MPS III

MPS III – Sanfilippo

For more information please download our Guide to MPS III.

What is MPS III?

Sanfilippo Disease is a Mucopolysaccharide storage disorder, also known as Mucopolysaccharidosis Type III. The disease takes its name from Dr. Sanfilippo who was one of the first doctors from the United States to describe the condition in 1963.

Although there is no cure for MPS diseases, there are ways of managing and treating the problems they cause.

What causes this disease?

Mucopolysaccharides are long chains of sugar molecule used in the building of connective tissues in the body.

  • “saccharide” is a general term for a sugar molecule (think of saccharin)
  • “poly” means many
  • “muco” refers to the thick jelly-like consistency of the molecules

In the course of normal life there is a continuous recycling process of building new Mucopolysaccharides and breaking down old ones. This process requires a series of biochemical tools called enzymes. Individuals with MPS III are missing an enzyme which is essential in cutting up the used Mucopolysaccharides. Incompletely broken down Mucopolysaccharides remain stored inside parts of the cells called lysosomes. The lysosomes become swollen and disrupt cell functioning causing progressive damage.

Babies may show little sign of the disease but symptoms start to appear as more and more cells become damaged by the accumulation of Mucopolysaccharides.

Are there different forms of Sanfilippo disease?

To date, four different enzyme deficiencies have been found to cause MPS III and thus the condition is described as MPS III Type A, B, C or D. Type A is the most common form found in most populations.

  • MPS III A is missing the enzyme heparan N sulphatase
  • MPS III B is missing the enzyme alpha-Nacetylglucosaminidase
  • MPS III C is missing acetyl-CoA:alpha-glucosaminide acetyltransferase
  • MPS III D is missing N-acetylglucosamine-6-sulphatase

It is important to note that there are no significant, clinical, physical differences between the different subtypes of MPS III disease, although there have been cases of late onset MPS III Type B where the individuals have remained relatively unaffected into adult life. The latest understanding is that some people seem to produce some enzyme activity which helps to slow down the progression of the disease whilst those with more severe symptoms appear to have no enzyme activity at all.

How common are these diseases?

The MPS Society, which co-ordinates the Registry for Mucopolysaccharide and Related Diseases, has shown that MPS III is a rare condition affecting one in 85,000 live births. Over a ten year period between 1988 and 1998, 97 babies were born with MPS III in the United Kingdom.

How is the disease inherited?

MPS III is an autosomal recessive disease whereby both parents must carry the same defective gene and each pass this same defective gene to their child. Where both parents are carriers of the MPS III gene there is a 25% (1:4) chance of having an affected child in each pregnancy. There is a 50% (1:2) chance of a child receiving only one copy of the defective gene and therefore being a carrier. A carrier will not be affected but can pass the defective gene to his/her offspring. The remaining 25% (1:4) will be neither affected nor a carrier. Using information from an affected individual’s DNA, it may be possible to determine whether brothers and sisters are carriers of, or if they are affected by MPS III.

There is a more detailed explanation of this complex subject in the booklet on inheritance available from the MPS Society.