Clinical overview of Hurler syndrome (MPS I-H)
Hurler syndrome (severe MPS I, MPS I-H) is a rapidly progressive, multisystem lysosomal storage disorder caused by profound deficiency of alpha L iduronidase. Without timely recognition and disease modifying treatment, affected children develop early neurocognitive decline, skeletal dysplasia, cardiorespiratory disease and shortened survival.
This clinical overview summarises the key aspects of pathophysiology, natural history, clinical presentation, diagnosis and current management of Hurler syndrome for healthcare professionals, with links to detailed pages on specific topics.
Note: This information is for healthcare professionals. It does not replace local and national guidelines or formal specialist advice.
What is Hurler syndrome?
Hurler syndrome is the severe end of the MPS I spectrum, characterised by near complete loss of alpha L iduronidase activity and early onset multisystem disease.
It sits within a clinical continuum that also includes intermediate (Hurler–Scheie) and attenuated (Scheie) phenotypes.
In practice, “MPS I-H” usually refers to children who:
- Present in infancy or early childhood
- Show progressive neurocognitive involvement
- Are considered for haematopoietic stem cell transplantation (HSCT) as the main disease modifying option
Underlying biology and organ involvement
Hurler syndrome results from biallelic pathogenic variants in IDUA, leading to markedly reduced or absent alpha L iduronidase activity. This causes progressive lysosomal accumulation of dermatan sulfate and heparan sulfate in multiple tissues.
Key points for clinicians:
- Lysosomal storage leads to cellular dysfunction, inflammation and fibrosis
Long term effects include:
— Neurocognitive decline due to CNS storage and secondary white matter changes
— Dysostosis multiplex, growth failure and joint contractures
— Valvular heart disease, cardiomyopathy and pulmonary hypertension
— Upper and lower airway obstruction, sleep disordered breathing and restrictive lung disease
— Hepatosplenomegaly and abdominal protuberance
Prevalence and disease course without treatment
Hurler syndrome is ultra rare, with incidence varying by region and screening strategy.
In the absence of disease modifying therapy:
- Onset is typically in the first 1–2 years of life
- Children develop progressive developmental delay or regression, skeletal abnormalities, cardiorespiratory disease and recurrent infections
- Life expectancy is often within the first or second decade, usually due to cardiorespiratory complications
- With HSCT and adjunctive therapies, survival has improved, but residual multisystem morbidity remains common
How Hurler syndrome typically presents
Hurler syndrome is a classic multisystem condition. Individual features are non specific but the evolving pattern is characteristic.
Early signs (infancy)
- Inguinal or umbilical hernias
- Recurrent ear infections, glue ear and noisy breathing
- Subtle coarsening of facial features, frontal bossing
- Increasing head circumference on growth chart
- Delayed motor milestones but often social and language skills initially preserved
Features in early childhood
As disease progresses:
- Coarse facies, macroglossia and enlarged head
- Hepatosplenomegaly, abdominal distension
- Joint stiffness, clawed hands, kyphosis or gibbus deformity
- Recurrent respiratory infections, snoring, sleep apnoea
- Developmental slowing or regression, particularly in language and cognition
- Corneal clouding, hearing loss
Multisystem involvement
Neurological
Developmental delay/regression, hydrocephalus, cervical cord compression
Skeletal
Dysostosis multiplex, genu valgum, hip dysplasia, contractures
Cardiac
Valvular thickening, regurgitation, cardiomyopathy
Respiratory/ENT
Adenoidal hypertrophy, airway narrowing, OSA
Hepatosplenic
Organomegaly
Ophthalmic/audiology
Corneal clouding, retinal changes, conductive and sensorineural hearing loss
Diagnostic work up and assigning phenotype
Early and accurate diagnosis is essential to allow timely transplant assessment and tailored counselling.
Biochemical confirmation
- Urinary GAGs (screening)
- Leukocyte or dried blood spot alpha L iduronidase activity
Molecular confirmation
- IDUA gene sequencing with classification of variants
- Use of genotype–phenotype data where available, alongside clinical features
Phenotypic classification
- Integration of age at onset, neurocognitive profile, clinical severity and genotype
- Determination of likely MPS I-H vs attenuated forms, informing urgency of HSCT referral
- Regional newborn screening programmes alter the sequence, with biochemical and genetic data preceding overt clinical features
Current standard of care
Disease modifying therapy
- HSCT for eligible children with classic Hurler phenotype, ideally early in life.
- ERT as a bridge to transplant and as long term therapy in those not undergoing HSCT.
Structured multidisciplinary care
- Cardiology, respiratory, ENT, orthopaedics, neurology, ophthalmology, audiology.
- Physiotherapy, occupational therapy, speech and language therapy
Proactive surveillance
- Regular assessment of neurocognition, motor function, skeletal status, cardiac and respiratory function.
Transition and adult care
- Planned transfer to adult metabolic and specialty services for survivors of childhood treatment.
Residual morbidity after HSCT and ERT
HSCT, particularly when undertaken early, can stabilise or improve neurocognition and improve survival. However, many survivors experience:
- Persistent or progressive skeletal disease and pain
- •Cardiac valve disease requiring long term surveillance and sometimes surgery
- Ongoing respiratory and ENT complications
- Educational needs and neurocognitive challenges
- Adults with a history of MPS I-H and HSCT represent a growing cohort with complex, evolving needs
Key considerations for acute care
Patients with Hurler syndrome are at increased risk during acute illness, anaesthesia and surgery.
Points for rapid reference:
- Anticipate difficult airway and consider early expert anaesthetic input
- Avoid excessive neck manipulation due to possible cervical spine instability
- •Review recent cardiac and respiratory assessments where available
- Prefer centres with experience in complex paediatric airway and metabolic disease where feasible
- Families should be encouraged to carry an emergency summary. Acute teams should access existing documentation wherever possible
Emerging therapies and ongoing research
Ongoing work includes systemic and CNS directed gene and cell therapies, next generation ERT, and adjunctive small molecule approaches. These remain investigational and are accessed via clinical trials.
Clinicians should understand the broad rationale and stage of development to counsel families and interpret media reports.
Key clinical takeaways for professionals
- Hurler syndrome (MPS I-H) is a severe, rapidly progressive lysosomal storage disorder with early onset multisystem involvement and neurocognitive decline.
- Early recognition and rapid referral to a specialist metabolic and transplant centre are crucial, particularly in infants and young children.
- HSCT, often supported by ERT, is the main disease modifying treatment in classic Hurler syndrome, but does not fully prevent long term skeletal, cardiac and other complications.
- Ongoing multidisciplinary care, structured surveillance and planned transition to adult services are required for all survivors.
- Investigational approaches, including systemic gene therapy, may expand future options but should be discussed in the context of robust evidence and regulated clinical trials.
What to read next
For healthcare professionals
Overview, recognition, referral and resources
Symptoms and diagnosis
Early signs, multisystem features and diagnostic pathways
Treatments and care
HSCT, ERT, supportive and multidisciplinary care
Emergency and anaesthetic information
High risk situations and perioperative guidance
Living with Hurler syndrome
Patient and family facing information
Research hub
Gene therapy, preclinical work and clinical trials