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Hunter Syndrome
Sunday, 08 August 2004
Monday, 29 November 2004
Mucopolysaccharidosis II

What

Hunter Syndrome is a very rare, inherited, genetic disorder that most commonly affects children but can also affect adults. This disease is characterized by the development of coarse facial features, multi-organ dysfunction, and progressive mental retardation. Hunter syndrome is a type of lysosomal storage disorder that results in the accumulation of toxic byproducts in the tissues within the body. It is the absence of a certain enzyme (protein that degrades cellular byproducts) within the lysosome (cellular trashcan) that leads to problems. The specific compound that cannot be degraded is the mucopolysaccharide.

Who

The incidence of Hunter syndrome has been estimated to be 1 case per 65,000 to 132,000 persons. Only males are affected because of the X-linked inheritance pattern. Persons of Jewish descent seem to be affected more frequently.

Signs and Symptoms

Hunter Syndrome usually first manifests itself in infancy or early childhood (between 18-36 months). Children first present with common childhood sicknesses like ear infections and colds. As the disease progresses, children begin to show the major signs and symptoms of the disease which include:

  • Coarse facial features – prominent forehead, flattened nasal bridge, enlarged tongue.
  • Progressive mental retardation.
  • Enlarged head.
  • Aggressive behavior and hyperactivity.
  • Stiff joints and carpal tunnel syndrome.
  • Excessive hair.
  • Progressive deafness
  • Enlargement of the liver and spleen.
  • Eye involvement – damage to the retina
  • Hernias in the groin.
  • Heart abnormalities.

Possible Causes

Hunter Syndrome is a lysosomal storage disorder that affects a cellular item called a lysosome. Each of our cells has small digestive units called lysosomes. These lysosomes contain digestive enzymes that eat discarded carbohydrates and fats in our cells; they are the trash incinerators in our cells. Hunter Syndrome is a special type of lysosomal storage disorder known as a mucopolysaccharide storage disease where there is a deficiency of a certain enzyme (iduronate sulfatase in Hunter Syndrome). When there is a deficiency of the enzymes in Hunter Syndrome, there is an accumulation of substances that are toxic to cells and can cause them to malfunction and/or die. When these cells are damaged, the symptoms of Hunter Syndrome occur. The gene defect responsible for Hunter Syndrome has been identified and follows an X-linked inheritance pattern (this means the gene is on the X chromosome). Since males have only one X chromosome, they have no normal copies of the gene and thus develop the disease. It is rare for a female to be affected, this requires the passage of a defective gene from both parents.

Diagnosis

Children with Hunter Syndrome usually present at first with symptoms of the common cold or flu. As the child ages, certain symptoms become more progressive and prominent like enlarged liver and facial features. Hunter Syndrome is diagnosed by examining the clinical picture and using x-rays and blood work to confirm a diagnosis. When Hunter Syndrome is suspected, a child’s urine is checked for excessive dermatan sulfate and heparan sulfate. If there is dermatan sulfate and heparan sulfate present and Hunter Syndrome is suspected, a special test can be done to confirm the diagnosis. White blood cells or special skin cells called fibroblasts may be taken by biopsy and examined. Examination of these specimens will reveal a lack of activity of iduronate sulfatase in these cells. This evidence will support the diagnosis of Hunter Syndrome. X-rays may also be taken to examine bone changes and see if the bone abnormalities support a diagnosis of Hunter Syndrome.

Treatment

Current treatment for Hunter Syndrome involves management of symptoms and complications of the disease. While currently there is no cure for Hunter Syndrome itself, a company named Transkaryotic Therapies, Inc. (http://www.tktx.com/) is currently providing a treatment where researchers are trying to synthetically replace the deficient enzymes of Hunter Syndrome. This therapy seems to help with some normal lysosome function. Other treatments for Hunter Syndrome include treatment of respiratory and neurological complications and bone marrow transplantation for the less affected children. Current research is promising for the use of gene therapy to treat patients of this disease

Prognosis

Hunter Syndrome has many serious complications including neurological and respiratory problems. Cardiac abnormalities can also causes severe problems, even fatal ones for Hunter Syndrome patients. Unfortunately, because there is no cure at this point, most patients die from one of the complications of their disease. Hunter Syndrome Type A is more severe and the patients with this form usually live to their 20’s or 30’s. Hunter Syndrome Type B is less severe and is usually not diagnosed until adulthood. These patients usually live until their 70’s.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

National MPS Society
This organization was founded by families of children with mucopolysaccharidoses and mucolipidoses. They provide information and support, such as regional meetings in which families can meet each other.

The Canadian Society for MPS and related diseases
Organization whose purpose is to provide information and support to individuals and their families afflicted with a Mucopolysaccharide (MPS) disease, increase public awareness of MPS diseases, and raise funds to further research into MPS and related diseases.

Transkaryotic Therapies, Inc.
Pharmacuetical company that currently is researching a new enzyme replacement therapy. Some patients have benefited form this therapy.

Lysosomal Storage Disease Network
Great website the provides information, resources, and services to physicians and patients alike in their efforts to cope with Hunter Syndrome.

CLIMB (Children Living with Inherited Metabolic Diseases)
UK Organization dedicated to fighting metabolic diseases through research, awareness and support. This organization provides advice, information and support on all metabolic diseases to children, young adults, and families.

Google Search for Hunter Syndrome

References and Sources

Emedicine.com: Mucopolysaccharidoses www.emedicine.com/derm/topic710.htm MedlinePlus: Hunter Syndrome www.nlm.nih.gov/medlineplus/ency/article/001203.htm OMIM: Hunter Syndrome www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=309900 National MPS (Mucopolysaccharidoses/Mucolipidoses) Society, Inc . www.mpssociety.org/mps2.html National Organization of Rare Diseases: Hunter Syndrome www.rarediseases.about.com/cs/huntersyndrome/a/022204.htm