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USHER SYNDROME - MEDICAL

Related Information:

Definition:

Usher Syndrome means a child is born with deafness or hearing loss and then loses vision due to RP (Retinitis Pigmentosa).  Both conditions must be present and together are caused by a single gene.

Frequency:

About 3-6% of all deaf children and perhaps an equal number of hard-of-hearing children have Usher Syndrome, which itself is more than one genetic condition.   It has been estimated that about 1 in 10,000 adults have Usher Syndrome (all types).

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Types:

On the basis of clinical findings at least three types exist (Table 1) while gene localization studies show that one clinical type may be due to several different genes located on different chromosomes. The most important clinical distinctions are based on the differences in hearing and balance while the RP may look the same even to an experienced eye doctor except that the symptoms can begin earlier in Type I. Usher Syndrome is one of several conditions in which both hearing loss and retinitis pigmentosa (RP) are present. In this article the symptoms of RP, the various forms of Usher Syndrome and some of the features of other syndromes will be discussed. Suggestions will be given on where to go for further diagnosis and information.

Table 1: Types of Usher Syndrome

SymptomType 1Type 2Type 3
Hearing LossBorn deaf with profound hearing loss and have a "corner audiogram" with responses only to very loud low tones.Born hard of hearing with a sloping sensorineural loss from mild loss in low frequencies to severe-profound loss in high frequencies.Onset of hearing loss 0-40yr. Progresses rapidly (often over 10-15yr.) to profound deafness. Ski-slope audiogram with speed bump.
BalanceAbsent inner ear balanceNormal inner ear balanceSome balance disturbance, progressive
Gene LocationNight blindness in infancy or early childhood. Blind spots by late childhood or teens. Legally blind by early adulthood.Night blindness in childhood or teens. Blind spots by late teens or early adulthood. Legally blind in early to mid adulthood.Similar to Type 2
Vision Loss from RP1A: Long arm of 14
1B: Long arm of 11 (most common worldwide)
1C: Short arm of 11 (most of Acadian descent from Louisiana)
1D: Long arm of 10
1E: Long arm of 21
1F: Long arm of 10
1G Long arm of 17
2a: Long arm of 1
2b: Short arm of 3
2c: Long arm of 5
3: Long arm of 3

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Retinitis Pigmentosa:

RP affects the sensory cells in the retina, which is the layer lining the inside of the eye. The retina itself is made up of several layers of interconnecting cells, two of which are called rods and cones. These cells gradually deteriorate and die in RP and many other so-called retinal dystrophies. The 150 million rods in each eye control night vision so that people can see in dim light. Rods are spread throughout the retina except in the fovea, which is the spot in the center back directly behind the pupil. The fovea contains only cones which control day vision and are important for seeing fine details and color. Surrounding the fovea is the macula which is rich in cones, but cones are also scattered throughout the rest of the retina. About 7 million cones are present in each retina. By the time the cones deteriorate doctors can see distinctive changes when they look at the retina. These include pigment dispersion, which means that some parts appear lighter than others, followed by "bone spicules" which are jagged black spots which look like small fragments of bone. The blood vessels become narrow or "attenuated" and the optic disc (nerve) develops a pale and waxy yellow appearance. All of these changes get worse as the disease progresses.

Symptoms Of RP:

In RP rods deteriorate first, then cones. This means night blindness occurs first followed by blind spots and then slowly progressive tunnel vision during the day. When night blindness is present early in life, infants may not be able to reach for a bottle in the dark. In some cases toilet training is delayed because young children may be afraid to go to the bathroom unless night lights are on. When leaving the car at night to go into the house, they may have to hold on to an adult's hand or follow a railing. Later at camp, they may not be able to find the way to the latrine. In residential school dormitories, they may have problems going down the darkened halls or recognizing friends waving to them. Seeing people signing in a dark room or theater becomes difficult or impossible.

