Usher syndrome is the most common genetic condition that affects both vision and hearing. The major symptoms of Usher syndrome are hearing loss and vision loss from an eye disorder called retinitis pigmentosa, or RP.
Vision loss from RP can begin anywhere from early childhood to adolescence.
Who is at risk for Usher syndrome?
Usher syndrome is a recessive disorder. This means that a person has to inherit the change in the gene from both parents. A person who inherits the changed gene from one parent does not have the syndrome but is a carrier for it. When two carriers of the same Usher syndrome gene have a child together, there is a one-in-four chance that the child will have Usher syndrome.
The main visual symptom of Usher syndrome is loss of vision from retinitis pigmentosa (RP).
In people with RP, the light-sensing cells in the retina slowly degenerate (die). These cells are called rods and cones. This causes a gradual loss of vision. With most forms of RP, rods start dying first. This causes a loss of side and night vision. When the cones begin dying, the result is loss of color perception and central (reading) vision. Generally, after many years, blindness results.
Usher syndrome affects vision, hearing, and sometimes balance. Several types of Usher syndrome exist depending on the genes involved.
The best way to precisely diagnose Usher syndrome is with genetic testing, which can determine the genes involved.
An ophthalmologist evaluation of the eyes may include:
- a visual field test to measure peripheral (side) vision
- an electroretinogram (ERG) to measure the response of the eye's light-sensitive cells
- a retinal examination to observe the retina and other structures in the back of the eye.
- optical coherence tomography (OCT), which takes a cross-sectional image of your retina.
How is Usher syndrome treated?
Currently there is no known cure for Usher syndrome or for retinitis pigmentosa (RP). Knowing the genes responsible for Usher syndrome can help you look for an ongoing gene therapy trial and an eventually approved therapy. The best treatment involves early diagnosis so that educational programs can begin as soon as possible, depending on the severity of the vision loss and the age and ability of the child.
Treatment may include:
Some research has shown that vitamin A may slow the progression of certain forms of RP, but there is concern that high intake of vitamin A may lead to worsening of other eye conditions. Your ophthalmologist can advise you about the risks and benefits of Vitamin A and how much you can safely take. Taking too much vitamin A can be harmful, and evidence of vitamin A’s effect on RP progression is not substantial. So vitamin A supplements are not currently recommended.
Gene therapy clinical trials are underway for several forms of RP and Usher syndrome. In 2017, the FDA approved the first gene therapy for one type of RP (linked to the RPE65 gene). This therapy places a normal copy of the disease-causing gene inside the retina. The normal gene helps the retina work better.
Other types of gene therapy and RNA therapy (a type of genetic therapy) are also being tested. Hopefully, one day we will be able to treat more hereditary eye conditions.