Usher Syndrome

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Usher Syndrome

Definition

Usher syndrome is an inherited condition that causes hearing loss and a form of vision loss, called retinitis pigmentosa (RP), which worsens over time. Some people with Usher syndrome also have difficulties with balance and/or psychological problems. Although the symptoms of Usher syndrome were first described in 1858 by an ophthalmologist named Albrecht von Graefe, it was not until 1914 that it was well documented and recognized to be a genetic condition by another ophthalmologist, Charles Usher. There are three forms of Usher syndrome: type I, type II, and type III. Genetic research has shown there are many genes located on different chromosomes, all of which can lead to one of the types of Usher syndrome if they are altered.

Description

Usher syndrome is sometimes called hereditary deafness—retinitis pigmentosa, or retinitis pigmentosa and congenital deafness. Usher syndrome causes a specific type of hearing impairment called sensorineural hearing loss (SNHL). In order to understand how SNHL occurs, it is important to first understand how normal hearing works. The ear can be divided into three main parts: the outer ear, the middle ear and the inner ear. The parts of the outer ear include the pinna (the visible portion of the ear), the ear canal and eardrum. The pinna directs sound waves from the environment through the ear canal, toward the eardrum. The eardrum vibrates, and causes tiny bones (called ossicles), which are located in the middle ear, to move. This movement causes pressure changes in fluids surrounding the parts that make up the inner ear. The main structures of the inner ear are the cochlea and the vestibular system. These structures send information regarding hearing and balance to the brain. The cochlea is shaped like a snail shell, and it contains specialized sensory cells (called hair cells) that change the sound waves into electrical messages. These messages are then sent to the brain through a nerve (called the auditory nerve) that allows the brain to "hear" sounds from the environment. The vestibular system is a specialized organ that helps people maintain their balance. The vestibular system contains three structures called semi-circular canals, which send electrical messages to the brain about movement and body position. This allows people to maintain their balance when moving by sensing changes in their direction and speed.

Sensorineural hearing loss occurs when parts of the inner ear (including the cochlea and/or auditory nerve) do not work correctly. The amount (or degree) of hearing loss can be described by measuring the hearing threshold (the sound level that a person can just barely hear) in decibels (dB). The greater a person's dB hearing level, the louder the sound must be to just barely be heard. Hearing loss is often defined as mild, moderate, severe, or profound. For people with mild hearing loss (26-45 dB), understanding conversations in a noisy environment, at a distance, or with a soft-spoken person is difficult. Moderate hearing loss (46-65 dB) causes people to have difficulty understanding conversations, even if the environment is quiet. People with severe hearing loss (66-85 dB) have difficulty hearing conversation unless the speaker is nearby or is talking loudly. Profound hearing loss (>85 dB) may prevent people from hearing sounds from their environment or even loud conversation. People with Usher syndrome generally have moderate, severe or profound SNHL, depending upon the type (I, II, or III) diagnosed.

Usher syndrome also causes a specific type of vision loss called retinitis pigmentosa (RP). In order to understand how RP occurs, it is helpful to first understand how normal vision works. The eye is made up of many different types of cells and tissues that all work together to send images from the environment to the brain, similar to the way a camera records images. When light enters the eye, it passes through the lens and lands on the retina, a very thin tissue lining the inside of the eye. The retina is actually made up of 10 different layers of specialized cells, which allow the retina to function similarly to film in a camera, by recording images. There is a small, yellow-pigmented area called the macula, located in the back of the eye in the center of the retina. The retina contains many specialized cells called photoreceptors, which sense light coming into the eye and convert it into electrical messages that are then sent to the brain through the optic nerve. This allows the brain to "see" the environment.

The retina contains two types of photoreceptor cells: rod cells and cone cells. Rod cells are located primarily outside of the macula and they allow for peripheral (side) and night vision. Most of the photoreceptor cells inside of the macula, however, are the cone cells, which are responsible for perceiving color and for viewing objects directly in front of the eye (central vision). If the retina is diseased, as in RP, night vision and peripheral vision are altered. This happens in RP because the rod and cone cells degenerate (breakdown) and die over time, resulting in night blindness and decreased peripheral vision (also called "tunnel vision"). People with Usher syndrome develop RP at different ages depending upon the type (I, II, or III) diagnosed. Although most people with Usher syndrome have fairly good vision before they reach their 30s, it worsens slowly over time and approximately 75% of people in their 70s are blind.

