Symptoms and causes


Hunter syndrome is one type of a group of inherited metabolic disorders called mucopolysaccharidoses (MPSs), and Hunter syndrome is referred to as MPS II.

Hunter syndrome symptoms vary and range from mild to severe. Symptoms aren't present at birth, but often begin around ages 2 to 4.

Signs and symptoms may include:

  • An enlarged head (macrocephaly)
  • Thickening of the lips
  • A broad nose and flared nostrils
  • A protruding tongue
  • A deep, hoarse voice
  • Abnormal bone size or shape and other skeletal irregularities
  • A distended abdomen, as a result of enlarged internal organs
  • Diarrhea
  • White skin growths that resemble pebbles
  • Joint stiffness
  • Aggressive behavior
  • Stunted growth
  • Delayed development, such as late walking or talking

When to see a doctor



Hunter syndrome develops when a defective chromosome is inherited from the child's mother. Because of that defective chromosome, an enzyme that's needed to break down complex sugar molecules is missing or malfunctioning.

Without this enzyme, massive amounts of these complex sugar molecules collect in the cells, blood and connective tissues, causing permanent and progressive damage.

Risk factors

There are two major risk factors for developing Hunter syndrome:

  • Sex. Hunter syndrome nearly always occurs in males. Girls are far less at risk of developing this disease because they inherit two X chromosomes. If one of the X chromosomes is defective, their normal X chromosome can provide a functioning gene. If the X chromosome of a male is defective, however, there isn't another normal X chromosome to compensate for the problem.


A variety of complications can occur with Hunter syndrome depending on the type and severity of the disease. Complications can affect the lungs, heart, joints, connective tissue, and brain and nervous system.

Respiratory complications



Cardiac complications



Skeletal and connective tissue complications

The storage of undigested complex sugar molecules in connective tissues results in abnormalities in bones, joints and ligaments. This reduces your child's growth, causing pain and physical malformations and making it difficult for him or her to move.




Hernias (inguinal and umbilical) are common in Hunter syndrome. A hernia occurs when soft tissue, usually part of the intestine, pokes through a weak spot or tear in the lower abdominal wall.

Hernias associated with Hunter syndrome can become quite large and are often one of the first signs of the disorder. Enlargement of the liver and spleen (hepatosplenomegaly) may increase pressure in the abdomen, causing a hernia.

Brain and nervous system complications


Many neurological problems are caused by buildup of excess fluids in your child's brain (hydrocephalus). Pressure from these fluids can cause other problems that may affect your child's eyes, ears and other sensory organs, which can cause severe headaches, interfere with vision or hearing and change your child's mental state.


Other disorders, such as carpal tunnel syndrome, can result from nerve compression that happens because of bone deformities and storage of complex sugar molecules in tissues.


Seizures also may occur in children with Hunter syndrome.

Longer recovery from other illnesses

Recovery times from normal childhood illnesses may be longer for children with Hunter syndrome. As a result, be sure to take general preventive measures — for example, get your child a flu shot and ensure your child receives all necessary vaccinations.