About usher syndrome

What is usher syndrome?

Usher syndrome is the most common condition that affects both hearing and vision. A syndrome is a disease or disorder that has more than one feature or symptom. The major symptoms of Usher syndrome are hearing loss and an eye disorder called retinitis pigmentosa, or RP. RP causes night-blindness and a loss of peripheral vision (side vision) through the progressive degeneration of the retina. The retina is a light-sensitive tissue at the back of the eye and is crucial for vision. As RP progresses, the field of vision narrows - a condition known as "tunnel vision" - until only central vision (the ability to see straight ahead) remains. Many people with Usher syndrome also have severe balance problems.

There are three clinical types of Usher syndrome:

  • type 1,
  • type 2, and
  • type 3.

In the United States, types 1 and 2 are the most common types. Together, they account for approximately 90 to 95 percent of all cases of children who have Usher syndrome.

Photograph of the retina of a patient with Usher syndrome (left) compared to a normal retina (right). The optic nerve (arrow) looks very pale, the vessels (stars) are very thin and there is characteristic pigment, called bone spicules (double arrows).

What are the symptoms for usher syndrome?

Usher syndrome is characterized by deafness due to an impaired ability of the inner ear and auditory nerves to transmit sensory (sound) input to the brain (sensorineural hearing loss) as well as abnormal accumulation of colored (pigmented) material on the nerve-rich membrane (the retina) lining the eyes (retinitis pigmentosa or RP). RP eventually causes retinal Degeneration leading to progressive loss of vision and legal blindness. Sensorineural nerve deafness may be profound or mild, and may be progressive. The Vision loss caused by RP may begin during childhood or later during life, and often first presents with difficulty seeing at night or in low light (“night blindness”). Studies show that clear central vision may be maintained for many years even while side (peripheral) vision decreases. These narrowed visual fields are also referred to as “tunnel vision.” Issues with balance are seen in individuals with Usher syndrome types 1 and 3.

Usher syndrome type 1 is characterized by profound Hearing loss in both ears at birth (congenital deafness) and balance problems. In many cases, affected children do not learn to walk until 18 months of age or later. Vision problems usually begin at approximately the age of ten years to early teens, although some parents report onset in children younger than 10. Usher syndrome type 2 is characterized by moderate to severe Hearing loss in both ears at birth. In some cases, Hearing loss may worsen over time. Onset of night Blindness occurs during the late teens or early twenties. Peripheral Vision loss is ongoing, but central vision is usually retained into adulthood. Visual problems associated with Usher syndrome type 2 tend to progress more slowly than those associated with type 1.

Usher syndrome type 3 is characterized by later onset hearing loss, variable balance (vestibular) dysfunction and RP that can present between the second and fourth decade of life. Balance issues occur in approximately 50% of individuals with Usher syndrome type 3.

What are the causes for usher syndrome?

Usher syndrome is caused by mutations in specific genes. So far, Usher syndrome has been associated with mutations in at least ten genes:

Usher syndrome type 1: MYO7A (USH1B), USH1C, CDH23, PCDH15 (USH1F), SANS (USH1G), and possibly CIB2

Usher syndrome type 2: USH2A, ADGRV1 (previously called VLGR1) WHRN (DFNB31)

Usher syndrome type 3: USH3A (CLRN1), HARS

These genes provide instructions for making proteins involved in normal hearing, vision and balance. Some of these proteins help specialized cells called hair cells to transmit sound from the inner ear to the brain and to sense light and color in the retina of the eye. The function of the some of the proteins produced by genes associated with Usher syndrome is not known.

Some people with Usher syndrome do not have mutations in any of these genes, so there are probably other genes associated with the condition that have not yet been identified.

All types of Usher syndrome are inherited as autosomal recessive traits. Most genetic diseases are determined by the status of two copies of a gene, one received from the father and one from the mother. Recessive genetic disorders occur when an individual inherits two copies of an abnormal gene for the same trait, one from each parent. If an individual inherits one normal gene and one gene for the disease, the person will be a carrier for the disease but usually will not show symptoms. The risk for two carrier parents to both pass on the altered gene and have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents is 25%. The risk is the same for males and females.

Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.

What are the treatments for usher syndrome?

Currently, there is no cure for Usher syndrome. The best treatment involves early identification so that educational programs can begin as soon as possible. The exact nature of these programs will depend on the severity of the hearing and vision loss as well as the age and abilities of the person. Typically, treatment will include hearing aids, assistive listening devices, cochlear implants, or other communication methods such as American Sign Language; orientation and mobility training; and communication services and independent-living training that may include Braille instruction, low-vision services, or auditory training.

Some ophthalmologists believe that a high dose of vitamin A palmitate may slow, but not halt, the progression of retinitis pigmentosa. This belief stems from the results of a long-term clinical trial supported by the National Eye Institute and the Foundation for Fighting Blindness. Based on these findings, the researchers recommend that most adult patients with the common forms of RP take a daily supplement of 15,000 IU (international units) of vitamin A in the palmitate form under the supervision of their eye care professional. (Because people with type 1 Usher syndrome did not take part in the study, high-dose vitamin A is not recommended for these patients.) People who are considering taking vitamin A should discuss this treatment option with their health care provider before proceeding. Other guidelines regarding this treatment option include:

  • Do not substitute vitamin A palmitate with a beta-carotene supplement.
  • Do not take vitamin A supplements greater than the recommended dose of 15,000 IU or modify your diet to select foods with high levels of vitamin A.
  • Women who are considering pregnancy should stop taking the high-dose supplement of vitamin A three months before trying to conceive due to the increased risk of birth defects.
  • Women who are pregnant should stop taking the high-dose supplement of vitamin A due to the increased risk of birth defects.

In addition, according to the same study, people with RP should avoid using supplements of more than 400 IU of vitamin E per day.

What are the risk factors for usher syndrome?

Usher syndrome affects approximately three to ten in 100,000 people worldwide. Higher than average numbers of people with Usher syndrome have been found among Jewish people in Israel, Berlin, Germany; French Canadians of Louisiana; Argentineans of Spanish descent; and Nigerian Africans. USH3, the rarest form in most populations, comprises about 40% of Usher patients in Finland. Usher syndrome is the most common genetic disorder involving both hearing and vision abnormalities. Usher syndrome types 1 and 2 account for approximately 10 percent of all cases of moderate to profound deafness in children.

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