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 resulting from a deficiency of the enzyme neuraminidase. Clinical presentation can vary and phenotypes are typically categorized by age of onset: type I is characterized by a cherry-red spot on the retina, progressive decreased acuity, impaired color vision, or night blindness. Neurologic problems include poorly controlled myoclonus, painful neuropathy, and delayed nerve conduction. Type II sialidosis is distinguished from type I by the presence of abnormal somatic features, including coarse facies, hepatosplenomegaly, and dysostosis multiplex. The congenital form is typically associated with hydrops.
In addition to primary neuraminidase deficiency disorders, galactosialidosis is an autosomal recessive lysosomal storage disease associated with a combined deficiency of beta-galactosidase and neuraminidase secondary to a defect in the cathepsin A protein. The disorder can be classified into 3 subtypes that vary with regard to age of onset and clinical presentation. Typical clinical presentation is coarse facial features, cherry-red spots, or skeletal dysplasia. The early infantile form is associated with fetal hydrops, skeletal dysplasia, and early death. The late infantile form typically presents with short stature dysostosis multiplex, coarse facial features, hepatosplenomegaly, and/or heart valve problems. The juvenile/adult form is typically characterized by progressive neurologic degeneration, ataxia, and/or angiokeratomas. The incidence of the juvenile/adult form is greater in individuals of Japanese ancestry.
An aid 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 CR Scriver, AL Beuadet, WS Sly, DE Valle. 2001, pp 3507
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