Understanding Hurler Syndrome (MPS I): Symptoms, Causes, and Care
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What Is Hurler Syndrome?
Hurler syndrome is a genetic disorder where a mutation in the IDUA gene prevents the body from producing enough alpha-L-iduronidase enzyme. [1] Without this enzyme, cells cannot recycle certain sugar molecules, leading to toxic buildup. [1] This buildup results in distinct facial features, skeletal abnormalities, enlarged organs, and cognitive decline. [1] It is an autosomal recessive condition, affecting 1 in 100,000 newborns. [1]
What the research says
Earlier stem cell transplant and preserved thinking skills predict better long-term outcomes. In 217 children who engrafted after transplant (median follow-up age 9.2 years), a younger age at transplant and preserved cognitive function at transplant were the major predictors of better cognitive development, though most still had considerable residual disease burden (Aldenhoven et al., Blood, 2015 [2]).
Enzyme replacement alone was not enough for the severe form. In a comparison of 95 children with Hurler syndrome (18 on enzyme therapy alone, 54 transplanted, 23 untreated), survival was worse with enzyme therapy alone than with transplant, and hydrocephalus and cervical spinal cord compression were more common (Eisengart et al., Genet Med, 2018 [3]).
Key Takeaways
Feature | Details |
Medical Name | Mucopolysaccharidosis Type I (MPS I), Hurler type. [1] |
Primary Cause | Mutation in the IDUA gene; lack of the alpha-L-iduronidase enzyme. [1] |
Inheritance | Autosomal recessive (inherited from both parents). [1] |
Core Symptoms | Coarse facial features, skeletal deformities, heart valve issues, and cognitive decline. [1] |
Diagnosis | Prenatal screening, physical exams, and enzyme activity assays. [1] |
Primary Treatments | Enzyme Replacement Therapy (ERT) and Stem Cell Transplants (HSCT). [1] |
What is Hurler syndrome (MPS I)?
Hurler syndrome represents the most severe end of the MPS I spectrum. [1] Other forms include Hurler-Scheie syndrome (intermediate) and Scheie syndrome (mild), collectively referred to as "attenuated MPS I." [1] Unlike the milder forms, Hurler syndrome shows physical signs within the first year of life and causes rapid physical and cognitive decline. [1]
What causes Hurler syndrome at the enzyme and cell level?
The condition is rooted in a "recycling" failure within the body's cells.
The role of lysosomes: Lysosomes are cellular structures responsible for breaking down and digesting waste molecules. [1]
The missing enzyme: In Hurler syndrome, the body fails to produce enough of the enzyme alpha-L-iduronidase.
The toxic buildup: Without the enzyme, sugar molecules called glycosaminoglycans (GAGs) accumulate to toxic levels, causing cells to malfunction or die prematurely. [1]
What are the signs and symptoms of Hurler syndrome (MPS I)?
Symptoms are unique to each child but generally follow a progressive pattern, with physical signs appearing during the first year of life. [1]
Physical Characteristics
Facial features: Widely spaced eyes, large forehead, flat nasal bridge, and enlarged lips (coarse features). [1]
Skeletal changes: Short stature, rounding of the upper back (kyphosis), and bones forming incorrectly (dysostosis). [1]
Skin and hair: Excessive body hair growth (hirsutism). [1]
Organ enlargement: Enlarged liver (hepatomegaly) and spleen (splenomegaly). [1]
Systemic Complications
Cardiovascular: Heart valve problems and cardiomyopathy. [1]
Respiratory: Recurring ear and sinus infections, sleep apnea, and chronic difficulty breathing. [1]
Neurological: Buildup of fluid around the brain (hydrocephalus) and significant developmental delays. [1]
Sensory: Progressive hearing loss and vision problems like glaucoma or cloudy corneas. [1]
How is Hurler syndrome inherited, and who is at risk?
Hurler syndrome is an autosomal recessive condition. This means a child must inherit one copy of the mutated IDUA gene from each parent to develop the syndrome. [1]
If both parents are carriers, there is a 25% chance with each pregnancy that the child will have the condition.
The mutation occurs randomly, though a family history of MPS I increases the risk. [1]
How is Hurler syndrome diagnosed and screened for?
Prenatal testing: Amniocentesis or chorionic villus sampling (CVS) can identify genetic abnormalities before birth. [1]
Newborn screening: Many regions now include MPS I in standard newborn blood spot tests.
Diagnostic assays: Enzyme activity tests and genetic sequencing confirm the diagnosis after birth.
Imaging: X-rays and echocardiograms assess the impact on bones and the heart. [1]
How is Hurler syndrome managed and treated?
Modern medical interventions focus on replacing the missing enzyme and protecting cognitive function.
