OBJECTIVE: To evaluate visual function in 2 boys and their maternal aunt affected with Danon disease due to a mutation in the X-linked lysosome-associated membrane protein-2 (LAMP2) gene. METHODS: Linkage analysis using microsatellite markers from the X chromosome was done in family members from the paternal side. Visual acuity testing, fundus analysis, fluorescence angiography, and full-field electroretinography were performed in all 3 patients. RESULTS: Eye examinations confirmed the presence of retinopathy in the 2 boys and their maternal aunt, obligate carrier for the S157X mutation in LAMP2. The expression of the disease was milder in the female carrier than in the hemizygous boys, possibly due to lyonization. CONCLUSIONS: Our report further expands the phenotype of Danon disease by describing retinopathy in 3 cases. A thorough clinical examination, including ophthalmic investigation, is needed in all cases of Danon disease. CLINICAL RELEVANCE: LAMP2 belongs to a growing number of retinopathy genes. Genes involved in systemic diseases associated with poor survival may see their effect in other organs, not only in the eyes, becoming a major source of concern once a good and reliable therapy is available. This also represents a major issue for genetic counseling for patients undergoing gene therapy in the future.