Twelve-lead ECGs were performed at a consistent time of day throughout the study. Electrocardiograms were performed only after the participant was in the supine position, resting, and quiet for a minimum of 15 minutes. The ECG was manually reviewed and interpreted by medically qualified personnel. Number of participants with potentially clinically significant abnormalities in ECG reported as TEAEs presented here. The Investigator determined whether abnormal assessment results were potentially clinically significant or not.

Standard, 2-dimensional ECHOs were performed at a consistent time of day throughout the study. Cardiac function events included cardiomegaly, tachycardia, and dyspnoea. The ECHO was reviewed and interpreted by medically qualified personnel. Number of participants with potentially clinically significant abnormalities in ECHO were reported.

6MWT was performed by standardized procedures for all participants. Participants were asked to walk a set course of 25 meters for 6 minutes (timed), and the distance walked (in meters) was recorded. Change from baseline in 6MWT distance at Week 144 in total golodirsen group was reported.

6MWT was performed by standardized procedures for all participants. Participants were asked to walk a set course of 25 meters for 6 minutes (timed), and the distance walked (in meters) was recorded. Change from baseline in 6MWT distance at Week 144 in untreated group (non-exon 53 amenable participants) was calculated.

Change from baseline in dystrophin protein levels (in muscle biopsy samples) was determined by Western blot in total golodirsen group.

Area under the concentration-time curve from time zero extrapolated to the infinity was evaluated.

Volume of distribution was defined as the theoretical volume in which the total amount of drug would need to be uniformly distributed to produce the desired plasma concentration of a drug. Apparent volume of distribution at steady state of golodirsen was evaluated.

T1/2 is the time measured for the plasma concentration of drug to decrease by one half. T1/2 of golodirsen was evaluated.

Drug clearance is a quantitative measure of the rate at which a drug substance is removed from the blood.

MRT= AUMCinf/AUCinf, where AUMCinf is the area under the first moment curve from time 0 extrapolated to infinite time, calculated using the linear/log trapezoidal method. Mean residence time of golodirsen was evaluated.

Renal clearance was calculated using the partial AUC0-24 from the non-compartmental analysis in plasma and AE0-24. AUC0-24 was defined as area under the plasma concentration-time curve, from time 0 to 24 hours after completion of dosing. AE0-24 was defined as total cumulative amount excreted from 0 to 24 hours. Summarized data of all urine collection intervals are reported.

FVC was the total amount of air exhaled during the forced expiratory volume test that was measured during spirometry and the most important measurement of lung function. This test required participant to breath into a tube connected to a machine that measures the amount of air that can be moved in and out of the lungs after taking an inhaled bronchodilator medicine which was used to dilate participant bronchial (breathing) tubes. Percent of predicted FVC = (observed value)/ (predicted value) * 100%.

FVC was the total amount of air exhaled during the forced expiratory volume test that was measured during spirometry and is the most important measurement of lung function. This test requires participant to breath into a tube connected to a machine that measures the amount of air that can be moved in and out of the lungs after taking an inhaled bronchodilator medicine which was used to dilate participant bronchial (breathing) tubes. Percent of predicted FVC = (observed value)/ (predicted value) * 100%.

Change from baseline in dystrophin Intensity levels (in muscle biopsy samples) was determined by Immunohistochemistry in total golodirsen group.

Percent change from baseline in Exon 53 skipping (in muscle biopsy samples) was determined by reverse transcription polymerase chain reaction in total golodirsen group.

Percent change from baseline in dystrophin positive fibers (in muscle biopsy samples) were determined by Immunohistochemistry at Week 48 in total golodirsen group.

All participants from Part 1 (who previously received placebo or golodirsen) and including additional new participants received golodirsen 30 milligram (mg)/kilogram (kg) once weekly, for up to 168 weeks. Dosing was interrupted or halted when any specific predefined stopping criteria was met or if warranted at the discretion of the Sponsor or Investigator.