Treatment | Description |
Enzyme Replacement Therapy (ERT) | Regular IV infusions of laronidase (Aldurazyme) to replace the missing enzyme. |
Stem Cell Transplant (HSCT) | |
Supportive Surgery | Procedures to repair hernias, clear blocked airways, or treat hydrocephalus. |
Physical/Occupational Therapy | To manage joint stiffness and improve daily functioning. [1] |
What is the outlook and prognosis for Hurler syndrome?
Without treatment, Hurler syndrome is typically fatal in early childhood, often due to heart or respiratory failure. [1] However, early intervention with stem cell transplants has significantly improved the outlook, allowing many children to live longer and helping to preserve cognitive function when the transplant is done early. [1] [2]
Conclusion
Hurler syndrome is a profound medical challenge that requires lifelong, multidisciplinary care. While the diagnosis is overwhelming, the advancement of genetic screening and transplant technology offers a path toward managing symptoms and extending life. A dedicated team of specialists and a strong support network are vital for families navigating this journey.
Frequently Asked Questions
How is Hurler syndrome different from Hunter syndrome?
Hurler syndrome (MPS I) is caused by a lack of alpha-L-iduronidase and is autosomal recessive. Hunter syndrome (MPS II) is caused by a lack of iduronate 2-sulfatase and is X-linked (primarily affecting boys).
Is Hurler syndrome curable?
There is no cure that fixes the underlying genetic mutation, but treatments like stem cell transplants can significantly alter the course of the disease. [1]
What are glycosaminoglycans (GAGs)?
Glycosaminoglycans (GAGs) are long chains of sugar molecules that help build connective tissue. They were formerly called mucopolysaccharides, which is where the name "mucopolysaccharidosis" comes from. [1]
Why is early diagnosis so important?
Stem cell transplants (HSCT) are most effective at preserving brain function when performed before the age of two, before significant cognitive decline occurs. [1] [2]
Can parents be tested for the Hurler gene?
Yes. Carrier screening can determine if parents carry the mutated IDUA gene before they plan a pregnancy.
Does Hurler syndrome affect intelligence?
Yes. In its severe form, it causes progressive cognitive decline and significant developmental delays. [1]
What is Aldurazyme?
Aldurazyme (laronidase) is the brand name for the synthetic enzyme used in enzyme replacement therapy (ERT). [1]
How often is ERT needed?
ERT is typically a lifelong treatment administered as an intravenous infusion.
What is a "lysosomal storage condition"?
A lysosomal storage condition is a disease where the cell's "waste disposal" system (lysosomes) fails, causing toxic materials to be "stored" in the cell instead of recycled.
Can Hurler syndrome be seen on an ultrasound?
Some physical signs, like a large head or heart issues, might be seen, but a definitive diagnosis requires genetic or enzyme testing.
What is the life expectancy for Hurler syndrome?
Without treatment, children rarely live past about age 10. [1] With early stem cell transplant, many children live well beyond the first decade, though most still face significant long-term health challenges.
Does the syndrome affect both boys and girls?
Yes. Hurler syndrome affects males and females equally. [1]
What are "coarse" facial features?
The term coarse facial features refers to the thickening of facial tissues, resulting in a flat nose, large tongue, and prominent forehead.
Can Hurler syndrome cause blindness?
Hurler syndrome can cause clouding of the cornea and glaucoma, which can lead to severe vision loss if not managed. [1]
What is kyphosis?
Kyphosis is the medical term for the forward rounding of the back, often called a "hunchback," which is common in children with MPS I.
Why do children with Hurler syndrome have a large liver?
The liver acts as a major storage site for the excess sugar molecules (GAGs) that the body cannot break down.
Can HSCT fix the bone problems?
Stem cell transplants are better at helping the heart and brain than the bones; many children still require orthopedic surgeries.
Is there a "mild" version of Hurler syndrome?
Yes. Scheie syndrome is the mildest form of MPS I, where individuals have a normal lifespan and little to no cognitive impact.
What is "attenuated" MPS I?
Attenuated MPS I is the collective term for the intermediate (Hurler-Scheie) and mild (Scheie) forms of the disease. [1]
Does Hurler syndrome cause hearing loss?
Yes. Hearing loss is very common in affected children because of frequent infections and nerve damage.
What is the IDUA gene?
The IDUA gene is the gene that provides the instructions for making the alpha-L-iduronidase enzyme.
Can Hurler syndrome cause sleep apnea?
Yes. The thickening of the tongue and throat tissues can block the airway during sleep.
What is a carpal tunnel release?
A carpal tunnel release is a common surgery for children with MPS I to relieve pressure on the nerves in the wrist caused by GAG buildup.
How is the enzyme test performed?
A blood sample is taken to measure how much enzyme activity is present; very low activity confirms the diagnosis.
Can Hurler syndrome cause hernias?
Yes. Umbilical (belly button) and inguinal (groin) hernias are very common early signs.
What is dysostosis multiplex?
