The 6MWD test was performed in a 30 meters long flat corridor, where the participant was instructed to walk as far as possible, back and forth around two cones, with the permission to slow down, rest, or stop if needed. Ambulation was assessed via the 6MWD test following standardized procedures by measuring the 6MWD in meters. Participants were not permitted to use assistive devices (walker, long leg braces, or short leg braces) during the 6MWD test.

Intent-to-treat (ITT) population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Overall number of participants analyzed' signifies participants evaluable for this outcome measure.

If the time taken to perform this test exceeded 30 seconds or if a participant could not perform this test due to disease progression, a value of 30 seconds was used. Change from baseline data has been reported.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable at specified timepoint.

If the time taken to perform this test exceeded 30 seconds or if a participant could not perform this test due to disease progression, a value of 30 seconds was used. Change from baseline data has been reported.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable at specified timepoint.

If the time taken to perform this test exceeded 30 seconds or if a participant could not perform this test due to disease progression, a value of 30 seconds was used. Change from baseline data has been reported.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable at specified timepoint.

If the time taken to perform this test exceeded 30 seconds or if a participant could not perform this test due to disease progression, a value of 30 seconds was used. Change from baseline data has been reported.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable at specified timepoint.

Upper and lower extremity myometry was performed using a myometer following standardized procedures. Muscle groups evaluated included knee flexors, knee extensors, elbow flexors, elbow extensors, and shoulder abductors. Bilateral assessments were done and 3 measurements were recorded from each muscle group on each side if possible. Mean values for the left and right sides were calculated.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for specified categories.

The SAM is a pedometer (worn on the ankle) that continuously records the number of steps per time interval. Participants were instructed to continue to wear the SAM for at least 9 consecutive days. SAM was used to record the number of strides/minute following each visit. A stride is the leg motion that begins when the foot with SAM leaves the floor and ends when the same foot touches the floor again (that is, a stride generally equals 2 steps). Mean activity period/day/visit was computed for each participant. Mean obtained during Screening (Week -6 to -1) and following Week 1 visit were used as baseline data for analysis. For each day, an active period was defined as the first time after 3:00 AM that greater than (>) 2 strides/minute were recorded to the last time prior to midnight that >2 strides/minute were recorded. Days were deleted on which such an active period was less than (<) 50 percent (%) of the mean active period across all days for that participant's visit.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

The SAM is a pedometer (worn on the ankle) that continuously records the number of steps per time interval. Participants were instructed to continue to wear the SAM for at least 9 consecutive days. SAM was used to record the number of strides/minute following each visit. A stride is the leg motion that begins when the foot with SAM leaves the floor and ends when the same foot touches the floor again (that is, a stride generally equals 2 steps). Mean total step count/day/visit during the active periods was computed for each participant. Mean obtained during Screening (Week -6 to -1) and following Week 1 visit were used as baseline data for analysis. For each day, an active period was defined as the first time after 3:00 AM that >2 strides/minute were recorded to the last time prior to midnight that >2 strides/minute were recorded. Days were deleted on which such an active period was <50% of the mean active period across all days for that participant's visit.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

The SAM is a pedometer (worn on the ankle) that continuously records the number of steps per time interval. Participants were instructed to continue to wear the SAM for at least 9 consecutive days. SAM was used to record the number of strides/minute following each visit. A stride is the leg motion that begins when the foot with SAM leaves the floor and ends when the same foot touches the floor again (that is, a stride generally equals 2 steps). Mean total step count/hour during the active periods for the days in a visit was computed for each participant. Mean obtained during Screening (Week -6 to -1) and following Week 1 visit were used as baseline data for analysis. For each day, an active period was defined as the first time after 3:00 AM that >2 strides/minute were recorded to the last time prior to midnight that >2 strides/minute were recorded. Days were deleted on which such an active period was <50% of the mean active period across all days for that participant's visit.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

SAM is a pedometer (worn on the ankle) that continuously records the number of steps per time interval. Participants were instructed to continue to wear the SAM for at least 9 consecutive days. SAM was used to record the number of strides/minute following each visit. A stride is the leg motion that begins when the foot with SAM leaves the floor and ends when the same foot touches the floor again (that is, a stride generally equals 2 steps). The maximum continuous 10-minute, 20-minute, 30-minute, and 60-minute total step counts were computed for each participant. Mean obtained during Screening (Week -6 to -1) and following Week 1 visit were used as baseline data for analysis. For each day, an active period was defined as the first time after 3:00 AM that >2 strides/minute were recorded to the last time prior to midnight that >2 strides/minute were recorded. Days were deleted on which such an active period was <50% of the mean active period across all days for that participant's visit.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure for specified categories.

