Children's National

• Has a definitive diagnosis of DMD prior to Screening based on documentation of clinical findings and confirmatory genetic testing. Among participants recruited from routine clinical practice: - Is aged 4 through 5 years at the time of enrollment. - Is ambulatory per protocol specified criteria. - Is currently receiving or has been prescribed to start chronic glucocorticoid therapy at the time of this observational study enrollment. For Delandistrogene Moxeparvovec-exposed Participants: - Will be initiating usual care treatment with delandistrogene moxeparvovec at the time of study enrollment. For Comparators: - Is unexposed to DMD gene therapy at the time of study enrollment.

Among participants recruited from routine clinical practice: - Has any deletion of exon 8 and/or exon 9 in the DMD gene. - Is currently participating in any DMD interventional study at the time of this observational study enrollment. - Has a medical condition or confounding circumstances (for example, prior traumatic limitation for mobility or significant behavioral comorbidity) that, in the opinion of the Investigator, might compromise: - The participant's ability to comply with the protocol-required procedures, - The participant's wellbeing or safety, and/or - The clinical interpretability of the data collected from the participant. Other inclusion/exclusion criteria may apply.