This page explains in clear language what Hurler syndrome is, why it happens and how it fits within the wider MPS I spectrum, with links to more detailed sections on symptoms, diagnosis and treatment.
- Hurler syndrome is the severe form of mucopolysaccharidosis type I (MPS I), a lysosomal storage disorder.
- It is caused by deficiency of the lysosomal enzyme alpha L iduronidase (IDUA).
- GAGs, mainly dermatan sulphate and heparan sulphate, accumulate in cells and tissues throughout the body.
- Hurler syndrome is autosomal recessive. A child is affected when they inherit two non working copies of the IDUA gene.
- Symptoms usually begin in the first year of life and include developmental delay, coarse facial features, hernias, frequent infections and joint stiffness.
- Without treatment, most children do not survive beyond the first decade of life, often due to heart or respiratory complications.
- With early haematopoietic stem cell transplantation (HSCT), often combined with enzyme replacement therapy (ERT), survival and neurocognitive outcomes can be significantly improved, although long term disease burden remains.
Hurler syndrome and the MPS I spectrum
Mucopolysaccharidosis type I (MPS I) describes a group of related conditions that share the same underlying enzyme deficiency but differ in severity. Historically, three clinical syndromes were described: Hurler (MPS I-H), Hurler–Scheie (MPS I-H/S) and Scheie (MPS I-S). Hurler syndrome is the most severe form, with early onset and rapid progression. The attenuated forms usually present later and have little or no central nervous system involvement.
Because symptoms overlap across this spectrum, many experts now classify MPS I more simply as severe or attenuated disease. Hurler syndrome corresponds to the severe end of the spectrum. Early recognition is crucial, because children with severe MPS I benefit most from prompt referral for HSCT before irreversible neurological damage occurs.
For families: start here
A diagnosis of Hurler syndrome can feel overwhelming. You may be searching for clear explanations, practical advice and honest answers about what happens next. These pages are written in plain language and reviewed by clinicians and families who know MPS I-H well.
Brain & 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 & Blood Vessels
Thickened heart valves, cardiomyopathy and cardiopulmonary complications
Breathing and airways
Upper airway obstruction, obstructive sleep apnoea and recurrent chest infections
Abdomen & Organs
Enlarged liver and spleen, umbilical and inguinal hernias
Eyes & Vision
Corneal clouding and visual impairment
Ears & Hearing
Hearing loss and recurrent ear infections
Teeth & Oral Health
Dental anomalies and oral complications
Genetics of Hurler syndrome
Hurler syndrome is caused by disease causing variants in the IDUA gene, located on chromosome 4. More than 200 different IDUA mutations have been reported, and the specific combination of variants in an individual partly influences disease severity, although genotype phenotype correlations are not always straightforward.
The condition is autosomal recessive. This means:
- Affected individuals have two non working copies of the IDUA gene.
- Parents are usually healthy carriers who each have one non working and one working copy.
- For each pregnancy between two carriers, there is a 25 percent chance the child will have Hurler syndrome, a 50 percent chance the child will be a carrier and a 25 percent chance the child will inherit two working copies.
Families may be offered carrier testing, prenatal diagnosis or preimplantation genetic testing through a clinical genetics service.
- Often no clear symptoms at birth.
- Frequent infections, hernias, early feature changes.
- Joint stiffness, organ enlargement, delayed milestones.
- Plateau then regression, mobility and breathing problems.
How common is Hurler syndrome?
Hurler syndrome is rare. Population studies from Europe and North America estimate that all forms of MPS I occur in roughly 1 in 100,000 live births, with Hurler syndrome accounting for around half of these cases.
Although the number of affected children is small, the burden on families, health services and society is substantial because the disease is complex, lifelong and requires coordinated care from multiple specialists.
Why early diagnosis and treatment are critical
Because Hurler syndrome progresses rapidly, early diagnosis is essential. Several countries have introduced newborn screening for MPS I so that affected infants can be identified and referred to specialist centres before symptoms become advanced.
For children with severe MPS I, early haematopoietic stem cell transplantation (HSCT) remains the standard disease modifying treatment to preserve neurocognitive function. HSCT is often combined with enzyme replacement therapy (ERT) before and after transplant. Evidence from long term follow up shows that these interventions improve survival and many clinical outcomes; however, skeletal disease, airway problems and other complications often persist, which is why new approaches such as gene therapy are under investigation.
Early diagnosis saves function
For parents and caregivers
This page gives an overview of what Hurler syndrome is and why your child has it. The next pages in this section explain in more detail how the condition affects different parts of the body, what symptoms to look for and how it is diagnosed.
For healthcare professionals
This summary can be used as a quick reference when you suspect MPS I-H or are counselling families, with links to more detailed clinical guidance in the professional sections.
For researchers and students
The disease overview here sets the scene for more technical content in the Research Hub, including pathophysiology, natural history data and rationale for novel therapies.