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Hurler's Syndrome

Synonym: Mucopolysaccharidosis Type IH

The mucopolysaccharidoses are a group of inherited disorders caused by a lack of specific lysosomal enzymes involved in the degradation of glycosaminoglycans. Deficiency of alpha-L-iduronidase can result in a wide range of phenotypes including Hurler (severe), Scheie (mild) and Hurler-Scheie (intermediate) syndromes.1

Epidemiology
  • The incidence has been estimated at 1 in 75,000.2
  • The mode of inheritance is autosomal recessive.
Presentation

Affected children appear normal at birth but usually develop the characteristic appearance within the first year of life.

Differential Diagnosis
  • Other mucopolysaccharidoses: Hunter syndrome (Mucopolysaccharidosis Type II) has no corneal clouding and progression is slower.
  • Other causes of mental retardation and short stature.
Investigations
  • Urine: raised levels of dermatan sulphate and heparan sulphate are found in patients with mucopolysaccharidoses.
  • Definitive diagnosis is established by alpha-L-iduronidase enzyme assay using artificial substrates in cultured fibroblasts or isolated leukocytes.
  • Carrier testing can be performed by differentiating normal enzyme activity from half-normal levels of enzyme activity.
  • Prenatal diagnosis: using cultured amniotic fluid cells or chorionic villus biopsies.
  • Molecular diagnosis: difficult because of genetic heterogeneity.
  • Assessment of complications will include an echocardiogram and MRI brain scan.
Management
  • Palliative treatment includes the provision of multidisciplinary treatment and support for affected children and their families.
  • Orthopaedic surgery for joint contractures and skeletal deformities.
  • Corneal transplants may be required.
  • Enzyme replacement: laronidase is licensed for long-term replacement therapy in the treatment of non-neurological manifestations of Hurler's syndrome; it may reduce the excess carbohydrates stored in organs and lead to some functional improvements.
  • Allogenic marrow transplant and gene therapy may present treatment possibilities in the future.
Complications
  • Orthopaedic complications lead to pain and immobility.
  • Upper airways obstruction.
  • Increased susceptibility to infections of the respiratory tract.
Prognosis
  • Death usually occurs by the age of 14 years.
  • Common causes of death include upper airways obstruction, cardiac insufficiency and respiratory tract infections.

Document References
  1. Online Mendelian Inheritance in Man; Mucopolysaccharidosis Type IH
  2. Nelson J; Incidence of the mucopolysaccharidoses in Northern Ireland. Hum Genet. 1997 Dec;101(3):355-8. [abstract]
  3. Nash D; Mucopolysaccharidosis Type IH. eMedicine, December 2003
Acknowledgements EMIS is grateful to Dr Colin Tidy for writing this article. The final copy has passed scrutiny by the independent Mentor GP reviewing team. ©EMIS 2007.
DocID: 2279
Document Version: 20
DocRef: bgp1395
Last Updated: 30 Aug 2007
Review Date: 29 Aug 2009
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