Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Sialidosis, also known as mucolipidosis I, is an autosomal recessive lysosomal storage disorder (LSD) resulting from a deficiency of the enzyme neuraminidase. Clinical presentation can vary and phenotypes are typically categorized by age of onset. Type I is considered to be the milder form of sialidosis and is characterized by a cherry-red spot on the retina, progressive decreased acuity, impaired color vision, or night blindness. Neurologic problems include gait abnormalities and poorly controlled myoclonus. Type II sialidosis is distinguished from type I by the presence of dysmorphic features, including coarse facies, hepatosplenomegaly, and dysostosis multiplex, early age of onset, and its more rapid disease progression. Developmental delay is frequently present in type II sialidosis. The congenital form is typically associated with hydrops.
Galactosialidosis is an autosomal recessive lysosomal storage disease associated with a combined deficiency of neuraminidase and beta-galactosidase secondary to a defect in the cathepsin A protein. Clinical features are those typically associated with LSD including coarse facial features, cherry-red spots, and skeletal dysplasia. The disorder can be classified into 3 subtypes that vary with respect to age of onset and clinical presentation. The early infantile form is associated with fetal hydrops, visceromegaly, skeletal and ophthalmologic disorders, and early death. The late infantile form typically presents with short stature, dysostosis multiplex, coarse facial features, hepatosplenomegaly, and heart valve problems. The juvenile/adult form is characterized by progressive neurologic degeneration, ataxia, cognitive disability, and/or angiokeratomas. Most of the juvenile/adult onset cases have been found in individuals of Japanese ancestry. A diagnosis of galactosialidosis is obtained by demonstrating a combined deficiency of neuraminidase and beta-galactosidase in lymphocytes or cultured skin fibroblasts.
Aids in the diagnosis of sialidosis and galactosialidosis
Specimens with activity >0.10 nmol/min/mg protein are considered to be normal.
Specimens with activity < or =0.10 nmol/min/mg protein are considered to be abnormal and suggestive of neuraminidase deficiency. Molecular confirmation is recommended.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test cannot discriminate carriers, hence it is not recommended for carrier screening
Neuraminidase is a particularly unstable enzyme and may be quickly destroyed by freezing, sonication, solubilization, and most purification procedures.
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.
>0.10 nmol/min/mg Prot
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Thomas GH: Chapter 140: Disorders of Glycoprotein Degradation: Alpha-Mannosidosis, Beta-Mannosidosis, Fucosidosis, and Sialidosis. In The Metabolic Basis of Inherited Disease. Eighth edition. Edited by D Valle. AL Beaudet, B Vogelstein. New York, McGraw-Hill Book Company. Available at www.ommbid.com. Accessed 02/18/2015
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 725-726, 745-746
3. d'Azzo A, Andria G, Bonten E, Annunziata I: Chapter 152: Galactosialidosis. In The Metabolic Basis of Inherited Disease. Eighth edition. Edited by D Valle. AL Beaudet, B Vogelstein. New York, McGraw-Hill Book Company. Available at www.ommbid.com. Accessed 02/18/2015