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 chains of sugar molecules used to build connective tissues in the body.


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


The body constantly replaces used materials and breaks them down for disposal. Patients with MPS VII are missing the enzyme beta-glucuronidase, which is essential to breaking down the mucopolysaccharides heparan sulfate, chondroitin 4-, 6-sulfates, and dermatan sulfate. These materials remain stored in the body’s cells, causing progressive damage. Babies may show little sign of the disease, but as cells sustain damage, symptoms start to appear.


How common is MPS VII?

MPS VII is estimated to occur in 1 in 250,000 newborns. It is one of the rarest types of mucopolysaccharidosis.


How is the disease inherited?

MPS VII is caused by a recessive gene. There is a one in four chance with every pregnancy that the child will inherit the defective gene from each carrier 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.


Is there a cure?

There is no cure for MPS VII, but as of Nov. 15, 2017, the U.S. Food and Drug Administration has approved Mepsevii, vestronidase alfa, as an enzyme replacement therapy for MPS VII.


Clinical trials are research studies that determine whether treatments or devices are safe for humans. These studies also look for effective medical approaches for specific conditions and help provide reliable data for patients, researchers and doctors. Clinical trials are conducted on small groups to determine whether a drug or procedure causes negative reactions or unsatisfactory side effects.


MPS VII clinical trials, observational and natural history studies
Clinical trial process


Emerging treatments

As of Nov. 15, 2017, the U.S. Food and Drug Administration has approved Mepsevii as a treatment for MPS VII, after the drug showed efficacy during clinical trials. Click here for more information on Ultragenyx and Mepsevii.

Hematopoietic Stem Cell Transplantation (HSCT)

HSCT is a blood stem cell transplant. Possible sources of blood stem cells include bone marrow, peripheral blood and umbilical cord blood.

Use of HSCT for MPS VII is limited by the rarity of the disorder and tendency toward stillbirths, although there are also milder adult forms of this disease. In certain circumstances, MPS VII can be effectively treated by HSCT provided that the developmental and clinical status of the individual is sound at the time of HSCT.



MPS VII | Booklet
Daily Living with MPS and Related Diseases
Management of MPS & ML
Education Strategies & Ressources











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The National MPS Society exists to cure, support and advocate for MPS and ML.

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