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HelpTest ID PD2T Pompe Disease Second-Tier Newborn Screening, Blood Spot
Ordering Guidance
Due to reference range differences, this is the appropriate test for patients less than or equal to 6 weeks of age. For patients greater than 6 weeks of age, order PDBS / Pompe Disease, Blood Spot.
Necessary Information
1. Birth weight (grams)
2. Time of birth (24-hour time)
3. Gestational age (weeks)
Specimen Required
Supplies: Card-Blood Spot Collection (Filter Paper) (T493)
Container/Tube:
Preferred: Blood Spot Collection Card
Acceptable: PerkinElmer 226 filter paper, Munktell filter paper, Whatman Protein Saver 903 paper, local newborn screening card, or blood collected in tubes containing ACD or EDTA and then spotted and dried on filter paper.
Specimen Volume: 3 Blood spots
Collection Instructions:
12. Completely fill at least 3 circles on the filter paper card (approximately 100 microliters blood per circle).
2. Let blood dry on the filter paper at ambient temperature in a horizontal position for a minimum of 3 hours.
3. Do not expose specimen to heat or direct sunlight.
4. Do not stack wet specimens.
5. Keep specimen dry.
Additional Information:
1. For collection instructions, see Blood Spot Collection Instructions.
2. For collection instructions in Spanish, see Blood Spot Collection Card-Spanish Instructions (T777).
3. For collection instructions in Chinese, see Blood Spot Collection Card-Chinese Instructions (T800).
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:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. Biochemical Genetics Patient Information (T602)3. If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.
Useful For
Second-tier testing of newborns with an abnormal primary screening result for Pompe disease (decreased acid alpha-glucosidase enzyme activity)
Follow-up testing for evaluation of an abnormal newborn screening result for Pompe disease
Highlights
This test is used as a second-tier newborn screen for Pompe disease. It is based upon a ratio calculated between the creatine and creatinine ratio and the activity of acid-alpha glucosidase (GAA).
This test can help differentiate true cases of infantile and late-onset Pompe disease from false-positive cases (such as carriers and pseudodeficiency of GAA enzyme).
A positive test result supports the utility of follow-up molecular genetic analysis of the GAA gene.
Method Name
Flow Injection Analysis Tandem Mass Spectrometry (FIA-MS/MS)
Reporting Name
Pompe Disease 2ND Tier NBS, BSSpecimen Type
Whole bloodSpecimen Minimum Volume
1 Blood spot
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Whole blood | Refrigerated (preferred) | 90 days | |
| Frozen | 90 days | ||
| Ambient | 28 days |
Reject Due To
| Blood spot specimen that shows serum rings or has multiple layers | Reject |
| Insufficient specimen | Reject |
| Specimens known to have been exposed to elevated temperatures above ambient | 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 eventually, organ dysfunction. This leads to progressive muscle weakness, cardiomyopathy, and eventually, death. Patients with Pompe disease, especially those with infantile, childhood, and juvenile onset, can have elevated serum enzymes (such as creatine kinase) secondary to cellular dysfunction.
The clinical phenotype of Pompe disease lies on a spectrum, with differing clinical phenotypes 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 patients with all forms of Pompe disease, even before onset of symptoms. Newborn screening may also identify unaffected patients with GAA pseudodeficiency alleles and carriers.
The ratio calculated using the creatine:creatinine ratio as the numerator and the activity of GAA as the denominator can differentiate true cases of infantile and late-onset Pompe disease from false-positive cases, such as carriers and pseudodeficiency of GAA enzyme. When applied to the newborn screening setting, this second-tier testing can provide results in a timely fashion and provide guidance in the decision to submit samples for additional confirmatory testing by molecular genetic analysis (GAAZ / Pompe Disease, Full Gene Analysis, Varies).
Reference Values
An interpretive report will be provided.
Interpretation
The quantitative measurements of informative metabolites and related ratios are evaluated using the Collaborative Laboratory Integrated Reports (CLIR) system. The report is in text form only, indicating if the applicable ratio is normal or abnormal and whether the CLIR postanalytical tool is informative for Pompe disease. Abnormal results are not sufficient to conclusively establish a diagnosis of a particular disease. To verify a preliminary diagnosis, independent biochemical (ie, in vitro enzyme assay) or molecular genetic analyses are required, many of which are offered within Mayo Clinic Laboratories. Recommendations for additional biochemical testing and confirmatory studies (enzyme assay, molecular analysis) are provided in the interpretative report.
Cautions
This test may not detect some milder or later onset 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 using a stand-alone biochemical or molecular assay, which is best coordinated by local genetics providers.
Clinical Reference
1. ACMG Newborn Screening ACT Sheets. Accessed August 30, 2023. Available at www.acmg.net/ACMG/Medical-Genetics-Practice-Resources/ACT_Sheets_and_Algorithms/ACMG/Medical-Genetics-Practice-Resources/ACT_Sheets_and_Algorithms.aspx?hkey=9d6bce5a-182e-42a6-84a5-b2d88240c508
2. Pascual JM, Roe CR. Systemic metabolic abnormalities in adult-onset acid maltase deficiency: beyond muscle glycogen accumulation. JAMA Neurol. 2013;70(6):756-763
3. Tortorelli S, Eckerman JS, Orsini JJ, et al. Moonlighting newborn screening markers: The incidental discovery of a second-tier test for Pompe disease. Genet Med. 2018;20(8):840-846. doi:10.1038/gim.2017.190
4. Minter Baerg MM, Stoway SD, Hart J, et al. Precision newborn screening for lysosomal disorders. Genet Med. 2018;20(8):847-854. doi:10.1038/gim.2017.194
5. Ames EG, Fisher R, Kleyn M, Ahmad A. Current practices for U.S. newborn screening of Pompe disease and MPSI. Int J Neonatal Screen. 2020;6(3):72. doi:10.3390/ijns6030072
Method Description
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 containing known concentrations of isotopically labeled amino acids and acylcarnitines, which are used as internal standards. The extract is derivatized by the addition of 3M hydrochloric acid in n-butanol. From the residual blood spot, a second extraction and derivatization are performed and analyzed concurrently by flow injection tandem mass spectrometry for creatine and creatinine.(Turgeon C, Magera M, Allard P, et al. Combined newborns screening for succinylacetone, amino acids, and acylcarnitines in dried blood spots. Clin Chem. 2008;54[4]:657-664)
Protocol 2:
Three 1/8-inch dried blood spots (DBS) are excised from a single specimen. The enzymes are extracted from 2 DBS by incubating the specimens with a mix of substrate and internal standard for acid sphingomyelinase, beta-glucocerebrosidase, alpha-glucosidase, alpha-galactosidase, galactocerebrosidase, alpha-L-iduronidase, and iduronate 2-sulfatase. The sample is then purified by liquid-liquid extraction. The third DBS is extracted with methanol containing d4-C26 lysophosphatidylcholines. The resulting extracts are then combined, evaporated, and reconstituted before analysis by tandem mass spectrometry. (Tortorelli S, Turgeon CT, Gavrilov DK, et al. Simultaneous testing for 6 lysosomal storage disorders and X-adrenoleukodystrophy in dried blood spots by tandem mass spectrometry. Clin Chem. 2016;62[9]:1248-1254)
Day(s) Performed
Monday through Saturday
Report Available
2 to 3 daysTest Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.CPT Code Information
83789
NY State Approved
YesTesting Algorithm
If the patient has abnormal newborn screening result for Pompe disease, immediate action should be taken. Refer to the appropriate ACMG Newborn Screening ACT Sheet.(1)
For more information see Newborn Screen Follow-up for Pompe Disease
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