clinic in SickKids were approached to enrol in the Childhood Arthritis and Rheumatic Diseases (CARD) biobank. We identified patients with a diagnosis of JDM, enrolled between January 2015 and June 2022. NanoString IRG-score was calculated from extracted RNA. The Modified Disease Activity Score (mDAS) was calculated based on clinical data collected prospectively through SickKids JDM registry. Spearman's correlation was calculated using all enrolment visit samples, and linear mixed model regression was used for subjects with multiple samples. RESULTS: 43 subjects with 87 bio-samples were identified, including 18 treatment-naïve subjects. Spearman's correlation at the enrolment visit was strong (r CONCLUSION: This study shows evidence of a significant correlation between IRG-score and disease activity, which is maintained over time. This highlights the potential for IRG-score to be an important biomarker in JDM.