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

Key Inclusion Criteria:

• Signed Informed Consent Form and Signed Assent Form when appropriate

• Male at birth

• A definitive diagnosis of DMD prior to screening based on documentation of clinicalfindings and prior confirmatory genetic testing using a clinical diagnostic genetictest

• Age ≥ 8 and < 18 years at the time of signing Informed Consent Form

• 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:

1. Prior history of low-trauma fracture defined as: evidence of at least oneprevalent vertebral compression fracture of Genant Grade 1 or 2 (orradiographic signs of VF) or history of at least one low-trauma long-bonefracture (upper or lower extremity) OR

2. Non-ambulatory, characterized as being non-ambulatory for a minimum of 6 monthswith onset of non-ambulatory status defined as participant- orcaregiver-reported age of continuous wheelchair use approximated to the nearestmonth, and an North Star Ambulatory Assessment (NSAA) walk score of "0" andinability to perform the 10-Meter Walk/Run (10 MWR) at the baseline visit, withor without fractures

• Group 2 participants are required to meet the following criteria:

• Be fracture naïve, defined as: no history of prior low-trauma fractures beforethe baseline visit nor any radiological findings indicative of prevalent VF atthe screening visit

• Be ambulatory defined as able to walk independently without assistive devices

• Age ≥ 8 to < 12 years old at the time of screening

• Daily oral corticosteroids

Key Exclusion Criteria:

• Major surgery (e.g. spinal surgery) within 3 months prior to Baseline or plannedsurgery or procedure that would interfere with the conduct of the study for any timeduring this study

• Presence of any clinically significant illness

• Has serological evidence of current, chronic, or active human immunodeficiency virus (HIV), tuberculosis (TB), hepatitis C, or hepatitis B infection

• Has a symptomatic infection (e.g. upper respiratory tract infection, pneumonia,pyelonephritis, meningitis) within 4 weeks prior to baseline

• Body weight at screening <20 or > 100 kg

• Evidence of a severe vertebral fracture (VF) (defined as Grade 3), assessed byradiographic imaging at screening and quantified using the Genant semiquantitativemethod

• Treatment with prohibited therapies as defined by the protocol

• Has received a live or live attenuated virus vaccine within 6 weeks of the Baselinevisit or expects to receive a vaccination during the first 3 months after Baseline.

• Has abnormal laboratory values considered clinically significant as defined by theprotocol

• Any medical condition that might interfere with the evaluation of LS BMD, such assevere scoliosis or spinal fusion.

• Participant has previous or ongoing medical condition, medical history, physicalfindings or laboratory abnormalities that could affect safety, make it unlikely thattreatment and follow-up will be correctly completed or impair the assessment ofstudy results, in the opinion of the investigator

• Participant has an allergy or hypersensitivity to the study medication or to any ofits constituents

Other protocol defined inclusion and exclusion criteria may apply