NS-089/NCNP-02-201 in Boys With Duchenne Muscular Dystrophy (DMD)

Inclusion Criteria: * Male ≥ 4 years and \<15 years of age * Confirmed DMD mutation(s) in the dystrophin gene that is amenable to skipping of exon 44 to restore the dystrophin mRNA reading frame * Able to walk independently without assistive devices * Ability to complete the TTSTAND without assistance in \<20 seconds * Stable dose of glucocorticoid for at least 3 months and the dose is expected to remain on a stable dose for the duration of the study. * Other inclusion criteria may apply. Exclusion Criteria: * Has a body weight of \<20 kg at the time of informed consent (applies to participants screening for Part 1 only) * Evidence of symptomatic cardiomyopathy * Current or previous treatment with anabolic steroids (e.g., oxandrolone) or products containing resveratrol or adenosine triphosphate within 3 months prior to first dose of study drug * Current or previous treatment with any other investigational drug within 3 months prior to the first dose of study drug or within 5 times the half-life of a medication, whichever is longer * Surgery within the 3 months prior to the first dose of study drug or planned during the study duration * Previously treated in an interventional study of NS-089/NCNP-02 * Having received exon skipping oligonucleotide within 1 year prior to the first dose of IP * Other exclusion criteria may apply.