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Test Code G6ST N-Acetylgalactosamine-6-Sulfate Sulfatase, Fibroblasts

Performing Laboratory

Mayo Medical Laboratories in Rochester

Reporting Name

N-Acetylgalactosamine 6 Slft, Fibro

Specimen Type

Tissue


Advisory Information


This test is not recommended for prenatal testing.

 

The preferred test to rule-out mucopolysaccharidosis IVA (Morquio A syndrome) is G6SW / N-Acetylgalactosamine-6-Sulfatase, Leukocytes.



Specimen Required


Submit only 1 of the following specimens:

 

Specimen Type: Cultured fibroblasts

Container/Tube: T-75 or T-25 flask

Specimen Volume: 1 Full T-75 flask or 2 full T-25 flasks

Specimen Stability Information: Ambient (preferred)/Refrigerated <24 hours

 

Specimen Type: Skin biopsy

Supplies: Fibroblast Biopsy Transport Media (T115)

Container/Tube: Sterile container with any standard cell culture media (eg, minimal essential media, RPMI 1640). The solution should be supplemented with 1% penicillin and streptomycin. Tubes can be supplied upon request (Eagle's minimum essential medium with 1% penicillin and streptomycin [T115]).

Specimen Volume: 4-mm punch

Specimen Stability Information: Refrigerated (preferred)/Ambient


Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

Specimen received in formalin or fixative preservative

Specimen Stability Information

Specimen Type Temperature Time
Tissue Varies

Specimen Minimum Volume

See Specimen Required

Day(s) and Time(s) Performed

Varies

Specimen Retention Time

3 years - Check with the lab for availability

Analytic Time

30-60 days depending on rapidity of growth

Reference Values

≥163 nmol/17 hour/mg protein

Additional Tests

Test ID Reporting Name Available Separately Always Performed
FIBR Fibroblast Culture Yes Yes
CRYOB Cryopreserve for Biochem Studies No Yes

Useful For

Assisting in the diagnosis of Morquio A syndrome in fibroblast specimens

 

The test is not useful to establish carrier status for Morquio A syndrome.

Testing Algorithm

When this test is ordered, a fibroblast culture and cryopreservation for biochemical studies will always be performed at an additional charge. However, for multiple lysosomal enzyme assays on a patient utilizing fibroblast culture, only 1 culture is required regardless of the number of enzyme assays ordered. If viable cells are not obtained within 10 days, client will be notified.

Method Name

G6ST: Fluorometric

FIBR: Cultivated from Biopsy as Monolayer

CRYOB: Fibroblast Subculture Followed by Cryopreservation and Storage

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-N-Acetylgalactosamine-6-sulfate sulfatase

88233-Fibroblast culture

88240-Cryopreservation for biochemical studies

LOINC Code Information

Test ID Test Order Name Order LOINC Value
G6ST N-Acetylgalactosamine 6 Slft, Fibro 24095-2

 

Result ID Test Result Name Result LOINC Value
35766 N-Acetylgalactosamine 6 Slft, Fibro 24095-2
29726 Interpretation (G6ST) 59462-2
29728 Reviewed By 18771-6

Clinical Information

Mucopolysaccharidosis IVA, (MPS IVA, Morquio A syndrome) is an autosomal recessive mucopolysaccharidosis caused by reduced or absent N-acetylgalactosamine-6-sulfate sulfatase (GALNS) enzyme activity. The mucopolysaccharidoses are a group of disorders caused by the deficiency of any of the enzymes involved in the stepwise degradation of dermatan sulfate, heparan sulfate, keratan sulfate, or chondroitin sulfate (glycosaminoglycans, GAGs). Accumulation of GAGs (previously called mucopolysaccharides) in lysosomes interferes with normal functioning of cells, tissues, and organs.

 

Clinical features and severity of symptoms of MPS IVA are widely variable and affect multiple body systems. Clinical features may include skeletal dysplasia, short stature, dental anomalies, corneal clouding, respiratory insufficiency, and cardiac disease. Intelligence is usually normal. Treatment options are mostly limited to symptom management, however, more recently available enzyme replacement therapy has shown to be effective in improving some function and quality of life for individuals with Morquio A. Estimates of the incidence of Morquio A syndrome range from 1 in 200,000 to 1 in 300,000 live births.

 

A diagnostic workup in an individual with MPS IVA typically demonstrates elevated levels of urinary GAGs and increased keratan sulfate and chondroitin-6-sulfate detected via quantitative and qualitative liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis of the specific sulfates. Morquio B is a genetically distinct disorder caused by a deficiency of beta-galactosidase and has a significant number of overlapping clinical features with Morquio A. Enzyme analysis is necessary to distinguish between the 2 types. Reduced or absent activity of N-acetylgalactosamine-6-sulfate sulfatase enzyme in leukocytes or fibroblasts can confirm a diagnosis of MPS IVA. Sequencing of the GALNS gene allows for detection of disease-causing mutations in affected patients and identification of familial mutations allows for testing of at-risk family members.

Interpretation

Very low enzyme levels are consistent with Morquio A disease.

Cautions

No significant cautionary statements.

Clinical Reference

1. Hendriksz CJ, Harmatz P, Beck M, et al: Review of clinical presentation and diagnosis of mucopolysaccharidosis IVA. Mol Genet Metab 2013 Sep-Oct;110(1-2):54-64 doi: 10.1016/j.ymgme.2013.04.002

2. Enns GM, Steiner RD, Cowan TM: Lysosomal disorders. In Pediatric Endocrinology and Inborn Errors of Metabolism. Edited by K Sarafoglou, GF Hoffmann, KS Roth, New York, McGraw-Hill Medical Division, 2009, pp 732

3. Haddley K: Elosulfase alfa. Drugs Today (Barc) 2014 Jul;50(7):475-483 doi: 10.1358/dot.2014.50.7.2177904

Method Description

Morquio A disease (MPS IVA) results from a deficiency of the N-acetylgalactosamine-6-sulfate sulfatase enzyme. This enzyme hydrolyzes a sulfate group from the 6 position of galactose at the nonreducing terminus of the mucopolysaccharides, keratin sulfate and chondroitin-6 sulfate. In this procedure, 4MU-beta-D-galactoside-6-sulfate is used as the substrate. The enzyme will cleave the 6-sulfate from the galactose residue and a second incubation with excess beta-galactosidase will cleave the 4MU, which is measured fluorometrically and calculated against a calibration of 4MU.(Package insert: Laboratory protocol for enzyme analysis for Morquio A disease [MPS IV A]. Moscerdam Substrates, The Netherlands; van Diggelen OP, Zhao H, Kleijer WJ, et al: A fluorimetric enzyme assay for the diagnosis of Morquio disease type A. Clin Chim Acta 1990;187:131-140)

Genetics Test Information

Not recommended for carrier detection.

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.