Untreated participants intended to evaluate the natural history of the disease with DMD and various genetic mutations (not amenable to exon 53 skipping) were included in this group and did not received any treatment. Participants underwent the same study assessments as treated participants in other reporting groups (except for PK sampling and muscle biopsies), but at a reduced schedule through Week 144. Thus, the untreated participants were not considered as control group.

Total of all reporting groups

All participants who were previously randomized in Part 1 were moved to Part 2a (after completion of Part 1, n=12) along with 13 new participants. Hence, total number of participants in Part 2a were 25. In Part 2b, 14 untreated new participants were enrolled.

All participants who were previously randomized in Part 1 were moved to Part 2a (after completion of Part 1, n=12) along with 13 new participants. Hence, total number of participants in Part 2a were 25. In Part 2b, 14 untreated new participants were enrolled.

All participants who were previously randomized in Part 1 were moved to Part 2a (after completion of Part 1, n=12) along with 13 new participants. Hence, total number of participants in Part 2a were 25. In Part 2b, 14 untreated new participants were enrolled.

Participants received golodirsen IV infusions, at dose levels of 4 mg/kg, once weekly for 2 weeks in Part 1.

Participants received golodirsen IV infusions, at a dose levels of 10 mg/kg, once weekly for the next 2 weeks (i.e., up to Week 4) in Part 1.

Participants received golodirsen IV infusions, at a dose level of 20 mg/kg, once weekly for the next 2 weeks (i.e., up to Week 6) in Part 1.

Participants received golodirsen IV infusions, at a dose level of 30 mg/kg, once weekly from Week 7 to Week 12 in Part 1.

Laboratory parameters included hematology, serum chemistry (SC), urinalysis and coagulation. Number of participants with at least one potentially clinically significant abnormal finding were reported as TEAEs. The Investigator determined whether abnormal assessment results were potentially clinically significant or not. Potentially clinical significance was defined as any variation in assessment results that had medical relevance resulting in an alteration in medical care.

Part 1 safety set included all randomized participants who received at least one dose of study drug.

Vital sign parameters included systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and body temperature. Number of participants with at least one potentially clinically significant abnormal vital signs findings were reported as TEAEs. The Investigator determined whether abnormal assessment results were potentially clinically significant or not. Potential clinical significance was defined as any variation in assessment results that had medical relevance resulting in an alteration in medical care.

Part 1 safety set included all randomized participants who received at least one dose of study drug.

Physical examinations were performed by the Investigator, or qualified study staff. A full physical examination included a review of general appearance, head, eyes, ears, nose and throat, heart, lungs, abdomen, extremities, skin, lymph nodes, musculoskeletal, and neurological systems. Number of participants with potentially clinically significant abnormalities in physical examinations were reported. Potentially clinically significant abnormalities in physical examinations were based on Investigator's discretion.

Part 1 safety set included all randomized participants who received at least one dose of study drug.

Twelve-lead ECGs were performed at a consistent time of day throughout the study. Electrocardiograms were performed only after the participant was in the supine position, resting, and quiet for a minimum of 15 minutes. The ECG was manually reviewed and interpreted by medically qualified personnel. Number of participants with potentially clinically significant abnormalities in ECG reported as TEAEs presented here. The Investigator determined whether abnormal assessment results were potentially clinically significant or not.

Part 1 safety set included all randomized participants who received at least one dose of study drug.

Standard, 2-dimensional ECHOs were performed at a consistent time of day throughout the study. Cardiac function events included cardiomegaly, tachycardia, and dyspnoea. The ECHO was reviewed and interpreted by medically qualified personnel. Number of participants with potentially clinically significant abnormalities in ECHO were reported.

Part 1 safety set included all randomized participants who received at least one dose of study drug.

