What are USH2A-related Disorders?
There are three types of Usher syndrome, identified as type I, type II, and type III. The different types of Usher syndrome differ in the severity and the age of onset. Mutations in the USH2A gene cause Usher syndrome type II.
Usher syndrome type II causes mild to severe hearing loss beginning at birth (congenital) and progressive loss of vision, typically beginning in adolescence or adulthood. The hearing loss with this form is usually not progressive and mainly affects the ability to detect high frequency sounds. The degree of hearing loss varies both among individuals and within families with Usher syndrome type II. Unlike other forms of Usher syndrome, Usher syndrome type II is generally not associated with balance problems.
Vision loss in Usher syndrome type II is due to a condition called retinitis pigmentosa (RP) and usually begins in the late teens or early twenties. The vision loss is progressive but does not usually lead to complete blindness. Typically the first sign of vision loss is night blindness that progresses to loss of peripheral (side) vision, eventually causing tunnel vision. This progression generally takes place over years or decades.
Some affected individuals have retinitis pigmentosa (RP) without hearing loss, a condition known as retinitis pigmentosa 39 (RP39).
How common are USH2A-related Disorders?
In the United States, Usher syndrome is conservatively thought to affect 4.4 in 100,000 people. The frequency of Usher syndrome type II is not known. Usher syndrome is likely responsible for 3-6% of all childhood deafness.
How are USH2A-related Disorders treated?
Currently there is no cure for Usher syndrome type II, but 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. Cochlear implants may improve hearing loss symptoms for some individuals. Specialists can introduce other tools and methods of instruction available to people with hearing loss. It is often helpful if the family undergoes such instruction together to help the child adapt.
Routine hearing and vision evaluations are important to detect potentially treatable complications, such as cataracts. Use of UV-A and UV-B blocking sunglasses and other low vision aids may ease the discomfort and difficulties associated with RP. Affected individuals are sometimes prone to accidental injury due to their vision loss and may need to devise systems to avoid such problems. Activities such as sports and driving a car may be difficult or dangerous. Therapy with vitamin A palmitate may slow retinal degeneration for some. Counseling and lifestyle therapy may help affected individuals cope with the difficulties associated with vision loss.
What is the prognosis for a person with an USH2A-related Disorder?
Although the hearing loss symptoms are moderate to severe, most children with Usher syndrome type 2A can use oral communication. Cochlear implants may improve hearing loss in some children. Symptoms of vision loss typically begin in late childhood or early adolescence and the narrowing of the visual field progresses over time. This condition is not associated with balance problems associated other types of Usher syndrome. Usher syndrome type II does not affect intellectual ability or life span.