A Study to Assess the Efficacy and Safety of Satralizumab in Duchenne Muscular Dystrophy (DMD)

Key Inclusion Criteria: * Signed Informed Consent Form (ICF) and signed Assent Form when appropriate * Male at birth * A definitive diagnosis of DMD prior to screening based on documentation of clinical findings and prior confirmatory genetic testing using a clinical diagnostic genetic test * Age ≥ 8 and \< 18 years at the time of signing ICF * Group 1 participants are required to meet the following criteria: - Ambulatory (defined as able to walk independently without assistive devices) with a prior history of fractures: a) Prior history of low-trauma fracture defined as: evidence of at least one prevalent vertebral compression fracture of Genant Grade 1 or 2 (or radiographic signs of vertebral fractures \[VF\]) or history of at least one low-trauma long-bone fracture (upper or lower extremity) or b) Non-ambulatory, characterized as being non-ambulatory for a minimum of 6 months with onset of non-ambulatory status defined as participant- or caregiver-reported age of continuous wheelchair use, approximated to the nearest month, and an North Star Ambulatory Assessment (NSAA) walk score of "0" and inability to perform the 10-Meter Walk/Run (10 MWR) at the baseline visit, with or without fractures * Group 2 participants are required to meet the following criteria: - Be fracture-naïve, defined as: no history of prior low-trauma fractures before the baseline visit nor any radiological findings indicative of prevalent VF at the screening visit - Be ambulatory defined as able to wal…