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Hunter russel syndrome

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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)

FeatureHunter (MPS II)Hurler (MPS I)
InheritanceX-linked recessiveAutosomal recessive
Corneal cloudingAbsentPresent
GAG storedDermatan + heparan sulfateSame
Deficient enzymeIduronate-2-sulfataseAlpha-L-iduronidase
Skin lesionsCharacteristic papulesLess prominent

Diagnosis

  1. Urine GAG analysis: Elevated dermatan sulfate and heparan sulfate in urine
  2. Enzyme assay: Absent or markedly reduced iduronate-2-sulfatase activity in leukocytes or serum
  3. Molecular testing: Direct IDS gene analysis (confirms diagnosis, identifies carrier females)
  4. 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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