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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, 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
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