The following information may help to address your question:
What is glycogen storage disease type 2?
Glycogen storage disease type 2
, also known as Pompe disease or acid maltase deficiency disease, is an inherited metabolic disorder
While glycogen storage disease type 2 is a single disease, it may be classified in 2 forms according to the rates of disease progression, its severity and the age at which symptoms start. The classic infantile-onset starts before 12 month of age and involves the heart muscle (myocardiopathy). The later-onset form may start before 12 months of age (non-classic infantile-onset), or after 12 months of age, but does not affect the heart. Muscle weakness is a main symptom in all forms. The infantile-onset is the most severe form and, if untreated, it may lead to death from heart failure in the first year of life. The late-onset form is usually milder, but if untreated may lead to severe breathing problems.
Glycogen storage disease type 2 is caused by variants (mutations
) in the GAA gene
which have instructions to produce the enzyme
acid alpha-glucosidase (acid maltase), needed to break down glycogen, a substance that is a source of energy for the body. The enzyme deficiency results in the accumulation of glycogen inside lysosomes
, structures within cells
that break down waste products within the cell. Accumulation of glycogen in certain tissues
, especially muscles, impairs their function.
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. Another similar drug called Lumizyme has recently been approved for the treatment this disease.
Additional treatment of Pompe disease is symptomatic and supportive and may include respiratory and feeding support and physical therapy
Last updated: 6/1/2018
What are the signs and symptoms of glycogen storage disease type 2?
The classic 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).
Affected infants may also have poor feeding, failure to gain weight and grow at the expected rate (failure to thrive), breathing problems, and hearing loss
. Most infants with glycogen storage disease type 2 cannot hold up their heads or move normally. 
Without treatment, progressive cardiac failure usually causes life-threatening complications by the age of 12 to 18 months.
The non-classic infantile form of glycogen storage disease type 2 usually presents within the first year of life. Initial symptoms may include delayed motor skills (crawling, sitting) and myopathy. Cardiomegaly may be present, but unlike the classic infantile form, cardiac failure does not typically occur. Muscle weakness may lead to serious, life-compromising breathing problems by early childhood.
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.
Last updated: 6/20/2016
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.
Last updated: 5/14/2015
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.
Last updated: 5/14/2015
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
, 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. A drug called alglucosidase alfa (Myozyme©) has 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.
To find out more information on Myozyme, please visit the following link: http://www.myozyme.com/
. Another alglucosidase alfa drug called Lumizyme has also been approved for the treatment of this condition.
More information about Lumizyme can be accessed through the following link: http://www.lumizyme.com/patients.aspx
Last updated: 5/14/2015
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