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Hurler syndrome, also known as mucopolysaccharidosis type I (MPS I), Hurler’s disease or gargoylism, is a genetic disorder that results in the buildup of mucopolysaccharides due to a deficiency of alpha-L iduronidase, an enzyme responsible for the degradation of mucopolysaccharides in lysosomes. Without this enzyme, a buildup of heparan sulfate and dermatan sulfate occurs in the body. Symptoms appear during childhood and early death can occur due to organ damage.
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 a-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.
Hurler syndrome is often classified as a lysosomal storage disease, and is clinically related to Hunter’s Syndrome.[citation needed] Hunter is X-linked while Hurler is autosomal recessive.
It is named for Gertrud Hurler.[1][2]
Hurler syndrome has an overall frequency of 1 per 100,000. The mucopolysaccharidoses as a whole have a frequency of 1 in every 25,000 births.[citation needed]
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.
Because Hurler syndrome is an autosomal recessive disorder, affected persons have two bad copies of the IDUA gene. If someone is born with one normal and one defective copy of the gene (s)he is called a carrier and will produce less a-L-iduronidase than an individual with two normal copies of the gene. The slightly reduced production of the enzyme in carriers, however, remains sufficient for normal function and the person should not show any symptoms of the disease.
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