Usher Syndrome

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A scene as it might be viewed by a person with retinitis pigmentosa. Source: National Eye Institute, National Institutes of Health

Usher syndrome is an inherited condition that causes a serious hearing loss that is usually present at birth or shortly thereafter and a progressive vision loss caused by retinitis pigmentosa (RP). RP is a group of inherited diseases that cause night-blindness and peripheral (side) vision loss through the progressive degeneration of the retina, the light-sensitive tissue at the back of the eye that is crucial for vision. Usher syndrome is a genetic disease inherited in an autosomal recessive manner.

Contents

Other Names

  • Usher's syndrome
  • Deafness-retinitis pigmentosa syndrome
  • Dystrophia retinae pigmentosa-dysostosis syndrome
  • Graefe-Usher syndrome
  • Hallgren syndrome
  • Retinitis pigmentosa-deafness syndrome

Types

Researchers have described three types of Usher syndrome:

Type I

Individuals with Usher syndrome type I are nearly or completely deaf and experience problems with balance from a young age. They usually begin to exhibit signs of RP in early adolescence.

Type II

Individuals with Usher syndrome type II experience moderate to severe hearing impairment, have normal balance, and experience symptoms of RP later in adolescence.

Type III

Individuals with Usher syndrome type III are born with normal hearing but develop RP and then progressive hearing loss.

Signs and Symptoms

The signs and symptoms of Usher syndrome vary by the type of disease and are described in the "types" section of this page. Common symptoms to all types of the syndrome include hearing difficulty, progressive blindness and vestibular dysfunction (balance disturbance).

Causes

The Usher syndrome types are inherited as an autosomal recessive trait. This means that an affected person receives one abnormal gene from each of his or her parents. A person who inherits a gene from only one parent will be a carrier, but will not develop the disease. A person with Usher syndrome must pass on one disease gene to each of his or her children. However, unless the person has children with another carrier of Usher genes, the individual's children are not at risk for developing the disease. Currently there is no reliable method to reasonably test everyone for carrier status, but this may change in the years ahead.

Diagnosis

Exams and tests

Although some of the genes that cause Usher syndrome have been identified, the diagnosis is still based on ocular and clinical testing. Since individuals with Usher syndrome have both hearing and visual symptoms, testing of both systems is performed. This testing includes:

  • Visual function tests: visual fields and electroretinogram (ERG)
  • Retinal examination
  • Hearing tests
  • Balance tests for all patients age ten years and older

At this time, genetic testing for Usher syndrome is done only as part of research projects. This is due to many factors. Usher syndrome is not caused by only one gene. So far, 10 Usher genes have been mapped: 7 for type I, 3 for type II, and 1 for type 3. There are still more genes to find. A few of these genes have been sequenced and described. These are MYO7A, harmonin, CDH23, PCDH15, all causing type I. The USH2A and GPR98 genes cause type II disease. CLRN1 causes type III Usher syndrome.

Research to precisely identify the specific genes involved in each Usher syndrome type is moving at a rapid pace. In the near future it should be possible to perform a test on genetic material from blood and other cells to determine if the specific gene defect causing Usher syndrome is present. When available, this testing will provide an accurate genetic diagnosis useful for early detection of the disorder, and for defining the risks of other family members or future offspring being affected.

Treatment

Currently there is no way to halt the degeneration of the retina or to restore normal hearing. The hearing loss cannot be corrected with middle ear surgery. Some patients with severe hearing impairment have benefited from cochlear implants. Others with residual hearing may benefit from the use of hearing aids. The best treatment involves early identification so that educational programs can begin as soon as possible. The exact nature of these programs will depend on the severity of the hearing and vision loss as well as the age and abilities of the person. Typically, treatment will include hearing aids, assistive listening devices, cochlear implants, or other communication methods such as American Sign Language; orientation and mobility training; and communication services and independent-living training that may include Braille instruction, low-vision services, or auditory training.

There is evidence that treatment with vitamin A may slow (not halt) the progress of retinitis pigmentosa. [1] Because the study did not include patients with type I Usher syndrome, it is not recommended that these patients take high dose vitamin A supplements.

Chances of Developing Usher Syndrome

Usher syndrome is thought to be responsible for 3 percent to 6 percent of all childhood deafness and about 50 percent of deaf-blindness in adults. Usher syndrome type I is estimated to occur in at least 4 per 100,000 people. It may be more common in certain ethnic populations, such as people with Ashkenazi (central and eastern European) Jewish ancestry and the Acadian population in Louisiana. Type II is thought to be the most common form of Usher syndrome, although the frequency of this type is unknown. Type III Usher syndrome accounts for only a small percentage of all Usher syndrome cases in most populations. This form of the condition is more common in the Finnish population, however, where it accounts for about 40 percent of all cases. [2]

Clinical Trials

A list of ongoing clinical trials is available here

Research

Recent discoveries

  • A recently completed study assessed the benefit of cochlear implant in patients with type I Usher syndrome and looked at the relationship between phenotype (observable characteristics) and genotype (genetic constitution) in these patients. In this study, clinical symptoms did not correlate with genetic defects. In addition, reponse to cochlear implant appeared to be related to the age at which the procedure was performed. [3]
  • Another recent study contends that the different types of Usher syndrome may not be as separate as previously believed. There appears to be overlap between the types and it may be more helpful to look at genotypes rather than clinical symptoms in patients with Usher syndrome. [4]

Future research

Finding the genes is a very important advance in the fight against Usher syndrome. Further study is required to characterize these genes, and determine how the mutated genes cause Usher syndrome. Additional genes that cause Usher syndrome also need to be identified. Several researchers throughout the world are working on Usher syndrome. Findings from this research may one day allow treatments for Usher syndrome to be developed.

History

The earliest report of what was likely a case of Usher syndrome was described in 1858 by Albrecht von Graefe, a German opthamologist. The syndrome was named for Dr. Charles Usher, a Scottish opthamologist who described the syndrome and theorized that it was passed from parent to child. [5]

Interesting Facts

Famous People

Jockey Kent Desormeaux, who rode winning horses in the Kentucky Derby and Preakness races in 1998 and the Kentucky Derby in 2000 and 2002 was hoping to ride Big Brown to be the first Triple Crown winner in 30 years in 2008 (they did not succeed). Desormeaux's second son has Usher syndrome and received media attention before the June 7, 2008 race. [6]

References

  1. National Eye Institute Press Release. Treatment for Retinitis Pigmentosa Reported.
  2. Genetics Home Reference. What is Usher syndrome?
  3. Blanchet C, Roux AF, Hamel C. Usher type I syndrome in children: genotype/phenotype correlation and cochlear implant benefits. Rev Laryngol Otol Rhinol (Bord). 2007;128(3):137-43. Abstract
  4. Cohen M, Bitner-Glindzicz M, Luxon L. The changing face of Usher syndrome: clinical implications. Int J Audiol. 2007 Feb;46(2):82-93. Abstract
  5. Usher CH. On the inheritance of retinitis pigmentosa, with notes of cases. Royal London Ophthalmological Hospital Report. 1914, 19: 130-236.
  6. Stewart L. Jockey Kent Desormeaux wants a crowning moment in Belmont. Los Angeles Times. June 6, 2008.

External Links

Foundation Fighting Blindness: What is Usher Syndrome?

National Association for the Deaf-Blind

National Organization for Rare Disorders

American Association for the Deaf-Blind

Medpedia-logo.gif The basis of this article is contributed from Medpedia.com These articles are licensed under the GNU Free Documentation License It may have since been edited beyond all recognition. But we thank Medpedia for allowing its use.
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