Usher syndrome type I

People with Usher syndrome type I are born with profound SNHL that occurs in both ears. As a result, they do not learn to speak, and typically learn to use sign language to communicate with others. Hearing aids usually are not very helpful, due to the amount of hearing loss present. However, some individuals benefit from a procedure called cochlear implantation, in which a small electronic device is surgically placed behind the ear (underneath the skin) and is attached to a wire that stimulates the inner ear, allowing people to hear useful sounds.

Usher syndrome type I also causes vestibular areflexia, which means affected individuals have balance problems because they cannot sense changes in direction or speed when they are moving. This causes children to develop certain skills that involve motion (such as walking) more slowly, to be clumsier, and to have a hard time with activities that require good balance (such as riding a bicycle). As affected people age, they tend to have an ataxic gait, which means they tend to stumble and shuffle their feet when walking.

The visual problems caused by RP usually develop during childhood among people with this type of Usher syndrome, and they gradually worsen over time. Usually the rod cells in the peripheral retina are affected first, causing night blindness and tunnel vision during childhood. Cone cells may eventually be affected, causing blind spots to develop. Eventually, vision loss worsens and affected people can have vision problems during the day. Cataracts (cloudiness in the lens of the eye) may also develop and cause decreased central vision. Although most people with this type of Usher syndrome do not become completely blind, worsening vision may make communication via sign language and lip reading difficult.

Mental retardation and psychiatric problems (such as depression , bipolar disorder , and psychosis) have been diagnosed in a number of people with Usher syndrome type I as well. Although some authors believe that the stress of losing both hearing and vision may lead to psychological problems, at least one study has suggested that these problems may be due to an overall smaller brain size that has been measured in some affected individuals.

Usher syndrome type II

People with Usher syndrome type II are born with mild to severe SNHL for low frequency sound that occurs in both ears. The SNHL is profound for higher frequency sounds. The amount of hearing loss is different between affected individuals, even those within the same family, although the ability to hear low frequency sound is often maintained. While hearing problems may worsen very slowly over time, speech therapy and the use of hearing aids are often helpful. Unlike people with type I, the vestibular (balance) system is not affected in people with Usher syndrome type II. Thus, they learn to walk on time as children (i.e. at approximately one year) and do not have problems with clumsiness. Although the symptoms of RP do occur among individuals with type II, they generally occur later in life (teenage years or later), compared to people with type I. Symptoms are similar, including night blindness, tunnel vision, blind spots, cataracts, and generally decreased vision. In addition, mental retardation, psychiatric problems, and decreased brain size have been seen in some people with Usher syndrome type II.

Usher syndrome type III

People with Usher syndrome type III may be born with normal hearing or mild hearing loss. However, their hearing loss is progressive, which means that it tends to worsen over time. The vestibular system causes mild balance problems that worsen over time among individuals with Usher syndrome type III. Older affected people may have balance problems similar to those seen in type I. There is a broad age range when the symptoms of RP occur among people with type III, although usually they happen later in life (late teens to early adult years). Vision problems also worsen over time. In addition, mental retardation and psychiatric problems also have been seen in some people with Usher syndrome type III.

People with Usher syndrome and their families often experience emotional and psychological distress. Depression, anger, and grief are common among affected teenagers and adults. The vision and hearing problems create ongoing challenges for people, in terms of their ability to receive information from the world and to effectively communicate with others. Affected people have to continually learn new skills, such as Braille or tactile sign language (i.e. using their hands to physically feel the signs), to adapt to their gradually worsening vision.

Genetic profile

Usher syndrome is inherited in an autosomal recessive manner. "Autosomal" means that males and females are equally likely to be affected. "Recessive" refers to a specific type of inheritance in which both copies of a person's gene pair (i.e. both alleles) need to have a change or "mutation" in order for the disease to develop. In this situation, an affected individual receives a mutated copy of the same gene from each parent. If the parents are not affected, they each have one working copy of the gene and one non-working (mutated) copy, and are only "carriers" for Usher syndrome. The chance that two carrier parents will have a child affected with Usher syndrome is 25% for each pregnancy. They also have a 50% chance to have an unaffected child who is simply a carrier, and a 25% chance to have an unaffected child who is not a carrier, with each pregnancy. In the United States, as many as one in every 70 people may be carriers of a mutation that can lead to Usher syndrome.

Although there are three recognizable types of Usher syndrome (I, II, and III), genetic research has shown that there are numerous genes, located on different chromosomes, that can all lead to Usher syndrome. This indicates that there is genetic heterogeneity among different families with Usher syndrome, meaning that different genes can lead to the same or similar disease among different families. As of February 2001, researchers have identified six different subtypes of Usher syndrome type I (USH1A, USH1B, USH1C, USH1D, USH1E, and USH1F), four subtypes of Usher syndrome type II (USH 2A, USH2B, USH2C, and USH2D), and one type of Usher syndrome type III (USH3). Although specific genes have been identified for only four of the 11 subtypes, the other seven have been linked to specific chromosomal regions.

