Study to Assess the Efficacy and Safety of Viltolarsen in Ambulant Boys With DMD (RACER53)

This is a Phase 3 randomized, double-blind, placebo-controlled, multi-center study to assess the efficacy and safety of Viltolarsen in ambulant boys with Duchenne muscular dystrophy. Eligible patients with out-of-frame deletion mutations amenable to exon 53 skipping will be randomized to receive once weekly intravenous (IV) infusions of 80 mg/kg Viltolarsen or placebo for up to 48 weeks. The study will enroll approximately 74 patients amenable to exon 53 skipping. Clinical efficacy will be assessed at regularly scheduled study visits, including functional tests such as Time to Stand Test (TTSTAND), Time to Run/Walk 10 Meters Test (TTRW), Six-minute Walk Test (6MWT), North Star Ambulatory Assessment (NSAA), Time to Climb 4 Steps Test (TTCLIMB) and Hand-held dynamometer (elbow extension, elbow flexion, knee extension and knee flexion on the dominant side only). Safety will be assessed through the collection of adverse events (AEs), laboratory tests, electrocardiograms (ECGs), vital signs, and physical examinations throughout the study. Blood samples will be taken periodically throughout the study to assess the pharmacokinetics of study drug.