• 1: Home
• 2: MPS Diseases
  • 2.1: Overview of symptoms
  • 2.2: Overview of treatment
  • 2.3: Which are the MPS Diseases
    • 2.3.1: MPS I
    • 2.3.2: MPS II
    • 2.3.3: MPS III
    • 2.3.4: MPS IVA
    • 2.3.5: MPS VI
    • 2.3.6: MPS VII
    • 2.3.7: ML I
    • 2.3.8: ML II and III
    • 2.3.9: ML IV
    • 2.3.10: Fucosidosis
    • 2.3.11: Mannosidosis
    • 2.3.12: Sialic Acid Storage Disease
    • 2.3.13: MSD
    • 2.3.14: AGU
    • 2.3.15: Winchester
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• 3: Fabry Disease
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• 30: Terms and Conditions

MPS VII Sly Disease

Sly Disease is a mucopolysaccharide storage disorder also known as Mucopolysaccharidosis type VII (MPS VII). Sly disease takes its name from William Sly who originally first described the disorder in 1972.

All individuals with Sly disease have a deficiency of the enzyme beta-glucuronidase which results in the accumulation of mucopolysaccharides. The accumulation of mucopolysaccharides is responsible for many problems that affect individuals with Sly disease.

What causes MPS VII?

Mucopolysaccharides are long chains of sugar molecules used in the building of bones, cartilage, skin, tendons and many other tissues in the body. Muco- refers to the thick jelly like consistency of the molecules, -poly- means many, and -saccharide is a general term for a sugar molecule. An alternative word for mucopolysaccharides is glycosaminoglycans or GAGs.

In the course of normal life there is a continuous process of building new mucopolysaccharides and breaking down old ones - a recycling process. The breakdown and recycling process requires a series of special biochemical tools called enzymes. Individuals with Sly disease are missing or deficient in an enzyme called beta-glucuronidase which is essential in the breaking down mucopolysaccharides. The incompletely broken down mucopolysaccharides remain stored inside the cells of the body and begin to build up causing progressive damage. Babies may show little sign of the disease but as more and more cells become damaged by accumulation of mucopolysaccharides, symptoms start to appear.

Does MPS VII affect individuals differently?

Sly Disease, like most MPS and related disorders, is very variable. In its most extreme form, children are born with a condition called hydrops fetalis. This is a very severe condition in which the child retains an enormous amount of fluid throughout its body. Babies with hydrops fetalis rarely survive beyond a few weeks to a few months of age. Many individuals with Sly Disease are less severely affected and have clinical symptoms similar to other MPS and Related Diseases.

How is MPS VII inherited?

Sly Disease is an autosomal recessive disease; 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 Sly gene there is a 25% (1:4) chance of having an affected child with 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 affected by, MPS VII.

All families of affected children should seek further information from their doctor or from a genetic counsellor before planning to have more children. There is a more detailed explanation of this complex subject in a booklet available from the MPS Society on the Pattern of Inheritance in MPS diseases. Please visit our Information Resource section.

Can you test for MPS VII in pregnancy?

If you have a child with Sly Disease it is possible to have tests during any subsequent pregnancy to find out whether the foetus is affected. It is important to contact your doctor as soon as you suspect that you may be pregnant if you wish for tests to be arranged. Both amniocentesis and chorionic villus sampling can be used to diagnose Sly Disease in utero.

Further information

There is a detailed fact sheet on MPS VII produced by the MPS Society in collaboration with parents and doctors drawing on their experience and with reference to medical literature. The fact sheet includes detailed information on the presentation and clinical management of the disease and treatment options available. Please visit our Information Resource section.