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Mucopolysaccharidosis type I

Other Names for this Disease
  • Alpha-L-Iduronidase deficiency
  • Attenuated MPS I (subtype)
  • Hurler syndrome (former subtype)
  • Hurler-Scheie syndrome (former subtype)
  • IDUA deficiency
More Names
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Your Question

I would like general information on mucopolysaccharidosis I (MPS I). My grandson was recently diagnosed with this condition and is currently undergoing enzyme therapy. Is a person with MPS I less likely to have brain damage if a bone marrow transplant is performed early? 

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is mucopolysaccharidosis I?

Mucopolysaccharidosis I (MPS I) is a condition that affects many different parts of the body. It is a progressively debilitating disorder; however, the rate of progression varies among affected individuals. MPS I is caused by reduced levels or the complete lack of the IDUA enzyme. Without the proper amount of this enzyme, many different organs and tissues of the body become enlarged, resulting in various medical problems. This condition is usually divided into two subtypes, severe MPS I and attenuated MPS I. While both types can cause similar symptoms, people with severe MPS I typically have an earlier onset of symptoms, a decline in intellectual function, and a shorter lifespan. Although there is no cure for MPS I, bone marrow transplant and enzyme replacement therapy are treatment options that may help manage the symptoms of this condition.[1]
Last updated: 7/15/2008

What are the symptoms of mucopolysaccharidosis I (MPS I)?

The signs and symptoms of MPS I are not present at birth, but they begin to appear during childhood. People with severe MPS I develop the features of this condition earlier than those with attenuated MPS I. The following list includes the most common signs and symptoms of MPS I.[1]

Last updated: 7/15/2008

Why are there different names for mucopolysaccharidosis I (MPS I)?

MPS I was once divided into three separate subtypes, Hurler syndrome, Hurler-Scheie syndrome, and Scheie syndrome, based on disease severity. Because there is no clear distinction between these three syndromes, MPS I is currently divided into the severe and attenuated types.[1]
Last updated: 2/10/2009

What causes mucopolysaccharidosis I (MPS I)?

Mutations in the IDUA gene cause MPS I. The IDUA gene provides instructions for producing an enzyme that is involved in the breakdown of large sugar molecules called glycosaminoglycans (GAGs). Mutations in the IDUA gene reduce or completely eliminate the function of the IDUA enzyme. The lack of IDUA enzyme activity leads to the accumulation of GAGs within cells, specifically inside the lysosomes. Lysosomes are compartments in the cell that digest and recycle different types of molecules. Conditions that cause molecules to build up inside the lysosomes, including MPS I, are called lysosomal storage disorders. The accumulation of GAGs increases the size of the lysosomes, which is why many tissues and organs are enlarged in this disorder.[1]
Last updated: 7/15/2008

How is mucopolysaccharidosis I (MPS I) inherited?

MPS I is inherited from both parents in an autosomal recessive pattern.[1]
Last updated: 7/15/2008

What is autosomal recessive inheritance?

Autosomal recessive inheritance refers to the inheritance pattern in which two mutated copies of the gene that causes a disorder are present in each cell. An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers). Autosomal recessive disorders are typically not seen in every generation of an affected family. When two people who are carriers of an autosomal recessive condition have a child, there is a 25% (1 in 4) chance that the child will be affected.[2]

Last updated: 2/18/2009

What treatment is available for mucopolysaccharidosis I (MPS I)?

The two main treatments for MPS I are enzyme replacement therapy (ERT) and bone marrow transplant. Both of these treatments work by replacing the missing IDUA enzyme. A drug called laronidase or Aldurazyme is the enzyme replacement therapy for MPS I. Treatment with laronidase can improve problems with breathing, growth, the bones, joints and heart. However, this treatment is not expected to treat problems with mental development because laronidase cannot cross the blood-brain barrier. A bone marrow transplant is another treatment option that provides the person with MPS I with cells that can produce the IDUA enyzme. A bone marrow transplant can stop the progression of neurological problems.[3]
Last updated: 7/15/2008

Is a person with mucopolysaccharidosis I (MPS I) less likely to have brain damage if a bone marrow transplant is performed early? 

Individuals with MPS I are less likely to have problems with intellectual development if a bone marrow transplant is performed prior to the onset of neurological problems. Bone marrow transplants can sometimes stop the damage caused by the disorder before it becomes severe. However, a bone marrow transplant may not be helpful for all people with MPS I, and this surgery has serious risks that must be considered before making treatment decisions.[3]
Last updated: 7/15/2008

How can I learn about research involving mucopolysaccharidosis I (MPS I)?

The U.S. National Institutes of Health, through the National Library of Medicine, developed to provide patients, family members, and members of the public with current information on clinical research studies. Currently, 8 clinical trials are identified as enrolling individuals with mucopolysaccharidosis I. Click here for a list of these trials. After you click on a study, review its "eligibility" criteria to determine its appropriateness. Use the study’s contact information to learn more. Check this site often for regular updates.

You can also contact the Patient Recruitment and Public Liaison (PRPL) Office at the National Institutes of Health (NIH). We recommend calling the toll-free number listed below to speak with a specialist, who can help you determine if your grandson is eligible for any clinical trials.  

Patient Recruitment and Public Liaison Office
NIH Clinical Center
Bethesda, Maryland 20892-2655
Toll-free: 800-411-1222
Fax: 301-480-9793
Web site: 

Last updated: 7/15/2008

Are there any advocacy organizations for individuals and families with mucopolysaccharidosis I (MPS I)?

National MPS Society
4220 NC Hwy 55, Ste.140
Durham, NC 27713
Toll-free: 877-MPS-1001
Phone: 919-806-0101
Fax: 919-806-2055
Web site:

Society for Mucopolysaccharide (MPS) Diseases
MPS House Repton Place White Lion Road
Amersham Buckinghamshire
United Kingdom HP7 9LP
Phone: (+44) 0845 389 9901
Web site:

Last updated: 7/15/2008