Hunter syndrome is an inherited genetic disorder that leads to the buildup of sugar molecules called GAGs. The buildup of these sugars can lead to damage in many parts of your child’s body.

Hunter syndrome, also called mucopolysaccharidosis type II, is an inherited genetic disorder that occurs almost exclusively in males. It results from a gene mutation that leads to the buildup of a sugar molecule in the tissues called glycosaminoglycans (GAGs).

The severe form of Hunter syndrome is often fatal before adulthood. Children with the mild form usually live into late adulthood and generally have less severe symptoms.

Read on to learn more about Hunter Syndrome, including its symptoms, treatment options, and outlook.

How common is Hunter syndrome?

Hunter syndrome is estimated to occur in 1 in 162,000 live male births. It’s extremely rare in females.

Hunter syndrome is divided into two forms: neuronopathic and non-neuronopathic.

Neuronopathic Hunter syndrome symptoms

Children with the neuronopathic form of Hunter syndrome usually have typical development until around 2–4 years of age. The first sign is usually hydrocephalus, which is fluid buildup in the cavities of the brain, followed by:

Children may eventually develop other signs and symptoms, such as:

Non-neuronopathic Hunter syndrome symptoms

About 40% of children with Hunter syndrome have the non-neuronopathic form. It causes similar symptoms to the neuronopathic form, but symptoms tend to be less severe and children mostly have typical cognitive and intellectual development.

Hunter disease is caused by a recessive mutation in the iduronate-sulfatase (IDS) gene. This gene codes for the production of an enzyme called iduronate 2-sulfatase (I2S).

I2S deficiency results in the buildup of GAGs throughout the body in small structures in cells called lysosomes. The buildup of GAGs damages many different tissues and organs.

The IDS gene occurs on the X-sex chromosome. Males have one of these chromosomes, while females have two.

Because males only have one X chromosome, they only need to receive an affected IDSgene from one parent to develop Hunter syndrome. Since females have a second X chromosome, they require an affected gene from both parents to develop the syndrome. For this reason, almost all cases occur in males.

Females with an affected gene on one of their X chromosomes have a 25% chance of having a:

  • male child with Hunter syndrome
  • male child without Hunter syndrome
  • daughter who can pass the gene to their children
  • daughter who can’t pass the gene to their children

Children with the neuronopathic form of Hunter syndrome often pass away before the age of 20 due to either lung or heart problems.

Other complications can include:

  • hydrocephalus (water on the brain)
  • short stature
  • hip problems that require the use of a wheelchair
  • liver enlargement and impaired liver function

It’s important to see your child’s doctor if you notice any differences in your child’s development, such as delayed speech or physical development. Neurological symptoms of Hunter syndrome are usually detected by the age of 4 years.

Medical emergency

It’s critical to seek immediate emergency medical attention if your child has signs of hydrocephalus.

Signs and symptoms in infants include:

  • increasing head size
  • extreme sleepiness
  • frequent and severe vomiting
  • seizures

In older children, they include:

  • severe headaches with nausea and vomiting
  • blurred vision
  • balance problems
  • sudden personality changes
  • memory problems
  • development problems
  • fatigue

Hunter syndrome is diagnosed primarily with:

  • urine and blood tests to measure GAG levels
  • blood or skin cell tests to measure I2S levels
  • genetic blood tests to look for an associated gene mutation
  • imaging like X-rays to look for characteristic skeletal changes

Treatment options for Hunter syndrome include the following.

Enzyme replacement therapy

Enzyme replacement therapy normalizes levels of I2S in your child’s body. This therapy is administered intravenously once per week and should be started before the age of 6 years for maximum benefit.

Hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is a one-time therapy that involves injecting stem cells from a donor into your child’s bloodstream. HSCT has been shown to improve cognitive function and decrease the rate of neurodegeneration.

Nonsteroidal anti-inflammatory drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) may help reduce joint degeneration and improve mobility.

Gene therapy

Gene therapy is under investigation as a potential curative treatment option. It’s a one-time injection that involves replacing your missing gene. Clinical trials up to phase 3 are ongoing.

Most children with the severe form of Hunter syndrome pass away before age 20. People with the non-neuronopathic form often live into late adulthood.

Once neurological signs appear, they may be irreversible. It’s important to start treatment as soon as possible.

Although Hunter syndrome isn’t curable, supportive treatment can help reduce your child’s symptoms. Supportive treatment options include:

Hunter syndrome is an inherited condition, and there’s no known way to prevent it. If you’re a gene carrier, in vitro fertilization (IVF) may be an option to avoid passing the disease to your child.

Here are some frequently asked questions people have about Hunter syndrome.

Can Hunter syndrome be cured?

A cure hasn’t been developed for Hunter syndrome. Gene therapy may offer a cure in the future, but research is still ongoing.

How does Hunter syndrome affect you emotionally?

Children with Hunter syndrome may have trouble managing their emotions or have sudden outbursts of emotions. Symptoms of Hunter syndrome generally first appear between the ages of 2–4 years.

Although there’s no cure for Hunter syndrome, treatment like enzyme replacement therapy or HSCT can potentially improve the course of the disease if started quickly.