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. Each 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 along the disorder to a child. The word recessive means that to have Usher syndrome, an individual 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. Individuals 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 an individual who does not have a family history of Usher syndrome is a carrier. NIDCD scientists 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.
- 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