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Hunter syndrome

Mucopolysaccharidosis type II; Iduronate sulfatase deficiency

 

Hunter syndrome is a disease in which long chains of sugar molecules (glycosaminoglycans, formerly called mucopolysaccharides) are not broken down correctly and build up in the body.

The syndrome belongs to a group of diseases called mucopolysaccharidoses (MPS). Specifically, it is known as MPS II.

See also:

  • MPS I H (Hurler syndrome)
  • MPS IV (Morquio syndrome)
  • MPS III (Sanfilippo syndrome)
  • MPS I S (Scheie syndrome)

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

 

In the early-onset, severe form, symptoms include:

  • Aggressive behavior
  • Hyperactivity
  • Mental function gets worse over time
  • Severe intellectual disability
  • Jerky body movements

In the late (mild) form, there can be mild to no mental deficiency.

In both forms, symptoms include:

  • Carpal tunnel syndrome
  • Coarse features of the face
  • Deafness (gets worse over time)
  • Increased hair growth
  • Joint stiffness
  • Large head

 

Exams and Tests

 

A physical exam and tests in someone with Hunter syndrome may show:

  • Abnormal retina (back of the eye)
  • Decreased iduronate sulfatase enzyme in blood serum or cells
  • Heart murmur and leaky heart valves
  • Enlarged liver
  • Enlarged spleen
  • Hernia in the groin
  • Joint contractures (from joint stiffness)
  • Jerky movements

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 www.ncbi.nlm.nih.gov/pubmed/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.

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              Review Date: 4/20/2015

              Reviewed By: Chad Haldeman-Englert, MD, FACMG, Wake Forest School of Medicine, Department of Pediatrics, Section on Medical Genetics, Winston-Salem, NC. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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