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Interpretive Handbook

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Test 8814 :
Alpha-Fucosidase, Leukocytes

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

Fucosidosis is an autosomal recessive lysosomal storage disorder caused by reduced or absent alpha-L-fucosidase enzyme activity. This enzyme is involved in degrading asparagine-linked, fucose-containing complex molecules (oligosaccharides, glycoasparagines) present in cells. Reduced or absent activity of this enzyme results in the abnormal accumulation of these undigested molecules in the tissues and body fluids. Although the disorder is panethnic, the majority of reported patients with fucosidosis have been from Italy and southwestern United States. To date, less than 80 patients have been reported in the literature.

 

Severe and mild subgroups of fucosidosis, designated types I and II, have been described, although recent data suggests individual patients may represent a continuum within a wide spectrum of severity. The more severe type is characterized by infantile onset, rapid psychomotor regression, and severe neurologic deterioration. Additionally, dysostosis multiplex and elevated sweat sodium chloride are frequent findings. Death typically occurs within the first decade of life. Those with the milder phenotype express comparatively mild psychomotor and neurologic regression, radiologic signs of dysostosis multiplex and skin lesions (angiokeratoma corporis diffusum). Normal sweat salinity, the presence of the skin lesions, and survival into adulthood most readily distinguish milder from more severe phenotypes.

 

A diagnostic workup includes urine thin-layer chromatography (OLIGO / Oligosaccharide Screen, Urine), which may reveal the characteristic banding pattern associated with fucosidosis. In addition, enzyme assay of alpha-L-fucosidosis can confirm the diagnosis. Unless fucosidosis is the only lysosomal storage disease being considered, fibroblasts are preferred since they provide a long-term source of all of the lysosomal enzymes. Enzyme analysis should be pursued in cases with strong clinical suspicion regardless of the urine screening result. Sequencing of the FUCA1 gene allows for detection of disease-causing mutations in affected patients and identification of familial mutations allows for testing of at-risk family members.

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

Detection of fucosidosis

Interpretation Provides information to assist in interpretation of the test results

Low alpha-fucosidase suggests fucosidosis when accompanied with the clinical findings discussed above. Occasionally, values below the normal range occur. Since significant activity is present in those patients, these results do not suggest fucosidosis.

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

Low alpha-fucosidase variants in serum have been shown in the absence of fucosidosis. Though this has been associated with ovarian cancer, it is not a consistent finding and makes serum testing for fucosidosis unreliable.

 

If lysosomal storage diseases other than fucosidosis are being considered, the most appropriate test to order is FUCT / Alpha-Fucosidase, Fibroblasts; fibroblasts are preferred since the cultured cells can be used for additional lysosomal enzyme testing in the future as needed.

 

The current laboratory procedure is for disease testing only. Carrier status detection by this method is not possible as normal individuals may exhibit rather low levels of alpha-fucosidase activity.

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 =0.32 nmol/min/mg protein

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

1. Cowan TM, Yu C: Laboratory investigations of inborn errors of metabolism. In Pediatric Endocrinology and Inborn Errors of Metabolism. Edited by K Sarafoglou, GF Hoffmann, KS Roth, New York, McGraw-Hill Medical Division, 2009, pp 867-868

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 747-748

3. Thomas GH: Disorders of glycoprotein degradation: alpha-mannosidosis, beta-mannosidosis, fucosidosis, and sialidosis. In Scriver's The Online Metabolic and Molecular Basis of Inherited Disease (OMMBID) Edited by D Valle et al, McGraw-Hill Companies, Inc. Available from URL: http://www.ommbid.com/OMMBID/a/c.html/lysosomal_disorders/disorders_glycoprotein_degradation_mannosidosis_mannosidosis_fucosidosis_sialidosis/abstract

4. Barlow JJ, DiCioccio RA, Dillard PH, et al: Frequency of an allele for low activity of alpha-L-fucosidase in sera: possible increase in epithelial ovarian cancer patients. J Natl Cancer Inst 1981 Nov; 67(5):1005-1009


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