Usher syndrom

What is Usher Syndrome?

Usher syndrome is an inherited disorder that is characterized by moderate to profound hearing impairment, which is present at birth or shortly thereafter, and progressive vision loss due to retinitis pigmentosa (RP), a degeneration of the retina. It is the major cause of deaf blindness. About 10-15,000 people in the United States have Usher syndrome.

Clinical Description

There are three known forms of Usher syndrome. Individuals with Usher syndrome type I are born profoundly (completely) deaf and experience problems with balance. In adolescence, they usually begin to exhibit the first signs of RP: night blindness and loss of peripheral vision.

Individuals with Usher syndrome type II experience moderate to severe hearing impairment at birth, but they do not have balance problems. Symptoms of RP develop later in adolescence. With Usher syndrome type III, hearing loss and vision loss due to RP are both progressive.

Researchers believe that the hearing loss in Usher syndrome is due to a problem with the sensory (nerve) cells in the cochlea, a structure within the inner ear that is necessary for transmission of sound to the brain.

The vision loss is caused by a degeneration of the retina, a delicate tissue in the eye composed of multilayered light sensing cells. The retina lines the inside of the back of the eye and contains photoreceptor cells (rods and cones). The photoreceptors are responsible for converting light into electrical impulses that transfer messages to the brain where seeing actually occurs.

Inheritance

Usher syndrome is passed to succeeding family generations through the autosomal recessive inheritance pattern. In this type of inheritance, two copies of an Usher syndrome gene, one from each parent, are required for a person to have the syndrome. An individual who has only one copy of the gene, called a carrier, will have no symptoms of the disorder.

 

Treatment

Intensive research is currently under way to discover the cause, prevention, and treatment of the vision loss with Usher syndrome. While not a cure, a specified dose of vitamin A has been found to slow the progression of RP in some individuals with typical RP and Usher syndrome type II. Contact your doctor or The Foundation Fighting Blindness for more information.

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.

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.

Related Diseases

There are other inherited retinal degenerative diseases that share some of the clinical symptoms of RP. Some of these conditions are complicated by other symptoms besides loss of vision. The most common of these is Usher syndrome, which causes both hearing and vision loss. Other rare syndromes that researchers are studying with funding from The Foundation Fighting Blindness include Bardet-Biedl (Laurence-Moon) syndrome, Best disease, choroideremia, gyrate-atrophy, Leber Congenital Amaurosis, and Stargardt Disease.