General Condition Information
Other Names
- Hunter
- Hunter's Syndrome
- MPS II (Hunter's Syndrome)
Condition Type
Birth Prevalence
- It is estimated that fewer than 40 babies are born with this rare condition each year in the United States.
- Visit GeneReviews to learn more about how often this condition occurs.
Screening Finding
What is mucopolysaccharidosis type ii
Mucopolysaccharidosis type II (MPS II) is one of a group of inherited (genetic) conditions that prevents the body from processing sugars properly. Mucopolysaccharidosis Type I is another condition in this group.
Your body uses complicated sugars called glycosaminoglycans (GAGs) in several important processes. An enzyme called iduronate-2-sulfatase (I2S) breaks down GAGs for your body to use. This process occurs in special compartments inside your cells called lysosomes.
MPS II results when I2S is absent or present at low levels. The lysosomes then have trouble breaking down GAGs. This causes a buildup of GAGs in the tissues that can result in problems throughout the body. GAGs used to be called mucopolysaccharides, which is how the condition got its name.
There are two main types of MPS II – the severe type and the attenuated type – that differ in signs, symptoms, and age of onset. The severity of the condition depends on how much I2S activity is present in the body. The amount of I2S activity depends on the type of genetic change that causes the disorder.
High levels of GAGs can damage many parts of the body. This damage leads to the signs and symptoms of the condition.
Newborn Screening and Follow-Up
Newborn screening for MPS II requires collecting a small amount of blood from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.
Screening measures the activity of the enzyme I2S in your baby’s blood. Screening may also measure GAG levels. Babies with low activity levels of I2S and high levels of GAGs might have MPS II.
If your baby’s blood spot screening result for MPS II is out-of-range, your baby’s health care provider will contact you. Together, you will discuss next steps and follow-up plans.
An out-of-range screening result does not mean that your baby definitely has the condition. It does mean that your baby needs more follow-up testing. To learn more about screening results, visit the Blood Spot Screening Results page.
Your baby may need the following tests after an out-of-range screening result:
- Blood and/or urine tests
- Genetic testing using a blood sample
You should complete any recommended follow-up testing as soon as possible. Babies with this condition can have serious health problems if they are not diagnosed and treated quickly.
False-positive newborn screening results for this condition may happen. Some babies with positive newborn screening results for MPS II have a “pseudodeficiency.” Pseudodeficiency means that a baby’s enzyme levels are low on the screening but are normal in their body. These babies do not have and will never develop MPS II.
Condition Details
Newborn screening helps babies lead healthier lives. If your baby has an out-of-range result, follow up with your health care provider quickly. It is important to follow their instructions. Your baby may need to get treatment right away, even if they are not showing signs or symptoms. In some cases, your baby’s health care provider may decide it is best to watch (monitor) your baby to decide next steps. Careful monitoring and early treatment will help your baby stay as healthy as possible.
The timing that MPS II develops and the type of problems it causes vary between different people. Symptoms may appear as early as the first year of life or not until several years of age.
Signs of the condition may include the following:
- Frequent ear infections
- Frequent upper respiratory infections (like cold or flu)
- Chronic or frequent diarrhea
- Large head (macrocephaly)
- Large tongue (macroglossia)
- Large liver and spleen (hepatosplenomegaly)
- Facial features that are different from their parents
- Soft out-pouching around their belly button or groin (umbilical or inguinal hernia)
- Heart problems
- Stiff joints
- Sleep problems
- Hearing loss
The condition is caused by a change in the IDS gene. This gene gives your body instructions for making the IDS enzyme that breaks down the complex sugars called GAGs. Unlike some other sugars, you produce GAGs, rather than consume them from food.
When the IDS gene is changed, your baby’s body cannot properly break down these substances. They build up in cells throughout the body.
MPS II is a genetic condition that babies typically inherit from their biological mother. Mothers may have the changed gene and not have the condition (a carrier). MPS II can also occur for the first time in a family when the mother is not a carrier (de novo MPS II). Almost all children with MPS II are male. To learn more about genetic conditions, visit MedlinePlus Genetics.
- MPS II is inherited in an X-linked recessive pattern, which means babies inherit this condition on their X‑chromosome.
- Baby girls have two X-chromosomes. If they have a nonworking IDS gene on one of the two X-chromosomes, they typically have a working copy of the IDS gene on the other, which is enough to prevent disease.
- Baby boys only have one X-chromosome. All boys with one nonworking IDS gene (on their only X-chromosome) have MPS II.
- Girls with one working copy and one nonworking copy of the IDS gene are called carriers.
- Carriers may pass down a nonworking copy of the gene to their children.
- When a boy is diagnosed with MPS II, the mother needs to be tested to find out if she is a carrier. A carrier mother has a 1 in 2 chance of having another son being born with MPS II or having another daughter who is a carrier.
- Genetic counselors and medical geneticists can help families learn about this condition and the chance of having children with it. Visit the National Society of Genetic Counselors to find a genetic counselor and the American College of Medical Genetics and Genomics to find a medical geneticist.
Treatment and Management
It is important to talk to your health care provider about what type of evaluations may be useful to look for problems, and which treatment(s) are best for your baby. The goal of treatment is to prevent the health problems caused by this condition.
Testing may include:
- X-rays
- Ultrasound picture of the heart (echocardiogram)
- Hearing tests
Treatments may include the following:
- Enzyme replacement therapy (ERT)
- Stem cell transplantation
- Physical therapy
- Surgery
Health outcomes for MPS II vary based on a child’s form of the condition. For children with the attenuated form, early and ongoing treatment can lead to healthy growth and development. For children with the severe form, early treatment can prevent or delay some serious symptoms of the condition.