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Hurler Syndrome
Sunday, 08 August 2004
Monday, 29 November 2004
Mucopolysaccharidosis Type I


Hurler Syndrome is a genetic disorder caused by a missing or poorly functioning enzyme named α-L-iduronidase. This enzyme is located in small sacs called lysosomes. Lysosomes are the part of a cell that has the important function of breaking down old proteins and carbohydrates. Because there is a lack of α-L-iduronidase in Hurler Syndrome, certain molecules named glycosaminoglycans begin to build up. This build up of glycosaminoglycans causes a variety of symptoms that affect mental function, bone development, cardiac function, and hearing.


Hurler Syndrome occurs in approximately 1-2 out of every 100,000 people. Symptoms will begin to show early in infancy and the diagnosis is usually made at approximately 9-18 months of age.

Signs and Symptoms

Infants who have Hurler Syndrome will appear normal at birth, but will begin to show symptoms at approximately six months of age when glycosaminoglycans begin to build up in the lysosomes. Hurler Syndrome is a progressive and chronic disorder, meaning that symptoms will worsen as time passes. Some of the more common signs and symptoms include:

  • Coarsening of facial features (thickening of the skin of the nose, lips and ear lobes)
  • Developmental delay leading to mental retardation
  • Skeletal abnormalities
  • Joint stiffness
  • Stiffening of heart valves
  • Macrocephaly (large head) or abnormal shape of the head
  • Growth of hair in places where it does not normally grow
  • Clouding of the cornea
  • Chronic nasal infections and large amounts of nasal discharge
  • Hearing loss
  • Hydrocephalus (increased amounts of fluid in the skull that causes compression of brain matter)
  • Enlarged liver
  • Enlarged spleen
  • Breathing problems
  • Sleep apnea

Possible Causes

The gene for the enzyme α-L-iduronidase is located on chromosome 4. A person diagnosed with Hurler syndrome has two copies of the mutated gene, one from each parent. This inheritance pattern is called autosomal recessive. The lack of α-L-iduronidase causes the buildup of glycosaminoglycans, specifically heparan sulfate and dermatan sulfate. The build of these compounds interferes with the normal function of the cell and this leads to the symptoms of Hurler Syndrome.


Hurler Syndrome is diagnosed through physical examination and laboratory tests. One test looks at concentrations of heparan sulfate and dermatan sulfate in the urine. Increased amounts of these molecules are consistent with the diagnosis of Hurler Syndrome. A blood test can check the activity of α-L-iduronidase which would be very low or absent in Hurler Syndrome. Since Hurler Syndrome is an inherited disorder, prenatal testing is available. A sample of fetal tissue from chorionic villus sampling (swab from the mother) at 10-12 weeks gestation or an amniocentesis (fluid from the sack enveloping the fetus) at 16-18 weeks is needed to perform the α-L-iduronidase activity test. If a parent or sibling has been diagnosed with Hurler Syndrome, the fetal tissue can undergo mutational analysis, which takes fetal DNA and matches it with the affected family member’s DNA to determine whether the fetus carries a mutation in the gene.


Hurler Syndrome cannot be cured. Currently, the most effective treatment is bone marrow transplant; however, this is a very serious procedure and the response is variable. Mental retardation can be mostly prevented if transplantation occurs before 18 months to 2 years of age. Generally, with bone marrow transplantation most symptoms will improve; the liver and spleen will decrease in size, facial features will become less coarse, there will be improved hearing, and improved cardiac functioning. Abnormal skeletal development and clouding of the cornea do not seem to improve. The greatest benefit from bone marrow transplantation is increased life expectancy. Other treatments are prescribed to relieve symptoms. For example, orthotics or braces can help improve stability when walking. Corneal transplantation may be needed if the cornea becomes too cloudy. Another new therapy is the medication laronidase, which is an enzyme that works in a similar manner as α-L-iduronidase. It has been shown to relieve breathing problems, improve sleep, decrease joint stiffness, and reduce live size.


Hurler Syndrome is a progressive disease and if left untreated, life expectancy is less than ten years. With successful bone marrow transplantation, however, life expectancy increases by several years. Enzyme replacement therapy is new and very promising.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.


National MPS Society
This organization was founded by families of children with mucopolysaccharidoses and mucolipidoses. They provide information and support, such as regional meetings in which families can meet each other.

The Canadian Society for Mucopolysaccharide and Related Disorders, Inc
This organization provides information and support for families, while also increasing public awareness and raising funds for further research.
This website was created by a family with a child diagnosed with Hurler Syndrome. It has a journal about Molly s progress after bone marrow transplantation, and there are also several links to webpages made by other families affected by Hurler Syndrome.

Google Search for Hurler Syndrome

References and Sources

Baloghova J, Schwartz RA, Baranova Z, and Halagovec A. Mucopolysaccharidoses Types I-VII. eMedicine. Portigal CL and Clarke LA (2003). Mucopolysaccharidosis Type I. GeneReviews. Wraith JE (2001). Enzyme replacement therapy in mucopolysaccharidosis type I: Progress and emerging difficulties. Journal of inherited metabolic disease. 24, p. 245-250.