Danon disease is a metabolic disorder.

Danon disease is associated with heart muscle abnormalities resembling severe hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is a disease of the myocardium in which a portion of the myocardium is hypertrophied without any obvious cause...

.

It is associated with LAMP2

LAMP2

Lysosomal-associated membrane protein 2 also known as CD107b , is a human gene....

. The status of this condition as a glycogen storage disease

Glycogen storage disease

Glycogen storage disease is the result of defects in the processing of glycogen synthesis or breakdown within muscles, liver, and other cell types. GSD has two classes of cause: genetic and acquired. Genetic GSD is caused by any inborn error of metabolism involved in these processes...

 has been disputed.

It was characterized by Moris Danon, a Turkish

Turkish people

Turkish people, also known as the "Turks" , are an ethnic group primarily living in Turkey and in the former lands of the Ottoman Empire where Turkish minorities had been established in Bulgaria, Cyprus, Bosnia and Herzegovina, Georgia, Greece, Kosovo, Macedonia, and Romania...

 neurologist

Neurologist

A neurologist is a physician who specializes in neurology, and is trained to investigate, or diagnose and treat neurological disorders.Neurology is the medical specialty related to the human nervous system. The nervous system encompasses the brain, spinal cord, and peripheral nerves. A specialist...

 in 1981.

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, muscles from the Danon Disease patients 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.

Symptoms

MALES

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
  Wolff-Parkinson-White syndrome
  Wolff–Parkinson–White syndrome is a disorder of the heart in which the ventricles of the heart contract prematurely due to an accessory pathway known as the bundle of Kent. This accessory pathway is an abnormal electrical communication from the atria to the ventricles...
  
  .
• 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 retina
  Retina
  The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
  
  s (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.

FEMALES

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
  Cardiomyopathy
  Cardiomyopathy, which literally means "heart muscle disease," is the deterioration of the function of the myocardium for any reason. People with cardiomyopathy are often at risk of arrhythmia or sudden cardiac death or both. Cardiomyopathy can often go undetected, making it especially dangerous to...
  
  ) is often absent in girls: some women will develop this in adulthood
• Problems with the electrical conduction 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

Causes of Danon Disease

The cause of Danon Disease is known, but not well-understood. The genetic defect involves a gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 called LAMP2

LAMP2

Lysosomal-associated membrane protein 2 also known as CD107b , is a human gene....

. In persons with Danon Disease the LAMP2 gene is damaged (or 'mutated') and normal LAMP2 proteinis no longer made. While we do not fully understand what the function of the LAMP2 gene is, we do know that LAMP2 protein is located in small structures in our cells called lysosomes