The primary objective of this study is to evaluate the safety and tolerability of a single dose of INS1201 via IT administration in ambulatory male participants with DMD.
Participant must be male at birth, 3 to <5 years of age, inclusive (Part 1) and 2 to <3 years of age (Part 2), at the time of legally authorized representative (LAR) signing and dating the informed consent form.
Ambulatory -as defined as the ability to walk at least 10 meters unassisted (ie, without personal assistance or use of any assistive devices) Note: children who have not yet developed the ability to walk by the time of screening (for whatever reason) will not be eligible for the study.
Has a definitive diagnosis of DMD prior to Screening or as part of Screening based on genetic testing. Note that participants who rescreen do not have to repeat genetic testing for the diagnosis of DMD if one is already on file. Genetic reports must describe a frameshift deletion, frameshift duplication, premature stop ("nonsense"), canonical splice site mutation, or other pathogenic variant in the DMD gene fully contained between exons 18 to 58 (inclusive) that is expected to lead to absence of a functional dystrophin protein (mutations in exons 1-17 or 59-71 are therefore not permitted).
Able to cooperate with motor assessment testing.
Prior treatment with gene or cell-based therapy at any time.
Oligonucleotide-based exon skipping or small molecule stop codon readthrough-promoting therapies for at least 6 months prior to enrolment.
Has left ventricular ejection fraction < 50% on the screening echocardiogram (ECHO) or clinical signs and/or symptoms of cardiomyopathy.
Has cardiac arrhythmia or significant electrocardiogram (ECG) interval abnormalities.