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Usher syndrome

Background

Usher syndrome is a genetic condition that causes sensory neural hearing loss and retinosis pigmentosa (RP). Sensory neural hearing loss occurs because the sensitive hair cells inside the ear are damaged. Children and adults affected by Usher syndrome are usually totally (type 1) or partially (type 2) deaf from birth (known as congenital deafness).

The early symptoms of RP include difficulty seeing in the dark and in different lighting conditions. Over time, vision gradually deteriorates until tunnel vision develops and people cannot see objects unless they are directly in front of them. Reduced vision may not occur until adolescence or early adulthood. In some people, poor balance is an associated problem.

Credits

Medical text written November 1991 by Contact a Family. Approved November 1991 by Professor M Patton, Professor of Medical Genetics, St Georges Hospital Medical School, London, UK and Dr J E Wraith, Consultant Paediatrician, Royal Manchester Children's Hospital, Manchester, UK. Last updated July 2012 by Dr Maria Bitner-Glindzicz, Clinical and Molecular Genetics Unit, Institute of Child Health, London, UK.

What are the symptoms?

There are three types of the syndrome:

  • type I is characterised by profound congenital hearing loss, poor balance and RP usually around the age of ten years
  • type II presents moderate to severe congenital hearing loss, normal balance and RP develops in the late teens or early 20s
  • type III is characterised by progressive hearing loss often in childhood and RP progressing at a variable rate, generally with onset around the second or third decade of life.

What are the causes?

Usher syndrome is an inherited genetic condition caused by changes in DNA (mutations) in certain genes. The genes related to Usher syndrome play a role in the development and maintenance of hair cells which are important for transmitting sound in the ear and determining the structure and function of light-sensing cells, called rods and cones, in the eye.

Type I can result from mutations in the CDH23, MYO7A, PCDH15, USH1C or USH1G genes. Other unidentified genes also cause type 1 Usher syndrome. Type II is caused by mutations in at least four genes. Only three of these genes, USH2A, GPR98 (also called VLGR1) and DFNB31 have been identified. Mutations in at least two genes are responsible for Usher syndrome type III, however, CLRN1 is the only gene that has been identified.

How is it diagnosed?

Children with profound hearing loss and delayed motor milestones should be considered 'at risk' of having Usher syndrome type 1. Diagnosis of Usher syndrome type 1 in a deaf child may occur using an electroretinogram (ERG) at a time when the child has no visual problems. An ERG measures the electrical response of the eye's light-sensitive photoreceptor cells (rods and cones). Electrodes are placed on the cornea and the skin near the eye to measure the electrical currents coming from the cells when a light is flashed. More often, diagnosis may be delayed until the visual problems have become significant.

How is it treated?

Although there is no treatment available for Usher at the moment, many people with Usher have adjusted very successfully to their condition. Children with Type 1 Usher syndrome usually benefit from cochlear implantation. A cochlear implant is a small, electronic device that can help to provide a sense of sound to a person who is deaf. It consists of an external portion that sits behind the ear and a second portion that is surgically placed under the skin. The implant does not restore normal hearing. Instead, it can give a deaf person a useful representation of sounds in the environment and help him or her to understand speech.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
The genetic changes causing Usher syndrome are inherited in an autosomal recessive manner. Genetic advice should be sought by affected families.

Prenatal diagnosis
Several genes have been identified which in theory, allow prenatal diagnosis. However, genetic testing is difficult due to the number and size of the genes which have to be screened. Prenatal diagnosis can only be offered where the genetic mutation that causes Usher syndrome in a family is known.

Is there support?

Information and support for Usher Syndrome is provided by Sense (see Deafblindness).

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