General Condition Information
- MPS I (Hurler syndrome)
- MPS I (Hurler’s syndrome)
- MPS-I (Hurler syndrome)
- Mucopolysaccharidoses type I
- Mucopolysaccharidosis 1
- Mucopolysaccharidosis I
- Mucopolysaccharidosis type 1
- Mucopolysaccharidosis type I (Hurler syndrome)
- Mucopolysaccharidosis type-I
- Mucopolysaccharidosis, type I
What is Mucopolysaccharidosis type I
Mucopolysaccharidosis type I (MPS I) is one of a group of inherited (genetic) conditions that prevent the body from processing sugars properly.
Your body uses complicated sugars called glycosaminoglycans (GAGs) in several important processes. An enzyme called alpha-L-iduronidase (IDUA) breaks down GAGs so that the body can use them. This process occurs in special compartments inside your cells called lysosomes.
MPS I is a condition that occurs when IDUA 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 where the condition got its name.
There are two types of MPS I – severe and attenuated – that differ in signs, symptoms, and age of onset. The severity of the condition depends on how much IDUA activity is present. IDUA activity shows how well your baby can break down GAGs.
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 I is done using a small amount of blood collected from your baby’s heel. To learn more about this process, visit the Blood Spot Screening page.
During screening, a special machine measures the activity of the enzyme IDUA in your baby’s blood. Screening may also measure GAGs levels. Babies with low activity levels of IDUA and high levels of GAGs might have MPS I.
If your baby’s blood spot screening result for MPS I 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 I 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 I.
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 and type of problems caused by MPS I vary between different people. For the severe form of the condition, outward signs appear by age 2. For the milder form, signs or symptoms may not appear under later in childhood.
Signs of the condition may include the following:
- Soft out-pouching around their belly button or lower stomach (umbilical or inguinal hernia)
- A bony lump on their back (curvature of the spine)
- Large head (macrocephaly)
- Facial features that are different from their parents
- Delays in development or problems with learning
- Swollen abdomen
- Cloudy eyes
- Hearing loss
- Frequent runny noses
- Noisy breathing, or snoring
The condition is caused by a change in the IDUA gene. This gene gives your body instructions for making the IDUA enzyme to break down the complex sugars called GAGs. Unlike some other sugars, you produce GAGs rather than consume them from food.
When the IDUA gene is changed, your baby’s body cannot properly break down these substances. They build up in cells throughout the body.
- MPS I is an autosomal recessive condition. Babies inherit the condition when each parent passes down a nonworking IDUA gene to their baby. Only babies with two nonworking IDUA genes—one from the mom and one from the dad—have this condition.
- People with one working copy and one nonworking copy of the IDUA gene are called carriers.
- Carriers do not have or develop the condition. However, they may pass down a nonworking copy of the gene to their children.
- If two parents are carriers of a nonworking copy of the IDUA gene, they have a 1 in 4 chance of having a child with MPS I.
- Carriers for MPS I often do not know they are carriers before having a child with the condition. In most cases, families have no history of the condition until the birth of a child with MPS I.
- Parents who already have a child with MPS I still have a 1 in 4 chance of having another child with MPS I. This 1 in 4 chance stays the same for all future children.
- 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:
- MRI or CT scans
- Ultrasound picture of the heart (echocardiogram)
- Test of the heart’s electrical signals (electrocardiogram, ECG or EKG)
- Hearing tests
Treatments may include the following:
Health outcomes for MPS I vary based on a child’s form of the condition. For children with the less severe form, early and ongoing treatment can lead to healthy growth and development. For children with the more severe form, early treatment can prevent or delay some serious symptoms of the condition.