"The mucopolysaccharidoses (MPS) are lysosomal storage disorders caused by the deficiency of enzymes required for the stepwise breakdown of glycosaminoglycans (GAGs), previously referred to as mucopolysaccharides. Fragments of partially degraded GAGs accumulate in the lysosomes, resulting in cellular dysfunction and clinical abnormalities. The clinical features and diagnosis of the MPS are reviewed here. The management of these disorders and associated complications are discussed separately. (See "Mucopolysaccharidoses: Complications"). The MPS are rare conditions, with an estimated total incidence of all kinds of MPS of roughly 1 in 20,000 live births. Glycosaminoglycans (GAGs) are large, complex polymers of linear, repeating sulfated acidic and amino sugar disaccharide units attached to a protein core. They are widely distributed in many tissues, where they play important roles. As examples, they're components of the bottom substance of bone and cartilage, lubricant in joint fluid, and therefore the surface coating that originally binds growth factors to cells."