Hunter russel syndrome

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Hunter syndrome (Mucopolysaccharidosis type II) is an X-linked recessive lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase, leading to accumulation of heparan sulfate and dermatan sulfate in tissues.

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"Hunter syndrome" OR "mucopolysaccharidosis II"

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Hunter Syndrome (Mucopolysaccharidosis Type II)

Overview

Hunter syndrome (MPS II) is an X-linked recessive lysosomal storage disorder, making it unique among the mucopolysaccharidoses - all others are autosomal recessive. It almost exclusively affects males. The causative gene is IDS (iduronate-2-sulfatase gene on chromosome Xq28).

Goldman-Cecil Medicine, p. 2748 | Emery's Elements of Medical Genetics, p. 290

Pathophysiology

Deficient enzyme: Iduronate-2-sulfatase (iduronate sulfate sulfatase, I2S)

Consequence: Inability to break down glycosaminoglycans (GAGs), specifically:

Dermatan sulfate
Heparan sulfate

These accumulate progressively in lysosomes throughout the body - in connective tissue, viscera, the CNS, and the cardiovascular system.

Andrews' Diseases of the Skin, p. 628

Clinical Features

Males usually present between ages 2 and 5 years. The disease has a broad phenotypic spectrum from severe (neuronopathic) to attenuated forms.

Facial & Skeletal

Coarse facial features (gargoylism)
Large head, prominent forehead
Flattened nasal bridge
Large tongue (macroglossia)
Short stature
Joint stiffness and limited mobility
Abnormal vertebral shape on spinal X-ray

Neurological

Progressive mental and physical deterioration (severe form)
Cervical myelopathy (due to dural thickening and GAG deposition in the cervical spine)
Raised intracranial pressure (may require VP shunting)

Hearing

Combined conductive and sensorineural hearing loss - very characteristic of MPS II

Eyes

No corneal clouding (key distinguishing feature from Hurler syndrome/MPS I)

Cardiovascular

Cor pulmonale
Cardiac valvular thickening/dysfunction
Coronary involvement

Respiratory

Obstructive airway disease (narrowed upper airways)
Sleep apnea
Restrictive lung disease

Abdomen

Hepatosplenomegaly

Dermatological (Pathognomonic Skin Findings)

Extensive dermal melanocytosis (atypical Mongolian spots - large, in unusual locations beyond back and buttocks) - often the initial presentation in infancy
Pebbly skin lesions: firm, flesh-colored to white papules and nodules coalescing into a cobblestone/reticular pattern, seen on the upper back, neck, chest, proximal arms, or thighs (in ~10% of patients)
Histology: increased dermal mucin, metachromatic granules in dermal fibroblasts, eccrine sweat glands, and epidermal keratinocytes

Hunter syndrome skin papules - cobblestone/reticular pattern on skin

Fig. - Hunter syndrome papules showing cobblestone/reticular skin pattern (Andrews' Diseases of the Skin, p. 628)

Andrews' Diseases of the Skin, p. 628

How It Differs from Hurler Syndrome (MPS I)

Feature	Hunter (MPS II)	Hurler (MPS I)
Inheritance	X-linked recessive	Autosomal recessive
Corneal clouding	Absent	Present
GAG stored	Dermatan + heparan sulfate	Same
Deficient enzyme	Iduronate-2-sulfatase	Alpha-L-iduronidase
Skin lesions	Characteristic papules	Less prominent

Diagnosis

Urine GAG analysis: Elevated dermatan sulfate and heparan sulfate in urine
Enzyme assay: Absent or markedly reduced iduronate-2-sulfatase activity in leukocytes or serum
Molecular testing: Direct IDS gene analysis (confirms diagnosis, identifies carrier females)
Supportive investigations: Skeletal survey, echocardiography, ophthalmologic exam, audiology

Emery's Elements of Medical Genetics, p. 290 | Goldman-Cecil Medicine, p. 2748

Prognosis

Severe (neuronopathic) form: progressive deterioration, death usually in adolescence
Attenuated form: survival into adulthood is possible with less severe neurological involvement

Treatment

Enzyme Replacement Therapy (ERT)

Idursulfase (Elaprase) - recombinant I2S, given by IV infusion every 2 weeks
Reduces somatic burden (hepatosplenomegaly, joint mobility, respiratory function) but has limited CNS penetration for neurological disease
A 2024 systematic review (PMID 39201256) confirms its efficacy for somatic manifestations of MPS II

Hematopoietic Stem Cell Transplantation (HSCT)

Considered in selected patients, especially early in disease course
Better outcomes when done early; does not reliably prevent mental retardation
Less established for MPS II compared to MPS I (Hurler)

Supportive Management

VP shunting if intracranial hypertension develops
Hearing aids / ENT surveillance for combined hearing loss
Cardiology monitoring and surgery for valvular disease
Orthopedic surgery for joint replacement and spinal stabilization
Carpal tunnel release (common in adults)
Adenotonsillectomy / CPAP for obstructive airway disease and sleep apnea
Anesthesia precautions: high risk due to narrow airway and cervical instability - requires specialist preparation
Goldman-Cecil Medicine, p. 2748 | Andrews' Diseases of the Skin, p. 628 | K.J. Lee's Essential Otolaryngology, p. 1019

Key Memory Points

Only X-linked MPS (vs all others being autosomal recessive)
Enzyme: iduronate-2-sulfatase (IDS gene)
GAGs: dermatan + heparan sulfate in urine
No corneal clouding (unlike Hurler)
Cobblestone skin papules + atypical Mongolian spots = pathognomonic clues
Combined hearing loss is characteristic
Treatment: idursulfase (ERT) + supportive multisystem care

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