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# 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](https://durgical.com/en/anatomy/cornea/).

Updated 2026-11-01

## Structures involved

Tap one to see what it is and open it in 3D.

- [Liver](https://durgical.com/en/anatomy/liver/)
- [Spleen](https://durgical.com/en/anatomy/spleen/)
- [Mitral anterior leaflet](https://durgical.com/en/anatomy/anterior-leaflet-of-left-atrioventricular-valve/)
- [Skin](https://durgical.com/en/anatomy/skin/)
- [Tongue](https://durgical.com/en/anatomy/tongue/)
- [Trachea](https://durgical.com/en/anatomy/trachea/)
- [L1 vertebra](https://durgical.com/en/anatomy/lumbar-vertebra/)
- [Aortic right coronary cusp](https://durgical.com/en/anatomy/right-coronary-leaflet/)

## In biochemistry

- [Lysosomal storage diseases](https://durgical.com/en/biochemistry/topics/lysosomal-storage-diseases/)
- [Glycosaminoglycans (mucopolysaccharides)](https://durgical.com/en/biochemistry/topics/glycosaminoglycans/)
- [α-L-Iduronidase](https://durgical.com/en/biochemistry/enzymes/l-iduronidase/)
- [Iduronate 2-sulfatase (I2S)](https://durgical.com/en/biochemistry/enzymes/iduronate-2-sulfatase/)

## 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)

## Red flags

- Sleep apnoea or airway obstruction
- Valve disease with heart failure
- Cervical cord compression
- Difficult airway under anaesthesia

## Diagnosis

**Clinical**
A boy with coarse features, hepatosplenomegaly, stiff joints and clear corneas; sometimes pebbly [skin](https://durgical.com/en/anatomy/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](https://durgical.com/en/anatomy/region/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](https://durgical.com/en/anatomy/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.

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## Related conditions

- [Hurler syndrome (mucopolysaccharidosis type I)](https://durgical.com/en/conditions/hurler-syndrome/)
- [Carpal tunnel syndrome](https://durgical.com/en/conditions/carpal-tunnel-syndrome/)
- [Obstructive sleep apnoea](https://durgical.com/en/conditions/obstructive-sleep-apnoea/)
- [Hydrocephalus](https://durgical.com/en/conditions/hydrocephalus/)
- [Inguinal hernia](https://durgical.com/en/conditions/inguinal-hernia/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Mucopolysaccharidosis type II: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/mucopolysaccharidosis-type-ii/) (MedlinePlus, US National Library of Medicine, 2026); [IDS gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/ids/) (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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Source: https://durgical.com/en/conditions/hunter-syndrome/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/hunter-syndrome/