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Usher Syndrome

Usher syndrome is the most common condition that involves both hearing and vision problems. A syndrome is a disease or disorder that has more than one feature or symptom. The major symptoms of Usher syndrome are hearing impairment and retinitis pigmentosa, an eye disorder that causes a person's vision to worsen over time. Some people with Usher syndrome also have balance problems. Although the syndrome was first described by Albrecht Von Graefe in 1858, it was named for Charles Usher, a British eye doctor, who believed that the condition was inherited or passed from parents to their children.

There are three general types of Usher syndrome: Usher syndrome type 1 (USH1), Usher syndrome type 2 (USH2), and Usher syndrome type 3 (USH3). USH1 and USH2 are the most common types. Together, they account for approximately 90-95 percent of all cases of children who have Usher syndrome.

Symptoms

People with USH1 are profoundly deaf from birth and have severe balance problems. Many of these individuals obtain little or no benefit from hearing aids. Most use sign language as their primary means of communication. Because of the balance problems, children with USH1 are slow to sit without support and rarely learn to walk before they are 18 months old. These children usually begin to develop vision problems by the time they are ten. Visual problems most often begin with difficulty seeing at night, but tend to progress rapidly until the individual is completely blind.

Individuals with USH2 are born with moderate to severe hearing impairment and normal balance. Although the severity of hearing impairment varies, most of these children perform well in regular classrooms and can benefit from hearing aids. These children most commonly use speech to communicate. The visual problems in USH2 tend to progress more slowly than the visual problems in USH1. USH2 is characterized by blind spots that begin to appear shortly after the teenage years. When an individual's vision deteriorates to blindness, his or her ability to speechread is lost.

Children born with USH3 have normal hearing and normal to near-normal balance. Hearing worsens over time. However, the rate at which hearing and sight are lost can vary between affected individuals, even within the same family. Children develop noticeable hearing problems by their teenage years and usually become deaf by mid- to late adulthood. Night blindness usually begins sometime during puberty. Blind spots appear by the late teenage years to early adulthood. By mid-adulthood, the individual is usually blind.

Causes

Mutations in the CDH23, CLRN1, GPR98, MYO7A, PCDH15, USH1C, USH1G, and USH2A genes cause Usher syndrome.

The genes related to Usher syndrome provide instructions for making proteins that play important roles in normal hearing, balance, and vision. They function in the development and maintenance of hair cells, which are sensory cells in the inner ear that help transmit sound and motion signals to the brain. In the retina, these genes are also involved in determining the structure and function of light-sensing cells called rods and cones. In some cases, the exact role of these genes in hearing and vision is unknown. Most of the mutations responsible for Usher syndrome lead to a loss of hair cells in the inner ear and a gradual loss of rods and cones in the retina. Degeneration of these sensory cells causes hearing loss, balance problems, and vision loss characteristic of this condition.

Usher syndrome type I can result from mutations in the CDH23, MYO7A, PCHD15, USH1C, or USH1G gene. At least two other unidentified genes also cause this form of Usher syndrome.

Usher syndrome type II is caused by mutations in at least four genes. Only two of these genes, USH2A and GPR98 (also called VLGR1), have been identified.

Mutations in at least two genes are responsible for Usher syndrome type III; however, CLRN1 is the only gene that has been identified.

Treatment

Presently, there is no cure for Usher syndrome. The best treatment involves early identification in order to begin educational programs. The exact nature of these educational programs will depend on the severity of the hearing and vision impairments as well as the age and abilities of the individual. Typically, individuals will benefit from adjustment and career counseling; access to technology such as hearing aids, assistive listening devices, or cochlear implants; orientation and mobility training; and communication services and independent-living training that may include braille instruction, low-vision services, or auditory training.

 

References:

National Institute on Deafness and Other Communication Disorders, USA.

Genetics Home Reference, U. S. National Library of Medicine.