A Study in Participants With Duchenne Muscular Dystrophy Amenable to Exon 44 Skipping to Evaluate the Safety and Efficacy of ENTR-601-44

Principal inclusion criteria

• Genetic diagnosis of Duchenne muscular dystrophy (DMD) and confirmed pathologic variant in the dystrophin gene amenable to exon 44 skipping as reviewed by a central genetic counselor.
• Assigned male at birth with clinical signs compatible with Duchenne muscular dystrophy as determined by the investigator.
• Part A: 4-20 years of age, inclusive.
• Ambulatory Status Part A: ambulatory with a Performance of the Upper Limb v2.0 (PUL 2.0) Entry as per protocol at Screening
• Adequate muscle for obtaining tissue biopsy as assessed by the investigator.
• Other protocol-defined criteria apply.

Principal exclusion criteria

• Any significant concomitant medical condition that might interfere with the ability to comply with protocol requirements.
• Has an acute illness within 4 weeks prior to the first dose of study drug which may interfere with study measurements or jeopardize participant's safety.
• Use of the following medications:

• Prior treatment with any exon skipping therapy at any time
• Prior treatment with any gene therapy at any time
• Use of anti-coagulants, anti-thrombotics, or anti-platelet agents
• Use of an immunosuppressants (other than oral corticosteroids for DMD conditions)
• Has taken or is currently taking a histone deacetylase (HDAC) inhibitor, including (but not limited to) givinostat
• Laboratory abnormalities.
• Daytime ventilator dependence or any use of invasive mechanical ventilation via tracheostomy.
• Has an abnormal electrocardiogram (ECG) reading assessed as clinically significant by the investigator, and/or a QT interval with Fridericia correction method (QTcF) >450 msec at Screening or prior to the first dose of study drug on Day 1.
• Received any experimental or investigational drug, etc. within 3 months prior to first dose or within 5 half-lives (whichever is longer).
• Other protocol-defined criteria apply.