Clinical Research Directory

Inclusion Criteria: * Enrolled in DM-scope registry genetically diagnosed with DM1 or DM2. * Affiliation or beneficiary of a social security system or of such a regime. * Ability to comprehend and willingness to sign an informed consent (ICF). * Male or non-pregnant female ≥18 years of age at screening. * Body Mass Index (BMI) of 18.5 kg/m2 to 30 kg/m2, and weight ≥45 kg. * Medical history data covering up to 18 months prior to enrollment. * Clinical sign of myotonia * DM1 patients only - Muscular impairment rating scale (MIRS) score of 2, 3 or 4. * Be able to walk independently 10 meters (cane, walker, orthoses allowed). Exclusion Criteria: * No informed consent. * Pregnant or lactating women. * Subjects benefiting from laws aimed at protecting vulnerable adults: subjects being deprived of liberty by judicial or administrative decision, subjects under guardianship /curatorship. * Any medical condition or serious medical illness which in the opinion of the Investigator, precludes the participant's participation in the study or the participant is unlikely to comply with the protocol-defined procedures and therefore is unlikely to complete the study. * Medical conditions that could affect hand functioning including (but not limited to) rheumatoid arthritis, Dupuytren's contracture, hand deformity, severe arthritis or any other medical condition (other than DM1/DM2) that would significantly impact ambulation. * Patients with no documented record of myotonia assessment in the clinical records of the DM-scope database or myotonia absence at last visit prior to study enrolment. * Not able to perform study specific performance tests and evaluations e.g. hand grip dynamometry, 10mWT, etc. (in the opinion of the investigator). * Treatment with mexiletine within 18 months prior to baseline (Day 1).