|
Usher Syndrome
What is Usher syndrome?
Usher syndrome (US) 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 US are hearing impairment
and an eye disorder called retinitis pigmentosa, in which vision worsens
over time. Some people with US also have balance problems. There are three
different types of US. Although it was first described by Albrecht Von
Graefe in 1858, US was named for Charles Usher, a British eye doctor,
who believed that this condition was inherited or passed from parents
to their children.
Who
is affected by Usher syndrome?
More than half of
the estimated 16,000 deaf-blind people in the United States are believed
to have US.
What causes Usher syndrome?
US is inherited or
passed from parents to their children through genes. Genes are located
in every cell of the body and contain the instructions that tell cells
what to do. Some genes specify traits such as hair color. Other genes
are involved in the development of body parts, such as the ear. Still
others determine how parts of the body work. Each person inherits two
copies of each gene; one gene comes from each parent. Sometimes genes
are altered or mutated. Mutated genes may cause cells to act differently
than expected.
US is passed along in families
by autosomal recessive inheritance, which requires two copies of the
US gene before the disorder is seen. Each parent of a child with US
usually has one standard and one mutated US gene. A child with US receives
two mutated genes, one from each parent. Usually parents are unaware
that they have or carry a US gene. This is because they would need two
of the mutated genes in order to have signs of US. Presently, at least
eight different genes are thought to cause the various types of US.
What are the types of Usher syndrome?
The three types of
US are called US type 1 (US1), US type 2 (US2), and US type 3 (US3).
US1 and US2 are the most common types of US. Together, US1 and US2 account
for approximately 10 percent of all cases of children who are born deaf.
What are the characteristics of the three types of Usher syndrome?
People with US1 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 US1 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.
Those with US2 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. Retinitis pigmentosa,
which is a degeneration of the retina or the part of the eye that receives
images of objects, is characterized by blind spots that begin to appear
shortly after the teenage years. The visual problems in US2 tend to
progress more slowly than the visual problems in US1. When an individual's
vision deteriorates to blindness, his or her ability to read speech
from the lips is lost.
Children born with US3 have
normal hearing and normal to near-normal balance. Hearing worsens over
time. Children develop noticeable hearing problems by their teenage
years and usually become deaf by mid to late adulthood. Retinitis pigmentosa
in the form of 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.
How is Usher syndrome diagnosed?
Hearing loss and
retinitis pigmentosa are rarely found in combination. Therefore, most
people who have retinitis pigmentosa and hearing loss probably have
US1 or US2. Special tests such as electronystagmography (ENG) to detect
balance problems and electroretinography (ERG) to detect retinitis pigmentosa
help doctors to detect US early. Early diagnosis is important in order
to begin special educational training programs to help the individual
deal with the combined hearing and vision difficulties.
How is Usher syndrome treated?
Presently, there
is no cure for US. 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.
What research is being conducted on Usher syndrome?
The current emphasis
of US research is locating the genes that cause the syndrome and identifying
the function of those genes. This research will lead to improved genetic
counseling and early diagnosis, and may eventually expand treatment
options. Scientists are also developing mice that have the same characteristics
as humans who have the various types of US. Mouse models will make it
easier to determine the function of the various genes involved in US.
Research is also being conducted to improve the early identification
of children with the syndrome. Treatment strategies such as the use
of cochlear implants for hearing impairment and intervention strategies
to alleviate retinitis pigmentosa are also being examined.
Where
can I get additional information?
For further scientific information
about the molecular biology of US:
February 1999
Updated April 1999
NIH Pub. No. 98-4291
For more information, contact
the health.htm#contact">NIDCD Information Clearinghouse.
|
.gif)
