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. Type IV Usher Syndrome is the most recently described of the four known forms.
Five patients from three Yemenite Jewish families have been described. A progressive neurosensory hearing loss with onset in midlife together with night vision difficulties and a slow deterioration of visual acuity is characteristic. The peripheral field of vision is narrowed in older individuals and the appearance of the retina resembles a disorder known as retinitis pigmentosa with narrowing of the retinal vessels and pigmentary changes.
An ERG (electroretinogram) documents the progressive degeneration of the retinal photoreceptors known as rods and cones.
This condition follows an autosomal recessive pattern of inheritance. Mutations in both members of a specific pair of genes are responsible. Each clinically normal parent contributes one mutated gene and two such parents can expect that 25 per cent of their offspring will have this condition.
Symptoms of visual and hearing difficulties may have their onset at any time but usually not until midlife and no general health problems are known to be associated. Longevity is not impacted. Low vision devices and corrective lenses with special tinting can be helpful, especially in school-age children.
Hearing loss is neurosensory in etiology and may require cochlear implants for improvement.