This page explains the main conditions that can resemble Hurler syndrome, how specialists tell them apart, and what this means for families.

Why doctors consider other diagnoses

Differential diagnosis is not about “doubting” that something is wrong. It is about making sure that the exact cause of a child’s problems is identified so that they can receive the right treatment. Several inherited disorders can cause coarse facial features, skeletal changes and organ enlargement, including other mucopolysaccharidoses (MPS), mucolipidoses and some skeletal dysplasias.

Early on, different conditions can look very similar.
Specialised enzyme tests, genetic tests and X-rays are usually needed to separate them.
Once Hurler syndrome is confirmed, doctors can decide if early HSCT is appropriate and avoid inappropriate treatments meant for other disorders.

Other MPS disorders in the differential

Other types of MPS share many features with MPS I-H, such as coarse facial features, hepatosplenomegaly, skeletal dysplasia and joint stiffness. The most important differentials often include:

MPS II (Hunter syndrome)X-linked, almost always boys. No corneal clouding on average, often slower progression than Hurler. Caused by iduronate-2-sulfatase deficiency, not IDUA deficiency.

MPS III (Sanfilippo syndrome)prominent and early neurocognitive decline, often with behavioural problems. Somatic features are typically milder than in Hurler.

MPS IV (Morquio A/B)severe skeletal dysplasia and joint laxity rather than stiffness. Normal intelligence in many cases.

MPS VI (Maroteaux–Lamy)somatic features can resemble Hurler, but intelligence is usually normal.

MPS VII (Sly syndrome)overlaps with Hurler in skeletal, cardiac and pulmonary features.

How they are distinguished: urine GAG profiling and specific enzyme assays separate MPS I from other MPS disorders, and genetic testing confirms the exact subtype.

Mucolipidoses and other storage disorders

Several non-MPS lysosomal storage diseases can mimic Hurler syndrome with coarse facial features, skeletal abnormalities and developmental delay, for example:

Mucolipidosis II / III (I-cell disease)marked skeletal changes and coarse facies, often with earlier onset and a more severe presentation.

GM1 gangliosidosiscoarse facies and organ enlargement with neuroregression, but a different pattern of brain and eye findings.

Alpha-mannosidosis and other oligosaccharidosesoverlapping facial and skeletal features with characteristic biochemical signatures.

These conditions are usually distinguished by enzyme panels, specific storage markers and, where needed, gene panels or exome sequencing.

Skeletal dysplasias in the differential

Because kyphosis, hip dysplasia and genu valgum are prominent in Hurler syndrome, some children are initially thought to have a primary skeletal dysplasia. Common differentials may include:

Spondyloepiphyseal dysplasias
Achondroplasia and related short-stature disorders
Other inherited skeletal dysplasias that primarily affect spine and hips

Clues that favour Hurler syndrome over isolated skeletal dysplasia:

Hepatosplenomegaly, hernias, coarse facial features or corneal clouding
Progressive joint stiffness rather than joint laxity
Raised urine GAGs and abnormal lysosomal enzyme studies

Broader paediatric differential

Children with coarse facial features, short stature and intellectual disability may also be investigated for:

Endocrine disordershypothyroidism, growth hormone deficiency

Chromosomal and syndromic conditionsfor example some microdeletion syndromes or syndromes with skeletal involvement

Nutritional or metabolic bone diseasesuch as rickets, which can mimic some skeletal changes but lacks the full multisystem pattern and GAG storage

In many of these conditions, the liver and spleen are normal, urine GAGs are not elevated and lysosomal enzyme tests are normal.

Investigations that separate Hurler from its mimics

Specialist centres often use a stepwise approach:

Urine GAGs and GAG fractionationraised dermatan and heparan sulphate can suggest MPS I or II.

Specific enzyme assayslow alpha-L-iduronidase (IDUA) supports MPS I; other enzyme patterns point to other MPS types or other lysosomal disorders.

IDUA gene testingconfirms MPS I and supports carrier testing and family counselling.

Radiology and clinical patterndysostosis multiplex, corneal clouding, organomegaly and joint stiffness can make Hurler syndrome more likely than many skeletal dysplasias.

What to expect if doctors are “ruling things out”

If your child is being tested for Hurler syndrome or other rare disorders, you may hear doctors talk about “differentials” or “ruling things out”. In practice this usually means:
Sending blood and urine for panels of enzyme and genetic tests, not just a single condition
Asking radiologists to look at X-rays for patterns typical of MPS and related diseases
Sometimes repeating tests or adding new ones as results come back

This process can feel slow and confusing, but it is designed to avoid misdiagnosis and to make sure that the final diagnosis truly matches your child’s condition. How Hurler syndrome is diagnosed

Practical points for clinicians considering the differential

Think broadly, include MPS I, other MPS types, mucolipidoses and skeletal dysplasias early.
Look for multisystem involvement, liver/spleen, cardiac valves, airway, joints, cornea and neurocognition.
Order urine GAGs and a lysosomal enzyme panel, or coordinate testing via a metabolic centre, rather than a single enzyme in isolation.
Use radiology to distinguish dysostosis multiplex from other skeletal dysplasia families.
Once biochemistry points to MPS I, proceed quickly to IDUA sequencing and severity assessment to decide on HSCT.

Key points about differential diagnosis

Several conditions can mimic Hurler syndrome, especially other MPS types, mucolipidoses and skeletal dysplasias.
The multisystem pattern, coarse facies, organomegaly, joint stiffness, valve disease, corneal clouding and neurodevelopmental involvement, can strongly suggest MPS I-H rather than isolated skeletal or endocrine disorders.
Urine GAGs, specific lysosomal enzyme assays and IDUA gene testing are central to separating Hurler syndrome from its mimics.
Careful differential diagnosis helps avoid misdiagnosis and supports time-critical access to treatments such as HSCT when appropriate.

Differential diagnosis of Hurler syndrome (MPS I-H)