What are USH2A-related Disorders?
USH2A-related disorders are an inherited group of conditions associated with vision loss and, in many cases, hearing loss. This group of disorders does not affect intelligence or cause any other primary health problems. USH2A-related disorders are caused by harmful genetic changes (mutations) in the USH2A gene. USH2A plays an important role in the development of the inner ear and the light-sensitive tissue of the eyes (retina). The two types of USH2A-related disorders are Usher syndrome type II and retinitis pigmentosa type 39.
Usher Syndrome Type II
Mutations in USH2A are the most common cause of Usher syndrome type II (USH2). Individuals with USH2 have mild to severe hearing loss beginning at birth (congenital). The hearing loss is usually not progressive, and it mainly affects the ability to detect high-pitched (high-frequency) sounds. Individuals with USH2 do not typically have balance issues associated with other types of Usher syndrome.
USH2 also causes vision loss, typically beginning in adolescence or early adulthood. This is due to a condition called retinitis pigmentosa (RP). RP is an eye disease that causes night blindness and a gradual loss of side vision (peripheral vision). Eventually only the central vision remains, creating "tunnel vision." This central vision can also become impaired and can lead to total blindness in a small number of individuals with the disease. In some cases, individuals with USH2 develop clouding in the lens of the eye (cataracts), which can further impair vision.
Retinitis Pigmentosa 39 (RP39)
Some individuals with USH2A mutations have retinitis pigmentosa without hearing loss, a condition known as retinitis pigmentosa 39 (RP39).
How common are USH2A-related Disorders?
Several genes are known to cause Usher syndrome, which affects approximately 3-6 in 100,000 individuals worldwide. The proportion of Usher syndrome cases caused by USH2A differs significantly between ethnic groups.
The exact incidence of RP39 is not known. The prevalence of RP that occurs in the absence of other symptoms (non-syndromic RP) is approximately 1 in 3,000 and 1 in 7,000 worldwide. RP39 is thought to be the most common cause of non-syndromic RP, accounting for 10-15% of cases.
How are USH2A-related Disorders treated?
Currently there is no cure for hearing loss associated with USH2, but early treatment is important, as it provides a child the best opportunity to develop communication skills. While a child is young, his or her brain is most receptive to learning spoken language or sign language. Hearing aids can improve hearing. Some individuals with more severe hearing loss may benefit from surgical implantation of a small device that stimulates the hearing nerve (a cochlear implant). Specialists can introduce those with hearing loss to other available tools and methods of instruction. To help the child adapt, it is often helpful if the family undergoes such instruction together.
For vision loss due to RP, visual aids and specialized instruction (for example, in tactile signing) help individuals adapt to their limited vision. Use of UVA- and UVB-blocking sunglasses is recommended, and other optical aids may increase eye comfort. For some, therapy with vitamin A palmitate may slow retinal degeneration.
Research is currently being done to determine whether Usher syndrome can be treated with specific medications or gene therapy in the future.
What is the prognosis for an individual with a USH2A-related Disorder?
USH2 results in hearing and vision impairment, while RP39 results in vision impairment with normal hearing. However, neither of these conditions affect one's lifespan or intelligence.