Pompe disease (glycogen storage disease type II) is an inherited disorder of glycogen metabolism and a lysosomal storage disease, caused by a deficiency of the enzyme alpha-glucosidase (also called GAA and acid-maltase). Individuals with Pompe disease are unable to use the glycogen stored in the lysosomes for energy, resulting in the progressive storage of glycogen in the heart, liver, and skeletal muscle.

Pompe disease can present in infancy with profound hypotonia, cardiomegaly and cardiomyopathy or later in childhood and adulthood with progressive muscle weakness and respiratory insufficiency.

Late onset Pompe disease presenting in the second to seventh decade of life can appear with muscle weakness in the upper and/or lower extremeties, muscle weakness in the trunk and shortness of breath after exercise.

Diagnosis for Pompe disease can be made by measuring GAA activity in lymphocytes, blood spots, or cultured fibroblasts. Deficient activity is diagnostic for Pompe disease. Transfusion within 1 week may cause ambiguous results in blood. Individuals who appear to have Pompe disease but who do not demonstrate a significant enzyme deficiency in blood should be followed up with testing in cultured skin fibroblasts or DNA sequencing. Individuals with indeterminate activity in blood should also be followed up with either enzyme testing in cultured fibroblasts or DNA sequencing.