6MWT was performed by standardized procedures for all participants. Participants were asked to walk a set course of 25 meters for 6 minutes (timed), and the distance walked (in meters) was recorded. Change from baseline in 6MWT distance at Week 144 in total golodirsen group was reported.

Efficacy set consisted of all randomized participants who had at least one post baseline functional assessment. Here, overall number of participants analyzed signifies participants who were evaluable for this outcome measure.

6MWT was performed by standardized procedures for all participants. Participants were asked to walk a set course of 25 meters for 6 minutes (timed), and the distance walked (in meters) was recorded. Change from baseline in 6MWT distance at Week 144 in untreated group (non-exon 53 amenable participants) was calculated.

Efficacy set consisted of all randomized participants who had at least one post baseline functional assessment. Here, overall number of participants analyzed signifies participants who were evaluable for this outcome measure.

Change from baseline in dystrophin protein levels (in muscle biopsy samples) was determined by Western blot in total golodirsen group.

Muscle biopsy set included all participants who received at least one dose of study drug and who had data from both baseline (pre-treatment) and Part 2 Week 48 (on-treatment) muscle biopsy samples. Data was not planned to be collected and analyzed for untreated group.

Maximum Concentration (Cmax) of golodirsen in plasma was evaluated.

Pharmacokinetic (PK) set consisted of all randomized participants from Part 1 who received the planned full dose of study drug and for whom there were adequate PK samples from which to estimate PK parameters. Data were not planned to be collected and analyzed for the placebo arm.

Time to reach maximum plasma concentration (Tmax) of golodirsen was evaluated.

PK set consisted of all randomized participants from Part 1 who received the planned full dose of study drug and for whom there were adequate PK samples from which to estimate PK parameters. Data were not planned to be collected and analyzed for the placebo arm.

Area under the concentration-time curve from time zero extrapolated to the infinity was evaluated.

PK set: all randomized participants from Part 1 who received the planned full dose of study drug and for whom there were adequate PK samples from which to estimate PK parameters. "Overall number of participants analyzed"= number of participants evaluable for this outcome. Data were not planned to be collected and analyzed for the placebo arm.

Volume of distribution was defined as the theoretical volume in which the total amount of drug would need to be uniformly distributed to produce the desired plasma concentration of a drug. Apparent volume of distribution at steady state of golodirsen was evaluated.

PK set: all randomized participants from Part 1 who received planned full dose of study drug, for whom there were adequate PK samples from which to estimate PK parameters. "Overall number of participants analyzed"= number of participants evaluable for this outcome. Data were not planned to be collected and analyzed for the placebo arm.

T1/2 is the time measured for the plasma concentration of drug to decrease by one half. T1/2 of golodirsen was evaluated.

PK set: all randomized participants from Part 1 who received planned full dose of study drug, for whom there were adequate PK samples from which to estimate PK parameters. "Overall number of participants analyzed"= number of participants evaluable for this outcome. Data were not planned to be collected and analyzed for the placebo arm.

Drug clearance is a quantitative measure of the rate at which a drug substance is removed from the blood.

PK set: all randomized participants from Part 1 who received planned full dose of study drug, for whom there were adequate PK samples from which to estimate PK parameters. "Overall number of participants analyzed"= number of participants evaluable for this outcome. Data were not planned to be collected and analyzed for the placebo arm.

MRT= AUMCinf/AUCinf, where AUMCinf is the area under the first moment curve from time 0 extrapolated to infinite time, calculated using the linear/log trapezoidal method. Mean residence time of golodirsen was evaluated.

PK set: all randomized participants from Part 1 who received planned full dose of study drug, for whom there were adequate PK samples from which to estimate PK parameters. "Overall number of participants analyzed"= number of participants evaluable for this outcome. Data were not planned to be collected and analyzed for the placebo arm

Renal clearance was calculated using the partial AUC0-24 from the non-compartmental analysis in plasma and AE0-24. AUC0-24 was defined as area under the plasma concentration-time curve, from time 0 to 24 hours after completion of dosing. AE0-24 was defined as total cumulative amount excreted from 0 to 24 hours. Summarized data of all urine collection intervals are reported.

