Myotonic dystrophy type 1 (DM1) is an autosomal dominant multisystem disorder caused by an expanded CTG trinucleotide repeat in the 3' untranslated region of the DMPK gene. Beyond myotonia and progressive skeletal muscle weakness, DM1 involves the cardiac, respiratory, central nervous, gastrointestinal, endocrine, and ocular systems, and respiratory and cardiac involvement are the leading causes of disability and death. Systematic, long-term outcome data in Chinese DM1 patients are lacking.

C-DMCOS-DM1 is a multicenter, prospective, observational cohort study that systematically records demographic data, multisystem involvement, and predefined disability-related clinical outcome events in genetically confirmed Chinese DM1 patients, with regular follow-up every 3 to 6 months. The study also collects residual blood, skeletal muscle, myocardium (when a pacemaker is implanted), and urine specimens for transcriptomic and other molecular studies. The aims are to characterize the disease burden of Chinese DM1 patients, identify risk and prognostic factors for disabling outcomes, and build risk-prediction models to inform follow-up, management, and future clinical trials.

This multicenter, prospective, observational cohort study (no randomization, no control, no intervention) enrolls genetically confirmed DM1 patients across Chinese neuromuscular centers and follows them every 3 to 6 months. At baseline and each visit, the study collects demographics, clinical subtype, symptoms and rating scales, manual muscle testing and the Muscular Impairment Rating Scale (MIRS), quantitative motor measures (grip strength, 10-Metre Walk Test [10MWT], Video Hand Opening Time [vHOT]), cardiac assessment (electrocardiography and 24-hour Holter), pulmonary function testing, echocardiography, laboratory tests, computerized cognitive assessment, and video and voice recordings of gait, hand grip, and facial movement for artificial-intelligence analysis. Wearable devices are encouraged for continuous monitoring of heart rate and heart rate variability, blood oxygen saturation, respiratory rate, sleep and nocturnal respiratory events, and daily physical activity.

Predefined disability-related outcome events are tracked cumulatively, including loss of independent ambulation, respiratory failure, non-invasive or invasive mechanical ventilation, tracheostomy, cardiac pacemaker or implantable cardioverter-defibrillator (ICD) implantation, early cataract surgery, malignancy, and death. Residual blood, skeletal muscle, myocardium (when a pacemaker is implanted), and urine specimens are collected for RNA sequencing, mitochondrial DNA analysis, and other molecular studies. Statistical analysis includes descriptive characterization, Kaplan-Meier and Cox proportional-hazards survival analysis, competing-risk models, and multivariable regression to identify risk and prognostic factors and to build risk-prediction models.

Inclusion Criteria:

1. Genetically confirmed DM1 (CTG repeat expansion in the 3' untranslated region of the DMPK gene).
2. Any sex.
3. Able to attend regular follow-up and willing to provide and store residual blood, urine, and other biospecimens for research.
4. Voluntary participation with signed informed consent (signed by legal guardian for minors).
5. Consent to use of routine clinical, examination, and follow-up data for research.

Exclusion Criteria:

1. Unable to comply with study procedures.
2. Unable to provide informed consent, or guardian declines participation.
3. Pregnancy (for MRI safety).
4. Severe, unstable medical condition that precludes assessments.

The patients will be diagnosed and invited to join this trial in each participating neuromuscular diagnostic centers.

Individual participant data will not be shared publicly. The data are subject to China's Regulations on the Administration of Human Genetic Resources. All participant data are managed anonymously and identified by study number rather than name, and are accessible only to authorized study personnel.