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Hunter syndrome

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Alternative Names   

Mucopolysaccharidosis type II, Iduronate sulfatase deficiency

Definition    Return to top

Hunter syndrome is a hereditary disease in which the breakdown of a mucopolysaccharide (a chemical that is widely distributed in the body outside of cells) is defective. This chemical builds up and causes a characteristic facial appearance, abnormal function of multiple organs, and in severe cases, early death.

Causes    Return to top

Hunter syndrome is inherited as an X-linked recessive disease. This means that boys will be the ones most often affected, because the defective gene is on the X chromosome. Boys have only 1 copy of the X chromosome. Girls have 2 copies.

Because girls have two X chromosomes, their normal copy on one X can provide a functioning gene, even if their other X has the abnormal gene. Women can carry the defective gene and pass it on, without being affected themselves, unless both their copies are abnormal. But because boys have an X and a Y, there is no normal X gene to fix the problem if the X is defective.

The metabolic abnormality that causes Hunter syndrome is a lack of the enzyme iduronate sulfatase. Without this enzyme, mucopolysaccharides collect in various body tissues, causing damage.

Affected children may develop an early-onset type (severe form) shortly after age 2 that causes a large skull, coarse facial features, profound mental retardation, spasticity, aggressive behavior, joint stiffness, and death before age 20. A late-onset type (mild form) causes later and less severe symptoms.

Symptoms    Return to top

Juvenile form (early-onset, severe form):

Late (mild) form:

Both forms:

Exams and Tests    Return to top

Signs of the disorder that the doctor might look for include:

Tests that may indicate this disorder is present include:

Treatment    Return to top

The U.S. Food and Drug Administration has approved the first treatment for Hunter syndrome. The medicine, called idursulfase (Elaprase), is given through a vein (intravenously). Talk to your doctor for more information.

Bone marrow transplant has been tried for the early-onset form with variable results.

Individual problems should be addressed separately.

Outlook (Prognosis)    Return to top

Life expectancy for the early-onset (severe) form is 10 - 20 years. Life expectancy for the late-onset (mild) form is 20 - 60 years.

Possible Complications    Return to top

When to Contact a Medical Professional    Return to top

Call your health care provider if you or your child manifest a group of these symptoms, or if you know you are a genetic carrier and are considering having children.

Prevention    Return to top

Genetic counseling is recommended for prospective parents with a family history of Hunter syndrome. Prenatal testing is available. Carrier testing for female relatives of affected males is available at a few specialized centers.

References    Return to top

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.

Update Date: 9/28/2007

Updated by: David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Previously reviewed by Brian Kirmse, MD, Mount Sinai School of Medicine, Department of Human Genetics, New York, NY. Review provided by VeriMed Healthcare Network (8/11/2006).

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