Also known as:
- MPS II
- Hunter syndrome
- I2S deficiency
- Iduronate 2-sulfatase deficiency
Mucopolysaccharidosis type II (MPS II) is an inherited condition that affects many different parts of the body. It is considered a lysosomal storage disorder because people with MPS II have lysosomes (the recycling center of each cell) that cannot break down certain types of complex sugars. This causes undigested sugar molecules and other harmful substances to build up in cells throughout the body, resulting in a variety of symptoms.
MPS II is a continuous spectrum of disease with the most affected individuals on one end, the less severely affected (attenuated) on the other end and a range of different severities in between, For some babies with MPS II, detecting the condition early and beginning proper treatment may help prevent or delay some of the severe health outcomes associated with the condition.
Your baby’s doctor may ask you if your baby is showing any of the signs of mucopolysaccharidosis type II (see Early Signs below). If your baby has certain signs, your baby’s doctor may suggest starting immediate treatment.
If your baby’s newborn screening result for mucopolysaccharidosis type II (MPS II) was out of the normal range, your baby’s doctor or the state screening program will contact you to arrange for your infant to have additional testing. It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition. An out-of-range result may occur because the initial blood sample was too small or the test was performed too early. However, as a few babies do have the condition, it is very important that you go to your follow-up appointment for a confirmatory test. Because the harmful effects of untreated MPS II can occur soon after birth, follow-up testing must be completed as soon as possible to determine whether or not your baby has a condition.
Follow-up testing will involve checking your baby’s blood and urine for signs of MPS II. When a child has a lysosomal storage disorder, harmful amounts of certain substances build up in the body and enzymes that help the body breakdown sugars are either missing or have reduced activity. Measuring the amounts of these substances in your baby’s body can help doctors determine if your baby has a condition. High levels of sugars called glycosaminoglycans in the urine or deficient activity of the enzyme, iduronate sulfatase (I2S), in the blood may indicate that your baby has MPS II. Your baby’s doctor may also want to confirm the diagnosis with clinical genetic testing.
About Mucopolysaccharidosis Type II
The age of onset and severity of mucopolysaccharidosis type II (MPS II) differ depending on the form. Signs of severe MPS II usually begin between ages two and four and progress more rapidly than in attenuated MPS II. Individuals with the attenuated form of MPS II usually do not develop signs until age later in childhood, or even adolescence.
Early signs of MPS II:
- Distinctively large facial features (full lips, large rounded cheeks, broad nose, enlarged tongue)
- Enlargement of vocal cords causing deep, hoarse voice
- Frequent upper respiratory infections
- Short pauses in breathing during sleep (sleep apnea)
- Large head (macrocephaly)
- Swollen abdomen (due to enlarged liver and spleen)
- Soft out-pouching around belly-button (umbilical hernia) or lower abdomen (inguinal hernia)
- Thick, non-stretchy skin
- Pebble-like white growths on back and upper arms
- Hearing loss
- Frequent ear infections
- Poor vision
- Short stature
- Joint stiffness (contractures)
- Severe intellectual disability
- Loss of basic skills, functions, and intelligence (developmental regression)
If your baby shows any of these signs, be sure to contact your baby’s health care provider immediately.
There are several treatments your baby’s health care provider may recommend to address the signs of mucopolysaccharidosis type II (MPS II) and help your baby live a healthier life.
Enzyme Replacement Therapy (ERT)
Enzyme replacement therapy (ERT) can be an effective treatment for symptoms of MPS II that do not involve the central nervous system (the brain and spinal cord). This treatment aims to supplement the enzymes that are present at low levels in your baby’s lysosomes.
Physical therapy is a very important part of treating the signs and symptoms of MPS II. Consistent physical therapy early on can help preserve mobility and lessen pain and joint stiffness. Some children also may require developmental or occupational therapy to help reach and retain milestones.
As your child grows, your child’s health care provider may recommend surgeries to improve quality of life. Removal of the tonsils and adenoids and insertion of ventilating tubes can prevent some upper respiratory infections and may reduce hearing loss. In children with attenuated to severe MPS II who develop a build-up of fluid in the brain (hydrocephaly), a surgery to relieve the pressure inside the skull may be recommended. Other surgeries would not take place until later in life, if at all. Joint replacement surgery and surgery to treat carpal tunnel syndrome can improve mobility and lessen pain. Heart valve replacement may prevent later heart complications.
A dietician can help you create a nutrition plan to help your baby control diarrhea and constipation, which may occur in those with severe MPS II. There is no diet that can prevent the storage of GAGs because they are actually created by the body.
For some babies with MPS II, detecting the condition early and beginning proper treatment may help prevent or delay some of the severe health outcomes associated with the condition. This is why newborn screening for MPS II is so important.
Though treatment may improve the length and quality of life for children with MPS II, those affected with the severe form often die before reaching their mid-teens from heart disease or airway obstruction. Those with the attenuated form usually live into adulthood, although they may have a shortened lifespan.
Structures called lysosomes are the recycling centers within our cells. Lysosomes contain enzymes that help the cell breakdown and reuse certain materials from the foods we eat. Some enzymes help the lysosome breakdown complex sugars, specifically. One of these enzymes is called iduronate 2-sulfatase (I2S).
If your baby has Mucopolysaccharidosis type II (MPS II), his or her body is missing or making non-working copies of I2S enzymes. When these enzymes are not working correctly, your baby’s body cannot break down large sugar molecules called glycosaminoglycans (GAGs) into smaller components. This causes sugar molecules and other harmful substances to build up in cells throughout the body, resulting in the many signs and symptoms of MPS II.
MPS II is an X-linked recessive condition. This means a male must inherit one copy of the non-working gene from his mother to have the condition. Although rare, females have been diagnosed with MPS II. A female must inherit two copies of the non-working gene, one from each parent, in order to have the condition. In X-linked conditions, the gene is carried on the X sex chromosome, and the condition generally affects males. While having a child with MPS II is rare, when one or both parents carry the non-working gene for the condition, they can have more than one child with the condition. Learn more about X-linked recessive inheritance.
Support for Mucopolysaccharidosis Type II
Support groups can help connect families who have a child or other family member affected with mucopolysaccharidosis type II with a supportive community of people who have experience and expertise in living with the condition. These organizations offer resources for families, affected individuals, health care providers, and advocates.
Work with your baby’s health care provider to determine the next steps for your baby’s care. Your baby’s doctor may help you coordinate care with a dietician or nutritionist, physical therapists, neurologists, physicians that specialize in metabolism, cardiology, and pulmonology, and other medical resources in your community. Some children with mucopolysaccharidosis type II (MPS II) have developmental delays. If you think that your baby is not meeting his or her developmental milestones, ask your baby’s doctor about the next steps in accessing a developmental evaluation and care.
Because MPS II is a genetic condition, you may want to talk with a genetics specialist. A genetic counselor or geneticist can help you understand the causes of the condition, discuss genetic testing for MPS II, and understand what this diagnosis means for other family members and future pregnancies. Speak with your baby’s doctor about getting a referral. The Clinic Services Search Engine offered by the National Coordinating Center for the Regional Genetic and Newborn Screening Service Collaboratives and the Find a Genetic Counselor tool on the National Society of Genetic Counselors (NSGC) website are two good resources for you or your baby's health care provider to use to identify local specialists.
Archie is a loving boy whose smiles and hugs bring joy to everyone around him. He was diagnosed with MPS II at age three. Read about Archie’s struggles and successes in school and how enzyme replacement therapy has helped him live a more normal life.