What Is Usher Syndrome?

Overview

Usher syndrome is a rare genetic disorder which is characterised by sensorineural hearing impairment that worsens over time and the progressive deterioration of vision caused by retinitis pigmentosa. In some cases, the condition results in abnormalities of the vestibular system (balance).

There are three types of Usher syndrome, with Type I and Type II being the most common, accounting for 95% of Usher syndrome cases.¹ These types can be distinguished by their severity and the age of onset of signs and symptoms. 

Causes of usher syndrome

All types of Usher syndrome are inherited in an autosomal recessive pattern.

• Autosomal means that the disorder is inherited independently of sex.
• Recessive means that the child needs to inherit two copies of the mutated genes responsible for Usher syndrome, one from each parent. Therefore, both of the child’s parents must be carriers.  

Therefore, if both parents are carriers of the mutated genes responsible for Usher syndrome, then there is a one-in-four chance that the child will have Usher syndrome.  Researchers have so far identified nine genes responsible for Usher syndrome with genetic testing available for all nine genes.

What causes vision loss in usher syndrome?

The loss of vision associated with  Usher syndrome is caused by an eye disease called retinitis pigmentosa (RP). It is a disease that affects the retina (the light-sensitive tissue at the back of the eye) causing  its progressive deterioration, and eventually causing vision loss. Initial signs of RP  include night blindness followed by the development of blind spots in the peripheral (side) vision. 

Eventually, these blind spots merge to produce tunnel vision. In some cases, vision is further impaired by the clouding of the lens (cataracts) or the development of cysts in the macula (central part of the retina); it can sometimes result in the early decline of central vision in those with Usher syndrome.

What causes hearing loss in usher syndrome?

The hearing loss observed in Usher syndrome is sensorineural, which is caused by the abnormal development of hair cells in the inner ear. 

Signs and symptoms of usher syndrome

The symptoms of Usher syndrome vary greatly depending on the type. Common symptoms include:

• Hearing loss
• Vision loss
• Balance problems

Usher type I

Individuals with Type I Usher syndrome are born with severe hearing loss or deafness. Deterioration of vision caused by RP  is apparent during childhood. With the loss of night vision occurring by age 10.⁴ Individuals may also exhibit abnormalities with balance. For example, they may have trouble sitting up and start walking later than other children (after the age of 18 months). Additionally, children with Type I can have difficulty riding a bicycle.²   

Usher type II

People with Usher Type II have moderate to severe hearing loss during early childhood. The hearing loss experienced mainly affects the child’s ability to hear high-frequency sounds. Night-time blindness occurs during adolescence, with severe vision deterioration by midlife. Individuals with Usher Type II do not have vestibular abnormalities; therefore, they have normal balance.³ 

Usher type III

Individuals with Usher Type III  have normal hearing at birth. Hearing loss begins in late childhood after the development of speech. This continues to deteriorate throughout the individual's life. Vision loss also develops in late childhood. Vestibular abnormalities are also reported, with 50% of Usher Type III exhibiting balance problems in later life.

Management and treatment for usher syndrome

Unfortunately, there is currently no cure for Usher syndrome. Instead, treatments focus on methods to help individuals make the most of their hearing and vision. Therefore, it is imperative that you tell your child’s doctor immediately if you notice a difficulty with balance, hearing loss, or vision changes in your child.

Treatment for vision problems

Treatment options include vision aids such as braille and vision rehabilitation options. These aids can help people with Usher syndrome make the most of the vision that they have.

According to a long-term clinical trial supported by both the National Eye Institute and the Foundation Fighting Blindness, Vitamin A may slow the progression of RP. However, discussing these treatment options with your doctor is important as there can be some adverse side effects to Vitamin A supplementation. 

General precautions for Vitamin A supplementation include: 

• Do not substitute Vitamin A palmitate with beta-carotene
• Pregnant people are recommended not to take high doses of Vitamin A supplements as they can increase the risk of birth defects
• Do not modify your diet to consume foods with high levels of Vitamin A or take more than 15,000 IU 

Treatment for hearing problems

Individuals with Usher syndrome can be provided with communication services such as cochlear implants, auditory training as well as lessons in British sign language. Currently, researchers are trying to improve the treatment strategies for individuals that use hearing aids or cochlear implants.

FAQs

How is usher syndrome diagnosed?

Early detection of Usher syndrome improves treatment success. If you suspect Usher syndrome, it is important that you make an appointment with your GP. Your GP will ask questions about medical history and conduct tests for hearing, balance, and vision. Following this, they can refer you to specialists.

Vision tests: An ophthalmologist (a doctor specialised in managing eye diseases) can perform a comprehensive dilated eye exam in order to assess your child’s vision. They do this by using dilating drops which allow them to observe the retina and check for RP . The exam also comprises a visual field test in order to check peripheral vision. Additional tests include electroretinography, optical coherence tomography, videonystagmography, and fundus autofluorescence imaging (looking at health of retina). 

Hearing tests: An otolaryngologist (doctor who specialises in conditions of the ears) and an audiologist (a doctor who specialises in hearing issues) can perform tests to check for signs of hearing loss or deafness.

Genetic tests: Usher syndrome can be confirmed by a genetic test. 

How can I prevent usher syndrome?

Unfortunately, because Usher syndrome is an inherited disorder, it cannot be prevented.  Genetic testing can determine if you are a carrier and genetic counselling can help you and your partner understand the risks of your children developing Usher syndrome. 

Who is at risk of usher syndrome?

Usher syndrome is an autosomal recessive disorder which means that if both of a child’s parents are carriers of alleles responsible for Usher syndrome then there is a one-in-four chance that the child will have Usher syndrome.

What are the types of usher syndrome?

There are three types of Usher syndrome described:

• Type I: severe hearing loss/deafness, visual problems (from RP) from an early age, may have difficulties with balance 
• Type II: moderate to severe hearing loss/deafness, vision gets worse with age, normal balance 
• Type III: normal hearing at birth, hearing and vision loss begins in late childhood, balance problems may occur

How common is usher syndrome?

Usher syndrome is the most common condition that affects both hearing and vision, with 3 to 6% of children who are deaf having an Usher syndrome diagnosis. It is estimated to affect 4 to 17 people per 100,000 worldwide.^4,5 Of the  three types of Usher syndrome, Type I and II  are the most common as they account for up to 95% of Usher syndrome cases.¹

When should I see a doctor?

You should contact your GP if you notice difficulty with balance, hearing loss, or vision changes in your child.

Summary

Usher syndrome, a rare genetic disorder that is inherited in an autosomal recessive manner, causes both hearing and vision loss. In some cases, it can also cause vestibular (balance) problems. Unfortunately, there is no cure however, current therapies aim to manage the symptoms of Usher syndrome.