The DanonDisease.org is a website developed primarily to provide patients and families with information about Danon disease. Information is also available for physicians. A registry has been developed that patients can join to learn more about this rare condition. Danon disease is a rare genetic disorder of which males are more severely affected than females. Among boys, the key features are diseased heart muscle (cardiomyopathy), weakness of the body muscles (skeletal myopathy) and intellectual disability ranging from mild learning problems to mental retardation. In many males, the disease progresses until a heart transplant is required or death occurs in the second to third decade of life. Females are also affected, although usually more mildly, and often onset is delayed until they reach adulthood.