About Usher Syndrome
What is Usher syndrome?
Usher syndrome is the most common cause of deaf-blindness in the United States. It is a combination of Retinitis Pigmentosa (RP) and some level of hearing loss. There are about 10-15,000 people with Usher syndrome in the United States today.
How is Usher syndrome diagnosed?
- Visual function tests
- Visual fields
- Electroretinogram (ERG)
- Retinal examination
- Hearing tests
- Balance tests
Types of Usher Syndrome
There are three different clinical types of Usher syndrome. They are called Usher syndrome type 1 (US1), Usher syndrome type 2 (US2), and Usher syndrome type 3 (US3). All types of the syndrome are inherited in the same pattern — as autosomal recessive traits.
Usher syndrome type 1 (US1) – People with US1 are born nearly deaf. Eyesight usually begins degrading around the age of 5-10, beginning with night blindness. Generally night blindness precedes tunnel vision by years or even decades. The duration of becoming legally blind spans from as early as childhood to as late as the 40’s. People with US1 also struggle with balance or homeostasis, which is the biological balance within the human body. 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.
Usher syndrome type 2 (US2) – People 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. Retinitis Pigmentosa, which is a degeneration of the retina (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.
Usher syndrome type 3 (US3) – With US3, hearing loss and vision loss due to RP are both progressive.
How is Usher Syndrome Treated?
There is currently no medical treatment for Usher syndrome. Research and genetic testing is currently being conducted.
Cochlear implants have been found to be very affective in patients with severe or profound hearing loss.
How is Usher Syndrome Inherited?
Usher syndrome is inherited or passed from parents to their children through genes. The syndrome is transmitted (passed along) in families by autosomal recessive inheritance, which requires the presence of two copies of the Usher gene for the disorder to be manifest. Each parent of a boy or girl with Usher syndrome is a “carrier” with one standard and one mutated Usher gene but no sign of the syndrome. A child with the syndrome has it because he or she received two mutated Usher genes, one from each of the carrier parents.
The parents’ risk with each future pregnancy is:
- 1 in 4 (25%) that the child will have two mutated Usher genes and have the syndrome.
- 2 in 4 (50%) that the child will have one mutated Usher gene and one standard gene and be an unaffected carrier.
- 1 in 4 (25%) that the child will have two standard and no Usher gene.
If a child without the syndrome from an Usher family marries at random (they don’t marry someone from another known Usher family), the risks for their offspring to have Usher syndrome are less than 1%.
Is Genetic Testing Available?
At this time, genetic testing for Usher syndrome is done only as part of research projects. Usher syndrome is not caused by only one gene. So far, 10 Usher genes have been mapped: 7 for type I, 3 for type II, and 1 for type 3. There are still more genes to find.
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. 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.
Retinitis pigmentosa (RP) is the name given to a group of inherited eye diseases that affect the retina. Retinitis pigmentosa causes the degeneration of photoreceptor cells in the retina. Photoreceptor cells capture and process light helping us to see. As these cells degenerate and die, patients experience progressive vision loss.
There are types of photoreceptor cells: rod cells and cone cells.
Rod cells are concentrated along the outer perimeter of the retina. Rod cells help us to see images that come into our peripheral or side vision. They also help us to see in dark and dimly lit environments.
Cone cells are concentrated in the macula, the center of the retina, and allow us to see fine visual detail in the center of our vision. Cone cells also allow us to perceive color.
Together, rods and cones are the cells responsible for converting light into electrical impulses that are transmitted to the brain where “seeing” actually occurs.
One of the outstanding recent scientific accomplishments that has benefited people affected by hearing loss, is the cochlear implant. The cochlear implant is a small electronic device that is surgically implanted in the mastoid bone behind the ear and in the inner ear. The surgeon places the device through an incision that is masked by the ear.
A cochlear implant consists of four parts:
- microphone that picks up sounds from the environment.
- speech processor that chooses and organizes sounds from the microphone.
- transmitter and receiver stimulator that translates the sounds into electrical impulses.
- series of electrodes that transmit the electrical impulses to the auditory nerve.
In a normal healthy ear, sound waves travel from the outer ear through the middle ear to the inner ear where they are converted into electrical signals by special sensory cells known as nerve hair cells. The electrical signals are then sent to the brain via the auditory nerve.
In people affected by Usher syndrome (as well as other forms of deafness), the nerve hair cells are dead or deformed. The cochlear implant takes the place of these nerve hair cells by converting sounds into the electrical impulses which trigger the auditory nerve.