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Hunter syndrome

Definition

Hunter syndrome is an inherited disease in which long chains of sugar molecules (mucopolysaccharides) are not broken down correctly and build up in the body.

Alternative Names

Mucopolysaccharidosis type II, Iduronate sulfatase deficiency

Causes

Hunter syndrome is an inherited condition. Boys are most often affected.

The condition is caused by a lack of the enzyme iduronate sulfatase. Without this enzyme, mucopolysaccharides 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

Juvenile form (early-onset, severe form):

• Aggressive behavior
• Hyperactivity
• Mental function gets worse over time
• Severe mental retardation
• Spasticity

Late (mild) form:

• Mild to no mental deficiency

Both forms:

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

Exams and Tests

Signs of the disorder include:

• Abnormal retina (back of the eye)
• Decreased iduronate sulfatase enzyme in blood serum or cells
• Heart murmur and leaky heart valves
• Enlarged liver (hepatomegaly)
• Enlarged spleen (splenomegaly)
• Inguinal hernia
• Joint contractures
• Spasticity

Tests may include:

• Enzyme study
• Genetic testing for change (mutation) in the iduronate sulfatase gene
• Urine test for heparan sulfate and dermatan sulfate

Treatment

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, but the results can vary.

Each health problem should be treated separately.

Outlook (Prognosis)

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

Possible Complications

• 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 health care 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

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.

Wraith JE. Mucopolysaccharidoses and oligosaccharidoses. In: Fernandes J, Saudubray J-m, van den Berghe G, Walter JH, eds. Inborn Metabolic Diseases: Diagnosis and Treatment. New York, NY: Springer;2006:chap 39.

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