To assess change from baseline in North Star Ambulatory Assessment(NSAA) Total Score at Wk52. NSAA is clinician-reported outcome instrument designed to measure ambulatory function in males with Duchenne muscular dystrophy(DMD). Patients asked to perform 17 different functional activities,including 10MWT,rising from sit to stand,standing on one leg,climbing & descending a step,stand from supine, lifting the head, standing on heels, & jumping. Each function activity will be scored as0=(unable to achieve independently),scored as1=(modified method but achieves goal independent of physical assistance from another),or scored as2=(no obvious modification of activity)or "Not Scored". If NSAA test was performed & any of the individual items are scored as "not scored"(i.e, for reasons unrelated to patients physical capabilities), corresponding total score will be set to missing. Sum of 17 scores will be used to form an ordinal total score(range 0-34).Higher scores imply better functional status

Full Analysis population: All patients in the Randomized Population who received at least 1 dose of study drug and provided at least 1 valid post Baseline NSAA efficacy assessment.

To assess the changes from baseline to Week 52 on the 10-meter walk/run test (10MWT). For timed function tests (TFTs), the time will be set to 12 seconds and the speed to 0 if the TFT assessment meets the following TFT grading criteria. Grade of 1 or 2 (from a 6-point scale). 1=Unable to walk independently 2=Unable to walk independently but can walk with knee-ankle foot orthoses or support from a person 3=Highly adapted wide based lordotic gait. Cannot increase walking speed 4=Moderately adapted gait. Can pick up speed but cannot run 5=Able to pick up speed, but runs with a double stance phase, i.e. cannot achieve both feet off the ground 6=Runs and gets both feet off the ground (with no double stance phase)

Full Analysis population: All patients in the Randomized Population who received at least 1 dose of study drug and provided at least 1 valid post Baseline NSAA efficacy assessment.

To assess the change from baseline in the stand from supine speed at Week 52. For timed function tests (TFTs) , the time will be set to 12 seconds and the speed to 0 if the TFT assessment meets the following TFT grading criteria. Grade of 1 or 2 (from a 6-point scale). 1 = Unable to stand from supine, even with use of a chair, 2 = Assisted Gowers - requires furniture for assist in arising from supine to full upright posture (no time to be recorded) 3=Rolls over, stands up with both hands "climbing up" the legs to achieve full upright posture 4=Rolls over, stands up with 1 hand support on leg 5=Rolls to the side and stands up with one or both hands on the floor to start to rise but does not touch legs 6=Stands up without rolling over or using hands on legs or floor

Full Analysis population: All patients in the Randomized Population who received at least 1 dose of study drug and provided at least 1 valid post Baseline NSAA efficacy assessment.

To assess the change from baseline to Week 52 on the 4-Stair Climb. For timed function tests (TFTs) , the time will be set to 12 seconds and the speed to 0 if the TFT assessment meets the following TFT grading criteria. Grade of 1(from a 6-point scale)1=Unable to climb 4 standard stairs(no time recorded) 2=Climbs 4 standard stairs "marking time"(climbs one foot at a time, with both feet on a step before moving to next step), uses both arms on one or both handrails or uses 1 handrail and the other arm pushes on the leg 3=Climbs 4 standard stairs "marking time", using one arm on one handrail or one hand pushing on leg or body 4=Climbs 4 standard stairs "marking time", not needing handrail and not using hands to push on leg 5=Climbs 4 standard stairs alternating feet, needs handrail/s for support or uses arms to push on the leg or body 6=Climbs 4 standard stairs alternating feet, not needing handrail support or using arm to push on the leg

Full Analysis Population: All patients in the Randomized Population who received at least 1 dose of study drug and provided at least 1 valid post Baseline NSAA efficacy assessment).

Adverse events that occurred from the time of the administration of the first dose of investigational product (IP) through the end of the safety follow-up were considered treatment-emergent AEs (TEAEs). Serious adverse event (SAE).

Safety population: All patients who received at least 1 dose of study drug, with patients analyzed based on the actual study treatment received. This included the set of patients who were assigned the same treatment as their randomized sibling.