Background: Duchenne muscular dystrophy (DMD) is caused by DMD gene mutations. Delandistrogene moxeparvovec is an investigational gene transfer therapy, developed to address the underlying cause of DMD. We report findings from Part 1 (52 weeks) of the two-part EMBARK trial (NCT05096221). Methods: Key inclusion criteria: Ambulatory patients aged ≥4-<8 years with a confirmed DMD mutation within exons 18–79 (inclusive); North Star Ambulatory Assessment (NSAA) score >16 and <29 at screening. Eligible patients were randomized 1:1 to intravenous delandistrogene moxeparvovec (1.33×1014 vg/kg) or placebo. The primary endpoint was change from baseline in NSAA total score to Week 52. Results: At Week 52 (n=125), the primary endpoint did not reach statistical significance, although there was a nominal difference in change from baseline in NSAA total score in the delandistrogene moxeparvovec (2.6, n=63) versus placebo groups (1.9, n=61). Key secondary endpoints (time to rise, micro-dystrophin expression, 10-meter walk/run) demonstrated treatment benefit in both age groups (4-5 and 6-7 years; p<0.05).There were no new safety signals, reinforcing the favorable and manageable safety profile observed to date. Conclusions: Based on the totality of functional assessments including the timed function tests, treatment with delandistrogene moxeparvovec indicates beneficial modification of disease trajectory.