Usher Syndrome is a genetic disorder with hearing loss and retinitis pigmentosa which causes a progressive loss of vision. Some individuals also have balance problems. There are three types of Usher Syndrome.
Type I: born with a profound hearing loss, retinitis pigmentosa, and balance problems.
Type II: born with a moderate to severe hearing loss, retinitis pigmentosa, and no balance problems.
Type III: hearing loss that gets worse over time, retinitis pigmentosa, and may have balance problems.
Individuals with Type I Usher Syndrome have a profound hearing loss in all frequencies and are considered to be deaf from birth.
Individuals with Type II Usher Syndrome have a moderate hearing loss in the lower frequencies. In the higher frequencies it is severe or profound. The loss does not get worse as the person ages. These persons are considered to be hard-of-hearing and usually find hearing aids to be useful.
Individuals with Type III Usher Syndrome have a progressive hearing loss which gets significantly worse as the person ages. Most of the documented Type III cases are in Finland.
RP is an eye disease that causes gradual loss of vision. The eye becomes less able to adjust to low light, resulting in night blindness. As RP progresses, the field of vision narrows until only central vision remains. This is called "tunnel vision". Many persons with Usher Syndrome will retain at least some central vision for a long time.
There are three senses we use to keep our balance: vision (we see where we are), proprioception (we feel the position of our bodies and limbs), and vestibular (we feel changes in speed and direction).
Persons with Type I have a vestibular system that does not work. They cannot feel changes in speed or direction and as their vision decreases, their visual balance system becomes less reliable.
Persons with Type II have a normal vestibular system but their visual system also becomes less reliable as their vision decreases.
We don't know much about the vestibular system of persons with Type III. As more information on Type III becomes available, a more clear picture of vestibular function will emerge.
Usher Syndrome is a genetic condition. Genes carry the "blueprint" for each living thing. Genes always come in pairs. One of each pair comes from our mother and the other from our father. In turn, we pass only one gene from each pair to each of our children. Which gene we receive from a parent is determined randomly. Just as when we flip a coin, whether it comes up heads or tails is a random event.
When the genes from our mother and father come together in the fertilized egg cell, they arrange themselves in pairs. Genes carry the necessary information to cause that single cell to grow into a human being.
Occasionally, something happens that causes a gene to change. Geneticists call this a mutation. It is estimated that each of us have several mutated genes. Most of the time these mutations have no effect on the individual, but sometimes they do.
A person, who has a pair of genes made up of one gene that is changed (could cause Usher Syndrome) and one gene that has not been changed, will not have Usher Syndrome. However, this person will be a carrier of Usher Syndrome. It is estimated that about 1 in every 70 people carry an Usher gene. Most of them do not know they carry the gene. If a couple are both carriers, they could have children with Usher Syndrome. If the child receives the changed gene from each parent, that child will have a pair of changed genes. When a person has a pair of changed genes, he or she will have Usher Syndrome. (see diagram below)
Usher Syndrome is called a recessive condition because a person must have a pair of altered genes before they have the syndrome. If a person receives only one Usher causing gene (the other gene of the pair cannot cause Usher), that person will not have Usher Syndrome. But, like the parents, that person will be a carrier of Usher Syndrome.
If a person who has Usher Syndrome marries a person who is not a carrier, none of their children will have Usher Syndrome. However, all of their children will be carriers. If a person who carries Usher Syndrome marries a person who does not, none of their children will have Usher Syndrome. But, there is a 1 in 2 chance that each child will be a carrier. If two people with Usher Syndrome (caused by the same gene) marry, all of their children will have Usher Syndrome.
Your local genetic counseling clinic can provide additional information if you are interested. That information will be tailored to your situation and needs.
The geneticists at Boys Town National Research Hospital, under the direction of Dr. William Kimberling are conducting studies designed to identify the genes that cause Usher Syndrome.
They have identified the gene which causes most of the cases of Usher Type I. It is on chromosome 11 and has been named Ush 1b. Although it is now known to be a Myosin VIIa gene, much work remains to be done toward understanding how the gene causes Usher Type I. Two additional genes that cause Usher Type I have also been localized. One of the genes is on the other end of chromosome 11 and is called Ush 1c. The other gene is on chromosome 14 and is called Ush 1a. Both genes remain to be identified.
In 1998, Dr. Kimberling's group identified the gene that causes most cases of Usher Type II. It is called Ush 2a and codes for a newly identified protein, laminush. Their test results also indicate that another gene exists that causes Usher Type II symptoms. It is called Ush 2b.
The gene that causes Usher Type III has been localized to chromosome 3 but remains to be identified.
Dr. Kimberling needs additional families to help identify these other genes. All families will be screened for the Ush 1b or Ush 2a gene. Those families whose Usher Syndrome is caused by one of these genes will be notified and offered the information about the mutations. As other genes are identified, families with the mutations will be notified.
As these genes are identified, they will be described and studied to determine how they produce the various types of Usher Syndrome. This information will be a significant addition to our understanding of how we hear and see. Additionally, we hope that clinical testing will be developed to positively diagnose these conditions and identify the carriers.
The success of our research is dependent upon the participation of individuals with Usher Syndrome and their families. Participation involves completion of a family medical history form, release of medical records documenting the diagnosis of Usher Syndrome, and (in most cases) donation of blood samples by various family members. In some cases hearing, balance, and visual testing may be requested. The research group is eager to make participation easy with no cost to families. All information is kept strictly confidential.
If you would like more information or would like to participate in the Usher Syndrome study, the research group can be contacted at:
Or Call/E-mail us at:
(800) 835-1468 (TTY/V)
Kimber@Boystown.Org
Fowler@Boystown.Org
World Wide Web: http://www.boystown.org
Since 1989, the Usher Syndrome Research Group of Boystown National Research Hospital have described their findings in over 25 papers published in various scientific journals. Some of them are: The American Journal of Human Genetics, Journal of American Academy of Audiologists, Journal of Medical Genetics, Genomics, International Journal of Pediatric Otorhinolaryngology, Nature, and Laryngoscope.
Original address of this page:
www.boystown.org/genetics/usher.htm
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