AVI-4658

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 96 was reported.

TEAEs were defined as adverse events (AEs) with an onset following administration of the first dose of study drug. An AE was any untoward medical occurrence in a participant, which does not necessarily have a causal relationship with the study drug. Abnormalities presented at Baseline were considered AEs if they reoccurred after resolution or worsen during the AE collection period. An SAE was defined as any AE that, in the view of either the Investigator or Sponsor, resulted in any of the following outcomes as fatal, life-threatening, required hospitalization or prolongation of existing hospitalization, persistent or significant disability/incapacity, a congenital anomaly/birth defect, or an important medical event. A summary of all SAEs and Other AEs (nonserious) regardless of causality is located in the 'Adverse Events' Section.

Clinical laboratory parameters that were evaluated included * Any Grade ≥2 (moderate) or serious event without an alternative etiology that the Investigator deemed was related to study drug * Two consecutive drug-related serum creatinine levels ≥2\*upper limit of normal (ULN) without an alternative etiology * Creatine kinase (CK) levels \>50,000 units/liter (U/L) * A confirmed, unexplained, increase in gamma glutamyl transferase (GGT) \>3\*ULN and either an increase in bilirubin \>2\*ULN or nascent prothrombin time \>2\*ULN concurrently, without an alternative etiology

The vital sign parameters that were evaluated included blood pressure, heart rate, respiration, and temperature. A summary of all SAEs and Other AEs (nonserious) regardless of causality is located in the 'Adverse Events' Section.

Data not collected during the study for this Outcome Measure. A summary of all SAEs and Other AEs (nonserious) regardless of causality is located in the 'Adverse Events' Section.

The ECG was manually reviewed and interpreted by medically qualified personnel using a central vendor according to pre-specified criteria. The Investigator determined if the findings in the centrally read ECG report were clinically significant. Clinical significance was defined as any variation in ECG findings that had medical relevance resulting in an alteration in medical care. The ECHO was reviewed and interpreted by medically qualified personnel using a central vendor according to pre-specified criteria. The Investigator determined if the findings in the ECHO report were clinically significant. Clinical significance was defined as any variation in ECHO findings that had medical relevance resulting in an alteration in medical care. A summary of all SAEs and Other AEs (nonserious) regardless of causality is located in the 'Adverse Events' Section.

Adverse Event (AE) was any untoward medical occurrence in a participant that did not necessarily have a causal relationship with the study drug. Serious adverse event (SAE) was an AE resulting in any of the following outcomes: death; Life-threatening event; required or prolonged inpatient hospitalization; persistent or significant disability/incapacity; congenital anomaly. Treatment emergent adverse events were events that developed or worsened during the on-treatment period (defined as time from first dose of study drug and up to 28 days after last dose of study drug \[up to 100 weeks\]) that were absent before treatment or that worsened relative to pre-treatment state. AEs included both serious and non-serious adverse events.

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

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 clinically significant or not clinically significant. Clinical significance was defined as any variation in assessment results that had medical relevance resulting in an alteration in medical care.

Physical examinations, full and brief, were performed by the Investigator, a physician Sub-Investigator, or a Nurse Practitioner (if licensed in the state or province to perform physical examinations). Full physical examinations included examination of general appearance; head, ears, eyes, nose, and throat; heart; lungs; chest; abdomen; skin; lymph nodes; and musculoskeletal and neurological systems. Number of participants with at least one abnormal physical examination findings were reported. Abnormality in physical examinations was based on Investigator's discretion.

Twelve-lead ECGs and Holter 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 at least one abnormalities in ECGs were reported as TEAEs.

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 at least one abnormalities in ECHO were reported as TEAEs.

An adverse event (AE) was any untoward medical occurrence in a participant that did not necessarily have a causal relationship with the study drug. A serious adverse event (SAE) was an AE resulting in any of the following outcomes: death; Life-threatening event; Required or prolonged inpatient hospitalization; persistent or significant disability/incapacity; congenital anomaly. Treatment-emergent AEs were events that developed or worsened during the on-treatment period (defined as time from first dose of study drug and up to 28 days after last dose of study drug (up to 100 weeks) that were absent before treatment or that worsened relative to pretreatment state. AEs included both serious and non-serious adverse events.

This study used a modified version of the 6MWT test procedure described in American Thoracic Society (ATS) 2002 guidelines, specifically adapted for patients with Duchenne muscular dystrophy. The participant was asked to walk a set course of 25 meters for 6 minutes (timed) and the distance walked in meters was recorded. Increases from baseline in 6MWT distance are indicative of improvement and decreases from baseline indicate worsening. Baseline here corresponds to the baseline in the parent study (4658-us-201, NCT01396239).

Dystrophin expression as assessed by percent dystrophin positive fibers was measured by immunohistochemistry (IHC) technique using primary anti-dystrophin antibody. Percent change from baseline is the arithmetic difference of the treatment time point minus baseline divided by baseline calculated for individual subjects. Baseline here corresponds to the baseline in the parent study (4658-us-201, NCT01396239).

The primary efficacy endpoint will be based on the pre-treatment and post-treatment change in the number (%) of dystrophin positive fibers as measured in the muscle biopsy tissue on immunohistochemistry (IHC).

Number of subjects with 1 or more Treatment Emergent Adverse Event that are possibly related to the investigational drug

Number of Patients with Treatment Emergent Adverse Events