Safety, Tolerability, and Efficacy of Viltolarsen in Boys With Duchenne Muscular Dystrophy Amenable to Exon 53 Skipping: A Phase 2 Randomized Clinical Trial.

Importance: An unmet need remains for safe and efficacious treatments for Duchenne muscular dystrophy (DMD). To date, there are limited agents available that address the underlying cause of the disease.

Objective: To evaluate the safety, tolerability, and efficacy of viltolarsen, a novel antisense oligonucleotide, in participants with DMD amenable to exon 53 skipping.

Orthogonal analysis of dystrophin protein and mRNA as a surrogate outcome for drug development.

Detection of drug-induced dystrophin in patient muscle biopsy is a surrogate outcome measure for Duchenne muscular dystrophy. We sought to establish and validate an orthogonal approach to measurement of dystrophin protein and RNA in muscle biopsies. Validated methods were developed for dystrophin western blotting, mass spectrometry, immunostaining and reverse transcriptase PCR of biopsy mRNA using muscle biopsy standards.