Usher Syndrome

About

Usher syndrome is a rare genetic disease that is the most frequent cause of deaf-blindness in humans. The condition involves sensoneural hearing loss and retinitis pigmentosa, a condition of the eye that eventually leads to blindness.

Deafness is the first impairment to be identified in a child with Usher syndrome. Therefore, the parents who do not know that their child, besides being deaf, will eventually be blind too, start preparing to manage hearing loss even when the child is as young as four months. They often take important and critical decisions regarding communications, interventions and educational options without being aware of the visual loss that is in store for the child. An audiologist is often their most frequent contact.

Usher syndrome got its name in 1914 from the British ophthalmologist Charles Usher. The exact prevalence of Usher syndrome is not known although researchers have estimated it to be around 17% of all deaf individuals. The word 'syndrome' is used because hearing loss is accompanied by other defects too.

Although of late, it has been made possible to diagnose a vast number of syndromes, there is always a great deal of delay in diagnosing Usher syndrome. This rare condition is inherited in an autosomal recessive manner and the parents usually do not usually suffer from the same condition, though they do possess the defective genes.

Types of Usher syndrome

Usher syndrome can be categorized into three types-

• Type I- These individuals are born deaf and they experience severe problems in maintaining balance right from childhood. Vision impairment develop by age 10, eventually leading to blindness

• Type II- In these individuals, the hearing loss is moderate to severe but they have no issues with balance. Vision impairment too is slow to develop; it starts in the teens and progresses much more slowly than in type I
• Type III- These individuals are born with normal hearing, have a fairly normal balance but eventually develop vision impairment and, later, hearing loss

It is very important for professionals to understand the differences between the different types of Usher syndrome individuals and to realize that with time, the lines demarking the types change.

The blindness associated with Usher syndrome is due to Retinitis pigmentosa (RP), which is a condition affecting the eye leading to vision loss over time. RP results from a vital protein being either absent or abnormal. The delayed expression of vision-related problems remains a challenge in diagnosing and dealing with the disease.

Diagnosis of Usher syndrome

Testing for eye problems is initially done through direct examination of the retina by an ophthalmologist, who is likely to discover a waxy pallor, attenuated blood vessels and groups of dead retinal cells (bone spicules). These retinal changes can be seen only after symptoms of Usher syndrome set in and not before.

A more specific test for RP is an electroretinogram (ERG), which is an evoked response from the retinal rods and cones. ERG uses electrode rays, therefore the procedure is done in children under general anesthesia, while in adults, application of topical medications is the norm. In those with RP or Usher syndrome, ERG would be reduced or absent, although it may yet be normal in children. The advantage of ERG is that the test will show abnormal results even before the retinal cells actually perish.

Hearing loss may be detected by an audiologist either with the help of behavioral measures or through objective tests like the tuning fork test or an audiometer test.

Genetic tests may be carried out, in some countries, to detect Usher syndrome. Patients may find the test an additional burden as Usher syndrome is incurable; however, they could be genetically typed and also, they would be contributing towards the body of research being undertaken to understand the mechanism of the disease and towards finding a better treatment for the condition. They may also be listed, if they so wish, for future clinical trials.

Treatment of Usher syndrome

There is no cure for Usher syndrome. The hearing impairment in Usher syndrome is cochlear in nature and hence cochlear implants are likely to improve the social skills and auditory functioning of those with Usher syndrome.

Retinitis Pigmentosum too does not have any cure. Many people can manage to maintain some degree of visibility until they are fifty or sixty years. Some of the measures that a person with RP should follow are-

• Wear 100% UVA/UVB sunglasses
• Maintain a healthy diet, including plenty of seafood containing omega-3. But go easy on vitamin A because too much of vitamin can cause hypervitaminosis which can lead to blindness, paucity in growth and even death

• Maintain overall health with good exercise / diet

Usher syndrome is likely to have psychosocial implications. A proper understanding of the condition along with support from audiologists and support groups can help the parents of children with Usher syndrome or the suffering individuals to cope with their problem.

References:

1. Usher Syndrome - (http://www.nlm.nih.gov/medlineplus/ushersyndrome.html)
2. About Usher syndrome - (http://en.wikipedia.org/wiki/Usher_syndrome)

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