Usher Syndrome: Most Common Genetic Disorder Causing Deaf and Blindness

Usher syndrome may be why someone you know is both deaf and blind

Deaf and blind couple with a service dog.
Deaf and blind couple with a service dog. VisitBritain/Pawel Libera/Getty Images

Usher syndrome is a disorder that commonly causes both vision and hearing loss. This genetic disorder is considered to be autosomal recessive, meaning that both parents must pass on the trait for your child to be born with this disorder. In other words, both parents either have the disorder or are carriers (have 1 parent that passed on the trait, but it remains dormant) of the disorder.

While it is rare, only occurring in about 4 to 5 per 100,000 people, it is considered the most common cause of having both blindness and deafness, and accounts for about 50 percent of these cases.

There are three different types of Usher syndrome. Type I & II are unfortunately the most severe and most common forms. Type III, which is the least severe of the different types of Usher syndrome, only accounts for about 2 out of 100 cases unless you are of Finnish descent, and then it can account for as high as 40 percent of the cases.

Genetic Mutations

Usher syndrome is considered a congenital disorder, which means that the disorder is caused by the DNA during development. Even if Usher syndrome doesn't manifest until later in life, it is still related to development before birth. There are 11 known changes in DNA genes that affect proteins that can cause Usher syndrome. However the most common changes are:

  • MYO7A - Type I
  • CDH23 - Type I
  • USH2A - Type II
  • CLRN1 - Type III

The majority of the problems associated with the genetic changes are related to proteins that are necessary for the development of specialized hair cells in your inner ear (cilia), as well as rod and cone photoreceptors in your eyes.

Without the appropriate cilia (which in your inner ear, balance and hearing mechanisms will be impaired. The rod photoreceptors are light-sensitive allowing you to still when there is little light available. The cone photoreceptors allow you to see colors and in when the light is bright.

Symptoms of Usher Syndrome

The main symptoms of Usher syndrome are sensorineural hearing loss and a form of vision loss called retinitis pigmentosa (RP).

Retinitis pigmentosa is characterized by night vision loss followed by blind spots that affect the peripheral vision. This may eventually lead to tunnel vision and the development of cataracts. Symptoms vary depending on the type of Usher syndrome an individual has.

 Type I

  • usually completely or mostly deaf in both ears from the time of birth
  • balance problems - which often leads to delays in motor development (sitting, walking etc...)
  • RP- vision problems which begin to develop by age 10 and progress rapidly until total blindness occurs

Type II

  • born with moderate to severe deafness
  • born with normal balance
  • RP - vision loss that progresses more slowly than type I

Type III

  • normal hearing at birth
  • hearing loss may develop later in life
  • normal or near normal balance at birth
  • may develop balance problems later in life
  • usually develop vision problems at some point - the severity varies between individuals

Diagnosing Usher Syndrome

If you have a combination of hearing loss, vision loss, and or balance problems your doctor may suspect Usher syndrome.

Various visual tests including visual field tests, retinal examinations, and electroretinogram (ERG) are helpful in diagnosing Usher syndrome as well as audiology testing. An electronystagmogram (ENG) may be helpful in detecting balance problems.

Many different genes (approximately 11, with a potential of more to be discovered) have been linked to Usher syndrome. With so many genes implicated in this particular syndrome genetic testing has not been particularly helpful in aiding with the diagnosis of the condition.

Treatment for Usher Syndrome

There is no cure for Usher syndrome. However, you can aim treatment for Usher syndrome to manage symptoms. Treatment of symptoms can be based on your preferences along with collaboration of your doctor, and the type of Usher syndrome you have. A variety of medical professionals and types of therapies may be necessary at different points throughout an individual's life and may include audiologists, speech therapists, physical and occupational therapists, opthalmologists and more. The following treatments can be beneficial in managing Usher syndrome. 

Type I

Hearing aids are usually not beneficial in this type of Usher syndrome. Cochlear implants may be an option and may significantly improve the quality of life. Early diagnosis is important so that alternative forms of communication such as American Sign Language (ASL) can be taught. Special consideration should be used in choosing a form of communication, ASL for example may not be a good option for individuals with severe vision loss.

Balance and vestibular rehabilitation may be helpful in managing the effects of the inner ear including loss of balance or dizziness. Treatment for vision problems may include braille instruction, devices to help with night vision, or cataract surgery. Service animals, (such as a guide dog), may also be helpful depending on the circumstances.

Type II

Hearing aids may be beneficial along with other audiology treatments such as cochlear implants. Some research indicates that vitamin A supplementation may be beneficial in slowing the progression of RP in type II and III Usher syndrome. However, you should consult your doctor before trying this and ensure that you:

  • are not pregnant or planning pregnancy, as high doses of Vitamin A can cause birth defects
  • do not supplement with beta carotene
  • do not take more than 15,000 IU

Type III

A combination of the treatments used in type I and II depending on the severity of symptoms.

Ongoing research of Usher syndrome continues and future treatments may become available.

Sources:

American Speech-Language-Hearing Association. Understanding Usher Syndrome. Accessed: August 26, 2016 from http://www.asha.org/Articles/Understanding-Usher-Syndrome/

Genetics Home Reference. Usher Syndrome. Accessed: August 26, 2016 from https://ghr.nlm.nih.gov/condition/usher-syndrome

Kimberling, WJ & Lindenmuth, A. (2006). The Usher Syndromes. Seminars in Hearing, 27(3): 182-192.

National Institute of Deafness & Other Communication Disorders. Usher Syndrome. Accessed: August 26, 2016 from https://www.nidcd.nih.gov/health/usher-syndrome

National Organization for Rare Disorders. Usher Syndrome. Accessed: August 26, 2016 from http://rarediseases.org/rare-diseases/usher-syndrome/

Continue Reading