Description, Causes and Risk Factors:
Autosomal recessive inheritance with genetic heterogeneity; the three forms are distinguishable by linkage data: type 1 causes sensorineural hearing loss, loss of vestibular function, and retinitis pigmentosa; types 2 and 3 are characterized by hearing loss and retinitis pigmentosa.
Usher syndrome is an inherited disorder that involves both a hearing impairment and a vision impairment called retinitis pigmentosa. Some people also have varying problems with balance. Usher syndrome is passed from parents to their children genetically.
Usher syndrome is the most common condition that affects both hearing and vision. A syndrome is a disease or disorder that has more than one feature or symptom. The major symptoms of Usher syndrome are hearing loss and an eye disorder called retinitis pigmentosa, or RP. RP causes night-blindness and a loss of peripheral vision (side vision) through the progressive degeneration of the retina. The retina is a light-sensitive tissue at the back of the eye and is crucial for vision. As RP progresses, the field of vision narrows—a condition known as “tunnel vision”—until only central vision (the ability to see straight ahead) remains. Many people with Usher syndrome also have severe balance problems.
There are three clinical types of Usher syndrome: Type 1, type 2, and type 3.
Type 1 - characteristics include:
Do not usually benefit from hearing aids.
Severe balance problems.
Vision problems begin by age 10.
Blindness eventually occurs.
Profoundly deaf from birth.
Type 2 (US2) - characteristics include:
Usually benefit from hearing aids.
Use speech to communicate.
Retinitis pigmentosa begins in teenage years.
Moderate to severe hearing problems.
Type 3 (US3) - characteristics include:
Hearing problems develop in teenage years.
Near normal balance.
Deafness by late adulthood.
Retinitis pigmentosa begins around puberty.
Blindness by mid-adulthood.
Born with normal hearing.
Approximately 3 to 6 percent of all children who are deaf and another 3 to 6 percent of children who are hard-of-hearing have Usher syndrome. In developed countries such as the United States, about four babies in every 100,000 births have Usher syndrome.
Usher syndrome is inherited, which means that it is passed from parents to their children through genes. Genes are located in almost every cell of the body. Genes contain instructions that tell cells what to do. Every person inherits two copies of each gene, one from each parent. Sometimes genes are altered, or mutated. Mutated genes may cause cells to act differently than expected.
Usher syndrome is inherited as an autosomal recessive trait. The term autosomal means that the mutated gene is not located on either of the chromosomes that determine a person's sex; in other words, both males and females can have the disorder and can pass it along to a child. The word recessive means that, to have Usher syndrome, a person must receive a mutated form of the Usher syndrome gene from each parent. If a child has a mutation in one Usher syndrome gene but the other gene is normal, he or she is predicted to have normal vision and hearing. People with a mutation in a gene that can cause an autosomal recessive disorder are called carriers, because they “carry” the gene with a mutation, but show no symptoms of the disorder. If both parents are carriers of a mutated gene for Usher syndrome, they will have a one-in-four chance of having a child with Usher syndrome with each birth.
Usually, parents who have normal hearing and vision do not know if they are carriers of an Usher syndrome gene mutation. Currently, it is not possible to determine whether a person who does not have a family history of Usher syndrome is a carrier. Scientists at the National Institute on Deafness and Other Communication Disorders are hoping to change this, however, as they learn more about the genes responsible for Usher syndrome.
Because Usher syndrome affects hearing, balance, and vision, diagnosis of the disorder usually includes the evaluation of all three senses. Evaluation of the eyes may include a visual field test to measure a person's peripheral vision, an electroretinogram (ERG) to measure the electrical response of the eye's light-sensitive cells, and a retinal examination to observe the retina and other structures in the back of the eye. A hearing (audiologic) evaluation measures how loud sounds at a range of frequencies need to be before a person can hear them. An electronystagmogram (ENG) measures involuntary eye movements that could signify a balance problem.
Early diagnosis of Usher syndrome is very important. The earlier that parents know if their child has Usher syndrome, the sooner that child can begin special educational training programs to manage the loss of hearing and vision.
Special tests assist in the diagnosis of Usher syndrome, including:
Electronystagmography (ENG) to detect balance problems.
Electroretinography (ERG) to detect retinitis pigmentosa.
A retinal examination.
Balance tests for all patients age ten years and older.
Currently, there is no cure for Usher syndrome. Specific treatment for Usher syndrome will be determined by your physician based on:
Your age, overall health, and medical history.
Extent of the disease.
Your tolerance for specific medications, procedures, or therapies.
Expectations for the course of the disease.
Your opinion or preference.
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.
Some ophthalmologists believe that a high dose of vitamin A palmitate may slow, but not halt, the progression of retinitis pigmentosa. People who are considering taking vitamin A should discuss this treatment option with their health care provider before proceeding.
Treatment strategies such as the use of cochlear implants for hearing loss, and intervention strategies to help slow or stop the progression of RP.
Researchers are currently trying to identify all of the genes that cause Usher syndrome and determine the function of those genes. This research will lead to improved genetic counseling and early diagnosis, and may eventually expand treatment options.
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.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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