MPS VII (Sly syndrome)

MPS VII is a mucopolysaccharide disease also known as Sly syndrome. It takes its name from Dr. William Sly who originally described the condition in 1972.


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

There is a continuous process in the body of replacing used materials and breaking them down for disposal. Children with MPS VII are missing an enzyme called beta-glucuronidase, which is essential in cutting up the used mucopolysaccharides, called heparan sulfate, chondroitin 4-, 6-sulfates, and dermatan sulfate. The incomplete broken down mucopolysaccharides remain stored in cells in the body causing progressive damage. Babies may show little sign of the disease, but as more and more cells become damaged, symptoms start to appear.

How common is MPS VII?

MPS VII is one of the least common forms of MPS with an estimated frequency of less than 1 in 250,000 births. There is an estimate in the United States that 1 in 25,000 births will result in some form of MPS.

How is the disease inherited?

We all have genes inherited from our parents which control whether we are tall, short, fair, etc. Some genes we inherit are “recessive,” that is to say we carry the gene but it does not have any effect on our development. MPS VII is caused by a recessive gene. If the adult carrying the abnormal gene marries another carrier there will be a one in four chance with every pregnancy that the child will inherit the defective gene from each parent and will be affected with the disease. There is a two in three chance that unaffected brothers and sisters of Sly patients will be carriers. They can be reassured, however, that as the disease is so rare, the chance of marrying another carrier is very slight provided they do not marry a cousin or other close family member.

Is there a cure?

At present there is no cure for any of the mucopolysaccharide diseases. There has been little or no experience with bone marrow transplantation or with enzyme replacement therapy in individuals with MPS VII. Studies in animal models of this disease, however,suggest that both bone marrow transplantation and enzyme replacement therapy may be effective forms of therapy for problems affecting the body.

For more information please visit the Ultragenyx Website.

All families of affected children should seek further information from their doctor or from a Genetic Counselor.