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Blind spots (called scotomas) develop in well-lighted conditions when cones begin to die. These are recognized during the day several years after night vision problems are noted. At first, the children do not notice anything wrong because the blind spots are in the peripheral (side) vision. If something seems to be missing, individuals with RP usually move their eyes (called scanning) and then the image appears again because they are using the healthy part of the retina. Over several years the blinds spots get bigger, and more develop until a ring-shaped blind spot is present. At this stage a person can see at the extreme periphery (out toward the shoulder) but nothing between the outer rim of the glasses to the middle. Excellent vision, even 20/20 vision, may remain in the center. A person is declared "legally blind" when only 20 degrees of central vision remain even if some vision is still present way out to the sides. Even at this stage many people do not recognize how much they do not see because they have learned how to scan so rapidly. Nevertheless, they may miss curbs, stairs or other objects in front of their feet because they have a lower visual field defect. At the table they may reach for something they see clearly but knock over something else in the path which they have not seen. They may bump into open doors, not seeing the narrow edge of the door or lifting their heads at the kitchen counter, bang their heads on an open cupboard door. By this time bright lights become glaring and rapid changes in light (light going outside) may be dazzling. It takes longer to adapt to new lighting conditions.

Central vision loss may occur much later though some people may retain 5-10 degrees of good vision into old age. Three things may affect central vision: (1.) The cone cells in the fovea may die, though this is usually late in life. (2.) The macula may become swollen (called cystoid macular edema). This condition can be treated, at least for a while, with medication which makes the swelling go down. (3.) Cataracts may develop in the lens, which sits behind the pupil (black hole in the front of the eye) and focuses the image on the retina. Cataracts occur at about 20-40 years. Since they sit right in the line of sight, they may blur the central vision. Fortunately, cataract operations are quite safe and effective and removal can restore central vision though the retinal problems could have progressed in the meantime.

The symptoms of retinal disease follow this pattern in Usher Syndrome but may be somewhat different in other conditions known collectively as rod-cone dystrophy, cone-rod dystrophy or retinal dystrophy. In all cases, both rods and/or cones deteriorate, but the timing may be different.

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Hearing Loss In Usher Syndrome:

The hearing loss is profound in Type 1 (see audiograms). Many people say they get little or no benefit from hearing aids. Those few children who have had cochlear implants can distinguish some sounds, even those related to speech, but still do not understand speech clearly. The vast majority use sign language as their primary mode of communication and are culturally deaf.

In Type 2 children are born hard of hearing and are able to detect low tones better than high tones. Only a small amount of additional loss (about 10-20 dB) occurs over a lifetime and, at least in some instances, may be due to noise exposure or aging. Even within a family, however, there may be some difference in severity from person to person. With hearing aids they do well in regular classrooms, usually with preferential seating in the front of the class and sometimes separate classes. These children most commonly use oral speech and language and are culturally hearing though a few have moderate to profound hearing loss and have gone to schools for the deaf. When vision deteriorates, they lose the ability to read speech from the lips. Since the hearing aid does not fully correct the hearing loss, they may become functionally DeafBlind particularly in noisy dark environments such as restaurants or bars in the evening, at dances or other social events. They may then choose to use FM systems, avoid such environments, or learn sign language.

Type 3 has not been as well defined as the other two types. A fairly large group of people in central Finland are being studied and a couple of other cases have been reported elsewhere. Onset of hearing loss can be anytime from infancy to midadulthood. The hearing loss gets steadily worse over 10-15 years leading to profound deafness. The audiogram shape is much like Type 2 except for "speed-bump" upturn in the higher frequencies.

