Conditions · Metabolism (biochemistry)
Hunter syndrome (mucopolysaccharidosis type II) !
Hunter syndrome looks like Hurler syndrome but is X-linked, affects almost only boys and does not cloud the cornea.
Updated 2026-11-01
Structures involved
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In biochemistry
- Lysosomal storage diseases
- Glycosaminoglycans (mucopolysaccharides)
- α-L-Iduronidase
- Iduronate 2-sulfatase (I2S)
What it is
An X-linked mucopolysaccharidosis caused by iduronate 2-sulfatase deficiency (IDS gene); dermatan sulfate and heparan sulfate accumulate.
Who gets it
It occurs in about 1 in 100,000 to 170,000 males. Female carriers rarely have symptoms.
Causes
- Variants of the IDS gene on the X chromosome
Risk factors
- Carrier mother
- Male sex
Pathophysiology
Iduronate 2-sulfatase removes the sulfate from iduronic acid before α-L-iduronidase acts. Without it, dermatan and heparan sulfate accumulate in the lysosomes of connective tissue, organs, airways, valves and, in the neuronopathic form, neurons. The result is a multisystem picture like Hurler syndrome, with the cornea spared.
Classification
- Neuronopathic (severe) form: about two-thirds, with cognitive decline from childhood
- Attenuated form: preserved intelligence, slower somatic disease
Symptoms and signs
- Coarse facial features from age 2 to 4
- Hepatosplenomegaly and hernias
- Stiff joints and short stature
- Ivory-coloured papules on the back and arms ("pebbly skin")
- Repeated ear infections and hearing loss
- Hyperactivity, aggressive behaviour and speech delay (severe form)
Diagnosis
- Clinical
- A boy with coarse features, hepatosplenomegaly, stiff joints and clear corneas; sometimes pebbly skin.
- Tests
- High urinary glycosaminoglycans (dermatan and heparan sulfate); low iduronate 2-sulfatase activity in plasma or leukocytes, with another sulfatase normal to exclude multiple sulfatase deficiency; IDS gene testing; audiometry.
- Imaging
- X-rays with dysostosis multiplex; echocardiogram with thickened valves; brain and cervical spine MRI.
Treatment
- Medical
- Intravenous enzyme replacement with recombinant iduronate 2-sulfatase: improves organs, mobility and breathing, but not the brain.
- Surgical
- Adenotonsillectomy, hernia repair, carpal tunnel release, spinal surgery and valve replacement as needed.
- Procedure
- Non-invasive ventilation for sleep apnoea; stem cell transplant is used in some centres.
- Follow-up
- Cardiac, respiratory, hearing, orthopaedic and neurodevelopmental follow-up.
Complications
- Airway obstruction
- Valve disease and heart failure
- Hydrocephalus
- Hearing loss
- Carpal tunnel syndrome
Prognosis
In the severe form survival usually reaches the second decade. In the attenuated form many patients reach adulthood.
Test yourself
Think of the answer, then tap the question to see it.
Which enzyme is missing in Hunter syndrome?
Iduronate 2-sulfatase (IDS gene).
How is Hunter syndrome inherited, and what follows from that?
X-linked: almost only boys are affected.
Which skin finding is typical of Hunter syndrome?
Ivory-coloured papules on the back and arms, the so-called pebbly skin.
Why is a second sulfatase measured when diagnosing Hunter syndrome?
To exclude multiple sulfatase deficiency, in which all sulfatases fail together.
Related conditions
- Hurler syndrome (mucopolysaccharidosis type I)
- Carpal tunnel syndrome
- Obstructive sleep apnoea
- Hydrocephalus
- Inguinal hernia
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Mucopolysaccharidosis type II: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); IDS gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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