Usher syndrome causes deafness and progressive degeneration of the retina, leading to blindness. There are three different types of Usher syndrome which have been associated with mutations in several different genes.
- Children born with Type I are profoundly deaf at birth and have severe balance problems. Vision problems begin in childhood and generally progress to blindness.
- Children with Type II usually have less severe hearing loss and slower degeneration of vision.
- Children with Type III have normal hearing at birth. Their hearing and sight worsen over time. The rate of decline varies, but by mid-adulthood most affected people are legally blind and require hearing aids.
In the Ashkenazi Jewish population, mutations for both Usher syndrome Type I and Type III have been identified. The carrier rate is approximately 1 in 165 for Type I and 1 in 95 for Type III.
Screening for Type III will detect 95% of carriers. Screening for Type I will detect at least 75% of carriers, which is lower than the detection rate for other diseases on the Ashkenazi Jewish panel.