Usher Syndrome

Definition

Usher syndrome is a rare, inherited disorder that involves loss of hearing and sight. Hearing loss is due to the inability of the auditory nerves to send sensory input to the brain. This is called sensorineural hearing loss. The vision loss, called retinitis pigmentosa (RP), usually happens after age ten. RP is a deterioration of the retina. The retina is a layer of light-sensitive tissue that lines the back of the eye. It changes visual images into nerve impulses in the brain that allow us to see. RP slowly gets worse over time.
Nerve and Retina of the Eye
Normal Anatomy of the Eye
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Three types of Usher syndrome have been identified: types I, II, and III. The age of onset and severity of symptoms separate the different types.

Causes

Usher syndrome is caused by a genetic mutation. A child must inherit one defective gene from each parent in order to develop Usher syndrome. A child with one defective gene is a carrier and will not have any symptoms. It is not clear what causes the mutation in the gene.

Risk Factors

The only known factor that increases the risk of Usher syndrome is having parents with the disorder and/or parents who carry the genes for the disorder. If both parents carry the abnormal gene, a child has a 25% chance of inheriting both of these abnormal genes and developing Usher syndrome.

Symptoms

The main symptoms of Usher syndrome are hearing and vision loss. Psychological or behavioral disorders may occur before vision loss. Some people also have balance problems due to inner ear problems.RP limits a person’s ability to see in dim light or the dark. It also causes a person to lose side vision slowly over time. Eventually, any vision that is left is only in a small, tunnel-shaped area. Almost everyone with RP becomes legally blind. There is no way of knowing when or how quickly a person will lose vision.Symptoms and characteristics of each type include the following:
  • Type I
    • Deaf at birth and receives little or no benefit from hearing aids
    • Severe balance problems
    • Slow to sit without support
    • Rarely learn to walk before age 18 months
    • RP begins by age 10 with difficulty seeing at night, and quickly changes to blindness
  • Type II
    • Born with moderate to severe hearing loss, and can benefit from hearing aids
    • No balance problems
    • RP begins in the teenage years
  • Type III
    • Born with normal hearing that gets worse in the teenage years and leads to deafness by mid to late adulthood
    • Born with near-normal balance
    • RP begins in the early teenage years as difficulty seeing at night, and leads to blindness by mid-adulthood

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