Usher Syndrome (cont.)
Who is affected by Usher syndrome?
Approximately 3 to 6 percent of all children who are deaf and another 3 to 6
percent of children who are hard-of-hearing have Usher syndrome. In developed
countries such as the United States, about four babies in every 100,000 births
have Usher syndrome.
What causes Usher syndrome?
Usher syndrome is inherited, which means that it is passed from parents to
their children through genes. Genes are
located in almost every cell of the body. Genes contain instructions that tell
cells what to do. Every person inherits two copies of each gene, one from each parent. Sometimes genes are
altered, or mutated. Mutated genes may cause cells to act differently than
expected.
Usher syndrome is inherited as an autosomal recessive trait. The term
autosomal means that the mutated gene is not located on either of the
chromosomes that determine a person's sex; in other words, both males and
females can have the disorder and can pass it along to a child. The word
recessive means that, to have Usher syndrome, a person must receive a mutated
form of the Usher syndrome gene from each parent. If a child has a mutation in
one Usher syndrome gene but the other gene is normal, he or she is predicted to
have normal vision and hearing. People with a mutation in a gene that can cause
an autosomal recessive disorder are called carriers, because they "carry" the
gene with a mutation, but show no symptoms of the disorder. If both parents are
carriers of a mutated gene for Usher syndrome, they will have a one-in-four
chance of having a child with Usher syndrome with each birth.
Usually, parents who have normal hearing and vision do not know if they are
carriers of an Usher syndrome gene mutation. Currently, it is not possible to
determine whether a person who does not have a family history of
Usher syndrome is a carrier. Scientists at the National Institute on Deafness
and Other
Communication Disorders are hoping to change this, however, as they learn more
about the genes responsible for Usher syndrome.
Chances of Inheriting a Recessive Disorder
Genetic disorders can be caused by a change(s) in a gene. Every individual
has two copies of the same gene. Genetic disorders are inherited in different
ways. Usher syndrome is a recessive disorder.
Recessive means:
- a person must inherit a change in the same gene from each parent in order to
have the disorder
- a person with one changed gene does not have the disorder, but can pass
either the changed or the unchanged gene on to his or her child
An individual with Usher syndrome usually:
- has inherited a change in the same gene from each parent
An individual who has one changed Usher syndrome gene is called a carrier.
When two carriers of the same Usher syndrome gene have a child together, with
each birth there is a:
- 1-in-4 chance of having a child with Usher syndrome
- 2-in-4 chance of having a child who is a carrier
- 1-in-4 chance of having a child who neither has Usher syndrome nor is a
carrier
Next: What are the characteristics of the three types of Usher syndrome? »
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