Version 2 (Amendment 1) * Changed the dosing regimen from 50 or 100 mg/kg/wk eteplirsen administered for 12 weeks to 30 or 50 mg/kg/wk administered for 24 weeks. * Changed the overall duration of the study from 30 to 28 weeks. * Changed the design of the study from a dose escalation study to a randomized, double-blind, placebo-controlled, multiple-dose, efficacy, safety, tolerability, and PK study. * Changed the number of subjects from 5 subjects each in 4 groups to 4 subjects each in 3 groups (30 mg/kg/wk, 50 mg/kg/wk, and placebo), i.e., from an N of 20 to an N of 12 * Changed the age range for subject enrollment from 5 to 15 years of age to 7 to 13 years of age. * Added the requirement that subjects be able to walk between 200 and 350 meters on the 6MWT to the entry criteria. * Changed the entry requirement that subjects be on a stable dose of corticosteroids for at least 12 weeks before study entry to at least 24 weeks before study entry. * Added the requirement that the QTc interval at study entry not exceed 450 millisecond to the entry criteria. * Changed the infusion of study medication from “60 minutes for an IV infusion or 2 minutes for an IV bolus” to an IV infusion duration of 30 minutes. * Increased the frequency of laboratory assessments. * Modified the timing and frequency of PK sample collection. * Added post-treatment muscle biopsies to the list of required assessments. * Specified that the primary efficacy end point would be dystrophin production.

Version 3 (Amendment 2) * Changed the infusion time from 30 to 60 minutes. * Condensed the Screening assessments into 1 visit (Visit 1) to be performed within 4 weeks of week 1: day 1. * Added the Timed 4-Step Test to the efficacy assessments. * Expanded the maximum distance on the 6MWT inclusion criterion from 350 to 400 meters. * Changed the Week 24 brief physical examination to a full physical examination.

Version 4.0 (Amendment 3) * Clarified the frequency of urine collection for assessment of cystatin C. * Added urine kidney injury molecule -1 (KIM-1) analysis to the list of safety laboratory assessments.

Version 5.0 (Amendment 4) * Clarified that the 6MWT would be administered twice during the Screening visit and that the mean of the 2 assessments ± 10% of the lower or upper limit (200 m, 400 m) would be the value used to determine qualification. * Specified that the Screening Holter monitor recording would be reviewed prior to the subject undergoing a muscle biopsy, and that if the average heart rate during the recording exceeded 100 beats per minute (bpm), the subject would either be started on β-blockers and rescreened in 4 weeks or excluded from the study. * Increased the clinically significant range on 24-hour Holter monitoring from 100 to greater than equal to >= 110 bpm and symptomatic. * Added collection of serum cystatin C to the list of safety laboratory assessments.

Version 6.0 (Amendment 5) * Clarified that maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP) would be measured, not % predicted MIP and MEP. * Clarified that vital signs would not be collected 4 hours after dosing if subject had been allowed to leave the site prior to that time. * Deleted the 24-hour total urine protein collection from the protocol, because the results from the initial collection were confounded by the presence of nitrogen in eteplirsen.

Version 7.0 (Amendment 6) * Removed pulmonary function test (PFT) from the list of safety assessments as it was already included in the list of efficacy assessments. * Made the 6MWT a secondary end point. * Modified the statistical method to the Wilcoxon rank-sum test, because it was more appropriate for the sample size of this study. * Permitted subjects to be released 1 hour after completion of the study drug infusion after the first 4 doses at the discretion of the Principal Investigator if there were no infusion site reactions or other events associated with drug administration. * Removed peak inspiratory and expiratory flow from the list of PFT assessments, because these tests are measures for pulmonary obstruction, not intercostal or diaphragmatic muscle function. * The Extended upper limit of the window for the muscle biopsy was extended to 96 hours post dosing to allow the same surgeon to perform all biopsies. * Updated planned statistical analyses. * Removed the “mITT” and “per protocol” populations from the list of analysis populations and added a “full analysis population”, which, like the safety population, included all subjects who received any study medication.

Version 8.0 (Amendment 7) * Extended the duration of the study from 24 to 28 weeks. * Specified that beginning Week 25, subjects who received placebo for the first 24 weeks of the study would begin receiving the same dose of eteplirsen to which they were placebo-matched while those who received 50 or 30 mg/kg/wk eteplirsen for the first 24 weeks would continue to receive the same dose regimen of eteplirsen without interruption. * Specified that treatment assignment during the first 24 weeks of the study (eteplirsen vs. placebo) would remain blinded until the study was completed and the database had been locked. * Provided a schedule of assessments and guidance on the administration of study medication for Weeks 25 to 28.