Usher Syndrome Causes, Symptoms, Diagnosis, Treatment, Prevention

Usher Syndrome Causes, Symptoms, Diagnosis, Treatment, Prevention

What Is Usher Syndrome?

Usher syndrome is a rare inherited disorder that involves loss of both hearing and sight. Hearing Loss is usually present at birth or soon thereafter. It is due to an impaired ability of the auditory nerves to transmit sensory input to the brain. It is called sensorineural hearing loss.

The vision loss, called Retinitis Pigmentosa (RP), begins later in childhood, usually after age ten. It slowly gets worse over time. During the teen years, loss of vision is characterized by night blindness and loss of peripheral vision. RP is a deterioration of the retina. The retina is a layer of light-sensitive tissue that lines the back of the eye. It converts visual images into nerve impulses in the brain that allow us to see.

Researchers have described three types of Usher syndrome-type I, type II and type III.

  • Individuals with Usher syndrome type I are nearly or completely deaf and experience problems with balance from a young age. They usually begin to exhibit signs of RP in early adolescence.
  • Individuals with Usher syndrome type II experience moderate to severe hearing impairment, have normal balance, and experience symptoms of RP later in adolescence.
  • Individuals with Usher syndrome type III are born with normal hearing but develop RP and then progressive hearing loss.

Approximately 4 out of 100,000 infants born in the United States have Usher syndrome. Usher syndrome accounts for 3%-6% of all deaf children and 3%-6% of all hard-of-hearing children.

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.

The different categories

Usher syndrome is categorised into three broad groups according to the type and severity of symptoms. These groups are called Type 1, Type 2 and Type 3. Each type is further divided into subtypes.

Usher syndrome Type 1 

Usher syndrome Type 1 (US1)Although there are six subtypes, the characteristics of Usher syndrome Type 1 include:
  • The person is profoundly deaf from birth.
  • Speech difficulties are evident.
  • Other means of communication, like sign language (Auslan), are needed.
  • Balance may be affected and children are often late to sit, stand and walk.
  • Eye problems vary with each person, but may start to develop at around ten years of age.
  • Vision loss varies with each person, but often develops in the first ten years of life.

Usher syndrome Type 2

Usher syndrome Type 2 (US2)There are three subtypes of Type 2. The characteristics of Usher syndrome Type 2 include:
  • Moderate loss of hearing is experienced in the lower sound frequency range.
  • Severe loss of hearing is experienced in the higher sound frequency range.
  • Balance may be affected in later years.
  • Vision loss, such as blind spots, starts to develop during the teenage years and may progress during life.

Usher syndrome Type 3

Usher syndrome Type 3 (US3)Only one subtype of Type 3 has been discovered to date. The characteristics of Usher syndrome Type 3 include:
  • The person is born with normal hearing and close to normal balance.
  • The loss of hearing becomes more pronounced as the person gets older.
  • Measurable hearing loss occurs by puberty.
  • Vision loss starts to develop during the teenage years and may progress during life.
  • Balance deteriorates as the person gets older.
  • The majority of people with US3 live in Finland.

Usher Syndrome Risks

A risk factor is something that increases your chance of getting a disease or condition. The only known risk factor for Usher syndrome is having parents with the disorder and/or parents who carry the genes for the disorder. If both parents carry the abnormal gene, you have a 25% chance of inheriting both of these abnormal genes and therefore developing Usher syndrome.

Symptoms of Usher Syndrome

The main symptoms of Usher syndrome are hearing and vision loss. Some people also have balance problems due to inner ear problems.

The progression of RP limits a person's ability to see in dim light or the dark (night blindness). It also causes a person to lose peripheral (side) vision slowly over time. Eventually, any vision left is only in a small tunnel-shaped area. Almost everyone with RP becomes legally blind. There is no known way of predicting when or how quickly a person will lose vision.

Symptoms and characteristics of each type include the following:

Usher Syndrome Type I

  • Deaf at birth and receive little or no benefit from hearing aids
  • Severe balance problems
  • Slow to sit without support
  • Rarely learn to walk before age 18 months
  • RP begins by age 10 with difficulty seeing at night, and quickly progresses to blindness

Usher Syndrome Type II

  • Born with moderate to severe hearing loss, and can benefit from hearing aids
  • No balance problems
  • RP begins in the teenage years

Usher SyndromeType III

  • Born with normal hearing that gets worse in the teenage years and leads to deafness by mid to late adulthood
  • Born with near-normal balance
  • RP begins in the early teenage years as night blindness, and leads to blindness by mid-adulthood

How to Diagnose Usher Syndrome

The doctor will ask about symptoms and medical history and perform a physical exam. Hearing loss is determined with standard hearing tests. Balance problems can be detected with a test called electronystagmography (ENG). In this test, the doctor flushes the ears with warm and then cool water. This causes nystagmus, which is rapid eye movements that can help the doctor detect a balance disorder.

An eye doctor will perform an eye exam, which will likely include the following:

  • Visual field test to check side vision
  • Test to check for ability to adapt to seeing in the dark
  • Test to check sensitivity to color and contrast
If any problems are found on these tests, an electroretinography (ERG) is done. This test confirms a diagnosis of RP. It measures the electricity given off by the nerves in the retina. The test is done while wearing special contact lenses and looking at a flashing light.

Is genetic testing for Usher syndrome available?

At this time, genetic testing for Usher syndrome is done only as part of research projects. This is due to many factors. Usher syndrome is not caused by only one gene. So far, 10 Usher genes have been mapped: 7 for type I, 3 for type II, and 1 for type 3. There are still more genes to find. A few of these genes have been sequenced and described. These are MYO7A, harmonin, CDH23, PCDH15, all causing type I. The usherin gene causes type II disease.

Finding the genes is a very important advance in the fight against Usher syndrome. Further study is required to characterize these genes, and determine how the mutated genes cause Usher syndrome. Additional genes that cause Usher syndrome also need to be identified. Several researchers throughout the world are working on Usher syndrome. Findings from this research may one day allow treatments for Usher syndrome to be developed.

How is Usher syndrome treated?

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.

How to Prevent Usher Syndrome

Currently, there is no known way to prevent Usher syndrome.

Things to remember

  • Usher syndrome is a genetic disorder characterised by the progressive loss of both hearing and vision.
  • Some people with Usher syndrome also experience problems with their balance.
  • For a child to develop Usher syndrome, they must inherit the particular faulty gene from both their mother and their father.
  • There are information and support services available.