Mucopolysaccharidosis I (MPS I)

Medically Reviewed by Renee A. Alli, MD on September 04, 2023
5 min read

MPS I stands for mucopolysaccharidosis type I. It starts in childhood. You can't "catch" it -- it comes from your genes.

People with MPS I can't make a specific protein called alpha-L iduronidase, which is needed to break down sugars. These sugars build up in cells and cause damage throughout the body.

People who have this disease can have problems with how their bodies grow and work, as well as trouble with thinking and learning. They might look different, too.

Many people with milder MPS I can go to school and eventually work and have families. And even for people with more severe MPS I, there are treatments to help ease their symptoms and slow down the disease.

Because it affects people in so many different ways, doctors used to separate MPS I into groups: Hurler, Hurler-Scheie, and Scheie syndromes. Now they talk about a range between two forms:

  • Severe
  • Attenuated, or less severe

MPS I is passed down through families. But you get it only when both parents give you a broken gene.

If you get one normal gene and one "bad" gene, you won't have symptoms of MPS I. You could pass the gene to your children, though.

Many babies with MPS I don't show any signs of the disease at first. For those with less severe MPS I, symptoms show up later in childhood. People with this form, attenuated MPS I, probably can make a tiny bit of the protein, which is why their symptoms are milder and the disease moves very slowly.

Children who have the severe form usually start to have symptoms while they're still infants. They're often big when they're born and grow quickly for a year, but then stop by the time they're 3. They might never grow taller than 4 feet. They also tend to look similar:

  • Shorter than average, with stocky build
  • Large head, bulging forehead
  • Thick lips, widely spaced teeth, and large tongue
  • Short, flat nose with wide nostrils
  • Thick, tough skin
  • Short, broad hands with curving fingers
  • Knock-knees and walking on toes
  • Curved spine

MPS I can show up in a lot of different ways:

  • Eye problems, including cloudy eyes and a hard time seeing in bright light or at night
  • Bad breath, dental problems
  • Weak neck
  • Breathing problems and airway infections, including runny nose, sinus infections, and sleep apnea
  • Ear infections and hearing loss
  • Numbness and tingling in fingers or feet
  • Heart disease
  • Stiff joints and trouble moving
  • Hernias, which look like a bulge around the belly button or in the groin
  • Diarrhea
  • Enlarged liver or spleen

Your child might not have all of those symptoms. People with the milder form of the disease usually don't have as many physical problems. They typically have a normal intelligence and can do many things other people do.

The more severe the disease, the more of these problems your child is likely to have. Severe MPS I can also affect intelligence and learning. Some kids might lose their ability to speak.

Because it's a rare disease, doctors rule out other medical conditions first. Your doctor might ask:

  • What symptoms have you noticed?
  • When did you first see them?
  • Do they come and go?
  • Does anything make them better? Or worse?
  • Has anyone in your family had similar symptoms in the past?

If the doctors can't find another explanation for your child's symptoms, they'll test for MPS I by checking for:

  • A lot of a specific sugar in their urine
  • How active the "missing" protein is in their blood or skin cells

After doctors are sure it's MPS I, it's a good idea to let your extended family know about the gene problem, too.

If you are pregnant, know you are a carrier of the gene, and already have a child with MPS I, you can find out whether the baby you're carrrying is affected. Talk to your doctor about testing. 

  • Will my child's symptoms change over time? If so, how?
  • What treatments are best for them now?
  • Do these treatments have side effects? What can I do about them?
  • Is there a clinical trial that could help?
  • How do we check their progress? Are there new symptoms I should watch for?
  • How often do we need to see you?
  • Are there other specialists we should see?
  • If I have more children, how likely are they to have MPS I?

Enzyme replacement therapy (ERT) uses a drug called laronidase (Aldurazyme), a man-made version of the missing protein. It has changed the outlook for many kids with MPS I. It can relieve most symptoms and slow the progress of the disease, although it doesn't help treat symptoms from the brain, like problems with thinking or learning.

Another option may be a hematopoietic stem cell transplant (HSCT), in which doctors put new cells into your child's body that might make the protein their body is missing. These cells often come from bone marrow or umbilical cord blood. When children get a transplant before they're 2 years old, they might be able to learn better. But HSCT can't fix bone or eye problems.

Work with a doctor who specializes in lysosomal storage diseases, or LSDs. Depending on what symptoms your child has, you might need to see other specialists, too. Often they'll include a cardiologist, who focuses on the heart, and an eye doctor.

Encourage your child to be independent and make friends. Kids with MPS I are often well-liked and enjoy being with others. Include them in safe family activities.

Most important, be positive. Keep an open mind about other people's reactions when you introduce your child to them. They might not know what to say, possibly because they don't want to pry or offend or embarrass you. When people ask about your child, tell them about their condition and what they can and can't do. Also mention your child's interests, their curiosity, and their personality.

Talk to the staff at your child's school to come up with an individualized education program (IEP). Your child might need one-on-one attention in the classroom, a special desk, or other adjustments.

To protect their necks, kids with MPS I should avoid contact sports, gymnastics, trampolines, and similar activities.

Look for ways to change how your home is set up to make it easier for your child to move around and do things on their own.

Make time for yourself and your family, too. It's OK to have someone take over caregiving duties for a while. Step back and take a break to rest and recharge.

Although there is no cure for MPS I, treatments can improve the quality of life -- especially when started early. They slow the disease and help stop damage before it starts.

Most kids who have less severe MPS I can go to school with other children. They'll go through puberty and can have kids of their own. Adults are protected by the Americans with Disabilities Act, so they might be able to work and live on their own.

When the disease is more severe, it moves faster. Children with the most severe form usually get worse very quickly, and they might not live to be teenagers. Special care focuses on easing pain and offering support, so your child and your family can have the best quality of life.

To learn more about MPS I, visit the National MPS Society website. You can also find ways to connect with other people living with the disease.