Phaseout DMD: A Phase 2 Clinical Study to Assess the Activity and Safety of Utrophin Modulation With Ezutromid in Ambulatory Paediatric Male Subjects With Duchenne Muscular Dystrophy (SMT C11005)

• Be able to provide written informed consent/assent as per local requirements.

• Be male.

• Have phenotypic evidence of dystrophinopathy based on the onset of characteristic clinical symptoms or signs (e.g., proximal muscle weakness, waddling gait, and Gowers' manoeuvre), an elevated serum creatinine kinase level, and ongoing difficulty with walking.

• Have prior confirmation of the duchenne muscular dystrophy (DMD) diagnosis through:

⁃ Documentation of the presence of a mutation in the dystrophin gene as determined by gene sequencing from a laboratory certified by the College of American Pathologists, the Clinical Laboratory Improvement Act/Amendment or an equivalent organisation or documentation of the absence of dystrophin in the muscle (via biopsy).

• Be able to undergo MRI examination.

• Participants must have used stable systemic corticosteroids (prednisone, prednisolone or deflazacort) for a minimum of 6 months immediately prior to the start of the Treatment Phase, with no significant change in dosage or dosing regimen (not related to body weight change) and a reasonable expectation that dosage and dosing regimen will not change significantly for the duration of the study.

• Confirmed screening laboratory values within the central laboratory ranges (haematology, renal and serum electrolyte parameters and serum chemistry parameters) or considered not clinically significant in the opinion of the Investigator. Variations in specific parameters expected in a DMD population classed by the Investigator as not clinically significant will not exclude the participant.

• Be willing and able to comply with scheduled visits, drug administration plan, study procedures, laboratory tests and study restrictions.

⁃ Cohort 1 and 2 Specific Inclusion Criteria:

• Be aged ≥5 years to \<10 years of age (from 5th birthday to 10th birthday).

• Be willing and able to comply with 2 muscle biopsy procedures.

• Have the ability to walk at least 300 meters unassisted during the screening 6 minute walk distance (6MWD) and be below the protocol-specified threshold for 80%-predicted 6MWD.

• Have results of 2 6MWD by Baseline determined as valid. The results of the second 6MWD (baseline) must be within 20% of the first 6MWD (screening).

• Have cardiac echocardiogram (ECHO) measurements showing an ejection fraction of ≥55% and fractional shortening of ≥28%.

⁃ Cohort 3 Specific Inclusion Criteria:

• Have taken part in a prior SMT C1100 study.