Usher syndrome is a genetic disorder that is responsible for loss of hearing and deafness, vision loss and balance impairment. It is the most common cause for hereditary deaf blindness. It occurs in 4-17 per 100 000 of the population. It is responsible for 3-6 % of children that are born deaf as well as 3-6% of children born with hearing loss.
Usher syndrome is inherited in an autosomal recessive trait. There are three clinical types of Usher syndrome. Type 1 and type 2 are responsible for 95% of all Usher syndrome cases in the USA and is much more common than type 3.
Children with type 1 are born deaf or with profound hearing loss and suffer from severe balance problems, manifesting as a delay in early motor development such as time of onset of sitting and walking. Blindness are due to retinitis pigmentosa (RP) and usually begins with night blindness and tunnel vision at first progressing to total blindness before the age of 10. These patients are unlikely to benefit from conventional hearing aids and usually require cochlear implantation.
Type 2 patients have moderate hearing loss, develop vision loss due to RP in adolescence and do not have balance problems. They do not progress to total blindness. They will usually benefit from conventional hearing aids but may require cochlear implantation.
Type 3 patients are rare and most commonly found in patients of Askenazi Jewish and Finnish heritage. They are normal at birth. They develop hearing loss and vision loss due to RP in adolescence or early adulthood. Total blindness usually occurs by middle age. They may also suffer from balance problems.
It is very important to test vision in any baby or child who presents with sensori neural hearing loss. Visual field-testing test peripheral vision and an electroretinogram is often required to evaluate the electrical response to the cones (light sensitive resceptor cells) in the retina. Testing of the balance system may require videonystagmography(VNG) and vestibular evoked myogenic potentials (VEMP).
Genetic testing helps to confirm the diagnosis and classify the type. It is also important to council family members. So far, 9 genes have been implicated in Usher syndrome.
There is no cure for Usher disease. Gene therapy are currently still under investigation. Vision loss and balance problems require management by ophthalmologists, optometrists, physiotherapists and other specialists. Hearing loss may require hearing aids or cochlear implantation.