Study of SRP-1003 in Participants With Type 1 Myotonic Dystrophy

Key Inclusion Criteria: * Genetically confirmed diagnosis of DM1 * Clinician-assessed signs of DM1 including clinically apparent myotonia * Onset of DM1 symptoms occurred after the age of 12 years * Walk for at least 10 meters independently at screening * Participants of childbearing potential must agree to use highly effective contraception in addition to a condom during the study and for at least 90 days following the end of study or last dose of study drug, whichever is later. Participants must not donate sperm or eggs during the study and for at least 90 days following the end of study or last dose of study drug whichever is later. Key Exclusion Criteria: * Inadequately controlled diabetes * Confirmed diagnosis of congenital DM1 * Uncontrolled hypertension * History of tibialis anterior (TA) biopsy within 3 months of Day 1 or planning to undergo TA biopsies during the study period * Clinically significant cardiac, liver or renal disease * Human immunodeficiency virus infection (seropositive) at screening * Seropositive for hepatitis B or hepatitis C at screening * Untreated or poorly controlled epilepsy * Treatment with anti-myotonia medication within a period of 5 half-lives of the medication prior to screening. * Abnormal coagulation parameters at screening including platelet count, international normalized ratio, prothrombin time, and activated partial thromboplastin time Note: Additional inclusion/exclusion criteria may apply per protocol