Mucopolysaccharidosis type VII (MPS VII), also known as Sly syndrome, is a progressive condition that affects most tissues and organs. The severity of MPS VII varies widely among affected individuals.

Mutations in the GUSB gene cause MPS VII. This gene provides instructions for producing the beta-glucuronidase (β-glucuronidase) enzyme, which is involved in the breakdown of large sugar molecules called glycosaminoglycans (GAGs). GAGs were originally called mucopolysaccharides, which is where this condition gets its name. Mutations in the GUSB gene reduce or completely eliminate the function of β-glucuronidase. The shortage (deficiency) of β-glucuronidase leads to the accumulation of GAGs within cells, specifically inside the lysosomes. Lysosomes are compartments in the cell that digest and recycle different types of molecules. Conditions such as MPS VII that cause molecules to build up inside the lysosomes are called lysosomal storage disorders. The accumulation of GAGs increases the size of the lysosomes, which is why many tissues and organs are enlarged in this disorder. Researchers believe that the GAGs may also interfere with the functions of other proteins inside the lysosomes and disrupt many normal functions of cells.

The exact incidence of MPS VII is unknown, although it is estimated to occur in 1 in 250,000 newborns. It is one of the rarest types of mucopolysaccharidosis.

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Published Date: August 01, 2010Published By: National Institutes of Health