Usher syndrome, also known as Hallgren syndrome, is a rare genetic disorder that causes hearing loss, vision loss, and balance issues. Experts typically divide Usher syndrome into three subtypes depending on the gene responsible and the presentation of the symptoms. Though there is currently no cure, research efforts are ongoing and there are management options for people with the disorder.
Children with type 1 Usher syndrome have significant hearing loss or full deafness at birth. They also typically have balance issues. With type 1 Usher syndrome, a child’s night vision will worsen by age 10. Severe vision loss occurs by midlife. Doctors recommend immediate medical intervention for children with this type of Usher syndrome.
Type 2 Usher syndrome is similar to type 1. Children are born with moderate to severe hearing loss and will experience progressive vision loss throughout their lives. However, people with type 2 do not experience any balance issues. Additionally, the vision loss progresses slower than in type 1.
Of each type, the third is the least severe. Hearing loss intype 3 Usher syndrome begins during childhood or the early teenage years, rather than being present at birth. Vision loss can vary greatly in both severity and age of onset. A person with type 3 Usher syndrome often begins to notice night vision problems in their teens. Severe vision loss by midlife is common. Balance issues are rare during childhood but become more prevalent in later years.
Because Usher syndrome is a rare condition, much remains unknown about its mechanics and origins. However, researchers have recognized that it is inheritable and appears to result from genetic mutation. Each type of Usher syndrome stems from different mutations. Currently, experts have found nine mutations with links to type 1, four with links to type 2, and two to type 3.
Gene mutations in Usher syndrome affect the light-sensing rods and cones in the retinas at the back of the eye, triggering retinitis pigmentosa (RP). In RP, the rods and cones slowly begin to fail. This manifests as a loss of peripheral vision first, with central vision loss soon following. Gene mutations also affect the cochlea, which is a spiral structure in the inner ear that transmits sound. The mutations inhibit the cochlea’s function, causing hearing loss.
Usher syndrome has an autosomal recessive inheritance pattern. This means that a disease-causing mutation must be present in both copies of the gene that a child inherits — one from each parent —for them to have the condition. A person with only one of the mutated genes becomes a carrier who may pass Usher syndrome to their children. Carriers typically have no symptoms.
Diagnosing Usher syndrome begins with questions about medical history, as well as hearing, vision, and balance tests. Eye care specialists may use dilating drops to discover signs of RP. Other tests, such as visual field testing or electroretinogram, can discover the severity of vision loss. Audiology testing reveals a person’s hearing sensitivity across a range of frequencies. Some experts use genetic testing to search for the mutations that cause Usher syndrome.
Currently, there is no cure for Usher syndrome. However, there are methods to slow its progression and provide moderate quality-of-life improvements. Hearing aids, cochlear implants, and assistive listening devices can help with hearing loss. Long-term clinical trials have found that vitamin A can dramatically slow the progression of RP, stalling vision loss.
Researchers are currently attempting to identify gene mutations that could cause Usher syndrome. This could lead to a better understanding of the condition, speed up the diagnostic process, and improve treatment options. Other research efforts are focusing on better methods for early diagnosis in children, as well as improving overall treatment strategies.
Because Usher syndrome is an autosomal disorder, it impacts males and females equally. The condition affects around 1 in 23,000 people in the United States. Experts estimate that people with Usher syndrome represent around one-sixth of people who have RP. They also believe that Usher syndrome is responsible for the majority of deafblindness.
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