Hunter syndrome

  • Definition
  • Alternative Names
    • Mucopolysaccharidosis type II; Iduronate sulfatase deficiency

  • Causes
    • Hunter syndrome is an inherited condition, which means it is passed down through families. The affected gene is on the X chromosome. Therefore, boys are most often affected. Their mothers do not have symptoms of the disease, but they carry a nonworking copy of the gene.

      The condition is caused by a lack of the enzyme iduronate sulfatase. Without this enzyme, chains of sugar molecules build up in various body tissues, causing damage.

      The early-onset, severe form of the disease begins shortly after age 2. A late-onset, mild form causes less severe symptoms to appear later in life.

  • Symptoms
  • Exams and Tests
    • A physical exam and tests in someone with Hunter syndrome may show:

      Tests may include:

      • Enzyme study
      • Genetic testing for a change in the iduronate sulfatase gene
      • Urine test for heparan sulfate and dermatan sulfate
  • Treatment
    • The U.S. Food and Drug Administration (FDA) has approved the first treatment for Hunter syndrome. The medicine, called idursulfase (Elaprase), is given through a vein (IV, intravenously). Talk to your health care provider for more information.

      Bone marrow transplant has been tried for the early-onset form, but the results can vary.

      Each health problem caused by this disease should be treated separately.

  • Outlook (Prognosis)
    • People with the early-onset (severe) form usually live for 10 to 20 years. People with the late-onset (mild) form usually live 20 to 60 years.

  • Possible Complications
    • These complications may occur:

      • Airway obstruction
      • Carpal tunnel syndrome
      • Hearing loss that gets worse over time
      • Loss of ability to complete daily living activities
      • Joint stiffness that leads to contractures
      • Mental function that gets worse over time
  • When to Contact a Medical Professional
    • Call your provider if:

      • You or your child has a group of these symptoms
      • You know you are a genetic carrier and are considering having children
  • Prevention
    • Genetic counseling is recommended for couples who want to have children and who have a family history of Hunter syndrome. Prenatal testing is available. Carrier testing for female relatives of affected males is available at a few centers.

  • References
    • Ma, C, Ali S, Dorshi N, Dominguez R. Storage diseases. In: Pope TL, Bloem HL, Beltran J, Morrison WB, eds. Musculoskeletal Imaging. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 82.

      Muenzer J, Wraith JE, Beck M, et al. A phase II/III clinical study of enzyme replacement therapy with idursulfase in mucopolysaccharidosis II (Hunter syndrome). Genet Med. 2006 Aug;8(8):465-73. PMID: 16912578

      Pyeritz RE. Inherited diseases of connective tissue. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 260.

      Wraith JE. Mucopolysaccharidoses and oligosaccharidoses. In: Saudubray JM, van den Berghe G, Walter JH, eds. Inborn Metabolic Diseases: Diagnosis and Treatment. 5th ed. New York, NY: Springer; 2012:chap 40.