Mucopolysaccharidosis type III
(MPS III) is a genetic disorder that makes the body unable to break down large sugar molecules called glycosaminoglycans (GAGs, formerly called mucopolysaccharides). Specifically, people with this condition are unable to break down a GAG called heparan sulfate. Affected individuals can have severe neurological symptoms, including progressive dementia, aggressive behavior, hyperactivity, seizures, deafness, loss of vision, and an inability to sleep for more than a few hours at a time. MPS III is inherited in an autosomal recessive manner. There is no specific treatment for this condition. Most people with MPS III live into their teenage years, and some live longer.
MPS III is divided into four subtypes, known as A, B, C and D. Each subtype is caused by the alteration of a different enzyme needed to completely break down heparan sulfate. The different types of MPS III have similar signs and symptoms, although type A is the most severe.
To view the GARD pages on the subtypes of MPS III, click on the following links:
Mucopolysaccharidosis type IIIA Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.
Mucopolysaccharidosis type IIIB
Mucopolysaccharidosis type IIIC
Mucopolysaccharidosis type IIID