Efficacy and Tolerability of Idebenone in Boys With Cardiac Dysfunction Associated With Duchenne Muscular Dystrophy

Inclusion Criteria: * Patients 8 - 16 years of age at time of enrolment * Male * Presence of cardiac involvement/dysfunction, defined by abnormal peak systolic strain in left ventricle (LV) inferolateral wall * Confirmed diagnosis of DMD (out of frame dystrophin gene deletion OR absent/\<5% dystrophin protein on muscle biopsy; clinical picture consistent of typical DMD) * If on chronic glucocorticosteroids treatment (deflazacort, prednisone) for DMD (or any other disease) (i.e. concomitant medication): dosage must be stable (unchanged) 6 months prior to inclusion * If on chronic medication for DMD associated cardiomyopathy (β-blocker, diuretics): dosage must be stable (unchanged) 3 months prior to inclusion * Ability to provide reproducible repeat quantitative muscle testing (QMT) upper limb score within 15% of first assessment score (at Visit1/Day 1 versus Screening Visit Exclusion Criteria: * Symptomatic cardiomyopathy or heart failure * Asymptomatic but severe cardiac dysfunction on baseline (Screening) evaluation: Fractional shortening (FS) \< 20% and/or Ejection fraction (EF) \< 40% * Use of ACE-inhibitors * Previous history of ventricular arrhythmias (other than isolated ventricular extrasystole); ventricular arrhythmias presented at Screening * Previous (6 months or less) participation in any other therapeutic trial for DMD * Use of coenzymeQ10, idebenone, creatine, glutamine, oxatomide, or any herbal medicines within the last 6 months * History of significant concomitant illness or significant impairment of renal or hepatic function * Known individual hypersensitivity to idebenone