Mucopolysaccharide Storage Disorders


The mucopolysaccharidoses (MPSs) are a group of 11 distinct metabolic disorders that result from the deficiency of the various lysosomal enzymes required to degrade the glycosaminoglycans (GAGs) that constitute a major component of the extracellular matrix, joint fluid and connective tissue. The progressive lysosomal accumulation of GAGs ultimately impairs joint mobility and adversely affects the skeleton and cardiovascular system. Depending on the type or subtype of mucopolysaccharidosis, mental development may range from normal to profoundly impaired. Enzymatic and molecular diagnostic testing are available for all the MPSs. Hematopoietic stem cell transplantation (HSCT) and enzyme replacement therapy (ERT) are the only specific treatments for MPS currently available.

Key Concepts:

  • The degradation of glycosaminoglycans (or mucopolysaccharides) takes place in lysosomes that contain the acid hydrolases.

  • The deficiency of any one of 11 acid hydrolases, required to normally degrade the glycosaminoglycans, gives rise to the group of lysosomal storage disorders known as the mucopolysaccharidoses.

  • The progressive accumulation of glycosaminoglycans, a major component of the extracellular matrix, joint fluid and connective tissue, leads ultimately to multisystem involvement including organomegaly, dysostosis multiplex and abnormal facies.

  • The observation that the fraction of lysosomal enzymes that does not enter the lysosome is secreted from the cell and can be recaptured from other cells, suggests that lysosomal storage disorders are potentially treatable by enzyme replacement therapy.

Keywords: mucopolysaccharidosis; glycosaminoglycans; diagnosis; mutation; genotype–phenotype correlation; hematopoietic stem cell transplantation; enzyme replacement therapy

Figure 1.

Stepwise degradation of the main glycosaminoglycan chains, heparan sulfate (HS), dermatan sulfate (DS) and keratan sulfate (KS), as they are degraded by the indicated enzymes (the degradation pathway of chondroitin sulfates, being similar to that of DS is not shown). Enzyme names are shown in black. Defective enzyme activity leads to the different types of mucopolysaccharidosis (MPS) indicated in green. Note that although GM2 gangliosidosis (depicted in grey) results from a deficiency of β‐hexosaminidase, also required for glycosaminoglycan degradation, it is not considered an MPS sensu stricto since its clinical symptoms are due principally to defective sphingolipid degradation. To date, no deficiency for the glucuronate sulfatase enzyme has been described.



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Further Reading

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Filocamo, Mirella, Cooper, David N, and Di Rocco, Maja(Jan 2011) Mucopolysaccharide Storage Disorders. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0006095]