Inclusion Criteria:
* Previously participated in the SAT-3247-CL-101 parent clinical trials.
* Continued status of stable glucocorticosteroid dose or no glucocorticosteroid dose from parent clinical trial.
* Continued stable doses of prescription medicines (excluding glucocorticosteroids) and over-the-counter medicines and/or herbal supplements for supportive care from parent clinical trial.
* Ability to understand the nature of the trial and any hazards of participating.
* Ability to communicate satisfactorily with the investigator and physiotherapist and to participate in and comply with the requirements of the entire trial including scheduled visits, procedures, laboratory tests, questionnaires, wearable devices, and study restrictions.
* Willingness to give written consent or assent (if not of cognitive capacity of consent in the jurisdiction where the study is being conducted) and parent/legal guardian willing to give written consent to participate (if participant is not of cognitive capacity to consent) after reading the information and consent form, and after having the opportunity to discuss the trial with the investigator or their delegate.
* All participants, if sexually active, agree to follow the contraception requirements and sperm donation limitations of the trial as described in the protocol.
Exclusion Criteria:
* Presence of acute medical condition, chronic illness or history of chronic illness (other than DMD) sufficient to invalidate the participant's participation in the trial or make it unnecessarily hazardous in the judgment of the investigator.
* Participants expected to require spine surgeries or hospitalizations for non-acute health needs within 12 months.
* Participants with acute gastrointestinal symptoms (e.g., nausea, vomiting, diarrhea, heartburn) or acute infection (such as influenza) or a significant infection or known inflammatory process at Screening.
* Severe behavioral or cognitive problems that preclude participation in the study, in the opinion of the investigator.
* Development of symptomatic cardiomyopathy since completion of the parent trial.
* Inability to swallow tablets.
a. Tablets can be split or crushed and stirred into flavored beverages or food (e.g., apple sauce, yogurt) followed by immediate administration.
* Receipt of an investigational product (including prescription medicines and investigational devices) as part of another clinical trial since completion of the parent trial or in the follow-up period of another clinical trial at the time of Screening for this study.
a. Use of deflazacort or vamorolone in jurisdictions where these are considered investigational as they have not received health authority marketing authorization will not be exclusionary.
* Possibility that the participant will not cooperate with the requirements of the protocol or is unable or unwilling to comply with the study requirements according to investigator's decision.
* Employee, contractors, or consultants of the Sponsor, the CRO, and/or study site or their relatives.
