Overview

The purpose of this study is to learn about the effects of an investigational medicine, PGN-EDODM1, to see how safe and tolerable multiple administrations of PGN-EDODM1 are for people with myotonic dystrophy type 1 (DM1) compared to placebo.

Eligibility

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.