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Mucopolysaccharidosis I (MPS I)

What Is MPS I?

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 that's 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 body grows and works as well as trouble thinking and learning. They might look different, too.

If your child has MPS I, his future may be brighter than someone might think by just looking at him. Some 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 the disease 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, but you could pass the gene and the disease to your children.


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 an infant. They are often big when they're born and grow quickly for a year, but then stop by the time they're 3. They may 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, difficulty moving
  • Hernias, which look like a bulge around the belly button or in the groin
  • Diarrhea
  • Enlarged liver or spleen

Your child may not have all of those symptoms. People with the milder form of the disease usually don't have as many physical problems, 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.

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