An Open-Label Extension Study to Evaluate the Long-term Safety and Efficacy of BMN 351 in Participants With Duchenne Muscular Dystrophy

Inclusion Criteria: * Participants must have completed 351-201 without permanent discontinuation of the investigational medicinal product (IMP) or withdrawal from the study * Currently receiving treatment with oral corticosteroids, on a stable dose regimen during 351-201, and must remain on a consistent dose regimen throughout 351-202 or 351-203 except for modifications to accommodate changes in weight * Transition to the equivalent dose of vamorolone is permitted in 351-202 where approved in participating countries. * Willing and able to adhere to the study visit schedule and other protocol requirements * Willing to use contraception (sexually mature males) throughout the study and for 90 days after the final dose, if sexually active * Contraceptive use by males should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies. * Willing and able to provide written assent (if required by local regulations or the IRB/IEC) after the nature of the study has been explained and prior to performance of any research-related procedure * Willing and able to provide written, signed informed consent as parent or guardian after the nature of the study has been explained and prior to performance of any research-related procedure Exclusion Criteria: * Have known coagulation disorder * Are taking any prohibited medications * any approved exon skipping therapy within 12 weeks prior to baseline or with any gene therapy for the treatment of DMD at any time * anti-coagulants, anti-thrombotics, or anti-platelet agents * immunosuppressants