SAM is a pedometer(worn on the ankle) that continuously records the number of steps per time interval. Participants were instructed to continue to wear the SAM for at least 9 consecutive days. SAM was used to record the number of strides/minute following each visit. A stride is the leg motion that begins when the foot with SAM leaves the floor and ends when the same foot touches the floor again. Proportion of time during active periods spent at low activity(≤15 steps/minute), medium activity(16-30 steps/minute), and high activity(>30 steps/minute) were computed for each participant. Mean obtained during Screening and following Week 1 visit were used as baseline data for analysis. For each day, an active period was defined as first time after 3:00 AM that >2 strides/minute were recorded to the last time prior to midnight that >2 strides/minute were recorded. Days were deleted on which such an active period was <50% of the mean active period across all days for that participant's visit.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure for specified categories.

HRQL was measured via the PedsQL. The generic core module (including physical, emotional, social and school functioning scales) comprises 23 questions and the fatigue-specific module (including general fatigue, sleep/rest fatigue, and cognitive fatigue scales) comprises an additional 18 questions. The PedsQL was completed by both the participant and/or a parent/caregiver. Examples of items in each of the generic core module scales include: "It is hard for me to run"; "I feel sad or blue"; "I cannot do things that other kids my age can do;" and "It is hard to pay attention in class." Each of the generic core module items was scored on a 5-point likert response scale from 0 (never a problem) to 4 (almost always a problem). Scores were transformed on a scale from 0 to 100 (0=100, 1=75, 2=50, 3=25, 4=0), with higher scores indicating better health-related quality of life. Change from Baseline was calculated by subtracting the Baseline value from the value at Week 48.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure for specified categories.

HRQL was measured via the PedsQL. The generic core module (including physical, emotional, social and school functioning scales) comprises 23 questions and the fatigue-specific module (including general fatigue, sleep/rest fatigue, and cognitive fatigue scales) comprises an additional 18 questions. The PedsQL was completed by both the participant and/or a parent/caregiver. Examples of items in each of the generic core module scales include: "It is hard for me to run"; "I feel sad or blue"; "I cannot do things that other kids my age can do;" and "It is hard to pay attention in class." Each of the generic core module items was scored on a 5-point likert response scale from 0 (never a problem) to 4 (almost always a problem). Scores were transformed on a scale from 0 to 100 (0=100, 1=75, 2=50, 3=25, 4=0), with higher scores indicating better health-related quality of life. Change from Baseline was calculated by subtracting the Baseline value from the value at Week 48.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure for specified categories.

HRQL was measured via the PedsQL. The fatigue-specific module (including general fatigue, sleep/rest fatigue, and cognitive fatigue scales) comprises an additional 18 questions. PedsQL was completed by both the participant and/or a parent/caregiver. Fatigue-specific module obtains information relating to items such as: "I feel too tired to do things that I like to do"; "I spend a lot of time in bed"; and "I have trouble remembering more than one thing at a time;" Each of the fatigue-specific module items was scored on a 5-point likert response scale from 0 (never a problem) to 4 (almost always a problem). Scores were transformed on a scale from 0 to 100 (0=100, 1=75, 2=50, 3=25, 4=0), with higher scores indicating less fatigue. Total score was the sum of all items over the number of items answered on all scales. Change from Baseline was calculated by subtracting the Baseline value from the value at Week 48.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

HRQL was measured via the PedsQL. The fatigue-specific module (including general fatigue, sleep/rest fatigue, and cognitive fatigue scales) comprises an additional 18 questions. The PedsQL was completed by both the participant and/or a parent/caregiver. Fatigue-specific module obtains information relating to items such as: "I feel too tired to do things that I like to do"; "I spend a lot of time in bed"; and "I have trouble remembering more than one thing at a time;" Each of the fatigue-specific module items was scored on a 5-point likert response scale from 0 (never a problem) to 4 (almost always a problem). Scores were transformed on a scale from 0 to 100 (0=100, 1=75, 2=50, 3=25, 4=0), with higher scores indicating less fatigue. Total score was the sum of all items over the number of items answered on all scales. Change from Baseline was calculated by subtracting the Baseline value from the value at Week 48.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

