What Is Usher Syndrome Type 3?
Usher syndrome type 3, caused by mutations in the CLRN1 gene, is an inherited disease that causes progressive hearing loss and vision impairment. The rate at which hearing and vision decline varies greatly from person to person, even among those in the same family. In some individuals, the hearing and/or vision loss can be profound, while in others it can be milder.
Individuals with Usher syndrome type 3 are born with normal hearing and most commonly develop hearing loss in their teenage years, requiring hearing aids by mid-to-late adulthood. By middle age, they are often completely deaf.
Usher syndrome type 3 also causes an eye disease known as retinitis pigmentosa. Often arising during puberty, this causes night blindness that progresses to blind spots in the late teens or early adult years. Peripheral (side) vision is often the first to be reduced and often, by mid-life, the person is legally blind.
Unlike other forms of the disease, Usher syndrome type 3 does not usually cause major problems with balance though some problems may arise later in life.
The disease does not affect intelligence, nor does it cause any other health problems.
How Common Is Usher Syndrome Type 3?
Usher syndrome type 3 is rare, making up just 2% of all cases of Usher syndrome. Usher syndrome type 3 is more common in Finland and among Ashkenazi Jews. One study showed that in the New York City area, 0.7% of Ashkenazi Jews are carriers of an Usher syndrome type 3-causing mutation, which would mean that 1.2 in 100,000 Ashkenazi Jewish children would be affected.
How Is Usher Syndrome Type 3 Treated?
There is no cure for Usher syndrome, but there are ways to ameliorate the vision and hearing loss it causes.
Individuals with the disease will learn to speak normally before their hearing declines. They can explore a range of options including cochlear implants, hearing aids, or sign language.
An individual with Usher syndrome will eventually require low-vision aids and specialized instructions on how to cope with their limited vision. They can be prone to accidental injury due to their vision loss and may need to devise systems to avoid such problems.
Specialists in both hearing loss and vision loss can guide individuals to the best options to fit their needs.
What Is the Prognosis for an Individual with Usher Syndrome Type 3?
Usher syndrome type 3 will cause severe hearing and vision impairment by mid-life. However, it does not affect one's lifespan or intelligence.