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.
A: The catabolism of dermatan sulfate. B: The
catabolism of heparan sulfate. C: The catabolism of
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
Table 160-1. The Mucopolysaccharidoses |Favorite Table|Download (.pdf)
Table 160-1. The Mucopolysaccharidoses
|Disease (Eponym)||Enzyme Deficiency||Clinical Presentation||Storage Material||Genetics (OMIM Number, Chromosome, Common Mutations)||Treatment||Prognosis|
|MPS IH (Hurler)||α-L-Iduronidase||C, CF, CC, UAO, D, DM, H, HSM, CVD, JS, MR, SS||DS, HS||AR (OMIM 607014), Ch 4p16.3, Mns: p.W402X, p.Q70X)||HSCT||Untreated: death in first decade|
|IDUA (EC 22.214.171.124)|
|MPS IH/S (Hurler-Scheie)||α-L-Iduronidase||CC, D, UAO, HSM, CVD, DM(S) JS, MG, RRF||DS, HS||AR (OMIM 607015), Ch 4p16.3, Mns: p.R89Q Patients
often heterozygous for p.W402X/p.Q70X plus another uncommon
mutation ||ERT||Untreated: death from cardiac disease in third to
|IDUA (EC 126.96.36.199)|
|MPS IS (Scheie)||α-L-Iduronidase ||CC, CVD, D, JS, CTS||DS, HS||AR (OMIM 607016), Ch 4p16.3, Mns: c.590-7g>a||ERT||Untreated: survival into middle age and beyond|
|IDUA (EC 188.8.131.52)|
|MPS II (Hunter)||Iduronate-2-sulfatase||Severe: CF, UAO, D, DM, H, HSM, CVD, MR, JS, PR, SS||DS, HS||X-linked (OMIM 309900), Ch Xq28, no common mutations||ERT||Severe: death in second decade|
|IDS (EC 184.108.40.206)||Attenuated: D, DM, CM(D), CVD, JS, CTS,||Attenuated: survival into middle age and beyond|
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