Upon joining the study, an initial assessment is conducted to confirm eligibility. This includes verifying that the participant has previously received delandistrogene moxeparvovec for Duchenne muscular dystrophy in a prior clinical study.

The participant or their legal caregiver must demonstrate the ability to understand and comply with the study visit schedule and protocol requirements.

The study involves the administration of delandistrogene moxeparvovec, which is a solution for injection or infusion given intravenously.

This step is a follow-up to the initial treatment received in a previous study and does not involve new administration during this trial.

Participants are monitored for any treatment-emergent adverse events, serious adverse events, and adverse events of special interest.

The study aims to evaluate the long-term safety of delandistrogene moxeparvovec over a period of up to five years post-infusion.

Changes in physical abilities are assessed using various measures, including the North Star Ambulatory Assessment, time to rise from the floor, and time for a 10-meter walk or run.

These assessments are conducted from the pre-infusion baseline to five years post-infusion.

Changes in respiratory function are evaluated through measures such as forced vital capacity and peak expiratory flow percent predicted.

Cardiac function is assessed using cardiac magnetic resonance imaging (MRI) findings.

Musculoskeletal MRI findings are evaluated to assess any changes from the pre-infusion baseline to five years post-infusion.

The study is estimated to conclude by November 15, 2030, with all assessments and evaluations completed by this date.