Making a Diagnosis

After examining a patient’s symptoms and reviewing the results of several different tests, doctors may ultimately come to suspect Pompe disease. A conclusive way to confirm this diagnosis is by measuring the activity of the acid alpha-glucosidase (GAA) enzyme, which is always lower than normal in people with Pompe disease. The test used for this is called an enzyme assay.

Today, enzyme assays can be performed with simple blood tests that provide fast and accurate results.[1-5]

Real Stories: Learn why identifying Pompe disease is so difficult

Measuring Enzyme Levels

By definition, Pompe disease occurs when a genetic defect results in deficient or malfunctioning enzyme called GAA.[6]

Learn more about the underlying cause of Pompe disease 

All people with Pompe disease have lower than normal GAA activity levels—sometimes even none at all. The exact numbers can range from less than 1% of normal levels (usually found in infants) to up to 40%.[5-8]

An enzyme assay result of 1-40% of normal GAA levels usually identifies Pompe disease. However, within that range, a particular number cannot predict what kind of symptoms a person will have or how the disease will progress, as there is great variability among patients.[6]

Advantages of Blood Tests

An enzyme assay to measure GAA activity can be performed on a variety of samples from a patient's blood, skin cells, or muscle. Blood tests have advantages such as:[1-2]

  • They are not generally painful to the patient, requiring as little as just a few drops of blood obtained by a small prick
  • Results are usually available within just a few days (as opposed to several weeks with some other methods)
  • Recent updates to the tests have made them very accurate

Other Testing Options

While enzyme assays using blood samples are becoming widely available, in some areas doctors and labs may perform enzyme assays on skin cells or muscle tissue samples instead. These tests can also provide an accurate and definitive diagnosis of Pompe disease.[1-2], [6], [8]

One other testing option, mutation analysis, takes a completely different approach. Instead of measuring enzyme activity, this method (also called genotyping) uses a DNA sample to see if the person has the gene mutation, or defect, that causes Pompe disease. This is especially useful within families in which the particular mutation is known, or to identify carriers of the disease.

Find out more about Pompe disease diagnosis and testing within families 

References

  1. Zhang H, Kallwass H, Young SP et al. Comparison of maltose and acarbose as inhibitors of maltase-glucoamylase activity in assaying acid alpha-glucosidase activity in dried blood spots for the diagnosis of infantile Pompe disease. Genet Med 2006 8:302-306.
  2. Winchester B, Bali D, Bodamer OA et al. Methods for a prompt and reliable laboratory diagnosis of Pompe disease: Report from an international consensus meeting. Mol Genet Metab 2007 1-7.
  3. Okumiya T, Keulemans JL, Kroos MA et al. A new diagnostic assay for glycogen storage disease type II in mixed leukocytes. Mol Genet Metab 2006 88:22-28.
  4. Jack RM, Gordon C, Scott CR, Kishnani PS, Bali D. The use of acarbose inhibition in the measurement of acid alpha-glucosidase activity in blood lymphocytes for the diagnosis of Pompe disease. Genet Med 2006 8:307-312.
  5. Kallwass H, Carr C, Gerrein J et al. Rapid diagnosis of late-onset Pompe disease by fluorometric assay of alpha-glucosidase activities in dried blood spots. Mol Genet Metab 2007.
  6. Hirschhorn, Rochelle and Arnold J. J. Reuser. Glycogen Storage Disease Type II: Acid Alpha-glucosidase (Acid Maltase) Deficiency. In: Scriver C, Beaudet A, Sly W, Valle D, editors. The Metabolic and Molecular Bases of Inherited Disease. 8th Edition. New York: McGraw-Hill, 2001. 3389-3420.
  7. Chen YT, Amalfitano A. Towards a molecular therapy for glycogen storage disease type II (Pompe disease). Mol Med Today 2000 Jun;6(6):245-51.
  8. Kishnani PS, Steiner RD, Bali D et al. Pompe disease diagnosis and management guideline. Genet Med 2006 8:267-88.

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