Retinitis pigmentosa and congenital deafness

(Also called Usher syndrome.) A genetic disorder characterized by hearing impairment and an eye disorder called retinitis pigmentosa in which vision worsens over time. Some people with Usher syndrome also have balance problems.

It is the most common disease that compromises both hearing and vision. More than half of all deaf-blind people have Usher syndrome.

The syndrome is passed along in families by autosomal recessive inheritance, which requires two copies of the Usher gene for the disorder to be manifest. Each parent of a boy or girl with Usher syndrome has one standard and one mutated Usher gene. A child with the syndrome has received two mutated Usher genes, one from each parent.

There are three different types of Usher syndrome (US). They are called Usher syndrome type 1 (US1), Usher syndrome type 2 (US2), and Usher syndrome type 3 (US3). Types 1 and 2 are more common than type 3.

Usher syndrome type 1 (US1) — People with US1 are profoundly deaf from birth and have severe balance problems. Many of these individuals obtain little or no benefit from hearing aids. Most use sign language as their primary means of communication. Because of the balance problems, children with US1 are slow to sit without support and rarely learn to walk before they are 18 months old. These children usually begin to develop vision problems by the time they are ten. Visual problems most often begin with difficulty seeing at night, but tend to progress rapidly until the individual is completely blind.

Usher syndrome type 2 (US2) — People with US2 are born with moderate to severe hearing impairment and normal balance. Although the severity of hearing impairment varies, most of these children perform well in regular classrooms and can benefit from hearing aids. These children most commonly use speech to communicate. Retinitis pigmentosa, which is a degeneration of the retina or the part of the eye that receives images of objects, is characterized by blind spots that begin to appear shortly after the teenage years. The visual problems in US2 tend to progress more slowly than the visual problems in US1. When an individual’s vision deteriorates to blindness, his or her ability to read speech from the lips is lost.

Usher syndrome type 3 (US3) — Children born with US3 have normal hearing and normal to near-normal balance. Hearing worsens over time. Children develop noticeable hearing problems by their teenage years and usually become deaf by mid to late adulthood. Retinitis pigmentosa in the form of night blindness usually begins sometime during puberty. Blind spots appear by the late teenage years to early adulthood. By mid adulthood, the individual is usually blind.

The gene for US1 has been mapped to chromosome 10q21-22, a region that contains the protocadherin 15 gene (PCDH15) known to be mutated in “waltzer” mice that have deafness and vestibular dysfunction. This same gene was found mutated in US1. Thus, waltzer mice provide an animal model of US1.

Hearing loss and retinitis pigmentosa are rarely found in combination outside of Usher syndrome. Special tests such as electronystagmography (ENG) to detect balance problems and electroretinography (ERG) to detect retinitis pigmentosa help detect Usher syndrome early. Early diagnosis is important in order to begin special educational training programs to help the individual deal with the combined hearing and vision difficulties.

The best treatment depends on early identification to begin educational programs. The exact nature of these educational programs depend on the severity of the hearing and vision impairments as well as the age and abilities of the individual. Typically individuals benefit from adjustment and career counseling; access to technology such as hearing aids, assistive listening devices or cochlear implants; orientation and mobility training; and communication services and independent living training that may include Braille instruction, low vision services, or auditory training.

Although it was first described by Albrecht Von Graefe in 1858, the syndrome was named for Charles Usher, a British eye doctor, who was the first to recognize that this condition was inherited.