Mucopolysaccharidosis Type I (MPS I) (FAQ)

Answers to questions families often have about caring for their child with mucopolysaccharidosis type I

What is Mucopolysaccharidosis type I (MPSI) and what causes it?

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive lysosomal storage disorder resulting from deficiency of the enzyme α-L-iduronidase. Lysosomes are the parts of cells that dispose of unwanted materials; if a deficiency exists, the unwanted products build up in the lysosomes, causing problems. Deficiency of this enzyme results in the accumulation of complex sugars known as glycosaminoglycans (GAGs). The resulting accumulation of GAGs in the lysosomes leads to progressive, multi-system organ damage. You may hear the terms Hurler, Hurler-Scheie, and Scheie syndromes to describe your child's condition. These terms are going out of use as symptoms often overlap between categories. The disease is best characterized as severe or attenuated MPS I.

What are the symptoms of MSP I?

There is a wide range of symptoms in children identified with MPS I, ranging from mild to severe manifestations. Some of the manifestations observed in affected individuals include:

  • hernias, inguinal and umbilical
  • facial features that become coarse over time
  • frequent upper airway infections with ear infections
  • hepatosplenomegaly
  • corneal clouding
  • cardiac involvement, valve disease
  • progressive skeletal dysplasia (dysostosis multiplex)
  • growth delay
  • profound neurological involvement (in the severe form only)
  • macrocephaly

How is it diagnosed?

The diagnosis of MPS I is established by:

  • Confirming deficiency of α-L-iduronidase in peripheral blood leukocytes or cultured fibroblasts.
  • Molecular genetic testing for mutations in IDUA, the gene that encodes α-L-iduronidase, can be used for confirmatory diagnostic testing.

What is the prognosis?

For untreated children with MPS I (the severe form), prognosis is poor, with death in late childhood. Treatment is often successful in extending the life expectancy, although it may introduce its own complications. Children with attenuated MPS I often have normal or near normal life expectancy but need to be monitored closely and treated for any complications that may arise.

What is the risk for other family members or future babies?

MPS I is an autosomal recessive condition. Parents of children with MPS I are obligate carriers of the condition—they both carry a gene for MPS I. The parents of a child with MPS I have a 25% chance of having another child with MPS I with each subsequent pregnancy.

What treatments/therapies/medications are recommended or available?

Children with MPS I are treated by hematopoietic stem cell transplantation (HSCT), enzyme replacement therapy (ERT), or a combination of both. Other experimental surgeries are also being investigated. Children with attenuated forms are managed more conservatively but require stringent clinical management particularly related to their cardiac and skeletal manifestations.

How will my child and our family be impacted?

Having a child with this condition will significantly affect the life of the family. Families are encouraged to join support groups that may be helpful in adjusting to life-changes that may occur as a result of this condition (see below).

If my first child has severe MPS I, will my other affected children be similarly affected?

Yes. If 1 child has the severe phenotype, then all other affected children will be severely affected. If 1 sibling has attenuated MPS I, then it would be expected that other siblings would also have attenuated MPS I.

Is there a cure for MPS I?

While there is no treatment that is completely curative, the 2 available therapies, HSCT and ERT, can increase life expectancy, improve quality of life, and treat some of the symptoms associated with MPS I.

Will my child with MPS I be able to have children?

Individuals with the attenuated forms of MPS I do not appear to have problems with fertility, therefore, they should be able to have children. Women with MPS I should be followed closely by a maternal-fetal medicine specialist given the cardiac, respiratory, and musculoskeletal complications involved in the condition. Individuals with severe MPS I do not usually reach reproductive age if untreated.

Can the enzyme levels predict severity?

No. Most individuals with MPS I, regardless of their clinical diagnosis of severe or attenuated MPS I, will have little to no enzyme activity when assayed, therefore it can not be used to predict phenotype.

What research or clinical trials are available?

Research opportunities can be found on the National MPS Society website. See National MPS Society. This site provides information about the disorder, research, support for families, fundraising, and efforts to increase public awareness about MPS and related disorders. Allows users to contact and communicate directly with other parents and individuals with MSP I. Clinical studies can also be found on Children and Adolescents with MPS I (


Information & Support

Related Portal Content
Mucopolysaccharidosis Type I (MPS 1)
Assessment and management information for the primary care clinician caring for the child with mucopolysaccharidosis type I (MPS I).
Care Notebook
Medical information in one place with fillable templates to help both families and providers. Choose only the pages needed to keep track of the current health care summary, care team, care plan, health coverage, expenses, scheduling, and legal documents. Available in English and Spanish.

For Parents and Patients

Mucopolysaccharidosis Type I (MedlinePlus)
Information for families that includes description, frequency, causes, inheritance, other names, and additional resources; from the National Library of Medicine.

Mucopolysaccharidoses Fact Sheet (NINDS)
Addressing signs and symptoms, risks, types, treatments, research, and resources; National Institute of Neurological Disorders and Strokes.

Hurler Syndrome (MedlinePlus)
Information for families that includes description, frequency, causes, inheritance, other names, and additional resources; from the National Library of Medicine.

MPS I - Information for Families (Genzyme)
Information about treatment, clinical trials, support groups, and resources related to MPS 1. Discusses the use of Aldurazyme (laronidase) enzyme replacement therapy manufactured by Genzyme.

About Lysosomal Diseases (LDNZ)
Offers background information, family stories, newsletters, and research updates; Lysosomal Diseases New Zealand.

Starlight Children's Foundation
A non-profit organization dedicated to helping seriously ill children and their families. Programs include entertainment while hospitalized, getaways for families, patient education, and online chat rooms where kids can communicate with other seriously ill children.

Patient Education

MPS Fact Sheets (National MPS Society)
More than 25 fact sheets about mucopolysaccharidoses and related diseases for patients, families, and providers; topics include cardiac problems, caregiver support, family coping strategies, melatonin, transplants, pamidronate, tube feedings, stem cell transplants, and more.

Understanding MPS (National MPS Society)
Booklets for each type of MPS with in-depth information about related physical and emotional issues; available in English and Spanish.

Services for Patients & Families in New Mexico (NM)

For services not listed above, browse our Services categories or search our database.

* number of provider listings may vary by how states categorize services, whether providers are listed by organization or individual, how services are organized in the state, and other factors; Nationwide (NW) providers are generally limited to web-based services, provider locator services, and organizations that serve children from across the nation.


Children and Adolescents with MPS I (
Studies looking at better understanding, diagnosing, and treating this condition; from the National Library of Medicine.

MPS I Registry
An ongoing, observational database that tracks natural history and outcomes of patients with MPS I. The Registry was initiated worldwide in April 2003 as an international observational program sponsored by BioMarin/Genzyme LLC and administered by Genzyme Corporation. Registration is voluntary, free, and confidential.

Authors & Reviewers

Initial publication: October 2012; last update/revision: September 2016
Current Authors and Reviewers:
Author: Lynne M. Kerr, MD, PhD
Reviewer: Pilar L. Magoulas, MS, CGC