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Usher Syndrome
Usher Syndrome is a complex genetic condition and most common cause of combined visual and hearing loss. Retinitis Pigmentosa is the cause of reduced visual acuity in people living with Usher Syndrome, while incorrect development of the sensory receptor cells (hair cells) is what causes hearing loss.
As a result, a part of the inner ear called the cochlea is unable to detect sound and transmit this information to the brain. Usher syndrome exists in three main forms, type 1, type 2 and type 3, with type 1 being the most severe and type 3 the most moderate form.
What are the symptoms of Usher Syndrome?
People with Usher type 1 develop profound deafness from birth and in early childhood, symptoms of RP become evident. The deafness is generally so early in onset and so severe that hearing aids may not be of value, (although cochlear implants may be beneficial), and patients fail to develop intelligible speech.
Patients with Usher type 2 also have an early onset hearing loss but the deafness is less severe than in type 1 and thus the child will benefit from hearing aids and will develop intelligible speech. In type 2 usher syndrome, the features of retinitis pigmentosa usually become obvious during the teenage years and tend not to have difficulties with their balance.
Usher type 3 is a very rare form of Usher and is generally found in people with their family origins in Finland. Hearing loss generally happens in young children and adolescents, who also experience night vision but don’t generally have problems with balance.
What Causes Usher Syndrome?
A mutation in one of several genes can cause one of the three forms of Usher Syndrome. Type 1 is most commonly caused by MYO7A, while the USH2A gene and CLRN1 gene account for the majority of type 2 and type 3 cases respectively. Usher Syndrome is an autosomal recessive disorder, meaning two malfunctioning copies of a particular gene are required for the condition to develop. Men and women are equally affected in this way and “carriers” who have only one faulty gene copy are not affected by the disease. People living with a combination of early-onset partial deafness and retinitis pigmentosa due to alterations in the mitochondrial DNA do not fall into the category of usher syndrome.
For a more detailed description of the various modes of disease inheritance, please visit the Genetics and Inheritance Section.
If a family member is diagnosed with Usher Syndrome, it is strongly advised that other members of the family also have an eye exam by an eye doctor (ophthalmologist) who is specially trained to detect retinal diseases. As the deafness becomes obvious at a much earlier age than the retinitis pigmentosa in patients with usher syndrome, it is particularly important that younger siblings with a hearing problem have a detailed eye examination.
To accurately diagnose Usher Syndrome, electroretinograms are used to assess the integrity of the rod and cone photoreceptor cells and measure the electrical impulses produced by the retina in response to light. Visual field tests are also used to detect blind spots in an individual’s field of vision and emit flashes of light to measure how profound vision loss is. Balance tests are also used to measure a person’s ability to maintain balance, a problem which arises because of issues in the cochlea and is frequently used to clarify a diagnosis.
Genetic testing is another crucial part of the diagnostic process, as each form of Usher Syndrome is linked with a particular set of genes and confirming the implicated genes can explain how the disease may progress, as well as influence suitable treatments in the future.
If a family member is diagnosed with Usher Syndrome, it is strongly advised that other members of the family also have an eye exam by an eye doctor (ophthalmologist) who is specially trained to detect retinal diseases. As the deafness becomes obvious at a much earlier age than the Retinitis Pigmentosa in patients with Usher Syndrome, it is particularly important that younger siblings with a hearing problem have a careful eye examination.
What treatments are available?
Currently, there are no treatments approved for Usher Syndrome. However, clinical research in this space is very active, with a large number of clinical trials ongoing, all of which are available on the clinicaltrials.gov website.
As Usher Syndrome is passed down through generations in a recessive pattern of inheritance and only only one pair of genes is affected, it is therefore a prime candidate for gene therapy. Gene therapy involves using harmless viruses to deliver and insert a healthy copy of the gene into the retina, thereby restoring normal function and visual acuity. This approach has led to exciting initial results in a number of other retinal diseases, including Leber Congenital Amaurosis with the gene therapy, Luxturna approved for use. Although Usher Syndrome gene therapy is quite challenging as the genes affected tend to be extremely large in size and difficult to deliver, there is plenty of reason to remain optimistic as research in this field has never been more promising.
Despite the lack of current treatments for Usher Syndrome, general eye check-ups are important. This is because people with Usher Syndrome are still at risk for other kinds of eye problems that can affect the general population, such as cataracts, and may be treatable. Regular visits to your eye doctor can also make you aware of current advances as we learn more about these conditions.