Dysostosis multiplex is the medical term for the specific pattern of bone abnormalities seen on X-rays of children with MPS disorders.
Does ERT help the brain?
No. The synthetic enzyme cannot easily cross the blood-brain barrier, which is why stem cell transplants are used for cognitive protection. [3]
What is the role of a genetic counselor?
Genetic counselors help families understand the 25% recurrence risk and navigate options like IVF with embryo screening.
Can Hurler syndrome cause a large tongue?
Yes. Macroglossia (enlarged tongue) is a common feature that can affect speech and breathing.
What is corneal clouding?
Corneal clouding is a buildup of GAGs in the clear front part of the eye, making it look hazy or opaque.
Is Hurler syndrome contagious?
No. It is purely genetic and cannot be spread from person to person.
Can Hurler syndrome be detected through newborn screening?
Yes. Many states in the U.S. and other countries have added MPS I to their newborn screening panels.
What is a "storage" disease?
The term storage disease refers to the fact that the body "stores" waste products in cells instead of breaking them down.
Can Hurler syndrome cause heart valve failure?
Yes. The buildup of GAGs makes the heart valves thick and stiff, eventually requiring surgical replacement in some cases.
Does Hurler syndrome affect hair growth?
Yes. Many children develop thicker, coarser hair on their body and scalp.
What is a bone marrow transplant?
A bone marrow transplant is the original form of HSCT, where healthy bone marrow is used to provide the missing enzymes.
Can Hurler syndrome cause hydrocephalus?
Yes. The buildup of sugars can block the flow of spinal fluid, leading to increased pressure in the brain.
How is kyphosis treated?
Kyphosis may be managed with bracing or, more commonly, spinal fusion surgery to stabilize the back.
Can Hurler syndrome cause frequent ear infections?
Yes. GAG buildup in the Eustachian tubes prevents proper drainage, leading to chronic infections.
What is alpha-L-iduronidase?
Alpha-L-iduronidase is the specific enzyme that people with Hurler syndrome are missing.
Can children with Hurler syndrome walk?
Most children learn to walk, but joint stiffness and bone deformities can make mobility difficult as they get older.
Does Hurler syndrome cause a short neck?
Yes. Skeletal abnormalities in the neck vertebrae lead to a characteristically short neck.
What is the "intermediate" form?
Hurler-Scheie syndrome is the intermediate form, where symptoms are more severe than Scheie but less so than Hurler. [1]
Can Hurler syndrome cause dental problems?
Yes. Children often have small, widely spaced teeth and overgrown gums.
What is the role of an endocrinologist in Hurler syndrome?
Endocrinologists often help manage the growth delays and hormonal aspects of the condition.
Is there a special diet for Hurler syndrome?
No specific diet can fix the enzyme deficiency, but a healthy, balanced diet is important for overall health.
Can Hurler syndrome be prevented?
Hurler syndrome cannot be prevented if both parents are carriers, but genetic testing can help with family planning decisions.
What is the most common cause of death in Hurler syndrome?
Most deaths are caused by heart failure or respiratory complications. [1]
How can I support a family with Hurler syndrome?
Offer practical help, listen without judgment, and encourage them to connect with specialized support organizations.
Where can I find more information?
Reputable sources include the National MPS Society and the National Organization for Rare Disorders (NORD).
Medical disclaimer: The information provided in this article is for educational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional for diagnosis and treatment of any health condition.
Source date: August 17, 2022. This article is current based on the most recent available data from the primary source.
Related Reading
Understanding Hunter Syndrome (MPS II): Causes, Symptoms, and Care covers Hunter syndrome, a closely related mucopolysaccharidosis.
Morquio Syndrome: Symptoms, Causes, and Management of MPS IV explains Morquio syndrome, another type of MPS affecting the skeleton.
Lysosomal Storage Diseases: Symptoms, Types, Causes, Diagnosis, and Treatment explains the wider group of enzyme disorders that includes Hurler syndrome.
Stem Cell Transplant (Bone Marrow Transplant): Types, Risks, and Recovery describes the transplant used to treat severe Hurler syndrome.
References
Cleveland Clinic. Mucopolysaccharidosis Type I: Hurler Syndrome - Symptoms & Causes. Cleveland Clinic. Last updated August 17, 2022. https://my.clevelandclinic.org/health/diseases/24000-hurler-syndrome
Aldenhoven M, Wynn RF, Orchard PJ, et al. Long-term outcome of Hurler syndrome patients after hematopoietic cell transplantation: an international multicenter study. Blood. 2015;125(13):2164-72. PMID 25624320. https://doi.org/10.1182/blood-2014-11-608075
Eisengart JB, Rudser KD, Xue Y, et al. Long-term outcomes of systemic therapies for Hurler syndrome: an international multicenter comparison. Genet Med. 2018;20(11):1423-1429. PMID 29517765. https://doi.org/10.1038/gim.2018.29
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