Usher syndrome is a genetic condition that causes loss of hearing and an eye disorder called retinitis pigmentosa (RP). RP is a group of eye problems affecting the retina. It alters how the retina responds to light leading to difficulties with sight. Vision loss is gradual with RP and can start anywhere from early childhood to adolescence.
Usher syndrome most commonly involves both hearing and sight. It may also affect balance.
- Type I - Individuals are born deaf with severe balance issues from a young age. Those affected start having problems before age 10. Vision problems can lead to blindness.
- Type II - Individuals experience moderate to severe loss of hearing and normal balance. Problems with sight begin when they are in their early teens. Vision problems get worse a lot more slowly than in type I.
- Type III - Individuals are born with normal hearing and almost normal balance but develop problems with vision and experience loss of hearing.
Causes and Risk Factors
Usher syndrome falls in the category of autosomal recessive disorder. It is genetic where the genes are mutated or altered causing them to develop abnormally. For one to develop Usher syndrome, he/she must inherit the altered gene from both parents. Children of either sex can inherit it.
If only one parent has the gene, the individual will be a carrier of the syndrome with a 50% chance of passing it on to his/her children. The probability of a child developing Usher syndrome from both parents who carry the gene is one-in-four.
Signs & Symptoms
The main symptom that indicates an individual has Usher syndrome is the loss of vision occasioned by RP. Other symptoms may include:
- Night blindness
- Gradual loss of vision
- Hearing and balance is affected
- Blindness after many years of cell degeneration
- The slow degeneration or death of the light-sensing cells (rods and cones) in the retina for people with RP
- Loss of color perception when the rods begin degenerating. There is also the deterioration of the central vision responsible for activities like reading and driving
The eye care professional will need to assess both sight and hearing. He/she may do the following:
- Take the medical history of the individual
- A visual field test to check if side vision has been affected
- An examination to check the retina and the back of the eye
- An electroretinogram to measure the response of the cells
- Genetic testing for all nine genes that cause Usher syndrome
- Optical coherence tomography (OCT) to examine cystic macular changes
- Audiology testing to assess hearing sensitivity at a range of frequencies
- Videonystagmography to measure involuntary eye movements which might indicate a problem with balance
Treatment of Usher syndrome aims to manage the hearing, vision and balance problems.
Doctors are yet to discover the cure for Usher syndrome or RP. Early diagnosis of RP can help to improve visual outcomes. Once diagnosed with the disease, the patient can be given valuable education to enable him/her maximize on both hearing and vision aids. The following forms of education are critical for a patient with Usher syndrome:
- Instruction in sign language
- Instruction on how to read Braille
- The patient will receive instruction on mobility training which involves how to use low-vision devices and techniques. These devices include new glasses, magnifiers or electronic devices. Besides, a team of professionals will help the patient learn to complete everyday tasks and maintain a high quality of life. The patient will be issued with hearing aids for both quiet and noisy environments. A patient who develops severe hearing loss can use cochlear implants. The implants assists one to understand speech. One can also benefit from assistive listening devices to hear and understand what is being said.
Vitamin A is said to slow the progression of some forms of RP. The doctor will recommend the quantities that a patient can take safely. He/will also advise on the advantages and disadvantages of Vitamin A. Research has shown that excessive consumption of Vitamin A can be harmful.
Macular holes (tiny breaks in the macula located inside the retina) and cataracts (clouded lens) are sometimes responsible for the early decline in the central vision of a patient with Usher syndrome.
There are similar genetic diseases currently being treated using genetic therapy. In genetic therapy, the scientists create a gene in a laboratory which in turn is inserted into the body. The idea is that the inserted gene will eventually replace the defective gene that caused the disease. Genetic therapy might benefit Usher syndrome patients in future.