Mucopolysaccharidoses, commonly referred to as MPS, are a group of rare genetic metabolic disorders, and are regarded as lysosomal storage disorders.

Normally, the body makes enzymes to break down materials for our cells. For people with MPS and related diseases, the missing or insufficient enzyme prevents that normal process for the sugar glycosaminoglycans (or mucopolysaccharides), so they become stored in almost every cell of the body. As a result, cells do not function properly and cause progressive damage to the person throughout the body, including the heart, bones, joints, respiratory system, and nervous system. While the disease is not immediately apparent at birth, signs and symptoms develop with age as more cells become damaged by the accumulation of cell deposits. Most patients usually do not live through their twenties.

Mucopolysaccharidoses exist in a total of seven types — MPS I, II, III, IV, VI, VII, IX — and numerous subtypes. There are no type V and VIII. The seven types are subdivided to subtypes according to enzyme defect and symptoms shown by the body. Although each type of MPS is clinically different, most patients generally experience a period of normal development and then followed by a decline in physical and/or mental function.