TEST CATALOG ORDERING & RESULTS SPECIMEN HANDLING CUSTOMER SERVICE EDUCATION & INSIGHTS
Test Catalog

Test ID: GAAZ    
Pompe Disease, Full Gene Analysis, Varies

Useful For Suggests clinical disorders or settings where the test may be helpful

Confirmation of diagnosis of Pompe disease (as a follow-up to biochemical analyses)

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

If skin biopsy is received, fibroblast culture and cryopreservation for biochemical studies will be performed at an additional charge.

 

See the following in Special Instructions.

-Newborn Screen Follow-up for Pompe Disease 

-Newborn Screening Act Sheet Pompe Disease: Decreased Acid Alpha-Glucosidase

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Pompe disease, also known as glycogen storage disease type II, is an autosomal recessive condition caused by deficiency of acid alpha-glucosidase. Enzyme insufficiency results in symptoms such as muscle weakness, cardiomyopathy, and respiratory problems. Pathogenic alterations in the GAA gene (which encodes acid alpha-glucosidase) are associated with Pompe disease.

 

The diagnosis of this heterogeneous condition relies on both clinical and laboratory evaluation. Clinically, the condition is categorized into infantile and late-onset forms based on age of onset, organ involvement, and rate of progression. The infantile form (or classic Pompe disease) is the most severe form and is characterized by early onset and rapid progression of cardiac, liver, and muscle problems resulting in death within the first year. The infantile variant form has a similar age of onset but a milder clinical presentation. On the less severe end of the spectrum is the late-onset form with childhood, juvenile, or adult onset. The rate of progression and severity of symptoms is quite variable, particularly in the late-onset forms. The incidence varies by clinical type and ethnic population; the combined incidence is approximately 1 in 40,000 individuals.

 

The calculated ratio of creatine (Cre) and creatinine (Crn) to acid-alpha glucosidase (GAA) activity is useful for individuals with a suspected diagnosis of Pompe disease; for patients older than 6 weeks, order PDBS / Pompe Disease, Blood Spot; for patients 6 weeks and younger, order PD2T / Pompe Disease Second-Tier Newborn Screening, Blood Spot. Alternatively, enzyme studies can be ordered on blood via GAAW / Acid Alpha-Glucosidase, Leukocytes. When clinical manifestations and results of that analysis are supportive of a diagnosis of Pompe disease, variant analysis of the GAA gene is warranted. Additionally, measurement of the urine glucotetrasaccharide biomarker can aid in diagnosis and ongoing therapeutic monitoring (HEX4 / Glucotetrasaccharides, Random, Urine)

 

Over 250 different variants have been identified in this gene including point alterations and large deletions. GAA full gene sequencing provided by this test will detect 2 variants in approximately 83% to 93% of individuals with confirmed GAA enzyme deficiency. Identification of genetic variants provides confirmation of the diagnosis and allows for subsequent testing of at risk family members.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation Provides information to assist in interpretation of the test results

All detected alterations are evaluated according to American College of Medical Genetics and Genomics (ACMG) recommendations.(1) Variants are classified based on known, predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or known significance.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

A small percentage of individuals who are carriers or have a diagnosis of Pompe disease may have a genetic variant that is not identified by this method (eg, large genomic deletions or duplications, promoter alterations). The absence of a variant, therefore, does not eliminate the possibility of positive carrier status or the diagnosis of Pompe disease. For carrier testing, it is important to first document the presence of a GAA gene variant in an affected family member.

 

In some cases, DNA alterations of undetermined significance may be identified.

 

Rare alterations exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.

 

Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in the interpretation of results may occur if information given is inaccurate or incomplete.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Richards S, Aziz N, Bale S, et al: Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology. Genet Med. 2015 May;17(5):405-424

2. Kishnani PS, Steiner RD, Bali D, et al: Pompe disease diagnosis and management guideline. Genet Med. 2006 May;8(5):267-288

3. Van der Ploeg AT, Reuser AJJ: Pompe's disease. Lancet. 2008;372(9646):1342-1353

4. Kroos M, Pomponio RJ, van Vliet L, et al: Update of the Pompe disease mutation database with 107 sequence variants and a format for severity rating. Hum Mut. 2008;29(6):E13-26

5. Reuser AJJ, Hirschhorn R, Kroos MA: Pompe disease: Glycogen storage disease type II, acid a-glucosidase (acid maltase) deficiency. In: Valle DL, Antonarakis S, Ballabio A, Beaudet AL, Mitchell GA. eds. Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2019. Accessed June 30, 2020. Available at: https://ommbid.mhmedical.com/content.aspx?bookid=2709&sectionid=225890450

Special Instructions Library of PDFs including pertinent information and forms related to the test