The Mucopolysaccharidoses (MPS) are a group of inherited metabolic disorders caused by missing or absent enzymes that function to break down molecules called glycosaminoglycans. Also known as mucopolysaccharides, glycosaminoglycans are long chains of sugars that are important building blocks to form bone, cartilage, tendons, skin, and connective tissue. When one of these 11 enzymes are not working properly or are absent, the glycosaminoglycans build up in the bones, joints, heart, respiratory and gastrointestinal tracts, and in some patients, central nervous system.
The seven MPS disorders and the associated enzyme deficiency are as follows:
- MPS I H – Hurler; alpha-L-Iduronidase
- MPS I S – Scheie; alpha-L-Iduronidase
- MPS I H-S - Hurler-Scheie; alpha-L-Iduronidase
- MPS II – Hunter; Iduronate sulfatase
- MPS III A - Sanfilippo A; Heparan N-sulfatase
- MPS III B - Sanfilippo B; alpha-N-Acetylglucosaminidase
- MPS III C - Sanfilippo C; Acetyl CoA alpha-glycosaminide acetyltransferase
- MPS III D - Sanfilippo D; N-Acetylglucosamine 6-sulfatase
- MPS IV A - Morquio A; N-acetylgalactosamine-6 sulfatase
- MPS IV B - Morquio B; Beta-Galactosidase
- MPS VI - Maroteaux-Lamy; (arylsulfatase B) N-Acetylgalactosamine 4-sulfatase
- MPS VII - Sly Beta-Glucuronidase
There is FDA-approved treatment for several forms of MPS. ERT is available for four forms of the disease – Aldurazyme (MPS I), Elaprase (MPS II), Vimizim (MPS IVA), Naglazyme (MPS VI), and Mepsevii (MPS VII). HSCT (stem cell transplant) is also considered a beneficial therapy for three forms of MPS - severe MPS I (Hurler syndrome), MPS VI (Maroteaux-Lamy syndrome), and MPS VII (Sly syndrome).