What is Hunter syndrome?

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.

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

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