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About MPS I

MPS I (mucopolysaccharidosis I) is an inherited lysosomal storage disorder caused by a deficiency of alpha-L-iduronidase, a lysosomal enzyme normally required for the breakdown of certain complex carbohydrates known as glycosaminoglycans (GAGs). If the enzyme is not present in sufficient quantities, the normal breakdown of GAGs is incomplete or blocked. The cell is then unable to excrete the carbohydrate residues and they accumulate in the lysosomes of the cell. This accumulation disrupts the cell’s normal functioning and gives rise to the clinical manifestations of the disease.


Children diagnosed with MPS I have historically been classified into one of three categories based on the severity of their symptoms and rate of disease progression. It has now become clear, however, that there is a wide spectrum of severity in MPS I with much overlap between the categories. The following is a brief overview of the three categories of MPS I:

  • Hurler Syndrome: The most severe form of MPS I is characterized by progressive developmental delay and severe progressive physical problems. Death often occurs before 10 years of age.
  • Hurler-Scheie Syndrome: The intermediate form of MPS I is characterized by normal or near normal intelligence, but more severe physical symptoms than those with Scheie Syndrome.
  • Scheie Syndrome: The attenuated form of MPS I is characterized by normal intelligence, usually normal height, and milder physical problems than Hurler-Scheie. These individuals potentially have a normal life span.

Signs and Symptoms

The following are some of the features associated with MPS I:

  • Short stature
  • Macrocephaly
  • Coarse facial features
  • Progressively coarse facial features
  • Delayed or regressed mental development (the severe form)
  • Communicating hydrocephalus
  • Spinal cord compression
  • Carpal tunnel syndrome
  • Corneal clouding
  • Impaired vision
  • Recurrent otitis media
  • Impaired hearing
  • Recurrent sinopulmonary infections
  • Upper airway obstruction
  • Sleep apnea
  • Reduced pulmonary function
  • Cardiac abnormalities and valvular disease
  • Hepatosplenomegaly
  • Umbilical and inguinal hernias
  • Reduced joint range of motion
  • Dysostosis mutiplex (bone deformities)
  • Malaise and reduced endurance

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