Oligosaccharides

General Information

Lysosomal storage diseases describe a heterogeneous group of dozens of rare inherited disorders characterized by the accumulation of undigested or partially digested macromolecules, which ultimately results in cellular dysfunction and clinical abnormalities. Organomegaly, connective-tissue and ocular pathology, and central nervous system dysfunction may result. Classically, lysosomal storage diseases encompassed only enzyme deficiencies of the lysosomal hydrolases. More recently, the concept of lysosomal storage disease has been expanded to include deficiencies or defects in proteins necessary for the normal post-translational modification of lysosomal enzymes (which themselves are often glycoproteins), activator proteins, or proteins important for proper intracellular trafficking between the lysosome and other intracellular compartments.

Over 50 lysosomal storage diseases have been described. Age of onset and clinical manifestations may vary widely among patients with a given lysosomal storage disease, and significant phenotypic heterogeneity between family members carrying identical mutations has been reported. Lysosomal storage diseases are generally classified by the accumulated substrate and include the sphingolipidoses, oligosaccharidoses, mucolipidoses, mucopolysaccharidoses (MPSs), lipoprotein storage disorders, lysosomal transport defects, neuronal ceroid lipofuscinoses and others.

An oligosaccharide is a complex sugar consisting of 3 or more monomers, but not comparable with the high molecular weight polymers such as starch, dextrins and glycogen. They are constituents of the side chains of proteins including blood group proteins.

They are excreted in increased quantities in patients with certain inherited storage disorders such as:

• GM1-gangliosidosis
• Galactosialidosis
• Sialidosis (Mucolipidosis I, neuraminidase deficiency)
• Mucolipidosis type II (I-cell disease)
• Mucolipidosis type III (Pseudo-Hurler polydystrophy)
• Fucosidosis
• alpha-Mannosidosis
• Aspartylglucosaminuria

Positive results are then followed by specific enzyme assays to confirm diagnosis.

Excretion is also related to age, diet and blood group and these should be taken into account in the interpretation.