Long-term Use of Viltolarsen in Boys With Duchenne Muscular Dystrophy in Clinical Practice (VILT-502)

Inclusion Criteria: 1. Patient, patient's parent or legal guardian have provided written informed consent/medical record release authorization prior to any extension study-specific procedures, and the patient has provided assent appropriate for his age and developmental status. 2. Patient completed the NS-065/NCNP-01-202 study and was judged by the investigator as appropriate to participate in the VILT-502 study. 3. Patient and parent or legal guardian are willing and able to comply with scheduled visits, study treatment administration plan, and study procedures. Exclusion Criteria: 1. Patient has an allergy or hypersensitivity to the study drug or to any of its constituents. 2. Patient has severe behavioral or cognitive problems that preclude participation in the study, in the opinion of the investigator. 3. Patient has previous or ongoing medical condition, medical history, physical findings or laboratory abnormalities that could affect safety, make it unlikely that treatment and observation will be correctly completed or impair the assessment of study results, in the opinion of the investigator. 4. Patient had a treatment which was made for the purpose of dystrophin or its related protein induction after completing the NS-065/NCNP-01-202 study. 5. Patient took any other investigational drugs after completing the NS-065/NCNP-01-202 study. 6. Patient plans to participate in another clinical trial. 7. Patient was judged by the investigator and/or the Sponsor as not appropriate to participate in the study for reasons other than #1 - #6 above.