Diagnosis

Establish or confirm diagnosis

Evaluation of patients with a clinical presentation suggestive of Pompe disease (muscle hypotonia, weakness, or cardiomyopathy) outside of the newborn screening setting

Dried blood spots are processed using 2 analytical protocols with postanalytical integration of all test results. Protocol 1: A dried blood spot is extracted by the addition of methanol with known concentrations of isotopically labeled amino acids and acylcarnitines, which are used as internal standards. The extract is derivatized by … Dried blood spots are processed using 2 analytical protocols with postanalytical integration of all test results.   Protocol 1: A dried blood spot is extracted by the addition of methanol with known concentrations of isotopically labeled amino acids and acylcarnitines, which are used as internal standards. The extract is derivatized by the addition of 3M HCl in n-butanol. From the residual blood spot a second extraction and derivatization is performed and analyzed concurrently by flow injection tandem mass spectrometry for creatine and creatinine.   Protocol 2: Two 3-mm dried blood spots are excised from a single specimen and placed into individual plates. One spot is treated with a solution containing substrate and internal standard for acid sphingomyelinase, beta-glucocerebrosidase, alpha-glucosidase, alpha-galactosidase, galactocerebrosidase, and alpha-L-iduronidase. The enzyme plate is sealed and incubated overnight. Following incubation, the enzyme plate is purified by liquid-liquid extraction. The second dried blood spot is extracted with methanol containing d4-C26 lysophosphatidylcholines (LPC) on day 2 of the procedure. The LPC extracts and enzyme products are combined and analyzed concurrently by flow injection tandem mass spectrometry. View more

Tests performed
Entire test performed in-house

Recovery was used to assess accuracy; mean recovery was 105%. Method comparison was acceptable with 6 Pompe patients and >1000 normal specimens. Intra assay precision was performed at several levels: %CV ranged from 4%-17% (N=20 each). Inter assay precision was performed at several levels: %CV ranged from 4%-27% (N≥10 each).

For asymptomatic individuals, this test may not detect some late-onset and variant forms of Pompe disease. Carrier status (heterozygosity) for Pompe disease cannot be reliably detected. A positive test result is strongly suggestive of a diagnosis but requires follow-up molecular genetic analysis of the GAA gene, which is best coordinated … For asymptomatic individuals, this test may not detect some late-onset and variant forms of Pompe disease.   Carrier status (heterozygosity) for Pompe disease cannot be reliably detected.   A positive test result is strongly suggestive of a diagnosis but requires follow-up molecular genetic analysis of the GAA gene, which is best coordinated by local genetics providers. View more

Is proficiency testing performed for this test? Help
Yes

Method used for proficiency testing: Help
Formal PT program

PT Provider: Help
Centers for Disease Control and Prevention Newborn Screening Quality Assurance Program, CDC DLS

Description of PT method: Help
Formal PT program

Description of internal test validation method: Help
This test was laboratory developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements.