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Mucopolysaccharidosis

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The mucopolysaccharidoses (MPS) are a family of disorders that are caused by inherited defects in the catabolism of sulfated components of connective tissue known as glycosaminoglycans (GAGs). In affected patients, one or more of three specific polymers—dermatan sulfate (DS), heparan sulfate (HS), and keratan sulfate (KS)—accumulate within the cells, interfering with normal function, and are excreted in excess in the urine. The main enzymatic defects in the catabolism of the GAGs dermatan, heparan, and keratan sulfate are shown in eFigure 160.1.

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The enzymes associated with GAG catabolism are all lysosomal hydrolases, and patients with an MPS disorder usually have less than 1% residual enzyme activity. Heterozygote detection based on enzyme activity alone is inaccurate and is now, fortunately, no longer necessary, as the genes encoding the enzymes involved in GAG catabolism have been identified and sequenced. Phenotypic variability (heterogeneity) is very much a feature of MPS disease, and within each specific enzyme deficiency there is a very wide spectrum of clinical effects. Although the disorders are most often known by their eponymous titles (eg, Hurler syndrome), this has led to an oversimplification in the classification of the subtypes, which should be kept in mind when interpreting the data in Table 160-1. A comprehensive review of the biochemistry and molecular biology of these disorders can be found in Neufeld and Muenzer, 2001.1

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Table 160-1. The Mucopolysaccharidoses

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