The Expanded Access Use of Viltolarsen in Duchenne Muscular Dystrophy With Confirmed Exon 53 Amenable Mutation

Inclusion Criteria: * Male ≥ 3 and ≤ 12 years of age * Clinical signs compatible with DMD * Confirmed DMD mutation(s) in the dystrophin gene that is amenable to skipping of exon 53 to restore the dystrophin messenger ribonucleic acid (mRNA) reading frame * Able to walk independently without assistive device * Not able to participate in a Phase 3 trial Exclusion Criteria: * Chronic systemic fungal or viral infections * An acute illness within 4 weeks prior to the first dose of viltolarsen * Symptomatic cardiomyopathy * Patient has a previous or ongoing medical condition, medical history, physical findings, or laboratory abnormality that could affect participant safety in the opinion of the treating physician * Surgery within the 3 months prior to the first anticipated administration of viltolarsen and in the opinion of the treating physician would impact weekly treatment schedule * Positive test results for hepatitis B antigen, hepatitis C antibody, or human immunodeficiency virus (HIV) antibody at screening * Currently taking any other investigational drug or has taken any other investigational drug within 3 months prior to the first dose of viltolarsen * Previously enrollment in any viltolarsen study. * Currently taking any other exon skipping agent or has taken any other exon skipping agent within 2 weeks prior to the first dose of viltolarsen (would need to be discontinued in order to be eligible) * Any gene therapy for DMD * Inadequate renal function as defined by a serum cystatin C \> 1.5 x upper limit of normal (ULN). If the value is \> 1.5 x ULN then the measurement can be repeated once. If repeat measurement is still \> 1.5 x ULN then the patient should be excluded.