Genetic Classification of Usher syndrome—February, 2001

USH1A—Located on chromosome 14q32. Specific gene unknown.
USH1B—Located on chromosome 11q13.5. Specific gene called myosin VIIA.
USH1C—Located on chromosome 11p15.1. Specific gene called harmonin.
USH1D—Located on chromosome 10q21-22. Specific gene called CDH23.
USH1E—Located on chromosome 21q21. Specific gene unknown.
USH1F—Located on chromosome 10. Specific gene unknown.
USH2A—Located on chromosome 1q41. Specific gene called usherin.
USH2B—Located on chromosome 3p23-24.2. Specific gene unknown.
USH2C—Located on chromosome 5q14.3-21.3. Specific gene unknown.
USH2D—Chromosome location unknown. Specific gene unknown.
USH3—Located on chromosome 3q21-25. Specific gene unknown.

Although specific genes have been identified for some of the Usher syndrome subtypes (i.e. myosin VIIA, harmonin, CDH23, and usherin), not all mutations in these genes lead specifically to Usher syndrome. For example, although mutations in CDH23 can lead to Usher syndrome type 1D, some people who have certain types of mutations in both of their CDH23 gene copies have a form of autosomal recessive deafness (called DFNB12) in which affected individuals have profound SNHL at birth, but do not have balance or vision changes that are typically seen in Usher syndrome.

Demographics

It is estimated that 2.5-4.5 per 100,000 people are affected with Usher syndrome in various countries, including the United States, Denmark, Sweden, Norway, Finland, and Columbia, although it has been diagnosed in other parts of the world as well. There are some areas where Usher syndrome seems to be more common, including communities in northern Sweden and among the French Acadians in Louisiana. Certain types of Usher syndrome are more common in certain areas of the world as well. For example, among affected people in Finland, approximately 40% have type III. However, in the United States, types I and II are most common and occur with nearly equal frequency, while type III is very rare.

Signs and symptoms

Symptoms of Usher syndrome type I:

Profound hearing loss at birth, causing lack of speech
Lack of vestibular function at birth, leading to delayed ability to walk and increased clumsiness
Retinitis pigmentosa in childhood, causing night blindness, tunnel vision and decreased vision over time
May cause mental retardation or psychiatric problems in some people

Symptoms of Usher syndrome type II:

Mild to severe hearing loss (for low-frequency sound) and profound hearing loss (for high-frequency sound) at birth
Normal vestibular function, resulting in normal ability to maintain balance
Retinitis pigmentosa in teens or early adult years, causing night blindness, tunnel vision and decreased vision over time
May cause mental retardation or psychiatric problems in some people

Symptoms of Usher syndrome type III:

Normal hearing or mild hearing loss at birth that worsens over time
Abnormal vestibular function, causing mild balance problems that worsen over time
Retinitis pigmentosa by teenage or early adult years, causing night blindness, tunnel vision and decreased vision over time
May cause mental retardation or psychiatric problems in some people

Diagnosis

Genetic testing is not readily available for people with Usher syndrome to look for their specific mutations (and thus confirm their diagnosis), in spite of the fact that a number of important genes have been identified. Some families do participate in genetic research studies by providing blood samples, with the hope that useful information may be learned about their genetic mutations, as well as Usher syndrome in general.

The diagnosis of Usher syndrome is based on the results from a variety of tests that measure hearing, vision, and balance. Sometimes the diagnosis is not made until a person with SNHL reaches adolescence and develops vision problems. A follow-up eye examination may allow an eye care specialist to detect changes seen in RP, thus confirming the diagnosis of Usher syndrome. Specialized testing of an affected person's vestibular system can be done to help determine the type of Usher syndrome as well.

Treatment and management

There is no cure for Usher syndrome. However, there are a number of ways to treat various symptoms.

Treatment and management of SNHL

Regular hearing exams are important to check for changes in hearing ability, especially for people with type II or type III Usher syndrome. Among people with milder forms of hearing loss, hearing aids and speech therapy are often useful. Sign language training for people with profound SNHL and their families provides a method of communication, although these skills need to be modified into tactile sign language as vision decreases. Some people with severe to profound forms of hearing loss may have cochlear implants placed in an effort to improve their perception of sound.

