Study of SRP-4045 and SRP-4053 in DMD Patients

This is a double-blind, placebo-controlled, multi-center study to evaluate the efficacy and
safety of SRP-4045 and SRP-4053. Eligible patients with out-of-frame deletion mutations
amenable to exon 45 or 53 skipping will be randomized to receive once weekly intravenous (IV)
infusions of 30 mg/kg SRP-4045 or 30 mg/kg SRP-4053 respectively (combined-active group) or
placebo for up to 96 weeks (the placebo-controlled period of the trial). This will be
followed by an open label extension period in which all patients will receive open-label
active treatment for 48 weeks (up to Week 144 of study).

The study will enroll approximately 222 patients, with a planned minimum target of 111
patients amenable to exon 45 skipping and 111 patients amenable to exon 53 skipping.

Approximately 148 patients will be randomized to receive active treatment with either
SRP-4045 or SRP-4053 (depending on deletion mutation), and 74 patients will be randomized to
receive placebo. Twice as many patients will receive active treatment as will receive placebo
(2:1 randomization).

Clinical efficacy will be assessed at regularly scheduled study visits, including functional
tests such as the six-minute walk test (6MWT). All patients will undergo a muscle biopsy at
baseline and a second muscle biopsy either at Week 48 or Week 96.

Safety will be assessed through the collection of adverse events (AEs), laboratory tests,
electrocardiograms (ECGs), echocardiograms (ECHOs), vital signs, and physical examinations
throughout the study.

Blood samples will be taken periodically throughout the study to assess the pharmacokinetics
of both drugs.

Inclusion Criteria:

- Genotypically confirmed DMD, with genetic deletion amenable to exon 45 or exon 53
skipping

- Stable dose of oral corticosteroids for at least 24 weeks

- Intact right and left biceps or 2 alternative upper muscle groups

- Mean 6MWT greater than or equal 300 meters and less than or equal to 450 meters

- Stable pulmonary and cardiac function: forced vital capacity (FVC) equal to or greater
than 50% predicted and left ventricular ejection fraction (LVEF) greater than 50%

Exclusion Criteria:

- Previous treatment with SMT C1100 (BMN-195) at any time

- Treatment with gene therapy at any time

- Previous treatment with PRO045 or PRO053 within 24 weeks prior to Week 1

- Current or previous treatment with any other experimental treatment (other than
deflazacort) within 12 weeks prior to Week 1

- Participation in any other DMD interventional clinical study within 12 weeks prior to
Week 1

- Major surgery within 3 months prior to Week 1

- Presence of other clinically significant illness

- Major change in physical therapy regimen within 3 months prior to Week 1