Observational Study of Natural History of BAG3 Gene Mutation-Associated Dilated Cardiomyopathy in Chinese Adults

Inclusion Criteria: * Participants must meet all of the following criteria to be eligible for inclusion: 1. Age ≥18 years at screening, male or female; 2. Presence of a BAG3 pathogenic or likely pathogenic mutation interpreted according to the American College of Medical Genetics and Genomics (ACMG) guidelines; 3. Heart failure (HF) Stage B or C, New York Heart Association (NYHA) functional class I-III; 4. LVEF ≤50%. If LVEF is 45%-50% and the participant is classified as Stage B heart failure or NYHA Class I, N-terminal pro-B-type natriuretic peptide (NT-proBNP) must be ≥300 pg/mL. LVEF measurement must be based on echocardiography or cardiac magnetic resonance results within the past 12 months; 5. Willing and able to comply with all scheduled visits, laboratory tests, and other study procedures; 6. Capable of providing signed informed consent, including compliance with the requirements and restrictions listed in the informed consent form and this protocol. Exclusion Criteria: * Participants meeting any of the following criteria will be excluded: 1. Acute decompensated heart failure within 1 month prior to enrollment; 2. Any of the following within 3 months prior to screening: * Myocardial infarction * Cardiac surgical procedures (excluding pacemaker/implantable cardioverter defibrillator/cardiac resynchronization therapy implantation) * Implantable cardioverter defibrillator (ICD) implantation * Acute coronary syndrome * Hospitalization for cardiac arrhythmia 3. History of heart transplantation; 4. Estimated glomerular filtration rate (eGFR) \<30 mL/min/1.73 m² (calculated using the Chronic Kidney Disease Epidemiology Collaboration formula); 5. Active malignancy or malignancy diagnosed within 3 years prior to screening, except for: * Surgically cured in situ malignancies * Surgically cured early-stage cancers (including breast, prostate, skin \[basal cell carcinoma, squamous cell carcinoma\], thyroid, or cervical cancer) * Other early-stage malignancies with an expected 2-year recurrence rate ≤20%, approved by the Medical Monitor 6. Non-cardiac condition limiting life expectancy to \<1 year; 7. Presence of any of the following cardiac conditions: * Other forms of cardiomyopathy contributing to heart failure (e.g., inflammatory or infiltrative cardiomyopathy) * Clinically significant cardiac anatomic abnormalities (e.g., left ventricular aneurysm) * Significant coronary artery disease (e.g., prior revascularization, exercise-induced angina) * Uncorrected, hemodynamically significant (moderate to severe) primary structural valvular disease not due to heart failure (investigator's judgment) 8. Any severe concurrent disease (e.g., active systemic infection) that, in the investigator's judgment, would make the participant unsuitable for study participation; 9. Any medical or psychiatric condition that may increase study risk, including: * Active or recent (within 1 year) suicidal ideation/behavior * Laboratory abnormalities * Other conditions deemed unsuitable by the investigator 10. Administration of any investigational drug within 30 days prior to screening; 11. Prior gene or cell therapy treatment; 12. Anticipated need for cardiac transplantation, left ventricular assist device implantation, or other cardiac surgery within the next 3 months (investigator's assessment); 13. More than 3 first-degree relatives from the same family enrolled concurrently (excluding the participant).