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

Inclusion Criteria: 1. Patient has completed the NS-065/NCNP-01-301 study; 2. Patient's parent(s) or legal guardian(s) has (have) provided written informed consent and Health Insurance Portability and Accountability Act authorization, where applicable, prior to any study-related procedures; patients will be asked to give written or verbal assent according to local requirements; 3. Patient and parent(s)/guardian(s) are willing and able to comply with scheduled visits, investigational product (IP) administration plan, and study procedures. Exclusion Criteria: 1. Patient had an adverse event in Study NS-065/NCNP-01-301 that, in the opinion of the investigator and/or the sponsor, precludes safe use of viltolarsen for the patient in this study; 2. Patient had a treatment which was made for the purpose of dystrophin or dystrophin-related protein induction after completion of Study NS-065/NCNP-01-301; 3. Patient took any other investigational drug(s) during or after completion of Study NS-065/NCNP-01-301; 4. Patient is judged by the investigator and/or the sponsor not to be appropriate to participate in the extension study for any reason.