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Test ID: ARSU
Arylsulfatase A, Urine

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

Detection of metachromatic leukodystrophy as a secondary specimen to confirm results from leukocytes (preferred initial specimen).

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

Secondary specimen to confirm leukocyte results. Results may not

reflect carrier status due to individual variation of arylsulfatase A

enzyme levels.

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

Metachromatic leukodystrophy (MLD) is an inherited disorder of myelin metabolism characterized by accumulation of galactosyl sulfatide (cerebroside sulfate) in the white matter of the central nervous system (CNS) and in the peripheral nervous system (PNS). Galactosyl sulfatide and, to a smaller extent, lactosyl sulfatide, also accumulate within the kidney, gallbladder, and other visceral organs and are excreted in excessive amounts in the urine. Metachromatic granules are deposited in the CNS and PNS and many organs, and can be identified in stained frozen tissue sections. MLD is the result of decreased arylsulfatase A activity. The mode of inheritance is autosomal recessive. The human arylsulfatase A gene has been mapped to chromosome 22, several polymorphisms defined, and a number of disease-related mutations identified.

 

There are 3 forms of arylsulfatase: A, B, and C. Arylsulfatase A is associated with hydrolysis of galactosyl sulfatide. Arylsulfatase B is associated with mucopolysaccharide metabolism (Maroteaux-Lamy disease). Arylsulfatase C is a major component of myelin sheaths and is associated with X-linked icthyosis (steroid sulfatase deficiency). Extremely low arylsulfatase A levels have been found in some clinically normal parents and other relatives of MLD patients. These individuals do not have metachromatic deposits in peripheral nerve tissues, and their urine content of sulfatide is normal. Individuals with this "pseudodeficiency" have been recognized with increasing frequency among patients with other apparently unrelated neurologic conditions, as well as among the general population. This has been associated with a fairly common polymorphism in the arylsulfatase A gene which leads to low expression of the enzyme (5%-20% of normal). These patients can be difficult to differentiate from actual MLD patients.

 

Treatment options for MLD are few. Bone marrow transplantation appears to slow the progression of symptoms, but benefits are not seen for several months. Other promising research includes protease inhibitor treatments, enzyme replacement, and gene replacement therapies.

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.

>1 U/L

Note: Results from this assay may not reflect carrier status because of individual variation of arylsulfatase A enzyme levels.

Interpretation Provides information to assist in interpretation of the test results

Greatly reduced levels of arylsulfatase A in urine (<1 U/L), as well as in serum and various tissues, is seen in patients with metachromatic leukodystrophy.

 

See Lysosomal Storage Disorders in Special Instructions for further information on lysosomal storage diseases.

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

Leukocytes are the preferred screening specimen for metachromatic leukodystrophy.

 

Due to the use of artificial substrate, this test does not reliably pick up carriers.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

Kolodny EH: Metachromatic leukodystrophy and multiple sulfatase deficiency: sulfatide lipidosis. In The Metabolic Basis of Inherited Disease. Vol. 2. 6th edition. Edited by CR Scriver, AL Beaudet, WS Sly, D Valle. New York, McGraw-Hill, 1989, pp 1721-1750

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test