Safety and Efficacy of KER-065 in Participants With Duchenne Muscular Dystrophy

Key Inclusion Criteria: * Diagnosis of DMD, defined as the presence of phenotypic features at screening consistent with DMD AND documented mutation in the dystrophin gene consistent with the diagnosis of DMD using a clinically validated genetic test. * Receiving a stable regimen of systemic CS (including, but not limited to, prednisone, prednisolone, deflazacort, or vamorolone) for at least 90 days before screening. * Body weight of ≥ 25.0 kg. Ambulatory Participants Only (Cohort A1 and A2): * Ambulatory, defined as able to walk independently without assistive devices. * Able to TTR in \< 10 seconds. * Has a NSAA score ≥ 15 points. * Cohort 2 only: Documentation of a stable dose of an approved exon-skipping therapy. Nonambulatory Participants Only (Cohort N1): * Nonambulatory, characterized as being unable to ambulate for a minimum of 3 months before first dose with onset of nonambulatory status AND a NSAA walk score of 0 and inability to perform the 10MWR. * PUL v2.0 entry item score of 3 to 5, inclusive. Key Exclusion Criteria: * Clinical symptoms or signs of cardiomyopathy or heart failure. * Exposure to any approved or investigational dystrophin restoration gene therapy product. * Exposure to any approved or investigational dystrophin restoration product other than gene therapy (Except for exon-skipping therapy for Cohort A2). * Exposure to any approved or investigational histone deacetylase inhibitor, antimyostatin therapy, therapy targeting transforming growth factor-beta ligands, or cell-based therapy. * Use of any other pharmacological treatment, except for CS * Treatment with immunosuppressant therapy (other than CS) * History of fracture of the upper limb Nonambulatory Participants Only (Cohort N1): * Elbow-flexion contractures \> 30° in both upper extremities. * Forced vital capacity (FVC) of \< 50% or requirement for daytime or nocturnal ventilation, except for nocturnal non-invasive ventilation AND inability to perform consistent FVC measurements within ± 15% during paired testing.