Safety Study of Eteplirsen to Treat Early Stage Duchenne Muscular Dystrophy

Safety, including adverse event monitoring and routine laboratory assessments, will be
followed on an ongoing basis for all patients.

Clinical efficacy, including functional tests and MRI, will be assessed at regularly
scheduled study visits. Patients will undergo one baseline and one follow-up muscle biopsy.

Population and serial PK will be collected.

Inclusion Criteria:

- Male 4-6 years of age.

- Diagnosis of DMD, genotypically confirmed.

- Stable dose of oral corticosteroids for at least 12 weeks or has not received
corticosteroids for at least 12 weeks.

- Intact right and left biceps muscles or two alternative upper arm muscle groups.

- Parent that is willing to provide consent and comply with study procedures.

Exclusion Criteria:

- Use of any pharmacologic treatment (other than corticosteroids) within 12 weeks that
may have an effect on muscle strength or function (e.g., growth hormone, anabolic
steroids).

- Previous or current treatment with any other experimental treatments within 12 weeks
or participation in any other clinical trial within 6 months.

- Major surgery within 3 months prior to the first dose of study drug, or planned
surgery during this study which would interfere with the ability to perform study
activities.

- Presence of other clinically significant illness.