The purpose of this study is to see whether PRO044 is safe and effective to use as medication for Duchenne Muscular Dystrophy (DMD) patients with a mutation around location 44 in the DNA for the dystrophin protein.

A Phase II, open-label, extesion study. Following a Screening period of up to one month, subjects previously treated with PRO044, and eligible for enrolment in PRO044-CLIN-02, will be allocated to one of three groups to receive either 6 mg/kg or 9 mg/kg PRO044 weekly by IV infusion or 6 mg/kg weekly by SC injection for 48 weeks.

Safety and tolerability, pharmacokinetics (PK), pharmacodynamic (PD) and efficacy assessments will be conducted at regular intervals throughout the study.

Inclusion Criteria:

1. Subjects previously treated with PRO044.
2. Continued use of glucocorticoids for a minimum of 60 days prior to study entry with a reasonable expectation that the subject will remain on steroids for the duration of the study. Changes to the dose regimen or cessation of glucocorticoids will be at the discretion of the Principle Investigator (PI) in consultation with the subject/parent and the Medical Monitor. If the subject is not on steroids, involvement in the study needs to be discussed with the medical monitor

Exclusion Criteria:

1. Current, or history of, liver or renal disease.
2. Acute illness within 4 weeks prior to the first dose of PRO044 (Week 1) which may interfere with the measurements.
3. Severe cardiac myopathy which in the opinion of the Investigator prohibits participation in this study
4. Need for daytime mechanical ventilation.
5. Screening aPTT above the upper limit of normal (ULN).
6. Screening platelet count below the lower limit of normal (LLN).
7. Use of anticoagulants, antithrombotics or antiplatelet agents.
8. Use of any investigational product within 6 months prior to the start of Screening for the study.
9. Current or history of drug and/or alcohol abuse.