Whatis Usher Syndrome?
Usher Syndrome is a genetic disorder with hearing loss and retinitispigmentosa which causes a progressive loss of vision. Some individualsalso have balance problems. There are three types of Usher Syndrome.
Type I: born with a profound hearing loss, retinitis pigmentosa, andbalance 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 lossin all frequencies and are considered to be deaf from birth.
Individuals with Type II Usher Syndrome have a moderate hearing lossin 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 consideredto be hard-of-hearing and usually find hearing aids to be useful.
Individuals with Type III Usher Syndrome have a progressive hearingloss which gets significantly worse as the person ages. Most of the documentedType III cases are in Finland.
Retinitis Pigmentosa (RP)
RP is an eye disease that causes gradual loss of vision. The eye becomesless able to adjust to low light, resulting in night blindness. As RP progresses,the field of vision narrows until only central vision remains. This iscalled "tunnel vision". Many persons with Usher Syndrome will retain atleast some central vision for a long time.
There are three senses we use to keep our balance: vision (we see wherewe 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. Theycannot 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 visualsystem also becomes less reliable as their vision decreases.
We don't know much about the vestibular system of persons with TypeIII. As more information on Type III becomes available, a more clear pictureof vestibular function will emerge.
What causes Usher Syndrome?
Usher Syndrome is a genetic condition. Genes carry the "blueprint" foreach living thing. Genes always come in pairs. One of each pair comes fromour mother and the other from our father. In turn, we pass only one genefrom each pair to each of our children. Which gene we receive from a parentis determined randomly. Just as when we flip a coin, whether it comes upheads or tails is a random event.
When the genes from our mother and father come together in the fertilizedegg cell, they arrange themselves in pairs. Genes carry the necessary informationto cause that single cell to grow into a human being.
Occasionally, something happens that causes a gene to change. Geneticistscall this a mutation. It is estimated that each of us have several mutatedgenes. 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, willnot have Usher Syndrome. However, this person will be a carrier of UsherSyndrome. It is estimated that about 1 in every 70 people carry an Ushergene. Most of them do not know they carry the gene. If a couple are bothcarriers, they could have children with Usher Syndrome. If the child receivesthe changed gene from each parent, that child will have a pair of changedgenes. When a person has a pair of changed genes, he or she will have UsherSyndrome. (see diagram below)
Usher Syndrome is called a recessive condition because a person musthave a pair of altered genes before they have the syndrome. If a personreceives only one Usher causing gene (the other gene of the pair cannotcause 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 theirchildren will be carriers. If a person who carries Usher Syndrome marriesa 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 twopeople with Usher Syndrome (caused by the same gene) marry, all of theirchildren will have Usher Syndrome.
Your local genetic counseling clinic can provide additional informationif you are interested. That information will be tailored to your situationand needs.
What research is being done on Usher Syndrome?
The geneticists at Boys Town National Research Hospital, under the directionof Dr. William Kimberling are conducting studies designed to identify thegenes that cause Usher Syndrome.
They have identified the gene which causes most of the cases of UsherType I. It is on chromosome 11 and has been named Ush 1b. Although it isnow known to be a Myosin VIIa gene, much work remains to be done towardunderstanding how the gene causes Usher Type I. Two additional genes thatcause Usher Type I have also been localized. One of the genes is on theother end of chromosome 11 and is called Ush 1c. The other gene is on chromosome14 and is called Ush 1a. Both genes remain to be identified.
Dr. Kimberling's group has narrowed the search for the gene that causesmost cases of Usher Type II to a very small area on chromosome 1. It iscalled Ush 2a and they hope to identify it soon. Their test results alsoindicate that another gene exists that causes Usher Type II symptoms. Itis called Ush 2b and its location is unknown.
The gene that causes Usher Type III has been localized to chromosome3 but remains to be identified.
As these genes are identified, they will be described and studied todetermine how they produce the various types of Usher Syndrome. This informationwill be a significant addition to our understanding of how we hear andsee. Additionally, we hope that clinical testing will be developed to positivelydiagnose these conditions and identify the carriers.
Who may participate in Usher research?
The success of our research is dependent upon the participation of individualswith Usher Syndrome and
their families. Participation involves completion of a family medicalhistory form, release of medical records documenting the diagnosis of UsherSyndrome, and (in most cases) donation of blood samples by various familymembers. In some cases hearing, balance, and visual testing may be requested.The research group is eager to make participation easy with no cost tofamilies. All information is kept strictly confidential.
If you would like more information or would like to participate in theUsher Syndrome study, the research group can be contacted at:
BTNRH- Genetics Department
Usher Syndrome Project
555 N 30th Street
Omaha, NE 68131
Or Call/E-mail us at:
(800) 835-1468 (TTY/V)