A Gene Therapy Study of RP-A501 in Male Patients With Danon Disease

Key Inclusion Criteria: 1. Documentation of a pathogenic or likely pathogenic variant of the LAMP2 gene. 2. Male. 3. Age ≥8 years. 4. Evidence of left ventricular hypertrophy with preserved systolic function phenotype as defined by each of the following: 1. Abnormal thickening of left ventricular wall, 2. Left ventricular ejection fraction (LVEF) ≥ 50%. 5. New York Heart Association (NYHA) Class II to III. 6. High sensitivity Troponin I (hsTnI) ≥20% above the upper limit of normal (ULN) ≤ 12 months prior to screening. 7. Ability to comply with study procedures including investigational therapy and follow-up evaluations. Key Exclusion Criteria: 1. Anti-AAV9 neutralizing antibody titer \>1:40. 2. Severe heart failure or requirement for advanced therapies (requirement for intravenous inotropic, vasodilator, or diuretic therapy within the 30 days prior to enrollment, presence or requirement for mechanical circulatory support (MCS), and presence or requirement for mechanical ventilation). 3. History of intracardiac thrombosis or arterial thromboembolic events including stroke, transient ischemic attack (TIA), acute coronary syndrome, myocardial infarction or unstable angina. 4. Prior cardiac or other organ (lung, liver, other) transplantation.