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Test ID: AGAS Alpha-Galactosidase, Serum

Reporting Name

Alpha-Galactosidase, S

Useful For

Diagnosis of Fabry disease in males

 

Preferred screening test (serum) for Fabry disease

Testing Algorithm

The following algorithms are available in Special Instructions:

-Fabry Disease: Newborn Screen-Positive Follow-up

-Fabry Disease Testing Algorithm

Specimen Type

Serum


Specimen Required


Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 2 mL


Specimen Minimum Volume

0.2 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Frozen (preferred) 14 days
  Refrigerated  24 hours

Reference Values

0.074-0.457 U/L

Note: Results from this assay are not useful for carrier determination. Carriers usually have levels in the normal range.

Day(s) and Time(s) Performed

Tuesday

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
AGAS Alpha-Galactosidase, S 1813-5

 

Result ID Test Result Name Result LOINC Value
50578 Specimen 31208-2
50579 Specimen ID 57723-9
50580 Source 31208-2
50581 Order Date 82785-7
50582 Reason For Referral 42349-1
50583 Method 49549-9
50590 Alpha-Galactosidase,S 1813-5
50584 Interpretation 59462-2
50585 Amendment 48767-8
50586 Reviewed By No LOINC Needed
50587 Release Date 82772-5

Clinical Information

Fabry disease is an X-linked lysosomal storage disorder resulting from deficient activity of the enzyme alpha-galactosidase A (alpha-Gal A) and the subsequent deposition of glycosylsphingolipids in tissues throughout the body; in particular, the kidney, heart, and brain. Fabry disease is caused by mutations within the GLA gene, and more than 630 mutations have been identified in individuals diagnosed with Fabry disease. Severity and onset of symptoms are dependent on the amount of residual enzyme activity. The classic form of Fabry disease occurs in males who have less than 1% alpha-Gal A activity. Symptoms usually appear in childhood or adolescence and can include acroparesthesias (burning pain in the extremities), gastrointestinal issues, multiple angiokeratomas, reduced or absent sweating, corneal opacity, and proteinuria. In addition, progressive renal involvement leading to end-stage renal disease typically occurs in adulthood, followed by cardiovascular and cerebrovascular disease. The estimated incidence varies from 1 in 3,000 infants detected via newborn screening to 1 in 10,000 males diagnosed after onset of symptoms.

 

Males with residual a-Gal A activity greater than 1% may present with 1 of 3 variant forms of Fabry disease with onset of symptoms later in life: a renal variant associated with end stage renal disease (ESRD) but without the pain or skin lesions; a cardiac variant typically presenting in the sixth to eighth decade with left ventricular hypertrophy, cardiomyopathy and arrhythmia, and proteinuria, but without ESRD; and a cerebrovascular variant presenting as stroke or transient ischemic attack. The variant forms of Fabry disease may be underdiagnosed.

 

Females who are carriers of Fabry disease can have clinical presentations ranging from asymptomatic to severely affected. Measurement of alpha-Gal A activity is not generally useful for identifying carriers of Fabry disease, as many of these individuals have normal levels of alpha-Gal A. Therefore, molecular genetic analysis of the GLA gene (FABRZ / Fabry Disease, Full Gene Analysis) is recommended to detect carriers.

 

Unless irreversible damage has already occurred, treatment with enzyme replacement therapy (ERT) has led to significant clinical improvement in affected individuals. For this reason, early diagnosis and treatment are desirable, and in a few US states early detection of Fabry disease through newborn screening has been implemented.

 

Absent or reduced alpha-Gal A in blood spots, leukocytes (AGA / Alpha-Galactosidase, Leukocytes), or serum (AGAS / Alpha-Galactosidase, Serum) can indicate a diagnosis of classic or variant Fabry disease. Molecular sequence analysis of the GLA gene (FABRZ / Fabry Disease, Full Gene Analysis) allows for detection of the disease-causing mutation in males and females.

 

See Fabry Disease Testing Algorithm and Fabry Disease: Newborn Screen-Positive Follow-up in Special Instructions.

Interpretation

Deficiency (<0.016 U/L) of alpha-galactosidase in properly submitted specimens is diagnostic for Fabry disease in males. If concerned about specimen integrity, recheck using leukocyte testing (AGA / Alpha-Galactosidase, Leukocytes).

 

Urine sediment analysis (CTSA / Ceramide Trihexosides and Sulfatides, Urine) for the accumulating trihexoside substrate is also recommended.

 

Carrier females usually have alpha-galactosidase levels in the normal range; therefore, molecular sequence analysis of the GLA gene (FABRZ / Fabry Disease, Full Gene Analysis) is recommended as the appropriate diagnostic test for females.

Clinical Reference

1. Desnick RJ, Ioannou YA, Eng CM: Chapter 150: Alpha-galactosidase A deficiency: Fabry disease. In The Metabolic Basis of Inherited Disease. Eighth edition. Edited by D Valle, AL Beaudet, B Vogelstein. New York, McGraw-Hill Book Company. Accessed 01/23/15. Available at www.ommbid.com

2. De Schoenmakere G, Poppe B, Wuyts B, et al: Two-tier approach for the detection of alpha-galactosidase A deficiency in kidney transplant recipients. Nephrol Dial Transplant 2008;23:4044-4048

3. Mehta A, Hughes DA: Fabry Disease. In GeneReviews. 2002 Aug 5, Updated 2013 Oct 17. Edited by RA Pagon, MP Adam, HH Ardinger, et al: Seattle, WA. University of Washington, Seattle; 1993-2015. Accessed 1/23/17. Available at www.ncbi.nlm.nih.gov/books/NBK1292/

4. Laney DA, Bennett RL, Clarke V, et al: Fabry disease practice guidelines: recommendations of the National Society of Genetic Counselors. J Genet Couns 2013;22:555-564

5. Laney DA, Peck DS, Atherton AM, et al: Fabry disease in infancy and early childhood: a systematic literature review. Genet Med 2014;Epub ahead of print. Accessed 1/23/15. Available at www.nature.com/gim/journal/vaop/ncurrent/pdf/gim2014120a.pdf

Analytic Time

8 days

Method Name

Fluorometric

Forms

1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

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

Mayo Medical Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

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