Hurler syndrome
Hurler syndrome | |
---|---|
Prognosis | Death usually occurs before 12 years |
Frequency | 1 in 100,000 |
Hurler syndrome, also known as .
The underlying mechanism is a deficiency of
Hurler syndrome is classified as a
Signs and symptoms
Children with Hurler syndrome may appear normal at birth and develop symptoms over the first years of life. Symptoms vary between patients.[citation needed]
One of the first abnormalities that may be detected is coarsening of the facial features; these symptoms can begin at 3–6 months of age. The
Other early symptoms may include inguinal and umbilical hernias. These may be present at birth, or they may develop within the first months of life. Clouding of the cornea and retinal degeneration may occur within the first year of life, leading to blindness. Enlarged liver and spleen are common. There is no organ dysfunction, but GAG deposition in these organs may lead to a massive increase in size. Patients may also have diarrhea. Aortic valve disease may occur.[citation needed]
Airway obstruction is frequent, usually secondary to abnormal cervical vertebrae.[3] Upper and lower respiratory tract infections can be frequent.[citation needed]
Developmental delay may become apparent by age 1–2 years, with a maximum functional age of 2–4 years. Progressive deterioration follows. Most children develop limited language capabilities. Death usually occurs by age 10.[4][5]
Genetics
Children with Hurler syndrome carry two defective copies of the IDUA gene, which has been mapped to the 4p16.3 site on chromosome 4. This is the gene which encodes for the protein iduronidase. As of 2018[update], more than 201 different mutations in the IDUA gene have been shown to cause MPS I.[6]
Because Hurler syndrome is an
Mechanisms
The IDUA gene is responsible for encoding an enzyme called alpha-L-iduronidase. Through hydrolysis, alpha-L-iduronidase is responsible for breaking down a molecule called unsulfated alpha-L-iduronic acid. This is a uronic acid found in the GAGs dermatan sulfate and heparan sulfate. The alpha-L-iduronidase enzyme is located in lysosomes. Without sufficient enzymatic function, these GAGs cannot be digested properly.[7]
Diagnosis
Diagnosis often can be made through clinical examination and urine tests (excess
Classification
All members of the mucopolysaccharidosis family are also lysosomal storage diseases. Mucopolysaccharidosis type I (MPS I) is divided into three subtypes based on severity of symptoms. All three types result the absence or decreased functioning of the same enzyme. MPS-IH (Hurler syndrome) is the most severe of the MPS I subtypes. The other two types are MPS-IS (Scheie syndrome) and MPS-IHS (Hurler–Scheie syndrome).[citation needed]
Because of the substantial overlap between Hurler syndrome, Hurler–Scheie syndrome, and Scheie syndrome, some sources consider these terms to be outdated. Instead, MPS I may be divided into "severe" and "attenuated" forms.[8]
Treatment
There is currently no cure for Hurler syndrome. Enzyme replacement therapy with iduronidase (Aldurazyme) may improve pulmonary function and mobility. It can reduce the amount of carbohydrates being improperly stored in organs. Surgical correction of hand and foot deformities may be necessary. Corneal surgery may help alleviate vision problems.[5]
Children often lack access to a suitable bone marrow donor. In these cases, UCBT from unrelated donors can increase survival, decrease physical signs of the disease, and improve cognition. Complications from this treatment may include
Prognosis
A British study from 2008 found a median estimated life expectancy of 8.7 years for patients with Hurler syndrome. In comparison, the median life expectancy for all forms of MPS type I was 11.6 years. Patients who received successful bone marrow transplants had a 2-year survival rate of 68% and a 10-year survival rate of 64%. Patients who did not receive bone marrow transplants had a significantly reduced lifespan, with a median age of 6.8 years.[4]
Epidemiology
Hurler syndrome has an overall frequency of one per 100,000.[5] Combined, all of the mucopolysaccharidoses have a frequency of approximately one in every 25,000 births in the United States.[2]
Research
Gene therapy
A great deal of interest exists in treating MPS I with
History
In 1919, Gertrud Hurler, a German pediatrician, described a syndrome involving corneal clouding, skeletal abnormalities, and mental retardation. A similar disease of "gargoylism" had been described in 1917 by Charles A. Hunter. Hurler did not mention Hunter's paper. Because of the communications interruptions caused by World War I, it is likely that she was unaware of his study. Hurler syndrome now refers to MPS IH, while Hunter syndrome refers to MPS II.[13][14] In 1962, a milder form of MPS I was identified by Scheie, leading to the designation of Scheie syndrome.[4]
See also
- Hunter syndrome (MPS II)
- Sanfilippo syndrome (MPS III)
- Morquio syndrome (MPS IV)
- Maroteaux–Lamy syndrome (MPS VI)
References
- ISBN 978-0-7216-2921-6.
- ^ a b "Mucopolysaccharidoses Fact Sheet". National Institute of Neurological Disorders and Stroke. 15 Nov 2017. Retrieved 11 May 2018.
- PMID 1917344.
- ^ PMID 18796143.
- ^ a b c Banikazemi M (12 Oct 2014). "Hurler syndrome, Hurler-Scheie Syndrome, and Scheie Syndrome (Mucopolysaccharidosis Type I)". Medscape. Retrieved 10 May 2018.
- PMID 29843745.
- ^ "IDUA gene". Genetics Home Reference. 11 June 2019. Retrieved 18 June 2019.
- ^ "Mucopolysaccharidosis type I". Genetics Home Reference. Retrieved 10 May 2018.
- PMID 9516162.
- S2CID 43572313.
- PMID 17727324.
- U.S. National Library of Medicine. Retrieved 7 February 2019.
- Who Named It?
- S2CID 34471544.