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

Test ID: G6SW    
N-Acetylgalactosamine-6-Sulfatase, Leukocytes

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

Preferred test to rule-out mucopolysaccharidosis IVA (Morquio A syndrome)

 

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

Genetics Test Information Provides information that may help with selection of the correct genetic test or proper submission of the test request

This is the preferred test to rule-out mucopolysaccharidosis IVA, (MPS IVA; Morquio A syndrome).

 

Morquio A is an autosomal recessive mucopolysaccharidosis caused by reduced or absent N-acetylgalactosamine-6-sulfate sulfatase (GALNS) enzyme activity.

 

Although clinically similar, Morquio A is distinct from Morquio B at the molecular and enzyme levels. Enzyme analysis is necessary to distinguish between the two.

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

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

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 (referred to as mucopolysaccharides: MPS or glycosaminoglycans: GAG). Accumulation of MPS 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 MPS IVA. Estimates of the incidence of MPS IVA 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 MPS 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 distinct disorder caused by a deficiency of beta-galactosidase and has a significant number of overlapping clinical features with MPS IVA. Enzyme analysis is necessary to distinguish between the 2 types. Reduced or absent activity of N-acetylgalactosamine-6-sulfate sulfatase enzyme in leukocytes and/or fibroblasts can confirm a diagnosis of MPS IVA. Sequencing of the GALNS gene allows for detection of disease-causing variants in affected patients and identification of familial variants allows for 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.

> or =92 nmol/17 hour/mg protein

Interpretation Provides information to assist in interpretation of the test results

Very low enzyme activity levels are consistent with mucopolysaccharidosis IVA (Morquio A syndrome).

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

No significant cautionary statements

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

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: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. McGraw-Hill Medical Division; 2009:732

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

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