About Hurler Syndrome (MPS I-H)
Hurler syndrome, also known as mucopolysaccharidosis type I-H (MPS I-H), is a severe, inherited lysosomal storage disorder. It is caused by a deficiency of the enzyme alpha L iduronidase (IDUA). When this enzyme is missing or not working properly, glycosaminoglycans (GAGs) build up inside cells and gradually damage many organs, including the brain, skeleton, heart, lungs, liver, eyes and ears. (NCBI)
This section explains what Hurler syndrome is, how it fits within the MPS I spectrum, why it happens, how it affects the body and what is known about its natural history.
The information on these pages is based on peer reviewed research and clinical experience, and is written for families, patients, healthcare professionals and researchers.
Key Facts About Hurler Syndrome
A quick, evidence based summary in a clean, scannable format.
Hurler Syndrome and the MPS I Spectrum
Mucopolysaccharidosis type I (MPS I) is a group of related conditions that share the same underlying enzyme deficiency but differ in severity. Hurler syndrome (MPS I-H) is the most severe form. Attenuated forms, sometimes called Hurler–Scheie and Scheie syndromes, start later and usually have milder or limited central nervous system involvement. Hurler syndrome typically presents in infancy with rapid progression, while attenuated MPS I may present in later childhood or adulthood. (Orpha)
Paragraph on frequency: MPS I is rare. Studies from different countries suggest an overall incidence of roughly 1 in 100,000 live births, with Hurler syndrome representing about half or more of MPS I cases. (PMC)
Small highlighted note: Although the older labels Hurler, Hurler–Scheie and Scheie are still in use, many experts now describe MPS I as severe or attenuated, reflecting the continuous spectrum of disease. (Wikipedia)
What causes Hurler syndrome?
Causes and genetics
Hurler syndrome is caused by pathogenic variants in the IDUA gene, which provides instructions for the alpha L iduronidase enzyme. This enzyme normally helps break down GAGs such as dermatan sulphate and heparan sulphate within lysosomes. When IDUA activity is very low or absent, GAGs accumulate in cells and tissues throughout the body. Over time, this storage leads to progressive damage in multiple organs. (NCBI)
The condition follows an autosomal recessive pattern. A child is affected when they inherit two non working copies of the IDUA gene, one from each parent. Parents who each carry one non working copy are usually healthy themselves but have a 25 percent chance in each pregnancy of having a child with Hurler syndrome. Carrier testing and prenatal diagnostic options can be discussed with a clinical genetics service. (MedlinePlus)
Genetic counselling and family planning →
What Happens Inside the Body in Hurler Syndrome
Because IDUA deficiency occurs in every tissue, Hurler syndrome affects many organs at the same time. Symptoms usually start in the first year of life and progress rapidly without treatment. Common features include coarse facial appearance, enlarged liver and spleen, hernias, frequent respiratory infections, sleep disordered breathing, joint stiffness, spinal deformities, carpal tunnel syndrome, corneal clouding, hearing problems and delayed development. (Boston Children’s Hospital)
Brain and Nervous System
developmental delay, cognitive decline, hydrocephalus and spinal cord compression
Skeleton and Joints
dysostosis multiplex, short stature, hip dysplasia, joint contractures and spine deformities
Heart and Blood Vessels
thickened heart valves, cardiomyopathy and cardiopulmonary complications
Breathing and Airways
upper airway obstruction, obstructive sleep apnoea and recurrent chest infections
Abdomen and Organs
enlarged liver and spleen, umbilical and inguinal hernias
Eyes, Ears, Teeth
corneal clouding, visual impairment, hearing loss and dental anomalies
Natural history and prognosis
Natural history of Hurler syndrome
If Hurler syndrome is not treated, symptoms usually appear in infancy, with progressive developmental delay, loss of acquired skills and increasing somatic disease in many organs. Historical data show that most untreated children with Hurler syndrome die within the first decade of life, often due to respiratory infections or cardiac complications. (ScienceDirect)
Over recent decades, early haematopoietic stem cell transplantation has transformed the natural history of MPS I-H. When performed in experienced centres and timed early in life, HSCT can preserve neurocognitive function and significantly improve survival. Enzyme replacement therapy, often used around the time of transplant, can further reduce GAG storage and improve organ function. However, long term follow up studies show that many transplanted patients continue to experience skeletal disease, joint problems, airway issues and other chronic complications, which require ongoing specialist care into adolescence and adulthood. (PMC)
Who This Page Is For
For parents and caregivers
These pages explain the science behind Hurler syndrome in clear language. You can explore how the condition affects different parts of the body, how it usually progresses, and why early treatment and ongoing follow up are important.
For healthcare professionals
The section provides a concise reference on underlying biology, multisystem involvement, epidemiology and natural history, with links to more detailed clinical guidance and key publications.
For researchers and students
The scientific pages outline pathophysiology, disease burden and long term outcomes, to support further work on biomarkers, new therapies and models of care.