Alpha-mannosidosis
| Alpha-mannosidosis | |
|---|---|
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| Alpha-mannosidosis has an autosomal recessive pattern of inheritance | |
| Classification and external resources | |
| Specialty | endocrinology |
| ICD-10 | E77.1 |
| ICD-9-CM | 271 |
| OMIM | 248500 |
| DiseasesDB | 31422 |
| MeSH | D008363 |
| GeneReviews | |
Alpha-mannosidosis is a lysosomal storage disorder caused by deficient activity of the enzyme alpha-D-mannosidase. In humans it is known to be caused by an autosomal recessive genetic mutation. In it is caused by chronic poisoning with swainsonine from locoweed.
Symptoms range widely in their onset and severity. The onset of the most severe form, type III, begins within the first months of life and includes a quick progression of intellectual disability, liver and spleen enlargement (splenomegaly), hearing loss, respiratory infections and skeletal abnormalities. Often the appearance of an affected individual includes the following facial features: protruding forehead, leveled nasal bridge, small nose and wide mouth. Muscular weakness or spinal abnormalities can occur due to the buildup of storage materials in the muscle. A milder form of alpha-mannosidosis involves mild to moderate intellectual disability which develops during childhood or adolescence.
A defective alpha-mannosidase enzyme, which normally helps to break down complex sugars derived from glycoproteins in the lysosome, causes sugar build up and impairs cell function. Complete absence of functionality in this enzyme leads to death during early childhood due to deterioration of the central nervous system. Enzymes with low residual activity lead to a milder type of the disease, with symptoms like reduced hearing, mental disabilities, susceptibility to bacterial infections, and skeletal deformities. The course of the disease is progressive.
Alpha-mannosidosis is classified into types I through III based on severity and age of onset. In contrast to the usual classifications scheme of these disorders, type III is the most severe.
A diagnosis is made by measuring the enzymatic activity of alpha-D-mannosidase in white blood cells. If there is a decreased level of the enzyme in comparison to standard levels, a diagnosis can be made. It is thought that this disorder might be under-diagnosed for a few different reasons—the diagnosis is often made late in the disease's progression, symptoms are often mild, or the biochemical diagnosis does not yield conclusive results.
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