TSQM consisted of 14 questions about treatment satisfaction with drug in 4 domains: Effectiveness (Questions 1-3 scored as 1 [extremely dissatisfied] to 7 [extremely satisfied]), Side Effects (question 4 scored as 0 [no] or 1 [yes]; question 5 scored as 1 [extremely bothersome] to 5 [not at all bothersome]; questions 6 - 8 scored as 1 [a great deal] to 5 [not at all]), Convenience (questions 9 and 10 scored as 1 [extremely difficult] to 7 [extremely easy]; question 11 scored as 1 [extremely inconvenient] to 5 [extremely convenient]) and Global Satisfaction (question 12 scored as 1 [not at all confident] to 7 [extremely confident]; question 13 scored as 1 [not at all certain] to 5 [extremely certain]; question 14 scored as 1 [extremely dissatisfied] to 5 [extremely satisfied]). The scores of each of the domains were added together and an algorithm was used to create a score of 0 to 100, with higher scores indicating better treatment satisfaction.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure for specified categories.

Number of falls was determined by daily diary records maintained by participants and/or parent/caregivers.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

Basic attention and working memory was measured using the digit span task. A series of digits (0-9) were presented to the child in an auditory format only. The task had 2 parts; in the forward condition, the child was requested to repeat back the digits in the order they were presented and in the backward condition, he was requested to reverse the order of presentation. A raw score of the total number of correct responses was converted to an age-scaled-score (z-score) by subtracting the corresponding mean and dividing by the corresponding standard deviation of a reference population for that age.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure for specified categories.

The heart rate was measured with a Polar RS400 heart rate monitor, which consists of a transmitter strap worn around the chest and a wristwatch receiver. The monitor produces a digital text file with 1 value per minute that represents the mean heart rate for that minute. Mean heart rates values were collected prior to, during, and after the 6MWT. The participant rested for 5 minutes in a sitting position prior to the 6MWT, and the mean heart rate for the last minute of this rest period was collected and documented as the resting heart rate. During the 6MWT, the mean heart rate was collected and documented as the active heart rate. After completing the 6MWT and resting for 3 minutes, the mean heart rate for 1 minute was collected and documented as the recovery heart rate.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure for specified categories.

Blood samples collected for chemistry assays were used to quantify serum CK concentrations. Serum CK was assessed as a potential biomarker for muscle fragility, with a reduction in serum CK considered to be a positive outcome.

ITT population included all participants who were randomized and received any study treatment; and had a valid baseline, and at least one valid post-baseline 6MWD value. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

Immunofluorescence evidence of a change in dystrophin expression on biceps muscle biopsy was defined as an increase in the staining of the sarcolemmal membrane with an antibody to the C-terminal portion of the dystrophin protein (excluding revertant fibers) between the pre-treatment (1 week prior to Baseline visit) and post-treatment (Week 36) biopsies. The biceps muscle was biopsied from one arm for confirmation of the absence or reduced levels of dystrophin prior to treatment initiation and from the other arm to assess for production of dystrophin post-treatment.

As-treated population included all randomized participants who actually received any study treatment. Here, 'Number analyzed' signifies participants evaluable for this outcome measure at specified timepoint.

An AE was any untoward medical occurrence in a participant who received study drug without regard to possibility of causal relationship. Serious adverse event (SAE) was an AE resulting in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly. AEs included both SAEs and non-serious AEs. Treatment-emergent adverse event (TEAE) was defined as an adverse event that occurred or worsened in the period extending from first dose of study drug to 6 weeks after the last dose of study drug. A summary of other non-serious AEs and all SAEs, regardless of causality is located in the 'Reported AE section'.

As-treated population included all randomized participants who actually received any study treatment.

Study drug compliance was assessed by participant daily diary and quantification of used and unused study drug. Compliance was assessed in terms of the percentage of drug actually taken relative to the amount that should have been taken during the study.

As-treated population included all randomized participants who actually received any study treatment.