Usher syndrome is the most common genetic condition that affects both hearing and vision, and sometimes balance. It accounts for more than 50 percent of all hereditary deaf-blindness cases in the United States and affects roughly 4 to 17 per 100,000 people worldwide. The condition causes hearing loss or deafness alongside a progressive eye disease called retinitis pigmentosa, which gradually narrows the field of vision over years to decades.
The Three Types of Usher Syndrome
Usher syndrome is classified into three types based on how severe the hearing loss is at birth, when vision problems begin, and whether balance is affected.
Type 1 is the most severe. Children are born profoundly deaf, with hearing thresholds often above 110 decibels, meaning they cannot detect even very loud sounds without intervention. Balance problems are present from infancy, which typically causes delays in sitting up and walking independently. Night blindness and loss of peripheral (side) vision usually appear in early adolescence as retinitis pigmentosa sets in.
Type 2 is the most common form. Children are born with moderate to severe hearing loss rather than complete deafness, and their balance is generally normal. Vision symptoms from retinitis pigmentosa typically start shortly after adolescence, beginning with difficulty seeing in dim light and a gradual narrowing of the visual field.
Type 3 is the rarest form, though it is more prevalent in certain populations, particularly people of Finnish and Ashkenazi Jewish descent. Children with type 3 are often born with normal or near-normal hearing, but both their hearing and vision progressively decline starting around puberty.
What Causes It
Usher syndrome is inherited in an autosomal recessive pattern, meaning a child must receive a mutated copy of the same gene from both parents to develop the condition. Parents who each carry one copy typically have no symptoms themselves. Mutations in at least six different genes can cause type 1, though mutations in the MYO7A gene are the most common, followed by the CDH23 gene. Type 2 most often results from mutations in the USH2A gene. Type 3 is usually caused by mutations in the CLRN1 gene.
The condition is estimated to account for 3 to 6 percent of all children who are deaf and another 3 to 6 percent of children who are hard of hearing, making genetic screening especially relevant for families with childhood hearing loss.
How Vision Loss Progresses
The vision component of Usher syndrome is retinitis pigmentosa, a condition where the light-sensing cells in the retina gradually break down. It almost always starts with night blindness, a difficulty adjusting to low-light environments like dimly lit restaurants or driving at dusk. Over time, the field of vision narrows from the edges inward, creating what people often describe as “tunnel vision.” Central vision, used for reading and recognizing faces, is usually the last to go and can be preserved for years or even decades depending on the type.
The timeline varies. In type 1, retinitis pigmentosa signs appear in early adolescence. In type 2, symptoms typically begin shortly after adolescence. In type 3, vision loss is progressive starting around puberty but can follow a less predictable course. The rate of decline differs from person to person, even within the same type.
How It Is Diagnosed
Diagnosis usually begins when a child shows hearing loss or deafness that prompts further investigation. Doctors assess hearing, balance, and vision through a combination of tests. Hearing tests identify the degree and type of hearing loss. Balance testing, including videonystagmography (which tracks involuntary eye movements linked to balance problems), helps distinguish type 1 from type 2.
For the eyes, a comprehensive dilated eye exam looks for signs of retinitis pigmentosa. Additional tests may include:
- Electroretinography (ERG): measures how well the retina responds to light, often detecting retinitis pigmentosa before symptoms are noticeable
- Optical coherence tomography (OCT): uses light waves to create a detailed cross-section image of the retina
- Visual field testing: maps peripheral vision to track any narrowing
- Fundus autofluorescence imaging: uses blue light to photograph the retina and reveal areas of damage
Genetic testing can confirm the diagnosis and identify the specific type, which helps predict how the condition will progress and informs family planning decisions.
Managing Hearing Loss
Hearing aids are often the first approach, particularly for children with type 2, who have moderate to severe hearing loss rather than complete deafness. For many people with type 2 or type 3, hearing aids work well for years, though progressive hearing loss may eventually outpace what they can provide.
Cochlear implants are the standard treatment for type 1, where children are born profoundly deaf and hearing aids are not effective. Early and bilateral implantation (both ears) leads to the best results for speech perception and language development in these children. For people with type 2 or type 3 whose hearing deteriorates to the point where hearing aids no longer help, cochlear implants offer significant improvement. Studies show that post-operative hearing levels improve dramatically, with word recognition scores significantly better after implantation regardless of the patient’s age at the time of surgery.
Because people with Usher syndrome may eventually lose both hearing and vision, early language development is a priority. Many families use a combination of spoken language, sign language, and tactile communication strategies depending on the child’s hearing level and type.
Managing Vision Loss
There is currently no approved treatment that stops or reverses retinitis pigmentosa, but several strategies help people adapt. Orientation and mobility training teaches techniques for navigating with reduced peripheral vision. Low-vision aids, including magnifiers and specialized lighting, can extend functional vision. As the visual field narrows, many people transition to using screen readers, braille, and other assistive technologies.
Regular eye exams are important for tracking the rate of vision change and catching treatable complications like cataracts, which can develop alongside retinitis pigmentosa.
Therapies in Development
Several clinical trials are testing treatments that target the genetic roots of Usher syndrome. For type 1, a dual gene therapy delivered by injection beneath the retina is currently recruiting participants. This approach uses two viral vectors working together to deliver a functional copy of the MYO7A gene, which is too large for a single vector. An earlier trial using a different delivery method was terminated by its sponsor for reasons unrelated to safety.
For type 2, a therapy called QR-421a is in phase 2 trials. It uses short pieces of genetic material injected into the eye to correct the way cells read the mutated USH2A gene, potentially restoring some protein function in retinal cells. Patients receive an initial injection followed by doses every six months.
For type 3, an oral medication called BF844 is entering phase 1 trials targeting both the inner ear and retina. Another oral treatment, NPI-001, is in active phase 1/2 trials and aims to protect retinal cells across all Usher types. No gene-editing therapies have reached clinical trials yet, though preclinical work is underway building on techniques being tested for other inherited retinal diseases.