Hurler syndrome overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aditya Govindavarjhulla, M.B.B.S. [2]

Overview

Hurler syndrome, also known as mucopolysaccharidosis type I (MPS I), Hurler's disease and gargoylism, is a genetic disorder that results in the deficiency of alpha-L iduronidase, which is an enzyme that breaks down mucopolysaccharides. Without this enzyme, the buildup of heparan sulfate and dermatan sulfate occurs in the body (the heart, liver, brain etc.). Symptoms appear during childhood and early death can occur due to organ damage.

Classification

MPS I is divided into three subtypes based on severity of symptoms. All three types result from an absence of, or insufficient levels of, the enzyme alpha-L-iduronidase. MPS I H or Hurler syndrome is the most severe of the MPS I subtypes. The other two types are MPS I S or Scheie syndrome and MPS I H-S or Hurler-Scheie syndrome.

Pathophysiology

Children born to an MPS I parent carry a defective IDUA gene, which has been mapped to the 4p16.3 site on chromosome 4. The gene is named IDUA because of its iduronidase enzyme protein product. As of 2001, 52 different mutations in the IDUA gene have been shown to cause Hurler syndrome.

Causes

Persons with Hurler syndrome do not make a substance called lysosomal alpha-L-iduronidase. This substance, called an enzyme, helps break down long chains of sugar molecules called glycosaminoglycans (formerly called mucopolysaccharides). These molecules are found throughout the body, often in mucus and in fluid around the joints.

Epidemiology and Demographics

Hurler syndrome has an overall frequency of 1 per 115,000 population.

Natural History, Complications and Prognosis

Children with Hurler syndrome often die before age 10 from obstructive airway disease, respiratory infections, or cardiac complications. Hurler syndrome is a disease with a poor outlook. Children with this disease develop nervous system problems, and can die young.