A Clinical Study of PGN-EDODM1 in People 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 * Presence of myotonia * Have sufficient muscle mass in bilateral tibialis anterior (TA) muscles that a needle biopsy can safely be performed * Body Mass Index (BMI) of \< 35.0 kg/m\^2 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 considered clinically significant by the Investigator * Medications specific for the treatment of myotonia within 2 weeks prior to screening * Percent predicted forced vital capacity (FVC) \<40% * Use of an investigational drug, device, or product within 30 days of 5 half-lives of the study drug (whichever is longer) prior to Screening Note: Other inclusion and exclusion criteria may apply.