Study of Tideglusib in Adolescent and Adult Patients With Myotonic Dystrophy

Inclusion Criteria: * Adolescents or adults with diagnosis of congenital or juvenile-onset type 1 myotonic dystrophy (DM-1) * Diagnosis must be genetically confirmed * Subjects must be male or female aged 12 years to 45 years * Subjects must have a Clinical Global Impression - Severity (CGI-S) score of 4 or greater at Screening and Run-in (V2) * Subjects must be ambulatory and able to complete the 10 metre walk/run test (splints allowed) * Subject's legally authorized representative (LAR) must provide written informed consent and there must be written consent or assent (as age applicable and developmentally appropriate) by the subject before any study-related procedures are conducted Exclusion Criteria: * Non-ambulatory (full time) wheel chair user * Receiving stimulant medication * Receiving other medications/therapies not stable (changed) within 4 weeks prior to Run-in (V2) * Medical illness or other concern which would cause investigator to conclude subjects will not be able to perform the study procedures or assessments or would confound interpretation of data obtained during assessment. * Current enrolment in a clinical trial of an investigational drug or enrolment in a clinical trial of an investigational drug in the last 6 months * Women of child bearing potential who are pregnant, lactating or not willing to use a protocol defined acceptable contraception method if sexually active and not surgically sterile. * Gastrointestinal disease which may interfere with the a…