Mucopolysaccharidosis type IV

What causes mucopolysaccharidosis type IV?

There are two forms of mucopolysaccharidosis type IV (MPS IV): type A and type B. Type A is caused by changes (mutations) in the GALNS gene and type B is caused by mutations in the GLB1 gene. Both of these genes encode enzymes that help the body breakdown large sugar molecules called glycosaminoglycans (GAGs). If mutations reduce or eliminate the amount of these enzymes functioning in the body, GAGs accumulate in specialized cell structures called lysosomes (compartments in the cell that break down and recycle different types of molecules). This buildup of GAGs is toxic to various tissues in the body and leads to the signs and symptoms associated with the condition.

Last updated on 05-01-20

How is mucopolysaccharidosis type IV diagnosed?

A diagnosis of mucopolysaccharidosis type IV is often suspected based on the presence of characteristic signs and symptoms. Additional testing can then be ordered to confirm the diagnosis, determine the severity of the condition and rule out other conditions that can be associated with similar features. These tests may include:

  • X-rays
  • Specialized urine and blood tests
  • Eye exam
  • Skin fibroblast culture
  • Genetic testing to identify mutations in the GALNS or GLB1 genes

Last updated on 05-01-20

Is mucopolysaccharidosis type IV inherited?

****Mucopolysaccharidosis type IV is inherited in an autosomal recessive manner. This means that to be affected, a person must have a mutation in both copies of the responsible gene in each cell. Affected people inherit one mutated copy of the gene from each parent, who is referred to as a carrier. Carriers of an autosomal recessive condition typically do not have any signs or symptoms (they are unaffected). When 2 carriers of an autosomal recessive condition have children, each child has a:

  • 25% (1 in 4) chance to be affected
  • 50% (1 in 2) chance to be an unaffected carrier like each parent
  • 25% chance to be unaffected and not be a carrier

Last updated on 05-01-20

Name: Canadian Society for Mucopolysaccharide and Related Diseases Inc. (Canadian MPS Society) #218-2055 Commercial Drive Vancouver, BC V5N OC7
Phone: 604-924-5130 Toll Free: 800-667-1846 Fax : 604-924-5131 Email: Url:
Name: National MPS Society P.O. Box 14686
Durham, NC, 27709-4686, United States
Phone: +1-919-806-0101 Toll Free: 1-877-MPS-1001 (1-877-677-1001) Fax : +1-919-806-2055 Email: Url:
Name: Society for Mucopolysaccharide (MPS) Diseases MPS House Repton Place White Lion Road Amersham Buckinghamshire
United Kingdom
Phone: (+44) 0345 389 9901 Email: Url:

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The RareGuru disease database is regularly updated using data generously provided by GARD, the United States Genetic and Rare Disease Information Center.

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