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Hunter Syndrome: Causes, Symptoms, Diagnosis, Treatment

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Hunter syndrome is a rare, inherited disorder in which the body does not properly digest (break down) sugar molecules in the body. When these molecules build up in organs and tissues over time, they can cause damage that affects physical and mental development and abilities. The disorder almost always occurs in boys.

Hunter syndrome is one of a group of diseases called mucopolysaccharidoses. It is also known as mucopolysaccharidosis type II, or MPS II.

Hunter syndrome

How common is Hunter syndrome?

Hunter syndrome is almost always diagnosed in males. Doctors diagnose it in roughly 1 out of 100,000 to 170,000 males. Females can be carriers of the genetic mutation that causes MPS II.

What are the risk factors for Hunter syndrome?

People are at a higher risk for Hunter syndrome if they have a family member with the disease.

Boys have a higher risk of inheriting the disease than girls do. This difference exists because the disease is linked to the X chromosome. Girls inherit 2 X chromosomes, while boys have only 1. If a girl inherits the faulty gene, her other X chromosome can provide the necessary enzyme.

What causes Hunter syndrome?

Hunter syndrome results from a gene mutation (abnormality) passed down from a mother to her child. The affected gene is responsible for regulating the production of a specific enzyme (substance that sparks chemical reactions in the body). This enzyme breaks down complex sugars the body produces.

In people with the disease, the body does not produce any or enough of this enzyme. The missing enzyme causes molecules of the sugars to build up in organs and tissues throughout the body. These buildups can damage organs and tissues throughout the body.

What are the signs and symptoms of Hunter syndrome?

Signs and symptoms of both types of Hunter syndrome typically begin to appear in children between ages 2 and 4. Hunter syndrome symptoms vary in severity and include:

  • Stiff joints
  • Thickening of facial features including nostrils, lips and tongue
  • Delayed appearance of teeth or wide spaces between teeth
  • Larger than normal head, wide chest and short neck
  • Hearing loss that gets worse with time
  • Delayed growth, especially starting around age 5
  • Enlarged spleen and liver
  • White growths on the skin

How is Hunter syndrome diagnosed?

A doctor uses several tests to diagnose Hunter syndrome:

  • Urine test: checks for unusually high levels of sugar molecules
  • Blood tests: can show low or absent levels of enzyme activity, which is also a sign of the disease
  • Genetic testing: identifies mutations (changes) in the gene to confirm diagnosis

How is Hunter syndrome managed or treated?

Treatment for Hunter syndrome depends on the symptoms. A team approach, with specialists in different areas of expertise, could help manage the potential problems associated with the condition and give patients the best possible care. The goal of treatment is to slow the progression of the disease and improve quality of life.

The treatment shown to do this best is enzyme replacement therapy. Doctors replace the missing enzyme with a human-made version of the enzyme, called Elaprase®. Doctors usually deliver this treatment intravenously (through a needle inserted into the vein) once a week.

What complications are associated with Hunter syndrome?

Doctors classify Hunter syndrome into severe and mild types. The severe type progresses faster and involves impaired intellectual abilities.

In the most severe cases, people begin to experience problems with basic functioning around ages 6 to 8.

Depending on its severity, Hunter syndrome can involve many complications. Doctors use medications and sometimes surgery to manage these complications. They include:

  • Breathing problems due to thickened tissue and blocked airways
  • Heart disease
  • Joint and bone abnormalities
  • Declining brain function
  • Carpal tunnel syndrome
  • Hernias
  • Seizures
  • Behavioral problems

Can Hunter syndrome be prevented?

Because it is genetic, you cannot prevent Hunter syndrome. People who have a child with Hunter syndrome should talk to a genetic counselor before having another baby. This specialist can help parents understand the chances of passing the disease on to another child.

What is the prognosis (outlook) for people with Hunter syndrome?

No cure is available for Hunter syndrome. The most severe cases can be life-threatening, with life expectancy typically between 10 and 20 years. People with mild cases of the disease typically live longer into adulthood.

For many people, treatments including medicines, physical therapy and surgery can help manage the challenges the disease presents and improve quality of life.

When should I call the doctor concerning Hunter syndrome?

Contact your doctor if your child begins showing signs and symptoms of Hunter syndrome or experiences developmental delays. Early treatment can help prevent permanent organ and tissue damage.

What questions should I ask my doctor?

If your child has Hunter syndrome, you may want to ask your doctor:

  • How severe is Hunter syndrome?
  • What is the short-term and long-term prognosis for my child?
  • How will the disease affect my child’s life?
  • What are the treatment options?

When can my child go back to regular activities?

People with Hunter syndrome may have to modify their daily activities due to progressive symptoms that affect function and mobility. Your doctor will tell you about activities and therapies that can help make the symptoms of the disease more manageable.

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