PK set: all randomized participants from Part 1 who received planned full dose of study drug, for whom there were adequate PK samples from which to estimate PK parameters. "Overall number of participants analyzed"= number of participants evaluable for this outcome. Data were not planned to be collected and analyzed for the placebo arm.

FVC was the total amount of air exhaled during the forced expiratory volume test that was measured during spirometry and the most important measurement of lung function. This test required participant to breath into a tube connected to a machine that measures the amount of air that can be moved in and out of the lungs after taking an inhaled bronchodilator medicine which was used to dilate participant bronchial (breathing) tubes. Percent of predicted FVC = (observed value)/ (predicted value) * 100%.

Efficacy set consisted of all randomized participants who had at least 1 post-baseline functional assessment. Here, "overall number of participants analyzed" = number of participants evaluable for this outcome.

FVC was the total amount of air exhaled during the forced expiratory volume test that was measured during spirometry and is the most important measurement of lung function. This test requires participant to breath into a tube connected to a machine that measures the amount of air that can be moved in and out of the lungs after taking an inhaled bronchodilator medicine which was used to dilate participant bronchial (breathing) tubes. Percent of predicted FVC = (observed value)/ (predicted value) * 100%.

Efficacy set consisted of all randomized participants who had at least 1 post-baseline functional assessment. Here, "overall number of participants analyzed" = number of participants evaluable for this outcome.

Change from baseline in dystrophin Intensity levels (in muscle biopsy samples) was determined by Immunohistochemistry in total golodirsen group.

Muscle biopsy set included all participants who received at least 1 dose of study drug and who had data from both baseline (pre-treatment) and Part 2 Week 48 (on-treatment) muscle biopsy samples. Data were not planned to be collected and analyzed for the untreated group.

Percent change from baseline in Exon 53 skipping (in muscle biopsy samples) was determined by reverse transcription polymerase chain reaction in total golodirsen group.

Muscle biopsy set included all participants who received at least 1 dose of study drug and who had data from both baseline (pre-treatment) and Part 2 Week 48 (on-treatment) muscle biopsy samples. Data were not planned to be collected and analyzed for the untreated group.

Percent change from baseline in dystrophin positive fibers (in muscle biopsy samples) were determined by Immunohistochemistry at Week 48 in total golodirsen group.

Muscle biopsy set included all participants who received at least 1 dose of study drug and who had data from both baseline (pre-treatment) and Part 2 Week 48 (on-treatment) muscle biopsy samples. Data were not planned to be collected and analyzed for the untreated group.

Participants received golodirsen IV infusions, at dose levels of 4 mg/kg, once weekly for 2 weeks in Part 1.

Participants received golodirsen IV infusions, at a dose levels of 10 mg/kg, once weekly for the next 2 weeks (i.e., up to Week 4) in Part 1.

Participants received golodirsen IV infusions, at a dose level of 20 mg/kg, once weekly for the next 2 weeks (i.e., up to Week 6) in Part 1.

Participants received golodirsen IV infusions, at a dose level of 30 mg/kg, once weekly from Week 7 to Week 12 in Part 1.

All participants from Part 1 (who previously received placebo or golodirsen) and including additional new participants received golodirsen 30 mg/kg once weekly, for up to 168 weeks in Part 2. Dosing was interrupted or halted when any specific predefined stopping criteria was met or if warranted at the discretion of the Sponsor or Investigator.

Untreated participants intended to evaluate the natural history of the disease with DMD and various genetic mutations (not amenable to exon 53 skipping) were included in this group and did not received any treatment. Participants underwent the same study assessments as treated participants in other reporting groups (except for PK sampling and muscle biopsies), but at a reduced schedule through Week 144. Thus, the untreated participants were not considered as control group.