The incidence of type II glycogen-storage disease (Pompe disease) varies depending on ethnicity and geographic region. As of 2010, nine studies have been published documenting the incidence of Pompe disease. It is most common within the African American population, with an incidence of 1 in 14,000. In the U.S. more broadly speaking, the combined incidence of all three variants of the disease is 1 in 40,000. These estimates relied on the frequencies of three mutations in the gene acid alpha-glucosidase (GAA), leading to variants of the disease. Criteria for inclusion in the studies were often non-selective; in many cases, molecular genetic screening was done at birth. With such a high prevalence of Pompe disease reported, it is expected that large university medical centers specializing in neuromuscular diseases would see a higher incidence of Pompe disease among their patients. From a comparable Italian multicenter study, it appears that Pompe disease accounts for 3% of all patients presenting with proximal weakness with or without CK elevation.

This study will measure the incidence of Pompe disease based on manifest laboratory abnormality, namely low GAA enzyme activity. Analysis of GAA enzyme activity will be determined through a blood sample of 4 mL. The study seeks to measure the epidemiology of Pompe disease by symptomatically screening all patients who present with symptoms of hitherto undiagnosed proximal weakness with or without elevation of the muscle enzyme, creatinine kinase (CK), or elevation of CK alone, at thirteen academic tertiary neuromuscular practices throughout the United States and Canada. Total recruitment is expected to be ~1,500 participants. It is anticipated that the number of incident Pompe cases in this cohort would be between 3-5%, i.e. 45-75 newly diagnosed cases of Pompe disease.

Inclusion Criteria:

• Age 8 years or older.
• Geographically accessible to one of the sites.
• One of these following three clinical situations: Complaint of proximal muscle weakness with or without elevation in creatinine kinase (CK); neck muscle weakness (either flexor or extensor) with or without elevation in CK; or elevation of CK in isolation.
• Capable and willing to provide informed consent or assent and follow study procedures.

Exclusion Criteria:

• Less than 8 years of age.
• Subjects with an alternative neuromuscular diagnosis that is responsible for subject's symptoms
• Incapable or unwilling to provide informed consent and to follow research procedures.

Patients age of 8 years and older suspected of late-onset Pompe disease.