Usher syndrome is comprised of a group of diseases with a distinctive combination of hearing and progressive vision loss. It is named for a Scottish ophthalmologist, Charles Howard Usher, who recognized their hereditary nature although he was not the first to describe the condition.
Most infants are born with normal hearing but hearing loss begins sometime in the first two decades and by midlife most individuals are profoundly deaf. Speech at least early is normal. Vision loss may begin about the same time with nightblindness and tunnel vision becoming severe by young adulthood. Some adults lose all functional vision. The balance mechanism of the inner ear is variably damaged and can cause considerable unsteadiness in walking and physical activities. The mental problems sometimes seen in Type I are not present in type III.
Like other types of Usher syndrome, the inheritance pattern in type III is autosomal recessive. This is the rarest form of Usher syndrome. Carrier parents with one copy of the mutation are clinically normal but if both mother and father are carriers, they have a 25% risk of each giving the mutation to each of their children. Only one gene with mutations has been identified as causative.
Patients can lead a productive life and longevity is not impacted. The diagnosis is often delayed because no symptoms are present at birth. Nightblindness may be the first symptom and should be investigated by consultation with an ophthalmologist. Auditory testing is important at the first sign of problems and hearing needs to be monitored, especially in adults. Precautions are suggested during physical activities, especially swimming because of the risk of underwater disorientation. Side vision constriction and nightblindness make driving hazardous.