Danon Disease Natural History Study

Prospective Cohort: 1. Documentation of a pathogenic or likely pathogenic variant of the LAMP2 gene by a CLIA-certified genetic testing laboratory 2. Patient or parent/legal guardian are capable and willing to provide signed informed consent 3. Age ≥ 8 years at enrollment Female Prospective Cohort: 4. Evidence of left ventricular hypertrophy in the 12 months prior to or at enrollment. Retrospective (only) Cohort: 5. Documentation of a pathogenic or likely pathogenic variant of the LAMP2 gene by a CLIA-certified genetic testing laboratory 6. Patient or parent/legal guardian are capable and willing to provide signed informed consent, as required by local regulations 7. Age ≥ 8 years at enrollment 8. Prior cardiac transplantation or prior mechanical circulatory support 9. At least 30 days of retrospective medical records available prior to cardiac transplantation or mechanical circulatory support Female Retrospective (only) Cohort: 10. Prior evidence of left ventricular hypertrophy. Key Exclusion Criteria: All Cohorts: 1. Concurrent enrollment in any other clinical investigation involving use of an investigational agent for any condition at time of enrollment to this study that could confound interpretation of this study 2. Previous treatment with a gene therapy Prospective Cohort: 3. Prior mechanical circulatory support at time of enrollment to this study 4. Prior cardiac transplantation at time of enrollment to this study Female patients: 5. Age \>51 years at enrollment