Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Alpha-mannosidosis is an autosomal recessive lysosomal storage disorder caused by reduced or absent acid alpha-mannosidase enzyme activity. This enzyme is involved in glycoprotein catabolism, with absent or reduced activity resulting in the accumulation of undigested mannose-containing complex oligosaccharides in the lysosomes, disrupting the normal functioning of cells.
Clinical features and severity of symptoms are widely variable within alpha-mannosidosis but, in general, the disorder is characterized by skeletal abnormalities, immune deficiency, hearing impairment, and mental retardation. Three clinical subtypes of the disorder have been described and vary with respect to age of onset and clinical presentation. Type 1 is generally classified by a mild presentation and slow progression with onset after 10 years of age and absence of skeletal abnormalities. Type 2 is generally a more moderate form with slow progression and onset prior to 10 years of age with skeletal abnormalities and myopathy. Type 3 is the most severe form with onset in early infancy, skeletal abnormalities (dysostosis multiplex), and severe central nervous system involvement. Although treatment is mostly supportive and aimed at preventing complications, hematopoietic stem cell transplant has been reported to be a feasible therapeutic option. The incidence of alpha-mannosidosis is estimated at 1 in 500,000 live births.
An initial diagnostic workup may include a multi-enzyme screening assay for several oligosaccharidoses, including mannosidosis in leukocytes or fibroblasts (OLIGU / Oligosaccharide Screen, Urine or OLIWB / Oligosaccharidoses Screen, Leukocytes or OLITC / Oligosaccharidoses Screen, Fibroblasts). If the screening assay is suggestive of alpha-mannosidosis, enzyme analysis of acid alpha-mannosidase can confirm the diagnosis.
Diagnosis of alpha-mannosidosis
Values <0.54 nmol/min/mg protein are consistent with a diagnosis of alpha-mannosidosis.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test cannot be used to establish carrier status for alpha-mannosidosis.
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 =0.54 nmol/min/mg protein
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Malm D, Nilssen O: Alpha-Mannosidosis. In GeneReviews. Edited by RA Pagon, MP Adam, HH Ardinger, et al. University of Washington, Seattle. 2001 Oct 11 (Updated 2012 May 3). Accessed 3/6/2017. Available at www.ncbi.nlm.nih.gov/books/NBK1396/
2. Thomas GH: Chapter 140: 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, B Vogelstein, SE Antonarakis, et al. McGraw-Hill Medical Division. Accessed 3/16/2017. Available at http://ommbid.mhmedical.com/
3. Mynarek M, Tolar J, Albert MH, et al: Allogeneic hematopoietic SCT for alpha-mannosidosis: an analysis of 17 patients. Bone Marrow Transplant 2012 Mar;47(3):352-359. doi: 10.1038/bmt.2011.99