Usher syndrome is a condition characterized by the gradual loss of both hearing and visual acuity in affected individuals. Hearing loss is progressive, bilateral, sensorineural and in the case of USH3A, post-lingual. Vision loss is caused by retinitis pigmentosa, a gradual deterioration of the retina, resulting in loss of night vision and subsequently peripheral vision. In about half of USH3A cases, patients also suffer from vestibular dysfunction, resulting in difficulties maintaining balance.
USH3A is a rare subset of Usher syndrome, representing about 2% of all Usher cases. However, due to founder mutations, it is found to be highly prevalent in the Finnish and Ashkenazi Jewish populations. Unlike other forms of Usher syndrome, type III has a later onset; hearing and vision problems usually develop during late childhood or adolescence. As a progressive disorder, the prognosis of USH3A remains bleak; by middle age, most affected individuals suffer from blindness and profound hearing loss.