Mucopolysaccharidoses are a group of metabolic lysosomal storage diseases caused by the absence or impaired function of lysosomal enzymes required for glycosaminoglycan metabolism. As a result, glycosaminoglycans accumulate in the cells, causing cellular damage which affects the function of multiple organs and, in most cases, leads to mental retardation.
Mucopolysaccharidosis II (MPS II, Hunter syndrome) is caused by an iduronate sulfatase (IDS) deficiency.