Definition of Hunter syndrome:

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.

Causes, incidence, and risk factors:

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)

Signs 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.

Expectations (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.

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

Calling your health care provider:

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.