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Mucopolysaccharidosis type IV
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Mucopolysaccharidosis type IV

Mucopolysaccharidosis type IV (MPS IV), or Morquio syndrome, is a progressive condition that primarily affects the skeleton and is caused by the inability to break down specific sugar molecules.

Overview

MPS IV is a progressive condition that mainly affects the skeleton. It is estimated to occur in 1 in 200,000 to 300,000 individuals. Unlike some other types of mucopolysaccharidosis, MPS IV does not affect intelligence.

Symptoms

Signs and symptoms typically appear in early childhood and include:

  • Skeletal abnormalities: Short stature, knock knees, and abnormalities of the ribs, chest, spine, hips, and wrists.
  • Joint issues: Joints may be loose and flexible (hypermobile) or have restricted movement.
  • Odontoid hypoplasia: Underdevelopment of a peg-like bone in the neck, which can lead to spinal cord compression, paralysis, or death.
  • Vision and hearing: Cloudy corneas (causing vision loss) and recurrent ear infections or hearing loss.
  • Respiratory issues: Narrow airways, frequent upper respiratory infections, and sleep apnea.
  • Other features: Thin tooth enamel, multiple cavities, heart valve abnormalities, enlarged liver (hepatomegaly), and hernias.

Causes

MPS IV is caused by mutations in the GALNS gene (MPS IVA) or the GLB1 gene (MPS IVB). These genes produce enzymes necessary to break down large sugar molecules called glycosaminoglycans (GAGs).

When these enzymes are missing or reduced, GAGs accumulate to toxic levels inside the lysosomes of cells. This buildup interferes with normal cellular function and is particularly damaging to bone tissue, leading to the characteristic skeletal deformities of the disorder.

Inheritance

This condition is inherited in an autosomal recessive pattern. This means both copies of the gene in each cell must have mutations for the condition to occur. Parents of an affected individual typically carry one copy of the mutated gene but do not show signs or symptoms of the condition.

Prognosis

Life expectancy depends on the severity of symptoms. Severely affected individuals may only survive until late childhood or adolescence, while those with milder forms may live into adulthood. Major causes of death include spinal cord compression and airway obstruction.

Frequently Asked Questions

Children with MPS IV should have a baseline cervical spine MRI by age 4, followed by repeat imaging every 1–2 years or sooner if new neurologic symptoms appear (e.g., gait changes, hand weakness, or neck pain). If the odontoid is markedly hypoplastic or the spinal canal diameter is < 12 mm, a neurosurgeon may recommend posterior cervical fusion to prevent irreversible cord injury.
While enzyme deficiency cannot be corrected by diet alone, maintaining optimal vitamin D and calcium intake supports bone health. Low‑impact activities such as swimming or aquatic therapy help preserve joint range of motion without over‑loading fragile bones. Regular physiotherapy and use of orthotic devices can improve posture and reduce the risk of falls.
Two enzyme replacement therapies (ERT) are approved: elosulfase alfa (for MPS IVA) and a investigational gene‑therapy trial for GLB1‑related MPS IVB. ERT is given as a weekly intravenous infusion (2 mg/kg) in a hospital infusion center; pre‑medication with antihistamines may reduce infusion reactions. Early initiation (ideally before age 5) has been shown to improve endurance and respiratory function, though skeletal changes respond slowly.
Look for a combination of short stature, knock‑knees, chest or rib abnormalities, and frequent ear infections or hearing loss before age 3. The presence of corneal clouding or unusually loose joints alongside these skeletal signs is a red flag that warrants urinary GAG testing and referral to a metabolic specialist.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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