The goal of this observational study is to assess movement in individuals with Myotonic Dystrophy Type 1 (DM1) and Type 2 (DM2) using digital biomarker tools. The long-term aim of this study is to incorporate these outcomes into clinical trials of DM1 and DM2 therapies. Participants will complete a series of assessments that allow for researchers to measure hand myotonia and walking quality, including a Video Hand Opening Test (VHOT), grip strength, 10 meter walk/run test, 6 minute walk test, Timed Up and Go (TUG), Motor Function Measures-32 (MFM-32) test, and more. These assessments may be recorded to detect and map participants motion and walking patterns. Several patient reported outcome (PROs) questionnaires will also be recorded. Participants may also be asked to monitor exercise and sleep activity at home using an Actigraph wearable device. This study is divided into 2 parts: Part A consists of a single visit. Part B consists of a 1-year longitudinal study with 3 clinical follow-up visits.

Inclusion Criteria:

• Ability to provide informed consent
• Age 12-90 years old at the time of informed consent
• Genetic confirmation of DM1 or DM2
• Ability to comply with study assessments
• Clinically apparent myotonia equivalent to hand opening time of at least 2 seconds, in the opinion of the Investigator
• Ambulatory (orthoses allowed, canes and walkers not allowed) and able to walk at least 25 meters at screening

Exclusion Criteria:

• Ongoing medical condition (e.g. wasting or cachexia, severe anemia) that would, in the opinion of the Investigator, interfere with the conduct or assessments of the study
• Significant cognitive impairment, clinical dementia, or unstable psychiatric illness, including psychosis, suicidal ideation, suicide attempt, or untreated major depression ≤ 90 days of screening, which in the opinion of the Investigator may interfere with the study procedures
• Treatment with an investigational drug, biologic agent, or device within one month of screening, or 5 half-lives of investigational agent, whichever is longer
• Inability to comply with study requirements
• Other unspecified reasons that, in the opinion of the Investigator or the Sponsor, make the participant unsuitable for enrolment

Individuals with genetic confirmation of DM1 or DM2, or with DMPK CTG repeat length >100, or CCTG repeat length >100. We will recruit from our database of subjects with Myotonic Dystrophy that have been seen in the Stanford clinic in the past 5 years. Other neuromuscular specialists in the Bay Area will be informed and will be asked to refer patients to us for the study. We work closely with the Myotonic Dystrophy Foundation, Muscular Dystrophy Foundation, and Myotonic Dystrophy support groups and will spread the word about the study through these as well. We have a separate database of healthy controls that have expressed interest in our research. We will enroll healthy controls via this database, or from laboratory personnel who volunteer.

Biogen and their collaborators will have access to coded study data. Protected Health Information (PHI)/identifiers will not be shared with Biogen or research collaborators and they will not have the key to the code linking study identification/code to the participants. When data needs to be shared, it will be via secure network using encrypted files.

Biogen and their collaborators will have access to coded study data. PHI/identifiers will not be shared with Biogen or their collaborators, and they will not have the key linking the code to study participants.