Pompe disease is a rare and debilitating muscle disease affecting infants, children and adults. The infantile-onset form of the disease generally manifests within a few months of birth and is often fatal within the first year of life. The late-onset form appears anytime during childhood to adulthood in a more gradual progression. Both types are generally characterised by progressive muscle weakness and breathing difficulty, but the severity of the disease can vary widely depending on the age of onset and the extent of organ involvement. In the infantile-onset form, patients typically display a markedly enlarged heart.
People born with Pompe disease have an inherited deficiency of an enzyme known as acid alpha-glucosidase (GAA). Enzymes, which are protein-based molecules within cells, trigger biochemical reactions in the body. In a healthy person with normal GAA activity, this particular enzyme would assist in the breakdown of glycogen, a complex sugar molecule stored within a compartment of the cell known as the lysosome. But in Pompe disease, the GAA activity may be dramatically reduced, dysfunctional, or non-existent, resulting in an excessive accumulation of glycogen in the lysosome.
Eventually, the lysosome may become so clogged with glycogen that normal cellular function is disrupted and muscle function is impaired. In later stages of the disease, the lysosomes may even rupture, releasing glycogen into the rest of the cell. Although there is glycogen storage in the cells of multiple tissues, heart and skeletal muscles are usually the most seriously affected.
Based on the available data, researchers have estimated that Pompe disease occurs in approximately 1 in 40,000 live births1,2.
At present, Pompe disease is thought to affect all races. Some ethnic groups may experience Pompe disease at higher rates, however. In the African-American population, the incidence of the infantile-onset form has been estimated to be much higher at approximately 1 in 14,000 3. In comparison, the incidence for Caucasian adults has been estimated to be 1 in 60,000, and for Caucasian infants, 1 in 100,000 2. Further studies will be needed to determine if there are other ethnicities that may experience a higher disease frequency.
Pompe disease is a broard spectrum disease. Researchers have found that the age of onset and the range of organ involvement for Pompe disease usually correlate with the amount of residual GAA enzyme activity. Most infants generally have less than 1% of normal activity, juveniles less than 10%, and adults less than 40%. The disease can be characterised based on the rate of disease progression (rapid or gradual) and the presence of cardiac involvement (common or infrequent). This results in two major classifications of the disease - infantile-onset and late-onset.
Specifically, the level of GAA enzyme activity is thought to correspond with the presence of heart problems, a key feature of the infantile-onset form of the disease. Most patients who develop symptoms later in life typically have a higher level of enzyme activity, which is thought to help protect their hearts. Typically, only infantile-onset patients, whose GAA activity is usually very low or non-existent, have heart problems.
Within the late-onset classification especially, patients may exhibit mild, moderate, or severe symptoms. It is estimated that approximately one-third of those with Pompe disease have the infantile-onset form, while the majority of patients have the slowly progressive late-onset form.
Tarryn, Australia, Pompe patient
To learn more about Pompe disease contact your doctor or other healthcare professionals, or the following patient associations:
Ausems MG, Verbiest J, Hermans MP, et al. Frequency of glycogen storage disease type II in The Netherlands: implications for diagnosis and genetic counseling. Eur J Hum Genet 1999 Sep; 7(6): 713-6.
Martiniuk F, Chen A, Mack A, et al. Carrier frequency for glycogen storage disease type II in New York and estimates of affected individuals born with the disease. Am J Med Genet 1999; 79: 69.
Hirschhorn, Rochelle and Arnold J. J. Reuser. Glycogen Storage Disease Type II: Acid Alpha-Glucosidase (Acid Maltase) Deficiency. In: Wonsiewicz M, Noujaim S, Boyle P, eds. The Metabolic and Molecular Bases of Inherited Disease. 8th Edition. New York: McGraw-Hill; 2001; 3389-3420.