Real-world outcomes of delandistrogene moxeparvovec gene therapy: Motor outcomes and emerging safety concerns

Delandistrogene moxeparvovec is currently the only commercially approved gene therapy for Duchenne muscular dystrophy (DMD). Herein, we report real-world data of 11 ambulatory patients with DMD, ages 4-6, treated with commercial delandistrogene moxeparvovec. Patients were prospectively and uniformly monitored for 1 year post-gene transfer for safety and motor outcomes. Nine patients experienced 15 treatment-related toxicities, and 4 required escalation of corticosteroids. Side effects included gastrointestinal symptoms (n = 7), liver enzyme abnormalities (n = 4), acute liver injury (n = 2), and troponin I elevations (n = 3). In both patients with acute liver injury, troponin I elevations occurred in close temporal association beginning 8-9 weeks post-gene transfer and were responsive to corticosteroids. The clinical courses of these two patients were at least partially consistent with a cellular immune response to the adeno-associated viral vector (AAV) capsid. Troponin I elevations were asymptomatic and without acute functional changes on echocardiogram. The cohort had improvements in year 1 motor function assessments relative to baseline, including a statistically significant median 4-point increase in North Star Ambulatory Assessment score; however, important confounding factors, e.g., baseline corticosteroid use, limit interpretation and will be important to control for in future real-world datasets. Additional follow-up is required to determine long-term safety and motor outcomes, with unclear generalizability of our results.