An Open-Label Extension Study of Edasalonexent in Boys With Duchenne Muscular Dystrophy

For Patients who Completed CAT-1004-201 or CAT-1004-301: Inclusion Criteria: * Written consent/assent by patient and/or legal guardian as per regional and/or Institutional Review Board (IRB)/Independent Ethics Committee (IEC) requirements * Completion of either CAT-1004-201 or CAT-1004-301 Exclusion Criteria: * In the Investigator's opinion, unwilling or unable for any reason to complete all study assessments and laboratory tests and comply with scheduled visits, administration of drug, and all other study procedures For Siblings of Patients who Completed CAT-1004-201 or CAT-1004-301: Inclusion Criteria: * Written consent/assent by patient and/or legal guardian as per regional and/or Institutional Review Board (IRB)/Independent Ethics Committee (IEC) requirements * A sibling of a patient who completed either CAT-1004-201 or CAT-1004-301 * Diagnosis of DMD based on a clinical phenotype with increased serum creatine kinase (CK) and documentation of mutation(s) in the dystrophin gene known to be associated with a DMD phenotype * Followed by a doctor or medical professional who coordinates Duchenne care on a regular basis and willingness to disclose patient's study participation with medical professionals Exclusion Criteria: * Use of oral corticosteroids at screening; use of inhaled, intranasal, and topical corticosteroids is permitted * Use of another investigational drug, idebenone, or dystrophin-focused therapy within 4 weeks. Exception: Patients who are currently on or plan to initiate treatment with approved oligonucleotide exon-skipping therapies, and expected to continue treatment throughout the study, will be eligible * Use of the following within 4 weeks prior to Day 1: immunosuppressive therapy, anticoagulants, cyclosporine, dihydroergotamine, ergotamine, fentanyl, alfentanil, pimozide, quinidine, sirolimus or tacrolimus * Use of human growth hormone within 3 months prior to Day 1 * Other prior or ongoing significant medical conditions