Hurler syndrome. Coloured X-ray of the hand of a 28 month old child with Hurler syndrome (also called mucopolysaccharidosis type I, MPS I). This is a rare inherited disorder that affects 1 in 115,000 people. Hurler syndrome is caused by a defective enzyme that is unable to break down glycosaminoglycans (mucopolysaccharides). Glycosaminoglycans are large molecules normally found in the fluid lubricating the joints. If they are not broken down by the enzyme when entering the cells, they cause permanent cell damage that progressively hinders physical development, organ functioning and causes mental retardation. There is no known cure and individuals rarely live past the age of 10 years old.