Mucopolysaccharidosis Type I (MPS I)
Mucopolysaccharidosis Type I, or MPS I, is classified as a lysosomal storage disease. It is caused by a deficiency in the enzyme alpha-iduronidase, leading to the accumulation of glycosaminoglycans (GAGs) in cells. This buildup affects multiple organs and causes progressive damage. MPS I is inherited in an autosomal recessive manner and has three forms—Hurler, Hurler-Scheie, and Scheie—varying in severity.
Forms of Mucopolysaccharidosis Type I
MPS I takes three forms: Hurler Disease, Hurler and Scheie Disease and Scheie Disease, which differ in the severity of symptoms. The most severe of these is MPS I Hurler Disease, which is characterised by severe mental retardation and rapidly progressive deterioration, with patients surviving for about 10 years.
In the milder form, Scheie Disease, the intensity of symptoms is less severe and patients are characterised by normal mental development. Mutations in people with Scheie Disease result in low alpha-iduronidase activity, so that somatic changes progress more slowly; and at the same time, the residual activity of the enzyme is sufficient to protect the central nervous system.
The Hurler-Scheie form is an intermediate form accompanied by a slight mental disability in addition to somatic changes.
Incidence and Prognosis
The incidence of Mucopolysaccharidoses Type I is estimated to be 1:100,000. More than half of all MPS I cases are its most severe form, Hurler Syndrome. The occurrence of Hurler Disease is also associated with a significant reduction in the life expectancy of patients, due to serious complications both cardiovascular and respiratory.