Treatment and management of RP

People with night blindness, tunnel vision and decreasing vision may benefit from a variety of techniques that help them cope with their ever-changing vision. The use of walking canes, guide dogs, magnifying lenses, flashlights, and Braille may be helpful. Specialized filtering lenses may decrease glare and make the eye more comfortable. Some people also find it useful to meet with low-vision specialists who can help them adapt to new lifestyle changes that help with daily living. Regular eye exams are important and allow early detection of cataracts, which may be treated with surgery.

Although there is no way to completely halt the symptoms of RP, studies published in the 1990s found that 15,000 IU of vitamin A palmitate can slow the course of the retinal changes among people with Usher syndrome type II. This therapy has not been recommended for people under 18 years of age, and women who may become pregnant need to discuss with their doctor the potential harms that vitamin A can cause for a developing baby. People who want to take the vitamin should speak with their doctor first and have regular blood tests to check vitamin levels as well as to rule out liver problems caused by the supplement.

There are a number of support groups available that provide education, support, and helpful advice to help people cope with the symptoms of Usher syndrome.

Prognosis

Usher syndrome generally does not cause a shortened life span for affected individuals. Although people live for many years with Usher syndrome, the physical symptoms and emotional side effects change over time. The vision problems usually worsen slowly over the years, forcing people to adapt their lifestyles, habits, and sometimes change professions. Regular eye exams can help diagnose cataracts that may be removed in an effort to maintain the best vision possible. Regular monitoring of hearing may be helpful for people with mild, moderate, and/or severe hearing loss, so that they can receive appropriate hearing aids. As vision problems (and sometimes hearing and/or balance problems) worsen, people are more likely to suffer emotionally, due to decreasing quality of life and independence. However, many low-vision devices, lifestyle modifications, and various support groups often provide much needed assistance to help maintain and/or improve quality of life for affected individuals.

Resources

BOOKS

Duncan, Earlene, et al. Usher's Syndrome: What It Is, How to Cope, and How to Help. New York: Charles C. Thomas Publisher, 1988.

Gorlin, R.J., H.V. Toriello, and M.M. Cohen. "Retinitis Pigmentosa and Sensorineural Hearing Loss (Usher Syndrome)." Hereditary Hearing Loss and Its Syndromes. Oxford Monographs on Medical Genetics, no. 28. New York and Oxford: Oxford University Press, 1995.

Stiefel, Dorothy H., and Richard A. Lewis. The Madness of Usher's: Coping With Vision and Hearing Loss/Usher Syndrome Type II. Business of Living Publishing, 1991.

PERIODICALS

Keats, Bronya J.B., and David P. Corey. "The Usher Syndromes." American Journal of Medical Genetics 89, no. 3 (September 24, 1999): 158-166.

Kimberling, William J., Dana Orten, and Sandra Pieke-Dahl. "Genetic Heterogeneity of Usher Syndrome." Advances in Oto-rhino-laryngology 56 (December 2000): 11-18.

Miner, I.D. "People with Usher Syndrome, Type II: Issues and Adaptations." Journal of Visual Impairment & Blindness 91, no. 6 (November/December 1997): 579-590.

Miner, I.D. "Psychosocial Implications of Usher Syndrome, Type I, Throughout the Life Cycle." Journal of Visual Impairment & Blindness 89, no. 3 (May/June 1995): 287-297.

Steel, Karen P. "New Interventions in Hearing Impairment." British Medical Journal 7235 (March 4, 2000): 622-626.

ORGANIZATIONS

American Council of the Blind. 1155 15th St. NW, Suite 720, Washington, DC 20005. (202) 467-5081 or (800) 424-8666. <http://www.acb.org>.

Boys Town National Research Hospital. 555 N. 30th St., Omaha, NE 68131. (402) 498-6749. <http://www.boystown.org/Btnrh/Index.htm>.

DB-LINK, Teaching Research. 345 N. Monmouth Ave., Monmouth, OR 97361. (800) 438-9376. <http://www.tr.wou.edu/dblink/about.htm>.

Foundation Fighting Blindness Executive Plaza 1, Suite 800, 11350 McCormick Rd., Hunt Valley, MD 21031. (888) 394-3937. <http://www.blindness.org>.

Helen Keller National Center for Deaf-Blind Youths and Adults. 111 Middle Neck Rd., Sands Point, NY 11050. (516) 944-8900. <http://www.helenkeller.org/national/index.htm>.

Usher Family Support. 4918 42nd Ave. South, Minneapolis, MN 55417. (612) 724-6982.

Vestibular Disorders Association. PO Box 4467, Portland, OR 97208-4467. (800) 837-8428. <http://www.vestibular.org>.