The first description of Danon Disease was in 1981 when 2 boys with heart and skeletal muscle disease (muscle weakness) and mental retardation were described. The disease is named after Dr. Danon who first wrote about the disease. Danon Disease looked initially like another rare genetic condition called 'Pompe' disease. Under the microscope, the muscles from the Danon Disease patiens looked similar to muscles from Pompe disease patients. However the tests for Pompe disease are normal in Danon Disease patients. This shows that Danon Disease is caused by something different than Pompe disease.
	In MALES the symptoms of Danon Disease are more severe. Features of Danon Disease in MALES are: An early age of onset of muscle weakness and heart disease (onset in childhood or adolescence) Some learning problems or mental retardation can be present The muscle weakness can be severe and can affect endurance and even the ability to walk The heart disease can be severe and can lead to a need for medications. Sometimes the heart disease can require a heart transplant or can lead to death Problems with the electrical conduction in the heart can occur. Sometimes the conduction problem is called 'Wolff-Parkinson-White' syndrome. The symptoms are usually progressive and the boys tend to gradually get worse Some boys may have problems with their vision or a problem with the pigment in their retinas (in the back of their eyes) Danon Disease is rare and unfamiliar to most physicians. It can be mistaken for other forms of heart disease and/or muscular dystrophies.
	In FEMALES the symptoms of Danon Disease are less severe. Common symptoms of Danon Disease in females are: A later age of onset of symptoms. Many females will not have obvious symptoms until late adolescence or even adulthood. Learning problems and mental retardation are usually ABSENT Muscle weakness is often absent or subtle. Some females will tire easily with exercise Heart muscle disease (cardiomyopathy) is often absent in girls and some women will develop this in adulthood Problems with the electrical condution in the heart can occur. Sometimes the conduction problem is called 'Wolff-Parkinson-White' syndrome Symptoms in females progress more slowly than in males. Heart disease may not be a problem for females until adulthood Some females will have problems with their vision or a problem with the pigment in the back of their retinas (in the back of their eyes) Danon Disease is rare and unfamiliar to most physicians. The milder and more subtle symptoms in females probably make it harder to diagnose females who have Danon Disease