Also known as:
- MPS I
- Alpha-L-iduronidase deficiency
- Hurler-Scheie syndrome
- Hurler syndrome
- IDUA deficiency
- Scheie syndrome
- Mucopolysaccharidosis I
- MPS I H-S
Mucopolysaccharidosis type I (MPS I) is an inherited condition that affects many different parts of the body. It is considered a lysosomal storage disorder because people with MPS I 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.
Based on the current understanding of the enzyme and its gene, MPS I comprises a wide spectrum of severity and individuals may be categorized anywhere from severe to attenuated (less severe). Along with age of onset, the symptoms and long term outcome within the spectrum of disease vary widely. For some babies with MPS I, 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 I (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 I (MPS I) 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 than 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 I 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 I. 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 MPS I. High levels of sugars called glycosaminoglycans (GAGs) in the urine or deficient activity of the enzyme, alpha-L-iduronidase, in the blood may indicate that your baby has MPS I. Your baby’s doctor may also want to confirm the diagnosis with clinical genetic testing.
About Mucopolysaccharidosis Type I
The severity and age of onset of mucopolysaccharidosis type I (MPS I) differ due to the wide spectrum of severity. Babies with severe MPS I usually develop serious signs and symptoms in the first year of life and have a rapid disease progression. In the attenuated form of MPS I, symptoms are generally milder and do not appear until later in childhood.
Early Signs of MPS I include:
- Soft out-pouching around the belly-button (umbilical hernia) or lower abdomen (inguinal hernia)
- Large head (macrocephaly)
- Distinctive facial features that appear “coarse”
- Varying degrees of developmental delay and learning disabilities
- Swollen abdomen (due to enlarged liver and spleen)
- Clouding of the eye (corneal clouding)
- Hearing loss
- Frequent “runny nose"
If your baby shows any of these signs, be sure to contact your baby’s health care provider immediately.
There are many treatments your baby’s health care provider may recommend to address the signs of mucopolysaccharidosis type I (MPS I) and help your baby live a healthier life.
Physical therapy is a very important part of treating the signs and symptoms of MPS I. Consistent physical therapy early on can help preserve mobility and lessen pain and joint stiffness.
Your child’s health care provider may recommend surgeries to improve your child’s quality of life. Removal of the tonsils and adenoids and insertion of ventilating (ear) tubes can prevent some upper respiratory infections and may reduce hearing loss. Hearing aids may be recommended for some individuals. Children with mild to severe MPS I may develop a buildup of fluid in the brain (hydrocephaly), a surgery to relieve the pressure inside the skull may be recommended.
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 I. There is no diet that can prevent the storage of GAGs because they are actually created by the body.
If your baby has periods of constipation, your baby’s health care provider may recommend laxatives to be used very conservatively to relieve discomfort.
Enzyme Replacement Therapy (ERT)
Enzyme replacement therapy (ERT) can be an effective treatment for symptoms of MPS I 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. ERT may improve growth, joint movement, sleep apnea, respiratory function, pain levels, vision, and liver/spleen enlargement.
Hematopoietic Stem Cell Transplantation (HSCT)
Your baby’s doctor may recommend your baby receive hematopoietic stem cell transplantation (HSCT) to improve the signs and symptoms of MPS I. Hematopoietic stem cells can be found in bone marrow (the spongy tissue inside bones), the bloodstream, or the umbilical cord blood of newborn babies. Transplanted hematopoietic stem cells are administered through an intravenous (IV) line, much like a blood transfusion. This therapy may reduce facial coarseness and liver/spleen enlargement, improve hearing, stabilize heart function, and slow the decline of cognitive function.
For some babies with MPS I, 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 I is so important.
Life expectancy in MPS I is varied. Individuals with attenuated MPS I can have a reasonably normal life span while severely affected individuals may die before becoming teenagers. The most common cause of death, even with treatment is heart or respiratory failure.
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 alpha-L-iduronidase (IDUA).
If your baby has Mucopolysaccharidosis type I (MPS I), his or her body is missing or making non-working copies of IDUA 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 I.
MPS I is an autosomal recessive genetic condition. This means that a child must inherit two copies of the non-working gene for MPS I, one from each parent, in order to have the condition. The parents of a child with an autosomal recessive condition each carry one copy of the non-working gene, but they typically do not show signs and symptoms of the condition.
While having a child with MPS I is rare, when both parents are carriers, they can have more than one child with the condition. Learn more about autosomal recessive inheritance.
Support for Mucopolysaccharidosis Type I
Support groups can help connect families who have a child or other family member affected with mucopolysaccharidosis type I 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 I (MPS I) 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 I 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 I, 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.
Matteo is a bright, happy boy who loves to play guitar. He was diagnosed with MPS I at seven months and is always in and out of the hospital for visits, therapies, and surgeries. Read about Matteo’s diagnosis, progress, and his family’s hope for his health and happiness.
Emily is a sweet girl who was diagnosed with MPS I two months before her second birthday. Read about her success on enzyme replacement therapy and the challenges through which she and her family has faced and survived.