Safety, Tolerability, PK, and PD Study of PGN-EDODM1 in Participants With Myotonic Dystrophy Type 1

Inclusion Criteria: * Confirmed diagnosis of DM1, as defined as having a repeat sequence in the DMPK gene with at least 100 CTG repeats * Medical Research Council (MRC) score of ≥ Grade 4- in bilateral tibialis anterior (TA) muscles (the ability to move through full range of motion and hold against at least moderate pressure from the examiner) * Presence of myotonia Exclusion Criteria: * Congenital DM1 * Known history or presence of any clinically significant conditions that may interfere with study safety assessments * Abnormal laboratory tests at screening * Medications specific for the treatment of myotonia within 2 weeks prior to screening * Percent predicted forced vital capacity (FVC) \<40% Note: Other inclusion and exclusion criteria may apply.