A Study to Assess Vamorolone in Boys With Duchenne Muscular Dystrophy (DMD)

Inclusion Criteria: 1. Subject's parent or legal guardian has provided written informed consent/Health Insurance Portability and Accountability Act (HIPAA) authorization prior to any study-related procedures; 2. Subject has a confirmed (by Central Genetic Counselor) diagnosis of DMD as defined as: 1. Dystrophin immunofluorescence and/or immunoblot showing complete dystrophin deficiency, and clinical picture consistent with typical DMD, OR 2. Identifiable mutation within the DMD gene (deletion/duplication of one or more exons) where reading frame can be predicted as 'out-of-frame', and clinical picture consistent with typical DMD, OR 3. Complete dystrophin gene sequencing showing an alteration (point mutation, duplication, other) that is expected to preclude production of the dystrophin protein (i.e. nonsense mutation, deletion/duplication leading to a downstream stop codon), with a typical clinical picture of DMD; 3. Subject is ≥ 4 years and \< 7 years of age at time of enrollment in the study; 4. Subject is able to complete the Time to Stand Test (TTSTAND) without assistance, as assessed at the Screening and Baseline Visits; 5. Clinical laboratory test results are within the normal range at the Screening Visit, or if abnormal, are not clinically significant, in the opinion of the Investigator. (Note: Serum gamma glutamyl transferase \[GGT\], creatinine, and total bilirubin all must be ≤ upper limit of the normal range at the Screening Visit); 6. Subject has evidence of chicken pox immunity as determined by presence of IgG antibodies to varicella, as documented by a positive test result from the testing laboratory at the Screening Visit; and 7. Subject and parent/guardian are willing and able to comply with scheduled visits, study drug administration plan, and study procedures. Exclusion Criteria: 1. Subject has current or history of major renal or hepatic impairment, diabetes mellitus or immunosuppression; 2. Subject has current or history of chronic systemic fungal or viral infections; 3. Subject has had an acute illness within 4 weeks prior to the first dose of study medication; 4. Subject has used mineralocorticoid receptor agents, such as spironolactone, eplerenone, canrenone (canrenoate potassium), prorenone (prorenoate potassium), mexrenone (mexrenoate potassium) within 4 weeks prior to the first dose of study medication; 5. Subject has evidence of symptomatic cardiomyopathy. \[Note: Asymptomatic cardiac abnormality on investigation would not be exclusionary\]; 6. Subject is currently being treated or has received previous treatment with oral glucocorticoids or other immunosuppressive agents. \[Notes: Past transient use of oral glucocorticoids or other oral immunosuppressive agents for no longer than 3 months cumulative, with last use at least 3 months prior to first dose of study medication, will be considered for eligibility on a case-by-case basis. Inhaled and/or topical corticosteroids prescribed for an indication other than DMD are permitted but must be administered at stable dose for at least 3 months prior to study drug administration\]; 7. Subject has used idebenone within 4 weeks prior to the first dose of study medication; 8. Subject has an allergy or hypersensitivity to the study medication or to any of its constituents; 9. Subject has severe behavioral or cognitive problems that preclude participation in the study, in the opinion of the Investigator; 10. Subject has previous or ongoing medical condition, medical history, physical findings or laboratory abnormalities that could affect safety, make it unlikely that treatment and follow-up will be correctly completed or impair the assessment of study results, in the opinion of the Investigator; 11. Subject is taking any other investigational drug currently or has taken any other investigational drug within 3 months prior to the start of study treatment; or 12. Subject has previously been enrolled in the study.