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Test Code GAAW Acid Alpha-Glucosidase, Leukocytes


Shipping Instructions


For optimal isolation of leukocytes, it is recommended the specimen arrive refrigerate within 96 hours of collection to be stabilized. Collect specimen Monday through Thursday only and not the day before a holiday. Specimen should be collected and packaged as close to shipping time as possible.



Specimen Required


Container/Tube:

Preferred: Yellow top (ACD solution B)

Acceptable: Yellow top (ACD solution A) or lavender top (EDTA)

Specimen Volume: 6 mL

Collection Instructions: Send specimen in original tube. Do not transfer blood to other containers.


Forms

1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Biochemical Genetics Patient Information (T602) in Special Instructions

Secondary ID

606267

Useful For

Diagnosis of Pompe disease

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Reporting Name

Acid Alpha-Glucosidase, Leukocytes

Specimen Type

Whole Blood ACD

Specimen Minimum Volume

2 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Whole Blood ACD Refrigerated (preferred) 4 days
  Ambient  72 hours

Reject Due To

Gross hemolysis Reject

Clinical Information

Pompe disease, also known as glycogen storage disease type II, is an autosomal recessive disorder caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA; acid maltase) due to variants in the GAA gene. The estimated incidence is 1 in 40,000 live births. In Pompe disease, glycogen that is taken up by lysosomes during physiologic cell turnover accumulates, causing lysosomal swelling, cell damage, and  organ dysfunction. This leads to progressive muscle weakness, cardiomyopathy, and, eventually, death. Individuals with Pompe disease, especially those with infantile, childhood, and juvenile onset, can have elevations of serum enzymes (such as creatine kinase) secondary to cellular dysfunction.

 

The clinical phenotype of Pompe disease lies on a spectrum dependent on age of onset and residual enzyme activity. Complete loss of enzyme activity causes onset in infancy leading to death, typically within the first year of life when left untreated. Juvenile and adult-onset forms, as the names suggest, are characterized by later onset and longer survival. All disease variants are eventually associated with progressive muscle weakness and respiratory insufficiency. Cardiomyopathy is associated almost exclusively with the infantile form. Treatment with enzyme replacement therapy is available, making early diagnosis of Pompe disease desirable, as early initiation of treatment may improve prognosis. Newborn screening can identify individuals with all forms of Pompe disease, even before onset of symptoms. Unaffected individuals with GAA pseudodeficiency alleles and carriers may also be identified by newborn screening.

 

Determination of GAA enzyme activity in leukocytes can be helpful in distinguishing between infantile and later onset Pompe disease, but it may also be deficient in individuals with pseudodeficiency alleles and in some carriers. Urine glucotetrasaccharides (HEX4 / Glucotetrasaccharides, Random, Urine) have been shown to be elevated in some individuals, particularly those with infantile onset, and may aid in initial diagnosis and for treatment monitoring.

 

Molecular genetic analysis of the GAA gene (GAAZ / Pompe Disease, Full Gene Analysis, Varies) is necessary for differentiating alterations from disease-causing variants in affected individuals and for carrier detection in family members.

Reference Values

≥1.50 nmol/hour/mg protein

An interpretive report is provided.

Interpretation

When abnormal results are detected, a detailed interpretation is given, including an overview of the results and of their significance, a correlation to available clinical information, elements of differential diagnosis, recommendations for additional biochemical testing and in vitro, confirmatory studies (enzyme assay, molecular analysis), and a phone number to reach one of the laboratory directors in case the referring physician has additional questions.

Clinical Reference

1. Elliott S, Buroker N, Cournoyer JJ, et al: Pilot study of newborn screening for six lysosomal storage diseases using tandem mass spectrometry. Mol Genet Metab. 2016 Aug;118(4):304-309

2. Matern D, Gavrilov D, Oglesbee D, et al: Newborn screening for lysosomal storage disorders. Semin Perinatol. 2015 Apr;39(3):206-216

3. Valle D, Beaudet AL, Vogelstein B, Kinzler KW, et al, eds. Lysosomal disorders. In: The Online Metabolic and Molecular Bases of Inherited Disease (OMMBID). Part 16. McGraw-Hill; 2014. Accessed 2/11/2019.  Available at http://ommbid.mhmedical.com/book.aspx?bookid=971

4. Lin N, Huang J, Violante S, et al: Liquid chromatography-tandem mass spectrometry assay of leukocyte acid alpha-glucosidase for post-newborn screening evaluation of Pompe disease. Clin Chem. 2017 Apr;63(4):842-851

5. Leslie N, Bailey L: Pompe disease. In: Adam MP, Ardinger HH, Pagon RA, et al. GeneReviews. [Internet] University of Washington, Seattle; 2007. Updated May 2017. Accessed February 11, 2019. Available at www.ncbi.nlm.nih.gov/books/NBK1261/

Day(s) and Time(s) Performed

Specimens are processed Monday through Sunday.

Assay is performed: Varies

Analytic Time

5 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

82657

LOINC Code Information

Test ID Test Order Name Order LOINC Value
GAAW Acid Alpha-Glucosidase, Leukocytes 24051-5

 

Result ID Test Result Name Result LOINC Value
606267 Acid Alpha-Glucosidase, Leukocytes 24051-5
606268 Interpretation 59462-2
606269 Reviewed By 18771-6