Carrier rate in Jewish population:
Currently unknown in the Jewish population but has been identified in
Israeli and Iranian Jewish families.
Carrier rate in the general population:
The carrier frequency in the general population may be as high as 1 in 70.
Other ethnic groups in which it occurs:
Scandinavian descent prevalence estimated at around 3.6 in 100,000;
Usher syndrome has been estimated to be responsible for 3%-6% of all childhood deafness and approximately 50% of all deaf-blindness.
Age of onset of symptoms:
Usher syndrome type II symptoms of hearing loss begins from birth and progressive vision loss begins in adolescence or adulthood.
Usher syndrome type II is characterized by congenital (i.e., prelingual) bilateral sensorineural hearing loss that is mild to moderate in the low frequencies and severe to profound in the higher frequencies, intact vestibular responses, and retinitis pigmentosa (RP). RP is progressive, bilateral, symmetrical retinal degeneration that begins with night blindness and constricted visual fields (tunnel vision) and eventually includes decreased central visual acuity; the rate and degree of vision loss vary within and among families.
The lifespan of
patients with Usher syndrome is normal but requires lifelong
supportive care and management.
What causes the features of the disease:
Usher syndrome type II may be caused by mutations in any of three different genes: USH2A, GPR98 and DFNB31. The protein encoded by the USH2A gene, usherin, is located in the supportive tissue in the inner ear and retina. Usherin is critical for the proper development and maintenance of these structures, which may help explain its role in hearing and vision loss. The location and function of the other two proteins are not yet known.
Treatment or management:
There is currently no cure for Usher syndrome but promising research and development of treatment is being conducted. At present the management of Usher syndrome is mainly supportive and preventive. Management includes early fitting of hearing aids; speech training to normalize language; routine auditory evaluation to detect changes that may require modifications to hearing aids; routine ophthalmologic evaluation to detect potentially treatable complications such as cataracts; avoidance of physical activity such as sports and driving a car to prevent accidental injury. The hearing of at-risk siblings should be assessed as soon after birth as possible to allow early diagnosis and treatment of hearing loss.
Carrier testing - number of mutations screened for and detection rate:
Usher syndrome type II may be caused by mutations in any of three different genes: USH2A
or Type 2A
(causes 80% of cases), GPR98 or Type 2C (causes 15% of cases) and DFNB31
or Type 2D. Three novel mutations and twelve polymorphisms have been identified in the USH2A gene in Israeli USH2 families
Other testing information:
Carrier testing is available to
individuals with a family history of the disease.
Testing is available to those with a
previously affected child or to couples found to be at risk as
Molecular genetic testing for USH2A is clinically available. Testing for mutations in GPR98 is available on a research basis only.
The diagnosis of Usher syndrome type II is established on clinical grounds using electrophysiologic and subjective tests of hearing and retinal function.
Intensive research is under way to discover the causes of, and treatments for, all forms of Usher syndrome.
Gene therapy to replace defective Usher genes is being studied in
preclinical settings. With gene therapy, a normal gene is delivered to the retina to replace the mutated, disease-causing gene. The gene therapy may also be used to treat hearing loss.
Researchers have also identified a nutritional therapy to slow the rate of vision loss in some RP patients. Although not a cure, they found that vitamin A palmitate can slow retinal degeneration in some people with RP and Usher syndrome type 2.
A Phase II/lll human clinical trial is underway to test encapsulated cell technology (ECT) for delivery of a vision-preserving, therapeutic agent (ciliary neurotrophic factor or CNTF) to the retina.
In addition, numerous researchers are experimenting with artificial retinal implants. The devices are placed on the surface of the retina and restore rudimentary, functional vision.
Retinal cell transplantation is another area of growing interest. In these potential treatments, transplanted retinal cells would replace retinal cells lost to RP and other retinal degenerative diseases.
For more information:
Foundation Fighting Blindness:
National Institute on Deafness and Other Communication Disorders: