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About 3-6 percent of all deaf children and perhaps an equal number of hard-of-hearing children have Usher syndrome (US), which itself is more than one genetic condition. On the basis of clinical findings, at least three types exist . 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. The retinitis pigmentosa (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 are present. In this article, the symptoms of RP and the various forms of Usher syndrome will be discussed. Suggestions will be given on where to go for further diagnosis and information.

Retinitis Pigmentosa (RP)

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 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 little jagged spots. 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.

Other Hearing Loss/Retinitis Pigmentosa (RP) Conditions.

There are a number of conditions which may be confused with Usher syndrome. Rubella (German measles) used to be one of the most commonly suspected conditions. Because the pigment disperses leaving light and dark spots, the retina is said to have a "salt and pepper" appearance. Sometimes this pattern can be seen in early RP and the eye doctor can misinterpret the condition as Rubella. Since Rubella is much less common now than in the 1960s and early 1970s, the diagnosis of Usher syndrome should be considered in cases with salt and pepper pigmentation patterns. Other syndromes have eye findings or hearing loss patterns which are different from those in Usher syndrome as well as abnormalities of other body parts.

Find Your Own Blind Spot.

Everyone has a blind spot in each eye where the nerve to the brain connects to the back of the eyeball. To find yours, try the following. Draw two X's on a piece of paper about 3 inches apart. Hold the paper away at normal reading distance. Close your right eye. With your left eye look at the right X but notice the left X in your peripheral vision. Continue looking at the right X as you move the paper toward your eyes. At about 10 inches from your eye, the left X will disappear.

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. Two of these genes are on chromosome #11 and one on #14. Most people have the Usher gene on the long arm of chromosome #11. Those individuals of Acadian heritage, most of whom live in Louisiana, have the gene on the short arm of #11. The first of the genes discovered was on the long arm of #14 and was described in a small region of France; however, now people in the United States have been found who also have the Usher gene in this region. So far, most people with Type 2 have a deficient gene on the long arm of chromosome #1. A few families with typical Type 2 symptoms do not have the gene in this region, implying that there is another locus. No gene has yet been located for Type 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.

Information & Referral.

Genetic Evaluation.

If you have questions about a hearing/vision loss syndrome, the staff at Boys Town may be able to assist you, but some questions cannot be answered without a detailed genetics 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
 

The American Society of Human Genetics,
9650 Rockville Pike,
Bethesda MD 20814-3889,
(301) 571-1825.

Note that any degree of hearing loss combined with any degree of vision loss which interferes with communication and acquiring information is considered deaf-blind 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).

The National Information Clearinghouse on Children Who Are Deaf-Blind at DB-Link,
(800) 438-9376 (Voice),
(800) 854-7013 (TTY).

The RP Foundation Fighting Blindness,
1401 Mount Royal Avenue,
Baltimore MD 21217,
(800) 638-2300 (Voice),
(310) 225-9400 (Voice)
(301) 225-9409 (TTY).

Usher Family Support [a newsletter by and for families of people with any type of Usher Syndrome],
c/o Helen Anderson,
4918 42nd Avenue South,
Minneapolis
MN 55417

About US [a newsletter by and for people with Usher syndrome Type 2],
c/o Vision Screening Project,
5801 Southwood Drive,
Bloomington MN 55437,
(612) 831-5522 (Voice/TTY).

If you have questions about this or other related topics,contact:
 

The NIDCD Hereditary Hearing Impairment Resource Registry,
c/o Boys Town National Research Hospital,
555 N. 30th St.,
Omaha, NE 68131,
(V/TDD) 800 320-1171.

Source:  "Usher Syndrome," Factsheet, Hereditary Hearing Impairment Resource Registry.

The National Institute on Deafness and Other Communication Disorders (NIDCD) Hereditary Hearing Impairment Resource Registry (HHIRR) was established to become a resource to the biomedical community in the area of hereditary hearing impairment research. The HHIRR disseminates information about hereditary hearing impairment, and collects information from hearing impaired individuals to match families with scientists for appropriate research projects. For more information, contact the

NIDCD HHIRR,
555 N.
30th Street,
Omaha,
NE 68131
or call 1-800-320-1171 (Voice/TDD).

You can find this article and more information from Healthtouch Online at http://www.healthtouch.com

 Copyright © 1999 by Medical Strategies,

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