What Is Hunter Syndrome (MPS II)?

Hunter syndrome is an inherited disease caused by a faulty gene.

Children with Hunter syndrome lack an enzyme called iduronate 2-sulfatase that the body needs to digest sugar. As a result, undigested sugar molecules build up in the body.

This causes progressive organ damage, especially to the brain and heart, and breathing problems.

The medical name for Hunter syndrome is mucopolysaccharidosis type II, or MPS II.

Doctors at the Center for Rare Disease Therapy at UPMC Children's Hospital of Pittsburgh will work with you and your child to:

  • Confirm their Hunter syndrome diagnosis.
  • Manage their MPS II symptoms.
  • Improve their quality of life.

Make an appointment for your child for MPS II care at 412-692-7273 or rarecare@chp.edu.

How Common is MPS II?

About 1 in 100,000 to 170,000 babies are born with MPS II.

It nearly always occurs in males. Females can carry the gene that causes MPS II.

Causes of Hunter Syndrome

Changes in the IDS gene cause MPS II.

This gene tells the body how to make the enzyme you need to break down sugar. If you can't break sugar down, the molecules build up and affect the body's organs.

The gene that causes Hunter syndrome is on the X chromosome.

Because males only have one X chromosome, one altered gene can cause the condition.

Females have two X chromosomes, meaning they need two copies of the faulty gene to get MPS II. This is why Hunter syndrome is very rare in females.

Hunter Syndrome (MPS II) Symptoms

MPS II mostly affects boys, and symptoms often appear around age two.

Hunter syndrome symptoms include:

  • Changes in facial features, with lips and tongue getting thicker and cheeks getting larger.
  • A very large head.
  • Joint stiffness, especially in the hands and wrist.
  • Recurring upper respiratory infections.
  • Chronic runny nose.
  • Frequent ear infections and hearing loss.
  • Enlarged liver and spleen.
  • Failure to grow as normal after about age five.
  • Bone and joint abnormalities that continue to worsen.

Common MPS II complications

There are two types of Hunter syndrome: severe and mild.

Severe Hunter syndrome

For children with severe MPS II, the disease will progress more quickly.

By around age eight, they:

  • Will struggle with basic functional and cognitive skills.
  • May have breathing problems, heart issues, and trouble moving as bones get weaker and joints get stiffer.
  • May also have behavioral issues and trouble sleeping.

Mild Hunter syndrome complications

The disease progresses more slowly for children with the mild type of MPS II.

They typically don't have cognitive issues. But they will have heart and breathing issues that continue into adulthood.

Diagnosing Hunter Syndrome in Children

A doctor who suspects Hunter syndrome will test a child's urine to see if there's a build-up of sugar molecules. They will also order a blood test to measure enzyme levels.

Testing a child's genes can confirm the MPS II diagnosis.

Hunter Syndrome Treatment

There is no cure for Hunter syndrome.

Enzyme replacement drugs may help some children. This type of medicine does the job of the missing enzyme.

A stem cell transplant can also help some children with MPS II. Transplant isn't an option for all children with MPS II, but your child's doctor may discuss it with you.

Some supportive techniques that may help kids with MPS II include:

  • Physical therapy (PT). PT can help improve a child's mobility and help with joint stiffness. We can also provide adaptive devices, like walkers and wheelchairs, to help them move better.
  • Speech therapy. This technique helps children with speech and language problems. This is especially helpful since MPS II can affect hearing and the ability to talk.
  • Medications. Doctors can prescribe medicines to help children sleep better or to prevent seizures.
  • Breathing devices. These can help open up a child's airways.

Doctors may also suggest surgery to address certain symptoms. For instance, surgery to replace a damaged heart valve can extend a child's life.

Your Child's MPS II Consult and Care: What to Expect

If a doctor diagnosed your child with Hunter syndrome, we want you to know you're not alone. The Center for Rare Disease Therapy is here to help.

The Program for the Study of NDRD can often schedule a visit within one week.

To make an appointment for your child or refer a patient for MPS II care, contact us by:

Here's what you can expect when you come to us for your child's first consult.

What should I expect at my child's first MPS II visit?

You can expect your first visit to take from four hours to a few days. Your child will have a thorough exam from Dr. Rajan, the NDRD program director.

She will make or confirm a precise diagnosis and find out how much the disease has progressed.

Because we work as a team at the center, other doctors and staff might see your child during your visit.

These may include experts in:

  • Genetic diseases.
  • Brain diseases.
  • Child development.
  • Hearing.
  • PT.

During your visit, we'll talk with you about:

  • Next steps for your child in the near future.
  • Options for treating your child's Hunter syndrome.
  • Ways to improve your child's quality of life at home.

We'll discuss the details of stem cell transplant if we think it might be a good option for your child. We want to make sure you know what the transplant entails and how you may need to prepare.

By the end of your visit, you'll have a care plan tailored to your child's MPS II needs. We'll also schedule a follow-up visit in three months.

You'll meet our nurse practitioner, who can answer questions by phone or video call between visits.

Before you leave, feel free to ask us about your child's diagnosis, treatment, or anything else.

When should I expect the results if my child had tests at the Center for Rare Disease Therapy?

Dr. Escolar will meet with you during your visit to go over test results and explain the next steps for treatment.

You can also find your child's test results on MyCHP — Children's patient portal. MyCHP portal lets you manage your child's health online.

It's free to kids getting treatment at UPMC Children's Hospital and their parents or guardians.

Partners in Your Child's MPS II Care

A rare disease like MPS II affects the whole family.

At the Center for Rare Disease Therapy, every child we see receives a tailored treatment plan and family-centered care.

We treat each family member as our partner. The best care approach happens when we merge our MPS II knowledge with your insight into what's best for your child.

For an appointment, consult, or referral for a child diagnosed with Hunter syndrome, please contact us at:

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Clinical Studies

MPS II (Hunter Syndrome) Outcome Survey – The HOS Study

A Global, Multi-Center, Long-Term, Observational Registry of Patients with Hunter Syndrome (Mucopolysaccharidosis Type II, MPS II)

Read more

MPS II Biomarkers Study

Study of Potential Treatment-Responsive Biomarkers in Hunter Syndrome

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MPS II Treatment with DNL310 – Phase I/II

Study to Determine the Safety, Pharmacokinetics, and Pharmacodynamics of DNL310 in Pediatric Subjects with Hunter Syndrome

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MPS II Treatment with RGX-121: The CAMPSIITE™ Study – Phase I/II

Study to Evaluate the Safety, Tolerability, and Pharmacodynamics of RGX-121 in Pediatric Subjects with MPS II (Hunter Syndrome)

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MPS II Treatment with RGX-121 – Long-Term Observation

A Long-term Follow-up Study to Evaluate the Safety and Efficacy of RGX-121

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*Non-Malignant Marrow Disorder Treatment using Reduced Intensity Conditioning – Phase II

Study of Reduced-Intensity Conditioning In Patients With Non-Malignant Disorders Undergoing Umbilical Cord, Bone Marrow, or Peripheral Blood Stem Cell Transplantation

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*Original research initiated by investigators at UPMC Children’s Hospital of Pittsburgh.