What is Mucopolysaccharidosis?

Mucopolysaccharidosis is one of the diseases classified as “Lysosomal Storage Diseases*”.
Mucopolysaccharidosis occurs when the enzymes needed to break down the Mucopolysaccharides are missing or defective in the cell. The accumulation of mucopolysaccharides causes various symptoms.

*Lysosomes are one of the intracellular organelles that work as one of the “waste processing factories” by using various enzymes to break down unnecessary substances in the body. Recently, lysosomes are considered to be involved a variety of cellular functions, not just waste disposal. With Lysosomal storage diseases, enzymes in the lysosomes do not function properly, causing an accumulation of unnecessary and a variety of symptoms. Currently, some 60 diseases have been identified, and 31 of them are registered as designated intractable diseases in Japan.

There are more than 10 enzymes required for the breakdown of mucopolysaccharides. Mucopolysaccharidosis can be classified into several types depending on which enzyme is missing or defective.

For more information, visit “ムコ多糖症.com” by the below link (Japanese only).
ムコ多糖症.com　https://mps-jcr.com/

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What is Mucopolysaccharidosis type III?

Mucopolysaccharidosis type III (MPS III) occurs when the enzymes needed to break down the heparan sulfate sugar chain are missing or defective.

Subtypes of MPS III

Mucopolysaccharidosis type III is classified into four types A, B, C, and D, depending on which enzyme is deficient. Each enzyme is related to heparan sulfate degradation. The accumulation of heparan sulfate causes various symptoms.

Subtype

Affected Enzyme

Type A

Heparan N-sulfatase

Type B

Alpha-N-acetylglucosaminidase

Type C

Acetyl-CoA:alpha-glucosaminide N-acetyltransferase

Type D

N-acetylglucosamine 6-sulfatase

Symptoms

The age of onset and severity vary among patients, but the following symptoms are generally seen in MPS III.

Diagnosis

If there are concerns about mucopolysaccharidosis, the following tests will be performed for determination of mucopolysaccharidosis, X-rays, urinary GAG, leukocyte or fibroblast enzyme activity, and genetic testing.

Since coarse facial features and abnormal skeletal morphology are mild, the definitive diagnosis of MPS III is difficult and often delayed.

MPS type III is often first diagnosed with Autism Spectrum Disorder (ASD) or Attention-Deficit/Hyperactivity Disorder (ADHD) because of delayed speech development and hyperactivity.

Treatment

As of April 2024, there is no approved drug for mucopolysaccharidosis type III. Treatment is tailored to the symptoms, such as the use of anti-epileptic medications for seizures.

Prognosis

In general, lysosomal storage disease progresses gradually as unwanted material accumulates in the cells. MPS III is a progressive and fatal disease that most patients become bedridden in their teens.

For more information about Mucopolysaccharidosis type III, visit “Information Center for Specific Pediatric Chronic Diseases” by the below link.
Information Center for Specific Pediatric Chronic Diseases, Japan Mucopolysaccharidosis Type III　https://www.shouman.jp/disease/details/08_06_077/

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Please note that the linked websites are not operated by MEDIPAL Group.

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Editorial supervision: Yasutsugu Chinen, MD, PhD, Department of Pediatrics, Faculty of Medicine, University of the Ryukyus