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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 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 planned surgery or procedure that would interfere with the conduct of the study for any time during this study
* Presence of any clinically significant illness
* Has serological evidence of current, chronic, or active human immunodeficiency virus (HIV), tuberculosis (TB), hepatitis C virus (HCV), or hepatitis B virus (HBV) 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 kilograms (kg)
* Evidence of a severe VF (defined as Grade 3), assessed by radiographic imaging at screening and quantified using the Genant semiquantitative method
* Treatment with prohibited therapies as defined by the protocol
* Has received a live or live attenuated virus vaccine within 6 weeks of the baseline visit or expects to receive a live or live attenuated virus vaccine during the study
* Has abnormal laboratory values considered clinically significant as defined by the protocol
* Any medical condition that might interfere with the evaluation of LS BMD, such as severe scoliosis or spinal fusion
* Participant has previous or ongoing medical condition, medical history, physical findings or laboratory abnormalities that could affect safety, make it unlikely that treatment and follow-up will be correctly completed or impair the assessment of study results, in the opinion of the investigator
* Participant has an allergy or hypersensitivity to the study medication or to any of its constituents. Other protocol defined inclusion and exclusion criteria may apply

• Little Rock, Arkansas, United States
• Sacramento, California, United States
• Atlanta, Georgia, United States
• Grand Rapids, Michigan, United States
• Flower Mound, Texas, United States
• Norfolk, Virginia, United States
• København Ø, Denmark
• Rome, Lazio, Italy
• Milan, Lombardy, Italy
• Gdansk, Poland
• Lodz, Poland
• Warsaw, Poland
• Esplugues de Llobregas, Barcelona, Spain
• Asturias, Principality of Asturias, Spain
• Almería, Spain
• Valencia, Spain
• Kyiv, Ukraine
• Lviv, Ukraine