What are USH1C-related Disorders?
USH1C-related disorders represent a group of disorders associated with hearing loss with or without vision loss. This group of disorders does not affect intelligence or cause any other primary health problems.
Usher Syndrome Type IC
There are three types of Usher syndrome, identified as type I, type II and type III. The different types of Usher syndrome are grouped by the severity of the disease and the age when symptoms appear. Mutations in USH1C cause Usher syndrome type 1.
Usher syndrome type I is an inherited disease that causes hearing loss, balance problems, and progressive vision loss. Infants with this disorder are profoundly deaf in both ears at birth. They have severe balance problems caused by abnormalities of the inner ear (vestibular system) that can lead to delayed development. In general children with Usher syndrome type I sit and walk at later ages and have difficulties sensing changes in speed or direction. In childhood or by early adolescence, affected individuals develop retinitis pigmentosa (RP), an eye disease which causes night blindness and a gradual loss of peripheral vision. Eventually only the central vision remains, creating “tunnel vision.” This central vision too can be impaired and can lead to blindness in a small number of people with the disease. In some cases, people with Usher syndrome type 1 develop cataracts, which can further impair vision.
Some mutations in USH1C have been reported in recessive nonsyndromic hearing loss and deafness (isolated hearing loss), referred to as DFNB18A. Individuals with DFNB18A typically have severe-profound hearing loss at birth. Unlike other forms of hearing loss, DFNB18A does not affect movement or balance.
How common are USH1C-related Disorders?
The global incidence is unknown for both conditions. The incidence/prevalence of Usher syndrome type I overall has been estimated in a few countries. In most countries, the frequency ranges from ~1 in 45,000 to ~1 in 65,000, with the exception of Germany where the frequency is ~1 in 90,000. Approximately 1-15% of people with Usher syndrome type I have USH1C. It is estimated that 1 in 100 to 1 in 225 French Canadians/Acadians (in Quebec and Louisiana) are a carrier of USH1C-related disorders.
How are USH1C-related Disorders treated?
There is no cure for USH1C-related disorders, however early treatment is important to give an affected child the best opportunity to develop communication skills. While a child is young, his or her brain is most receptive to learning language, either spoken or signed. It is also important to take advantage of the time when the child’s vision is normal.
People with Usher syndrome type 1C generally do not respond to hearing aids, however cochlear implants may help regain some form of hearing. Sign language is a good option for communication. Specialists can introduce other tools and methods of instruction available to people with hearing loss. It is often helpful if the whole family undergoes such instruction and, as a family unit, helps the child adapt.
For those individuals that develop vision loss, visual aids and specialized instruction (for example in tactile signing) help children adapt to their limited vision. Individuals can be prone to accidental injury due to their vision loss and balance problems. Well-supervised participation in sports may help an individual with Usher syndrome type 1 compensate for balance issues, but swimming may be particularly difficult and strategies to ensure safety are needed. Use of UV-A and UV-B blocking sunglasses is recommended, and other optical aids may increase eye comfort. Therapy with vitamin A palmitate may slow retinal degeneration for some.
What is the prognosis for a person with an USH1C-related Disorder?
Usher syndrome type IC results in severe hearing and vision impairment and DFNB18A results in hearing impairment only. However, neither condition affects one’s lifespan or intelligence.