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Balance In Usher Syndrome:

All individuals with Type 1 tested, to date, in the balance laboratory have absent vestibular function. This means that the semicircular canals of the inner ear, which let a person know what position the head is in, have not worked since birth. The consequence of vestibular dysfunction is that babies have a hard time learning how to crawl and walk. They may prefer to roll rather than get up on all fours, or they may have a "five-point" crawl with their heads down on the ground. Walking is delayed to 15-18 months or even later. Children are considered clumsy at least until they establish good control of their muscles and joints. Physical education teachers can often pick out the children with balance problems if they cannot turn quickly, walk on a balance beam, etc. On the other hand, they love twirling and merry-go-rounds because they do not get dizzy. Once children have developed good muscle control, they have no problem walking or running as long as they can see or they know where they are going. When they lose vision, they become unsure of themselves again and are less steady on their feet. Those with Type 2 have perfectly normal inner ear balance. About half of those with Type 3 have poor but not absent vestibular function. Whether the loss is progressive is not yet known. The other half have normal vestibules.

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Gene Studies In Usher Syndrome:

All types of Usher Syndrome are caused by autosomal recessive genes. This means that each parent has one normal and one Usher gene, and each gives the affected child the Usher gene. The child then has no normal gene at that locus but two Usher genes. Table 1 shows that 6 separate genes have been located for Type 1. Two of these genes are on chromosome number 11 and one on 14. Most people tested "map" to the long arm of 11 (USH 1B). Those individuals of Acadian heritage, most of whom live in Louisiana, have the gene locus on the short arm of 11 (USH 1C). The first of the genes discovered was on the long arm of 14 (USH 1A) and was described in a small region of France; however, now people in the United States have also mapped to this region. The USH 1D and 1F may be the same gene.

Three genes have been identified for Type 2. The gene Type 3 is located on the long arm of chromosome number 3. What all this means is that there is more than one underlying biochemical cause for combined hearing loss and RP. Even when people appear to have the same clinical subtype, the genes causing the condition may be different. This is much like having a measles-like rash, which can be caused by many different viruses including those which cause regular measles and German measles.

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Other Hearing Loss/RP Conditions:

Usher Syndrome only affects the eyes and ears!  If something else is present, like mental retardation, obesity, extra fingers, etc., another syndrome may be the cause.  A number of conditions may be confused with Usher Syndrome. Each of these syndromes has eye findings like RP or hearing loss patterns similar to Usher but have abnormalities of other body parts as well. In addition, it is possible for a person to have genetic RP and non-genetic or even a different genetic type of hearing loss. Sometimes the diagnosis of Usher Syndrome is given by an eye doctor or ear doctor who may not be aware of these other syndromes or is not aware that the patient they are examining has other problems. If families suspect that one of these other conditions may be present, they can request an evaluation by a clinical geneticist.

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Resources:

Genetic evaluation: Most medical schools have a clinical genetics division, which may be part of the department of pediatrics, internal medicine or obstetrics/gynecology. Your doctor should be able to locate the nearest geneticist or call:

American College of Medical Genetics  (ACMG)
9650 Rockville Pike
Bethesda, MD 20814-3998
Telephone 301-530-7127
Fax 301-571-0677
E-mail: acmg@faseb.org

Deafblindness: Note that any degree of hearing loss combined with any degree of vision loss which interferes with communication and acquiring information is considered DeafBlind even though a person may still have some useful vision and hearing.

The Helen Keller National Center
(Ask for the Helen Keller representative or affiliate in your region)
111 Middle Neck Road
Sands Point NY 11050
(516) 944-8900 (Voice & TTY)
(516) 944-7302 (FAX)
Website: http://www.hknc.orgOpen in new window. Link to a different web site.

The National Consortium on Deaf-Blindness
The Teaching Research Institute
345 N Monmouth Avenue
Monmouth, OR 97361
(800) 438-9376 (Voice)
Website: http://nationaldb.orgOpen in new window. Link to a different web site.

Prepared by

Sandra L.H. Davenport, M.D.
Sensory Genetics/Neuro-development
5801 Southwood Drive
Bloomington, MN 55437-1739
(952) 831-5522 (V/TTY), 831-0381 (FAX)
Email: slhdaven@tc.umn.edu

This article was originally written for Boys Town National Research Hospital and is accessible on their web site in a slightly different version.  http://www.boystownhospital.org/research/molecularstudies/Pages/Ushersyndrome.aspxOpen in new window. Link to a different web site.

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