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Genetic and Rare Diseases Information Center (GARD)

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Glycogen storage disease type 2


Other Names for this Disease
  • Acid maltase deficiency disease
  • Aglucosidase alfa
  • Alpha-1,4-glucosidase deficiency
  • Cardiomegalia glycogenica diffusa
  • Deficiency of alpha-glucosidase
More Names
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What is glycogen storage disease type 2?

Glycogen storage disease type 2, also known as Pompe disease and acid maltase deficiency disease, is an inherited metabolic disorder caused by an inborn lack of the enzyme alpha-1,4 glucosidase (lysosomal glucosidase; acid maltase), which is necessary to break down glycogen, a substance that is a source of energy for the body. This enzyme deficiency causes excess amounts of glycogen to accumulate in the lysosomes, which are structures within cells that break down waste products within the cell.[1] This accumulation of glycogen in certain tissues, especially muscles, impairs their ability to function normally.[2] Glycogen storage disease type 2 is a single disease continuum with variable rates of disease progression. In 2006, the U.S. Food and Drug Administration (FDA) approved the enzyme replacement therapy Myozyme as a treatment for all patients with glycogen storage disease type 2.[1]
 
Last updated: 12/24/2008

What are the signs and symptoms of glycogen storage disease type 2?

The infantile form of glycogen storage disease type 2 is characterized by severe muscle weakness (myopathy) and abnormally diminished muscle tone (hypotonia) without muscle wasting, and usually manifests within the first few months of life. Additional abnormalities may include enlargement of the heart (cardiomegaly), the liver (hepatomegaly), and/or the tongue (macroglossia).[1] Affected infants may also have poor feeding, failure to gain weight and grow at the expected rate (failure to thrive), and breathing problems. Most infants with glycogen storage disease type 2 cannot hold up their heads or move normally. [2] Progressive cardiac failure usually causes life-threatening complications by the age of 12 to 18 months; most children with this form of glycogen storage disease type 2 do not survive beyond the age of two.[1][2] 

In the late onset form of glycogen storage disease type 2, symptoms may not be evident until childhood, adolescence, or adulthood. This form is usually milder than the infantile-onset form of the disorder. Most individuals experience progressive muscle weakness, especially in the legs and the trunk, including the muscles that control breathing.[2]
Last updated: 12/24/2008

What causes glycogen storage disease type 2?

Mutations in the GAA gene cause glycogen storage disease type 2. The GAA gene provides instructions for producing an enzyme called acid alpha-glucosidase (commonly called acid maltase). This enzyme is active in lysosomes, which are structures that serve as the cell's recycling center. The enzyme normally breaks down glycogen into a simpler sugar called glucose, which is the main energy source for most cells. Mutations in the GAA gene prevent acid alpha-glucosidase from breaking down glycogen, allowing it to build up in the body's cells. Over time, this buildup damages cells throughout the body, particularly muscle cells.[2]
Last updated: 12/24/2008

Is glycogen storage disease type 2 inherited?

Glycogen storage disease type 2 is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.[2]
Last updated: 12/24/2008

How might glycogen storage disease type 2 be treated?

Individuals with glycogen storage disease type 2 are best treated by a team of specialists (such as cardiologist, neurologist, and respiratory therapist) knowledgeable about the disease, who can offer supportive and symptomatic care.  The discovery of the GAA gene has led to rapid progress in understanding the biological mechanisms and properties of the GAA enzyme.  As a result, an enzyme replacement therapy has been developed that has shown, in clinical trials with infantile-onset patients, to decrease heart size, maintain normal heart function, improve muscle function, tone, and strength, and reduce glycogen accumulation.  In 2006, a drug called alglucosidase alfa (Myozyme©) received FDA approval for the treatment of glycogen storage disease type 2. Myozyme is a form of GAA—the enzyme that is absent or reduced in this condition. The drug is usually administered via intravenous infusion every other week. Myozyme has been remarkably successful in reversing cardiac muscle damage and in improving life expectancy in those with the infantile form of the disease. [1][3][4] To find out more information on Myozyme, please visit the following link: http://www.myozyme.com/
Last updated: 2/24/2014

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