Danon disease (DD) is a rare, X-linked disorder associated with severe cardiomyopathy, and in many cases, skeletal myopathy, and cognitive impairment caused by mutations in the LAMP2 gene. There is still uncertainty regarding the natural history of DD because of its rarity.

This study aims to determine the natural history of DD through the collection and analysis of retrospective and prospective data. To achieve this, the investigators will perform surveys and obtain medical records from DD patients. The same cohort of patients will also be assessed by a multidisciplinary team with expertise in DD (cardiologist, neurologist, ophthalmologist, psychologist, geneticist) at the University of California, San Diego. All patients with DD are eligible, including those who underwent a heart transplant. Additionally, data and records from deceased patients will provide valuable retrospective data for this study.

The study design will include:

1. Collection of information for all patients from:

   • Survey of patient or caregiver (if the patient has deceased)
   • Medical Charts

2. Collection of information from living patients assessed by the multidisciplinary team at the University of California, San Diego including:

   • A complete medical history and physical examination
   • Cardiac Testing (Electrocardiography; Echocardiography; Cardiac magnetic resonance imaging with gadolinium contrast agent-gadolinium contrast is optional-; Cardiopulmonary Test)
   • Pulmonary function testing (PFT)
   • Neuromuscular Assessment
   • Cognitive Tests
   • Vision exam including retinal evaluation
   • Laboratory Tests
   • Questionnaires on Quality of life
   • Needle Skeletal muscle biopsy (only for patients over 18 years old)
   • Abdominal Ultrasound for assessment of the liver structure

Inclusion Criteria:

• Living or deceased patients with a diagnosis of Danon disease(including patients who may or may not have undergone heart transplantation) based on a genetic test positive for the LAMP2 mutation

Exclusion Criteria:

• Patients without a genetic test positive for a LAMP2 mutation

Patients diagnosed with Danon Disease (LAMP2 mutation) of any sex and any age.