• 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 clinical findings and prior confirmatory genetic testing using a clinical diagnostic genetic test

• 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:

‣ 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 VF) or history of at least one low-trauma long-bone fracture (upper or lower extremity) OR

‣ 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