Usher syndrome is a condition characterized by partial or total hearing loss and vision loss that worsens over time. The hearing loss is classified as sensorineural, which means that it is caused by abnormalities of the inner ear. The loss of vision is caused by an eye disease called retinitis pigmentosa (RP), which affects the layer of light-sensitive tissue at the back of the eye (the retina). Vision loss occurs as the light-sensing cells of the retina gradually break down. Loss of night vision begins first, followed by blind spots that develop in the side (peripheral) vision. Over time, these blind spots enlarge and merge to produce tunnel vision. In some cases, vision is further impaired by clouding of the lens of the eye (cataracts). However, many people with retinitis pigmentosa retain some central vision throughout their lives.
Usher syndrome can be caused by mutations in several different genes. Mutations in at least six genes can cause Usher syndrome type I. The most common of these are MYO7A gene mutations, followed by mutations in the CDH23 gene. Usher syndrome type II can result from mutations in three genes; USH2A gene mutations account for most cases of type II. Usher syndrome type III is most often caused by mutations in the CLRN1 gene.
Usher syndrome affects around 4 to 17 in 100,000 people. Types I and II are the most common forms of Usher syndrome in most countries. Certain genetic mutations resulting in type 1 Usher syndrome are more common among people of Ashkenazi (eastern and central European) Jewish or French Acadian heritage than in the general population.
All of the types of Usher syndrome are inherited in an autosomal recessive pattern, which means both copies of a gene in each cell have a mutation. The parents of an individual with Usher syndrome each carry one copy of the mutated gene, but they do not have any signs and symptoms of the condition.
Published Date: May 17, 2021Published By: National Institutes of Health